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NAME

       gcc - GNU project C and C++ compiler

SYNOPSIS

       gcc [-c|-S|-E] [-std=standard]
           [-g] [-pg] [-Olevel]
           [-Wwarn...] [-Wpedantic]
           [-Idir...] [-Ldir...]
           [-Dmacro[=defn]...] [-Umacro]
           [-foption...] [-mmachine-option...]
           [-o outfile] [@file] infile...

       Only the most useful options are listed here; see below for the remainder.  g++ accepts
       mostly the same options as gcc.

DESCRIPTION

       When you invoke GCC, it normally does preprocessing, compilation, assembly and linking.
       The "overall options" allow you to stop this process at an intermediate stage.  For
       example, the -c option says not to run the linker.  Then the output consists of object
       files output by the assembler.

       Other options are passed on to one or more stages of processing.  Some options control the
       preprocessor and others the compiler itself.  Yet other options control the assembler and
       linker; most of these are not documented here, since you rarely need to use any of them.

       Most of the command-line options that you can use with GCC are useful for C programs; when
       an option is only useful with another language (usually C++), the explanation says so
       explicitly.  If the description for a particular option does not mention a source
       language, you can use that option with all supported languages.

       The usual way to run GCC is to run the executable called gcc, or machine-gcc when cross-
       compiling, or machine-gcc-version to run a specific version of GCC.  When you compile C++
       programs, you should invoke GCC as g++ instead.

       The gcc program accepts options and file names as operands.  Many options have multi-
       letter names; therefore multiple single-letter options may not be grouped: -dv is very
       different from -d -v.

       You can mix options and other arguments.  For the most part, the order you use doesn't
       matter.  Order does matter when you use several options of the same kind; for example, if
       you specify -L more than once, the directories are searched in the order specified.  Also,
       the placement of the -l option is significant.

       Many options have long names starting with -f or with -W---for example,
       -fmove-loop-invariants, -Wformat and so on.  Most of these have both positive and negative
       forms; the negative form of -ffoo is -fno-foo.  This manual documents only one of these
       two forms, whichever one is not the default.

OPTIONS

   Option Summary
       Here is a summary of all the options, grouped by type.  Explanations are in the following
       sections.

       Overall Options
           -c  -S  -E  -o file  -x language -v  -###  --help[=class[,...]]  --target-help
           --version -pass-exit-codes  -pipe  -specs=file  -wrapper @file
           -ffile-prefix-map=old=new -fplugin=file  -fplugin-arg-name=arg -fdump-ada-spec[-slim]
           -fada-spec-parent=unit  -fdump-go-spec=file

       C Language Options
           -ansi  -std=standard  -fgnu89-inline -fpermitted-flt-eval-methods=standard -aux-info
           filename  -fallow-parameterless-variadic-functions -fno-asm  -fno-builtin
           -fno-builtin-function  -fgimple -fhosted  -ffreestanding  -fopenacc  -fopenmp
           -fopenmp-simd -fms-extensions  -fplan9-extensions  -fsso-struct=endianness
           -fallow-single-precision  -fcond-mismatch  -flax-vector-conversions -fsigned-bitfields
           -fsigned-char -funsigned-bitfields  -funsigned-char

       C++ Language Options
           -fabi-version=n  -fno-access-control -faligned-new=n  -fargs-in-order=n  -fcheck-new
           -fconstexpr-depth=n  -fconstexpr-loop-limit=n -ffriend-injection
           -fno-elide-constructors -fno-enforce-eh-specs -ffor-scope  -fno-for-scope
           -fno-gnu-keywords -fno-implicit-templates -fno-implicit-inline-templates
           -fno-implement-inlines  -fms-extensions -fnew-inheriting-ctors -fnew-ttp-matching
           -fno-nonansi-builtins  -fnothrow-opt  -fno-operator-names -fno-optional-diags
           -fpermissive -fno-pretty-templates -frepo  -fno-rtti  -fsized-deallocation
           -ftemplate-backtrace-limit=n -ftemplate-depth=n -fno-threadsafe-statics
           -fuse-cxa-atexit -fno-weak  -nostdinc++ -fvisibility-inlines-hidden
           -fvisibility-ms-compat -fext-numeric-literals -Wabi=n  -Wabi-tag  -Wconversion-null
           -Wctor-dtor-privacy -Wdelete-non-virtual-dtor  -Wliteral-suffix
           -Wmultiple-inheritance -Wnamespaces  -Wnarrowing -Wnoexcept  -Wnoexcept-type
           -Wclass-memaccess -Wnon-virtual-dtor  -Wreorder  -Wregister -Weffc++
           -Wstrict-null-sentinel  -Wtemplates -Wno-non-template-friend  -Wold-style-cast
           -Woverloaded-virtual  -Wno-pmf-conversions -Wsign-promo  -Wvirtual-inheritance

       Objective-C and Objective-C++ Language Options
           -fconstant-string-class=class-name -fgnu-runtime  -fnext-runtime -fno-nil-receivers
           -fobjc-abi-version=n -fobjc-call-cxx-cdtors -fobjc-direct-dispatch -fobjc-exceptions
           -fobjc-gc -fobjc-nilcheck -fobjc-std=objc1 -fno-local-ivars
           -fivar-visibility=[public|protected|private|package] -freplace-objc-classes
           -fzero-link -gen-decls -Wassign-intercept -Wno-protocol  -Wselector
           -Wstrict-selector-match -Wundeclared-selector

       Diagnostic Message Formatting Options
           -fmessage-length=n -fdiagnostics-show-location=[once|every-line]
           -fdiagnostics-color=[auto|never|always] -fno-diagnostics-show-option
           -fno-diagnostics-show-caret -fdiagnostics-parseable-fixits
           -fdiagnostics-generate-patch -fdiagnostics-show-template-tree -fno-elide-type
           -fno-show-column

       Warning Options
           -fsyntax-only  -fmax-errors=n  -Wpedantic -pedantic-errors -w  -Wextra  -Wall
           -Waddress  -Waggregate-return  -Waligned-new -Walloc-zero  -Walloc-size-larger-than=n
           -Walloca  -Walloca-larger-than=n -Wno-aggressive-loop-optimizations  -Warray-bounds
           -Warray-bounds=n -Wno-attributes  -Wbool-compare  -Wbool-operation
           -Wno-builtin-declaration-mismatch -Wno-builtin-macro-redefined  -Wc90-c99-compat
           -Wc99-c11-compat -Wc++-compat  -Wc++11-compat  -Wc++14-compat -Wcast-align
           -Wcast-align=strict  -Wcast-function-type  -Wcast-qual -Wchar-subscripts  -Wchkp
           -Wcatch-value  -Wcatch-value=n -Wclobbered  -Wcomment  -Wconditionally-supported
           -Wconversion  -Wcoverage-mismatch  -Wno-cpp  -Wdangling-else  -Wdate-time
           -Wdelete-incomplete -Wno-deprecated  -Wno-deprecated-declarations
           -Wno-designated-init -Wdisabled-optimization -Wno-discarded-qualifiers
           -Wno-discarded-array-qualifiers -Wno-div-by-zero  -Wdouble-promotion
           -Wduplicated-branches  -Wduplicated-cond -Wempty-body  -Wenum-compare
           -Wno-endif-labels  -Wexpansion-to-defined -Werror  -Werror=*  -Wextra-semi
           -Wfatal-errors -Wfloat-equal  -Wformat  -Wformat=2 -Wno-format-contains-nul
           -Wno-format-extra-args -Wformat-nonliteral -Wformat-overflow=n -Wformat-security
           -Wformat-signedness  -Wformat-truncation=n -Wformat-y2k  -Wframe-address
           -Wframe-larger-than=len  -Wno-free-nonheap-object  -Wjump-misses-init -Wif-not-aligned
           -Wignored-qualifiers  -Wignored-attributes  -Wincompatible-pointer-types -Wimplicit
           -Wimplicit-fallthrough  -Wimplicit-fallthrough=n -Wimplicit-function-declaration
           -Wimplicit-int -Winit-self  -Winline  -Wno-int-conversion  -Wint-in-bool-context
           -Wno-int-to-pointer-cast  -Winvalid-memory-model  -Wno-invalid-offsetof -Winvalid-pch
           -Wlarger-than=len -Wlogical-op  -Wlogical-not-parentheses  -Wlong-long -Wmain
           -Wmaybe-uninitialized  -Wmemset-elt-size  -Wmemset-transposed-args
           -Wmisleading-indentation  -Wmissing-attributes -Wmissing-braces
           -Wmissing-field-initializers  -Wmissing-include-dirs -Wno-multichar
           -Wmultistatement-macros  -Wnonnull  -Wnonnull-compare -Wnormalized=[none|id|nfc|nfkc]
           -Wnull-dereference  -Wodr  -Wno-overflow  -Wopenmp-simd -Woverride-init-side-effects
           -Woverlength-strings -Wpacked  -Wpacked-bitfield-compat -Wpacked-not-aligned -Wpadded
           -Wparentheses  -Wno-pedantic-ms-format -Wplacement-new  -Wplacement-new=n
           -Wpointer-arith  -Wpointer-compare  -Wno-pointer-to-int-cast -Wno-pragmas
           -Wredundant-decls  -Wrestrict  -Wno-return-local-addr -Wreturn-type  -Wsequence-point
           -Wshadow  -Wno-shadow-ivar -Wshadow=global,  -Wshadow=local,
           -Wshadow=compatible-local -Wshift-overflow  -Wshift-overflow=n -Wshift-count-negative
           -Wshift-count-overflow  -Wshift-negative-value -Wsign-compare  -Wsign-conversion
           -Wfloat-conversion -Wno-scalar-storage-order  -Wsizeof-pointer-div
           -Wsizeof-pointer-memaccess  -Wsizeof-array-argument -Wstack-protector
           -Wstack-usage=len  -Wstrict-aliasing -Wstrict-aliasing=n  -Wstrict-overflow
           -Wstrict-overflow=n -Wstringop-overflow=n -Wstringop-truncation
           -Wsuggest-attribute=[pure|const|noreturn|format|malloc] -Wsuggest-final-types
           -Wsuggest-final-methods  -Wsuggest-override -Wmissing-format-attribute
           -Wsubobject-linkage -Wswitch  -Wswitch-bool  -Wswitch-default  -Wswitch-enum
           -Wswitch-unreachable  -Wsync-nand -Wsystem-headers  -Wtautological-compare
           -Wtrampolines  -Wtrigraphs -Wtype-limits  -Wundef -Wuninitialized  -Wunknown-pragmas
           -Wunsuffixed-float-constants  -Wunused  -Wunused-function -Wunused-label
           -Wunused-local-typedefs  -Wunused-macros -Wunused-parameter  -Wno-unused-result
           -Wunused-value  -Wunused-variable -Wunused-const-variable  -Wunused-const-variable=n
           -Wunused-but-set-parameter  -Wunused-but-set-variable -Wuseless-cast
           -Wvariadic-macros  -Wvector-operation-performance -Wvla  -Wvla-larger-than=n
           -Wvolatile-register-var  -Wwrite-strings -Wzero-as-null-pointer-constant  -Whsa

       C and Objective-C-only Warning Options
           -Wbad-function-cast  -Wmissing-declarations -Wmissing-parameter-type
           -Wmissing-prototypes  -Wnested-externs -Wold-style-declaration  -Wold-style-definition
           -Wstrict-prototypes  -Wtraditional  -Wtraditional-conversion
           -Wdeclaration-after-statement  -Wpointer-sign

       Debugging Options
           -g  -glevel  -gdwarf  -gdwarf-version -ggdb  -grecord-gcc-switches
           -gno-record-gcc-switches -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf
           -gas-loc-support  -gno-as-loc-support -gas-locview-support  -gno-as-locview-support
           -gcolumn-info  -gno-column-info -gstatement-frontiers  -gno-statement-frontiers
           -gvariable-location-views  -gno-variable-location-views
           -ginternal-reset-location-views  -gno-internal-reset-location-views -ginline-points
           -gno-inline-points -gvms  -gxcoff  -gxcoff+  -gz[=type] -fdebug-prefix-map=old=new
           -fdebug-types-section -fno-eliminate-unused-debug-types -femit-struct-debug-baseonly
           -femit-struct-debug-reduced -femit-struct-debug-detailed[=spec-list]
           -feliminate-unused-debug-symbols  -femit-class-debug-always -fno-merge-debug-strings
           -fno-dwarf2-cfi-asm -fvar-tracking  -fvar-tracking-assignments

       Optimization Options
           -faggressive-loop-optimizations  -falign-functions[=n] -falign-jumps[=n]
           -falign-labels[=n]  -falign-loops[=n] -fassociative-math  -fauto-profile
           -fauto-profile[=path] -fauto-inc-dec  -fbranch-probabilities
           -fbranch-target-load-optimize  -fbranch-target-load-optimize2 -fbtr-bb-exclusive
           -fcaller-saves -fcombine-stack-adjustments  -fconserve-stack -fcompare-elim
           -fcprop-registers  -fcrossjumping -fcse-follow-jumps  -fcse-skip-blocks
           -fcx-fortran-rules -fcx-limited-range -fdata-sections  -fdce  -fdelayed-branch
           -fdelete-null-pointer-checks  -fdevirtualize  -fdevirtualize-speculatively
           -fdevirtualize-at-ltrans  -fdse -fearly-inlining  -fipa-sra  -fexpensive-optimizations
           -ffat-lto-objects -ffast-math  -ffinite-math-only  -ffloat-store
           -fexcess-precision=style -fforward-propagate  -ffp-contract=style  -ffunction-sections
           -fgcse  -fgcse-after-reload  -fgcse-las  -fgcse-lm  -fgraphite-identity -fgcse-sm
           -fhoist-adjacent-loads  -fif-conversion -fif-conversion2  -findirect-inlining
           -finline-functions  -finline-functions-called-once  -finline-limit=n
           -finline-small-functions  -fipa-cp  -fipa-cp-clone -fipa-bit-cp -fipa-vrp -fipa-pta
           -fipa-profile  -fipa-pure-const  -fipa-reference  -fipa-icf -fira-algorithm=algorithm
           -fira-region=region  -fira-hoist-pressure -fira-loop-pressure
           -fno-ira-share-save-slots -fno-ira-share-spill-slots
           -fisolate-erroneous-paths-dereference  -fisolate-erroneous-paths-attribute -fivopts
           -fkeep-inline-functions  -fkeep-static-functions -fkeep-static-consts
           -flimit-function-alignment  -flive-range-shrinkage -floop-block  -floop-interchange
           -floop-strip-mine -floop-unroll-and-jam  -floop-nest-optimize -floop-parallelize-all
           -flra-remat  -flto  -flto-compression-level -flto-partition=alg  -fmerge-all-constants
           -fmerge-constants  -fmodulo-sched  -fmodulo-sched-allow-regmoves
           -fmove-loop-invariants  -fno-branch-count-reg -fno-defer-pop
           -fno-fp-int-builtin-inexact  -fno-function-cse -fno-guess-branch-probability
           -fno-inline  -fno-math-errno  -fno-peephole -fno-peephole2  -fno-printf-return-value
           -fno-sched-interblock -fno-sched-spec  -fno-signed-zeros -fno-toplevel-reorder
           -fno-trapping-math  -fno-zero-initialized-in-bss -fomit-frame-pointer
           -foptimize-sibling-calls -fpartial-inlining  -fpeel-loops  -fpredictive-commoning
           -fprefetch-loop-arrays -fprofile-correction -fprofile-use  -fprofile-use=path
           -fprofile-values -fprofile-reorder-functions -freciprocal-math  -free
           -frename-registers  -freorder-blocks -freorder-blocks-algorithm=algorithm
           -freorder-blocks-and-partition  -freorder-functions -frerun-cse-after-loop
           -freschedule-modulo-scheduled-loops -frounding-math  -fsched2-use-superblocks
           -fsched-pressure -fsched-spec-load  -fsched-spec-load-dangerous
           -fsched-stalled-insns-dep[=n]  -fsched-stalled-insns[=n] -fsched-group-heuristic
           -fsched-critical-path-heuristic -fsched-spec-insn-heuristic  -fsched-rank-heuristic
           -fsched-last-insn-heuristic  -fsched-dep-count-heuristic -fschedule-fusion
           -fschedule-insns  -fschedule-insns2  -fsection-anchors -fselective-scheduling
           -fselective-scheduling2 -fsel-sched-pipelining  -fsel-sched-pipelining-outer-loops
           -fsemantic-interposition  -fshrink-wrap  -fshrink-wrap-separate -fsignaling-nans
           -fsingle-precision-constant  -fsplit-ivs-in-unroller  -fsplit-loops -fsplit-paths
           -fsplit-wide-types  -fssa-backprop  -fssa-phiopt -fstdarg-opt  -fstore-merging
           -fstrict-aliasing -fthread-jumps  -ftracer  -ftree-bit-ccp -ftree-builtin-call-dce
           -ftree-ccp  -ftree-ch -ftree-coalesce-vars  -ftree-copy-prop  -ftree-dce
           -ftree-dominator-opts -ftree-dse  -ftree-forwprop  -ftree-fre  -fcode-hoisting
           -ftree-loop-if-convert  -ftree-loop-im -ftree-phiprop  -ftree-loop-distribution
           -ftree-loop-distribute-patterns -ftree-loop-ivcanon  -ftree-loop-linear
           -ftree-loop-optimize -ftree-loop-vectorize -ftree-parallelize-loops=n  -ftree-pre
           -ftree-partial-pre  -ftree-pta -ftree-reassoc  -ftree-sink  -ftree-slsr  -ftree-sra
           -ftree-switch-conversion  -ftree-tail-merge -ftree-ter  -ftree-vectorize  -ftree-vrp
           -funconstrained-commons -funit-at-a-time  -funroll-all-loops  -funroll-loops
           -funsafe-math-optimizations  -funswitch-loops -fipa-ra
           -fvariable-expansion-in-unroller  -fvect-cost-model  -fvpt -fweb  -fwhole-program
           -fwpa  -fuse-linker-plugin --param name=value -O  -O0  -O1  -O2  -O3  -Os  -Ofast  -Og

       Program Instrumentation Options
           -p  -pg  -fprofile-arcs  --coverage  -ftest-coverage -fprofile-abs-path
           -fprofile-dir=path  -fprofile-generate  -fprofile-generate=path -fsanitize=style
           -fsanitize-recover  -fsanitize-recover=style -fasan-shadow-offset=number
           -fsanitize-sections=s1,s2,...  -fsanitize-undefined-trap-on-error  -fbounds-check
           -fcheck-pointer-bounds  -fchkp-check-incomplete-type -fchkp-first-field-has-own-bounds
           -fchkp-narrow-bounds -fchkp-narrow-to-innermost-array  -fchkp-optimize
           -fchkp-use-fast-string-functions  -fchkp-use-nochk-string-functions
           -fchkp-use-static-bounds  -fchkp-use-static-const-bounds
           -fchkp-treat-zero-dynamic-size-as-infinite  -fchkp-check-read -fchkp-check-read
           -fchkp-check-write  -fchkp-store-bounds -fchkp-instrument-calls
           -fchkp-instrument-marked-only -fchkp-use-wrappers
           -fchkp-flexible-struct-trailing-arrays -fcf-protection=[full|branch|return|none]
           -fstack-protector  -fstack-protector-all  -fstack-protector-strong
           -fstack-protector-explicit  -fstack-check -fstack-limit-register=reg
           -fstack-limit-symbol=sym -fno-stack-limit  -fsplit-stack
           -fvtable-verify=[std|preinit|none] -fvtv-counts  -fvtv-debug -finstrument-functions
           -finstrument-functions-exclude-function-list=sym,sym,...
           -finstrument-functions-exclude-file-list=file,file,...

       Preprocessor Options
           -Aquestion=answer -A-question[=answer] -C  -CC  -Dmacro[=defn] -dD  -dI  -dM  -dN  -dU
           -fdebug-cpp  -fdirectives-only  -fdollars-in-identifiers -fexec-charset=charset
           -fextended-identifiers -finput-charset=charset -fmacro-prefix-map=old=new
           -fno-canonical-system-headers  -fpch-deps  -fpch-preprocess -fpreprocessed
           -ftabstop=width  -ftrack-macro-expansion -fwide-exec-charset=charset
           -fworking-directory -H  -imacros file  -include file -M  -MD  -MF  -MG  -MM  -MMD  -MP
           -MQ  -MT -no-integrated-cpp  -P  -pthread  -remap -traditional  -traditional-cpp
           -trigraphs -Umacro  -undef -Wp,option  -Xpreprocessor option

       Assembler Options
           -Wa,option  -Xassembler option

       Linker Options
           object-file-name  -fuse-ld=linker  -llibrary -nostartfiles  -nodefaultlibs  -nostdlib
           -pie  -pthread  -rdynamic -s  -static -static-pie -static-libgcc  -static-libstdc++
           -static-libasan  -static-libtsan  -static-liblsan  -static-libubsan -static-libmpx
           -static-libmpxwrappers -shared  -shared-libgcc  -symbolic -T script  -Wl,option
           -Xlinker option -u symbol  -z keyword

       Directory Options
           -Bprefix  -Idir  -I- -idirafter dir -imacros file  -imultilib dir -iplugindir=dir
           -iprefix file -iquote dir  -isysroot dir  -isystem dir -iwithprefix dir
           -iwithprefixbefore dir -Ldir  -no-canonical-prefixes  --no-sysroot-suffix -nostdinc
           -nostdinc++  --sysroot=dir

       Code Generation Options
           -fcall-saved-reg  -fcall-used-reg -ffixed-reg  -fexceptions -fnon-call-exceptions
           -fdelete-dead-exceptions  -funwind-tables -fasynchronous-unwind-tables -fno-gnu-unique
           -finhibit-size-directive  -fno-common  -fno-ident -fpcc-struct-return  -fpic  -fPIC
           -fpie  -fPIE  -fno-plt -fno-jump-tables -frecord-gcc-switches -freg-struct-return
           -fshort-enums  -fshort-wchar -fverbose-asm  -fpack-struct[=n] -fleading-underscore
           -ftls-model=model -fstack-reuse=reuse_level -ftrampolines  -ftrapv  -fwrapv
           -fvisibility=[default|internal|hidden|protected] -fstrict-volatile-bitfields
           -fsync-libcalls

       Developer Options
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -dumpfullversion  -fchecking
           -fchecking=n  -fdbg-cnt-list -fdbg-cnt=counter-value-list -fdisable-ipa-pass_name
           -fdisable-rtl-pass_name -fdisable-rtl-pass-name=range-list -fdisable-tree-pass_name
           -fdisable-tree-pass-name=range-list -fdump-noaddr  -fdump-unnumbered
           -fdump-unnumbered-links -fdump-class-hierarchy[-n] -fdump-final-insns[=file]
           -fdump-ipa-all  -fdump-ipa-cgraph  -fdump-ipa-inline -fdump-lang-all
           -fdump-lang-switch -fdump-lang-switch-options -fdump-lang-switch-options=filename
           -fdump-passes -fdump-rtl-pass  -fdump-rtl-pass=filename -fdump-statistics
           -fdump-tree-all -fdump-tree-switch -fdump-tree-switch-options
           -fdump-tree-switch-options=filename -fcompare-debug[=opts]  -fcompare-debug-second
           -fenable-kind-pass -fenable-kind-pass=range-list -fira-verbose=n -flto-report
           -flto-report-wpa  -fmem-report-wpa -fmem-report  -fpre-ipa-mem-report
           -fpost-ipa-mem-report -fopt-info  -fopt-info-options[=file] -fprofile-report
           -frandom-seed=string  -fsched-verbose=n -fsel-sched-verbose  -fsel-sched-dump-cfg
           -fsel-sched-pipelining-verbose -fstats  -fstack-usage  -ftime-report
           -ftime-report-details -fvar-tracking-assignments-toggle  -gtoggle
           -print-file-name=library  -print-libgcc-file-name -print-multi-directory
           -print-multi-lib  -print-multi-os-directory -print-prog-name=program
           -print-search-dirs  -Q -print-sysroot  -print-sysroot-headers-suffix -save-temps
           -save-temps=cwd  -save-temps=obj  -time[=file]

       Machine-Dependent Options
           AArch64 Options -mabi=name  -mbig-endian  -mlittle-endian -mgeneral-regs-only
           -mcmodel=tiny  -mcmodel=small  -mcmodel=large -mstrict-align -momit-leaf-frame-pointer
           -mtls-dialect=desc  -mtls-dialect=traditional -mtls-size=size -mfix-cortex-a53-835769
           -mfix-cortex-a53-843419 -mlow-precision-recip-sqrt  -mlow-precision-sqrt
           -mlow-precision-div -mpc-relative-literal-loads -msign-return-address=scope
           -march=name  -mcpu=name  -mtune=name -moverride=string  -mverbose-cost-dump

           Adapteva Epiphany Options -mhalf-reg-file  -mprefer-short-insn-regs -mbranch-cost=num
           -mcmove  -mnops=num  -msoft-cmpsf -msplit-lohi  -mpost-inc  -mpost-modify
           -mstack-offset=num -mround-nearest  -mlong-calls  -mshort-calls  -msmall16
           -mfp-mode=mode  -mvect-double  -max-vect-align=num -msplit-vecmove-early  -m1reg-reg

           ARC Options -mbarrel-shifter -mjli-always -mcpu=cpu  -mA6  -mARC600  -mA7  -mARC700
           -mdpfp  -mdpfp-compact  -mdpfp-fast  -mno-dpfp-lrsr -mea  -mno-mpy  -mmul32x16
           -mmul64  -matomic -mnorm  -mspfp  -mspfp-compact  -mspfp-fast  -msimd  -msoft-float
           -mswap -mcrc  -mdsp-packa  -mdvbf  -mlock  -mmac-d16  -mmac-24  -mrtsc  -mswape
           -mtelephony  -mxy  -misize  -mannotate-align  -marclinux  -marclinux_prof -mlong-calls
           -mmedium-calls  -msdata -mirq-ctrl-saved -mrgf-banked-regs -mlpc-width=width -G num
           -mvolatile-cache  -mtp-regno=regno -malign-call  -mauto-modify-reg  -mbbit-peephole
           -mno-brcc -mcase-vector-pcrel  -mcompact-casesi  -mno-cond-exec  -mearly-cbranchsi
           -mexpand-adddi  -mindexed-loads  -mlra  -mlra-priority-none -mlra-priority-compact
           mlra-priority-noncompact  -mno-millicode -mmixed-code  -mq-class  -mRcq  -mRcw
           -msize-level=level -mtune=cpu  -mmultcost=num -munalign-prob-threshold=probability
           -mmpy-option=multo -mdiv-rem  -mcode-density  -mll64  -mfpu=fpu -mrf16

           ARM Options -mapcs-frame  -mno-apcs-frame -mabi=name -mapcs-stack-check
           -mno-apcs-stack-check -mapcs-reentrant  -mno-apcs-reentrant -msched-prolog
           -mno-sched-prolog -mlittle-endian  -mbig-endian -mbe8 -mbe32 -mfloat-abi=name
           -mfp16-format=name -mthumb-interwork  -mno-thumb-interwork -mcpu=name  -march=name
           -mfpu=name -mtune=name  -mprint-tune-info -mstructure-size-boundary=n
           -mabort-on-noreturn -mlong-calls  -mno-long-calls -msingle-pic-base
           -mno-single-pic-base -mpic-register=reg -mnop-fun-dllimport -mpoke-function-name
           -mthumb  -marm  -mflip-thumb -mtpcs-frame  -mtpcs-leaf-frame
           -mcaller-super-interworking  -mcallee-super-interworking -mtp=name
           -mtls-dialect=dialect -mword-relocations -mfix-cortex-m3-ldrd -munaligned-access
           -mneon-for-64bits -mslow-flash-data -masm-syntax-unified -mrestrict-it
           -mverbose-cost-dump -mpure-code -mcmse

           AVR Options -mmcu=mcu  -mabsdata  -maccumulate-args -mbranch-cost=cost
           -mcall-prologues  -mgas-isr-prologues  -mint8 -mn_flash=size  -mno-interrupts
           -mmain-is-OS_task -mrelax  -mrmw  -mstrict-X  -mtiny-stack -mfract-convert-truncate
           -mshort-calls  -nodevicelib -Waddr-space-convert  -Wmisspelled-isr

           Blackfin Options -mcpu=cpu[-sirevision] -msim  -momit-leaf-frame-pointer
           -mno-omit-leaf-frame-pointer -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly
           -mno-csync-anomaly -mlow-64k  -mno-low64k  -mstack-check-l1  -mid-shared-library
           -mno-id-shared-library  -mshared-library-id=n -mleaf-id-shared-library
           -mno-leaf-id-shared-library -msep-data  -mno-sep-data  -mlong-calls  -mno-long-calls
           -mfast-fp  -minline-plt  -mmulticore  -mcorea  -mcoreb  -msdram -micplb

           C6X Options -mbig-endian  -mlittle-endian  -march=cpu -msim  -msdata=sdata-type

           CRIS Options -mcpu=cpu  -march=cpu  -mtune=cpu -mmax-stack-frame=n
           -melinux-stacksize=n -metrax4  -metrax100  -mpdebug  -mcc-init  -mno-side-effects
           -mstack-align  -mdata-align  -mconst-align -m32-bit  -m16-bit  -m8-bit
           -mno-prologue-epilogue  -mno-gotplt -melf  -maout  -melinux  -mlinux  -sim  -sim2
           -mmul-bug-workaround  -mno-mul-bug-workaround

           CR16 Options -mmac -mcr16cplus  -mcr16c -msim  -mint32  -mbit-ops -mdata-model=model

           Darwin Options -all_load  -allowable_client  -arch  -arch_errors_fatal -arch_only
           -bind_at_load  -bundle  -bundle_loader -client_name  -compatibility_version
           -current_version -dead_strip -dependency-file  -dylib_file  -dylinker_install_name
           -dynamic  -dynamiclib  -exported_symbols_list -filelist  -flat_namespace
           -force_cpusubtype_ALL -force_flat_namespace  -headerpad_max_install_names -iframework
           -image_base  -init  -install_name  -keep_private_externs -multi_module
           -multiply_defined  -multiply_defined_unused -noall_load
           -no_dead_strip_inits_and_terms -nofixprebinding  -nomultidefs  -noprebind
           -noseglinkedit -pagezero_size  -prebind  -prebind_all_twolevel_modules -private_bundle
           -read_only_relocs  -sectalign -sectobjectsymbols  -whyload  -seg1addr -sectcreate
           -sectobjectsymbols  -sectorder -segaddr  -segs_read_only_addr  -segs_read_write_addr
           -seg_addr_table  -seg_addr_table_filename  -seglinkedit -segprot  -segs_read_only_addr
           -segs_read_write_addr -single_module  -static  -sub_library  -sub_umbrella
           -twolevel_namespace  -umbrella  -undefined -unexported_symbols_list
           -weak_reference_mismatches -whatsloaded  -F  -gused  -gfull
           -mmacosx-version-min=version -mkernel  -mone-byte-bool

           DEC Alpha Options -mno-fp-regs  -msoft-float -mieee  -mieee-with-inexact
           -mieee-conformant -mfp-trap-mode=mode  -mfp-rounding-mode=mode -mtrap-precision=mode
           -mbuild-constants -mcpu=cpu-type  -mtune=cpu-type -mbwx  -mmax  -mfix  -mcix
           -mfloat-vax  -mfloat-ieee -mexplicit-relocs  -msmall-data  -mlarge-data -msmall-text
           -mlarge-text -mmemory-latency=time

           FR30 Options -msmall-model  -mno-lsim

           FT32 Options -msim  -mlra  -mnodiv  -mft32b  -mcompress  -mnopm

           FRV Options -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64 -mhard-float  -msoft-float
           -malloc-cc  -mfixed-cc  -mdword  -mno-dword -mdouble  -mno-double -mmedia  -mno-media
           -mmuladd  -mno-muladd -mfdpic  -minline-plt  -mgprel-ro  -multilib-library-pic
           -mlinked-fp  -mlong-calls  -malign-labels -mlibrary-pic  -macc-4  -macc-8 -mpack
           -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move -moptimize-membar
           -mno-optimize-membar -mscc  -mno-scc  -mcond-exec  -mno-cond-exec -mvliw-branch
           -mno-vliw-branch -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
           -mno-nested-cond-exec  -mtomcat-stats -mTLS  -mtls -mcpu=cpu

           GNU/Linux Options -mglibc  -muclibc  -mmusl  -mbionic  -mandroid -tno-android-cc
           -tno-android-ld

           H8/300 Options -mrelax  -mh  -ms  -mn  -mexr  -mno-exr  -mint32  -malign-300

           HPPA Options -march=architecture-type -mcaller-copies  -mdisable-fpregs
           -mdisable-indexing -mfast-indirect-calls  -mgas  -mgnu-ld   -mhp-ld
           -mfixed-range=register-range -mjump-in-delay  -mlinker-opt  -mlong-calls
           -mlong-load-store  -mno-disable-fpregs -mno-disable-indexing  -mno-fast-indirect-calls
           -mno-gas -mno-jump-in-delay  -mno-long-load-store -mno-portable-runtime
           -mno-soft-float -mno-space-regs  -msoft-float  -mpa-risc-1-0 -mpa-risc-1-1
           -mpa-risc-2-0  -mportable-runtime -mschedule=cpu-type  -mspace-regs  -msio  -mwsio
           -munix=unix-std  -nolibdld  -static  -threads

           IA-64 Options -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld  -mno-pic
           -mvolatile-asm-stop  -mregister-names  -msdata  -mno-sdata -mconstant-gp  -mauto-pic
           -mfused-madd -minline-float-divide-min-latency -minline-float-divide-max-throughput
           -mno-inline-float-divide -minline-int-divide-min-latency
           -minline-int-divide-max-throughput -mno-inline-int-divide -minline-sqrt-min-latency
           -minline-sqrt-max-throughput -mno-inline-sqrt -mdwarf2-asm  -mearly-stop-bits
           -mfixed-range=register-range  -mtls-size=tls-size -mtune=cpu-type  -milp32  -mlp64
           -msched-br-data-spec  -msched-ar-data-spec  -msched-control-spec
           -msched-br-in-data-spec  -msched-ar-in-data-spec  -msched-in-control-spec
           -msched-spec-ldc  -msched-spec-control-ldc -msched-prefer-non-data-spec-insns
           -msched-prefer-non-control-spec-insns -msched-stop-bits-after-every-cycle
           -msched-count-spec-in-critical-path -msel-sched-dont-check-control-spec
           -msched-fp-mem-deps-zero-cost -msched-max-memory-insns-hard-limit
           -msched-max-memory-insns=max-insns

           LM32 Options -mbarrel-shift-enabled  -mdivide-enabled  -mmultiply-enabled
           -msign-extend-enabled  -muser-enabled

           M32R/D Options -m32r2  -m32rx  -m32r -mdebug -malign-loops  -mno-align-loops
           -missue-rate=number -mbranch-cost=number -mmodel=code-size-model-type -msdata=sdata-
           type -mno-flush-func  -mflush-func=name -mno-flush-trap  -mflush-trap=number -G num

           M32C Options -mcpu=cpu  -msim  -memregs=number

           M680x0 Options -march=arch  -mcpu=cpu  -mtune=tune -m68000  -m68020  -m68020-40
           -m68020-60  -m68030  -m68040 -m68060  -mcpu32  -m5200  -m5206e  -m528x  -m5307  -m5407
           -mcfv4e  -mbitfield  -mno-bitfield  -mc68000  -mc68020 -mnobitfield  -mrtd  -mno-rtd
           -mdiv  -mno-div  -mshort -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
           -malign-int  -mstrict-align  -msep-data  -mno-sep-data -mshared-library-id=n
           -mid-shared-library  -mno-id-shared-library -mxgot  -mno-xgot
           -mlong-jump-table-offsets

           MCore Options -mhardlit  -mno-hardlit  -mdiv  -mno-div  -mrelax-immediates
           -mno-relax-immediates  -mwide-bitfields  -mno-wide-bitfields -m4byte-functions
           -mno-4byte-functions  -mcallgraph-data -mno-callgraph-data  -mslow-bytes
           -mno-slow-bytes  -mno-lsim -mlittle-endian  -mbig-endian  -m210  -m340
           -mstack-increment

           MeP Options -mabsdiff  -mall-opts  -maverage  -mbased=n  -mbitops -mc=n  -mclip
           -mconfig=name  -mcop  -mcop32  -mcop64  -mivc2 -mdc  -mdiv  -meb  -mel  -mio-volatile
           -ml  -mleadz  -mm  -mminmax -mmult  -mno-opts  -mrepeat  -ms  -msatur  -msdram  -msim
           -msimnovec  -mtf -mtiny=n

           MicroBlaze Options -msoft-float  -mhard-float  -msmall-divides  -mcpu=cpu -mmemcpy
           -mxl-soft-mul  -mxl-soft-div  -mxl-barrel-shift -mxl-pattern-compare  -mxl-stack-check
           -mxl-gp-opt  -mno-clearbss -mxl-multiply-high  -mxl-float-convert  -mxl-float-sqrt
           -mbig-endian  -mlittle-endian  -mxl-reorder  -mxl-mode-app-model

           MIPS Options -EL  -EB  -march=arch  -mtune=arch -mips1  -mips2  -mips3  -mips4
           -mips32  -mips32r2  -mips32r3  -mips32r5 -mips32r6  -mips64  -mips64r2  -mips64r3
           -mips64r5  -mips64r6 -mips16  -mno-mips16  -mflip-mips16 -minterlink-compressed
           -mno-interlink-compressed -minterlink-mips16  -mno-interlink-mips16 -mabi=abi
           -mabicalls  -mno-abicalls -mshared  -mno-shared  -mplt  -mno-plt  -mxgot  -mno-xgot
           -mgp32  -mgp64  -mfp32  -mfpxx  -mfp64  -mhard-float  -msoft-float -mno-float
           -msingle-float  -mdouble-float -modd-spreg  -mno-odd-spreg -mabs=mode  -mnan=encoding
           -mdsp  -mno-dsp  -mdspr2  -mno-dspr2 -mmcu  -mmno-mcu -meva  -mno-eva -mvirt
           -mno-virt -mxpa  -mno-xpa -mmicromips  -mno-micromips -mmsa  -mno-msa -mfpu=fpu-type
           -msmartmips  -mno-smartmips -mpaired-single  -mno-paired-single  -mdmx  -mno-mdmx
           -mips3d  -mno-mips3d  -mmt  -mno-mt  -mllsc  -mno-llsc -mlong64  -mlong32  -msym32
           -mno-sym32 -Gnum  -mlocal-sdata  -mno-local-sdata -mextern-sdata  -mno-extern-sdata
           -mgpopt  -mno-gopt -membedded-data  -mno-embedded-data -muninit-const-in-rodata
           -mno-uninit-const-in-rodata -mcode-readable=setting -msplit-addresses
           -mno-split-addresses -mexplicit-relocs  -mno-explicit-relocs -mcheck-zero-division
           -mno-check-zero-division -mdivide-traps  -mdivide-breaks -mload-store-pairs
           -mno-load-store-pairs -mmemcpy  -mno-memcpy  -mlong-calls  -mno-long-calls -mmad
           -mno-mad  -mimadd  -mno-imadd  -mfused-madd  -mno-fused-madd  -nocpp -mfix-24k
           -mno-fix-24k -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400 -mfix-r10000
           -mno-fix-r10000  -mfix-rm7000  -mno-fix-rm7000 -mfix-vr4120  -mno-fix-vr4120
           -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1 -mflush-func=func
           -mno-flush-func -mbranch-cost=num  -mbranch-likely  -mno-branch-likely
           -mcompact-branches=policy -mfp-exceptions  -mno-fp-exceptions -mvr4130-align
           -mno-vr4130-align  -msynci  -mno-synci -mlxc1-sxc1 -mno-lxc1-sxc1 -mmadd4 -mno-madd4
           -mrelax-pic-calls  -mno-relax-pic-calls  -mmcount-ra-address -mframe-header-opt
           -mno-frame-header-opt

           MMIX Options -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon  -mabi=gnu
           -mabi=mmixware  -mzero-extend  -mknuthdiv  -mtoplevel-symbols -melf  -mbranch-predict
           -mno-branch-predict  -mbase-addresses -mno-base-addresses  -msingle-exit
           -mno-single-exit

           MN10300 Options -mmult-bug  -mno-mult-bug -mno-am33  -mam33  -mam33-2  -mam34
           -mtune=cpu-type -mreturn-pointer-on-d0 -mno-crt0  -mrelax  -mliw  -msetlb

           Moxie Options -meb  -mel  -mmul.x  -mno-crt0

           MSP430 Options -msim  -masm-hex  -mmcu=  -mcpu=  -mlarge  -msmall  -mrelax -mwarn-mcu
           -mcode-region=  -mdata-region= -msilicon-errata=  -msilicon-errata-warn= -mhwmult=
           -minrt

           NDS32 Options -mbig-endian  -mlittle-endian -mreduced-regs  -mfull-regs -mcmov
           -mno-cmov -mext-perf  -mno-ext-perf -mext-perf2  -mno-ext-perf2 -mext-string
           -mno-ext-string -mv3push  -mno-v3push -m16bit  -mno-16bit -misr-vector-size=num
           -mcache-block-size=num -march=arch -mcmodel=code-model -mctor-dtor  -mrelax

           Nios II Options -G num  -mgpopt=option  -mgpopt  -mno-gpopt -mgprel-sec=regexp
           -mr0rel-sec=regexp -mel  -meb -mno-bypass-cache  -mbypass-cache -mno-cache-volatile
           -mcache-volatile -mno-fast-sw-div  -mfast-sw-div -mhw-mul  -mno-hw-mul  -mhw-mulx
           -mno-hw-mulx  -mno-hw-div  -mhw-div -mcustom-insn=N  -mno-custom-insn
           -mcustom-fpu-cfg=name -mhal  -msmallc  -msys-crt0=name  -msys-lib=name -march=arch
           -mbmx  -mno-bmx  -mcdx  -mno-cdx

           Nvidia PTX Options -m32  -m64  -mmainkernel  -moptimize

           PDP-11 Options -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10 -mbcopy
           -mbcopy-builtin  -mint32  -mno-int16 -mint16  -mno-int32  -mfloat32  -mno-float64
           -mfloat64  -mno-float32  -mabshi  -mno-abshi -mbranch-expensive  -mbranch-cheap
           -munix-asm  -mdec-asm

           picoChip Options -mae=ae_type  -mvliw-lookahead=N -msymbol-as-address
           -mno-inefficient-warnings

           PowerPC Options See RS/6000 and PowerPC Options.

           PowerPC SPE Options -mcpu=cpu-type -mtune=cpu-type -mmfcrf  -mno-mfcrf  -mpopcntb
           -mno-popcntb -mfull-toc   -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc -m32
           -mxl-compat  -mno-xl-compat -malign-power  -malign-natural -msoft-float  -mhard-float
           -mmultiple  -mno-multiple -msingle-float  -mdouble-float -mupdate  -mno-update
           -mavoid-indexed-addresses  -mno-avoid-indexed-addresses -mstrict-align
           -mno-strict-align  -mrelocatable -mno-relocatable  -mrelocatable-lib
           -mno-relocatable-lib -mtoc  -mno-toc  -mlittle  -mlittle-endian  -mbig  -mbig-endian
           -msingle-pic-base -mprioritize-restricted-insns=priority
           -msched-costly-dep=dependence_type -minsert-sched-nops=scheme -mcall-sysv
           -mcall-netbsd -maix-struct-return  -msvr4-struct-return -mabi=abi-type  -msecure-plt
           -mbss-plt -mblock-move-inline-limit=num -misel  -mno-isel -misel=yes  -misel=no -mspe
           -mno-spe -mspe=yes  -mspe=no -mfloat-gprs=yes  -mfloat-gprs=no  -mfloat-gprs=single
           -mfloat-gprs=double -mprototype  -mno-prototype -msim  -mmvme  -mads  -myellowknife
           -memb  -msdata -msdata=opt  -mvxworks  -G num -mrecip  -mrecip=opt  -mno-recip
           -mrecip-precision -mno-recip-precision -mpointers-to-nested-functions
           -mno-pointers-to-nested-functions -msave-toc-indirect  -mno-save-toc-indirect
           -mcompat-align-parm  -mno-compat-align-parm -mfloat128  -mno-float128 -mgnu-attribute
           -mno-gnu-attribute -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
           -mstack-protector-guard-offset=offset

           RISC-V Options -mbranch-cost=N-instruction -mplt  -mno-plt -mabi=ABI-string -mfdiv
           -mno-fdiv -mdiv  -mno-div -march=ISA-string -mtune=processor-string
           -mpreferred-stack-boundary=num -msmall-data-limit=N-bytes -msave-restore
           -mno-save-restore -mstrict-align -mno-strict-align -mcmodel=medlow -mcmodel=medany
           -mexplicit-relocs  -mno-explicit-relocs -mrelax -mno-relax

           RL78 Options -msim  -mmul=none  -mmul=g13  -mmul=g14  -mallregs -mcpu=g10  -mcpu=g13
           -mcpu=g14  -mg10  -mg13  -mg14 -m64bit-doubles  -m32bit-doubles
           -msave-mduc-in-interrupts

           RS/6000 and PowerPC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model
           -mpowerpc64 -maltivec  -mno-altivec -mpowerpc-gpopt  -mno-powerpc-gpopt
           -mpowerpc-gfxopt  -mno-powerpc-gfxopt -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb
           -mpopcntd  -mno-popcntd -mfprnd  -mno-fprnd -mcmpb  -mno-cmpb  -mmfpgpr  -mno-mfpgpr
           -mhard-dfp  -mno-hard-dfp -mfull-toc   -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc
           -m64  -m32  -mxl-compat  -mno-xl-compat  -mpe -malign-power  -malign-natural
           -msoft-float  -mhard-float  -mmultiple  -mno-multiple -msingle-float  -mdouble-float
           -msimple-fpu -mupdate  -mno-update -mavoid-indexed-addresses
           -mno-avoid-indexed-addresses -mfused-madd  -mno-fused-madd  -mbit-align
           -mno-bit-align -mstrict-align  -mno-strict-align  -mrelocatable -mno-relocatable
           -mrelocatable-lib  -mno-relocatable-lib -mtoc  -mno-toc  -mlittle  -mlittle-endian
           -mbig  -mbig-endian -mdynamic-no-pic  -maltivec  -mswdiv  -msingle-pic-base
           -mprioritize-restricted-insns=priority -msched-costly-dep=dependence_type
           -minsert-sched-nops=scheme -mcall-aixdesc  -mcall-eabi  -mcall-freebsd -mcall-linux
           -mcall-netbsd  -mcall-openbsd -mcall-sysv  -mcall-sysv-eabi  -mcall-sysv-noeabi
           -mtraceback=traceback_type -maix-struct-return  -msvr4-struct-return -mabi=abi-type
           -msecure-plt  -mbss-plt -mblock-move-inline-limit=num -mblock-compare-inline-limit=num
           -mblock-compare-inline-loop-limit=num -mstring-compare-inline-limit=num -misel
           -mno-isel -misel=yes  -misel=no -mpaired -mvrsave  -mno-vrsave -mmulhw  -mno-mulhw
           -mdlmzb  -mno-dlmzb -mprototype  -mno-prototype -msim  -mmvme  -mads  -myellowknife
           -memb  -msdata -msdata=opt  -mreadonly-in-sdata  -mvxworks  -G num -mrecip
           -mrecip=opt  -mno-recip  -mrecip-precision -mno-recip-precision -mveclibabi=type
           -mfriz  -mno-friz -mpointers-to-nested-functions  -mno-pointers-to-nested-functions
           -msave-toc-indirect  -mno-save-toc-indirect -mpower8-fusion  -mno-mpower8-fusion
           -mpower8-vector  -mno-power8-vector -mcrypto  -mno-crypto  -mhtm  -mno-htm
           -mquad-memory  -mno-quad-memory -mquad-memory-atomic  -mno-quad-memory-atomic
           -mcompat-align-parm  -mno-compat-align-parm -mfloat128  -mno-float128
           -mfloat128-hardware  -mno-float128-hardware -mgnu-attribute  -mno-gnu-attribute
           -mstack-protector-guard=guard -mstack-protector-guard-reg=reg
           -mstack-protector-guard-offset=offset

           RX Options -m64bit-doubles  -m32bit-doubles  -fpu  -nofpu -mcpu= -mbig-endian-data
           -mlittle-endian-data -msmall-data -msim  -mno-sim -mas100-syntax  -mno-as100-syntax
           -mrelax -mmax-constant-size= -mint-register= -mpid -mallow-string-insns
           -mno-allow-string-insns -mjsr -mno-warn-multiple-fast-interrupts
           -msave-acc-in-interrupts

           S/390 and zSeries Options -mtune=cpu-type  -march=cpu-type -mhard-float  -msoft-float
           -mhard-dfp  -mno-hard-dfp -mlong-double-64  -mlong-double-128 -mbackchain
           -mno-backchain  -mpacked-stack  -mno-packed-stack -msmall-exec  -mno-small-exec
           -mmvcle  -mno-mvcle -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch -mhtm  -mvx
           -mzvector -mtpf-trace  -mno-tpf-trace  -mfused-madd  -mno-fused-madd -mwarn-framesize
           -mwarn-dynamicstack  -mstack-size  -mstack-guard -mhotpatch=halfwords,halfwords

           Score Options -meb  -mel -mnhwloop -muls -mmac -mscore5  -mscore5u  -mscore7
           -mscore7d

           SH Options -m1  -m2  -m2e -m2a-nofpu  -m2a-single-only  -m2a-single  -m2a -m3  -m3e
           -m4-nofpu  -m4-single-only  -m4-single  -m4 -m4a-nofpu  -m4a-single-only  -m4a-single
           -m4a  -m4al -mb  -ml  -mdalign  -mrelax -mbigtable  -mfmovd  -mrenesas  -mno-renesas
           -mnomacsave -mieee  -mno-ieee  -mbitops  -misize  -minline-ic_invalidate  -mpadstruct
           -mprefergot  -musermode  -multcost=number  -mdiv=strategy -mdivsi3_libfunc=name
           -mfixed-range=register-range -maccumulate-outgoing-args -matomic-model=atomic-model
           -mbranch-cost=num  -mzdcbranch  -mno-zdcbranch -mcbranch-force-delay-slot -mfused-madd
           -mno-fused-madd  -mfsca  -mno-fsca  -mfsrra  -mno-fsrra -mpretend-cmove  -mtas

           Solaris 2 Options -mclear-hwcap  -mno-clear-hwcap  -mimpure-text  -mno-impure-text
           -pthreads

           SPARC Options -mcpu=cpu-type -mtune=cpu-type -mcmodel=code-model -mmemory-model=mem-
           model -m32  -m64  -mapp-regs  -mno-app-regs -mfaster-structs  -mno-faster-structs
           -mflat  -mno-flat -mfpu  -mno-fpu  -mhard-float  -msoft-float -mhard-quad-float
           -msoft-quad-float -mstack-bias  -mno-stack-bias -mstd-struct-return
           -mno-std-struct-return -munaligned-doubles  -mno-unaligned-doubles -muser-mode
           -mno-user-mode -mv8plus  -mno-v8plus  -mvis  -mno-vis -mvis2  -mno-vis2  -mvis3
           -mno-vis3 -mvis4 -mno-vis4 -mvis4b -mno-vis4b -mcbcond  -mno-cbcond  -mfmaf  -mno-fmaf
           -mfsmuld  -mno-fsmuld -mpopc  -mno-popc  -msubxc  -mno-subxc -mfix-at697f  -mfix-ut699
           -mfix-ut700  -mfix-gr712rc -mlra  -mno-lra

           SPU Options -mwarn-reloc  -merror-reloc -msafe-dma  -munsafe-dma -mbranch-hints
           -msmall-mem  -mlarge-mem  -mstdmain -mfixed-range=register-range -mea32  -mea64
           -maddress-space-conversion  -mno-address-space-conversion -mcache-size=cache-size
           -matomic-updates  -mno-atomic-updates

           System V Options -Qy  -Qn  -YP,paths  -Ym,dir

           TILE-Gx Options -mcpu=CPU  -m32  -m64  -mbig-endian  -mlittle-endian -mcmodel=code-
           model

           TILEPro Options -mcpu=cpu  -m32

           V850 Options -mlong-calls  -mno-long-calls  -mep  -mno-ep -mprolog-function
           -mno-prolog-function  -mspace -mtda=n  -msda=n  -mzda=n -mapp-regs  -mno-app-regs
           -mdisable-callt  -mno-disable-callt -mv850e2v3  -mv850e2  -mv850e1  -mv850es -mv850e
           -mv850  -mv850e3v5 -mloop -mrelax -mlong-jumps -msoft-float -mhard-float -mgcc-abi
           -mrh850-abi -mbig-switch

           VAX Options -mg  -mgnu  -munix

           Visium Options -mdebug  -msim  -mfpu  -mno-fpu  -mhard-float  -msoft-float -mcpu=cpu-
           type  -mtune=cpu-type  -msv-mode  -muser-mode

           VMS Options -mvms-return-codes  -mdebug-main=prefix  -mmalloc64 -mpointer-size=size

           VxWorks Options -mrtp  -non-static  -Bstatic  -Bdynamic -Xbind-lazy  -Xbind-now

           x86 Options -mtune=cpu-type  -march=cpu-type -mtune-ctrl=feature-list
           -mdump-tune-features  -mno-default -mfpmath=unit -masm=dialect  -mno-fancy-math-387
           -mno-fp-ret-in-387  -m80387  -mhard-float  -msoft-float -mno-wide-multiply  -mrtd
           -malign-double -mpreferred-stack-boundary=num -mincoming-stack-boundary=num -mcld
           -mcx16  -msahf  -mmovbe  -mcrc32 -mrecip  -mrecip=opt -mvzeroupper  -mprefer-avx128
           -mprefer-vector-width=opt -mmmx  -msse  -msse2  -msse3  -mssse3  -msse4.1  -msse4.2
           -msse4  -mavx -mavx2  -mavx512f  -mavx512pf  -mavx512er  -mavx512cd  -mavx512vl
           -mavx512bw  -mavx512dq  -mavx512ifma  -mavx512vbmi  -msha  -maes -mpclmul  -mfsgsbase
           -mrdrnd  -mf16c  -mfma -mpconfig -mwbnoinvd -mprefetchwt1  -mclflushopt  -mclwb
           -mxsavec  -mxsaves -msse4a  -m3dnow  -m3dnowa  -mpopcnt  -mabm  -mbmi  -mtbm  -mfma4
           -mxop -madx  -mlzcnt  -mbmi2  -mfxsr  -mxsave  -mxsaveopt  -mrtm  -mlwp  -mmpx
           -mmwaitx  -mclzero  -mpku  -mthreads -mgfni  -mvaes -mshstk -mforce-indirect-call
           -mavx512vbmi2 -mvpclmulqdq -mavx512bitalg -mmovdiri -mmovdir64b -mavx512vpopcntdq
           -mavx5124fmaps  -mavx512vnni  -mavx5124vnniw  -mprfchw  -mrdpid -mrdseed  -msgx
           -mms-bitfields  -mno-align-stringops  -minline-all-stringops
           -minline-stringops-dynamically  -mstringop-strategy=alg -mmemcpy-strategy=strategy
           -mmemset-strategy=strategy -mpush-args  -maccumulate-outgoing-args
           -m128bit-long-double -m96bit-long-double  -mlong-double-64  -mlong-double-80
           -mlong-double-128 -mregparm=num  -msseregparm -mveclibabi=type  -mvect8-ret-in-mem
           -mpc32  -mpc64  -mpc80  -mstackrealign -momit-leaf-frame-pointer  -mno-red-zone
           -mno-tls-direct-seg-refs -mcmodel=code-model  -mabi=name  -maddress-mode=mode -m32
           -m64  -mx32  -m16  -miamcu  -mlarge-data-threshold=num -msse2avx  -mfentry
           -mrecord-mcount  -mnop-mcount  -m8bit-idiv -mavx256-split-unaligned-load
           -mavx256-split-unaligned-store -malign-data=type  -mstack-protector-guard=guard
           -mstack-protector-guard-reg=reg -mstack-protector-guard-offset=offset
           -mstack-protector-guard-symbol=symbol -mmitigate-rop -mgeneral-regs-only
           -mcall-ms2sysv-xlogues -mindirect-branch=choice -mfunction-return=choice
           -mindirect-branch-register

           x86 Windows Options -mconsole  -mcygwin  -mno-cygwin  -mdll -mnop-fun-dllimport
           -mthread -municode  -mwin32  -mwindows  -fno-set-stack-executable

           Xstormy16 Options -msim

           Xtensa Options -mconst16  -mno-const16 -mfused-madd  -mno-fused-madd -mforce-no-pic
           -mserialize-volatile  -mno-serialize-volatile -mtext-section-literals
           -mno-text-section-literals -mauto-litpools  -mno-auto-litpools -mtarget-align
           -mno-target-align -mlongcalls  -mno-longcalls

           zSeries Options See S/390 and zSeries Options.

   Options Controlling the Kind of Output
       Compilation can involve up to four stages: preprocessing, compilation proper, assembly and
       linking, always in that order.  GCC is capable of preprocessing and compiling several
       files either into several assembler input files, or into one assembler input file; then
       each assembler input file produces an object file, and linking combines all the object
       files (those newly compiled, and those specified as input) into an executable file.

       For any given input file, the file name suffix determines what kind of compilation is
       done:

       file.c
           C source code that must be preprocessed.

       file.i
           C source code that should not be preprocessed.

       file.ii
           C++ source code that should not be preprocessed.

       file.m
           Objective-C source code.  Note that you must link with the libobjc library to make an
           Objective-C program work.

       file.mi
           Objective-C source code that should not be preprocessed.

       file.mm
       file.M
           Objective-C++ source code.  Note that you must link with the libobjc library to make
           an Objective-C++ program work.  Note that .M refers to a literal capital M.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.h
           C, C++, Objective-C or Objective-C++ header file to be turned into a precompiled
           header (default), or C, C++ header file to be turned into an Ada spec (via the
           -fdump-ada-spec switch).

       file.cc
       file.cp
       file.cxx
       file.cpp
       file.CPP
       file.c++
       file.C
           C++ source code that must be preprocessed.  Note that in .cxx, the last two letters
           must both be literally x.  Likewise, .C refers to a literal capital C.

       file.mm
       file.M
           Objective-C++ source code that must be preprocessed.

       file.mii
           Objective-C++ source code that should not be preprocessed.

       file.hh
       file.H
       file.hp
       file.hxx
       file.hpp
       file.HPP
       file.h++
       file.tcc
           C++ header file to be turned into a precompiled header or Ada spec.

       file.f
       file.for
       file.ftn
           Fixed form Fortran source code that should not be preprocessed.

       file.F
       file.FOR
       file.fpp
       file.FPP
       file.FTN
           Fixed form Fortran source code that must be preprocessed (with the traditional
           preprocessor).

       file.f90
       file.f95
       file.f03
       file.f08
           Free form Fortran source code that should not be preprocessed.

       file.F90
       file.F95
       file.F03
       file.F08
           Free form Fortran source code that must be preprocessed (with the traditional
           preprocessor).

       file.go
           Go source code.

       file.brig
           BRIG files (binary representation of HSAIL).

       file.d
           D source code.

       file.di
           D interface file.

       file.dd
           D documentation code (Ddoc).

       file.ads
           Ada source code file that contains a library unit declaration (a declaration of a
           package, subprogram, or generic, or a generic instantiation), or a library unit
           renaming declaration (a package, generic, or subprogram renaming declaration).  Such
           files are also called specs.

       file.adb
           Ada source code file containing a library unit body (a subprogram or package body).
           Such files are also called bodies.

       file.s
           Assembler code.

       file.S
       file.sx
           Assembler code that must be preprocessed.

       other
           An object file to be fed straight into linking.  Any file name with no recognized
           suffix is treated this way.

       You can specify the input language explicitly with the -x option:

       -x language
           Specify explicitly the language for the following input files (rather than letting the
           compiler choose a default based on the file name suffix).  This option applies to all
           following input files until the next -x option.  Possible values for language are:

                   c  c-header  cpp-output
                   c++  c++-header  c++-cpp-output
                   objective-c  objective-c-header  objective-c-cpp-output
                   objective-c++ objective-c++-header objective-c++-cpp-output
                   assembler  assembler-with-cpp
                   ada
                   d
                   f77  f77-cpp-input f95  f95-cpp-input
                   go
                   brig

       -x none
           Turn off any specification of a language, so that subsequent files are handled
           according to their file name suffixes (as they are if -x has not been used at all).

       If you only want some of the stages of compilation, you can use -x (or filename suffixes)
       to tell gcc where to start, and one of the options -c, -S, or -E to say where gcc is to
       stop.  Note that some combinations (for example, -x cpp-output -E) instruct gcc to do
       nothing at all.

       -c  Compile or assemble the source files, but do not link.  The linking stage simply is
           not done.  The ultimate output is in the form of an object file for each source file.

           By default, the object file name for a source file is made by replacing the suffix .c,
           .i, .s, etc., with .o.

           Unrecognized input files, not requiring compilation or assembly, are ignored.

       -S  Stop after the stage of compilation proper; do not assemble.  The output is in the
           form of an assembler code file for each non-assembler input file specified.

           By default, the assembler file name for a source file is made by replacing the suffix
           .c, .i, etc., with .s.

           Input files that don't require compilation are ignored.

       -E  Stop after the preprocessing stage; do not run the compiler proper.  The output is in
           the form of preprocessed source code, which is sent to the standard output.

           Input files that don't require preprocessing are ignored.

       -o file
           Place output in file file.  This applies to whatever sort of output is being produced,
           whether it be an executable file, an object file, an assembler file or preprocessed C
           code.

           If -o is not specified, the default is to put an executable file in a.out, the object
           file for source.suffix in source.o, its assembler file in source.s, a precompiled
           header file in source.suffix.gch, and all preprocessed C source on standard output.

       -v  Print (on standard error output) the commands executed to run the stages of
           compilation.  Also print the version number of the compiler driver program and of the
           preprocessor and the compiler proper.

       -###
           Like -v except the commands are not executed and arguments are quoted unless they
           contain only alphanumeric characters or "./-_".  This is useful for shell scripts to
           capture the driver-generated command lines.

       --help
           Print (on the standard output) a description of the command-line options understood by
           gcc.  If the -v option is also specified then --help is also passed on to the various
           processes invoked by gcc, so that they can display the command-line options they
           accept.  If the -Wextra option has also been specified (prior to the --help option),
           then command-line options that have no documentation associated with them are also
           displayed.

       --target-help
           Print (on the standard output) a description of target-specific command-line options
           for each tool.  For some targets extra target-specific information may also be
           printed.

       --help={class|[^]qualifier}[,...]
           Print (on the standard output) a description of the command-line options understood by
           the compiler that fit into all specified classes and qualifiers.  These are the
           supported classes:

           optimizers
               Display all of the optimization options supported by the compiler.

           warnings
               Display all of the options controlling warning messages produced by the compiler.

           target
               Display target-specific options.  Unlike the --target-help option however, target-
               specific options of the linker and assembler are not displayed.  This is because
               those tools do not currently support the extended --help= syntax.

           params
               Display the values recognized by the --param option.

           language
               Display the options supported for language, where language is the name of one of
               the languages supported in this version of GCC.

           common
               Display the options that are common to all languages.

           These are the supported qualifiers:

           undocumented
               Display only those options that are undocumented.

           joined
               Display options taking an argument that appears after an equal sign in the same
               continuous piece of text, such as: --help=target.

           separate
               Display options taking an argument that appears as a separate word following the
               original option, such as: -o output-file.

           Thus for example to display all the undocumented target-specific switches supported by
           the compiler, use:

                   --help=target,undocumented

           The sense of a qualifier can be inverted by prefixing it with the ^ character, so for
           example to display all binary warning options (i.e., ones that are either on or off
           and that do not take an argument) that have a description, use:

                   --help=warnings,^joined,^undocumented

           The argument to --help= should not consist solely of inverted qualifiers.

           Combining several classes is possible, although this usually restricts the output so
           much that there is nothing to display.  One case where it does work, however, is when
           one of the classes is target.  For example, to display all the target-specific
           optimization options, use:

                   --help=target,optimizers

           The --help= option can be repeated on the command line.  Each successive use displays
           its requested class of options, skipping those that have already been displayed.

           If the -Q option appears on the command line before the --help= option, then the
           descriptive text displayed by --help= is changed.  Instead of describing the displayed
           options, an indication is given as to whether the option is enabled, disabled or set
           to a specific value (assuming that the compiler knows this at the point where the
           --help= option is used).

           Here is a truncated example from the ARM port of gcc:

                     % gcc -Q -mabi=2 --help=target -c
                     The following options are target specific:
                     -mabi=                                2
                     -mabort-on-noreturn                   [disabled]
                     -mapcs                                [disabled]

           The output is sensitive to the effects of previous command-line options, so for
           example it is possible to find out which optimizations are enabled at -O2 by using:

                   -Q -O2 --help=optimizers

           Alternatively you can discover which binary optimizations are enabled by -O3 by using:

                   gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
                   gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
                   diff /tmp/O2-opts /tmp/O3-opts | grep enabled

       --version
           Display the version number and copyrights of the invoked GCC.

       -pass-exit-codes
           Normally the gcc program exits with the code of 1 if any phase of the compiler returns
           a non-success return code.  If you specify -pass-exit-codes, the gcc program instead
           returns with the numerically highest error produced by any phase returning an error
           indication.  The C, C++, and Fortran front ends return 4 if an internal compiler error
           is encountered.

       -pipe
           Use pipes rather than temporary files for communication between the various stages of
           compilation.  This fails to work on some systems where the assembler is unable to read
           from a pipe; but the GNU assembler has no trouble.

       -specs=file
           Process file after the compiler reads in the standard specs file, in order to override
           the defaults which the gcc driver program uses when determining what switches to pass
           to cc1, cc1plus, as, ld, etc.  More than one -specs=file can be specified on the
           command line, and they are processed in order, from left to right.

       -wrapper
           Invoke all subcommands under a wrapper program.  The name of the wrapper program and
           its parameters are passed as a comma separated list.

                   gcc -c t.c -wrapper gdb,--args

           This invokes all subprograms of gcc under gdb --args, thus the invocation of cc1 is
           gdb --args cc1 ....

       -ffile-prefix-map=old=new
           When compiling files residing in directory old, record any references to them in the
           result of the compilation as if the files resided in directory new instead.
           Specifying this option is equivalent to specifying all the individual -f*-prefix-map
           options.  This can be used to make reproducible builds that are location independent.
           See also -fmacro-prefix-map and -fdebug-prefix-map.

       -fplugin=name.so
           Load the plugin code in file name.so, assumed to be a shared object to be dlopen'd by
           the compiler.  The base name of the shared object file is used to identify the plugin
           for the purposes of argument parsing (See -fplugin-arg-name-key=value below).  Each
           plugin should define the callback functions specified in the Plugins API.

       -fplugin-arg-name-key=value
           Define an argument called key with a value of value for the plugin called name.

       -fdump-ada-spec[-slim]
           For C and C++ source and include files, generate corresponding Ada specs.

       -fada-spec-parent=unit
           In conjunction with -fdump-ada-spec[-slim] above, generate Ada specs as child units of
           parent unit.

       -fdump-go-spec=file
           For input files in any language, generate corresponding Go declarations in file.  This
           generates Go "const", "type", "var", and "func" declarations which may be a useful way
           to start writing a Go interface to code written in some other language.

       @file
           Read command-line options from file.  The options read are inserted in place of the
           original @file option.  If file does not exist, or cannot be read, then the option
           will be treated literally, and not removed.

           Options in file are separated by whitespace.  A whitespace character may be included
           in an option by surrounding the entire option in either single or double quotes.  Any
           character (including a backslash) may be included by prefixing the character to be
           included with a backslash.  The file may itself contain additional @file options; any
           such options will be processed recursively.

   Compiling C++ Programs
       C++ source files conventionally use one of the suffixes .C, .cc, .cpp, .CPP, .c++, .cp, or
       .cxx; C++ header files often use .hh, .hpp, .H, or (for shared template code) .tcc; and
       preprocessed C++ files use the suffix .ii.  GCC recognizes files with these names and
       compiles them as C++ programs even if you call the compiler the same way as for compiling
       C programs (usually with the name gcc).

       However, the use of gcc does not add the C++ library.  g++ is a program that calls GCC and
       automatically specifies linking against the C++ library.  It treats .c, .h and .i files as
       C++ source files instead of C source files unless -x is used.  This program is also useful
       when precompiling a C header file with a .h extension for use in C++ compilations.  On
       many systems, g++ is also installed with the name c++.

       When you compile C++ programs, you may specify many of the same command-line options that
       you use for compiling programs in any language; or command-line options meaningful for C
       and related languages; or options that are meaningful only for C++ programs.

   Options Controlling C Dialect
       The following options control the dialect of C (or languages derived from C, such as C++,
       Objective-C and Objective-C++) that the compiler accepts:

       -ansi
           In C mode, this is equivalent to -std=c90. In C++ mode, it is equivalent to
           -std=c++98.

           This turns off certain features of GCC that are incompatible with ISO C90 (when
           compiling C code), or of standard C++ (when compiling C++ code), such as the "asm" and
           "typeof" keywords, and predefined macros such as "unix" and "vax" that identify the
           type of system you are using.  It also enables the undesirable and rarely used ISO
           trigraph feature.  For the C compiler, it disables recognition of C++ style //
           comments as well as the "inline" keyword.

           The alternate keywords "__asm__", "__extension__", "__inline__" and "__typeof__"
           continue to work despite -ansi.  You would not want to use them in an ISO C program,
           of course, but it is useful to put them in header files that might be included in
           compilations done with -ansi.  Alternate predefined macros such as "__unix__" and
           "__vax__" are also available, with or without -ansi.

           The -ansi option does not cause non-ISO programs to be rejected gratuitously.  For
           that, -Wpedantic is required in addition to -ansi.

           The macro "__STRICT_ANSI__" is predefined when the -ansi option is used.  Some header
           files may notice this macro and refrain from declaring certain functions or defining
           certain macros that the ISO standard doesn't call for; this is to avoid interfering
           with any programs that might use these names for other things.

           Functions that are normally built in but do not have semantics defined by ISO C (such
           as "alloca" and "ffs") are not built-in functions when -ansi is used.

       -std=
           Determine the language standard.   This option is currently only supported when
           compiling C or C++.

           The compiler can accept several base standards, such as c90 or c++98, and GNU dialects
           of those standards, such as gnu90 or gnu++98.  When a base standard is specified, the
           compiler accepts all programs following that standard plus those using GNU extensions
           that do not contradict it.  For example, -std=c90 turns off certain features of GCC
           that are incompatible with ISO C90, such as the "asm" and "typeof" keywords, but not
           other GNU extensions that do not have a meaning in ISO C90, such as omitting the
           middle term of a "?:" expression. On the other hand, when a GNU dialect of a standard
           is specified, all features supported by the compiler are enabled, even when those
           features change the meaning of the base standard.  As a result, some strict-conforming
           programs may be rejected.  The particular standard is used by -Wpedantic to identify
           which features are GNU extensions given that version of the standard. For example
           -std=gnu90 -Wpedantic warns about C++ style // comments, while -std=gnu99 -Wpedantic
           does not.

           A value for this option must be provided; possible values are

           c90
           c89
           iso9899:1990
               Support all ISO C90 programs (certain GNU extensions that conflict with ISO C90
               are disabled). Same as -ansi for C code.

           iso9899:199409
               ISO C90 as modified in amendment 1.

           c99
           c9x
           iso9899:1999
           iso9899:199x
               ISO C99.  This standard is substantially completely supported, modulo bugs and
               floating-point issues (mainly but not entirely relating to optional C99 features
               from Annexes F and G).  See <http://gcc.gnu.org/c99status.html> for more
               information.  The names c9x and iso9899:199x are deprecated.

           c11
           c1x
           iso9899:2011
               ISO C11, the 2011 revision of the ISO C standard.  This standard is substantially
               completely supported, modulo bugs, floating-point issues (mainly but not entirely
               relating to optional C11 features from Annexes F and G) and the optional Annexes K
               (Bounds-checking interfaces) and L (Analyzability).  The name c1x is deprecated.

           c17
           c18
           iso9899:2017
           iso9899:2018
               ISO C17, the 2017 revision of the ISO C standard (expected to be published in
               2018).  This standard is same as C11 except for corrections of defects (all of
               which are also applied with -std=c11) and a new value of "__STDC_VERSION__", and
               so is supported to the same extent as C11.

           gnu90
           gnu89
               GNU dialect of ISO C90 (including some C99 features).

           gnu99
           gnu9x
               GNU dialect of ISO C99.  The name gnu9x is deprecated.

           gnu11
           gnu1x
               GNU dialect of ISO C11.  The name gnu1x is deprecated.

           gnu17
           gnu18
               GNU dialect of ISO C17.  This is the default for C code.

           c++98
           c++03
               The 1998 ISO C++ standard plus the 2003 technical corrigendum and some additional
               defect reports. Same as -ansi for C++ code.

           gnu++98
           gnu++03
               GNU dialect of -std=c++98.

           c++11
           c++0x
               The 2011 ISO C++ standard plus amendments.  The name c++0x is deprecated.

           gnu++11
           gnu++0x
               GNU dialect of -std=c++11.  The name gnu++0x is deprecated.

           c++14
           c++1y
               The 2014 ISO C++ standard plus amendments.  The name c++1y is deprecated.

           gnu++14
           gnu++1y
               GNU dialect of -std=c++14.  This is the default for C++ code.  The name gnu++1y is
               deprecated.

           c++17
           c++1z
               The 2017 ISO C++ standard plus amendments.  The name c++1z is deprecated.

           gnu++17
           gnu++1z
               GNU dialect of -std=c++17.  The name gnu++1z is deprecated.

           c++2a
               The next revision of the ISO C++ standard, tentatively planned for 2020.  Support
               is highly experimental, and will almost certainly change in incompatible ways in
               future releases.

           gnu++2a
               GNU dialect of -std=c++2a.  Support is highly experimental, and will almost
               certainly change in incompatible ways in future releases.

       -fgnu89-inline
           The option -fgnu89-inline tells GCC to use the traditional GNU semantics for "inline"
           functions when in C99 mode.

           Using this option is roughly equivalent to adding the "gnu_inline" function attribute
           to all inline functions.

           The option -fno-gnu89-inline explicitly tells GCC to use the C99 semantics for
           "inline" when in C99 or gnu99 mode (i.e., it specifies the default behavior).  This
           option is not supported in -std=c90 or -std=gnu90 mode.

           The preprocessor macros "__GNUC_GNU_INLINE__" and "__GNUC_STDC_INLINE__" may be used
           to check which semantics are in effect for "inline" functions.

       -fpermitted-flt-eval-methods=style
           ISO/IEC TS 18661-3 defines new permissible values for "FLT_EVAL_METHOD" that indicate
           that operations and constants with a semantic type that is an interchange or extended
           format should be evaluated to the precision and range of that type.  These new values
           are a superset of those permitted under C99/C11, which does not specify the meaning of
           other positive values of "FLT_EVAL_METHOD".  As such, code conforming to C11 may not
           have been written expecting the possibility of the new values.

           -fpermitted-flt-eval-methods specifies whether the compiler should allow only the
           values of "FLT_EVAL_METHOD" specified in C99/C11, or the extended set of values
           specified in ISO/IEC TS 18661-3.

           style is either "c11" or "ts-18661-3" as appropriate.

           The default when in a standards compliant mode (-std=c11 or similar) is
           -fpermitted-flt-eval-methods=c11.  The default when in a GNU dialect (-std=gnu11 or
           similar) is -fpermitted-flt-eval-methods=ts-18661-3.

       -aux-info filename
           Output to the given filename prototyped declarations for all functions declared and/or
           defined in a translation unit, including those in header files.  This option is
           silently ignored in any language other than C.

           Besides declarations, the file indicates, in comments, the origin of each declaration
           (source file and line), whether the declaration was implicit, prototyped or
           unprototyped (I, N for new or O for old, respectively, in the first character after
           the line number and the colon), and whether it came from a declaration or a definition
           (C or F, respectively, in the following character).  In the case of function
           definitions, a K&R-style list of arguments followed by their declarations is also
           provided, inside comments, after the declaration.

       -fallow-parameterless-variadic-functions
           Accept variadic functions without named parameters.

           Although it is possible to define such a function, this is not very useful as it is
           not possible to read the arguments.  This is only supported for C as this construct is
           allowed by C++.

       -fno-asm
           Do not recognize "asm", "inline" or "typeof" as a keyword, so that code can use these
           words as identifiers.  You can use the keywords "__asm__", "__inline__" and
           "__typeof__" instead.  -ansi implies -fno-asm.

           In C++, this switch only affects the "typeof" keyword, since "asm" and "inline" are
           standard keywords.  You may want to use the -fno-gnu-keywords flag instead, which has
           the same effect.  In C99 mode (-std=c99 or -std=gnu99), this switch only affects the
           "asm" and "typeof" keywords, since "inline" is a standard keyword in ISO C99.

       -fno-builtin
       -fno-builtin-function
           Don't recognize built-in functions that do not begin with __builtin_ as prefix.

           GCC normally generates special code to handle certain built-in functions more
           efficiently; for instance, calls to "alloca" may become single instructions which
           adjust the stack directly, and calls to "memcpy" may become inline copy loops.  The
           resulting code is often both smaller and faster, but since the function calls no
           longer appear as such, you cannot set a breakpoint on those calls, nor can you change
           the behavior of the functions by linking with a different library.  In addition, when
           a function is recognized as a built-in function, GCC may use information about that
           function to warn about problems with calls to that function, or to generate more
           efficient code, even if the resulting code still contains calls to that function.  For
           example, warnings are given with -Wformat for bad calls to "printf" when "printf" is
           built in and "strlen" is known not to modify global memory.

           With the -fno-builtin-function option only the built-in function function is disabled.
           function must not begin with __builtin_.  If a function is named that is not built-in
           in this version of GCC, this option is ignored.  There is no corresponding
           -fbuiltin-function option; if you wish to enable built-in functions selectively when
           using -fno-builtin or -ffreestanding, you may define macros such as:

                   #define abs(n)          __builtin_abs ((n))
                   #define strcpy(d, s)    __builtin_strcpy ((d), (s))

       -fgimple
           Enable parsing of function definitions marked with "__GIMPLE".  This is an
           experimental feature that allows unit testing of GIMPLE passes.

       -fhosted
           Assert that compilation targets a hosted environment.  This implies -fbuiltin.  A
           hosted environment is one in which the entire standard library is available, and in
           which "main" has a return type of "int".  Examples are nearly everything except a
           kernel.  This is equivalent to -fno-freestanding.

       -ffreestanding
           Assert that compilation targets a freestanding environment.  This implies
           -fno-builtin.  A freestanding environment is one in which the standard library may not
           exist, and program startup may not necessarily be at "main".  The most obvious example
           is an OS kernel.  This is equivalent to -fno-hosted.

       -fopenacc
           Enable handling of OpenACC directives "#pragma acc" in C/C++ and "!$acc" in Fortran.
           When -fopenacc is specified, the compiler generates accelerated code according to the
           OpenACC Application Programming Interface v2.0 <https://www.openacc.org>.  This option
           implies -pthread, and thus is only supported on targets that have support for
           -pthread.

       -fopenacc-dim=geom
           Specify default compute dimensions for parallel offload regions that do not explicitly
           specify.  The geom value is a triple of ':'-separated sizes, in order 'gang', 'worker'
           and, 'vector'.  A size can be omitted, to use a target-specific default value.

       -fopenmp
           Enable handling of OpenMP directives "#pragma omp" in C/C++ and "!$omp" in Fortran.
           When -fopenmp is specified, the compiler generates parallel code according to the
           OpenMP Application Program Interface v4.5 <http://www.openmp.org/>.  This option
           implies -pthread, and thus is only supported on targets that have support for
           -pthread. -fopenmp implies -fopenmp-simd.

       -fopenmp-simd
           Enable handling of OpenMP's SIMD directives with "#pragma omp" in C/C++ and "!$omp" in
           Fortran. Other OpenMP directives are ignored.

       -fgnu-tm
           When the option -fgnu-tm is specified, the compiler generates code for the Linux
           variant of Intel's current Transactional Memory ABI specification document (Revision
           1.1, May 6 2009).  This is an experimental feature whose interface may change in
           future versions of GCC, as the official specification changes.  Please note that not
           all architectures are supported for this feature.

           For more information on GCC's support for transactional memory,

           Note that the transactional memory feature is not supported with non-call exceptions
           (-fnon-call-exceptions).

       -fms-extensions
           Accept some non-standard constructs used in Microsoft header files.

           In C++ code, this allows member names in structures to be similar to previous types
           declarations.

                   typedef int UOW;
                   struct ABC {
                     UOW UOW;
                   };

           Some cases of unnamed fields in structures and unions are only accepted with this
           option.

           Note that this option is off for all targets but x86 targets using ms-abi.

       -fplan9-extensions
           Accept some non-standard constructs used in Plan 9 code.

           This enables -fms-extensions, permits passing pointers to structures with anonymous
           fields to functions that expect pointers to elements of the type of the field, and
           permits referring to anonymous fields declared using a typedef.    This is only
           supported for C, not C++.

       -fcond-mismatch
           Allow conditional expressions with mismatched types in the second and third arguments.
           The value of such an expression is void.  This option is not supported for C++.

       -flax-vector-conversions
           Allow implicit conversions between vectors with differing numbers of elements and/or
           incompatible element types.  This option should not be used for new code.

       -funsigned-char
           Let the type "char" be unsigned, like "unsigned char".

           Each kind of machine has a default for what "char" should be.  It is either like
           "unsigned char" by default or like "signed char" by default.

           Ideally, a portable program should always use "signed char" or "unsigned char" when it
           depends on the signedness of an object.  But many programs have been written to use
           plain "char" and expect it to be signed, or expect it to be unsigned, depending on the
           machines they were written for.  This option, and its inverse, let you make such a
           program work with the opposite default.

           The type "char" is always a distinct type from each of "signed char" or "unsigned
           char", even though its behavior is always just like one of those two.

       -fsigned-char
           Let the type "char" be signed, like "signed char".

           Note that this is equivalent to -fno-unsigned-char, which is the negative form of
           -funsigned-char.  Likewise, the option -fno-signed-char is equivalent to
           -funsigned-char.

       -fsigned-bitfields
       -funsigned-bitfields
       -fno-signed-bitfields
       -fno-unsigned-bitfields
           These options control whether a bit-field is signed or unsigned, when the declaration
           does not use either "signed" or "unsigned".  By default, such a bit-field is signed,
           because this is consistent: the basic integer types such as "int" are signed types.

       -fsso-struct=endianness
           Set the default scalar storage order of structures and unions to the specified
           endianness.  The accepted values are big-endian, little-endian and native for the
           native endianness of the target (the default).  This option is not supported for C++.

           Warning: the -fsso-struct switch causes GCC to generate code that is not binary
           compatible with code generated without it if the specified endianness is not the
           native endianness of the target.

   Options Controlling C++ Dialect
       This section describes the command-line options that are only meaningful for C++ programs.
       You can also use most of the GNU compiler options regardless of what language your program
       is in.  For example, you might compile a file firstClass.C like this:

               g++ -g -fstrict-enums -O -c firstClass.C

       In this example, only -fstrict-enums is an option meant only for C++ programs; you can use
       the other options with any language supported by GCC.

       Some options for compiling C programs, such as -std, are also relevant for C++ programs.

       Here is a list of options that are only for compiling C++ programs:

       -fabi-version=n
           Use version n of the C++ ABI.  The default is version 0.

           Version 0 refers to the version conforming most closely to the C++ ABI specification.
           Therefore, the ABI obtained using version 0 will change in different versions of G++
           as ABI bugs are fixed.

           Version 1 is the version of the C++ ABI that first appeared in G++ 3.2.

           Version 2 is the version of the C++ ABI that first appeared in G++ 3.4, and was the
           default through G++ 4.9.

           Version 3 corrects an error in mangling a constant address as a template argument.

           Version 4, which first appeared in G++ 4.5, implements a standard mangling for vector
           types.

           Version 5, which first appeared in G++ 4.6, corrects the mangling of attribute
           const/volatile on function pointer types, decltype of a plain decl, and use of a
           function parameter in the declaration of another parameter.

           Version 6, which first appeared in G++ 4.7, corrects the promotion behavior of C++11
           scoped enums and the mangling of template argument packs, const/static_cast, prefix ++
           and --, and a class scope function used as a template argument.

           Version 7, which first appeared in G++ 4.8, that treats nullptr_t as a builtin type
           and corrects the mangling of lambdas in default argument scope.

           Version 8, which first appeared in G++ 4.9, corrects the substitution behavior of
           function types with function-cv-qualifiers.

           Version 9, which first appeared in G++ 5.2, corrects the alignment of "nullptr_t".

           Version 10, which first appeared in G++ 6.1, adds mangling of attributes that affect
           type identity, such as ia32 calling convention attributes (e.g. stdcall).

           Version 11, which first appeared in G++ 7, corrects the mangling of sizeof...
           expressions and operator names.  For multiple entities with the same name within a
           function, that are declared in different scopes, the mangling now changes starting
           with the twelfth occurrence.  It also implies -fnew-inheriting-ctors.

           Version 12, which first appeared in G++ 8, corrects the calling conventions for empty
           classes on the x86_64 target and for classes with only deleted copy/move constructors.
           It accidentally changes the calling convention for classes with a deleted copy
           constructor and a trivial move constructor.

           Version 13, which first appeared in G++ 8.2, fixes the accidental change in version
           12.

           See also -Wabi.

       -fabi-compat-version=n
           On targets that support strong aliases, G++ works around mangling changes by creating
           an alias with the correct mangled name when defining a symbol with an incorrect
           mangled name.  This switch specifies which ABI version to use for the alias.

           With -fabi-version=0 (the default), this defaults to 11 (GCC 7 compatibility).  If
           another ABI version is explicitly selected, this defaults to 0.  For compatibility
           with GCC versions 3.2 through 4.9, use -fabi-compat-version=2.

           If this option is not provided but -Wabi=n is, that version is used for compatibility
           aliases.  If this option is provided along with -Wabi (without the version), the
           version from this option is used for the warning.

       -fno-access-control
           Turn off all access checking.  This switch is mainly useful for working around bugs in
           the access control code.

       -faligned-new
           Enable support for C++17 "new" of types that require more alignment than "void*
           ::operator new(std::size_t)" provides.  A numeric argument such as "-faligned-new=32"
           can be used to specify how much alignment (in bytes) is provided by that function, but
           few users will need to override the default of "alignof(std::max_align_t)".

           This flag is enabled by default for -std=c++17.

       -fcheck-new
           Check that the pointer returned by "operator new" is non-null before attempting to
           modify the storage allocated.  This check is normally unnecessary because the C++
           standard specifies that "operator new" only returns 0 if it is declared "throw()", in
           which case the compiler always checks the return value even without this option.  In
           all other cases, when "operator new" has a non-empty exception specification, memory
           exhaustion is signalled by throwing "std::bad_alloc".  See also new (nothrow).

       -fconcepts
           Enable support for the C++ Extensions for Concepts Technical Specification, ISO 19217
           (2015), which allows code like

                   template <class T> concept bool Addable = requires (T t) { t + t; };
                   template <Addable T> T add (T a, T b) { return a + b; }

       -fconstexpr-depth=n
           Set the maximum nested evaluation depth for C++11 constexpr functions to n.  A limit
           is needed to detect endless recursion during constant expression evaluation.  The
           minimum specified by the standard is 512.

       -fconstexpr-loop-limit=n
           Set the maximum number of iterations for a loop in C++14 constexpr functions to n.  A
           limit is needed to detect infinite loops during constant expression evaluation.  The
           default is 262144 (1<<18).

       -fdeduce-init-list
           Enable deduction of a template type parameter as "std::initializer_list" from a brace-
           enclosed initializer list, i.e.

                   template <class T> auto forward(T t) -> decltype (realfn (t))
                   {
                     return realfn (t);
                   }

                   void f()
                   {
                     forward({1,2}); // call forward<std::initializer_list<int>>
                   }

           This deduction was implemented as a possible extension to the originally proposed
           semantics for the C++11 standard, but was not part of the final standard, so it is
           disabled by default.  This option is deprecated, and may be removed in a future
           version of G++.

       -ffriend-injection
           Inject friend functions into the enclosing namespace, so that they are visible outside
           the scope of the class in which they are declared.  Friend functions were documented
           to work this way in the old Annotated C++ Reference Manual.  However, in ISO C++ a
           friend function that is not declared in an enclosing scope can only be found using
           argument dependent lookup.  GCC defaults to the standard behavior.

           This option is deprecated and will be removed.

       -fno-elide-constructors
           The C++ standard allows an implementation to omit creating a temporary that is only
           used to initialize another object of the same type.  Specifying this option disables
           that optimization, and forces G++ to call the copy constructor in all cases.  This
           option also causes G++ to call trivial member functions which otherwise would be
           expanded inline.

           In C++17, the compiler is required to omit these temporaries, but this option still
           affects trivial member functions.

       -fno-enforce-eh-specs
           Don't generate code to check for violation of exception specifications at run time.
           This option violates the C++ standard, but may be useful for reducing code size in
           production builds, much like defining "NDEBUG".  This does not give user code
           permission to throw exceptions in violation of the exception specifications; the
           compiler still optimizes based on the specifications, so throwing an unexpected
           exception results in undefined behavior at run time.

       -fextern-tls-init
       -fno-extern-tls-init
           The C++11 and OpenMP standards allow "thread_local" and "threadprivate" variables to
           have dynamic (runtime) initialization.  To support this, any use of such a variable
           goes through a wrapper function that performs any necessary initialization.  When the
           use and definition of the variable are in the same translation unit, this overhead can
           be optimized away, but when the use is in a different translation unit there is
           significant overhead even if the variable doesn't actually need dynamic
           initialization.  If the programmer can be sure that no use of the variable in a non-
           defining TU needs to trigger dynamic initialization (either because the variable is
           statically initialized, or a use of the variable in the defining TU will be executed
           before any uses in another TU), they can avoid this overhead with the
           -fno-extern-tls-init option.

           On targets that support symbol aliases, the default is -fextern-tls-init.  On targets
           that do not support symbol aliases, the default is -fno-extern-tls-init.

       -ffor-scope
       -fno-for-scope
           If -ffor-scope is specified, the scope of variables declared in a for-init-statement
           is limited to the "for" loop itself, as specified by the C++ standard.  If
           -fno-for-scope is specified, the scope of variables declared in a for-init-statement
           extends to the end of the enclosing scope, as was the case in old versions of G++, and
           other (traditional) implementations of C++.

           This option is deprecated and the associated non-standard functionality will be
           removed.

       -fno-gnu-keywords
           Do not recognize "typeof" as a keyword, so that code can use this word as an
           identifier.  You can use the keyword "__typeof__" instead.  This option is implied by
           the strict ISO C++ dialects: -ansi, -std=c++98, -std=c++11, etc.

       -fno-implicit-templates
           Never emit code for non-inline templates that are instantiated implicitly (i.e. by
           use); only emit code for explicit instantiations.

       -fno-implicit-inline-templates
           Don't emit code for implicit instantiations of inline templates, either.  The default
           is to handle inlines differently so that compiles with and without optimization need
           the same set of explicit instantiations.

       -fno-implement-inlines
           To save space, do not emit out-of-line copies of inline functions controlled by
           "#pragma implementation".  This causes linker errors if these functions are not
           inlined everywhere they are called.

       -fms-extensions
           Disable Wpedantic warnings about constructs used in MFC, such as implicit int and
           getting a pointer to member function via non-standard syntax.

       -fnew-inheriting-ctors
           Enable the P0136 adjustment to the semantics of C++11 constructor inheritance.  This
           is part of C++17 but also considered to be a Defect Report against C++11 and C++14.
           This flag is enabled by default unless -fabi-version=10 or lower is specified.

       -fnew-ttp-matching
           Enable the P0522 resolution to Core issue 150, template template parameters and
           default arguments: this allows a template with default template arguments as an
           argument for a template template parameter with fewer template parameters.  This flag
           is enabled by default for -std=c++17.

       -fno-nonansi-builtins
           Disable built-in declarations of functions that are not mandated by ANSI/ISO C.  These
           include "ffs", "alloca", "_exit", "index", "bzero", "conjf", and other related
           functions.

       -fnothrow-opt
           Treat a "throw()" exception specification as if it were a "noexcept" specification to
           reduce or eliminate the text size overhead relative to a function with no exception
           specification.  If the function has local variables of types with non-trivial
           destructors, the exception specification actually makes the function smaller because
           the EH cleanups for those variables can be optimized away.  The semantic effect is
           that an exception thrown out of a function with such an exception specification
           results in a call to "terminate" rather than "unexpected".

       -fno-operator-names
           Do not treat the operator name keywords "and", "bitand", "bitor", "compl", "not", "or"
           and "xor" as synonyms as keywords.

       -fno-optional-diags
           Disable diagnostics that the standard says a compiler does not need to issue.
           Currently, the only such diagnostic issued by G++ is the one for a name having
           multiple meanings within a class.

       -fpermissive
           Downgrade some diagnostics about nonconformant code from errors to warnings.  Thus,
           using -fpermissive allows some nonconforming code to compile.

       -fno-pretty-templates
           When an error message refers to a specialization of a function template, the compiler
           normally prints the signature of the template followed by the template arguments and
           any typedefs or typenames in the signature (e.g. "void f(T) [with T = int]" rather
           than "void f(int)") so that it's clear which template is involved.  When an error
           message refers to a specialization of a class template, the compiler omits any
           template arguments that match the default template arguments for that template.  If
           either of these behaviors make it harder to understand the error message rather than
           easier, you can use -fno-pretty-templates to disable them.

       -frepo
           Enable automatic template instantiation at link time.  This option also implies
           -fno-implicit-templates.

       -fno-rtti
           Disable generation of information about every class with virtual functions for use by
           the C++ run-time type identification features ("dynamic_cast" and "typeid").  If you
           don't use those parts of the language, you can save some space by using this flag.
           Note that exception handling uses the same information, but G++ generates it as
           needed. The "dynamic_cast" operator can still be used for casts that do not require
           run-time type information, i.e. casts to "void *" or to unambiguous base classes.

       -fsized-deallocation
           Enable the built-in global declarations

                   void operator delete (void *, std::size_t) noexcept;
                   void operator delete[] (void *, std::size_t) noexcept;

           as introduced in C++14.  This is useful for user-defined replacement deallocation
           functions that, for example, use the size of the object to make deallocation faster.
           Enabled by default under -std=c++14 and above.  The flag -Wsized-deallocation warns
           about places that might want to add a definition.

       -fstrict-enums
           Allow the compiler to optimize using the assumption that a value of enumerated type
           can only be one of the values of the enumeration (as defined in the C++ standard;
           basically, a value that can be represented in the minimum number of bits needed to
           represent all the enumerators).  This assumption may not be valid if the program uses
           a cast to convert an arbitrary integer value to the enumerated type.

       -fstrong-eval-order
           Evaluate member access, array subscripting, and shift expressions in left-to-right
           order, and evaluate assignment in right-to-left order, as adopted for C++17.  Enabled
           by default with -std=c++17.  -fstrong-eval-order=some enables just the ordering of
           member access and shift expressions, and is the default without -std=c++17.

       -ftemplate-backtrace-limit=n
           Set the maximum number of template instantiation notes for a single warning or error
           to n.  The default value is 10.

       -ftemplate-depth=n
           Set the maximum instantiation depth for template classes to n.  A limit on the
           template instantiation depth is needed to detect endless recursions during template
           class instantiation.  ANSI/ISO C++ conforming programs must not rely on a maximum
           depth greater than 17 (changed to 1024 in C++11).  The default value is 900, as the
           compiler can run out of stack space before hitting 1024 in some situations.

       -fno-threadsafe-statics
           Do not emit the extra code to use the routines specified in the C++ ABI for thread-
           safe initialization of local statics.  You can use this option to reduce code size
           slightly in code that doesn't need to be thread-safe.

       -fuse-cxa-atexit
           Register destructors for objects with static storage duration with the "__cxa_atexit"
           function rather than the "atexit" function.  This option is required for fully
           standards-compliant handling of static destructors, but only works if your C library
           supports "__cxa_atexit".

       -fno-use-cxa-get-exception-ptr
           Don't use the "__cxa_get_exception_ptr" runtime routine.  This causes
           "std::uncaught_exception" to be incorrect, but is necessary if the runtime routine is
           not available.

       -fvisibility-inlines-hidden
           This switch declares that the user does not attempt to compare pointers to inline
           functions or methods where the addresses of the two functions are taken in different
           shared objects.

           The effect of this is that GCC may, effectively, mark inline methods with
           "__attribute__ ((visibility ("hidden")))" so that they do not appear in the export
           table of a DSO and do not require a PLT indirection when used within the DSO.
           Enabling this option can have a dramatic effect on load and link times of a DSO as it
           massively reduces the size of the dynamic export table when the library makes heavy
           use of templates.

           The behavior of this switch is not quite the same as marking the methods as hidden
           directly, because it does not affect static variables local to the function or cause
           the compiler to deduce that the function is defined in only one shared object.

           You may mark a method as having a visibility explicitly to negate the effect of the
           switch for that method.  For example, if you do want to compare pointers to a
           particular inline method, you might mark it as having default visibility.  Marking the
           enclosing class with explicit visibility has no effect.

           Explicitly instantiated inline methods are unaffected by this option as their linkage
           might otherwise cross a shared library boundary.

       -fvisibility-ms-compat
           This flag attempts to use visibility settings to make GCC's C++ linkage model
           compatible with that of Microsoft Visual Studio.

           The flag makes these changes to GCC's linkage model:

           1.  It sets the default visibility to "hidden", like -fvisibility=hidden.

           2.  Types, but not their members, are not hidden by default.

           3.  The One Definition Rule is relaxed for types without explicit visibility
               specifications that are defined in more than one shared object: those declarations
               are permitted if they are permitted when this option is not used.

           In new code it is better to use -fvisibility=hidden and export those classes that are
           intended to be externally visible.  Unfortunately it is possible for code to rely,
           perhaps accidentally, on the Visual Studio behavior.

           Among the consequences of these changes are that static data members of the same type
           with the same name but defined in different shared objects are different, so changing
           one does not change the other; and that pointers to function members defined in
           different shared objects may not compare equal.  When this flag is given, it is a
           violation of the ODR to define types with the same name differently.

       -fno-weak
           Do not use weak symbol support, even if it is provided by the linker.  By default, G++
           uses weak symbols if they are available.  This option exists only for testing, and
           should not be used by end-users; it results in inferior code and has no benefits.
           This option may be removed in a future release of G++.

       -nostdinc++
           Do not search for header files in the standard directories specific to C++, but do
           still search the other standard directories.  (This option is used when building the
           C++ library.)

       In addition, these optimization, warning, and code generation options have meanings only
       for C++ programs:

       -Wabi (C, Objective-C, C++ and Objective-C++ only)
           Warn when G++ it generates code that is probably not compatible with the vendor-
           neutral C++ ABI.  Since G++ now defaults to updating the ABI with each major release,
           normally -Wabi will warn only if there is a check added later in a release series for
           an ABI issue discovered since the initial release.  -Wabi will warn about more things
           if an older ABI version is selected (with -fabi-version=n).

           -Wabi can also be used with an explicit version number to warn about compatibility
           with a particular -fabi-version level, e.g. -Wabi=2 to warn about changes relative to
           -fabi-version=2.

           If an explicit version number is provided and -fabi-compat-version is not specified,
           the version number from this option is used for compatibility aliases.  If no explicit
           version number is provided with this option, but -fabi-compat-version is specified,
           that version number is used for ABI warnings.

           Although an effort has been made to warn about all such cases, there are probably some
           cases that are not warned about, even though G++ is generating incompatible code.
           There may also be cases where warnings are emitted even though the code that is
           generated is compatible.

           You should rewrite your code to avoid these warnings if you are concerned about the
           fact that code generated by G++ may not be binary compatible with code generated by
           other compilers.

           Known incompatibilities in -fabi-version=2 (which was the default from GCC 3.4 to 4.9)
           include:

           *   A template with a non-type template parameter of reference type was mangled
               incorrectly:

                       extern int N;
                       template <int &> struct S {};
                       void n (S<N>) {2}

               This was fixed in -fabi-version=3.

           *   SIMD vector types declared using "__attribute ((vector_size))" were mangled in a
               non-standard way that does not allow for overloading of functions taking vectors
               of different sizes.

               The mangling was changed in -fabi-version=4.

           *   "__attribute ((const))" and "noreturn" were mangled as type qualifiers, and
               "decltype" of a plain declaration was folded away.

               These mangling issues were fixed in -fabi-version=5.

           *   Scoped enumerators passed as arguments to a variadic function are promoted like
               unscoped enumerators, causing "va_arg" to complain.  On most targets this does not
               actually affect the parameter passing ABI, as there is no way to pass an argument
               smaller than "int".

               Also, the ABI changed the mangling of template argument packs, "const_cast",
               "static_cast", prefix increment/decrement, and a class scope function used as a
               template argument.

               These issues were corrected in -fabi-version=6.

           *   Lambdas in default argument scope were mangled incorrectly, and the ABI changed
               the mangling of "nullptr_t".

               These issues were corrected in -fabi-version=7.

           *   When mangling a function type with function-cv-qualifiers, the un-qualified
               function type was incorrectly treated as a substitution candidate.

               This was fixed in -fabi-version=8, the default for GCC 5.1.

           *   "decltype(nullptr)" incorrectly had an alignment of 1, leading to unaligned
               accesses.  Note that this did not affect the ABI of a function with a "nullptr_t"
               parameter, as parameters have a minimum alignment.

               This was fixed in -fabi-version=9, the default for GCC 5.2.

           *   Target-specific attributes that affect the identity of a type, such as ia32
               calling conventions on a function type (stdcall, regparm, etc.), did not affect
               the mangled name, leading to name collisions when function pointers were used as
               template arguments.

               This was fixed in -fabi-version=10, the default for GCC 6.1.

           It also warns about psABI-related changes.  The known psABI changes at this point
           include:

           *   For SysV/x86-64, unions with "long double" members are passed in memory as
               specified in psABI.  For example:

                       union U {
                         long double ld;
                         int i;
                       };

               "union U" is always passed in memory.

       -Wabi-tag (C++ and Objective-C++ only)
           Warn when a type with an ABI tag is used in a context that does not have that ABI tag.
           See C++ Attributes for more information about ABI tags.

       -Wctor-dtor-privacy (C++ and Objective-C++ only)
           Warn when a class seems unusable because all the constructors or destructors in that
           class are private, and it has neither friends nor public static member functions.
           Also warn if there are no non-private methods, and there's at least one private member
           function that isn't a constructor or destructor.

       -Wdelete-non-virtual-dtor (C++ and Objective-C++ only)
           Warn when "delete" is used to destroy an instance of a class that has virtual
           functions and non-virtual destructor. It is unsafe to delete an instance of a derived
           class through a pointer to a base class if the base class does not have a virtual
           destructor.  This warning is enabled by -Wall.

       -Wliteral-suffix (C++ and Objective-C++ only)
           Warn when a string or character literal is followed by a ud-suffix which does not
           begin with an underscore.  As a conforming extension, GCC treats such suffixes as
           separate preprocessing tokens in order to maintain backwards compatibility with code
           that uses formatting macros from "<inttypes.h>".  For example:

                   #define __STDC_FORMAT_MACROS
                   #include <inttypes.h>
                   #include <stdio.h>

                   int main() {
                     int64_t i64 = 123;
                     printf("My int64: %" PRId64"\n", i64);
                   }

           In this case, "PRId64" is treated as a separate preprocessing token.

           Additionally, warn when a user-defined literal operator is declared with a literal
           suffix identifier that doesn't begin with an underscore. Literal suffix identifiers
           that don't begin with an underscore are reserved for future standardization.

           This warning is enabled by default.

       -Wlto-type-mismatch
           During the link-time optimization warn about type mismatches in global declarations
           from different compilation units.  Requires -flto to be enabled.  Enabled by default.

       -Wno-narrowing (C++ and Objective-C++ only)
           For C++11 and later standards, narrowing conversions are diagnosed by default, as
           required by the standard.  A narrowing conversion from a constant produces an error,
           and a narrowing conversion from a non-constant produces a warning, but -Wno-narrowing
           suppresses the diagnostic.  Note that this does not affect the meaning of well-formed
           code; narrowing conversions are still considered ill-formed in SFINAE contexts.

           With -Wnarrowing in C++98, warn when a narrowing conversion prohibited by C++11 occurs
           within { }, e.g.

                   int i = { 2.2 }; // error: narrowing from double to int

           This flag is included in -Wall and -Wc++11-compat.

       -Wnoexcept (C++ and Objective-C++ only)
           Warn when a noexcept-expression evaluates to false because of a call to a function
           that does not have a non-throwing exception specification (i.e. "throw()" or
           "noexcept") but is known by the compiler to never throw an exception.

       -Wnoexcept-type (C++ and Objective-C++ only)
           Warn if the C++17 feature making "noexcept" part of a function type changes the
           mangled name of a symbol relative to C++14.  Enabled by -Wabi and -Wc++17-compat.

           As an example:

                   template <class T> void f(T t) { t(); };
                   void g() noexcept;
                   void h() { f(g); }

           In C++14, "f" calls "f<void(*)()>", but in C++17 it calls "f<void(*)()noexcept>".

       -Wclass-memaccess (C++ and Objective-C++ only)
           Warn when the destination of a call to a raw memory function such as "memset" or
           "memcpy" is an object of class type, and when writing into such an object might bypass
           the class non-trivial or deleted constructor or copy assignment, violate const-
           correctness or encapsulation, or corrupt virtual table pointers.  Modifying the
           representation of such objects may violate invariants maintained by member functions
           of the class.  For example, the call to "memset" below is undefined because it
           modifies a non-trivial class object and is, therefore, diagnosed.  The safe way to
           either initialize or clear the storage of objects of such types is by using the
           appropriate constructor or assignment operator, if one is available.

                   std::string str = "abc";
                   memset (&str, 0, sizeof str);

           The -Wclass-memaccess option is enabled by -Wall.  Explicitly casting the pointer to
           the class object to "void *" or to a type that can be safely accessed by the raw
           memory function suppresses the warning.

       -Wnon-virtual-dtor (C++ and Objective-C++ only)
           Warn when a class has virtual functions and an accessible non-virtual destructor
           itself or in an accessible polymorphic base class, in which case it is possible but
           unsafe to delete an instance of a derived class through a pointer to the class itself
           or base class.  This warning is automatically enabled if -Weffc++ is specified.

       -Wregister (C++ and Objective-C++ only)
           Warn on uses of the "register" storage class specifier, except when it is part of the
           GNU Explicit Register Variables extension.  The use of the "register" keyword as
           storage class specifier has been deprecated in C++11 and removed in C++17.  Enabled by
           default with -std=c++17.

       -Wreorder (C++ and Objective-C++ only)
           Warn when the order of member initializers given in the code does not match the order
           in which they must be executed.  For instance:

                   struct A {
                     int i;
                     int j;
                     A(): j (0), i (1) { }
                   };

           The compiler rearranges the member initializers for "i" and "j" to match the
           declaration order of the members, emitting a warning to that effect.  This warning is
           enabled by -Wall.

       -fext-numeric-literals (C++ and Objective-C++ only)
           Accept imaginary, fixed-point, or machine-defined literal number suffixes as GNU
           extensions.  When this option is turned off these suffixes are treated as C++11 user-
           defined literal numeric suffixes.  This is on by default for all pre-C++11 dialects
           and all GNU dialects: -std=c++98, -std=gnu++98, -std=gnu++11, -std=gnu++14.  This
           option is off by default for ISO C++11 onwards (-std=c++11, ...).

       The following -W... options are not affected by -Wall.

       -Weffc++ (C++ and Objective-C++ only)
           Warn about violations of the following style guidelines from Scott Meyers' Effective
           C++ series of books:

           *   Define a copy constructor and an assignment operator for classes with dynamically-
               allocated memory.

           *   Prefer initialization to assignment in constructors.

           *   Have "operator=" return a reference to *this.

           *   Don't try to return a reference when you must return an object.

           *   Distinguish between prefix and postfix forms of increment and decrement operators.

           *   Never overload "&&", "||", or ",".

           This option also enables -Wnon-virtual-dtor, which is also one of the effective C++
           recommendations.  However, the check is extended to warn about the lack of virtual
           destructor in accessible non-polymorphic bases classes too.

           When selecting this option, be aware that the standard library headers do not obey all
           of these guidelines; use grep -v to filter out those warnings.

       -Wstrict-null-sentinel (C++ and Objective-C++ only)
           Warn about the use of an uncasted "NULL" as sentinel.  When compiling only with GCC
           this is a valid sentinel, as "NULL" is defined to "__null".  Although it is a null
           pointer constant rather than a null pointer, it is guaranteed to be of the same size
           as a pointer.  But this use is not portable across different compilers.

       -Wno-non-template-friend (C++ and Objective-C++ only)
           Disable warnings when non-template friend functions are declared within a template.
           In very old versions of GCC that predate implementation of the ISO standard,
           declarations such as friend int foo(int), where the name of the friend is an
           unqualified-id, could be interpreted as a particular specialization of a template
           function; the warning exists to diagnose compatibility problems, and is enabled by
           default.

       -Wold-style-cast (C++ and Objective-C++ only)
           Warn if an old-style (C-style) cast to a non-void type is used within a C++ program.
           The new-style casts ("dynamic_cast", "static_cast", "reinterpret_cast", and
           "const_cast") are less vulnerable to unintended effects and much easier to search for.

       -Woverloaded-virtual (C++ and Objective-C++ only)
           Warn when a function declaration hides virtual functions from a base class.  For
           example, in:

                   struct A {
                     virtual void f();
                   };

                   struct B: public A {
                     void f(int);
                   };

           the "A" class version of "f" is hidden in "B", and code like:

                   B* b;
                   b->f();

           fails to compile.

       -Wno-pmf-conversions (C++ and Objective-C++ only)
           Disable the diagnostic for converting a bound pointer to member function to a plain
           pointer.

       -Wsign-promo (C++ and Objective-C++ only)
           Warn when overload resolution chooses a promotion from unsigned or enumerated type to
           a signed type, over a conversion to an unsigned type of the same size.  Previous
           versions of G++ tried to preserve unsignedness, but the standard mandates the current
           behavior.

       -Wtemplates (C++ and Objective-C++ only)
           Warn when a primary template declaration is encountered.  Some coding rules disallow
           templates, and this may be used to enforce that rule.  The warning is inactive inside
           a system header file, such as the STL, so one can still use the STL.  One may also
           instantiate or specialize templates.

       -Wmultiple-inheritance (C++ and Objective-C++ only)
           Warn when a class is defined with multiple direct base classes.  Some coding rules
           disallow multiple inheritance, and this may be used to enforce that rule.  The warning
           is inactive inside a system header file, such as the STL, so one can still use the
           STL.  One may also define classes that indirectly use multiple inheritance.

       -Wvirtual-inheritance
           Warn when a class is defined with a virtual direct base class.  Some coding rules
           disallow multiple inheritance, and this may be used to enforce that rule.  The warning
           is inactive inside a system header file, such as the STL, so one can still use the
           STL.  One may also define classes that indirectly use virtual inheritance.

       -Wnamespaces
           Warn when a namespace definition is opened.  Some coding rules disallow namespaces,
           and this may be used to enforce that rule.  The warning is inactive inside a system
           header file, such as the STL, so one can still use the STL.  One may also use using
           directives and qualified names.

       -Wno-terminate (C++ and Objective-C++ only)
           Disable the warning about a throw-expression that will immediately result in a call to
           "terminate".

   Options Controlling Objective-C and Objective-C++ Dialects
       (NOTE: This manual does not describe the Objective-C and Objective-C++ languages
       themselves.

       This section describes the command-line options that are only meaningful for Objective-C
       and Objective-C++ programs.  You can also use most of the language-independent GNU
       compiler options.  For example, you might compile a file some_class.m like this:

               gcc -g -fgnu-runtime -O -c some_class.m

       In this example, -fgnu-runtime is an option meant only for Objective-C and Objective-C++
       programs; you can use the other options with any language supported by GCC.

       Note that since Objective-C is an extension of the C language, Objective-C compilations
       may also use options specific to the C front-end (e.g., -Wtraditional).  Similarly,
       Objective-C++ compilations may use C++-specific options (e.g., -Wabi).

       Here is a list of options that are only for compiling Objective-C and Objective-C++
       programs:

       -fconstant-string-class=class-name
           Use class-name as the name of the class to instantiate for each literal string
           specified with the syntax "@"..."".  The default class name is "NXConstantString" if
           the GNU runtime is being used, and "NSConstantString" if the NeXT runtime is being
           used (see below).  The -fconstant-cfstrings option, if also present, overrides the
           -fconstant-string-class setting and cause "@"..."" literals to be laid out as constant
           CoreFoundation strings.

       -fgnu-runtime
           Generate object code compatible with the standard GNU Objective-C runtime.  This is
           the default for most types of systems.

       -fnext-runtime
           Generate output compatible with the NeXT runtime.  This is the default for NeXT-based
           systems, including Darwin and Mac OS X.  The macro "__NEXT_RUNTIME__" is predefined if
           (and only if) this option is used.

       -fno-nil-receivers
           Assume that all Objective-C message dispatches ("[receiver message:arg]") in this
           translation unit ensure that the receiver is not "nil".  This allows for more
           efficient entry points in the runtime to be used.  This option is only available in
           conjunction with the NeXT runtime and ABI version 0 or 1.

       -fobjc-abi-version=n
           Use version n of the Objective-C ABI for the selected runtime.  This option is
           currently supported only for the NeXT runtime.  In that case, Version 0 is the
           traditional (32-bit) ABI without support for properties and other Objective-C 2.0
           additions.  Version 1 is the traditional (32-bit) ABI with support for properties and
           other Objective-C 2.0 additions.  Version 2 is the modern (64-bit) ABI.  If nothing is
           specified, the default is Version 0 on 32-bit target machines, and Version 2 on 64-bit
           target machines.

       -fobjc-call-cxx-cdtors
           For each Objective-C class, check if any of its instance variables is a C++ object
           with a non-trivial default constructor.  If so, synthesize a special "- (id)
           .cxx_construct" instance method which runs non-trivial default constructors on any
           such instance variables, in order, and then return "self".  Similarly, check if any
           instance variable is a C++ object with a non-trivial destructor, and if so, synthesize
           a special "- (void) .cxx_destruct" method which runs all such default destructors, in
           reverse order.

           The "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods thusly generated only
           operate on instance variables declared in the current Objective-C class, and not those
           inherited from superclasses.  It is the responsibility of the Objective-C runtime to
           invoke all such methods in an object's inheritance hierarchy.  The "- (id)
           .cxx_construct" methods are invoked by the runtime immediately after a new object
           instance is allocated; the "- (void) .cxx_destruct" methods are invoked immediately
           before the runtime deallocates an object instance.

           As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has support for
           invoking the "- (id) .cxx_construct" and "- (void) .cxx_destruct" methods.

       -fobjc-direct-dispatch
           Allow fast jumps to the message dispatcher.  On Darwin this is accomplished via the
           comm page.

       -fobjc-exceptions
           Enable syntactic support for structured exception handling in Objective-C, similar to
           what is offered by C++.  This option is required to use the Objective-C keywords @try,
           @throw, @catch, @finally and @synchronized.  This option is available with both the
           GNU runtime and the NeXT runtime (but not available in conjunction with the NeXT
           runtime on Mac OS X 10.2 and earlier).

       -fobjc-gc
           Enable garbage collection (GC) in Objective-C and Objective-C++ programs.  This option
           is only available with the NeXT runtime; the GNU runtime has a different garbage
           collection implementation that does not require special compiler flags.

       -fobjc-nilcheck
           For the NeXT runtime with version 2 of the ABI, check for a nil receiver in method
           invocations before doing the actual method call.  This is the default and can be
           disabled using -fno-objc-nilcheck.  Class methods and super calls are never checked
           for nil in this way no matter what this flag is set to.  Currently this flag does
           nothing when the GNU runtime, or an older version of the NeXT runtime ABI, is used.

       -fobjc-std=objc1
           Conform to the language syntax of Objective-C 1.0, the language recognized by GCC 4.0.
           This only affects the Objective-C additions to the C/C++ language; it does not affect
           conformance to C/C++ standards, which is controlled by the separate C/C++ dialect
           option flags.  When this option is used with the Objective-C or Objective-C++
           compiler, any Objective-C syntax that is not recognized by GCC 4.0 is rejected.  This
           is useful if you need to make sure that your Objective-C code can be compiled with
           older versions of GCC.

       -freplace-objc-classes
           Emit a special marker instructing ld(1) not to statically link in the resulting object
           file, and allow dyld(1) to load it in at run time instead.  This is used in
           conjunction with the Fix-and-Continue debugging mode, where the object file in
           question may be recompiled and dynamically reloaded in the course of program
           execution, without the need to restart the program itself.  Currently, Fix-and-
           Continue functionality is only available in conjunction with the NeXT runtime on Mac
           OS X 10.3 and later.

       -fzero-link
           When compiling for the NeXT runtime, the compiler ordinarily replaces calls to
           "objc_getClass("...")" (when the name of the class is known at compile time) with
           static class references that get initialized at load time, which improves run-time
           performance.  Specifying the -fzero-link flag suppresses this behavior and causes
           calls to "objc_getClass("...")"  to be retained.  This is useful in Zero-Link
           debugging mode, since it allows for individual class implementations to be modified
           during program execution.  The GNU runtime currently always retains calls to
           "objc_get_class("...")"  regardless of command-line options.

       -fno-local-ivars
           By default instance variables in Objective-C can be accessed as if they were local
           variables from within the methods of the class they're declared in.  This can lead to
           shadowing between instance variables and other variables declared either locally
           inside a class method or globally with the same name.  Specifying the -fno-local-ivars
           flag disables this behavior thus avoiding variable shadowing issues.

       -fivar-visibility=[public|protected|private|package]
           Set the default instance variable visibility to the specified option so that instance
           variables declared outside the scope of any access modifier directives default to the
           specified visibility.

       -gen-decls
           Dump interface declarations for all classes seen in the source file to a file named
           sourcename.decl.

       -Wassign-intercept (Objective-C and Objective-C++ only)
           Warn whenever an Objective-C assignment is being intercepted by the garbage collector.

       -Wno-protocol (Objective-C and Objective-C++ only)
           If a class is declared to implement a protocol, a warning is issued for every method
           in the protocol that is not implemented by the class.  The default behavior is to
           issue a warning for every method not explicitly implemented in the class, even if a
           method implementation is inherited from the superclass.  If you use the -Wno-protocol
           option, then methods inherited from the superclass are considered to be implemented,
           and no warning is issued for them.

       -Wselector (Objective-C and Objective-C++ only)
           Warn if multiple methods of different types for the same selector are found during
           compilation.  The check is performed on the list of methods in the final stage of
           compilation.  Additionally, a check is performed for each selector appearing in a
           "@selector(...)"  expression, and a corresponding method for that selector has been
           found during compilation.  Because these checks scan the method table only at the end
           of compilation, these warnings are not produced if the final stage of compilation is
           not reached, for example because an error is found during compilation, or because the
           -fsyntax-only option is being used.

       -Wstrict-selector-match (Objective-C and Objective-C++ only)
           Warn if multiple methods with differing argument and/or return types are found for a
           given selector when attempting to send a message using this selector to a receiver of
           type "id" or "Class".  When this flag is off (which is the default behavior), the
           compiler omits such warnings if any differences found are confined to types that share
           the same size and alignment.

       -Wundeclared-selector (Objective-C and Objective-C++ only)
           Warn if a "@selector(...)" expression referring to an undeclared selector is found.  A
           selector is considered undeclared if no method with that name has been declared before
           the "@selector(...)" expression, either explicitly in an @interface or @protocol
           declaration, or implicitly in an @implementation section.  This option always performs
           its checks as soon as a "@selector(...)" expression is found, while -Wselector only
           performs its checks in the final stage of compilation.  This also enforces the coding
           style convention that methods and selectors must be declared before being used.

       -print-objc-runtime-info
           Generate C header describing the largest structure that is passed by value, if any.

   Options to Control Diagnostic Messages Formatting
       Traditionally, diagnostic messages have been formatted irrespective of the output device's
       aspect (e.g. its width, ...).  You can use the options described below to control the
       formatting algorithm for diagnostic messages, e.g. how many characters per line, how often
       source location information should be reported.  Note that some language front ends may
       not honor these options.

       -fmessage-length=n
           Try to format error messages so that they fit on lines of about n characters.  If n is
           zero, then no line-wrapping is done; each error message appears on a single line.
           This is the default for all front ends.

       -fdiagnostics-show-location=once
           Only meaningful in line-wrapping mode.  Instructs the diagnostic messages reporter to
           emit source location information once; that is, in case the message is too long to fit
           on a single physical line and has to be wrapped, the source location won't be emitted
           (as prefix) again, over and over, in subsequent continuation lines.  This is the
           default behavior.

       -fdiagnostics-show-location=every-line
           Only meaningful in line-wrapping mode.  Instructs the diagnostic messages reporter to
           emit the same source location information (as prefix) for physical lines that result
           from the process of breaking a message which is too long to fit on a single line.

       -fdiagnostics-color[=WHEN]
       -fno-diagnostics-color
           Use color in diagnostics.  WHEN is never, always, or auto.  The default depends on how
           the compiler has been configured, it can be any of the above WHEN options or also
           never if GCC_COLORS environment variable isn't present in the environment, and auto
           otherwise.  auto means to use color only when the standard error is a terminal.  The
           forms -fdiagnostics-color and -fno-diagnostics-color are aliases for
           -fdiagnostics-color=always and -fdiagnostics-color=never, respectively.

           The colors are defined by the environment variable GCC_COLORS.  Its value is a colon-
           separated list of capabilities and Select Graphic Rendition (SGR) substrings. SGR
           commands are interpreted by the terminal or terminal emulator.  (See the section in
           the documentation of your text terminal for permitted values and their meanings as
           character attributes.)  These substring values are integers in decimal representation
           and can be concatenated with semicolons.  Common values to concatenate include 1 for
           bold, 4 for underline, 5 for blink, 7 for inverse, 39 for default foreground color, 30
           to 37 for foreground colors, 90 to 97 for 16-color mode foreground colors, 38;5;0 to
           38;5;255 for 88-color and 256-color modes foreground colors, 49 for default background
           color, 40 to 47 for background colors, 100 to 107 for 16-color mode background colors,
           and 48;5;0 to 48;5;255 for 88-color and 256-color modes background colors.

           The default GCC_COLORS is

                   error=01;31:warning=01;35:note=01;36:range1=32:range2=34:locus=01:\
                   quote=01:fixit-insert=32:fixit-delete=31:\
                   diff-filename=01:diff-hunk=32:diff-delete=31:diff-insert=32:\
                   type-diff=01;32

           where 01;31 is bold red, 01;35 is bold magenta, 01;36 is bold cyan, 32 is green, 34 is
           blue, 01 is bold, and 31 is red.  Setting GCC_COLORS to the empty string disables
           colors.  Supported capabilities are as follows.

           "error="
               SGR substring for error: markers.

           "warning="
               SGR substring for warning: markers.

           "note="
               SGR substring for note: markers.

           "range1="
               SGR substring for first additional range.

           "range2="
               SGR substring for second additional range.

           "locus="
               SGR substring for location information, file:line or file:line:column etc.

           "quote="
               SGR substring for information printed within quotes.

           "fixit-insert="
               SGR substring for fix-it hints suggesting text to be inserted or replaced.

           "fixit-delete="
               SGR substring for fix-it hints suggesting text to be deleted.

           "diff-filename="
               SGR substring for filename headers within generated patches.

           "diff-hunk="
               SGR substring for the starts of hunks within generated patches.

           "diff-delete="
               SGR substring for deleted lines within generated patches.

           "diff-insert="
               SGR substring for inserted lines within generated patches.

           "type-diff="
               SGR substring for highlighting mismatching types within template arguments in the
               C++ frontend.

       -fno-diagnostics-show-option
           By default, each diagnostic emitted includes text indicating the command-line option
           that directly controls the diagnostic (if such an option is known to the diagnostic
           machinery).  Specifying the -fno-diagnostics-show-option flag suppresses that
           behavior.

       -fno-diagnostics-show-caret
           By default, each diagnostic emitted includes the original source line and a caret ^
           indicating the column.  This option suppresses this information.  The source line is
           truncated to n characters, if the -fmessage-length=n option is given.  When the output
           is done to the terminal, the width is limited to the width given by the COLUMNS
           environment variable or, if not set, to the terminal width.

       -fdiagnostics-parseable-fixits
           Emit fix-it hints in a machine-parseable format, suitable for consumption by IDEs.
           For each fix-it, a line will be printed after the relevant diagnostic, starting with
           the string "fix-it:".  For example:

                   fix-it:"test.c":{45:3-45:21}:"gtk_widget_show_all"

           The location is expressed as a half-open range, expressed as a count of bytes,
           starting at byte 1 for the initial column.  In the above example, bytes 3 through 20
           of line 45 of "test.c" are to be replaced with the given string:

                   00000000011111111112222222222
                   12345678901234567890123456789
                     gtk_widget_showall (dlg);
                     ^^^^^^^^^^^^^^^^^^
                     gtk_widget_show_all

           The filename and replacement string escape backslash as "\\", tab as "\t", newline as
           "\n", double quotes as "\"", non-printable characters as octal (e.g. vertical tab as
           "\013").

           An empty replacement string indicates that the given range is to be removed.  An empty
           range (e.g. "45:3-45:3") indicates that the string is to be inserted at the given
           position.

       -fdiagnostics-generate-patch
           Print fix-it hints to stderr in unified diff format, after any diagnostics are
           printed.  For example:

                   --- test.c
                   +++ test.c
                   @ -42,5 +42,5 @

                    void show_cb(GtkDialog *dlg)
                    {
                   -  gtk_widget_showall(dlg);
                   +  gtk_widget_show_all(dlg);
                    }

           The diff may or may not be colorized, following the same rules as for diagnostics (see
           -fdiagnostics-color).

       -fdiagnostics-show-template-tree
           In the C++ frontend, when printing diagnostics showing mismatching template types,
           such as:

                     could not convert 'std::map<int, std::vector<double> >()'
                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

           the -fdiagnostics-show-template-tree flag enables printing a tree-like structure
           showing the common and differing parts of the types, such as:

                     map<
                       [...],
                       vector<
                         [double != float]>>

           The parts that differ are highlighted with color ("double" and "float" in this case).

       -fno-elide-type
           By default when the C++ frontend prints diagnostics showing mismatching template
           types, common parts of the types are printed as "[...]" to simplify the error message.
           For example:

                     could not convert 'std::map<int, std::vector<double> >()'
                       from 'map<[...],vector<double>>' to 'map<[...],vector<float>>

           Specifying the -fno-elide-type flag suppresses that behavior.  This flag also affects
           the output of the -fdiagnostics-show-template-tree flag.

       -fno-show-column
           Do not print column numbers in diagnostics.  This may be necessary if diagnostics are
           being scanned by a program that does not understand the column numbers, such as
           dejagnu.

   Options to Request or Suppress Warnings
       Warnings are diagnostic messages that report constructions that are not inherently
       erroneous but that are risky or suggest there may have been an error.

       The following language-independent options do not enable specific warnings but control the
       kinds of diagnostics produced by GCC.

       -fsyntax-only
           Check the code for syntax errors, but don't do anything beyond that.

       -fmax-errors=n
           Limits the maximum number of error messages to n, at which point GCC bails out rather
           than attempting to continue processing the source code.  If n is 0 (the default),
           there is no limit on the number of error messages produced.  If -Wfatal-errors is also
           specified, then -Wfatal-errors takes precedence over this option.

       -w  Inhibit all warning messages.

       -Werror
           Make all warnings into errors.

       -Werror=
           Make the specified warning into an error.  The specifier for a warning is appended;
           for example -Werror=switch turns the warnings controlled by -Wswitch into errors.
           This switch takes a negative form, to be used to negate -Werror for specific warnings;
           for example -Wno-error=switch makes -Wswitch warnings not be errors, even when -Werror
           is in effect.

           The warning message for each controllable warning includes the option that controls
           the warning.  That option can then be used with -Werror= and -Wno-error= as described
           above.  (Printing of the option in the warning message can be disabled using the
           -fno-diagnostics-show-option flag.)

           Note that specifying -Werror=foo automatically implies -Wfoo.  However, -Wno-error=foo
           does not imply anything.

       -Wfatal-errors
           This option causes the compiler to abort compilation on the first error occurred
           rather than trying to keep going and printing further error messages.

       You can request many specific warnings with options beginning with -W, for example
       -Wimplicit to request warnings on implicit declarations.  Each of these specific warning
       options also has a negative form beginning -Wno- to turn off warnings; for example,
       -Wno-implicit.  This manual lists only one of the two forms, whichever is not the default.
       For further language-specific options also refer to C++ Dialect Options and Objective-C
       and Objective-C++ Dialect Options.

       Some options, such as -Wall and -Wextra, turn on other options, such as -Wunused, which
       may turn on further options, such as -Wunused-value. The combined effect of positive and
       negative forms is that more specific options have priority over less specific ones,
       independently of their position in the command-line. For options of the same specificity,
       the last one takes effect. Options enabled or disabled via pragmas take effect as if they
       appeared at the end of the command-line.

       When an unrecognized warning option is requested (e.g., -Wunknown-warning), GCC emits a
       diagnostic stating that the option is not recognized.  However, if the -Wno- form is used,
       the behavior is slightly different: no diagnostic is produced for -Wno-unknown-warning
       unless other diagnostics are being produced.  This allows the use of new -Wno- options
       with old compilers, but if something goes wrong, the compiler warns that an unrecognized
       option is present.

       -Wpedantic
       -pedantic
           Issue all the warnings demanded by strict ISO C and ISO C++; reject all programs that
           use forbidden extensions, and some other programs that do not follow ISO C and ISO
           C++.  For ISO C, follows the version of the ISO C standard specified by any -std
           option used.

           Valid ISO C and ISO C++ programs should compile properly with or without this option
           (though a rare few require -ansi or a -std option specifying the required version of
           ISO C).  However, without this option, certain GNU extensions and traditional C and
           C++ features are supported as well.  With this option, they are rejected.

           -Wpedantic does not cause warning messages for use of the alternate keywords whose
           names begin and end with __.  Pedantic warnings are also disabled in the expression
           that follows "__extension__".  However, only system header files should use these
           escape routes; application programs should avoid them.

           Some users try to use -Wpedantic to check programs for strict ISO C conformance.  They
           soon find that it does not do quite what they want: it finds some non-ISO practices,
           but not all---only those for which ISO C requires a diagnostic, and some others for
           which diagnostics have been added.

           A feature to report any failure to conform to ISO C might be useful in some instances,
           but would require considerable additional work and would be quite different from
           -Wpedantic.  We don't have plans to support such a feature in the near future.

           Where the standard specified with -std represents a GNU extended dialect of C, such as
           gnu90 or gnu99, there is a corresponding base standard, the version of ISO C on which
           the GNU extended dialect is based.  Warnings from -Wpedantic are given where they are
           required by the base standard.  (It does not make sense for such warnings to be given
           only for features not in the specified GNU C dialect, since by definition the GNU
           dialects of C include all features the compiler supports with the given option, and
           there would be nothing to warn about.)

       -pedantic-errors
           Give an error whenever the base standard (see -Wpedantic) requires a diagnostic, in
           some cases where there is undefined behavior at compile-time and in some other cases
           that do not prevent compilation of programs that are valid according to the standard.
           This is not equivalent to -Werror=pedantic, since there are errors enabled by this
           option and not enabled by the latter and vice versa.

       -Wall
           This enables all the warnings about constructions that some users consider
           questionable, and that are easy to avoid (or modify to prevent the warning), even in
           conjunction with macros.  This also enables some language-specific warnings described
           in C++ Dialect Options and Objective-C and Objective-C++ Dialect Options.

           -Wall turns on the following warning flags:

           -Waddress -Warray-bounds=1 (only with -O2) -Wbool-compare -Wbool-operation
           -Wc++11-compat  -Wc++14-compat -Wcatch-value (C++ and Objective-C++ only)
           -Wchar-subscripts -Wcomment -Wduplicate-decl-specifier (C and Objective-C only)
           -Wenum-compare (in C/ObjC; this is on by default in C++) -Wformat
           -Wint-in-bool-context -Wimplicit (C and Objective-C only) -Wimplicit-int (C and
           Objective-C only) -Wimplicit-function-declaration (C and Objective-C only) -Winit-self
           (only for C++) -Wlogical-not-parentheses -Wmain (only for C/ObjC and unless
           -ffreestanding) -Wmaybe-uninitialized -Wmemset-elt-size -Wmemset-transposed-args
           -Wmisleading-indentation (only for C/C++) -Wmissing-attributes -Wmissing-braces (only
           for C/ObjC) -Wmultistatement-macros -Wnarrowing (only for C++) -Wnonnull
           -Wnonnull-compare -Wopenmp-simd -Wparentheses -Wpointer-sign -Wreorder -Wrestrict
           -Wreturn-type -Wsequence-point -Wsign-compare (only in C++) -Wsizeof-pointer-div
           -Wsizeof-pointer-memaccess -Wstrict-aliasing -Wstrict-overflow=1 -Wstringop-truncation
           -Wswitch -Wtautological-compare -Wtrigraphs -Wuninitialized -Wunknown-pragmas
           -Wunused-function -Wunused-label -Wunused-value -Wunused-variable
           -Wvolatile-register-var

           Note that some warning flags are not implied by -Wall.  Some of them warn about
           constructions that users generally do not consider questionable, but which
           occasionally you might wish to check for; others warn about constructions that are
           necessary or hard to avoid in some cases, and there is no simple way to modify the
           code to suppress the warning. Some of them are enabled by -Wextra but many of them
           must be enabled individually.

       -Wextra
           This enables some extra warning flags that are not enabled by -Wall. (This option used
           to be called -W.  The older name is still supported, but the newer name is more
           descriptive.)

           -Wclobbered -Wcast-function-type -Wempty-body -Wignored-qualifiers
           -Wimplicit-fallthrough=3 -Wmissing-field-initializers -Wmissing-parameter-type (C
           only) -Wold-style-declaration (C only) -Woverride-init -Wsign-compare (C only)
           -Wtype-limits -Wuninitialized -Wshift-negative-value (in C++03 and in C99 and newer)
           -Wunused-parameter (only with -Wunused or -Wall) -Wunused-but-set-parameter (only with
           -Wunused or -Wall)

           The option -Wextra also prints warning messages for the following cases:

           *   A pointer is compared against integer zero with "<", "<=", ">", or ">=".

           *   (C++ only) An enumerator and a non-enumerator both appear in a conditional
               expression.

           *   (C++ only) Ambiguous virtual bases.

           *   (C++ only) Subscripting an array that has been declared "register".

           *   (C++ only) Taking the address of a variable that has been declared "register".

           *   (C++ only) A base class is not initialized in the copy constructor of a derived
               class.

       -Wchar-subscripts
           Warn if an array subscript has type "char".  This is a common cause of error, as
           programmers often forget that this type is signed on some machines.  This warning is
           enabled by -Wall.

       -Wchkp
           Warn about an invalid memory access that is found by Pointer Bounds Checker
           (-fcheck-pointer-bounds).

       -Wno-coverage-mismatch
           Warn if feedback profiles do not match when using the -fprofile-use option.  If a
           source file is changed between compiling with -fprofile-gen and with -fprofile-use,
           the files with the profile feedback can fail to match the source file and GCC cannot
           use the profile feedback information.  By default, this warning is enabled and is
           treated as an error.  -Wno-coverage-mismatch can be used to disable the warning or
           -Wno-error=coverage-mismatch can be used to disable the error.  Disabling the error
           for this warning can result in poorly optimized code and is useful only in the case of
           very minor changes such as bug fixes to an existing code-base.  Completely disabling
           the warning is not recommended.

       -Wno-cpp
           (C, Objective-C, C++, Objective-C++ and Fortran only)

           Suppress warning messages emitted by "#warning" directives.

       -Wdouble-promotion (C, C++, Objective-C and Objective-C++ only)
           Give a warning when a value of type "float" is implicitly promoted to "double".  CPUs
           with a 32-bit "single-precision" floating-point unit implement "float" in hardware,
           but emulate "double" in software.  On such a machine, doing computations using
           "double" values is much more expensive because of the overhead required for software
           emulation.

           It is easy to accidentally do computations with "double" because floating-point
           literals are implicitly of type "double".  For example, in:

                   float area(float radius)
                   {
                      return 3.14159 * radius * radius;
                   }

           the compiler performs the entire computation with "double" because the floating-point
           literal is a "double".

       -Wduplicate-decl-specifier (C and Objective-C only)
           Warn if a declaration has duplicate "const", "volatile", "restrict" or "_Atomic"
           specifier.  This warning is enabled by -Wall.

       -Wformat
       -Wformat=n
           Check calls to "printf" and "scanf", etc., to make sure that the arguments supplied
           have types appropriate to the format string specified, and that the conversions
           specified in the format string make sense.  This includes standard functions, and
           others specified by format attributes, in the "printf", "scanf", "strftime" and
           "strfmon" (an X/Open extension, not in the C standard) families (or other target-
           specific families).  Which functions are checked without format attributes having been
           specified depends on the standard version selected, and such checks of functions
           without the attribute specified are disabled by -ffreestanding or -fno-builtin.

           The formats are checked against the format features supported by GNU libc version 2.2.
           These include all ISO C90 and C99 features, as well as features from the Single Unix
           Specification and some BSD and GNU extensions.  Other library implementations may not
           support all these features; GCC does not support warning about features that go beyond
           a particular library's limitations.  However, if -Wpedantic is used with -Wformat,
           warnings are given about format features not in the selected standard version (but not
           for "strfmon" formats, since those are not in any version of the C standard).

           -Wformat=1
           -Wformat
               Option -Wformat is equivalent to -Wformat=1, and -Wno-format is equivalent to
               -Wformat=0.  Since -Wformat also checks for null format arguments for several
               functions, -Wformat also implies -Wnonnull.  Some aspects of this level of format
               checking can be disabled by the options: -Wno-format-contains-nul,
               -Wno-format-extra-args, and -Wno-format-zero-length.  -Wformat is enabled by
               -Wall.

           -Wno-format-contains-nul
               If -Wformat is specified, do not warn about format strings that contain NUL bytes.

           -Wno-format-extra-args
               If -Wformat is specified, do not warn about excess arguments to a "printf" or
               "scanf" format function.  The C standard specifies that such arguments are
               ignored.

               Where the unused arguments lie between used arguments that are specified with $
               operand number specifications, normally warnings are still given, since the
               implementation could not know what type to pass to "va_arg" to skip the unused
               arguments.  However, in the case of "scanf" formats, this option suppresses the
               warning if the unused arguments are all pointers, since the Single Unix
               Specification says that such unused arguments are allowed.

           -Wformat-overflow
           -Wformat-overflow=level
               Warn about calls to formatted input/output functions such as "sprintf" and
               "vsprintf" that might overflow the destination buffer.  When the exact number of
               bytes written by a format directive cannot be determined at compile-time it is
               estimated based on heuristics that depend on the level argument and on
               optimization.  While enabling optimization will in most cases improve the accuracy
               of the warning, it may also result in false positives.

               -Wformat-overflow
               -Wformat-overflow=1
                   Level 1 of -Wformat-overflow enabled by -Wformat employs a conservative
                   approach that warns only about calls that most likely overflow the buffer.  At
                   this level, numeric arguments to format directives with unknown values are
                   assumed to have the value of one, and strings of unknown length to be empty.
                   Numeric arguments that are known to be bounded to a subrange of their type, or
                   string arguments whose output is bounded either by their directive's precision
                   or by a finite set of string literals, are assumed to take on the value within
                   the range that results in the most bytes on output.  For example, the call to
                   "sprintf" below is diagnosed because even with both a and b equal to zero, the
                   terminating NUL character ('\0') appended by the function to the destination
                   buffer will be written past its end.  Increasing the size of the buffer by a
                   single byte is sufficient to avoid the warning, though it may not be
                   sufficient to avoid the overflow.

                           void f (int a, int b)
                           {
                             char buf [13];
                             sprintf (buf, "a = %i, b = %i\n", a, b);
                           }

               -Wformat-overflow=2
                   Level 2 warns also about calls that might overflow the destination buffer
                   given an argument of sufficient length or magnitude.  At level 2, unknown
                   numeric arguments are assumed to have the minimum representable value for
                   signed types with a precision greater than 1, and the maximum representable
                   value otherwise.  Unknown string arguments whose length cannot be assumed to
                   be bounded either by the directive's precision, or by a finite set of string
                   literals they may evaluate to, or the character array they may point to, are
                   assumed to be 1 character long.

                   At level 2, the call in the example above is again diagnosed, but this time
                   because with a equal to a 32-bit "INT_MIN" the first %i directive will write
                   some of its digits beyond the end of the destination buffer.  To make the call
                   safe regardless of the values of the two variables, the size of the
                   destination buffer must be increased to at least 34 bytes.  GCC includes the
                   minimum size of the buffer in an informational note following the warning.

                   An alternative to increasing the size of the destination buffer is to
                   constrain the range of formatted values.  The maximum length of string
                   arguments can be bounded by specifying the precision in the format directive.
                   When numeric arguments of format directives can be assumed to be bounded by
                   less than the precision of their type, choosing an appropriate length modifier
                   to the format specifier will reduce the required buffer size.  For example, if
                   a and b in the example above can be assumed to be within the precision of the
                   "short int" type then using either the %hi format directive or casting the
                   argument to "short" reduces the maximum required size of the buffer to 24
                   bytes.

                           void f (int a, int b)
                           {
                             char buf [23];
                             sprintf (buf, "a = %hi, b = %i\n", a, (short)b);
                           }

           -Wno-format-zero-length
               If -Wformat is specified, do not warn about zero-length formats.  The C standard
               specifies that zero-length formats are allowed.

           -Wformat=2
               Enable -Wformat plus additional format checks.  Currently equivalent to -Wformat
               -Wformat-nonliteral -Wformat-security -Wformat-y2k.

           -Wformat-nonliteral
               If -Wformat is specified, also warn if the format string is not a string literal
               and so cannot be checked, unless the format function takes its format arguments as
               a "va_list".

           -Wformat-security
               If -Wformat is specified, also warn about uses of format functions that represent
               possible security problems.  At present, this warns about calls to "printf" and
               "scanf" functions where the format string is not a string literal and there are no
               format arguments, as in "printf (foo);".  This may be a security hole if the
               format string came from untrusted input and contains %n.  (This is currently a
               subset of what -Wformat-nonliteral warns about, but in future warnings may be
               added to -Wformat-security that are not included in -Wformat-nonliteral.)

           -Wformat-signedness
               If -Wformat is specified, also warn if the format string requires an unsigned
               argument and the argument is signed and vice versa.

           -Wformat-truncation
           -Wformat-truncation=level
               Warn about calls to formatted input/output functions such as "snprintf" and
               "vsnprintf" that might result in output truncation.  When the exact number of
               bytes written by a format directive cannot be determined at compile-time it is
               estimated based on heuristics that depend on the level argument and on
               optimization.  While enabling optimization will in most cases improve the accuracy
               of the warning, it may also result in false positives.  Except as noted otherwise,
               the option uses the same logic -Wformat-overflow.

               -Wformat-truncation
               -Wformat-truncation=1
                   Level 1 of -Wformat-truncation enabled by -Wformat employs a conservative
                   approach that warns only about calls to bounded functions whose return value
                   is unused and that will most likely result in output truncation.

               -Wformat-truncation=2
                   Level 2 warns also about calls to bounded functions whose return value is used
                   and that might result in truncation given an argument of sufficient length or
                   magnitude.

           -Wformat-y2k
               If -Wformat is specified, also warn about "strftime" formats that may yield only a
               two-digit year.

       -Wnonnull
           Warn about passing a null pointer for arguments marked as requiring a non-null value
           by the "nonnull" function attribute.

           -Wnonnull is included in -Wall and -Wformat.  It can be disabled with the -Wno-nonnull
           option.

       -Wnonnull-compare
           Warn when comparing an argument marked with the "nonnull" function attribute against
           null inside the function.

           -Wnonnull-compare is included in -Wall.  It can be disabled with the
           -Wno-nonnull-compare option.

       -Wnull-dereference
           Warn if the compiler detects paths that trigger erroneous or undefined behavior due to
           dereferencing a null pointer.  This option is only active when
           -fdelete-null-pointer-checks is active, which is enabled by optimizations in most
           targets.  The precision of the warnings depends on the optimization options used.

       -Winit-self (C, C++, Objective-C and Objective-C++ only)
           Warn about uninitialized variables that are initialized with themselves.  Note this
           option can only be used with the -Wuninitialized option.

           For example, GCC warns about "i" being uninitialized in the following snippet only
           when -Winit-self has been specified:

                   int f()
                   {
                     int i = i;
                     return i;
                   }

           This warning is enabled by -Wall in C++.

       -Wimplicit-int (C and Objective-C only)
           Warn when a declaration does not specify a type.  This warning is enabled by -Wall.

       -Wimplicit-function-declaration (C and Objective-C only)
           Give a warning whenever a function is used before being declared. In C99 mode
           (-std=c99 or -std=gnu99), this warning is enabled by default and it is made into an
           error by -pedantic-errors. This warning is also enabled by -Wall.

       -Wimplicit (C and Objective-C only)
           Same as -Wimplicit-int and -Wimplicit-function-declaration.  This warning is enabled
           by -Wall.

       -Wimplicit-fallthrough
           -Wimplicit-fallthrough is the same as -Wimplicit-fallthrough=3 and
           -Wno-implicit-fallthrough is the same as -Wimplicit-fallthrough=0.

       -Wimplicit-fallthrough=n
           Warn when a switch case falls through.  For example:

                   switch (cond)
                     {
                     case 1:
                       a = 1;
                       break;
                     case 2:
                       a = 2;
                     case 3:
                       a = 3;
                       break;
                     }

           This warning does not warn when the last statement of a case cannot fall through, e.g.
           when there is a return statement or a call to function declared with the noreturn
           attribute.  -Wimplicit-fallthrough= also takes into account control flow statements,
           such as ifs, and only warns when appropriate.  E.g.

                   switch (cond)
                     {
                     case 1:
                       if (i > 3) {
                         bar (5);
                         break;
                       } else if (i < 1) {
                         bar (0);
                       } else
                         return;
                     default:
                       ...
                     }

           Since there are occasions where a switch case fall through is desirable, GCC provides
           an attribute, "__attribute__ ((fallthrough))", that is to be used along with a null
           statement to suppress this warning that would normally occur:

                   switch (cond)
                     {
                     case 1:
                       bar (0);
                       __attribute__ ((fallthrough));
                     default:
                       ...
                     }

           C++17 provides a standard way to suppress the -Wimplicit-fallthrough warning using
           "[[fallthrough]];" instead of the GNU attribute.  In C++11 or C++14 users can use
           "[[gnu::fallthrough]];", which is a GNU extension.  Instead of these attributes, it is
           also possible to add a fallthrough comment to silence the warning.  The whole body of
           the C or C++ style comment should match the given regular expressions listed below.
           The option argument n specifies what kind of comments are accepted:

           *<-Wimplicit-fallthrough=0 disables the warning altogether.>
           *<-Wimplicit-fallthrough=1 matches ".*" regular>
               expression, any comment is used as fallthrough comment.

           *<-Wimplicit-fallthrough=2 case insensitively matches>
               ".*falls?[ \t-]*thr(ough|u).*" regular expression.

           *<-Wimplicit-fallthrough=3 case sensitively matches one of the>
               following regular expressions:

               *<"-fallthrough">
               *<"@fallthrough@">
               *<"lint -fallthrough[ \t]*">
               *<"[ \t.!]*(ELSE,? |INTENTIONAL(LY)? )?FALL(S | |-)?THR(OUGH|U)[
               \t.!]*(-[^\n\r]*)?">
               *<"[ \t.!]*(Else,? |Intentional(ly)? )?Fall((s | |-)[Tt]|t)hr(ough|u)[
               \t.!]*(-[^\n\r]*)?">
               *<"[ \t.!]*([Ee]lse,? |[Ii]ntentional(ly)? )?fall(s | |-)?thr(ough|u)[
               \t.!]*(-[^\n\r]*)?">
           *<-Wimplicit-fallthrough=4 case sensitively matches one of the>
               following regular expressions:

               *<"-fallthrough">
               *<"@fallthrough@">
               *<"lint -fallthrough[ \t]*">
               *<"[ \t]*FALLTHR(OUGH|U)[ \t]*">
           *<-Wimplicit-fallthrough=5 doesn't recognize any comments as>
               fallthrough comments, only attributes disable the warning.

           The comment needs to be followed after optional whitespace and other comments by
           "case" or "default" keywords or by a user label that precedes some "case" or "default"
           label.

                   switch (cond)
                     {
                     case 1:
                       bar (0);
                       /* FALLTHRU */
                     default:
                       ...
                     }

           The -Wimplicit-fallthrough=3 warning is enabled by -Wextra.

       -Wif-not-aligned (C, C++, Objective-C and Objective-C++ only)
           Control if warning triggered by the "warn_if_not_aligned" attribute should be issued.
           This is enabled by default.  Use -Wno-if-not-aligned to disable it.

       -Wignored-qualifiers (C and C++ only)
           Warn if the return type of a function has a type qualifier such as "const".  For ISO C
           such a type qualifier has no effect, since the value returned by a function is not an
           lvalue.  For C++, the warning is only emitted for scalar types or "void".  ISO C
           prohibits qualified "void" return types on function definitions, so such return types
           always receive a warning even without this option.

           This warning is also enabled by -Wextra.

       -Wignored-attributes (C and C++ only)
           Warn when an attribute is ignored.  This is different from the -Wattributes option in
           that it warns whenever the compiler decides to drop an attribute, not that the
           attribute is either unknown, used in a wrong place, etc.  This warning is enabled by
           default.

       -Wmain
           Warn if the type of "main" is suspicious.  "main" should be a function with external
           linkage, returning int, taking either zero arguments, two, or three arguments of
           appropriate types.  This warning is enabled by default in C++ and is enabled by either
           -Wall or -Wpedantic.

       -Wmisleading-indentation (C and C++ only)
           Warn when the indentation of the code does not reflect the block structure.
           Specifically, a warning is issued for "if", "else", "while", and "for" clauses with a
           guarded statement that does not use braces, followed by an unguarded statement with
           the same indentation.

           In the following example, the call to "bar" is misleadingly indented as if it were
           guarded by the "if" conditional.

                     if (some_condition ())
                       foo ();
                       bar ();  /* Gotcha: this is not guarded by the "if".  */

           In the case of mixed tabs and spaces, the warning uses the -ftabstop= option to
           determine if the statements line up (defaulting to 8).

           The warning is not issued for code involving multiline preprocessor logic such as the
           following example.

                     if (flagA)
                       foo (0);
                   #if SOME_CONDITION_THAT_DOES_NOT_HOLD
                     if (flagB)
                   #endif
                       foo (1);

           The warning is not issued after a "#line" directive, since this typically indicates
           autogenerated code, and no assumptions can be made about the layout of the file that
           the directive references.

           This warning is enabled by -Wall in C and C++.

       -Wmissing-attributes
           Warn when a declaration of a function is missing one or more attributes that a related
           function is declared with and whose absence may adversely affect the correctness or
           efficiency of generated code.  For example, in C++, the warning is issued when an
           explicit specialization of a primary template declared with attribute "alloc_align",
           "alloc_size", "assume_aligned", "format", "format_arg", "malloc", or "nonnull" is
           declared without it.  Attributes "deprecated", "error", and "warning" suppress the
           warning..

           -Wmissing-attributes is enabled by -Wall.

           For example, since the declaration of the primary function template below makes use of
           both attribute "malloc" and "alloc_size" the declaration of the explicit
           specialization of the template is diagnosed because it is missing one of the
           attributes.

                   template <class T>
                   T* __attribute__ ((malloc, alloc_size (1)))
                   allocate (size_t);

                   template <>
                   void* __attribute__ ((malloc))   // missing alloc_size
                   allocate<void> (size_t);

       -Wmissing-braces
           Warn if an aggregate or union initializer is not fully bracketed.  In the following
           example, the initializer for "a" is not fully bracketed, but that for "b" is fully
           bracketed.  This warning is enabled by -Wall in C.

                   int a[2][2] = { 0, 1, 2, 3 };
                   int b[2][2] = { { 0, 1 }, { 2, 3 } };

           This warning is enabled by -Wall.

       -Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)
           Warn if a user-supplied include directory does not exist.

       -Wmultistatement-macros
           Warn about unsafe multiple statement macros that appear to be guarded by a clause such
           as "if", "else", "for", "switch", or "while", in which only the first statement is
           actually guarded after the macro is expanded.

           For example:

                   #define DOIT x++; y++
                   if (c)
                     DOIT;

           will increment "y" unconditionally, not just when "c" holds.  The can usually be fixed
           by wrapping the macro in a do-while loop:

                   #define DOIT do { x++; y++; } while (0)
                   if (c)
                     DOIT;

           This warning is enabled by -Wall in C and C++.

       -Wparentheses
           Warn if parentheses are omitted in certain contexts, such as when there is an
           assignment in a context where a truth value is expected, or when operators are nested
           whose precedence people often get confused about.

           Also warn if a comparison like "x<=y<=z" appears; this is equivalent to "(x<=y ? 1 :
           0) <= z", which is a different interpretation from that of ordinary mathematical
           notation.

           Also warn for dangerous uses of the GNU extension to "?:" with omitted middle operand.
           When the condition in the "?": operator is a boolean expression, the omitted value is
           always 1.  Often programmers expect it to be a value computed inside the conditional
           expression instead.

           For C++ this also warns for some cases of unnecessary parentheses in declarations,
           which can indicate an attempt at a function call instead of a declaration:

                   {
                     // Declares a local variable called mymutex.
                     std::unique_lock<std::mutex> (mymutex);
                     // User meant std::unique_lock<std::mutex> lock (mymutex);
                   }

           This warning is enabled by -Wall.

       -Wsequence-point
           Warn about code that may have undefined semantics because of violations of sequence
           point rules in the C and C++ standards.

           The C and C++ standards define the order in which expressions in a C/C++ program are
           evaluated in terms of sequence points, which represent a partial ordering between the
           execution of parts of the program: those executed before the sequence point, and those
           executed after it.  These occur after the evaluation of a full expression (one which
           is not part of a larger expression), after the evaluation of the first operand of a
           "&&", "||", "? :" or "," (comma) operator, before a function is called (but after the
           evaluation of its arguments and the expression denoting the called function), and in
           certain other places.  Other than as expressed by the sequence point rules, the order
           of evaluation of subexpressions of an expression is not specified.  All these rules
           describe only a partial order rather than a total order, since, for example, if two
           functions are called within one expression with no sequence point between them, the
           order in which the functions are called is not specified.  However, the standards
           committee have ruled that function calls do not overlap.

           It is not specified when between sequence points modifications to the values of
           objects take effect.  Programs whose behavior depends on this have undefined behavior;
           the C and C++ standards specify that "Between the previous and next sequence point an
           object shall have its stored value modified at most once by the evaluation of an
           expression.  Furthermore, the prior value shall be read only to determine the value to
           be stored.".  If a program breaks these rules, the results on any particular
           implementation are entirely unpredictable.

           Examples of code with undefined behavior are "a = a++;", "a[n] = b[n++]" and "a[i++] =
           i;".  Some more complicated cases are not diagnosed by this option, and it may give an
           occasional false positive result, but in general it has been found fairly effective at
           detecting this sort of problem in programs.

           The C++17 standard will define the order of evaluation of operands in more cases: in
           particular it requires that the right-hand side of an assignment be evaluated before
           the left-hand side, so the above examples are no longer undefined.  But this warning
           will still warn about them, to help people avoid writing code that is undefined in C
           and earlier revisions of C++.

           The standard is worded confusingly, therefore there is some debate over the precise
           meaning of the sequence point rules in subtle cases.  Links to discussions of the
           problem, including proposed formal definitions, may be found on the GCC readings page,
           at <http://gcc.gnu.org/readings.html>.

           This warning is enabled by -Wall for C and C++.

       -Wno-return-local-addr
           Do not warn about returning a pointer (or in C++, a reference) to a variable that goes
           out of scope after the function returns.

       -Wreturn-type
           Warn whenever a function is defined with a return type that defaults to "int".  Also
           warn about any "return" statement with no return value in a function whose return type
           is not "void" (falling off the end of the function body is considered returning
           without a value).

           For C only, warn about a "return" statement with an expression in a function whose
           return type is "void", unless the expression type is also "void".  As a GNU extension,
           the latter case is accepted without a warning unless -Wpedantic is used.

           For C++, a function without return type always produces a diagnostic message, even
           when -Wno-return-type is specified.  The only exceptions are "main" and functions
           defined in system headers.

           This warning is enabled by default for C++ and is enabled by -Wall.

       -Wshift-count-negative
           Warn if shift count is negative. This warning is enabled by default.

       -Wshift-count-overflow
           Warn if shift count >= width of type. This warning is enabled by default.

       -Wshift-negative-value
           Warn if left shifting a negative value.  This warning is enabled by -Wextra in C99 and
           C++11 modes (and newer).

       -Wshift-overflow
       -Wshift-overflow=n
           Warn about left shift overflows.  This warning is enabled by default in C99 and C++11
           modes (and newer).

           -Wshift-overflow=1
               This is the warning level of -Wshift-overflow and is enabled by default in C99 and
               C++11 modes (and newer).  This warning level does not warn about left-shifting 1
               into the sign bit.  (However, in C, such an overflow is still rejected in contexts
               where an integer constant expression is required.)

           -Wshift-overflow=2
               This warning level also warns about left-shifting 1 into the sign bit, unless
               C++14 mode is active.

       -Wswitch
           Warn whenever a "switch" statement has an index of enumerated type and lacks a "case"
           for one or more of the named codes of that enumeration.  (The presence of a "default"
           label prevents this warning.)  "case" labels outside the enumeration range also
           provoke warnings when this option is used (even if there is a "default" label).  This
           warning is enabled by -Wall.

       -Wswitch-default
           Warn whenever a "switch" statement does not have a "default" case.

       -Wswitch-enum
           Warn whenever a "switch" statement has an index of enumerated type and lacks a "case"
           for one or more of the named codes of that enumeration.  "case" labels outside the
           enumeration range also provoke warnings when this option is used.  The only difference
           between -Wswitch and this option is that this option gives a warning about an omitted
           enumeration code even if there is a "default" label.

       -Wswitch-bool
           Warn whenever a "switch" statement has an index of boolean type and the case values
           are outside the range of a boolean type.  It is possible to suppress this warning by
           casting the controlling expression to a type other than "bool".  For example:

                   switch ((int) (a == 4))
                     {
                     ...
                     }

           This warning is enabled by default for C and C++ programs.

       -Wswitch-unreachable
           Warn whenever a "switch" statement contains statements between the controlling
           expression and the first case label, which will never be executed.  For example:

                   switch (cond)
                     {
                      i = 15;
                     ...
                      case 5:
                     ...
                     }

           -Wswitch-unreachable does not warn if the statement between the controlling expression
           and the first case label is just a declaration:

                   switch (cond)
                     {
                      int i;
                     ...
                      case 5:
                      i = 5;
                     ...
                     }

           This warning is enabled by default for C and C++ programs.

       -Wsync-nand (C and C++ only)
           Warn when "__sync_fetch_and_nand" and "__sync_nand_and_fetch" built-in functions are
           used.  These functions changed semantics in GCC 4.4.

       -Wunused-but-set-parameter
           Warn whenever a function parameter is assigned to, but otherwise unused (aside from
           its declaration).

           To suppress this warning use the "unused" attribute.

           This warning is also enabled by -Wunused together with -Wextra.

       -Wunused-but-set-variable
           Warn whenever a local variable is assigned to, but otherwise unused (aside from its
           declaration).  This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

           This warning is also enabled by -Wunused, which is enabled by -Wall.

       -Wunused-function
           Warn whenever a static function is declared but not defined or a non-inline static
           function is unused.  This warning is enabled by -Wall.

       -Wunused-label
           Warn whenever a label is declared but not used.  This warning is enabled by -Wall.

           To suppress this warning use the "unused" attribute.

       -Wunused-local-typedefs (C, Objective-C, C++ and Objective-C++ only)
           Warn when a typedef locally defined in a function is not used.  This warning is
           enabled by -Wall.

       -Wunused-parameter
           Warn whenever a function parameter is unused aside from its declaration.

           To suppress this warning use the "unused" attribute.

       -Wno-unused-result
           Do not warn if a caller of a function marked with attribute "warn_unused_result" does
           not use its return value. The default is -Wunused-result.

       -Wunused-variable
           Warn whenever a local or static variable is unused aside from its declaration. This
           option implies -Wunused-const-variable=1 for C, but not for C++. This warning is
           enabled by -Wall.

           To suppress this warning use the "unused" attribute.

       -Wunused-const-variable
       -Wunused-const-variable=n
           Warn whenever a constant static variable is unused aside from its declaration.
           -Wunused-const-variable=1 is enabled by -Wunused-variable for C, but not for C++. In C
           this declares variable storage, but in C++ this is not an error since const variables
           take the place of "#define"s.

           To suppress this warning use the "unused" attribute.

           -Wunused-const-variable=1
               This is the warning level that is enabled by -Wunused-variable for C.  It warns
               only about unused static const variables defined in the main compilation unit, but
               not about static const variables declared in any header included.

           -Wunused-const-variable=2
               This warning level also warns for unused constant static variables in headers
               (excluding system headers).  This is the warning level of -Wunused-const-variable
               and must be explicitly requested since in C++ this isn't an error and in C it
               might be harder to clean up all headers included.

       -Wunused-value
           Warn whenever a statement computes a result that is explicitly not used. To suppress
           this warning cast the unused expression to "void". This includes an expression-
           statement or the left-hand side of a comma expression that contains no side effects.
           For example, an expression such as "x[i,j]" causes a warning, while "x[(void)i,j]"
           does not.

           This warning is enabled by -Wall.

       -Wunused
           All the above -Wunused options combined.

           In order to get a warning about an unused function parameter, you must either specify
           -Wextra -Wunused (note that -Wall implies -Wunused), or separately specify
           -Wunused-parameter.

       -Wuninitialized
           Warn if an automatic variable is used without first being initialized or if a variable
           may be clobbered by a "setjmp" call. In C++, warn if a non-static reference or non-
           static "const" member appears in a class without constructors.

           If you want to warn about code that uses the uninitialized value of the variable in
           its own initializer, use the -Winit-self option.

           These warnings occur for individual uninitialized or clobbered elements of structure,
           union or array variables as well as for variables that are uninitialized or clobbered
           as a whole.  They do not occur for variables or elements declared "volatile".  Because
           these warnings depend on optimization, the exact variables or elements for which there
           are warnings depends on the precise optimization options and version of GCC used.

           Note that there may be no warning about a variable that is used only to compute a
           value that itself is never used, because such computations may be deleted by data flow
           analysis before the warnings are printed.

       -Winvalid-memory-model
           Warn for invocations of __atomic Builtins, __sync Builtins, and the C11 atomic generic
           functions with a memory consistency argument that is either invalid for the operation
           or outside the range of values of the "memory_order" enumeration.  For example, since
           the "__atomic_store" and "__atomic_store_n" built-ins are only defined for the
           relaxed, release, and sequentially consistent memory orders the following code is
           diagnosed:

                   void store (int *i)
                   {
                     __atomic_store_n (i, 0, memory_order_consume);
                   }

           -Winvalid-memory-model is enabled by default.

       -Wmaybe-uninitialized
           For an automatic (i.e. local) variable, if there exists a path from the function entry
           to a use of the variable that is initialized, but there exist some other paths for
           which the variable is not initialized, the compiler emits a warning if it cannot prove
           the uninitialized paths are not executed at run time.

           These warnings are only possible in optimizing compilation, because otherwise GCC does
           not keep track of the state of variables.

           These warnings are made optional because GCC may not be able to determine when the
           code is correct in spite of appearing to have an error.  Here is one example of how
           this can happen:

                   {
                     int x;
                     switch (y)
                       {
                       case 1: x = 1;
                         break;
                       case 2: x = 4;
                         break;
                       case 3: x = 5;
                       }
                     foo (x);
                   }

           If the value of "y" is always 1, 2 or 3, then "x" is always initialized, but GCC
           doesn't know this. To suppress the warning, you need to provide a default case with
           assert(0) or similar code.

           This option also warns when a non-volatile automatic variable might be changed by a
           call to "longjmp".  The compiler sees only the calls to "setjmp".  It cannot know
           where "longjmp" will be called; in fact, a signal handler could call it at any point
           in the code.  As a result, you may get a warning even when there is in fact no problem
           because "longjmp" cannot in fact be called at the place that would cause a problem.

           Some spurious warnings can be avoided if you declare all the functions you use that
           never return as "noreturn".

           This warning is enabled by -Wall or -Wextra.

       -Wunknown-pragmas
           Warn when a "#pragma" directive is encountered that is not understood by GCC.  If this
           command-line option is used, warnings are even issued for unknown pragmas in system
           header files.  This is not the case if the warnings are only enabled by the -Wall
           command-line option.

       -Wno-pragmas
           Do not warn about misuses of pragmas, such as incorrect parameters, invalid syntax, or
           conflicts between pragmas.  See also -Wunknown-pragmas.

       -Wstrict-aliasing
           This option is only active when -fstrict-aliasing is active.  It warns about code that
           might break the strict aliasing rules that the compiler is using for optimization.
           The warning does not catch all cases, but does attempt to catch the more common
           pitfalls.  It is included in -Wall.  It is equivalent to -Wstrict-aliasing=3

       -Wstrict-aliasing=n
           This option is only active when -fstrict-aliasing is active.  It warns about code that
           might break the strict aliasing rules that the compiler is using for optimization.
           Higher levels correspond to higher accuracy (fewer false positives).  Higher levels
           also correspond to more effort, similar to the way -O works.  -Wstrict-aliasing is
           equivalent to -Wstrict-aliasing=3.

           Level 1: Most aggressive, quick, least accurate.  Possibly useful when higher levels
           do not warn but -fstrict-aliasing still breaks the code, as it has very few false
           negatives.  However, it has many false positives.  Warns for all pointer conversions
           between possibly incompatible types, even if never dereferenced.  Runs in the front
           end only.

           Level 2: Aggressive, quick, not too precise.  May still have many false positives (not
           as many as level 1 though), and few false negatives (but possibly more than level 1).
           Unlike level 1, it only warns when an address is taken.  Warns about incomplete types.
           Runs in the front end only.

           Level 3 (default for -Wstrict-aliasing): Should have very few false positives and few
           false negatives.  Slightly slower than levels 1 or 2 when optimization is enabled.
           Takes care of the common pun+dereference pattern in the front end:
           "*(int*)&some_float".  If optimization is enabled, it also runs in the back end, where
           it deals with multiple statement cases using flow-sensitive points-to information.
           Only warns when the converted pointer is dereferenced.  Does not warn about incomplete
           types.

       -Wstrict-overflow
       -Wstrict-overflow=n
           This option is only active when signed overflow is undefined.  It warns about cases
           where the compiler optimizes based on the assumption that signed overflow does not
           occur.  Note that it does not warn about all cases where the code might overflow: it
           only warns about cases where the compiler implements some optimization.  Thus this
           warning depends on the optimization level.

           An optimization that assumes that signed overflow does not occur is perfectly safe if
           the values of the variables involved are such that overflow never does, in fact,
           occur.  Therefore this warning can easily give a false positive: a warning about code
           that is not actually a problem.  To help focus on important issues, several warning
           levels are defined.  No warnings are issued for the use of undefined signed overflow
           when estimating how many iterations a loop requires, in particular when determining
           whether a loop will be executed at all.

           -Wstrict-overflow=1
               Warn about cases that are both questionable and easy to avoid.  For example the
               compiler simplifies "x + 1 > x" to 1.  This level of -Wstrict-overflow is enabled
               by -Wall; higher levels are not, and must be explicitly requested.

           -Wstrict-overflow=2
               Also warn about other cases where a comparison is simplified to a constant.  For
               example: "abs (x) >= 0".  This can only be simplified when signed integer overflow
               is undefined, because "abs (INT_MIN)" overflows to "INT_MIN", which is less than
               zero.  -Wstrict-overflow (with no level) is the same as -Wstrict-overflow=2.

           -Wstrict-overflow=3
               Also warn about other cases where a comparison is simplified.  For example: "x + 1
               > 1" is simplified to "x > 0".

           -Wstrict-overflow=4
               Also warn about other simplifications not covered by the above cases.  For
               example: "(x * 10) / 5" is simplified to "x * 2".

           -Wstrict-overflow=5
               Also warn about cases where the compiler reduces the magnitude of a constant
               involved in a comparison.  For example: "x + 2 > y" is simplified to "x + 1 >= y".
               This is reported only at the highest warning level because this simplification
               applies to many comparisons, so this warning level gives a very large number of
               false positives.

       -Wstringop-overflow
       -Wstringop-overflow=type
           Warn for calls to string manipulation functions such as "memcpy" and "strcpy" that are
           determined to overflow the destination buffer.  The optional argument is one greater
           than the type of Object Size Checking to perform to determine the size of the
           destination.  The argument is meaningful only for functions that operate on character
           arrays but not for raw memory functions like "memcpy" which always make use of Object
           Size type-0.  The option also warns for calls that specify a size in excess of the
           largest possible object or at most "SIZE_MAX / 2" bytes.  The option produces the best
           results with optimization enabled but can detect a small subset of simple buffer
           overflows even without optimization in calls to the GCC built-in functions like
           "__builtin_memcpy" that correspond to the standard functions.  In any case, the option
           warns about just a subset of buffer overflows detected by the corresponding overflow
           checking built-ins.  For example, the option will issue a warning for the "strcpy"
           call below because it copies at least 5 characters (the string "blue" including the
           terminating NUL) into the buffer of size 4.

                   enum Color { blue, purple, yellow };
                   const char* f (enum Color clr)
                   {
                     static char buf [4];
                     const char *str;
                     switch (clr)
                       {
                         case blue: str = "blue"; break;
                         case purple: str = "purple"; break;
                         case yellow: str = "yellow"; break;
                       }

                     return strcpy (buf, str);   // warning here
                   }

           Option -Wstringop-overflow=2 is enabled by default.

           -Wstringop-overflow
           -Wstringop-overflow=1
               The -Wstringop-overflow=1 option uses type-zero Object Size Checking to determine
               the sizes of destination objects.  This is the default setting of the option.  At
               this setting the option will not warn for writes past the end of subobjects of
               larger objects accessed by pointers unless the size of the largest surrounding
               object is known.  When the destination may be one of several objects it is assumed
               to be the largest one of them.  On Linux systems, when optimization is enabled at
               this setting the option warns for the same code as when the "_FORTIFY_SOURCE"
               macro is defined to a non-zero value.

           -Wstringop-overflow=2
               The -Wstringop-overflow=2 option uses type-one Object Size Checking to determine
               the sizes of destination objects.  At this setting the option will warn about
               overflows when writing to members of the largest complete objects whose exact size
               is known.  It will, however, not warn for excessive writes to the same members of
               unknown objects referenced by pointers since they may point to arrays containing
               unknown numbers of elements.

           -Wstringop-overflow=3
               The -Wstringop-overflow=3 option uses type-two Object Size Checking to determine
               the sizes of destination objects.  At this setting the option warns about
               overflowing the smallest object or data member.  This is the most restrictive
               setting of the option that may result in warnings for safe code.

           -Wstringop-overflow=4
               The -Wstringop-overflow=4 option uses type-three Object Size Checking to determine
               the sizes of destination objects.  At this setting the option will warn about
               overflowing any data members, and when the destination is one of several objects
               it uses the size of the largest of them to decide whether to issue a warning.
               Similarly to -Wstringop-overflow=3 this setting of the option may result in
               warnings for benign code.

       -Wstringop-truncation
           Warn for calls to bounded string manipulation functions such as "strncat", "strncpy",
           and "stpncpy" that may either truncate the copied string or leave the destination
           unchanged.

           In the following example, the call to "strncat" specifies a bound that is less than
           the length of the source string.  As a result, the copy of the source will be
           truncated and so the call is diagnosed.  To avoid the warning use "bufsize - strlen
           (buf) - 1)" as the bound.

                   void append (char *buf, size_t bufsize)
                   {
                     strncat (buf, ".txt", 3);
                   }

           As another example, the following call to "strncpy" results in copying to "d" just the
           characters preceding the terminating NUL, without appending the NUL to the end.
           Assuming the result of "strncpy" is necessarily a NUL-terminated string is a common
           mistake, and so the call is diagnosed.  To avoid the warning when the result is not
           expected to be NUL-terminated, call "memcpy" instead.

                   void copy (char *d, const char *s)
                   {
                     strncpy (d, s, strlen (s));
                   }

           In the following example, the call to "strncpy" specifies the size of the destination
           buffer as the bound.  If the length of the source string is equal to or greater than
           this size the result of the copy will not be NUL-terminated.  Therefore, the call is
           also diagnosed.  To avoid the warning, specify "sizeof buf - 1" as the bound and set
           the last element of the buffer to "NUL".

                   void copy (const char *s)
                   {
                     char buf[80];
                     strncpy (buf, s, sizeof buf);
                     ...
                   }

           In situations where a character array is intended to store a sequence of bytes with no
           terminating "NUL" such an array may be annotated with attribute "nonstring" to avoid
           this warning.  Such arrays, however, are not suitable arguments to functions that
           expect "NUL"-terminated strings.  To help detect accidental misuses of such arrays GCC
           issues warnings unless it can prove that the use is safe.

           Option -Wstringop-truncation is enabled by -Wall.

       -Wsuggest-attribute=[pure|const|noreturn|format|cold|malloc]
           Warn for cases where adding an attribute may be beneficial. The attributes currently
           supported are listed below.

           -Wsuggest-attribute=pure
           -Wsuggest-attribute=const
           -Wsuggest-attribute=noreturn
           -Wsuggest-attribute=malloc
               Warn about functions that might be candidates for attributes "pure", "const" or
               "noreturn" or "malloc". The compiler only warns for functions visible in other
               compilation units or (in the case of "pure" and "const") if it cannot prove that
               the function returns normally. A function returns normally if it doesn't contain
               an infinite loop or return abnormally by throwing, calling "abort" or trapping.
               This analysis requires option -fipa-pure-const, which is enabled by default at -O
               and higher.  Higher optimization levels improve the accuracy of the analysis.

           -Wsuggest-attribute=format
           -Wmissing-format-attribute
               Warn about function pointers that might be candidates for "format" attributes.
               Note these are only possible candidates, not absolute ones.  GCC guesses that
               function pointers with "format" attributes that are used in assignment,
               initialization, parameter passing or return statements should have a corresponding
               "format" attribute in the resulting type.  I.e. the left-hand side of the
               assignment or initialization, the type of the parameter variable, or the return
               type of the containing function respectively should also have a "format" attribute
               to avoid the warning.

               GCC also warns about function definitions that might be candidates for "format"
               attributes.  Again, these are only possible candidates.  GCC guesses that "format"
               attributes might be appropriate for any function that calls a function like
               "vprintf" or "vscanf", but this might not always be the case, and some functions
               for which "format" attributes are appropriate may not be detected.

           -Wsuggest-attribute=cold
               Warn about functions that might be candidates for "cold" attribute.  This is based
               on static detection and generally will only warn about functions which always
               leads to a call to another "cold" function such as wrappers of C++ "throw" or
               fatal error reporting functions leading to "abort".

       -Wsuggest-final-types
           Warn about types with virtual methods where code quality would be improved if the type
           were declared with the C++11 "final" specifier, or, if possible, declared in an
           anonymous namespace. This allows GCC to more aggressively devirtualize the polymorphic
           calls. This warning is more effective with link time optimization, where the
           information about the class hierarchy graph is more complete.

       -Wsuggest-final-methods
           Warn about virtual methods where code quality would be improved if the method were
           declared with the C++11 "final" specifier, or, if possible, its type were declared in
           an anonymous namespace or with the "final" specifier.  This warning is more effective
           with link-time optimization, where the information about the class hierarchy graph is
           more complete. It is recommended to first consider suggestions of
           -Wsuggest-final-types and then rebuild with new annotations.

       -Wsuggest-override
           Warn about overriding virtual functions that are not marked with the override keyword.

       -Walloc-zero
           Warn about calls to allocation functions decorated with attribute "alloc_size" that
           specify zero bytes, including those to the built-in forms of the functions
           "aligned_alloc", "alloca", "calloc", "malloc", and "realloc".  Because the behavior of
           these functions when called with a zero size differs among implementations (and in the
           case of "realloc" has been deprecated) relying on it may result in subtle portability
           bugs and should be avoided.

       -Walloc-size-larger-than=n
           Warn about calls to functions decorated with attribute "alloc_size" that attempt to
           allocate objects larger than the specified number of bytes, or where the result of the
           size computation in an integer type with infinite precision would exceed "SIZE_MAX /
           2".  The option argument n may end in one of the standard suffixes designating a
           multiple of bytes such as "kB" and "KiB" for kilobyte and kibibyte, respectively, "MB"
           and "MiB" for megabyte and mebibyte, and so on.  -Walloc-size-larger-than=PTRDIFF_MAX
           is enabled by default.  Warnings controlled by the option can be disabled by
           specifying n of SIZE_MAX or more.

       -Walloca
           This option warns on all uses of "alloca" in the source.

       -Walloca-larger-than=n
           This option warns on calls to "alloca" that are not bounded by a controlling predicate
           limiting its argument of integer type to at most n bytes, or calls to "alloca" where
           the bound is unknown.  Arguments of non-integer types are considered unbounded even if
           they appear to be constrained to the expected range.

           For example, a bounded case of "alloca" could be:

                   void func (size_t n)
                   {
                     void *p;
                     if (n <= 1000)
                       p = alloca (n);
                     else
                       p = malloc (n);
                     f (p);
                   }

           In the above example, passing "-Walloca-larger-than=1000" would not issue a warning
           because the call to "alloca" is known to be at most 1000 bytes.  However, if
           "-Walloca-larger-than=500" were passed, the compiler would emit a warning.

           Unbounded uses, on the other hand, are uses of "alloca" with no controlling predicate
           constraining its integer argument.  For example:

                   void func ()
                   {
                     void *p = alloca (n);
                     f (p);
                   }

           If "-Walloca-larger-than=500" were passed, the above would trigger a warning, but this
           time because of the lack of bounds checking.

           Note, that even seemingly correct code involving signed integers could cause a
           warning:

                   void func (signed int n)
                   {
                     if (n < 500)
                       {
                         p = alloca (n);
                         f (p);
                       }
                   }

           In the above example, n could be negative, causing a larger than expected argument to
           be implicitly cast into the "alloca" call.

           This option also warns when "alloca" is used in a loop.

           This warning is not enabled by -Wall, and is only active when -ftree-vrp is active
           (default for -O2 and above).

           See also -Wvla-larger-than=n.

       -Warray-bounds
       -Warray-bounds=n
           This option is only active when -ftree-vrp is active (default for -O2 and above). It
           warns about subscripts to arrays that are always out of bounds. This warning is
           enabled by -Wall.

           -Warray-bounds=1
               This is the warning level of -Warray-bounds and is enabled by -Wall; higher levels
               are not, and must be explicitly requested.

           -Warray-bounds=2
               This warning level also warns about out of bounds access for arrays at the end of
               a struct and for arrays accessed through pointers. This warning level may give a
               larger number of false positives and is deactivated by default.

       -Wattribute-alias
           Warn about declarations using the "alias" and similar attributes whose target is
           incompatible with the type of the alias.

       -Wbool-compare
           Warn about boolean expression compared with an integer value different from
           "true"/"false".  For instance, the following comparison is always false:

                   int n = 5;
                   ...
                   if ((n > 1) == 2) { ... }

           This warning is enabled by -Wall.

       -Wbool-operation
           Warn about suspicious operations on expressions of a boolean type.  For instance,
           bitwise negation of a boolean is very likely a bug in the program.  For C, this
           warning also warns about incrementing or decrementing a boolean, which rarely makes
           sense.  (In C++, decrementing a boolean is always invalid.  Incrementing a boolean is
           invalid in C++17, and deprecated otherwise.)

           This warning is enabled by -Wall.

       -Wduplicated-branches
           Warn when an if-else has identical branches.  This warning detects cases like

                   if (p != NULL)
                     return 0;
                   else
                     return 0;

           It doesn't warn when both branches contain just a null statement.  This warning also
           warn for conditional operators:

                     int i = x ? *p : *p;

       -Wduplicated-cond
           Warn about duplicated conditions in an if-else-if chain.  For instance, warn for the
           following code:

                   if (p->q != NULL) { ... }
                   else if (p->q != NULL) { ... }

       -Wframe-address
           Warn when the __builtin_frame_address or __builtin_return_address is called with an
           argument greater than 0.  Such calls may return indeterminate values or crash the
           program.  The warning is included in -Wall.

       -Wno-discarded-qualifiers (C and Objective-C only)
           Do not warn if type qualifiers on pointers are being discarded.  Typically, the
           compiler warns if a "const char *" variable is passed to a function that takes a "char
           *" parameter.  This option can be used to suppress such a warning.

       -Wno-discarded-array-qualifiers (C and Objective-C only)
           Do not warn if type qualifiers on arrays which are pointer targets are being
           discarded. Typically, the compiler warns if a "const int (*)[]" variable is passed to
           a function that takes a "int (*)[]" parameter.  This option can be used to suppress
           such a warning.

       -Wno-incompatible-pointer-types (C and Objective-C only)
           Do not warn when there is a conversion between pointers that have incompatible types.
           This warning is for cases not covered by -Wno-pointer-sign, which warns for pointer
           argument passing or assignment with different signedness.

       -Wno-int-conversion (C and Objective-C only)
           Do not warn about incompatible integer to pointer and pointer to integer conversions.
           This warning is about implicit conversions; for explicit conversions the warnings
           -Wno-int-to-pointer-cast and -Wno-pointer-to-int-cast may be used.

       -Wno-div-by-zero
           Do not warn about compile-time integer division by zero.  Floating-point division by
           zero is not warned about, as it can be a legitimate way of obtaining infinities and
           NaNs.

       -Wsystem-headers
           Print warning messages for constructs found in system header files.  Warnings from
           system headers are normally suppressed, on the assumption that they usually do not
           indicate real problems and would only make the compiler output harder to read.  Using
           this command-line option tells GCC to emit warnings from system headers as if they
           occurred in user code.  However, note that using -Wall in conjunction with this option
           does not warn about unknown pragmas in system headers---for that, -Wunknown-pragmas
           must also be used.

       -Wtautological-compare
           Warn if a self-comparison always evaluates to true or false.  This warning detects
           various mistakes such as:

                   int i = 1;
                   ...
                   if (i > i) { ... }

           This warning also warns about bitwise comparisons that always evaluate to true or
           false, for instance:

                   if ((a & 16) == 10) { ... }

           will always be false.

           This warning is enabled by -Wall.

       -Wtrampolines
           Warn about trampolines generated for pointers to nested functions.  A trampoline is a
           small piece of data or code that is created at run time on the stack when the address
           of a nested function is taken, and is used to call the nested function indirectly.
           For some targets, it is made up of data only and thus requires no special treatment.
           But, for most targets, it is made up of code and thus requires the stack to be made
           executable in order for the program to work properly.

       -Wfloat-equal
           Warn if floating-point values are used in equality comparisons.

           The idea behind this is that sometimes it is convenient (for the programmer) to
           consider floating-point values as approximations to infinitely precise real numbers.
           If you are doing this, then you need to compute (by analyzing the code, or in some
           other way) the maximum or likely maximum error that the computation introduces, and
           allow for it when performing comparisons (and when producing output, but that's a
           different problem).  In particular, instead of testing for equality, you should check
           to see whether the two values have ranges that overlap; and this is done with the
           relational operators, so equality comparisons are probably mistaken.

       -Wtraditional (C and Objective-C only)
           Warn about certain constructs that behave differently in traditional and ISO C.  Also
           warn about ISO C constructs that have no traditional C equivalent, and/or problematic
           constructs that should be avoided.

           *   Macro parameters that appear within string literals in the macro body.  In
               traditional C macro replacement takes place within string literals, but in ISO C
               it does not.

           *   In traditional C, some preprocessor directives did not exist.  Traditional
               preprocessors only considered a line to be a directive if the # appeared in column
               1 on the line.  Therefore -Wtraditional warns about directives that traditional C
               understands but ignores because the # does not appear as the first character on
               the line.  It also suggests you hide directives like "#pragma" not understood by
               traditional C by indenting them.  Some traditional implementations do not
               recognize "#elif", so this option suggests avoiding it altogether.

           *   A function-like macro that appears without arguments.

           *   The unary plus operator.

           *   The U integer constant suffix, or the F or L floating-point constant suffixes.
               (Traditional C does support the L suffix on integer constants.)  Note, these
               suffixes appear in macros defined in the system headers of most modern systems,
               e.g. the _MIN/_MAX macros in "<limits.h>".  Use of these macros in user code might
               normally lead to spurious warnings, however GCC's integrated preprocessor has
               enough context to avoid warning in these cases.

           *   A function declared external in one block and then used after the end of the
               block.

           *   A "switch" statement has an operand of type "long".

           *   A non-"static" function declaration follows a "static" one.  This construct is not
               accepted by some traditional C compilers.

           *   The ISO type of an integer constant has a different width or signedness from its
               traditional type.  This warning is only issued if the base of the constant is ten.
               I.e. hexadecimal or octal values, which typically represent bit patterns, are not
               warned about.

           *   Usage of ISO string concatenation is detected.

           *   Initialization of automatic aggregates.

           *   Identifier conflicts with labels.  Traditional C lacks a separate namespace for
               labels.

           *   Initialization of unions.  If the initializer is zero, the warning is omitted.
               This is done under the assumption that the zero initializer in user code appears
               conditioned on e.g. "__STDC__" to avoid missing initializer warnings and relies on
               default initialization to zero in the traditional C case.

           *   Conversions by prototypes between fixed/floating-point values and vice versa.  The
               absence of these prototypes when compiling with traditional C causes serious
               problems.  This is a subset of the possible conversion warnings; for the full set
               use -Wtraditional-conversion.

           *   Use of ISO C style function definitions.  This warning intentionally is not issued
               for prototype declarations or variadic functions because these ISO C features
               appear in your code when using libiberty's traditional C compatibility macros,
               "PARAMS" and "VPARAMS".  This warning is also bypassed for nested functions
               because that feature is already a GCC extension and thus not relevant to
               traditional C compatibility.

       -Wtraditional-conversion (C and Objective-C only)
           Warn if a prototype causes a type conversion that is different from what would happen
           to the same argument in the absence of a prototype.  This includes conversions of
           fixed point to floating and vice versa, and conversions changing the width or
           signedness of a fixed-point argument except when the same as the default promotion.

       -Wdeclaration-after-statement (C and Objective-C only)
           Warn when a declaration is found after a statement in a block.  This construct, known
           from C++, was introduced with ISO C99 and is by default allowed in GCC.  It is not
           supported by ISO C90.

       -Wshadow
           Warn whenever a local variable or type declaration shadows another variable,
           parameter, type, class member (in C++), or instance variable (in Objective-C) or
           whenever a built-in function is shadowed. Note that in C++, the compiler warns if a
           local variable shadows an explicit typedef, but not if it shadows a struct/class/enum.
           Same as -Wshadow=global.

       -Wno-shadow-ivar (Objective-C only)
           Do not warn whenever a local variable shadows an instance variable in an Objective-C
           method.

       -Wshadow=global
           The default for -Wshadow. Warns for any (global) shadowing.

       -Wshadow=local
           Warn when a local variable shadows another local variable or parameter.  This warning
           is enabled by -Wshadow=global.

       -Wshadow=compatible-local
           Warn when a local variable shadows another local variable or parameter whose type is
           compatible with that of the shadowing variable. In C++, type compatibility here means
           the type of the shadowing variable can be converted to that of the shadowed variable.
           The creation of this flag (in addition to -Wshadow=local) is based on the idea that
           when a local variable shadows another one of incompatible type, it is most likely
           intentional, not a bug or typo, as shown in the following example:

                   for (SomeIterator i = SomeObj.begin(); i != SomeObj.end(); ++i)
                   {
                     for (int i = 0; i < N; ++i)
                     {
                       ...
                     }
                     ...
                   }

           Since the two variable "i" in the example above have incompatible types, enabling only
           -Wshadow=compatible-local will not emit a warning.  Because their types are
           incompatible, if a programmer accidentally uses one in place of the other, type
           checking will catch that and emit an error or warning. So not warning (about
           shadowing) in this case will not lead to undetected bugs. Use of this flag instead of
           -Wshadow=local can possibly reduce the number of warnings triggered by intentional
           shadowing.

           This warning is enabled by -Wshadow=local.

       -Wlarger-than=len
           Warn whenever an object of larger than len bytes is defined.

       -Wframe-larger-than=len
           Warn if the size of a function frame is larger than len bytes.  The computation done
           to determine the stack frame size is approximate and not conservative.  The actual
           requirements may be somewhat greater than len even if you do not get a warning.  In
           addition, any space allocated via "alloca", variable-length arrays, or related
           constructs is not included by the compiler when determining whether or not to issue a
           warning.

       -Wno-free-nonheap-object
           Do not warn when attempting to free an object that was not allocated on the heap.

       -Wstack-usage=len
           Warn if the stack usage of a function might be larger than len bytes.  The computation
           done to determine the stack usage is conservative.  Any space allocated via "alloca",
           variable-length arrays, or related constructs is included by the compiler when
           determining whether or not to issue a warning.

           The message is in keeping with the output of -fstack-usage.

           *   If the stack usage is fully static but exceeds the specified amount, it's:

                         warning: stack usage is 1120 bytes

           *   If the stack usage is (partly) dynamic but bounded, it's:

                         warning: stack usage might be 1648 bytes

           *   If the stack usage is (partly) dynamic and not bounded, it's:

                         warning: stack usage might be unbounded

       -Wno-pedantic-ms-format (MinGW targets only)
           When used in combination with -Wformat and -pedantic without GNU extensions, this
           option disables the warnings about non-ISO "printf" / "scanf" format width specifiers
           "I32", "I64", and "I" used on Windows targets, which depend on the MS runtime.

       -Waligned-new
           Warn about a new-expression of a type that requires greater alignment than the
           "alignof(std::max_align_t)" but uses an allocation function without an explicit
           alignment parameter. This option is enabled by -Wall.

           Normally this only warns about global allocation functions, but -Waligned-new=all also
           warns about class member allocation functions.

       -Wplacement-new
       -Wplacement-new=n
           Warn about placement new expressions with undefined behavior, such as constructing an
           object in a buffer that is smaller than the type of the object.  For example, the
           placement new expression below is diagnosed because it attempts to construct an array
           of 64 integers in a buffer only 64 bytes large.

                   char buf [64];
                   new (buf) int[64];

           This warning is enabled by default.

           -Wplacement-new=1
               This is the default warning level of -Wplacement-new.  At this level the warning
               is not issued for some strictly undefined constructs that GCC allows as extensions
               for compatibility with legacy code.  For example, the following "new" expression
               is not diagnosed at this level even though it has undefined behavior according to
               the C++ standard because it writes past the end of the one-element array.

                       struct S { int n, a[1]; };
                       S *s = (S *)malloc (sizeof *s + 31 * sizeof s->a[0]);
                       new (s->a)int [32]();

           -Wplacement-new=2
               At this level, in addition to diagnosing all the same constructs as at level 1, a
               diagnostic is also issued for placement new expressions that construct an object
               in the last member of structure whose type is an array of a single element and
               whose size is less than the size of the object being constructed.  While the
               previous example would be diagnosed, the following construct makes use of the
               flexible member array extension to avoid the warning at level 2.

                       struct S { int n, a[]; };
                       S *s = (S *)malloc (sizeof *s + 32 * sizeof s->a[0]);
                       new (s->a)int [32]();

       -Wpointer-arith
           Warn about anything that depends on the "size of" a function type or of "void".  GNU C
           assigns these types a size of 1, for convenience in calculations with "void *"
           pointers and pointers to functions.  In C++, warn also when an arithmetic operation
           involves "NULL".  This warning is also enabled by -Wpedantic.

       -Wpointer-compare
           Warn if a pointer is compared with a zero character constant.  This usually means that
           the pointer was meant to be dereferenced.  For example:

                   const char *p = foo ();
                   if (p == '\0')
                     return 42;

           Note that the code above is invalid in C++11.

           This warning is enabled by default.

       -Wtype-limits
           Warn if a comparison is always true or always false due to the limited range of the
           data type, but do not warn for constant expressions.  For example, warn if an unsigned
           variable is compared against zero with "<" or ">=".  This warning is also enabled by
           -Wextra.

       -Wcomment
       -Wcomments
           Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a
           backslash-newline appears in a // comment.  This warning is enabled by -Wall.

       -Wtrigraphs
           Warn if any trigraphs are encountered that might change the meaning of the program.
           Trigraphs within comments are not warned about, except those that would form escaped
           newlines.

           This option is implied by -Wall.  If -Wall is not given, this option is still enabled
           unless trigraphs are enabled.  To get trigraph conversion without warnings, but get
           the other -Wall warnings, use -trigraphs -Wall -Wno-trigraphs.

       -Wundef
           Warn if an undefined identifier is evaluated in an "#if" directive.  Such identifiers
           are replaced with zero.

       -Wexpansion-to-defined
           Warn whenever defined is encountered in the expansion of a macro (including the case
           where the macro is expanded by an #if directive).  Such usage is not portable.  This
           warning is also enabled by -Wpedantic and -Wextra.

       -Wunused-macros
           Warn about macros defined in the main file that are unused.  A macro is used if it is
           expanded or tested for existence at least once.  The preprocessor also warns if the
           macro has not been used at the time it is redefined or undefined.

           Built-in macros, macros defined on the command line, and macros defined in include
           files are not warned about.

           Note: If a macro is actually used, but only used in skipped conditional blocks, then
           the preprocessor reports it as unused.  To avoid the warning in such a case, you might
           improve the scope of the macro's definition by, for example, moving it into the first
           skipped block.  Alternatively, you could provide a dummy use with something like:

                   #if defined the_macro_causing_the_warning
                   #endif

       -Wno-endif-labels
           Do not warn whenever an "#else" or an "#endif" are followed by text.  This sometimes
           happens in older programs with code of the form

                   #if FOO
                   ...
                   #else FOO
                   ...
                   #endif FOO

           The second and third "FOO" should be in comments.  This warning is on by default.

       -Wbad-function-cast (C and Objective-C only)
           Warn when a function call is cast to a non-matching type.  For example, warn if a call
           to a function returning an integer type is cast to a pointer type.

       -Wc90-c99-compat (C and Objective-C only)
           Warn about features not present in ISO C90, but present in ISO C99.  For instance,
           warn about use of variable length arrays, "long long" type, "bool" type, compound
           literals, designated initializers, and so on.  This option is independent of the
           standards mode.  Warnings are disabled in the expression that follows "__extension__".

       -Wc99-c11-compat (C and Objective-C only)
           Warn about features not present in ISO C99, but present in ISO C11.  For instance,
           warn about use of anonymous structures and unions, "_Atomic" type qualifier,
           "_Thread_local" storage-class specifier, "_Alignas" specifier, "Alignof" operator,
           "_Generic" keyword, and so on.  This option is independent of the standards mode.
           Warnings are disabled in the expression that follows "__extension__".

       -Wc++-compat (C and Objective-C only)
           Warn about ISO C constructs that are outside of the common subset of ISO C and ISO
           C++, e.g. request for implicit conversion from "void *" to a pointer to non-"void"
           type.

       -Wc++11-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++ 1998 and ISO C++ 2011,
           e.g., identifiers in ISO C++ 1998 that are keywords in ISO C++ 2011.  This warning
           turns on -Wnarrowing and is enabled by -Wall.

       -Wc++14-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++ 2011 and ISO C++ 2014.
           This warning is enabled by -Wall.

       -Wc++17-compat (C++ and Objective-C++ only)
           Warn about C++ constructs whose meaning differs between ISO C++ 2014 and ISO C++ 2017.
           This warning is enabled by -Wall.

       -Wcast-qual
           Warn whenever a pointer is cast so as to remove a type qualifier from the target type.
           For example, warn if a "const char *" is cast to an ordinary "char *".

           Also warn when making a cast that introduces a type qualifier in an unsafe way.  For
           example, casting "char **" to "const char **" is unsafe, as in this example:

                     /* p is char ** value.  */
                     const char **q = (const char **) p;
                     /* Assignment of readonly string to const char * is OK.  */
                     *q = "string";
                     /* Now char** pointer points to read-only memory.  */
                     **p = 'b';

       -Wcast-align
           Warn whenever a pointer is cast such that the required alignment of the target is
           increased.  For example, warn if a "char *" is cast to an "int *" on machines where
           integers can only be accessed at two- or four-byte boundaries.

       -Wcast-align=strict
           Warn whenever a pointer is cast such that the required alignment of the target is
           increased.  For example, warn if a "char *" is cast to an "int *" regardless of the
           target machine.

       -Wcast-function-type
           Warn when a function pointer is cast to an incompatible function pointer.  In a cast
           involving function types with a variable argument list only the types of initial
           arguments that are provided are considered.  Any parameter of pointer-type matches any
           other pointer-type.  Any benign differences in integral types are ignored, like "int"
           vs. "long" on ILP32 targets.  Likewise type qualifiers are ignored.  The function type
           "void (*) (void)" is special and matches everything, which can be used to suppress
           this warning.  In a cast involving pointer to member types this warning warns whenever
           the type cast is changing the pointer to member type.  This warning is enabled by
           -Wextra.

       -Wwrite-strings
           When compiling C, give string constants the type "const char[length]" so that copying
           the address of one into a non-"const" "char *" pointer produces a warning.  These
           warnings help you find at compile time code that can try to write into a string
           constant, but only if you have been very careful about using "const" in declarations
           and prototypes.  Otherwise, it is just a nuisance. This is why we did not make -Wall
           request these warnings.

           When compiling C++, warn about the deprecated conversion from string literals to "char
           *".  This warning is enabled by default for C++ programs.

       -Wcatch-value
       -Wcatch-value=n (C++ and Objective-C++ only)
           Warn about catch handlers that do not catch via reference.  With -Wcatch-value=1 (or
           -Wcatch-value for short) warn about polymorphic class types that are caught by value.
           With -Wcatch-value=2 warn about all class types that are caught by value. With
           -Wcatch-value=3 warn about all types that are not caught by reference. -Wcatch-value
           is enabled by -Wall.

       -Wclobbered
           Warn for variables that might be changed by "longjmp" or "vfork".  This warning is
           also enabled by -Wextra.

       -Wconditionally-supported (C++ and Objective-C++ only)
           Warn for conditionally-supported (C++11 [intro.defs]) constructs.

       -Wconversion
           Warn for implicit conversions that may alter a value. This includes conversions
           between real and integer, like "abs (x)" when "x" is "double"; conversions between
           signed and unsigned, like "unsigned ui = -1"; and conversions to smaller types, like
           "sqrtf (M_PI)". Do not warn for explicit casts like "abs ((int) x)" and "ui =
           (unsigned) -1", or if the value is not changed by the conversion like in "abs (2.0)".
           Warnings about conversions between signed and unsigned integers can be disabled by
           using -Wno-sign-conversion.

           For C++, also warn for confusing overload resolution for user-defined conversions; and
           conversions that never use a type conversion operator: conversions to "void", the same
           type, a base class or a reference to them. Warnings about conversions between signed
           and unsigned integers are disabled by default in C++ unless -Wsign-conversion is
           explicitly enabled.

       -Wno-conversion-null (C++ and Objective-C++ only)
           Do not warn for conversions between "NULL" and non-pointer types. -Wconversion-null is
           enabled by default.

       -Wzero-as-null-pointer-constant (C++ and Objective-C++ only)
           Warn when a literal 0 is used as null pointer constant.  This can be useful to
           facilitate the conversion to "nullptr" in C++11.

       -Wsubobject-linkage (C++ and Objective-C++ only)
           Warn if a class type has a base or a field whose type uses the anonymous namespace or
           depends on a type with no linkage.  If a type A depends on a type B with no or
           internal linkage, defining it in multiple translation units would be an ODR violation
           because the meaning of B is different in each translation unit.  If A only appears in
           a single translation unit, the best way to silence the warning is to give it internal
           linkage by putting it in an anonymous namespace as well.  The compiler doesn't give
           this warning for types defined in the main .C file, as those are unlikely to have
           multiple definitions.  -Wsubobject-linkage is enabled by default.

       -Wdangling-else
           Warn about constructions where there may be confusion to which "if" statement an
           "else" branch belongs.  Here is an example of such a case:

                   {
                     if (a)
                       if (b)
                         foo ();
                     else
                       bar ();
                   }

           In C/C++, every "else" branch belongs to the innermost possible "if" statement, which
           in this example is "if (b)".  This is often not what the programmer expected, as
           illustrated in the above example by indentation the programmer chose.  When there is
           the potential for this confusion, GCC issues a warning when this flag is specified.
           To eliminate the warning, add explicit braces around the innermost "if" statement so
           there is no way the "else" can belong to the enclosing "if".  The resulting code looks
           like this:

                   {
                     if (a)
                       {
                         if (b)
                           foo ();
                         else
                           bar ();
                       }
                   }

           This warning is enabled by -Wparentheses.

       -Wdate-time
           Warn when macros "__TIME__", "__DATE__" or "__TIMESTAMP__" are encountered as they
           might prevent bit-wise-identical reproducible compilations.

       -Wdelete-incomplete (C++ and Objective-C++ only)
           Warn when deleting a pointer to incomplete type, which may cause undefined behavior at
           runtime.  This warning is enabled by default.

       -Wuseless-cast (C++ and Objective-C++ only)
           Warn when an expression is casted to its own type.

       -Wempty-body
           Warn if an empty body occurs in an "if", "else" or "do while" statement.  This warning
           is also enabled by -Wextra.

       -Wenum-compare
           Warn about a comparison between values of different enumerated types.  In C++
           enumerated type mismatches in conditional expressions are also diagnosed and the
           warning is enabled by default.  In C this warning is enabled by -Wall.

       -Wextra-semi (C++, Objective-C++ only)
           Warn about redundant semicolon after in-class function definition.

       -Wjump-misses-init (C, Objective-C only)
           Warn if a "goto" statement or a "switch" statement jumps forward across the
           initialization of a variable, or jumps backward to a label after the variable has been
           initialized.  This only warns about variables that are initialized when they are
           declared.  This warning is only supported for C and Objective-C; in C++ this sort of
           branch is an error in any case.

           -Wjump-misses-init is included in -Wc++-compat.  It can be disabled with the
           -Wno-jump-misses-init option.

       -Wsign-compare
           Warn when a comparison between signed and unsigned values could produce an incorrect
           result when the signed value is converted to unsigned.  In C++, this warning is also
           enabled by -Wall.  In C, it is also enabled by -Wextra.

       -Wsign-conversion
           Warn for implicit conversions that may change the sign of an integer value, like
           assigning a signed integer expression to an unsigned integer variable. An explicit
           cast silences the warning. In C, this option is enabled also by -Wconversion.

       -Wfloat-conversion
           Warn for implicit conversions that reduce the precision of a real value.  This
           includes conversions from real to integer, and from higher precision real to lower
           precision real values.  This option is also enabled by -Wconversion.

       -Wno-scalar-storage-order
           Do not warn on suspicious constructs involving reverse scalar storage order.

       -Wsized-deallocation (C++ and Objective-C++ only)
           Warn about a definition of an unsized deallocation function

                   void operator delete (void *) noexcept;
                   void operator delete[] (void *) noexcept;

           without a definition of the corresponding sized deallocation function

                   void operator delete (void *, std::size_t) noexcept;
                   void operator delete[] (void *, std::size_t) noexcept;

           or vice versa.  Enabled by -Wextra along with -fsized-deallocation.

       -Wsizeof-pointer-div
           Warn for suspicious divisions of two sizeof expressions that divide the pointer size
           by the element size, which is the usual way to compute the array size but won't work
           out correctly with pointers.  This warning warns e.g. about "sizeof (ptr) / sizeof
           (ptr[0])" if "ptr" is not an array, but a pointer.  This warning is enabled by -Wall.

       -Wsizeof-pointer-memaccess
           Warn for suspicious length parameters to certain string and memory built-in functions
           if the argument uses "sizeof".  This warning triggers for example for "memset (ptr, 0,
           sizeof (ptr));" if "ptr" is not an array, but a pointer, and suggests a possible fix,
           or about "memcpy (&foo, ptr, sizeof (&foo));".  -Wsizeof-pointer-memaccess also warns
           about calls to bounded string copy functions like "strncat" or "strncpy" that specify
           as the bound a "sizeof" expression of the source array.  For example, in the following
           function the call to "strncat" specifies the size of the source string as the bound.
           That is almost certainly a mistake and so the call is diagnosed.

                   void make_file (const char *name)
                   {
                     char path[PATH_MAX];
                     strncpy (path, name, sizeof path - 1);
                     strncat (path, ".text", sizeof ".text");
                     ...
                   }

           The -Wsizeof-pointer-memaccess option is enabled by -Wall.

       -Wsizeof-array-argument
           Warn when the "sizeof" operator is applied to a parameter that is declared as an array
           in a function definition.  This warning is enabled by default for C and C++ programs.

       -Wmemset-elt-size
           Warn for suspicious calls to the "memset" built-in function, if the first argument
           references an array, and the third argument is a number equal to the number of
           elements, but not equal to the size of the array in memory.  This indicates that the
           user has omitted a multiplication by the element size.  This warning is enabled by
           -Wall.

       -Wmemset-transposed-args
           Warn for suspicious calls to the "memset" built-in function, if the second argument is
           not zero and the third argument is zero.  This warns e.g.@ about "memset (buf, sizeof
           buf, 0)" where most probably "memset (buf, 0, sizeof buf)" was meant instead.  The
           diagnostics is only emitted if the third argument is literal zero.  If it is some
           expression that is folded to zero, a cast of zero to some type, etc., it is far less
           likely that the user has mistakenly exchanged the arguments and no warning is emitted.
           This warning is enabled by -Wall.

       -Waddress
           Warn about suspicious uses of memory addresses. These include using the address of a
           function in a conditional expression, such as "void func(void); if (func)", and
           comparisons against the memory address of a string literal, such as "if (x == "abc")".
           Such uses typically indicate a programmer error: the address of a function always
           evaluates to true, so their use in a conditional usually indicate that the programmer
           forgot the parentheses in a function call; and comparisons against string literals
           result in unspecified behavior and are not portable in C, so they usually indicate
           that the programmer intended to use "strcmp".  This warning is enabled by -Wall.

       -Wlogical-op
           Warn about suspicious uses of logical operators in expressions.  This includes using
           logical operators in contexts where a bit-wise operator is likely to be expected.
           Also warns when the operands of a logical operator are the same:

                   extern int a;
                   if (a < 0 && a < 0) { ... }

       -Wlogical-not-parentheses
           Warn about logical not used on the left hand side operand of a comparison.  This
           option does not warn if the right operand is considered to be a boolean expression.
           Its purpose is to detect suspicious code like the following:

                   int a;
                   ...
                   if (!a > 1) { ... }

           It is possible to suppress the warning by wrapping the LHS into parentheses:

                   if ((!a) > 1) { ... }

           This warning is enabled by -Wall.

       -Waggregate-return
           Warn if any functions that return structures or unions are defined or called.  (In
           languages where you can return an array, this also elicits a warning.)

       -Wno-aggressive-loop-optimizations
           Warn if in a loop with constant number of iterations the compiler detects undefined
           behavior in some statement during one or more of the iterations.

       -Wno-attributes
           Do not warn if an unexpected "__attribute__" is used, such as unrecognized attributes,
           function attributes applied to variables, etc.  This does not stop errors for
           incorrect use of supported attributes.

       -Wno-builtin-declaration-mismatch
           Warn if a built-in function is declared with the wrong signature or as non-function.
           This warning is enabled by default.

       -Wno-builtin-macro-redefined
           Do not warn if certain built-in macros are redefined.  This suppresses warnings for
           redefinition of "__TIMESTAMP__", "__TIME__", "__DATE__", "__FILE__", and
           "__BASE_FILE__".

       -Wstrict-prototypes (C and Objective-C only)
           Warn if a function is declared or defined without specifying the argument types.  (An
           old-style function definition is permitted without a warning if preceded by a
           declaration that specifies the argument types.)

       -Wold-style-declaration (C and Objective-C only)
           Warn for obsolescent usages, according to the C Standard, in a declaration. For
           example, warn if storage-class specifiers like "static" are not the first things in a
           declaration.  This warning is also enabled by -Wextra.

       -Wold-style-definition (C and Objective-C only)
           Warn if an old-style function definition is used.  A warning is given even if there is
           a previous prototype.

       -Wmissing-parameter-type (C and Objective-C only)
           A function parameter is declared without a type specifier in K&R-style functions:

                   void foo(bar) { }

           This warning is also enabled by -Wextra.

       -Wmissing-prototypes (C and Objective-C only)
           Warn if a global function is defined without a previous prototype declaration.  This
           warning is issued even if the definition itself provides a prototype.  Use this option
           to detect global functions that do not have a matching prototype declaration in a
           header file.  This option is not valid for C++ because all function declarations
           provide prototypes and a non-matching declaration declares an overload rather than
           conflict with an earlier declaration.  Use -Wmissing-declarations to detect missing
           declarations in C++.

       -Wmissing-declarations
           Warn if a global function is defined without a previous declaration.  Do so even if
           the definition itself provides a prototype.  Use this option to detect global
           functions that are not declared in header files.  In C, no warnings are issued for
           functions with previous non-prototype declarations; use -Wmissing-prototypes to detect
           missing prototypes.  In C++, no warnings are issued for function templates, or for
           inline functions, or for functions in anonymous namespaces.

       -Wmissing-field-initializers
           Warn if a structure's initializer has some fields missing.  For example, the following
           code causes such a warning, because "x.h" is implicitly zero:

                   struct s { int f, g, h; };
                   struct s x = { 3, 4 };

           This option does not warn about designated initializers, so the following modification
           does not trigger a warning:

                   struct s { int f, g, h; };
                   struct s x = { .f = 3, .g = 4 };

           In C this option does not warn about the universal zero initializer { 0 }:

                   struct s { int f, g, h; };
                   struct s x = { 0 };

           Likewise, in C++ this option does not warn about the empty { } initializer, for
           example:

                   struct s { int f, g, h; };
                   s x = { };

           This warning is included in -Wextra.  To get other -Wextra warnings without this one,
           use -Wextra -Wno-missing-field-initializers.

       -Wno-multichar
           Do not warn if a multicharacter constant ('FOOF') is used.  Usually they indicate a
           typo in the user's code, as they have implementation-defined values, and should not be
           used in portable code.

       -Wnormalized=[none|id|nfc|nfkc]
           In ISO C and ISO C++, two identifiers are different if they are different sequences of
           characters.  However, sometimes when characters outside the basic ASCII character set
           are used, you can have two different character sequences that look the same.  To avoid
           confusion, the ISO 10646 standard sets out some normalization rules which when applied
           ensure that two sequences that look the same are turned into the same sequence.  GCC
           can warn you if you are using identifiers that have not been normalized; this option
           controls that warning.

           There are four levels of warning supported by GCC.  The default is -Wnormalized=nfc,
           which warns about any identifier that is not in the ISO 10646 "C" normalized form,
           NFC.  NFC is the recommended form for most uses.  It is equivalent to -Wnormalized.

           Unfortunately, there are some characters allowed in identifiers by ISO C and ISO C++
           that, when turned into NFC, are not allowed in identifiers.  That is, there's no way
           to use these symbols in portable ISO C or C++ and have all your identifiers in NFC.
           -Wnormalized=id suppresses the warning for these characters.  It is hoped that future
           versions of the standards involved will correct this, which is why this option is not
           the default.

           You can switch the warning off for all characters by writing -Wnormalized=none or
           -Wno-normalized.  You should only do this if you are using some other normalization
           scheme (like "D"), because otherwise you can easily create bugs that are literally
           impossible to see.

           Some characters in ISO 10646 have distinct meanings but look identical in some fonts
           or display methodologies, especially once formatting has been applied.  For instance
           "\u207F", "SUPERSCRIPT LATIN SMALL LETTER N", displays just like a regular "n" that
           has been placed in a superscript.  ISO 10646 defines the NFKC normalization scheme to
           convert all these into a standard form as well, and GCC warns if your code is not in
           NFKC if you use -Wnormalized=nfkc.  This warning is comparable to warning about every
           identifier that contains the letter O because it might be confused with the digit 0,
           and so is not the default, but may be useful as a local coding convention if the
           programming environment cannot be fixed to display these characters distinctly.

       -Wno-deprecated
           Do not warn about usage of deprecated features.

       -Wno-deprecated-declarations
           Do not warn about uses of functions, variables, and types marked as deprecated by
           using the "deprecated" attribute.

       -Wno-overflow
           Do not warn about compile-time overflow in constant expressions.

       -Wno-odr
           Warn about One Definition Rule violations during link-time optimization.  Requires
           -flto-odr-type-merging to be enabled.  Enabled by default.

       -Wopenmp-simd
           Warn if the vectorizer cost model overrides the OpenMP simd directive set by user.
           The -fsimd-cost-model=unlimited option can be used to relax the cost model.

       -Woverride-init (C and Objective-C only)
           Warn if an initialized field without side effects is overridden when using designated
           initializers.

           This warning is included in -Wextra.  To get other -Wextra warnings without this one,
           use -Wextra -Wno-override-init.

       -Woverride-init-side-effects (C and Objective-C only)
           Warn if an initialized field with side effects is overridden when using designated
           initializers.  This warning is enabled by default.

       -Wpacked
           Warn if a structure is given the packed attribute, but the packed attribute has no
           effect on the layout or size of the structure.  Such structures may be mis-aligned for
           little benefit.  For instance, in this code, the variable "f.x" in "struct bar" is
           misaligned even though "struct bar" does not itself have the packed attribute:

                   struct foo {
                     int x;
                     char a, b, c, d;
                   } __attribute__((packed));
                   struct bar {
                     char z;
                     struct foo f;
                   };

       -Wpacked-bitfield-compat
           The 4.1, 4.2 and 4.3 series of GCC ignore the "packed" attribute on bit-fields of type
           "char".  This has been fixed in GCC 4.4 but the change can lead to differences in the
           structure layout.  GCC informs you when the offset of such a field has changed in GCC
           4.4.  For example there is no longer a 4-bit padding between field "a" and "b" in this
           structure:

                   struct foo
                   {
                     char a:4;
                     char b:8;
                   } __attribute__ ((packed));

           This warning is enabled by default.  Use -Wno-packed-bitfield-compat to disable this
           warning.

       -Wpacked-not-aligned (C, C++, Objective-C and Objective-C++ only)
           Warn if a structure field with explicitly specified alignment in a packed struct or
           union is misaligned.  For example, a warning will be issued on "struct S", like,
           "warning: alignment 1 of 'struct S' is less than 8", in this code:

                   struct __attribute__ ((aligned (8))) S8 { char a[8]; };
                   struct __attribute__ ((packed)) S {
                     struct S8 s8;
                   };

           This warning is enabled by -Wall.

       -Wpadded
           Warn if padding is included in a structure, either to align an element of the
           structure or to align the whole structure.  Sometimes when this happens it is possible
           to rearrange the fields of the structure to reduce the padding and so make the
           structure smaller.

       -Wredundant-decls
           Warn if anything is declared more than once in the same scope, even in cases where
           multiple declaration is valid and changes nothing.

       -Wno-restrict
           Warn when an object referenced by a "restrict"-qualified parameter (or, in C++, a
           "__restrict"-qualified parameter) is aliased by another argument, or when copies
           between such objects overlap.  For example, the call to the "strcpy" function below
           attempts to truncate the string by replacing its initial characters with the last
           four.  However, because the call writes the terminating NUL into "a[4]", the copies
           overlap and the call is diagnosed.

                   void foo (void)
                   {
                     char a[] = "abcd1234";
                     strcpy (a, a + 4);
                     ...
                   }

           The -Wrestrict option detects some instances of simple overlap even without
           optimization but works best at -O2 and above.  It is included in -Wall.

       -Wnested-externs (C and Objective-C only)
           Warn if an "extern" declaration is encountered within a function.

       -Wno-inherited-variadic-ctor
           Suppress warnings about use of C++11 inheriting constructors when the base class
           inherited from has a C variadic constructor; the warning is on by default because the
           ellipsis is not inherited.

       -Winline
           Warn if a function that is declared as inline cannot be inlined.  Even with this
           option, the compiler does not warn about failures to inline functions declared in
           system headers.

           The compiler uses a variety of heuristics to determine whether or not to inline a
           function.  For example, the compiler takes into account the size of the function being
           inlined and the amount of inlining that has already been done in the current function.
           Therefore, seemingly insignificant changes in the source program can cause the
           warnings produced by -Winline to appear or disappear.

       -Wno-invalid-offsetof (C++ and Objective-C++ only)
           Suppress warnings from applying the "offsetof" macro to a non-POD type.  According to
           the 2014 ISO C++ standard, applying "offsetof" to a non-standard-layout type is
           undefined.  In existing C++ implementations, however, "offsetof" typically gives
           meaningful results.  This flag is for users who are aware that they are writing
           nonportable code and who have deliberately chosen to ignore the warning about it.

           The restrictions on "offsetof" may be relaxed in a future version of the C++ standard.

       -Wint-in-bool-context
           Warn for suspicious use of integer values where boolean values are expected, such as
           conditional expressions (?:) using non-boolean integer constants in boolean context,
           like "if (a <= b ? 2 : 3)".  Or left shifting of signed integers in boolean context,
           like "for (a = 0; 1 << a; a++);".  Likewise for all kinds of multiplications
           regardless of the data type.  This warning is enabled by -Wall.

       -Wno-int-to-pointer-cast
           Suppress warnings from casts to pointer type of an integer of a different size. In
           C++, casting to a pointer type of smaller size is an error. Wint-to-pointer-cast is
           enabled by default.

       -Wno-pointer-to-int-cast (C and Objective-C only)
           Suppress warnings from casts from a pointer to an integer type of a different size.

       -Winvalid-pch
           Warn if a precompiled header is found in the search path but cannot be used.

       -Wlong-long
           Warn if "long long" type is used.  This is enabled by either -Wpedantic or
           -Wtraditional in ISO C90 and C++98 modes.  To inhibit the warning messages, use
           -Wno-long-long.

       -Wvariadic-macros
           Warn if variadic macros are used in ISO C90 mode, or if the GNU alternate syntax is
           used in ISO C99 mode.  This is enabled by either -Wpedantic or -Wtraditional.  To
           inhibit the warning messages, use -Wno-variadic-macros.

       -Wvarargs
           Warn upon questionable usage of the macros used to handle variable arguments like
           "va_start".  This is default.  To inhibit the warning messages, use -Wno-varargs.

       -Wvector-operation-performance
           Warn if vector operation is not implemented via SIMD capabilities of the architecture.
           Mainly useful for the performance tuning.  Vector operation can be implemented
           "piecewise", which means that the scalar operation is performed on every vector
           element; "in parallel", which means that the vector operation is implemented using
           scalars of wider type, which normally is more performance efficient; and "as a single
           scalar", which means that vector fits into a scalar type.

       -Wno-virtual-move-assign
           Suppress warnings about inheriting from a virtual base with a non-trivial C++11 move
           assignment operator.  This is dangerous because if the virtual base is reachable along
           more than one path, it is moved multiple times, which can mean both objects end up in
           the moved-from state.  If the move assignment operator is written to avoid moving from
           a moved-from object, this warning can be disabled.

       -Wvla
           Warn if a variable-length array is used in the code.  -Wno-vla prevents the -Wpedantic
           warning of the variable-length array.

       -Wvla-larger-than=n
           If this option is used, the compiler will warn on uses of variable-length arrays where
           the size is either unbounded, or bounded by an argument that can be larger than n
           bytes.  This is similar to how -Walloca-larger-than=n works, but with variable-length
           arrays.

           Note that GCC may optimize small variable-length arrays of a known value into plain
           arrays, so this warning may not get triggered for such arrays.

           This warning is not enabled by -Wall, and is only active when -ftree-vrp is active
           (default for -O2 and above).

           See also -Walloca-larger-than=n.

       -Wvolatile-register-var
           Warn if a register variable is declared volatile.  The volatile modifier does not
           inhibit all optimizations that may eliminate reads and/or writes to register
           variables.  This warning is enabled by -Wall.

       -Wdisabled-optimization
           Warn if a requested optimization pass is disabled.  This warning does not generally
           indicate that there is anything wrong with your code; it merely indicates that GCC's
           optimizers are unable to handle the code effectively.  Often, the problem is that your
           code is too big or too complex; GCC refuses to optimize programs when the optimization
           itself is likely to take inordinate amounts of time.

       -Wpointer-sign (C and Objective-C only)
           Warn for pointer argument passing or assignment with different signedness.  This
           option is only supported for C and Objective-C.  It is implied by -Wall and by
           -Wpedantic, which can be disabled with -Wno-pointer-sign.

       -Wstack-protector
           This option is only active when -fstack-protector is active.  It warns about functions
           that are not protected against stack smashing.

       -Woverlength-strings
           Warn about string constants that are longer than the "minimum maximum" length
           specified in the C standard.  Modern compilers generally allow string constants that
           are much longer than the standard's minimum limit, but very portable programs should
           avoid using longer strings.

           The limit applies after string constant concatenation, and does not count the trailing
           NUL.  In C90, the limit was 509 characters; in C99, it was raised to 4095.  C++98 does
           not specify a normative minimum maximum, so we do not diagnose overlength strings in
           C++.

           This option is implied by -Wpedantic, and can be disabled with
           -Wno-overlength-strings.

       -Wunsuffixed-float-constants (C and Objective-C only)
           Issue a warning for any floating constant that does not have a suffix.  When used
           together with -Wsystem-headers it warns about such constants in system header files.
           This can be useful when preparing code to use with the "FLOAT_CONST_DECIMAL64" pragma
           from the decimal floating-point extension to C99.

       -Wno-designated-init (C and Objective-C only)
           Suppress warnings when a positional initializer is used to initialize a structure that
           has been marked with the "designated_init" attribute.

       -Whsa
           Issue a warning when HSAIL cannot be emitted for the compiled function or OpenMP
           construct.

   Options for Debugging Your Program
       To tell GCC to emit extra information for use by a debugger, in almost all cases you need
       only to add -g to your other options.

       GCC allows you to use -g with -O.  The shortcuts taken by optimized code may occasionally
       be surprising: some variables you declared may not exist at all; flow of control may
       briefly move where you did not expect it; some statements may not be executed because they
       compute constant results or their values are already at hand; some statements may execute
       in different places because they have been moved out of loops.  Nevertheless it is
       possible to debug optimized output.  This makes it reasonable to use the optimizer for
       programs that might have bugs.

       If you are not using some other optimization option, consider using -Og with -g.  With no
       -O option at all, some compiler passes that collect information useful for debugging do
       not run at all, so that -Og may result in a better debugging experience.

       -g  Produce debugging information in the operating system's native format (stabs, COFF,
           XCOFF, or DWARF).  GDB can work with this debugging information.

           On most systems that use stabs format, -g enables use of extra debugging information
           that only GDB can use; this extra information makes debugging work better in GDB but
           probably makes other debuggers crash or refuse to read the program.  If you want to
           control for certain whether to generate the extra information, use -gstabs+, -gstabs,
           -gxcoff+, -gxcoff, or -gvms (see below).

       -ggdb
           Produce debugging information for use by GDB.  This means to use the most expressive
           format available (DWARF, stabs, or the native format if neither of those are
           supported), including GDB extensions if at all possible.

       -gdwarf
       -gdwarf-version
           Produce debugging information in DWARF format (if that is supported).  The value of
           version may be either 2, 3, 4 or 5; the default version for most targets is 4.  DWARF
           Version 5 is only experimental.

           Note that with DWARF Version 2, some ports require and always use some non-conflicting
           DWARF 3 extensions in the unwind tables.

           Version 4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit.

           GCC no longer supports DWARF Version 1, which is substantially different than Version
           2 and later.  For historical reasons, some other DWARF-related options such as
           -fno-dwarf2-cfi-asm) retain a reference to DWARF Version 2 in their names, but apply
           to all currently-supported versions of DWARF.

       -gstabs
           Produce debugging information in stabs format (if that is supported), without GDB
           extensions.  This is the format used by DBX on most BSD systems.  On MIPS, Alpha and
           System V Release 4 systems this option produces stabs debugging output that is not
           understood by DBX.  On System V Release 4 systems this option requires the GNU
           assembler.

       -gstabs+
           Produce debugging information in stabs format (if that is supported), using GNU
           extensions understood only by the GNU debugger (GDB).  The use of these extensions is
           likely to make other debuggers crash or refuse to read the program.

       -gxcoff
           Produce debugging information in XCOFF format (if that is supported).  This is the
           format used by the DBX debugger on IBM RS/6000 systems.

       -gxcoff+
           Produce debugging information in XCOFF format (if that is supported), using GNU
           extensions understood only by the GNU debugger (GDB).  The use of these extensions is
           likely to make other debuggers crash or refuse to read the program, and may cause
           assemblers other than the GNU assembler (GAS) to fail with an error.

       -gvms
           Produce debugging information in Alpha/VMS debug format (if that is supported).  This
           is the format used by DEBUG on Alpha/VMS systems.

       -glevel
       -ggdblevel
       -gstabslevel
       -gxcofflevel
       -gvmslevel
           Request debugging information and also use level to specify how much information.  The
           default level is 2.

           Level 0 produces no debug information at all.  Thus, -g0 negates -g.

           Level 1 produces minimal information, enough for making backtraces in parts of the
           program that you don't plan to debug.  This includes descriptions of functions and
           external variables, and line number tables, but no information about local variables.

           Level 3 includes extra information, such as all the macro definitions present in the
           program.  Some debuggers support macro expansion when you use -g3.

           -gdwarf does not accept a concatenated debug level, to avoid confusion with
           -gdwarf-level.  Instead use an additional -glevel option to change the debug level for
           DWARF.

       -feliminate-unused-debug-symbols
           Produce debugging information in stabs format (if that is supported), for only symbols
           that are actually used.

       -femit-class-debug-always
           Instead of emitting debugging information for a C++ class in only one object file,
           emit it in all object files using the class.  This option should be used only with
           debuggers that are unable to handle the way GCC normally emits debugging information
           for classes because using this option increases the size of debugging information by
           as much as a factor of two.

       -fno-merge-debug-strings
           Direct the linker to not merge together strings in the debugging information that are
           identical in different object files.  Merging is not supported by all assemblers or
           linkers.  Merging decreases the size of the debug information in the output file at
           the cost of increasing link processing time.  Merging is enabled by default.

       -fdebug-prefix-map=old=new
           When compiling files residing in directory old, record debugging information
           describing them as if the files resided in directory new instead.  This can be used to
           replace a build-time path with an install-time path in the debug info.  It can also be
           used to change an absolute path to a relative path by using . for new.  This can give
           more reproducible builds, which are location independent, but may require an extra
           command to tell GDB where to find the source files. See also -ffile-prefix-map.

       -fvar-tracking
           Run variable tracking pass.  It computes where variables are stored at each position
           in code.  Better debugging information is then generated (if the debugging information
           format supports this information).

           It is enabled by default when compiling with optimization (-Os, -O, -O2, ...),
           debugging information (-g) and the debug info format supports it.

       -fvar-tracking-assignments
           Annotate assignments to user variables early in the compilation and attempt to carry
           the annotations over throughout the compilation all the way to the end, in an attempt
           to improve debug information while optimizing.  Use of -gdwarf-4 is recommended along
           with it.

           It can be enabled even if var-tracking is disabled, in which case annotations are
           created and maintained, but discarded at the end.  By default, this flag is enabled
           together with -fvar-tracking, except when selective scheduling is enabled.

       -gsplit-dwarf
           Separate as much DWARF debugging information as possible into a separate output file
           with the extension .dwo.  This option allows the build system to avoid linking files
           with debug information.  To be useful, this option requires a debugger capable of
           reading .dwo files.

       -gpubnames
           Generate DWARF ".debug_pubnames" and ".debug_pubtypes" sections.

       -ggnu-pubnames
           Generate ".debug_pubnames" and ".debug_pubtypes" sections in a format suitable for
           conversion into a GDB index.  This option is only useful with a linker that can
           produce GDB index version 7.

       -fdebug-types-section
           When using DWARF Version 4 or higher, type DIEs can be put into their own
           ".debug_types" section instead of making them part of the ".debug_info" section.  It
           is more efficient to put them in a separate comdat sections since the linker can then
           remove duplicates.  But not all DWARF consumers support ".debug_types" sections yet
           and on some objects ".debug_types" produces larger instead of smaller debugging
           information.

       -grecord-gcc-switches
       -gno-record-gcc-switches
           This switch causes the command-line options used to invoke the compiler that may
           affect code generation to be appended to the DW_AT_producer attribute in DWARF
           debugging information.  The options are concatenated with spaces separating them from
           each other and from the compiler version.  It is enabled by default.  See also
           -frecord-gcc-switches for another way of storing compiler options into the object
           file.

       -gstrict-dwarf
           Disallow using extensions of later DWARF standard version than selected with
           -gdwarf-version.  On most targets using non-conflicting DWARF extensions from later
           standard versions is allowed.

       -gno-strict-dwarf
           Allow using extensions of later DWARF standard version than selected with
           -gdwarf-version.

       -gas-loc-support
           Inform the compiler that the assembler supports ".loc" directives.  It may then use
           them for the assembler to generate DWARF2+ line number tables.

           This is generally desirable, because assembler-generated line-number tables are a lot
           more compact than those the compiler can generate itself.

           This option will be enabled by default if, at GCC configure time, the assembler was
           found to support such directives.

       -gno-as-loc-support
           Force GCC to generate DWARF2+ line number tables internally, if DWARF2+ line number
           tables are to be generated.

       gas-locview-support
           Inform the compiler that the assembler supports "view" assignment and reset assertion
           checking in ".loc" directives.

           This option will be enabled by default if, at GCC configure time, the assembler was
           found to support them.

       gno-as-locview-support
           Force GCC to assign view numbers internally, if -gvariable-location-views are
           explicitly requested.

       -gcolumn-info
       -gno-column-info
           Emit location column information into DWARF debugging information, rather than just
           file and line.  This option is enabled by default.

       -gstatement-frontiers
       -gno-statement-frontiers
           This option causes GCC to create markers in the internal representation at the
           beginning of statements, and to keep them roughly in place throughout compilation,
           using them to guide the output of "is_stmt" markers in the line number table.  This is
           enabled by default when compiling with optimization (-Os, -O, -O2, ...), and
           outputting DWARF 2 debug information at the normal level.

       -gvariable-location-views
       -gvariable-location-views=incompat5
       -gno-variable-location-views
           Augment variable location lists with progressive view numbers implied from the line
           number table.  This enables debug information consumers to inspect state at certain
           points of the program, even if no instructions associated with the corresponding
           source locations are present at that point.  If the assembler lacks support for view
           numbers in line number tables, this will cause the compiler to emit the line number
           table, which generally makes them somewhat less compact.  The augmented line number
           tables and location lists are fully backward-compatible, so they can be consumed by
           debug information consumers that are not aware of these augmentations, but they won't
           derive any benefit from them either.

           This is enabled by default when outputting DWARF 2 debug information at the normal
           level, as long as there is assembler support, -fvar-tracking-assignments is enabled
           and -gstrict-dwarf is not.  When assembler support is not available, this may still be
           enabled, but it will force GCC to output internal line number tables, and if
           -ginternal-reset-location-views is not enabled, that will most certainly lead to
           silently mismatching location views.

           There is a proposed representation for view numbers that is not backward compatible
           with the location list format introduced in DWARF 5, that can be enabled with
           -gvariable-location-views=incompat5.  This option may be removed in the future, is
           only provided as a reference implementation of the proposed representation.  Debug
           information consumers are not expected to support this extended format, and they would
           be rendered unable to decode location lists using it.

       -ginternal-reset-location-views
       -gnointernal-reset-location-views
           Attempt to determine location views that can be omitted from location view lists.
           This requires the compiler to have very accurate insn length estimates, which isn't
           always the case, and it may cause incorrect view lists to be generated silently when
           using an assembler that does not support location view lists.  The GNU assembler will
           flag any such error as a "view number mismatch".  This is only enabled on ports that
           define a reliable estimation function.

       -ginline-points
       -gno-inline-points
           Generate extended debug information for inlined functions.  Location view tracking
           markers are inserted at inlined entry points, so that address and view numbers can be
           computed and output in debug information.  This can be enabled independently of
           location views, in which case the view numbers won't be output, but it can only be
           enabled along with statement frontiers, and it is only enabled by default if location
           views are enabled.

       -gz[=type]
           Produce compressed debug sections in DWARF format, if that is supported.  If type is
           not given, the default type depends on the capabilities of the assembler and linker
           used.  type may be one of none (don't compress debug sections), zlib (use zlib
           compression in ELF gABI format), or zlib-gnu (use zlib compression in traditional GNU
           format).  If the linker doesn't support writing compressed debug sections, the option
           is rejected.  Otherwise, if the assembler does not support them, -gz is silently
           ignored when producing object files.

       -femit-struct-debug-baseonly
           Emit debug information for struct-like types only when the base name of the
           compilation source file matches the base name of file in which the struct is defined.

           This option substantially reduces the size of debugging information, but at
           significant potential loss in type information to the debugger.  See
           -femit-struct-debug-reduced for a less aggressive option.  See
           -femit-struct-debug-detailed for more detailed control.

           This option works only with DWARF debug output.

       -femit-struct-debug-reduced
           Emit debug information for struct-like types only when the base name of the
           compilation source file matches the base name of file in which the type is defined,
           unless the struct is a template or defined in a system header.

           This option significantly reduces the size of debugging information, with some
           potential loss in type information to the debugger.  See -femit-struct-debug-baseonly
           for a more aggressive option.  See -femit-struct-debug-detailed for more detailed
           control.

           This option works only with DWARF debug output.

       -femit-struct-debug-detailed[=spec-list]
           Specify the struct-like types for which the compiler generates debug information.  The
           intent is to reduce duplicate struct debug information between different object files
           within the same program.

           This option is a detailed version of -femit-struct-debug-reduced and
           -femit-struct-debug-baseonly, which serves for most needs.

           A specification has the syntax[dir:|ind:][ord:|gen:](any|sys|base|none)

           The optional first word limits the specification to structs that are used directly
           (dir:) or used indirectly (ind:).  A struct type is used directly when it is the type
           of a variable, member.  Indirect uses arise through pointers to structs.  That is,
           when use of an incomplete struct is valid, the use is indirect.  An example is struct
           one direct; struct two * indirect;.

           The optional second word limits the specification to ordinary structs (ord:) or
           generic structs (gen:).  Generic structs are a bit complicated to explain.  For C++,
           these are non-explicit specializations of template classes, or non-template classes
           within the above.  Other programming languages have generics, but
           -femit-struct-debug-detailed does not yet implement them.

           The third word specifies the source files for those structs for which the compiler
           should emit debug information.  The values none and any have the normal meaning.  The
           value base means that the base of name of the file in which the type declaration
           appears must match the base of the name of the main compilation file.  In practice,
           this means that when compiling foo.c, debug information is generated for types
           declared in that file and foo.h, but not other header files.  The value sys means
           those types satisfying base or declared in system or compiler headers.

           You may need to experiment to determine the best settings for your application.

           The default is -femit-struct-debug-detailed=all.

           This option works only with DWARF debug output.

       -fno-dwarf2-cfi-asm
           Emit DWARF unwind info as compiler generated ".eh_frame" section instead of using GAS
           ".cfi_*" directives.

       -fno-eliminate-unused-debug-types
           Normally, when producing DWARF output, GCC avoids producing debug symbol output for
           types that are nowhere used in the source file being compiled.  Sometimes it is useful
           to have GCC emit debugging information for all types declared in a compilation unit,
           regardless of whether or not they are actually used in that compilation unit, for
           example if, in the debugger, you want to cast a value to a type that is not actually
           used in your program (but is declared).  More often, however, this results in a
           significant amount of wasted space.

   Options That Control Optimization
       These options control various sorts of optimizations.

       Without any optimization option, the compiler's goal is to reduce the cost of compilation
       and to make debugging produce the expected results.  Statements are independent: if you
       stop the program with a breakpoint between statements, you can then assign a new value to
       any variable or change the program counter to any other statement in the function and get
       exactly the results you expect from the source code.

       Turning on optimization flags makes the compiler attempt to improve the performance and/or
       code size at the expense of compilation time and possibly the ability to debug the
       program.

       The compiler performs optimization based on the knowledge it has of the program.
       Compiling multiple files at once to a single output file mode allows the compiler to use
       information gained from all of the files when compiling each of them.

       Not all optimizations are controlled directly by a flag.  Only optimizations that have a
       flag are listed in this section.

       Most optimizations are only enabled if an -O level is set on the command line.  Otherwise
       they are disabled, even if individual optimization flags are specified.

       Depending on the target and how GCC was configured, a slightly different set of
       optimizations may be enabled at each -O level than those listed here.  You can invoke GCC
       with -Q --help=optimizers to find out the exact set of optimizations that are enabled at
       each level.

       -O
       -O1 Optimize.  Optimizing compilation takes somewhat more time, and a lot more memory for
           a large function.

           With -O, the compiler tries to reduce code size and execution time, without performing
           any optimizations that take a great deal of compilation time.

           -O turns on the following optimization flags:

           -fauto-inc-dec -fbranch-count-reg -fcombine-stack-adjustments -fcompare-elim
           -fcprop-registers -fdce -fdefer-pop -fdelayed-branch -fdse -fforward-propagate
           -fguess-branch-probability -fif-conversion2 -fif-conversion
           -finline-functions-called-once -fipa-pure-const -fipa-profile -fipa-reference
           -fmerge-constants -fmove-loop-invariants -fomit-frame-pointer -freorder-blocks
           -fshrink-wrap -fshrink-wrap-separate -fsplit-wide-types -fssa-backprop -fssa-phiopt
           -ftree-bit-ccp -ftree-ccp -ftree-ch -ftree-coalesce-vars -ftree-copy-prop -ftree-dce
           -ftree-dominator-opts -ftree-dse -ftree-forwprop -ftree-fre -ftree-phiprop -ftree-sink
           -ftree-slsr -ftree-sra -ftree-pta -ftree-ter -funit-at-a-time

       -O2 Optimize even more.  GCC performs nearly all supported optimizations that do not
           involve a space-speed tradeoff.  As compared to -O, this option increases both
           compilation time and the performance of the generated code.

           -O2 turns on all optimization flags specified by -O.  It also turns on the following
           optimization flags: -fthread-jumps -falign-functions  -falign-jumps -falign-loops
           -falign-labels -fcaller-saves -fcrossjumping -fcse-follow-jumps  -fcse-skip-blocks
           -fdelete-null-pointer-checks -fdevirtualize -fdevirtualize-speculatively
           -fexpensive-optimizations -fgcse  -fgcse-lm -fhoist-adjacent-loads
           -finline-small-functions -findirect-inlining -fipa-cp -fipa-bit-cp -fipa-vrp -fipa-sra
           -fipa-icf -fisolate-erroneous-paths-dereference -flra-remat -foptimize-sibling-calls
           -foptimize-strlen -fpartial-inlining -fpeephole2 -freorder-blocks-algorithm=stc
           -freorder-blocks-and-partition -freorder-functions -frerun-cse-after-loop
           -fsched-interblock  -fsched-spec -fschedule-insns  -fschedule-insns2 -fstore-merging
           -fstrict-aliasing -ftree-builtin-call-dce -ftree-switch-conversion -ftree-tail-merge
           -fcode-hoisting -ftree-pre -ftree-vrp -fipa-ra

           Please note the warning under -fgcse about invoking -O2 on programs that use computed
           gotos.

           NOTE: In Ubuntu 8.10 and later versions, -D_FORTIFY_SOURCE=2 is set by default, and is
           activated when -O is set to 2 or higher.  This enables additional compile-time and
           run-time checks for several libc functions.  To disable, specify either
           -U_FORTIFY_SOURCE or -D_FORTIFY_SOURCE=0.

       -O3 Optimize yet more.  -O3 turns on all optimizations specified by -O2 and also turns on
           the following optimization flags: -finline-functions -funswitch-loops
           -fpredictive-commoning -fgcse-after-reload -ftree-loop-vectorize
           -ftree-loop-distribution -ftree-loop-distribute-patterns -floop-interchange
           -floop-unroll-and-jam -fsplit-paths -ftree-slp-vectorize -fvect-cost-model
           -ftree-partial-pre -fpeel-loops -fipa-cp-clone

       -O0 Reduce compilation time and make debugging produce the expected results.  This is the
           default.

       -Os Optimize for size.  -Os enables all -O2 optimizations that do not typically increase
           code size.

           -Os disables the following optimization flags: -falign-functions  -falign-jumps
           -falign-loops -falign-labels  -freorder-blocks  -freorder-blocks-algorithm=stc
           -freorder-blocks-and-partition  -fprefetch-loop-arrays

           It also enables -finline-functions, causes the compiler to tune for code size rather
           than execution speed, and performs further optimizations designed to reduce code size.

       -Ofast
           Disregard strict standards compliance.  -Ofast enables all -O3 optimizations.  It also
           enables optimizations that are not valid for all standard-compliant programs.  It
           turns on -ffast-math and the Fortran-specific -fstack-arrays, unless
           -fmax-stack-var-size is specified, and -fno-protect-parens.

       -Og Optimize debugging experience.  -Og enables optimizations that do not interfere with
           debugging. It should be the optimization level of choice for the standard edit-
           compile-debug cycle, offering a reasonable level of optimization while maintaining
           fast compilation and a good debugging experience.

       If you use multiple -O options, with or without level numbers, the last such option is the
       one that is effective.

       Options of the form -fflag specify machine-independent flags.  Most flags have both
       positive and negative forms; the negative form of -ffoo is -fno-foo.  In the table below,
       only one of the forms is listed---the one you typically use.  You can figure out the other
       form by either removing no- or adding it.

       The following options control specific optimizations.  They are either activated by -O
       options or are related to ones that are.  You can use the following flags in the rare
       cases when "fine-tuning" of optimizations to be performed is desired.

       -fno-defer-pop
           Always pop the arguments to each function call as soon as that function returns.  For
           machines that must pop arguments after a function call, the compiler normally lets
           arguments accumulate on the stack for several function calls and pops them all at
           once.

           Disabled at levels -O, -O2, -O3, -Os.

       -fforward-propagate
           Perform a forward propagation pass on RTL.  The pass tries to combine two instructions
           and checks if the result can be simplified.  If loop unrolling is active, two passes
           are performed and the second is scheduled after loop unrolling.

           This option is enabled by default at optimization levels -O, -O2, -O3, -Os.

       -ffp-contract=style
           -ffp-contract=off disables floating-point expression contraction.  -ffp-contract=fast
           enables floating-point expression contraction such as forming of fused multiply-add
           operations if the target has native support for them.  -ffp-contract=on enables
           floating-point expression contraction if allowed by the language standard.  This is
           currently not implemented and treated equal to -ffp-contract=off.

           The default is -ffp-contract=fast.

       -fomit-frame-pointer
           Omit the frame pointer in functions that don't need one.  This avoids the instructions
           to save, set up and restore the frame pointer; on many targets it also makes an extra
           register available.

           On some targets this flag has no effect because the standard calling sequence always
           uses a frame pointer, so it cannot be omitted.

           Note that -fno-omit-frame-pointer doesn't guarantee the frame pointer is used in all
           functions.  Several targets always omit the frame pointer in leaf functions.

           Enabled by default at -O and higher.

       -foptimize-sibling-calls
           Optimize sibling and tail recursive calls.

           Enabled at levels -O2, -O3, -Os.

       -foptimize-strlen
           Optimize various standard C string functions (e.g. "strlen", "strchr" or "strcpy") and
           their "_FORTIFY_SOURCE" counterparts into faster alternatives.

           Enabled at levels -O2, -O3.

       -fno-inline
           Do not expand any functions inline apart from those marked with the "always_inline"
           attribute.  This is the default when not optimizing.

           Single functions can be exempted from inlining by marking them with the "noinline"
           attribute.

       -finline-small-functions
           Integrate functions into their callers when their body is smaller than expected
           function call code (so overall size of program gets smaller).  The compiler
           heuristically decides which functions are simple enough to be worth integrating in
           this way.  This inlining applies to all functions, even those not declared inline.

           Enabled at levels -O2, -O3, -Os.

       -findirect-inlining
           Inline also indirect calls that are discovered to be known at compile time thanks to
           previous inlining.  This option has any effect only when inlining itself is turned on
           by the -finline-functions or -finline-small-functions options.

           Enabled at levels -O3, -Os.  Also enabled by -fprofile-use and -fauto-profile.

       -finline-functions
           Consider all functions for inlining, even if they are not declared inline.  The
           compiler heuristically decides which functions are worth integrating in this way.

           If all calls to a given function are integrated, and the function is declared
           "static", then the function is normally not output as assembler code in its own right.

           Enabled at levels -O2, -O3, -Os.

       -finline-functions-called-once
           Consider all "static" functions called once for inlining into their caller even if
           they are not marked "inline".  If a call to a given function is integrated, then the
           function is not output as assembler code in its own right.

           Enabled at levels -O1, -O2, -O3 and -Os.

       -fearly-inlining
           Inline functions marked by "always_inline" and functions whose body seems smaller than
           the function call overhead early before doing -fprofile-generate instrumentation and
           real inlining pass.  Doing so makes profiling significantly cheaper and usually
           inlining faster on programs having large chains of nested wrapper functions.

           Enabled by default.

       -fipa-sra
           Perform interprocedural scalar replacement of aggregates, removal of unused parameters
           and replacement of parameters passed by reference by parameters passed by value.

           Enabled at levels -O2, -O3 and -Os.

       -finline-limit=n
           By default, GCC limits the size of functions that can be inlined.  This flag allows
           coarse control of this limit.  n is the size of functions that can be inlined in
           number of pseudo instructions.

           Inlining is actually controlled by a number of parameters, which may be specified
           individually by using --param name=value.  The -finline-limit=n option sets some of
           these parameters as follows:

           max-inline-insns-single
               is set to n/2.

           max-inline-insns-auto
               is set to n/2.

           See below for a documentation of the individual parameters controlling inlining and
           for the defaults of these parameters.

           Note: there may be no value to -finline-limit that results in default behavior.

           Note: pseudo instruction represents, in this particular context, an abstract
           measurement of function's size.  In no way does it represent a count of assembly
           instructions and as such its exact meaning might change from one release to an
           another.

       -fno-keep-inline-dllexport
           This is a more fine-grained version of -fkeep-inline-functions, which applies only to
           functions that are declared using the "dllexport" attribute or declspec.

       -fkeep-inline-functions
           In C, emit "static" functions that are declared "inline" into the object file, even if
           the function has been inlined into all of its callers.  This switch does not affect
           functions using the "extern inline" extension in GNU C90.  In C++, emit any and all
           inline functions into the object file.

       -fkeep-static-functions
           Emit "static" functions into the object file, even if the function is never used.

       -fkeep-static-consts
           Emit variables declared "static const" when optimization isn't turned on, even if the
           variables aren't referenced.

           GCC enables this option by default.  If you want to force the compiler to check if a
           variable is referenced, regardless of whether or not optimization is turned on, use
           the -fno-keep-static-consts option.

       -fmerge-constants
           Attempt to merge identical constants (string constants and floating-point constants)
           across compilation units.

           This option is the default for optimized compilation if the assembler and linker
           support it.  Use -fno-merge-constants to inhibit this behavior.

           Enabled at levels -O, -O2, -O3, -Os.

       -fmerge-all-constants
           Attempt to merge identical constants and identical variables.

           This option implies -fmerge-constants.  In addition to -fmerge-constants this
           considers e.g. even constant initialized arrays or initialized constant variables with
           integral or floating-point types.  Languages like C or C++ require each variable,
           including multiple instances of the same variable in recursive calls, to have distinct
           locations, so using this option results in non-conforming behavior.

       -fmodulo-sched
           Perform swing modulo scheduling immediately before the first scheduling pass.  This
           pass looks at innermost loops and reorders their instructions by overlapping different
           iterations.

       -fmodulo-sched-allow-regmoves
           Perform more aggressive SMS-based modulo scheduling with register moves allowed.  By
           setting this flag certain anti-dependences edges are deleted, which triggers the
           generation of reg-moves based on the life-range analysis.  This option is effective
           only with -fmodulo-sched enabled.

       -fno-branch-count-reg
           Avoid running a pass scanning for opportunities to use "decrement and branch"
           instructions on a count register instead of generating sequences of instructions that
           decrement a register, compare it against zero, and then branch based upon the result.
           This option is only meaningful on architectures that support such instructions, which
           include x86, PowerPC, IA-64 and S/390.  Note that the -fno-branch-count-reg option
           doesn't remove the decrement and branch instructions from the generated instruction
           stream introduced by other optimization passes.

           Enabled by default at -O1 and higher.

           The default is -fbranch-count-reg.

       -fno-function-cse
           Do not put function addresses in registers; make each instruction that calls a
           constant function contain the function's address explicitly.

           This option results in less efficient code, but some strange hacks that alter the
           assembler output may be confused by the optimizations performed when this option is
           not used.

           The default is -ffunction-cse

       -fno-zero-initialized-in-bss
           If the target supports a BSS section, GCC by default puts variables that are
           initialized to zero into BSS.  This can save space in the resulting code.

           This option turns off this behavior because some programs explicitly rely on variables
           going to the data section---e.g., so that the resulting executable can find the
           beginning of that section and/or make assumptions based on that.

           The default is -fzero-initialized-in-bss.

       -fthread-jumps
           Perform optimizations that check to see if a jump branches to a location where another
           comparison subsumed by the first is found.  If so, the first branch is redirected to
           either the destination of the second branch or a point immediately following it,
           depending on whether the condition is known to be true or false.

           Enabled at levels -O2, -O3, -Os.

       -fsplit-wide-types
           When using a type that occupies multiple registers, such as "long long" on a 32-bit
           system, split the registers apart and allocate them independently.  This normally
           generates better code for those types, but may make debugging more difficult.

           Enabled at levels -O, -O2, -O3, -Os.

       -fcse-follow-jumps
           In common subexpression elimination (CSE), scan through jump instructions when the
           target of the jump is not reached by any other path.  For example, when CSE encounters
           an "if" statement with an "else" clause, CSE follows the jump when the condition
           tested is false.

           Enabled at levels -O2, -O3, -Os.

       -fcse-skip-blocks
           This is similar to -fcse-follow-jumps, but causes CSE to follow jumps that
           conditionally skip over blocks.  When CSE encounters a simple "if" statement with no
           else clause, -fcse-skip-blocks causes CSE to follow the jump around the body of the
           "if".

           Enabled at levels -O2, -O3, -Os.

       -frerun-cse-after-loop
           Re-run common subexpression elimination after loop optimizations are performed.

           Enabled at levels -O2, -O3, -Os.

       -fgcse
           Perform a global common subexpression elimination pass.  This pass also performs
           global constant and copy propagation.

           Note: When compiling a program using computed gotos, a GCC extension, you may get
           better run-time performance if you disable the global common subexpression elimination
           pass by adding -fno-gcse to the command line.

           Enabled at levels -O2, -O3, -Os.

       -fgcse-lm
           When -fgcse-lm is enabled, global common subexpression elimination attempts to move
           loads that are only killed by stores into themselves.  This allows a loop containing a
           load/store sequence to be changed to a load outside the loop, and a copy/store within
           the loop.

           Enabled by default when -fgcse is enabled.

       -fgcse-sm
           When -fgcse-sm is enabled, a store motion pass is run after global common
           subexpression elimination.  This pass attempts to move stores out of loops.  When used
           in conjunction with -fgcse-lm, loops containing a load/store sequence can be changed
           to a load before the loop and a store after the loop.

           Not enabled at any optimization level.

       -fgcse-las
           When -fgcse-las is enabled, the global common subexpression elimination pass
           eliminates redundant loads that come after stores to the same memory location (both
           partial and full redundancies).

           Not enabled at any optimization level.

       -fgcse-after-reload
           When -fgcse-after-reload is enabled, a redundant load elimination pass is performed
           after reload.  The purpose of this pass is to clean up redundant spilling.

       -faggressive-loop-optimizations
           This option tells the loop optimizer to use language constraints to derive bounds for
           the number of iterations of a loop.  This assumes that loop code does not invoke
           undefined behavior by for example causing signed integer overflows or out-of-bound
           array accesses.  The bounds for the number of iterations of a loop are used to guide
           loop unrolling and peeling and loop exit test optimizations.  This option is enabled
           by default.

       -funconstrained-commons
           This option tells the compiler that variables declared in common blocks (e.g. Fortran)
           may later be overridden with longer trailing arrays. This prevents certain
           optimizations that depend on knowing the array bounds.

       -fcrossjumping
           Perform cross-jumping transformation.  This transformation unifies equivalent code and
           saves code size.  The resulting code may or may not perform better than without cross-
           jumping.

           Enabled at levels -O2, -O3, -Os.

       -fauto-inc-dec
           Combine increments or decrements of addresses with memory accesses.  This pass is
           always skipped on architectures that do not have instructions to support this.
           Enabled by default at -O and higher on architectures that support this.

       -fdce
           Perform dead code elimination (DCE) on RTL.  Enabled by default at -O and higher.

       -fdse
           Perform dead store elimination (DSE) on RTL.  Enabled by default at -O and higher.

       -fif-conversion
           Attempt to transform conditional jumps into branch-less equivalents.  This includes
           use of conditional moves, min, max, set flags and abs instructions, and some tricks
           doable by standard arithmetics.  The use of conditional execution on chips where it is
           available is controlled by -fif-conversion2.

           Enabled at levels -O, -O2, -O3, -Os.

       -fif-conversion2
           Use conditional execution (where available) to transform conditional jumps into
           branch-less equivalents.

           Enabled at levels -O, -O2, -O3, -Os.

       -fdeclone-ctor-dtor
           The C++ ABI requires multiple entry points for constructors and destructors: one for a
           base subobject, one for a complete object, and one for a virtual destructor that calls
           operator delete afterwards.  For a hierarchy with virtual bases, the base and complete
           variants are clones, which means two copies of the function.  With this option, the
           base and complete variants are changed to be thunks that call a common implementation.

           Enabled by -Os.

       -fdelete-null-pointer-checks
           Assume that programs cannot safely dereference null pointers, and that no code or data
           element resides at address zero.  This option enables simple constant folding
           optimizations at all optimization levels.  In addition, other optimization passes in
           GCC use this flag to control global dataflow analyses that eliminate useless checks
           for null pointers; these assume that a memory access to address zero always results in
           a trap, so that if a pointer is checked after it has already been dereferenced, it
           cannot be null.

           Note however that in some environments this assumption is not true.  Use
           -fno-delete-null-pointer-checks to disable this optimization for programs that depend
           on that behavior.

           This option is enabled by default on most targets.  On Nios II ELF, it defaults to
           off.  On AVR, CR16, and MSP430, this option is completely disabled.

           Passes that use the dataflow information are enabled independently at different
           optimization levels.

       -fdevirtualize
           Attempt to convert calls to virtual functions to direct calls.  This is done both
           within a procedure and interprocedurally as part of indirect inlining
           (-findirect-inlining) and interprocedural constant propagation (-fipa-cp).  Enabled at
           levels -O2, -O3, -Os.

       -fdevirtualize-speculatively
           Attempt to convert calls to virtual functions to speculative direct calls.  Based on
           the analysis of the type inheritance graph, determine for a given call the set of
           likely targets. If the set is small, preferably of size 1, change the call into a
           conditional deciding between direct and indirect calls.  The speculative calls enable
           more optimizations, such as inlining.  When they seem useless after further
           optimization, they are converted back into original form.

       -fdevirtualize-at-ltrans
           Stream extra information needed for aggressive devirtualization when running the link-
           time optimizer in local transformation mode.  This option enables more
           devirtualization but significantly increases the size of streamed data. For this
           reason it is disabled by default.

       -fexpensive-optimizations
           Perform a number of minor optimizations that are relatively expensive.

           Enabled at levels -O2, -O3, -Os.

       -free
           Attempt to remove redundant extension instructions.  This is especially helpful for
           the x86-64 architecture, which implicitly zero-extends in 64-bit registers after
           writing to their lower 32-bit half.

           Enabled for Alpha, AArch64 and x86 at levels -O2, -O3, -Os.

       -fno-lifetime-dse
           In C++ the value of an object is only affected by changes within its lifetime: when
           the constructor begins, the object has an indeterminate value, and any changes during
           the lifetime of the object are dead when the object is destroyed.  Normally dead store
           elimination will take advantage of this; if your code relies on the value of the
           object storage persisting beyond the lifetime of the object, you can use this flag to
           disable this optimization.  To preserve stores before the constructor starts (e.g.
           because your operator new clears the object storage) but still treat the object as
           dead after the destructor you, can use -flifetime-dse=1.  The default behavior can be
           explicitly selected with -flifetime-dse=2.  -flifetime-dse=0 is equivalent to
           -fno-lifetime-dse.

       -flive-range-shrinkage
           Attempt to decrease register pressure through register live range shrinkage.  This is
           helpful for fast processors with small or moderate size register sets.

       -fira-algorithm=algorithm
           Use the specified coloring algorithm for the integrated register allocator.  The
           algorithm argument can be priority, which specifies Chow's priority coloring, or CB,
           which specifies Chaitin-Briggs coloring.  Chaitin-Briggs coloring is not implemented
           for all architectures, but for those targets that do support it, it is the default
           because it generates better code.

       -fira-region=region
           Use specified regions for the integrated register allocator.  The region argument
           should be one of the following:

           all Use all loops as register allocation regions.  This can give the best results for
               machines with a small and/or irregular register set.

           mixed
               Use all loops except for loops with small register pressure as the regions.  This
               value usually gives the best results in most cases and for most architectures, and
               is enabled by default when compiling with optimization for speed (-O, -O2, ...).

           one Use all functions as a single region.  This typically results in the smallest code
               size, and is enabled by default for -Os or -O0.

       -fira-hoist-pressure
           Use IRA to evaluate register pressure in the code hoisting pass for decisions to hoist
           expressions.  This option usually results in smaller code, but it can slow the
           compiler down.

           This option is enabled at level -Os for all targets.

       -fira-loop-pressure
           Use IRA to evaluate register pressure in loops for decisions to move loop invariants.
           This option usually results in generation of faster and smaller code on machines with
           large register files (>= 32 registers), but it can slow the compiler down.

           This option is enabled at level -O3 for some targets.

       -fno-ira-share-save-slots
           Disable sharing of stack slots used for saving call-used hard registers living through
           a call.  Each hard register gets a separate stack slot, and as a result function stack
           frames are larger.

       -fno-ira-share-spill-slots
           Disable sharing of stack slots allocated for pseudo-registers.  Each pseudo-register
           that does not get a hard register gets a separate stack slot, and as a result function
           stack frames are larger.

       -flra-remat
           Enable CFG-sensitive rematerialization in LRA.  Instead of loading values of spilled
           pseudos, LRA tries to rematerialize (recalculate) values if it is profitable.

           Enabled at levels -O2, -O3, -Os.

       -fdelayed-branch
           If supported for the target machine, attempt to reorder instructions to exploit
           instruction slots available after delayed branch instructions.

           Enabled at levels -O, -O2, -O3, -Os.

       -fschedule-insns
           If supported for the target machine, attempt to reorder instructions to eliminate
           execution stalls due to required data being unavailable.  This helps machines that
           have slow floating point or memory load instructions by allowing other instructions to
           be issued until the result of the load or floating-point instruction is required.

           Enabled at levels -O2, -O3.

       -fschedule-insns2
           Similar to -fschedule-insns, but requests an additional pass of instruction scheduling
           after register allocation has been done.  This is especially useful on machines with a
           relatively small number of registers and where memory load instructions take more than
           one cycle.

           Enabled at levels -O2, -O3, -Os.

       -fno-sched-interblock
           Don't schedule instructions across basic blocks.  This is normally enabled by default
           when scheduling before register allocation, i.e.  with -fschedule-insns or at -O2 or
           higher.

       -fno-sched-spec
           Don't allow speculative motion of non-load instructions.  This is normally enabled by
           default when scheduling before register allocation, i.e.  with -fschedule-insns or at
           -O2 or higher.

       -fsched-pressure
           Enable register pressure sensitive insn scheduling before register allocation.  This
           only makes sense when scheduling before register allocation is enabled, i.e. with
           -fschedule-insns or at -O2 or higher.  Usage of this option can improve the generated
           code and decrease its size by preventing register pressure increase above the number
           of available hard registers and subsequent spills in register allocation.

       -fsched-spec-load
           Allow speculative motion of some load instructions.  This only makes sense when
           scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.

       -fsched-spec-load-dangerous
           Allow speculative motion of more load instructions.  This only makes sense when
           scheduling before register allocation, i.e. with -fschedule-insns or at -O2 or higher.

       -fsched-stalled-insns
       -fsched-stalled-insns=n
           Define how many insns (if any) can be moved prematurely from the queue of stalled
           insns into the ready list during the second scheduling pass.  -fno-sched-stalled-insns
           means that no insns are moved prematurely, -fsched-stalled-insns=0 means there is no
           limit on how many queued insns can be moved prematurely.  -fsched-stalled-insns
           without a value is equivalent to -fsched-stalled-insns=1.

       -fsched-stalled-insns-dep
       -fsched-stalled-insns-dep=n
           Define how many insn groups (cycles) are examined for a dependency on a stalled insn
           that is a candidate for premature removal from the queue of stalled insns.  This has
           an effect only during the second scheduling pass, and only if -fsched-stalled-insns is
           used.  -fno-sched-stalled-insns-dep is equivalent to -fsched-stalled-insns-dep=0.
           -fsched-stalled-insns-dep without a value is equivalent to
           -fsched-stalled-insns-dep=1.

       -fsched2-use-superblocks
           When scheduling after register allocation, use superblock scheduling.  This allows
           motion across basic block boundaries, resulting in faster schedules.  This option is
           experimental, as not all machine descriptions used by GCC model the CPU closely enough
           to avoid unreliable results from the algorithm.

           This only makes sense when scheduling after register allocation, i.e. with
           -fschedule-insns2 or at -O2 or higher.

       -fsched-group-heuristic
           Enable the group heuristic in the scheduler.  This heuristic favors the instruction
           that belongs to a schedule group.  This is enabled by default when scheduling is
           enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-critical-path-heuristic
           Enable the critical-path heuristic in the scheduler.  This heuristic favors
           instructions on the critical path.  This is enabled by default when scheduling is
           enabled, i.e. with -fschedule-insns or -fschedule-insns2 or at -O2 or higher.

       -fsched-spec-insn-heuristic
           Enable the speculative instruction heuristic in the scheduler.  This heuristic favors
           speculative instructions with greater dependency weakness.  This is enabled by default
           when scheduling is enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -fsched-rank-heuristic
           Enable the rank heuristic in the scheduler.  This heuristic favors the instruction
           belonging to a basic block with greater size or frequency.  This is enabled by default
           when scheduling is enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -fsched-last-insn-heuristic
           Enable the last-instruction heuristic in the scheduler.  This heuristic favors the
           instruction that is less dependent on the last instruction scheduled.  This is enabled
           by default when scheduling is enabled, i.e. with -fschedule-insns or -fschedule-insns2
           or at -O2 or higher.

       -fsched-dep-count-heuristic
           Enable the dependent-count heuristic in the scheduler.  This heuristic favors the
           instruction that has more instructions depending on it.  This is enabled by default
           when scheduling is enabled, i.e.  with -fschedule-insns or -fschedule-insns2 or at -O2
           or higher.

       -freschedule-modulo-scheduled-loops
           Modulo scheduling is performed before traditional scheduling.  If a loop is modulo
           scheduled, later scheduling passes may change its schedule.  Use this option to
           control that behavior.

       -fselective-scheduling
           Schedule instructions using selective scheduling algorithm.  Selective scheduling runs
           instead of the first scheduler pass.

       -fselective-scheduling2
           Schedule instructions using selective scheduling algorithm.  Selective scheduling runs
           instead of the second scheduler pass.

       -fsel-sched-pipelining
           Enable software pipelining of innermost loops during selective scheduling.  This
           option has no effect unless one of -fselective-scheduling or -fselective-scheduling2
           is turned on.

       -fsel-sched-pipelining-outer-loops
           When pipelining loops during selective scheduling, also pipeline outer loops.  This
           option has no effect unless -fsel-sched-pipelining is turned on.

       -fsemantic-interposition
           Some object formats, like ELF, allow interposing of symbols by the dynamic linker.
           This means that for symbols exported from the DSO, the compiler cannot perform
           interprocedural propagation, inlining and other optimizations in anticipation that the
           function or variable in question may change. While this feature is useful, for
           example, to rewrite memory allocation functions by a debugging implementation, it is
           expensive in the terms of code quality.  With -fno-semantic-interposition the compiler
           assumes that if interposition happens for functions the overwriting function will have
           precisely the same semantics (and side effects).  Similarly if interposition happens
           for variables, the constructor of the variable will be the same. The flag has no
           effect for functions explicitly declared inline (where it is never allowed for
           interposition to change semantics) and for symbols explicitly declared weak.

       -fshrink-wrap
           Emit function prologues only before parts of the function that need it, rather than at
           the top of the function.  This flag is enabled by default at -O and higher.

       -fshrink-wrap-separate
           Shrink-wrap separate parts of the prologue and epilogue separately, so that those
           parts are only executed when needed.  This option is on by default, but has no effect
           unless -fshrink-wrap is also turned on and the target supports this.

       -fcaller-saves
           Enable allocation of values to registers that are clobbered by function calls, by
           emitting extra instructions to save and restore the registers around such calls.  Such
           allocation is done only when it seems to result in better code.

           This option is always enabled by default on certain machines, usually those which have
           no call-preserved registers to use instead.

           Enabled at levels -O2, -O3, -Os.

       -fcombine-stack-adjustments
           Tracks stack adjustments (pushes and pops) and stack memory references and then tries
           to find ways to combine them.

           Enabled by default at -O1 and higher.

       -fipa-ra
           Use caller save registers for allocation if those registers are not used by any called
           function.  In that case it is not necessary to save and restore them around calls.
           This is only possible if called functions are part of same compilation unit as current
           function and they are compiled before it.

           Enabled at levels -O2, -O3, -Os, however the option is disabled if generated code will
           be instrumented for profiling (-p, or -pg) or if callee's register usage cannot be
           known exactly (this happens on targets that do not expose prologues and epilogues in
           RTL).

       -fconserve-stack
           Attempt to minimize stack usage.  The compiler attempts to use less stack space, even
           if that makes the program slower.  This option implies setting the large-stack-frame
           parameter to 100 and the large-stack-frame-growth parameter to 400.

       -ftree-reassoc
           Perform reassociation on trees.  This flag is enabled by default at -O and higher.

       -fcode-hoisting
           Perform code hoisting.  Code hoisting tries to move the evaluation of expressions
           executed on all paths to the function exit as early as possible.  This is especially
           useful as a code size optimization, but it often helps for code speed as well.  This
           flag is enabled by default at -O2 and higher.

       -ftree-pre
           Perform partial redundancy elimination (PRE) on trees.  This flag is enabled by
           default at -O2 and -O3.

       -ftree-partial-pre
           Make partial redundancy elimination (PRE) more aggressive.  This flag is enabled by
           default at -O3.

       -ftree-forwprop
           Perform forward propagation on trees.  This flag is enabled by default at -O and
           higher.

       -ftree-fre
           Perform full redundancy elimination (FRE) on trees.  The difference between FRE and
           PRE is that FRE only considers expressions that are computed on all paths leading to
           the redundant computation.  This analysis is faster than PRE, though it exposes fewer
           redundancies.  This flag is enabled by default at -O and higher.

       -ftree-phiprop
           Perform hoisting of loads from conditional pointers on trees.  This pass is enabled by
           default at -O and higher.

       -fhoist-adjacent-loads
           Speculatively hoist loads from both branches of an if-then-else if the loads are from
           adjacent locations in the same structure and the target architecture has a conditional
           move instruction.  This flag is enabled by default at -O2 and higher.

       -ftree-copy-prop
           Perform copy propagation on trees.  This pass eliminates unnecessary copy operations.
           This flag is enabled by default at -O and higher.

       -fipa-pure-const
           Discover which functions are pure or constant.  Enabled by default at -O and higher.

       -fipa-reference
           Discover which static variables do not escape the compilation unit.  Enabled by
           default at -O and higher.

       -fipa-pta
           Perform interprocedural pointer analysis and interprocedural modification and
           reference analysis.  This option can cause excessive memory and compile-time usage on
           large compilation units.  It is not enabled by default at any optimization level.

       -fipa-profile
           Perform interprocedural profile propagation.  The functions called only from cold
           functions are marked as cold. Also functions executed once (such as "cold",
           "noreturn", static constructors or destructors) are identified. Cold functions and
           loop less parts of functions executed once are then optimized for size.  Enabled by
           default at -O and higher.

       -fipa-cp
           Perform interprocedural constant propagation.  This optimization analyzes the program
           to determine when values passed to functions are constants and then optimizes
           accordingly.  This optimization can substantially increase performance if the
           application has constants passed to functions.  This flag is enabled by default at
           -O2, -Os and -O3.

       -fipa-cp-clone
           Perform function cloning to make interprocedural constant propagation stronger.  When
           enabled, interprocedural constant propagation performs function cloning when
           externally visible function can be called with constant arguments.  Because this
           optimization can create multiple copies of functions, it may significantly increase
           code size (see --param ipcp-unit-growth=value).  This flag is enabled by default at
           -O3.

       -fipa-bit-cp
           When enabled, perform interprocedural bitwise constant propagation. This flag is
           enabled by default at -O2. It requires that -fipa-cp is enabled.

       -fipa-vrp
           When enabled, perform interprocedural propagation of value ranges. This flag is
           enabled by default at -O2. It requires that -fipa-cp is enabled.

       -fipa-icf
           Perform Identical Code Folding for functions and read-only variables.  The
           optimization reduces code size and may disturb unwind stacks by replacing a function
           by equivalent one with a different name. The optimization works more effectively with
           link-time optimization enabled.

           Nevertheless the behavior is similar to Gold Linker ICF optimization, GCC ICF works on
           different levels and thus the optimizations are not same - there are equivalences that
           are found only by GCC and equivalences found only by Gold.

           This flag is enabled by default at -O2 and -Os.

       -fisolate-erroneous-paths-dereference
           Detect paths that trigger erroneous or undefined behavior due to dereferencing a null
           pointer.  Isolate those paths from the main control flow and turn the statement with
           erroneous or undefined behavior into a trap.  This flag is enabled by default at -O2
           and higher and depends on -fdelete-null-pointer-checks also being enabled.

       -fisolate-erroneous-paths-attribute
           Detect paths that trigger erroneous or undefined behavior due to a null value being
           used in a way forbidden by a "returns_nonnull" or "nonnull" attribute.  Isolate those
           paths from the main control flow and turn the statement with erroneous or undefined
           behavior into a trap.  This is not currently enabled, but may be enabled by -O2 in the
           future.

       -ftree-sink
           Perform forward store motion on trees.  This flag is enabled by default at -O and
           higher.

       -ftree-bit-ccp
           Perform sparse conditional bit constant propagation on trees and propagate pointer
           alignment information.  This pass only operates on local scalar variables and is
           enabled by default at -O and higher.  It requires that -ftree-ccp is enabled.

       -ftree-ccp
           Perform sparse conditional constant propagation (CCP) on trees.  This pass only
           operates on local scalar variables and is enabled by default at -O and higher.

       -fssa-backprop
           Propagate information about uses of a value up the definition chain in order to
           simplify the definitions.  For example, this pass strips sign operations if the sign
           of a value never matters.  The flag is enabled by default at -O and higher.

       -fssa-phiopt
           Perform pattern matching on SSA PHI nodes to optimize conditional code.  This pass is
           enabled by default at -O and higher.

       -ftree-switch-conversion
           Perform conversion of simple initializations in a switch to initializations from a
           scalar array.  This flag is enabled by default at -O2 and higher.

       -ftree-tail-merge
           Look for identical code sequences.  When found, replace one with a jump to the other.
           This optimization is known as tail merging or cross jumping.  This flag is enabled by
           default at -O2 and higher.  The compilation time in this pass can be limited using
           max-tail-merge-comparisons parameter and max-tail-merge-iterations parameter.

       -ftree-dce
           Perform dead code elimination (DCE) on trees.  This flag is enabled by default at -O
           and higher.

       -ftree-builtin-call-dce
           Perform conditional dead code elimination (DCE) for calls to built-in functions that
           may set "errno" but are otherwise free of side effects.  This flag is enabled by
           default at -O2 and higher if -Os is not also specified.

       -ftree-dominator-opts
           Perform a variety of simple scalar cleanups (constant/copy propagation, redundancy
           elimination, range propagation and expression simplification) based on a dominator
           tree traversal.  This also performs jump threading (to reduce jumps to jumps). This
           flag is enabled by default at -O and higher.

       -ftree-dse
           Perform dead store elimination (DSE) on trees.  A dead store is a store into a memory
           location that is later overwritten by another store without any intervening loads.  In
           this case the earlier store can be deleted.  This flag is enabled by default at -O and
           higher.

       -ftree-ch
           Perform loop header copying on trees.  This is beneficial since it increases
           effectiveness of code motion optimizations.  It also saves one jump.  This flag is
           enabled by default at -O and higher.  It is not enabled for -Os, since it usually
           increases code size.

       -ftree-loop-optimize
           Perform loop optimizations on trees.  This flag is enabled by default at -O and
           higher.

       -ftree-loop-linear
       -floop-strip-mine
       -floop-block
           Perform loop nest optimizations.  Same as -floop-nest-optimize.  To use this code
           transformation, GCC has to be configured with --with-isl to enable the Graphite loop
           transformation infrastructure.

       -fgraphite-identity
           Enable the identity transformation for graphite.  For every SCoP we generate the
           polyhedral representation and transform it back to gimple.  Using -fgraphite-identity
           we can check the costs or benefits of the GIMPLE -> GRAPHITE -> GIMPLE transformation.
           Some minimal optimizations are also performed by the code generator isl, like index
           splitting and dead code elimination in loops.

       -floop-nest-optimize
           Enable the isl based loop nest optimizer.  This is a generic loop nest optimizer based
           on the Pluto optimization algorithms.  It calculates a loop structure optimized for
           data-locality and parallelism.  This option is experimental.

       -floop-parallelize-all
           Use the Graphite data dependence analysis to identify loops that can be parallelized.
           Parallelize all the loops that can be analyzed to not contain loop carried dependences
           without checking that it is profitable to parallelize the loops.

       -ftree-coalesce-vars
           While transforming the program out of the SSA representation, attempt to reduce
           copying by coalescing versions of different user-defined variables, instead of just
           compiler temporaries.  This may severely limit the ability to debug an optimized
           program compiled with -fno-var-tracking-assignments.  In the negated form, this flag
           prevents SSA coalescing of user variables.  This option is enabled by default if
           optimization is enabled, and it does very little otherwise.

       -ftree-loop-if-convert
           Attempt to transform conditional jumps in the innermost loops to branch-less
           equivalents.  The intent is to remove control-flow from the innermost loops in order
           to improve the ability of the vectorization pass to handle these loops.  This is
           enabled by default if vectorization is enabled.

       -ftree-loop-distribution
           Perform loop distribution.  This flag can improve cache performance on big loop bodies
           and allow further loop optimizations, like parallelization or vectorization, to take
           place.  For example, the loop

                   DO I = 1, N
                     A(I) = B(I) + C
                     D(I) = E(I) * F
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = B(I) + C
                   ENDDO
                   DO I = 1, N
                      D(I) = E(I) * F
                   ENDDO

       -ftree-loop-distribute-patterns
           Perform loop distribution of patterns that can be code generated with calls to a
           library.  This flag is enabled by default at -O3.

           This pass distributes the initialization loops and generates a call to memset zero.
           For example, the loop

                   DO I = 1, N
                     A(I) = 0
                     B(I) = A(I) + I
                   ENDDO

           is transformed to

                   DO I = 1, N
                      A(I) = 0
                   ENDDO
                   DO I = 1, N
                      B(I) = A(I) + I
                   ENDDO

           and the initialization loop is transformed into a call to memset zero.

       -floop-interchange
           Perform loop interchange outside of graphite.  This flag can improve cache performance
           on loop nest and allow further loop optimizations, like vectorization, to take place.
           For example, the loop

                   for (int i = 0; i < N; i++)
                     for (int j = 0; j < N; j++)
                       for (int k = 0; k < N; k++)
                         c[i][j] = c[i][j] + a[i][k]*b[k][j];

           is transformed to

                   for (int i = 0; i < N; i++)
                     for (int k = 0; k < N; k++)
                       for (int j = 0; j < N; j++)
                         c[i][j] = c[i][j] + a[i][k]*b[k][j];

           This flag is enabled by default at -O3.

       -floop-unroll-and-jam
           Apply unroll and jam transformations on feasible loops.  In a loop nest this unrolls
           the outer loop by some factor and fuses the resulting multiple inner loops.  This flag
           is enabled by default at -O3.

       -ftree-loop-im
           Perform loop invariant motion on trees.  This pass moves only invariants that are hard
           to handle at RTL level (function calls, operations that expand to nontrivial sequences
           of insns).  With -funswitch-loops it also moves operands of conditions that are
           invariant out of the loop, so that we can use just trivial invariantness analysis in
           loop unswitching.  The pass also includes store motion.

       -ftree-loop-ivcanon
           Create a canonical counter for number of iterations in loops for which determining
           number of iterations requires complicated analysis.  Later optimizations then may
           determine the number easily.  Useful especially in connection with unrolling.

       -fivopts
           Perform induction variable optimizations (strength reduction, induction variable
           merging and induction variable elimination) on trees.

       -ftree-parallelize-loops=n
           Parallelize loops, i.e., split their iteration space to run in n threads.  This is
           only possible for loops whose iterations are independent and can be arbitrarily
           reordered.  The optimization is only profitable on multiprocessor machines, for loops
           that are CPU-intensive, rather than constrained e.g. by memory bandwidth.  This option
           implies -pthread, and thus is only supported on targets that have support for
           -pthread.

       -ftree-pta
           Perform function-local points-to analysis on trees.  This flag is enabled by default
           at -O and higher.

       -ftree-sra
           Perform scalar replacement of aggregates.  This pass replaces structure references
           with scalars to prevent committing structures to memory too early.  This flag is
           enabled by default at -O and higher.

       -fstore-merging
           Perform merging of narrow stores to consecutive memory addresses.  This pass merges
           contiguous stores of immediate values narrower than a word into fewer wider stores to
           reduce the number of instructions.  This is enabled by default at -O2 and higher as
           well as -Os.

       -ftree-ter
           Perform temporary expression replacement during the SSA->normal phase.  Single
           use/single def temporaries are replaced at their use location with their defining
           expression.  This results in non-GIMPLE code, but gives the expanders much more
           complex trees to work on resulting in better RTL generation.  This is enabled by
           default at -O and higher.

       -ftree-slsr
           Perform straight-line strength reduction on trees.  This recognizes related
           expressions involving multiplications and replaces them by less expensive calculations
           when possible.  This is enabled by default at -O and higher.

       -ftree-vectorize
           Perform vectorization on trees. This flag enables -ftree-loop-vectorize and
           -ftree-slp-vectorize if not explicitly specified.

       -ftree-loop-vectorize
           Perform loop vectorization on trees. This flag is enabled by default at -O3 and when
           -ftree-vectorize is enabled.

       -ftree-slp-vectorize
           Perform basic block vectorization on trees. This flag is enabled by default at -O3 and
           when -ftree-vectorize is enabled.

       -fvect-cost-model=model
           Alter the cost model used for vectorization.  The model argument should be one of
           unlimited, dynamic or cheap.  With the unlimited model the vectorized code-path is
           assumed to be profitable while with the dynamic model a runtime check guards the
           vectorized code-path to enable it only for iteration counts that will likely execute
           faster than when executing the original scalar loop.  The cheap model disables
           vectorization of loops where doing so would be cost prohibitive for example due to
           required runtime checks for data dependence or alignment but otherwise is equal to the
           dynamic model.  The default cost model depends on other optimization flags and is
           either dynamic or cheap.

       -fsimd-cost-model=model
           Alter the cost model used for vectorization of loops marked with the OpenMP simd
           directive.  The model argument should be one of unlimited, dynamic, cheap.  All values
           of model have the same meaning as described in -fvect-cost-model and by default a cost
           model defined with -fvect-cost-model is used.

       -ftree-vrp
           Perform Value Range Propagation on trees.  This is similar to the constant propagation
           pass, but instead of values, ranges of values are propagated.  This allows the
           optimizers to remove unnecessary range checks like array bound checks and null pointer
           checks.  This is enabled by default at -O2 and higher.  Null pointer check elimination
           is only done if -fdelete-null-pointer-checks is enabled.

       -fsplit-paths
           Split paths leading to loop backedges.  This can improve dead code elimination and
           common subexpression elimination.  This is enabled by default at -O2 and above.

       -fsplit-ivs-in-unroller
           Enables expression of values of induction variables in later iterations of the
           unrolled loop using the value in the first iteration.  This breaks long dependency
           chains, thus improving efficiency of the scheduling passes.

           A combination of -fweb and CSE is often sufficient to obtain the same effect.
           However, that is not reliable in cases where the loop body is more complicated than a
           single basic block.  It also does not work at all on some architectures due to
           restrictions in the CSE pass.

           This optimization is enabled by default.

       -fvariable-expansion-in-unroller
           With this option, the compiler creates multiple copies of some local variables when
           unrolling a loop, which can result in superior code.

       -fpartial-inlining
           Inline parts of functions.  This option has any effect only when inlining itself is
           turned on by the -finline-functions or -finline-small-functions options.

           Enabled at levels -O2, -O3, -Os.

       -fpredictive-commoning
           Perform predictive commoning optimization, i.e., reusing computations (especially
           memory loads and stores) performed in previous iterations of loops.

           This option is enabled at level -O3.

       -fprefetch-loop-arrays
           If supported by the target machine, generate instructions to prefetch memory to
           improve the performance of loops that access large arrays.

           This option may generate better or worse code; results are highly dependent on the
           structure of loops within the source code.

           Disabled at level -Os.

       -fno-printf-return-value
           Do not substitute constants for known return value of formatted output functions such
           as "sprintf", "snprintf", "vsprintf", and "vsnprintf" (but not "printf" of "fprintf").
           This transformation allows GCC to optimize or even eliminate branches based on the
           known return value of these functions called with arguments that are either constant,
           or whose values are known to be in a range that makes determining the exact return
           value possible.  For example, when -fprintf-return-value is in effect, both the branch
           and the body of the "if" statement (but not the call to "snprint") can be optimized
           away when "i" is a 32-bit or smaller integer because the return value is guaranteed to
           be at most 8.

                   char buf[9];
                   if (snprintf (buf, "%08x", i) >= sizeof buf)
                     ...

           The -fprintf-return-value option relies on other optimizations and yields best results
           with -O2 and above.  It works in tandem with the -Wformat-overflow and
           -Wformat-truncation options.  The -fprintf-return-value option is enabled by default.

       -fno-peephole
       -fno-peephole2
           Disable any machine-specific peephole optimizations.  The difference between
           -fno-peephole and -fno-peephole2 is in how they are implemented in the compiler; some
           targets use one, some use the other, a few use both.

           -fpeephole is enabled by default.  -fpeephole2 enabled at levels -O2, -O3, -Os.

       -fno-guess-branch-probability
           Do not guess branch probabilities using heuristics.

           GCC uses heuristics to guess branch probabilities if they are not provided by
           profiling feedback (-fprofile-arcs).  These heuristics are based on the control flow
           graph.  If some branch probabilities are specified by "__builtin_expect", then the
           heuristics are used to guess branch probabilities for the rest of the control flow
           graph, taking the "__builtin_expect" info into account.  The interactions between the
           heuristics and "__builtin_expect" can be complex, and in some cases, it may be useful
           to disable the heuristics so that the effects of "__builtin_expect" are easier to
           understand.

           The default is -fguess-branch-probability at levels -O, -O2, -O3, -Os.

       -freorder-blocks
           Reorder basic blocks in the compiled function in order to reduce number of taken
           branches and improve code locality.

           Enabled at levels -O, -O2, -O3, -Os.

       -freorder-blocks-algorithm=algorithm
           Use the specified algorithm for basic block reordering.  The algorithm argument can be
           simple, which does not increase code size (except sometimes due to secondary effects
           like alignment), or stc, the "software trace cache" algorithm, which tries to put all
           often executed code together, minimizing the number of branches executed by making
           extra copies of code.

           The default is simple at levels -O, -Os, and stc at levels -O2, -O3.

       -freorder-blocks-and-partition
           In addition to reordering basic blocks in the compiled function, in order to reduce
           number of taken branches, partitions hot and cold basic blocks into separate sections
           of the assembly and .o files, to improve paging and cache locality performance.

           This optimization is automatically turned off in the presence of exception handling or
           unwind tables (on targets using setjump/longjump or target specific scheme), for
           linkonce sections, for functions with a user-defined section attribute and on any
           architecture that does not support named sections.  When -fsplit-stack is used this
           option is not enabled by default (to avoid linker errors), but may be enabled
           explicitly (if using a working linker).

           Enabled for x86 at levels -O2, -O3, -Os.

       -freorder-functions
           Reorder functions in the object file in order to improve code locality.  This is
           implemented by using special subsections ".text.hot" for most frequently executed
           functions and ".text.unlikely" for unlikely executed functions.  Reordering is done by
           the linker so object file format must support named sections and linker must place
           them in a reasonable way.

           Also profile feedback must be available to make this option effective.  See
           -fprofile-arcs for details.

           Enabled at levels -O2, -O3, -Os.

       -fstrict-aliasing
           Allow the compiler to assume the strictest aliasing rules applicable to the language
           being compiled.  For C (and C++), this activates optimizations based on the type of
           expressions.  In particular, an object of one type is assumed never to reside at the
           same address as an object of a different type, unless the types are almost the same.
           For example, an "unsigned int" can alias an "int", but not a "void*" or a "double".  A
           character type may alias any other type.

           Pay special attention to code like this:

                   union a_union {
                     int i;
                     double d;
                   };

                   int f() {
                     union a_union t;
                     t.d = 3.0;
                     return t.i;
                   }

           The practice of reading from a different union member than the one most recently
           written to (called "type-punning") is common.  Even with -fstrict-aliasing, type-
           punning is allowed, provided the memory is accessed through the union type.  So, the
           code above works as expected.    However, this code might not:

                   int f() {
                     union a_union t;
                     int* ip;
                     t.d = 3.0;
                     ip = &t.i;
                     return *ip;
                   }

           Similarly, access by taking the address, casting the resulting pointer and
           dereferencing the result has undefined behavior, even if the cast uses a union type,
           e.g.:

                   int f() {
                     double d = 3.0;
                     return ((union a_union *) &d)->i;
                   }

           The -fstrict-aliasing option is enabled at levels -O2, -O3, -Os.

       -falign-functions
       -falign-functions=n
           Align the start of functions to the next power-of-two greater than n, skipping up to n
           bytes.  For instance, -falign-functions=32 aligns functions to the next 32-byte
           boundary, but -falign-functions=24 aligns to the next 32-byte boundary only if this
           can be done by skipping 23 bytes or less.

           -fno-align-functions and -falign-functions=1 are equivalent and mean that functions
           are not aligned.

           Some assemblers only support this flag when n is a power of two; in that case, it is
           rounded up.

           If n is not specified or is zero, use a machine-dependent default.  The maximum
           allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -flimit-function-alignment
           If this option is enabled, the compiler tries to avoid unnecessarily overaligning
           functions. It attempts to instruct the assembler to align by the amount specified by
           -falign-functions, but not to skip more bytes than the size of the function.

       -falign-labels
       -falign-labels=n
           Align all branch targets to a power-of-two boundary, skipping up to n bytes like
           -falign-functions.  This option can easily make code slower, because it must insert
           dummy operations for when the branch target is reached in the usual flow of the code.

           -fno-align-labels and -falign-labels=1 are equivalent and mean that labels are not
           aligned.

           If -falign-loops or -falign-jumps are applicable and are greater than this value, then
           their values are used instead.

           If n is not specified or is zero, use a machine-dependent default which is very likely
           to be 1, meaning no alignment.  The maximum allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -falign-loops
       -falign-loops=n
           Align loops to a power-of-two boundary, skipping up to n bytes like -falign-functions.
           If the loops are executed many times, this makes up for any execution of the dummy
           operations.

           -fno-align-loops and -falign-loops=1 are equivalent and mean that loops are not
           aligned.  The maximum allowed n option value is 65536.

           If n is not specified or is zero, use a machine-dependent default.

           Enabled at levels -O2, -O3.

       -falign-jumps
       -falign-jumps=n
           Align branch targets to a power-of-two boundary, for branch targets where the targets
           can only be reached by jumping, skipping up to n bytes like -falign-functions.  In
           this case, no dummy operations need be executed.

           -fno-align-jumps and -falign-jumps=1 are equivalent and mean that loops are not
           aligned.

           If n is not specified or is zero, use a machine-dependent default.  The maximum
           allowed n option value is 65536.

           Enabled at levels -O2, -O3.

       -funit-at-a-time
           This option is left for compatibility reasons. -funit-at-a-time has no effect, while
           -fno-unit-at-a-time implies -fno-toplevel-reorder and -fno-section-anchors.

           Enabled by default.

       -fno-toplevel-reorder
           Do not reorder top-level functions, variables, and "asm" statements.  Output them in
           the same order that they appear in the input file.  When this option is used,
           unreferenced static variables are not removed.  This option is intended to support
           existing code that relies on a particular ordering.  For new code, it is better to use
           attributes when possible.

           Enabled at level -O0.  When disabled explicitly, it also implies -fno-section-anchors,
           which is otherwise enabled at -O0 on some targets.

       -fweb
           Constructs webs as commonly used for register allocation purposes and assign each web
           individual pseudo register.  This allows the register allocation pass to operate on
           pseudos directly, but also strengthens several other optimization passes, such as CSE,
           loop optimizer and trivial dead code remover.  It can, however, make debugging
           impossible, since variables no longer stay in a "home register".

           Enabled by default with -funroll-loops.

       -fwhole-program
           Assume that the current compilation unit represents the whole program being compiled.
           All public functions and variables with the exception of "main" and those merged by
           attribute "externally_visible" become static functions and in effect are optimized
           more aggressively by interprocedural optimizers.

           This option should not be used in combination with -flto.  Instead relying on a linker
           plugin should provide safer and more precise information.

       -flto[=n]
           This option runs the standard link-time optimizer.  When invoked with source code, it
           generates GIMPLE (one of GCC's internal representations) and writes it to special ELF
           sections in the object file.  When the object files are linked together, all the
           function bodies are read from these ELF sections and instantiated as if they had been
           part of the same translation unit.

           To use the link-time optimizer, -flto and optimization options should be specified at
           compile time and during the final link.  It is recommended that you compile all the
           files participating in the same link with the same options and also specify those
           options at link time.  For example:

                   gcc -c -O2 -flto foo.c
                   gcc -c -O2 -flto bar.c
                   gcc -o myprog -flto -O2 foo.o bar.o

           The first two invocations to GCC save a bytecode representation of GIMPLE into special
           ELF sections inside foo.o and bar.o.  The final invocation reads the GIMPLE bytecode
           from foo.o and bar.o, merges the two files into a single internal image, and compiles
           the result as usual.  Since both foo.o and bar.o are merged into a single image, this
           causes all the interprocedural analyses and optimizations in GCC to work across the
           two files as if they were a single one.  This means, for example, that the inliner is
           able to inline functions in bar.o into functions in foo.o and vice-versa.

           Another (simpler) way to enable link-time optimization is:

                   gcc -o myprog -flto -O2 foo.c bar.c

           The above generates bytecode for foo.c and bar.c, merges them together into a single
           GIMPLE representation and optimizes them as usual to produce myprog.

           The only important thing to keep in mind is that to enable link-time optimizations you
           need to use the GCC driver to perform the link step.  GCC then automatically performs
           link-time optimization if any of the objects involved were compiled with the -flto
           command-line option.  You generally should specify the optimization options to be used
           for link-time optimization though GCC tries to be clever at guessing an optimization
           level to use from the options used at compile time if you fail to specify one at link
           time.  You can always override the automatic decision to do link-time optimization by
           passing -fno-lto to the link command.

           To make whole program optimization effective, it is necessary to make certain whole
           program assumptions.  The compiler needs to know what functions and variables can be
           accessed by libraries and runtime outside of the link-time optimized unit.  When
           supported by the linker, the linker plugin (see -fuse-linker-plugin) passes
           information to the compiler about used and externally visible symbols.  When the
           linker plugin is not available, -fwhole-program should be used to allow the compiler
           to make these assumptions, which leads to more aggressive optimization decisions.

           When -fuse-linker-plugin is not enabled, when a file is compiled with -flto, the
           generated object file is larger than a regular object file because it contains GIMPLE
           bytecodes and the usual final code (see -ffat-lto-objects.  This means that object
           files with LTO information can be linked as normal object files; if -fno-lto is passed
           to the linker, no interprocedural optimizations are applied.  Note that when
           -fno-fat-lto-objects is enabled the compile stage is faster but you cannot perform a
           regular, non-LTO link on them.

           Additionally, the optimization flags used to compile individual files are not
           necessarily related to those used at link time.  For instance,

                   gcc -c -O0 -ffat-lto-objects -flto foo.c
                   gcc -c -O0 -ffat-lto-objects -flto bar.c
                   gcc -o myprog -O3 foo.o bar.o

           This produces individual object files with unoptimized assembler code, but the
           resulting binary myprog is optimized at -O3.  If, instead, the final binary is
           generated with -fno-lto, then myprog is not optimized.

           When producing the final binary, GCC only applies link-time optimizations to those
           files that contain bytecode.  Therefore, you can mix and match object files and
           libraries with GIMPLE bytecodes and final object code.  GCC automatically selects
           which files to optimize in LTO mode and which files to link without further
           processing.

           There are some code generation flags preserved by GCC when generating bytecodes, as
           they need to be used during the final link stage.  Generally options specified at link
           time override those specified at compile time.

           If you do not specify an optimization level option -O at link time, then GCC uses the
           highest optimization level used when compiling the object files.

           Currently, the following options and their settings are taken from the first object
           file that explicitly specifies them: -fPIC, -fpic, -fpie, -fcommon, -fexceptions,
           -fnon-call-exceptions, -fgnu-tm and all the -m target flags.

           Certain ABI-changing flags are required to match in all compilation units, and trying
           to override this at link time with a conflicting value is ignored.  This includes
           options such as -freg-struct-return and -fpcc-struct-return.

           Other options such as -ffp-contract, -fno-strict-overflow, -fwrapv, -fno-trapv or
           -fno-strict-aliasing are passed through to the link stage and merged conservatively
           for conflicting translation units.  Specifically -fno-strict-overflow, -fwrapv and
           -fno-trapv take precedence; and for example -ffp-contract=off takes precedence over
           -ffp-contract=fast.  You can override them at link time.

           If LTO encounters objects with C linkage declared with incompatible types in separate
           translation units to be linked together (undefined behavior according to ISO C99
           6.2.7), a non-fatal diagnostic may be issued.  The behavior is still undefined at run
           time.  Similar diagnostics may be raised for other languages.

           Another feature of LTO is that it is possible to apply interprocedural optimizations
           on files written in different languages:

                   gcc -c -flto foo.c
                   g++ -c -flto bar.cc
                   gfortran -c -flto baz.f90
                   g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran

           Notice that the final link is done with g++ to get the C++ runtime libraries and
           -lgfortran is added to get the Fortran runtime libraries.  In general, when mixing
           languages in LTO mode, you should use the same link command options as when mixing
           languages in a regular (non-LTO) compilation.

           If object files containing GIMPLE bytecode are stored in a library archive, say
           libfoo.a, it is possible to extract and use them in an LTO link if you are using a
           linker with plugin support.  To create static libraries suitable for LTO, use gcc-ar
           and gcc-ranlib instead of ar and ranlib; to show the symbols of object files with
           GIMPLE bytecode, use gcc-nm.  Those commands require that ar, ranlib and nm have been
           compiled with plugin support.  At link time, use the flag -fuse-linker-plugin to
           ensure that the library participates in the LTO optimization process:

                   gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo

           With the linker plugin enabled, the linker extracts the needed GIMPLE files from
           libfoo.a and passes them on to the running GCC to make them part of the aggregated
           GIMPLE image to be optimized.

           If you are not using a linker with plugin support and/or do not enable the linker
           plugin, then the objects inside libfoo.a are extracted and linked as usual, but they
           do not participate in the LTO optimization process.  In order to make a static library
           suitable for both LTO optimization and usual linkage, compile its object files with
           -flto -ffat-lto-objects.

           Link-time optimizations do not require the presence of the whole program to operate.
           If the program does not require any symbols to be exported, it is possible to combine
           -flto and -fwhole-program to allow the interprocedural optimizers to use more
           aggressive assumptions which may lead to improved optimization opportunities.  Use of
           -fwhole-program is not needed when linker plugin is active (see -fuse-linker-plugin).

           The current implementation of LTO makes no attempt to generate bytecode that is
           portable between different types of hosts.  The bytecode files are versioned and there
           is a strict version check, so bytecode files generated in one version of GCC do not
           work with an older or newer version of GCC.

           Link-time optimization does not work well with generation of debugging information on
           systems other than those using a combination of ELF and DWARF.

           If you specify the optional n, the optimization and code generation done at link time
           is executed in parallel using n parallel jobs by utilizing an installed make program.
           The environment variable MAKE may be used to override the program used.  The default
           value for n is 1.

           You can also specify -flto=jobserver to use GNU make's job server mode to determine
           the number of parallel jobs. This is useful when the Makefile calling GCC is already
           executing in parallel.  You must prepend a + to the command recipe in the parent
           Makefile for this to work.  This option likely only works if MAKE is GNU make.

       -flto-partition=alg
           Specify the partitioning algorithm used by the link-time optimizer.  The value is
           either 1to1 to specify a partitioning mirroring the original source files or balanced
           to specify partitioning into equally sized chunks (whenever possible) or max to create
           new partition for every symbol where possible.  Specifying none as an algorithm
           disables partitioning and streaming completely.  The default value is balanced. While
           1to1 can be used as an workaround for various code ordering issues, the max
           partitioning is intended for internal testing only.  The value one specifies that
           exactly one partition should be used while the value none bypasses partitioning and
           executes the link-time optimization step directly from the WPA phase.

       -flto-odr-type-merging
           Enable streaming of mangled types names of C++ types and their unification at link
           time.  This increases size of LTO object files, but enables diagnostics about One
           Definition Rule violations.

       -flto-compression-level=n
           This option specifies the level of compression used for intermediate language written
           to LTO object files, and is only meaningful in conjunction with LTO mode (-flto).
           Valid values are 0 (no compression) to 9 (maximum compression).  Values outside this
           range are clamped to either 0 or 9.  If the option is not given, a default balanced
           compression setting is used.

       -fuse-linker-plugin
           Enables the use of a linker plugin during link-time optimization.  This option relies
           on plugin support in the linker, which is available in gold or in GNU ld 2.21 or
           newer.

           This option enables the extraction of object files with GIMPLE bytecode out of library
           archives. This improves the quality of optimization by exposing more code to the link-
           time optimizer.  This information specifies what symbols can be accessed externally
           (by non-LTO object or during dynamic linking).  Resulting code quality improvements on
           binaries (and shared libraries that use hidden visibility) are similar to
           -fwhole-program.  See -flto for a description of the effect of this flag and how to
           use it.

           This option is enabled by default when LTO support in GCC is enabled and GCC was
           configured for use with a linker supporting plugins (GNU ld 2.21 or newer or gold).

       -ffat-lto-objects
           Fat LTO objects are object files that contain both the intermediate language and the
           object code. This makes them usable for both LTO linking and normal linking. This
           option is effective only when compiling with -flto and is ignored at link time.

           -fno-fat-lto-objects improves compilation time over plain LTO, but requires the
           complete toolchain to be aware of LTO. It requires a linker with linker plugin support
           for basic functionality.  Additionally, nm, ar and ranlib need to support linker
           plugins to allow a full-featured build environment (capable of building static
           libraries etc).  GCC provides the gcc-ar, gcc-nm, gcc-ranlib wrappers to pass the
           right options to these tools. With non fat LTO makefiles need to be modified to use
           them.

           Note that modern binutils provide plugin auto-load mechanism.  Installing the linker
           plugin into $libdir/bfd-plugins has the same effect as usage of the command wrappers
           (gcc-ar, gcc-nm and gcc-ranlib).

           The default is -fno-fat-lto-objects on targets with linker plugin support.

       -fcompare-elim
           After register allocation and post-register allocation instruction splitting, identify
           arithmetic instructions that compute processor flags similar to a comparison operation
           based on that arithmetic.  If possible, eliminate the explicit comparison operation.

           This pass only applies to certain targets that cannot explicitly represent the
           comparison operation before register allocation is complete.

           Enabled at levels -O, -O2, -O3, -Os.

       -fcprop-registers
           After register allocation and post-register allocation instruction splitting, perform
           a copy-propagation pass to try to reduce scheduling dependencies and occasionally
           eliminate the copy.

           Enabled at levels -O, -O2, -O3, -Os.

       -fprofile-correction
           Profiles collected using an instrumented binary for multi-threaded programs may be
           inconsistent due to missed counter updates. When this option is specified, GCC uses
           heuristics to correct or smooth out such inconsistencies. By default, GCC emits an
           error message when an inconsistent profile is detected.

       -fprofile-use
       -fprofile-use=path
           Enable profile feedback-directed optimizations, and the following optimizations which
           are generally profitable only with profile feedback available: -fbranch-probabilities,
           -fvpt, -funroll-loops, -fpeel-loops, -ftracer, -ftree-vectorize, and ftree-loop-
           distribute-patterns.

           Before you can use this option, you must first generate profiling information.

           By default, GCC emits an error message if the feedback profiles do not match the
           source code.  This error can be turned into a warning by using -Wcoverage-mismatch.
           Note this may result in poorly optimized code.

           If path is specified, GCC looks at the path to find the profile feedback data files.
           See -fprofile-dir.

       -fauto-profile
       -fauto-profile=path
           Enable sampling-based feedback-directed optimizations, and the following optimizations
           which are generally profitable only with profile feedback available:
           -fbranch-probabilities, -fvpt, -funroll-loops, -fpeel-loops, -ftracer,
           -ftree-vectorize, -finline-functions, -fipa-cp, -fipa-cp-clone,
           -fpredictive-commoning, -funswitch-loops, -fgcse-after-reload, and
           -ftree-loop-distribute-patterns.

           path is the name of a file containing AutoFDO profile information.  If omitted, it
           defaults to fbdata.afdo in the current directory.

           Producing an AutoFDO profile data file requires running your program with the perf
           utility on a supported GNU/Linux target system.  For more information, see
           <https://perf.wiki.kernel.org/>.

           E.g.

                   perf record -e br_inst_retired:near_taken -b -o perf.data \
                       -- your_program

           Then use the create_gcov tool to convert the raw profile data to a format that can be
           used by GCC.  You must also supply the unstripped binary for your program to this
           tool.  See <https://github.com/google/autofdo>.

           E.g.

                   create_gcov --binary=your_program.unstripped --profile=perf.data \
                       --gcov=profile.afdo

       The following options control compiler behavior regarding floating-point arithmetic.
       These options trade off between speed and correctness.  All must be specifically enabled.

       -ffloat-store
           Do not store floating-point variables in registers, and inhibit other options that
           might change whether a floating-point value is taken from a register or memory.

           This option prevents undesirable excess precision on machines such as the 68000 where
           the floating registers (of the 68881) keep more precision than a "double" is supposed
           to have.  Similarly for the x86 architecture.  For most programs, the excess precision
           does only good, but a few programs rely on the precise definition of IEEE floating
           point.  Use -ffloat-store for such programs, after modifying them to store all
           pertinent intermediate computations into variables.

       -fexcess-precision=style
           This option allows further control over excess precision on machines where floating-
           point operations occur in a format with more precision or range than the IEEE standard
           and interchange floating-point types.  By default, -fexcess-precision=fast is in
           effect; this means that operations may be carried out in a wider precision than the
           types specified in the source if that would result in faster code, and it is
           unpredictable when rounding to the types specified in the source code takes place.
           When compiling C, if -fexcess-precision=standard is specified then excess precision
           follows the rules specified in ISO C99; in particular, both casts and assignments
           cause values to be rounded to their semantic types (whereas -ffloat-store only affects
           assignments).  This option is enabled by default for C if a strict conformance option
           such as -std=c99 is used.  -ffast-math enables -fexcess-precision=fast by default
           regardless of whether a strict conformance option is used.

           -fexcess-precision=standard is not implemented for languages other than C.  On the
           x86, it has no effect if -mfpmath=sse or -mfpmath=sse+387 is specified; in the former
           case, IEEE semantics apply without excess precision, and in the latter, rounding is
           unpredictable.

       -ffast-math
           Sets the options -fno-math-errno, -funsafe-math-optimizations, -ffinite-math-only,
           -fno-rounding-math, -fno-signaling-nans, -fcx-limited-range and
           -fexcess-precision=fast.

           This option causes the preprocessor macro "__FAST_MATH__" to be defined.

           This option is not turned on by any -O option besides -Ofast since it can result in
           incorrect output for programs that depend on an exact implementation of IEEE or ISO
           rules/specifications for math functions. It may, however, yield faster code for
           programs that do not require the guarantees of these specifications.

       -fno-math-errno
           Do not set "errno" after calling math functions that are executed with a single
           instruction, e.g., "sqrt".  A program that relies on IEEE exceptions for math error
           handling may want to use this flag for speed while maintaining IEEE arithmetic
           compatibility.

           This option is not turned on by any -O option since it can result in incorrect output
           for programs that depend on an exact implementation of IEEE or ISO
           rules/specifications for math functions. It may, however, yield faster code for
           programs that do not require the guarantees of these specifications.

           The default is -fmath-errno.

           On Darwin systems, the math library never sets "errno".  There is therefore no reason
           for the compiler to consider the possibility that it might, and -fno-math-errno is the
           default.

       -funsafe-math-optimizations
           Allow optimizations for floating-point arithmetic that (a) assume that arguments and
           results are valid and (b) may violate IEEE or ANSI standards.  When used at link time,
           it may include libraries or startup files that change the default FPU control word or
           other similar optimizations.

           This option is not turned on by any -O option since it can result in incorrect output
           for programs that depend on an exact implementation of IEEE or ISO
           rules/specifications for math functions. It may, however, yield faster code for
           programs that do not require the guarantees of these specifications.  Enables
           -fno-signed-zeros, -fno-trapping-math, -fassociative-math and -freciprocal-math.

           The default is -fno-unsafe-math-optimizations.

       -fassociative-math
           Allow re-association of operands in series of floating-point operations.  This
           violates the ISO C and C++ language standard by possibly changing computation result.
           NOTE: re-ordering may change the sign of zero as well as ignore NaNs and inhibit or
           create underflow or overflow (and thus cannot be used on code that relies on rounding
           behavior like "(x + 2**52) - 2**52".  May also reorder floating-point comparisons and
           thus may not be used when ordered comparisons are required.  This option requires that
           both -fno-signed-zeros and -fno-trapping-math be in effect.  Moreover, it doesn't make
           much sense with -frounding-math. For Fortran the option is automatically enabled when
           both -fno-signed-zeros and -fno-trapping-math are in effect.

           The default is -fno-associative-math.

       -freciprocal-math
           Allow the reciprocal of a value to be used instead of dividing by the value if this
           enables optimizations.  For example "x / y" can be replaced with "x * (1/y)", which is
           useful if "(1/y)" is subject to common subexpression elimination.  Note that this
           loses precision and increases the number of flops operating on the value.

           The default is -fno-reciprocal-math.

       -ffinite-math-only
           Allow optimizations for floating-point arithmetic that assume that arguments and
           results are not NaNs or +-Infs.

           This option is not turned on by any -O option since it can result in incorrect output
           for programs that depend on an exact implementation of IEEE or ISO
           rules/specifications for math functions. It may, however, yield faster code for
           programs that do not require the guarantees of these specifications.

           The default is -fno-finite-math-only.

       -fno-signed-zeros
           Allow optimizations for floating-point arithmetic that ignore the signedness of zero.
           IEEE arithmetic specifies the behavior of distinct +0.0 and -0.0 values, which then
           prohibits simplification of expressions such as x+0.0 or 0.0*x (even with
           -ffinite-math-only).  This option implies that the sign of a zero result isn't
           significant.

           The default is -fsigned-zeros.

       -fno-trapping-math
           Compile code assuming that floating-point operations cannot generate user-visible
           traps.  These traps include division by zero, overflow, underflow, inexact result and
           invalid operation.  This option requires that -fno-signaling-nans be in effect.
           Setting this option may allow faster code if one relies on "non-stop" IEEE arithmetic,
           for example.

           This option should never be turned on by any -O option since it can result in
           incorrect output for programs that depend on an exact implementation of IEEE or ISO
           rules/specifications for math functions.

           The default is -ftrapping-math.

       -frounding-math
           Disable transformations and optimizations that assume default floating-point rounding
           behavior.  This is round-to-zero for all floating point to integer conversions, and
           round-to-nearest for all other arithmetic truncations.  This option should be
           specified for programs that change the FP rounding mode dynamically, or that may be
           executed with a non-default rounding mode.  This option disables constant folding of
           floating-point expressions at compile time (which may be affected by rounding mode)
           and arithmetic transformations that are unsafe in the presence of sign-dependent
           rounding modes.

           The default is -fno-rounding-math.

           This option is experimental and does not currently guarantee to disable all GCC
           optimizations that are affected by rounding mode.  Future versions of GCC may provide
           finer control of this setting using C99's "FENV_ACCESS" pragma.  This command-line
           option will be used to specify the default state for "FENV_ACCESS".

       -fsignaling-nans
           Compile code assuming that IEEE signaling NaNs may generate user-visible traps during
           floating-point operations.  Setting this option disables optimizations that may change
           the number of exceptions visible with signaling NaNs.  This option implies
           -ftrapping-math.

           This option causes the preprocessor macro "__SUPPORT_SNAN__" to be defined.

           The default is -fno-signaling-nans.

           This option is experimental and does not currently guarantee to disable all GCC
           optimizations that affect signaling NaN behavior.

       -fno-fp-int-builtin-inexact
           Do not allow the built-in functions "ceil", "floor", "round" and "trunc", and their
           "float" and "long double" variants, to generate code that raises the "inexact"
           floating-point exception for noninteger arguments.  ISO C99 and C11 allow these
           functions to raise the "inexact" exception, but ISO/IEC TS 18661-1:2014, the C
           bindings to IEEE 754-2008, does not allow these functions to do so.

           The default is -ffp-int-builtin-inexact, allowing the exception to be raised.  This
           option does nothing unless -ftrapping-math is in effect.

           Even if -fno-fp-int-builtin-inexact is used, if the functions generate a call to a
           library function then the "inexact" exception may be raised if the library
           implementation does not follow TS 18661.

       -fsingle-precision-constant
           Treat floating-point constants as single precision instead of implicitly converting
           them to double-precision constants.

       -fcx-limited-range
           When enabled, this option states that a range reduction step is not needed when
           performing complex division.  Also, there is no checking whether the result of a
           complex multiplication or division is "NaN + I*NaN", with an attempt to rescue the
           situation in that case.  The default is -fno-cx-limited-range, but is enabled by
           -ffast-math.

           This option controls the default setting of the ISO C99 "CX_LIMITED_RANGE" pragma.
           Nevertheless, the option applies to all languages.

       -fcx-fortran-rules
           Complex multiplication and division follow Fortran rules.  Range reduction is done as
           part of complex division, but there is no checking whether the result of a complex
           multiplication or division is "NaN + I*NaN", with an attempt to rescue the situation
           in that case.

           The default is -fno-cx-fortran-rules.

       The following options control optimizations that may improve performance, but are not
       enabled by any -O options.  This section includes experimental options that may produce
       broken code.

       -fbranch-probabilities
           After running a program compiled with -fprofile-arcs, you can compile it a second time
           using -fbranch-probabilities, to improve optimizations based on the number of times
           each branch was taken.  When a program compiled with -fprofile-arcs exits, it saves
           arc execution counts to a file called sourcename.gcda for each source file.  The
           information in this data file is very dependent on the structure of the generated
           code, so you must use the same source code and the same optimization options for both
           compilations.

           With -fbranch-probabilities, GCC puts a REG_BR_PROB note on each JUMP_INSN and
           CALL_INSN.  These can be used to improve optimization.  Currently, they are only used
           in one place: in reorg.c, instead of guessing which path a branch is most likely to
           take, the REG_BR_PROB values are used to exactly determine which path is taken more
           often.

       -fprofile-values
           If combined with -fprofile-arcs, it adds code so that some data about values of
           expressions in the program is gathered.

           With -fbranch-probabilities, it reads back the data gathered from profiling values of
           expressions for usage in optimizations.

           Enabled with -fprofile-generate and -fprofile-use.

       -fprofile-reorder-functions
           Function reordering based on profile instrumentation collects first time of execution
           of a function and orders these functions in ascending order.

           Enabled with -fprofile-use.

       -fvpt
           If combined with -fprofile-arcs, this option instructs the compiler to add code to
           gather information about values of expressions.

           With -fbranch-probabilities, it reads back the data gathered and actually performs the
           optimizations based on them.  Currently the optimizations include specialization of
           division operations using the knowledge about the value of the denominator.

       -frename-registers
           Attempt to avoid false dependencies in scheduled code by making use of registers left
           over after register allocation.  This optimization most benefits processors with lots
           of registers.  Depending on the debug information format adopted by the target,
           however, it can make debugging impossible, since variables no longer stay in a "home
           register".

           Enabled by default with -funroll-loops.

       -fschedule-fusion
           Performs a target dependent pass over the instruction stream to schedule instructions
           of same type together because target machine can execute them more efficiently if they
           are adjacent to each other in the instruction flow.

           Enabled at levels -O2, -O3, -Os.

       -ftracer
           Perform tail duplication to enlarge superblock size.  This transformation simplifies
           the control flow of the function allowing other optimizations to do a better job.

           Enabled with -fprofile-use.

       -funroll-loops
           Unroll loops whose number of iterations can be determined at compile time or upon
           entry to the loop.  -funroll-loops implies -frerun-cse-after-loop, -fweb and
           -frename-registers.  It also turns on complete loop peeling (i.e. complete removal of
           loops with a small constant number of iterations).  This option makes code larger, and
           may or may not make it run faster.

           Enabled with -fprofile-use.

       -funroll-all-loops
           Unroll all loops, even if their number of iterations is uncertain when the loop is
           entered.  This usually makes programs run more slowly.  -funroll-all-loops implies the
           same options as -funroll-loops.

       -fpeel-loops
           Peels loops for which there is enough information that they do not roll much (from
           profile feedback or static analysis).  It also turns on complete loop peeling (i.e.
           complete removal of loops with small constant number of iterations).

           Enabled with -O3 and/or -fprofile-use.

       -fmove-loop-invariants
           Enables the loop invariant motion pass in the RTL loop optimizer.  Enabled at level
           -O1

       -fsplit-loops
           Split a loop into two if it contains a condition that's always true for one side of
           the iteration space and false for the other.

       -funswitch-loops
           Move branches with loop invariant conditions out of the loop, with duplicates of the
           loop on both branches (modified according to result of the condition).

       -ffunction-sections
       -fdata-sections
           Place each function or data item into its own section in the output file if the target
           supports arbitrary sections.  The name of the function or the name of the data item
           determines the section's name in the output file.

           Use these options on systems where the linker can perform optimizations to improve
           locality of reference in the instruction space.  Most systems using the ELF object
           format have linkers with such optimizations.  On AIX, the linker rearranges sections
           (CSECTs) based on the call graph.  The performance impact varies.

           Together with a linker garbage collection (linker --gc-sections option) these options
           may lead to smaller statically-linked executables (after stripping).

           On ELF/DWARF systems these options do not degenerate the quality of the debug
           information.  There could be issues with other object files/debug info formats.

           Only use these options when there are significant benefits from doing so.  When you
           specify these options, the assembler and linker create larger object and executable
           files and are also slower.  These options affect code generation.  They prevent
           optimizations by the compiler and assembler using relative locations inside a
           translation unit since the locations are unknown until link time.  An example of such
           an optimization is relaxing calls to short call instructions.

       -fbranch-target-load-optimize
           Perform branch target register load optimization before prologue / epilogue threading.
           The use of target registers can typically be exposed only during reload, thus hoisting
           loads out of loops and doing inter-block scheduling needs a separate optimization
           pass.

       -fbranch-target-load-optimize2
           Perform branch target register load optimization after prologue / epilogue threading.

       -fbtr-bb-exclusive
           When performing branch target register load optimization, don't reuse branch target
           registers within any basic block.

       -fstdarg-opt
           Optimize the prologue of variadic argument functions with respect to usage of those
           arguments.

           NOTE: In Ubuntu 14.10 and later versions, -fstack-protector-strong is enabled by
           default for C, C++, ObjC, ObjC++, if none of -fno-stack-protector, -nostdlib, nor
           -ffreestanding are found.

       -fsection-anchors
           Try to reduce the number of symbolic address calculations by using shared "anchor"
           symbols to address nearby objects.  This transformation can help to reduce the number
           of GOT entries and GOT accesses on some targets.

           For example, the implementation of the following function "foo":

                   static int a, b, c;
                   int foo (void) { return a + b + c; }

           usually calculates the addresses of all three variables, but if you compile it with
           -fsection-anchors, it accesses the variables from a common anchor point instead.  The
           effect is similar to the following pseudocode (which isn't valid C):

                   int foo (void)
                   {
                     register int *xr = &x;
                     return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
                   }

           Not all targets support this option.

       --param name=value
           In some places, GCC uses various constants to control the amount of optimization that
           is done.  For example, GCC does not inline functions that contain more than a certain
           number of instructions.  You can control some of these constants on the command line
           using the --param option.

           The names of specific parameters, and the meaning of the values, are tied to the
           internals of the compiler, and are subject to change without notice in future
           releases.

           In each case, the value is an integer.  The allowable choices for name are:

           predictable-branch-outcome
               When branch is predicted to be taken with probability lower than this threshold
               (in percent), then it is considered well predictable. The default is 10.

           max-rtl-if-conversion-insns
               RTL if-conversion tries to remove conditional branches around a block and replace
               them with conditionally executed instructions.  This parameter gives the maximum
               number of instructions in a block which should be considered for if-conversion.
               The default is 10, though the compiler will also use other heuristics to decide
               whether if-conversion is likely to be profitable.

           max-rtl-if-conversion-predictable-cost
           max-rtl-if-conversion-unpredictable-cost
               RTL if-conversion will try to remove conditional branches around a block and
               replace them with conditionally executed instructions.  These parameters give the
               maximum permissible cost for the sequence that would be generated by if-conversion
               depending on whether the branch is statically determined to be predictable or not.
               The units for this parameter are the same as those for the GCC internal seq_cost
               metric.  The compiler will try to provide a reasonable default for this parameter
               using the BRANCH_COST target macro.

           max-crossjump-edges
               The maximum number of incoming edges to consider for cross-jumping.  The algorithm
               used by -fcrossjumping is O(N^2) in the number of edges incoming to each block.
               Increasing values mean more aggressive optimization, making the compilation time
               increase with probably small improvement in executable size.

           min-crossjump-insns
               The minimum number of instructions that must be matched at the end of two blocks
               before cross-jumping is performed on them.  This value is ignored in the case
               where all instructions in the block being cross-jumped from are matched.  The
               default value is 5.

           max-grow-copy-bb-insns
               The maximum code size expansion factor when copying basic blocks instead of
               jumping.  The expansion is relative to a jump instruction.  The default value is
               8.

           max-goto-duplication-insns
               The maximum number of instructions to duplicate to a block that jumps to a
               computed goto.  To avoid O(N^2) behavior in a number of passes, GCC factors
               computed gotos early in the compilation process, and unfactors them as late as
               possible.  Only computed jumps at the end of a basic blocks with no more than max-
               goto-duplication-insns are unfactored.  The default value is 8.

           max-delay-slot-insn-search
               The maximum number of instructions to consider when looking for an instruction to
               fill a delay slot.  If more than this arbitrary number of instructions are
               searched, the time savings from filling the delay slot are minimal, so stop
               searching.  Increasing values mean more aggressive optimization, making the
               compilation time increase with probably small improvement in execution time.

           max-delay-slot-live-search
               When trying to fill delay slots, the maximum number of instructions to consider
               when searching for a block with valid live register information.  Increasing this
               arbitrarily chosen value means more aggressive optimization, increasing the
               compilation time.  This parameter should be removed when the delay slot code is
               rewritten to maintain the control-flow graph.

           max-gcse-memory
               The approximate maximum amount of memory that can be allocated in order to perform
               the global common subexpression elimination optimization.  If more memory than
               specified is required, the optimization is not done.

           max-gcse-insertion-ratio
               If the ratio of expression insertions to deletions is larger than this value for
               any expression, then RTL PRE inserts or removes the expression and thus leaves
               partially redundant computations in the instruction stream.  The default value is
               20.

           max-pending-list-length
               The maximum number of pending dependencies scheduling allows before flushing the
               current state and starting over.  Large functions with few branches or calls can
               create excessively large lists which needlessly consume memory and resources.

           max-modulo-backtrack-attempts
               The maximum number of backtrack attempts the scheduler should make when modulo
               scheduling a loop.  Larger values can exponentially increase compilation time.

           max-inline-insns-single
               Several parameters control the tree inliner used in GCC.  This number sets the
               maximum number of instructions (counted in GCC's internal representation) in a
               single function that the tree inliner considers for inlining.  This only affects
               functions declared inline and methods implemented in a class declaration (C++).
               The default value is 400.

           max-inline-insns-auto
               When you use -finline-functions (included in -O3), a lot of functions that would
               otherwise not be considered for inlining by the compiler are investigated.  To
               those functions, a different (more restrictive) limit compared to functions
               declared inline can be applied.  The default value is 30.

           inline-min-speedup
               When estimated performance improvement of caller + callee runtime exceeds this
               threshold (in percent), the function can be inlined regardless of the limit on
               --param max-inline-insns-single and --param max-inline-insns-auto.  The default
               value is 15.

           large-function-insns
               The limit specifying really large functions.  For functions larger than this limit
               after inlining, inlining is constrained by --param large-function-growth.  This
               parameter is useful primarily to avoid extreme compilation time caused by non-
               linear algorithms used by the back end.  The default value is 2700.

           large-function-growth
               Specifies maximal growth of large function caused by inlining in percents.  The
               default value is 100 which limits large function growth to 2.0 times the original
               size.

           large-unit-insns
               The limit specifying large translation unit.  Growth caused by inlining of units
               larger than this limit is limited by --param inline-unit-growth.  For small units
               this might be too tight.  For example, consider a unit consisting of function A
               that is inline and B that just calls A three times.  If B is small relative to A,
               the growth of unit is 300\% and yet such inlining is very sane.  For very large
               units consisting of small inlineable functions, however, the overall unit growth
               limit is needed to avoid exponential explosion of code size.  Thus for smaller
               units, the size is increased to --param large-unit-insns before applying --param
               inline-unit-growth.  The default is 10000.

           inline-unit-growth
               Specifies maximal overall growth of the compilation unit caused by inlining.  The
               default value is 20 which limits unit growth to 1.2 times the original size. Cold
               functions (either marked cold via an attribute or by profile feedback) are not
               accounted into the unit size.

           ipcp-unit-growth
               Specifies maximal overall growth of the compilation unit caused by interprocedural
               constant propagation.  The default value is 10 which limits unit growth to 1.1
               times the original size.

           large-stack-frame
               The limit specifying large stack frames.  While inlining the algorithm is trying
               to not grow past this limit too much.  The default value is 256 bytes.

           large-stack-frame-growth
               Specifies maximal growth of large stack frames caused by inlining in percents.
               The default value is 1000 which limits large stack frame growth to 11 times the
               original size.

           max-inline-insns-recursive
           max-inline-insns-recursive-auto
               Specifies the maximum number of instructions an out-of-line copy of a self-
               recursive inline function can grow into by performing recursive inlining.

               --param max-inline-insns-recursive applies to functions declared inline.  For
               functions not declared inline, recursive inlining happens only when
               -finline-functions (included in -O3) is enabled; --param max-inline-insns-
               recursive-auto applies instead.  The default value is 450.

           max-inline-recursive-depth
           max-inline-recursive-depth-auto
               Specifies the maximum recursion depth used for recursive inlining.

               --param max-inline-recursive-depth applies to functions declared inline.  For
               functions not declared inline, recursive inlining happens only when
               -finline-functions (included in -O3) is enabled; --param max-inline-recursive-
               depth-auto applies instead.  The default value is 8.

           min-inline-recursive-probability
               Recursive inlining is profitable only for function having deep recursion in
               average and can hurt for function having little recursion depth by increasing the
               prologue size or complexity of function body to other optimizers.

               When profile feedback is available (see -fprofile-generate) the actual recursion
               depth can be guessed from the probability that function recurses via a given call
               expression.  This parameter limits inlining only to call expressions whose
               probability exceeds the given threshold (in percents).  The default value is 10.

           early-inlining-insns
               Specify growth that the early inliner can make.  In effect it increases the amount
               of inlining for code having a large abstraction penalty.  The default value is 14.

           max-early-inliner-iterations
               Limit of iterations of the early inliner.  This basically bounds the number of
               nested indirect calls the early inliner can resolve.  Deeper chains are still
               handled by late inlining.

           comdat-sharing-probability
               Probability (in percent) that C++ inline function with comdat visibility are
               shared across multiple compilation units.  The default value is 20.

           profile-func-internal-id
               A parameter to control whether to use function internal id in profile database
               lookup. If the value is 0, the compiler uses an id that is based on function
               assembler name and filename, which makes old profile data more tolerant to source
               changes such as function reordering etc.  The default value is 0.

           min-vect-loop-bound
               The minimum number of iterations under which loops are not vectorized when
               -ftree-vectorize is used.  The number of iterations after vectorization needs to
               be greater than the value specified by this option to allow vectorization.  The
               default value is 0.

           gcse-cost-distance-ratio
               Scaling factor in calculation of maximum distance an expression can be moved by
               GCSE optimizations.  This is currently supported only in the code hoisting pass.
               The bigger the ratio, the more aggressive code hoisting is with simple
               expressions, i.e., the expressions that have cost less than gcse-unrestricted-
               cost.  Specifying 0 disables hoisting of simple expressions.  The default value is
               10.

           gcse-unrestricted-cost
               Cost, roughly measured as the cost of a single typical machine instruction, at
               which GCSE optimizations do not constrain the distance an expression can travel.
               This is currently supported only in the code hoisting pass.  The lesser the cost,
               the more aggressive code hoisting is.  Specifying 0 allows all expressions to
               travel unrestricted distances.  The default value is 3.

           max-hoist-depth
               The depth of search in the dominator tree for expressions to hoist.  This is used
               to avoid quadratic behavior in hoisting algorithm.  The value of 0 does not limit
               on the search, but may slow down compilation of huge functions.  The default value
               is 30.

           max-tail-merge-comparisons
               The maximum amount of similar bbs to compare a bb with.  This is used to avoid
               quadratic behavior in tree tail merging.  The default value is 10.

           max-tail-merge-iterations
               The maximum amount of iterations of the pass over the function.  This is used to
               limit compilation time in tree tail merging.  The default value is 2.

           store-merging-allow-unaligned
               Allow the store merging pass to introduce unaligned stores if it is legal to do
               so.  The default value is 1.

           max-stores-to-merge
               The maximum number of stores to attempt to merge into wider stores in the store
               merging pass.  The minimum value is 2 and the default is 64.

           max-unrolled-insns
               The maximum number of instructions that a loop may have to be unrolled.  If a loop
               is unrolled, this parameter also determines how many times the loop code is
               unrolled.

           max-average-unrolled-insns
               The maximum number of instructions biased by probabilities of their execution that
               a loop may have to be unrolled.  If a loop is unrolled, this parameter also
               determines how many times the loop code is unrolled.

           max-unroll-times
               The maximum number of unrollings of a single loop.

           max-peeled-insns
               The maximum number of instructions that a loop may have to be peeled.  If a loop
               is peeled, this parameter also determines how many times the loop code is peeled.

           max-peel-times
               The maximum number of peelings of a single loop.

           max-peel-branches
               The maximum number of branches on the hot path through the peeled sequence.

           max-completely-peeled-insns
               The maximum number of insns of a completely peeled loop.

           max-completely-peel-times
               The maximum number of iterations of a loop to be suitable for complete peeling.

           max-completely-peel-loop-nest-depth
               The maximum depth of a loop nest suitable for complete peeling.

           max-unswitch-insns
               The maximum number of insns of an unswitched loop.

           max-unswitch-level
               The maximum number of branches unswitched in a single loop.

           max-loop-headers-insns
               The maximum number of insns in loop header duplicated by the copy loop headers
               pass.

           lim-expensive
               The minimum cost of an expensive expression in the loop invariant motion.

           iv-consider-all-candidates-bound
               Bound on number of candidates for induction variables, below which all candidates
               are considered for each use in induction variable optimizations.  If there are
               more candidates than this, only the most relevant ones are considered to avoid
               quadratic time complexity.

           iv-max-considered-uses
               The induction variable optimizations give up on loops that contain more induction
               variable uses.

           iv-always-prune-cand-set-bound
               If the number of candidates in the set is smaller than this value, always try to
               remove unnecessary ivs from the set when adding a new one.

           avg-loop-niter
               Average number of iterations of a loop.

           dse-max-object-size
               Maximum size (in bytes) of objects tracked bytewise by dead store elimination.
               Larger values may result in larger compilation times.

           scev-max-expr-size
               Bound on size of expressions used in the scalar evolutions analyzer.  Large
               expressions slow the analyzer.

           scev-max-expr-complexity
               Bound on the complexity of the expressions in the scalar evolutions analyzer.
               Complex expressions slow the analyzer.

           max-tree-if-conversion-phi-args
               Maximum number of arguments in a PHI supported by TREE if conversion unless the
               loop is marked with simd pragma.

           vect-max-version-for-alignment-checks
               The maximum number of run-time checks that can be performed when doing loop
               versioning for alignment in the vectorizer.

           vect-max-version-for-alias-checks
               The maximum number of run-time checks that can be performed when doing loop
               versioning for alias in the vectorizer.

           vect-max-peeling-for-alignment
               The maximum number of loop peels to enhance access alignment for vectorizer. Value
               -1 means no limit.

           max-iterations-to-track
               The maximum number of iterations of a loop the brute-force algorithm for analysis
               of the number of iterations of the loop tries to evaluate.

           hot-bb-count-ws-permille
               A basic block profile count is considered hot if it contributes to the given
               permillage (i.e. 0...1000) of the entire profiled execution.

           hot-bb-frequency-fraction
               Select fraction of the entry block frequency of executions of basic block in
               function given basic block needs to have to be considered hot.

           max-predicted-iterations
               The maximum number of loop iterations we predict statically.  This is useful in
               cases where a function contains a single loop with known bound and another loop
               with unknown bound.  The known number of iterations is predicted correctly, while
               the unknown number of iterations average to roughly 10.  This means that the loop
               without bounds appears artificially cold relative to the other one.

           builtin-expect-probability
               Control the probability of the expression having the specified value. This
               parameter takes a percentage (i.e. 0 ... 100) as input.  The default probability
               of 90 is obtained empirically.

           align-threshold
               Select fraction of the maximal frequency of executions of a basic block in a
               function to align the basic block.

           align-loop-iterations
               A loop expected to iterate at least the selected number of iterations is aligned.

           tracer-dynamic-coverage
           tracer-dynamic-coverage-feedback
               This value is used to limit superblock formation once the given percentage of
               executed instructions is covered.  This limits unnecessary code size expansion.

               The tracer-dynamic-coverage-feedback parameter is used only when profile feedback
               is available.  The real profiles (as opposed to statically estimated ones) are
               much less balanced allowing the threshold to be larger value.

           tracer-max-code-growth
               Stop tail duplication once code growth has reached given percentage.  This is a
               rather artificial limit, as most of the duplicates are eliminated later in cross
               jumping, so it may be set to much higher values than is the desired code growth.

           tracer-min-branch-ratio
               Stop reverse growth when the reverse probability of best edge is less than this
               threshold (in percent).

           tracer-min-branch-probability
           tracer-min-branch-probability-feedback
               Stop forward growth if the best edge has probability lower than this threshold.

               Similarly to tracer-dynamic-coverage two parameters are provided.  tracer-min-
               branch-probability-feedback is used for compilation with profile feedback and
               tracer-min-branch-probability compilation without.  The value for compilation with
               profile feedback needs to be more conservative (higher) in order to make tracer
               effective.

           stack-clash-protection-guard-size
               Specify the size of the operating system provided stack guard as 2 raised to num
               bytes.  The default value is 12 (4096 bytes).  Acceptable values are between 12
               and 30.  Higher values may reduce the number of explicit probes, but a value
               larger than the operating system provided guard will leave code vulnerable to
               stack clash style attacks.

           stack-clash-protection-probe-interval
               Stack clash protection involves probing stack space as it is allocated.  This
               param controls the maximum distance between probes into the stack as 2 raised to
               num bytes.  Acceptable values are between 10 and 16 and defaults to 12.  Higher
               values may reduce the number of explicit probes, but a value larger than the
               operating system provided guard will leave code vulnerable to stack clash style
               attacks.

           max-cse-path-length
               The maximum number of basic blocks on path that CSE considers.  The default is 10.

           max-cse-insns
               The maximum number of instructions CSE processes before flushing.  The default is
               1000.

           ggc-min-expand
               GCC uses a garbage collector to manage its own memory allocation.  This parameter
               specifies the minimum percentage by which the garbage collector's heap should be
               allowed to expand between collections.  Tuning this may improve compilation speed;
               it has no effect on code generation.

               The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when RAM >= 1GB.
               If "getrlimit" is available, the notion of "RAM" is the smallest of actual RAM and
               "RLIMIT_DATA" or "RLIMIT_AS".  If GCC is not able to calculate RAM on a particular
               platform, the lower bound of 30% is used.  Setting this parameter and ggc-min-
               heapsize to zero causes a full collection to occur at every opportunity.  This is
               extremely slow, but can be useful for debugging.

           ggc-min-heapsize
               Minimum size of the garbage collector's heap before it begins bothering to collect
               garbage.  The first collection occurs after the heap expands by ggc-min-expand%
               beyond ggc-min-heapsize.  Again, tuning this may improve compilation speed, and
               has no effect on code generation.

               The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that tries to ensure
               that RLIMIT_DATA or RLIMIT_AS are not exceeded, but with a lower bound of 4096
               (four megabytes) and an upper bound of 131072 (128 megabytes).  If GCC is not able
               to calculate RAM on a particular platform, the lower bound is used.  Setting this
               parameter very large effectively disables garbage collection.  Setting this
               parameter and ggc-min-expand to zero causes a full collection to occur at every
               opportunity.

           max-reload-search-insns
               The maximum number of instruction reload should look backward for equivalent
               register.  Increasing values mean more aggressive optimization, making the
               compilation time increase with probably slightly better performance.  The default
               value is 100.

           max-cselib-memory-locations
               The maximum number of memory locations cselib should take into account.
               Increasing values mean more aggressive optimization, making the compilation time
               increase with probably slightly better performance.  The default value is 500.

           max-sched-ready-insns
               The maximum number of instructions ready to be issued the scheduler should
               consider at any given time during the first scheduling pass.  Increasing values
               mean more thorough searches, making the compilation time increase with probably
               little benefit.  The default value is 100.

           max-sched-region-blocks
               The maximum number of blocks in a region to be considered for interblock
               scheduling.  The default value is 10.

           max-pipeline-region-blocks
               The maximum number of blocks in a region to be considered for pipelining in the
               selective scheduler.  The default value is 15.

           max-sched-region-insns
               The maximum number of insns in a region to be considered for interblock
               scheduling.  The default value is 100.

           max-pipeline-region-insns
               The maximum number of insns in a region to be considered for pipelining in the
               selective scheduler.  The default value is 200.

           min-spec-prob
               The minimum probability (in percents) of reaching a source block for interblock
               speculative scheduling.  The default value is 40.

           max-sched-extend-regions-iters
               The maximum number of iterations through CFG to extend regions.  A value of 0 (the
               default) disables region extensions.

           max-sched-insn-conflict-delay
               The maximum conflict delay for an insn to be considered for speculative motion.
               The default value is 3.

           sched-spec-prob-cutoff
               The minimal probability of speculation success (in percents), so that speculative
               insns are scheduled.  The default value is 40.

           sched-state-edge-prob-cutoff
               The minimum probability an edge must have for the scheduler to save its state
               across it.  The default value is 10.

           sched-mem-true-dep-cost
               Minimal distance (in CPU cycles) between store and load targeting same memory
               locations.  The default value is 1.

           selsched-max-lookahead
               The maximum size of the lookahead window of selective scheduling.  It is a depth
               of search for available instructions.  The default value is 50.

           selsched-max-sched-times
               The maximum number of times that an instruction is scheduled during selective
               scheduling.  This is the limit on the number of iterations through which the
               instruction may be pipelined.  The default value is 2.

           selsched-insns-to-rename
               The maximum number of best instructions in the ready list that are considered for
               renaming in the selective scheduler.  The default value is 2.

           sms-min-sc
               The minimum value of stage count that swing modulo scheduler generates.  The
               default value is 2.

           max-last-value-rtl
               The maximum size measured as number of RTLs that can be recorded in an expression
               in combiner for a pseudo register as last known value of that register.  The
               default is 10000.

           max-combine-insns
               The maximum number of instructions the RTL combiner tries to combine.  The default
               value is 2 at -Og and 4 otherwise.

           integer-share-limit
               Small integer constants can use a shared data structure, reducing the compiler's
               memory usage and increasing its speed.  This sets the maximum value of a shared
               integer constant.  The default value is 256.

           ssp-buffer-size
               The minimum size of buffers (i.e. arrays) that receive stack smashing protection
               when -fstack-protection is used.

               This default before Ubuntu 10.10 was "8". Currently it is "4", to increase the
               number of functions protected by the stack protector.

           min-size-for-stack-sharing
               The minimum size of variables taking part in stack slot sharing when not
               optimizing. The default value is 32.

           max-jump-thread-duplication-stmts
               Maximum number of statements allowed in a block that needs to be duplicated when
               threading jumps.

           max-fields-for-field-sensitive
               Maximum number of fields in a structure treated in a field sensitive manner during
               pointer analysis.  The default is zero for -O0 and -O1, and 100 for -Os, -O2, and
               -O3.

           prefetch-latency
               Estimate on average number of instructions that are executed before prefetch
               finishes.  The distance prefetched ahead is proportional to this constant.
               Increasing this number may also lead to less streams being prefetched (see
               simultaneous-prefetches).

           simultaneous-prefetches
               Maximum number of prefetches that can run at the same time.

           l1-cache-line-size
               The size of cache line in L1 cache, in bytes.

           l1-cache-size
               The size of L1 cache, in kilobytes.

           l2-cache-size
               The size of L2 cache, in kilobytes.

           loop-interchange-max-num-stmts
               The maximum number of stmts in a loop to be interchanged.

           loop-interchange-stride-ratio
               The minimum ratio between stride of two loops for interchange to be profitable.

           min-insn-to-prefetch-ratio
               The minimum ratio between the number of instructions and the number of prefetches
               to enable prefetching in a loop.

           prefetch-min-insn-to-mem-ratio
               The minimum ratio between the number of instructions and the number of memory
               references to enable prefetching in a loop.

           use-canonical-types
               Whether the compiler should use the "canonical" type system.  By default, this
               should always be 1, which uses a more efficient internal mechanism for comparing
               types in C++ and Objective-C++.  However, if bugs in the canonical type system are
               causing compilation failures, set this value to 0 to disable canonical types.

           switch-conversion-max-branch-ratio
               Switch initialization conversion refuses to create arrays that are bigger than
               switch-conversion-max-branch-ratio times the number of branches in the switch.

           max-partial-antic-length
               Maximum length of the partial antic set computed during the tree partial
               redundancy elimination optimization (-ftree-pre) when optimizing at -O3 and above.
               For some sorts of source code the enhanced partial redundancy elimination
               optimization can run away, consuming all of the memory available on the host
               machine.  This parameter sets a limit on the length of the sets that are computed,
               which prevents the runaway behavior.  Setting a value of 0 for this parameter
               allows an unlimited set length.

           sccvn-max-scc-size
               Maximum size of a strongly connected component (SCC) during SCCVN processing.  If
               this limit is hit, SCCVN processing for the whole function is not done and
               optimizations depending on it are disabled.  The default maximum SCC size is
               10000.

           sccvn-max-alias-queries-per-access
               Maximum number of alias-oracle queries we perform when looking for redundancies
               for loads and stores.  If this limit is hit the search is aborted and the load or
               store is not considered redundant.  The number of queries is algorithmically
               limited to the number of stores on all paths from the load to the function entry.
               The default maximum number of queries is 1000.

           ira-max-loops-num
               IRA uses regional register allocation by default.  If a function contains more
               loops than the number given by this parameter, only at most the given number of
               the most frequently-executed loops form regions for regional register allocation.
               The default value of the parameter is 100.

           ira-max-conflict-table-size
               Although IRA uses a sophisticated algorithm to compress the conflict table, the
               table can still require excessive amounts of memory for huge functions.  If the
               conflict table for a function could be more than the size in MB given by this
               parameter, the register allocator instead uses a faster, simpler, and lower-
               quality algorithm that does not require building a pseudo-register conflict table.
               The default value of the parameter is 2000.

           ira-loop-reserved-regs
               IRA can be used to evaluate more accurate register pressure in loops for decisions
               to move loop invariants (see -O3).  The number of available registers reserved for
               some other purposes is given by this parameter.  The default value of the
               parameter is 2, which is the minimal number of registers needed by typical
               instructions.  This value is the best found from numerous experiments.

           lra-inheritance-ebb-probability-cutoff
               LRA tries to reuse values reloaded in registers in subsequent insns.  This
               optimization is called inheritance.  EBB is used as a region to do this
               optimization.  The parameter defines a minimal fall-through edge probability in
               percentage used to add BB to inheritance EBB in LRA.  The default value of the
               parameter is 40.  The value was chosen from numerous runs of SPEC2000 on x86-64.

           loop-invariant-max-bbs-in-loop
               Loop invariant motion can be very expensive, both in compilation time and in
               amount of needed compile-time memory, with very large loops.  Loops with more
               basic blocks than this parameter won't have loop invariant motion optimization
               performed on them.  The default value of the parameter is 1000 for -O1 and 10000
               for -O2 and above.

           loop-max-datarefs-for-datadeps
               Building data dependencies is expensive for very large loops.  This parameter
               limits the number of data references in loops that are considered for data
               dependence analysis.  These large loops are no handled by the optimizations using
               loop data dependencies.  The default value is 1000.

           max-vartrack-size
               Sets a maximum number of hash table slots to use during variable tracking dataflow
               analysis of any function.  If this limit is exceeded with variable tracking at
               assignments enabled, analysis for that function is retried without it, after
               removing all debug insns from the function.  If the limit is exceeded even without
               debug insns, var tracking analysis is completely disabled for the function.
               Setting the parameter to zero makes it unlimited.

           max-vartrack-expr-depth
               Sets a maximum number of recursion levels when attempting to map variable names or
               debug temporaries to value expressions.  This trades compilation time for more
               complete debug information.  If this is set too low, value expressions that are
               available and could be represented in debug information may end up not being used;
               setting this higher may enable the compiler to find more complex debug
               expressions, but compile time and memory use may grow.  The default is 12.

           max-debug-marker-count
               Sets a threshold on the number of debug markers (e.g. begin stmt markers) to avoid
               complexity explosion at inlining or expanding to RTL.  If a function has more such
               gimple stmts than the set limit, such stmts will be dropped from the inlined copy
               of a function, and from its RTL expansion.  The default is 100000.

           min-nondebug-insn-uid
               Use uids starting at this parameter for nondebug insns.  The range below the
               parameter is reserved exclusively for debug insns created by
               -fvar-tracking-assignments, but debug insns may get (non-overlapping) uids above
               it if the reserved range is exhausted.

           ipa-sra-ptr-growth-factor
               IPA-SRA replaces a pointer to an aggregate with one or more new parameters only
               when their cumulative size is less or equal to ipa-sra-ptr-growth-factor times the
               size of the original pointer parameter.

           sra-max-scalarization-size-Ospeed
           sra-max-scalarization-size-Osize
               The two Scalar Reduction of Aggregates passes (SRA and IPA-SRA) aim to replace
               scalar parts of aggregates with uses of independent scalar variables.  These
               parameters control the maximum size, in storage units, of aggregate which is
               considered for replacement when compiling for speed (sra-max-scalarization-size-
               Ospeed) or size (sra-max-scalarization-size-Osize) respectively.

           tm-max-aggregate-size
               When making copies of thread-local variables in a transaction, this parameter
               specifies the size in bytes after which variables are saved with the logging
               functions as opposed to save/restore code sequence pairs.  This option only
               applies when using -fgnu-tm.

           graphite-max-nb-scop-params
               To avoid exponential effects in the Graphite loop transforms, the number of
               parameters in a Static Control Part (SCoP) is bounded.  The default value is 10
               parameters, a value of zero can be used to lift the bound.  A variable whose value
               is unknown at compilation time and defined outside a SCoP is a parameter of the
               SCoP.

           loop-block-tile-size
               Loop blocking or strip mining transforms, enabled with -floop-block or
               -floop-strip-mine, strip mine each loop in the loop nest by a given number of
               iterations.  The strip length can be changed using the loop-block-tile-size
               parameter.  The default value is 51 iterations.

           loop-unroll-jam-size
               Specify the unroll factor for the -floop-unroll-and-jam option.  The default value
               is 4.

           loop-unroll-jam-depth
               Specify the dimension to be unrolled (counting from the most inner loop) for the
               -floop-unroll-and-jam.  The default value is 2.

           ipa-cp-value-list-size
               IPA-CP attempts to track all possible values and types passed to a function's
               parameter in order to propagate them and perform devirtualization.  ipa-cp-value-
               list-size is the maximum number of values and types it stores per one formal
               parameter of a function.

           ipa-cp-eval-threshold
               IPA-CP calculates its own score of cloning profitability heuristics and performs
               those cloning opportunities with scores that exceed ipa-cp-eval-threshold.

           ipa-cp-recursion-penalty
               Percentage penalty the recursive functions will receive when they are evaluated
               for cloning.

           ipa-cp-single-call-penalty
               Percentage penalty functions containing a single call to another function will
               receive when they are evaluated for cloning.

           ipa-max-agg-items
               IPA-CP is also capable to propagate a number of scalar values passed in an
               aggregate. ipa-max-agg-items controls the maximum number of such values per one
               parameter.

           ipa-cp-loop-hint-bonus
               When IPA-CP determines that a cloning candidate would make the number of
               iterations of a loop known, it adds a bonus of ipa-cp-loop-hint-bonus to the
               profitability score of the candidate.

           ipa-cp-array-index-hint-bonus
               When IPA-CP determines that a cloning candidate would make the index of an array
               access known, it adds a bonus of ipa-cp-array-index-hint-bonus to the
               profitability score of the candidate.

           ipa-max-aa-steps
               During its analysis of function bodies, IPA-CP employs alias analysis in order to
               track values pointed to by function parameters.  In order not spend too much time
               analyzing huge functions, it gives up and consider all memory clobbered after
               examining ipa-max-aa-steps statements modifying memory.

           lto-partitions
               Specify desired number of partitions produced during WHOPR compilation.  The
               number of partitions should exceed the number of CPUs used for compilation.  The
               default value is 32.

           lto-min-partition
               Size of minimal partition for WHOPR (in estimated instructions).  This prevents
               expenses of splitting very small programs into too many partitions.

           lto-max-partition
               Size of max partition for WHOPR (in estimated instructions).  to provide an upper
               bound for individual size of partition.  Meant to be used only with balanced
               partitioning.

           cxx-max-namespaces-for-diagnostic-help
               The maximum number of namespaces to consult for suggestions when C++ name lookup
               fails for an identifier.  The default is 1000.

           sink-frequency-threshold
               The maximum relative execution frequency (in percents) of the target block
               relative to a statement's original block to allow statement sinking of a
               statement.  Larger numbers result in more aggressive statement sinking.  The
               default value is 75.  A small positive adjustment is applied for statements with
               memory operands as those are even more profitable so sink.

           max-stores-to-sink
               The maximum number of conditional store pairs that can be sunk.  Set to 0 if
               either vectorization (-ftree-vectorize) or if-conversion (-ftree-loop-if-convert)
               is disabled.  The default is 2.

           allow-store-data-races
               Allow optimizers to introduce new data races on stores.  Set to 1 to allow,
               otherwise to 0.  This option is enabled by default at optimization level -Ofast.

           case-values-threshold
               The smallest number of different values for which it is best to use a jump-table
               instead of a tree of conditional branches.  If the value is 0, use the default for
               the machine.  The default is 0.

           tree-reassoc-width
               Set the maximum number of instructions executed in parallel in reassociated tree.
               This parameter overrides target dependent heuristics used by default if has non
               zero value.

           sched-pressure-algorithm
               Choose between the two available implementations of -fsched-pressure.  Algorithm 1
               is the original implementation and is the more likely to prevent instructions from
               being reordered.  Algorithm 2 was designed to be a compromise between the
               relatively conservative approach taken by algorithm 1 and the rather aggressive
               approach taken by the default scheduler.  It relies more heavily on having a
               regular register file and accurate register pressure classes.  See haifa-sched.c
               in the GCC sources for more details.

               The default choice depends on the target.

           max-slsr-cand-scan
               Set the maximum number of existing candidates that are considered when seeking a
               basis for a new straight-line strength reduction candidate.

           asan-globals
               Enable buffer overflow detection for global objects.  This kind of protection is
               enabled by default if you are using -fsanitize=address option.  To disable global
               objects protection use --param asan-globals=0.

           asan-stack
               Enable buffer overflow detection for stack objects.  This kind of protection is
               enabled by default when using -fsanitize=address.  To disable stack protection use
               --param asan-stack=0 option.

           asan-instrument-reads
               Enable buffer overflow detection for memory reads.  This kind of protection is
               enabled by default when using -fsanitize=address.  To disable memory reads
               protection use --param asan-instrument-reads=0.

           asan-instrument-writes
               Enable buffer overflow detection for memory writes.  This kind of protection is
               enabled by default when using -fsanitize=address.  To disable memory writes
               protection use --param asan-instrument-writes=0 option.

           asan-memintrin
               Enable detection for built-in functions.  This kind of protection is enabled by
               default when using -fsanitize=address.  To disable built-in functions protection
               use --param asan-memintrin=0.

           asan-use-after-return
               Enable detection of use-after-return.  This kind of protection is enabled by
               default when using the -fsanitize=address option.  To disable it use --param
               asan-use-after-return=0.

               Note: By default the check is disabled at run time.  To enable it, add
               "detect_stack_use_after_return=1" to the environment variable ASAN_OPTIONS.

           asan-instrumentation-with-call-threshold
               If number of memory accesses in function being instrumented is greater or equal to
               this number, use callbacks instead of inline checks.  E.g. to disable inline code
               use --param asan-instrumentation-with-call-threshold=0.

           use-after-scope-direct-emission-threshold
               If the size of a local variable in bytes is smaller or equal to this number,
               directly poison (or unpoison) shadow memory instead of using run-time callbacks.
               The default value is 256.

           chkp-max-ctor-size
               Static constructors generated by Pointer Bounds Checker may become very large and
               significantly increase compile time at optimization level -O1 and higher.  This
               parameter is a maximum number of statements in a single generated constructor.
               Default value is 5000.

           max-fsm-thread-path-insns
               Maximum number of instructions to copy when duplicating blocks on a finite state
               automaton jump thread path.  The default is 100.

           max-fsm-thread-length
               Maximum number of basic blocks on a finite state automaton jump thread path.  The
               default is 10.

           max-fsm-thread-paths
               Maximum number of new jump thread paths to create for a finite state automaton.
               The default is 50.

           parloops-chunk-size
               Chunk size of omp schedule for loops parallelized by parloops.  The default is 0.

           parloops-schedule
               Schedule type of omp schedule for loops parallelized by parloops (static, dynamic,
               guided, auto, runtime).  The default is static.

           parloops-min-per-thread
               The minimum number of iterations per thread of an innermost parallelized loop for
               which the parallelized variant is prefered over the single threaded one.  The
               default is 100.  Note that for a parallelized loop nest the minimum number of
               iterations of the outermost loop per thread is two.

           max-ssa-name-query-depth
               Maximum depth of recursion when querying properties of SSA names in things like
               fold routines.  One level of recursion corresponds to following a use-def chain.

           hsa-gen-debug-stores
               Enable emission of special debug stores within HSA kernels which are then read and
               reported by libgomp plugin.  Generation of these stores is disabled by default,
               use --param hsa-gen-debug-stores=1 to enable it.

           max-speculative-devirt-maydefs
               The maximum number of may-defs we analyze when looking for a must-def specifying
               the dynamic type of an object that invokes a virtual call we may be able to
               devirtualize speculatively.

           max-vrp-switch-assertions
               The maximum number of assertions to add along the default edge of a switch
               statement during VRP.  The default is 10.

           unroll-jam-min-percent
               The minimum percentage of memory references that must be optimized away for the
               unroll-and-jam transformation to be considered profitable.

           unroll-jam-max-unroll
               The maximum number of times the outer loop should be unrolled by the unroll-and-
               jam transformation.

   Program Instrumentation Options
       GCC supports a number of command-line options that control adding run-time instrumentation
       to the code it normally generates.  For example, one purpose of instrumentation is collect
       profiling statistics for use in finding program hot spots, code coverage analysis, or
       profile-guided optimizations.  Another class of program instrumentation is adding run-time
       checking to detect programming errors like invalid pointer dereferences or out-of-bounds
       array accesses, as well as deliberately hostile attacks such as stack smashing or C++
       vtable hijacking.  There is also a general hook which can be used to implement other forms
       of tracing or function-level instrumentation for debug or program analysis purposes.

       -p  Generate extra code to write profile information suitable for the analysis program
           prof.  You must use this option when compiling the source files you want data about,
           and you must also use it when linking.

       -pg Generate extra code to write profile information suitable for the analysis program
           gprof.  You must use this option when compiling the source files you want data about,
           and you must also use it when linking.

       -fprofile-arcs
           Add code so that program flow arcs are instrumented.  During execution the program
           records how many times each branch and call is executed and how many times it is taken
           or returns.  On targets that support constructors with priority support, profiling
           properly handles constructors, destructors and C++ constructors (and destructors) of
           classes which are used as a type of a global variable.

           When the compiled program exits it saves this data to a file called auxname.gcda for
           each source file.  The data may be used for profile-directed optimizations
           (-fbranch-probabilities), or for test coverage analysis (-ftest-coverage).  Each
           object file's auxname is generated from the name of the output file, if explicitly
           specified and it is not the final executable, otherwise it is the basename of the
           source file.  In both cases any suffix is removed (e.g. foo.gcda for input file
           dir/foo.c, or dir/foo.gcda for output file specified as -o dir/foo.o).

       --coverage
           This option is used to compile and link code instrumented for coverage analysis.  The
           option is a synonym for -fprofile-arcs -ftest-coverage (when compiling) and -lgcov
           (when linking).  See the documentation for those options for more details.

           *   Compile the source files with -fprofile-arcs plus optimization and code generation
               options.  For test coverage analysis, use the additional -ftest-coverage option.
               You do not need to profile every source file in a program.

           *   Compile the source files additionally with -fprofile-abs-path to create absolute
               path names in the .gcno files.  This allows gcov to find the correct sources in
               projects where compilations occur with different working directories.

           *   Link your object files with -lgcov or -fprofile-arcs (the latter implies the
               former).

           *   Run the program on a representative workload to generate the arc profile
               information.  This may be repeated any number of times.  You can run concurrent
               instances of your program, and provided that the file system supports locking, the
               data files will be correctly updated.  Unless a strict ISO C dialect option is in
               effect, "fork" calls are detected and correctly handled without double counting.

           *   For profile-directed optimizations, compile the source files again with the same
               optimization and code generation options plus -fbranch-probabilities.

           *   For test coverage analysis, use gcov to produce human readable information from
               the .gcno and .gcda files.  Refer to the gcov documentation for further
               information.

           With -fprofile-arcs, for each function of your program GCC creates a program flow
           graph, then finds a spanning tree for the graph.  Only arcs that are not on the
           spanning tree have to be instrumented: the compiler adds code to count the number of
           times that these arcs are executed.  When an arc is the only exit or only entrance to
           a block, the instrumentation code can be added to the block; otherwise, a new basic
           block must be created to hold the instrumentation code.

       -ftest-coverage
           Produce a notes file that the gcov code-coverage utility can use to show program
           coverage.  Each source file's note file is called auxname.gcno.  Refer to the
           -fprofile-arcs option above for a description of auxname and instructions on how to
           generate test coverage data.  Coverage data matches the source files more closely if
           you do not optimize.

       -fprofile-abs-path
           Automatically convert relative source file names to absolute path names in the .gcno
           files.  This allows gcov to find the correct sources in projects where compilations
           occur with different working directories.

       -fprofile-dir=path
           Set the directory to search for the profile data files in to path.  This option
           affects only the profile data generated by -fprofile-generate, -ftest-coverage,
           -fprofile-arcs and used by -fprofile-use and -fbranch-probabilities and its related
           options.  Both absolute and relative paths can be used.  By default, GCC uses the
           current directory as path, thus the profile data file appears in the same directory as
           the object file.

       -fprofile-generate
       -fprofile-generate=path
           Enable options usually used for instrumenting application to produce profile useful
           for later recompilation with profile feedback based optimization.  You must use
           -fprofile-generate both when compiling and when linking your program.

           The following options are enabled: -fprofile-arcs, -fprofile-values, -fvpt.

           If path is specified, GCC looks at the path to find the profile feedback data files.
           See -fprofile-dir.

           To optimize the program based on the collected profile information, use -fprofile-use.

       -fprofile-update=method
           Alter the update method for an application instrumented for profile feedback based
           optimization.  The method argument should be one of single, atomic or prefer-atomic.
           The first one is useful for single-threaded applications, while the second one
           prevents profile corruption by emitting thread-safe code.

           Warning: When an application does not properly join all threads (or creates an
           detached thread), a profile file can be still corrupted.

           Using prefer-atomic would be transformed either to atomic, when supported by a target,
           or to single otherwise.  The GCC driver automatically selects prefer-atomic when
           -pthread is present in the command line.

       -fsanitize=address
           Enable AddressSanitizer, a fast memory error detector.  Memory access instructions are
           instrumented to detect out-of-bounds and use-after-free bugs.  The option enables
           -fsanitize-address-use-after-scope.  See
           <https://github.com/google/sanitizers/wiki/AddressSanitizer> for more details.  The
           run-time behavior can be influenced using the ASAN_OPTIONS environment variable.  When
           set to "help=1", the available options are shown at startup of the instrumented
           program.  See
           <https://github.com/google/sanitizers/wiki/AddressSanitizerFlags#run-time-flags> for a
           list of supported options.  The option cannot be combined with -fsanitize=thread
           and/or -fcheck-pointer-bounds.

       -fsanitize=kernel-address
           Enable AddressSanitizer for Linux kernel.  See <https://github.com/google/kasan/wiki>
           for more details.  The option cannot be combined with -fcheck-pointer-bounds.

       -fsanitize=pointer-compare
           Instrument comparison operation (<, <=, >, >=) with pointer operands.  The option must
           be combined with either -fsanitize=kernel-address or -fsanitize=address The option
           cannot be combined with -fsanitize=thread and/or -fcheck-pointer-bounds.  Note: By
           default the check is disabled at run time.  To enable it, add
           "detect_invalid_pointer_pairs=2" to the environment variable ASAN_OPTIONS. Using
           "detect_invalid_pointer_pairs=1" detects invalid operation only when both pointers are
           non-null.

       -fsanitize=pointer-subtract
           Instrument subtraction with pointer operands.  The option must be combined with either
           -fsanitize=kernel-address or -fsanitize=address The option cannot be combined with
           -fsanitize=thread and/or -fcheck-pointer-bounds.  Note: By default the check is
           disabled at run time.  To enable it, add "detect_invalid_pointer_pairs=2" to the
           environment variable ASAN_OPTIONS. Using "detect_invalid_pointer_pairs=1" detects
           invalid operation only when both pointers are non-null.

       -fsanitize=thread
           Enable ThreadSanitizer, a fast data race detector.  Memory access instructions are
           instrumented to detect data race bugs.  See
           <https://github.com/google/sanitizers/wiki#threadsanitizer> for more details. The run-
           time behavior can be influenced using the TSAN_OPTIONS environment variable; see
           <https://github.com/google/sanitizers/wiki/ThreadSanitizerFlags> for a list of
           supported options.  The option cannot be combined with -fsanitize=address,
           -fsanitize=leak and/or -fcheck-pointer-bounds.

           Note that sanitized atomic builtins cannot throw exceptions when operating on invalid
           memory addresses with non-call exceptions (-fnon-call-exceptions).

       -fsanitize=leak
           Enable LeakSanitizer, a memory leak detector.  This option only matters for linking of
           executables and the executable is linked against a library that overrides "malloc" and
           other allocator functions.  See
           <https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer> for more
           details.  The run-time behavior can be influenced using the LSAN_OPTIONS environment
           variable.  The option cannot be combined with -fsanitize=thread.

       -fsanitize=undefined
           Enable UndefinedBehaviorSanitizer, a fast undefined behavior detector.  Various
           computations are instrumented to detect undefined behavior at runtime.  Current
           suboptions are:

           -fsanitize=shift
               This option enables checking that the result of a shift operation is not
               undefined.  Note that what exactly is considered undefined differs slightly
               between C and C++, as well as between ISO C90 and C99, etc.  This option has two
               suboptions, -fsanitize=shift-base and -fsanitize=shift-exponent.

           -fsanitize=shift-exponent
               This option enables checking that the second argument of a shift operation is not
               negative and is smaller than the precision of the promoted first argument.

           -fsanitize=shift-base
               If the second argument of a shift operation is within range, check that the result
               of a shift operation is not undefined.  Note that what exactly is considered
               undefined differs slightly between C and C++, as well as between ISO C90 and C99,
               etc.

           -fsanitize=integer-divide-by-zero
               Detect integer division by zero as well as "INT_MIN / -1" division.

           -fsanitize=unreachable
               With this option, the compiler turns the "__builtin_unreachable" call into a
               diagnostics message call instead.  When reaching the "__builtin_unreachable" call,
               the behavior is undefined.

           -fsanitize=vla-bound
               This option instructs the compiler to check that the size of a variable length
               array is positive.

           -fsanitize=null
               This option enables pointer checking.  Particularly, the application built with
               this option turned on will issue an error message when it tries to dereference a
               NULL pointer, or if a reference (possibly an rvalue reference) is bound to a NULL
               pointer, or if a method is invoked on an object pointed by a NULL pointer.

           -fsanitize=return
               This option enables return statement checking.  Programs built with this option
               turned on will issue an error message when the end of a non-void function is
               reached without actually returning a value.  This option works in C++ only.

           -fsanitize=signed-integer-overflow
               This option enables signed integer overflow checking.  We check that the result of
               "+", "*", and both unary and binary "-" does not overflow in the signed
               arithmetics.  Note, integer promotion rules must be taken into account.  That is,
               the following is not an overflow:

                       signed char a = SCHAR_MAX;
                       a++;

           -fsanitize=bounds
               This option enables instrumentation of array bounds.  Various out of bounds
               accesses are detected.  Flexible array members, flexible array member-like arrays,
               and initializers of variables with static storage are not instrumented.  The
               option cannot be combined with -fcheck-pointer-bounds.

           -fsanitize=bounds-strict
               This option enables strict instrumentation of array bounds.  Most out of bounds
               accesses are detected, including flexible array members and flexible array member-
               like arrays.  Initializers of variables with static storage are not instrumented.
               The option cannot be combined with -fcheck-pointer-bounds.

           -fsanitize=alignment
               This option enables checking of alignment of pointers when they are dereferenced,
               or when a reference is bound to insufficiently aligned target, or when a method or
               constructor is invoked on insufficiently aligned object.

           -fsanitize=object-size
               This option enables instrumentation of memory references using the
               "__builtin_object_size" function.  Various out of bounds pointer accesses are
               detected.

           -fsanitize=float-divide-by-zero
               Detect floating-point division by zero.  Unlike other similar options,
               -fsanitize=float-divide-by-zero is not enabled by -fsanitize=undefined, since
               floating-point division by zero can be a legitimate way of obtaining infinities
               and NaNs.

           -fsanitize=float-cast-overflow
               This option enables floating-point type to integer conversion checking.  We check
               that the result of the conversion does not overflow.  Unlike other similar
               options, -fsanitize=float-cast-overflow is not enabled by -fsanitize=undefined.
               This option does not work well with "FE_INVALID" exceptions enabled.

           -fsanitize=nonnull-attribute
               This option enables instrumentation of calls, checking whether null values are not
               passed to arguments marked as requiring a non-null value by the "nonnull" function
               attribute.

           -fsanitize=returns-nonnull-attribute
               This option enables instrumentation of return statements in functions marked with
               "returns_nonnull" function attribute, to detect returning of null values from such
               functions.

           -fsanitize=bool
               This option enables instrumentation of loads from bool.  If a value other than 0/1
               is loaded, a run-time error is issued.

           -fsanitize=enum
               This option enables instrumentation of loads from an enum type.  If a value
               outside the range of values for the enum type is loaded, a run-time error is
               issued.

           -fsanitize=vptr
               This option enables instrumentation of C++ member function calls, member accesses
               and some conversions between pointers to base and derived classes, to verify the
               referenced object has the correct dynamic type.

           -fsanitize=pointer-overflow
               This option enables instrumentation of pointer arithmetics.  If the pointer
               arithmetics overflows, a run-time error is issued.

           -fsanitize=builtin
               This option enables instrumentation of arguments to selected builtin functions.
               If an invalid value is passed to such arguments, a run-time error is issued.  E.g.
               passing 0 as the argument to "__builtin_ctz" or "__builtin_clz" invokes undefined
               behavior and is diagnosed by this option.

           While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined
           gives a diagnostic message.  This currently works only for the C family of languages.

       -fno-sanitize=all
           This option disables all previously enabled sanitizers.  -fsanitize=all is not
           allowed, as some sanitizers cannot be used together.

       -fasan-shadow-offset=number
           This option forces GCC to use custom shadow offset in AddressSanitizer checks.  It is
           useful for experimenting with different shadow memory layouts in Kernel
           AddressSanitizer.

       -fsanitize-sections=s1,s2,...
           Sanitize global variables in selected user-defined sections.  si may contain
           wildcards.

       -fsanitize-recover[=opts]
           -fsanitize-recover= controls error recovery mode for sanitizers mentioned in comma-
           separated list of opts.  Enabling this option for a sanitizer component causes it to
           attempt to continue running the program as if no error happened.  This means multiple
           runtime errors can be reported in a single program run, and the exit code of the
           program may indicate success even when errors have been reported.  The
           -fno-sanitize-recover= option can be used to alter this behavior: only the first
           detected error is reported and program then exits with a non-zero exit code.

           Currently this feature only works for -fsanitize=undefined (and its suboptions except
           for -fsanitize=unreachable and -fsanitize=return), -fsanitize=float-cast-overflow,
           -fsanitize=float-divide-by-zero, -fsanitize=bounds-strict, -fsanitize=kernel-address
           and -fsanitize=address.  For these sanitizers error recovery is turned on by default,
           except -fsanitize=address, for which this feature is experimental.
           -fsanitize-recover=all and -fno-sanitize-recover=all is also accepted, the former
           enables recovery for all sanitizers that support it, the latter disables recovery for
           all sanitizers that support it.

           Even if a recovery mode is turned on the compiler side, it needs to be also enabled on
           the runtime library side, otherwise the failures are still fatal.  The runtime library
           defaults to "halt_on_error=0" for ThreadSanitizer and UndefinedBehaviorSanitizer,
           while default value for AddressSanitizer is "halt_on_error=1". This can be overridden
           through setting the "halt_on_error" flag in the corresponding environment variable.

           Syntax without an explicit opts parameter is deprecated.  It is equivalent to
           specifying an opts list of:

                   undefined,float-cast-overflow,float-divide-by-zero,bounds-strict

       -fsanitize-address-use-after-scope
           Enable sanitization of local variables to detect use-after-scope bugs.  The option
           sets -fstack-reuse to none.

       -fsanitize-undefined-trap-on-error
           The -fsanitize-undefined-trap-on-error option instructs the compiler to report
           undefined behavior using "__builtin_trap" rather than a "libubsan" library routine.
           The advantage of this is that the "libubsan" library is not needed and is not linked
           in, so this is usable even in freestanding environments.

       -fsanitize-coverage=trace-pc
           Enable coverage-guided fuzzing code instrumentation.  Inserts a call to
           "__sanitizer_cov_trace_pc" into every basic block.

       -fsanitize-coverage=trace-cmp
           Enable dataflow guided fuzzing code instrumentation.  Inserts a call to
           "__sanitizer_cov_trace_cmp1", "__sanitizer_cov_trace_cmp2",
           "__sanitizer_cov_trace_cmp4" or "__sanitizer_cov_trace_cmp8" for integral comparison
           with both operands variable or "__sanitizer_cov_trace_const_cmp1",
           "__sanitizer_cov_trace_const_cmp2", "__sanitizer_cov_trace_const_cmp4" or
           "__sanitizer_cov_trace_const_cmp8" for integral comparison with one operand constant,
           "__sanitizer_cov_trace_cmpf" or "__sanitizer_cov_trace_cmpd" for float or double
           comparisons and "__sanitizer_cov_trace_switch" for switch statements.

       -fbounds-check
           For front ends that support it, generate additional code to check that indices used to
           access arrays are within the declared range.  This is currently only supported by the
           Fortran front end, where this option defaults to false.

       -fcheck-pointer-bounds
           Enable Pointer Bounds Checker instrumentation.  Each memory reference is instrumented
           with checks of the pointer used for memory access against bounds associated with that
           pointer.

           Currently there is only an implementation for Intel MPX available, thus x86 GNU/Linux
           target and -mmpx are required to enable this feature.  MPX-based instrumentation
           requires a runtime library to enable MPX in hardware and handle bounds violation
           signals.  By default when -fcheck-pointer-bounds and -mmpx options are used to link a
           program, the GCC driver links against the libmpx and libmpxwrappers libraries.  Bounds
           checking on calls to dynamic libraries requires a linker with -z bndplt support; if
           GCC was configured with a linker without support for this option (including the Gold
           linker and older versions of ld), a warning is given if you link with -mmpx without
           also specifying -static, since the overall effectiveness of the bounds checking
           protection is reduced.  See also -static-libmpxwrappers.

           MPX-based instrumentation may be used for debugging and also may be included in
           production code to increase program security.  Depending on usage, you may have
           different requirements for the runtime library.  The current version of the MPX
           runtime library is more oriented for use as a debugging tool.  MPX runtime library
           usage implies -lpthread.  See also -static-libmpx.  The runtime library  behavior can
           be influenced using various CHKP_RT_* environment variables.  See
           <https://gcc.gnu.org/wiki/Intel%20MPX%20support%20in%20the%20GCC%20compiler> for more
           details.

           Generated instrumentation may be controlled by various -fchkp-* options and by the
           "bnd_variable_size" structure field attribute and "bnd_legacy", and "bnd_instrument"
           function attributes.  GCC also provides a number of built-in functions for controlling
           the Pointer Bounds Checker.

       -fchkp-check-incomplete-type
           Generate pointer bounds checks for variables with incomplete type.  Enabled by
           default.

       -fchkp-narrow-bounds
           Controls bounds used by Pointer Bounds Checker for pointers to object fields.  If
           narrowing is enabled then field bounds are used.  Otherwise object bounds are used.
           See also -fchkp-narrow-to-innermost-array and -fchkp-first-field-has-own-bounds.
           Enabled by default.

       -fchkp-first-field-has-own-bounds
           Forces Pointer Bounds Checker to use narrowed bounds for the address of the first
           field in the structure.  By default a pointer to the first field has the same bounds
           as a pointer to the whole structure.

       -fchkp-flexible-struct-trailing-arrays
           Forces Pointer Bounds Checker to treat all trailing arrays in structures as possibly
           flexible.  By default only array fields with zero length or that are marked with
           attribute bnd_variable_size are treated as flexible.

       -fchkp-narrow-to-innermost-array
           Forces Pointer Bounds Checker to use bounds of the innermost arrays in case of nested
           static array access.  By default this option is disabled and bounds of the outermost
           array are used.

       -fchkp-optimize
           Enables Pointer Bounds Checker optimizations.  Enabled by default at optimization
           levels -O, -O2, -O3.

       -fchkp-use-fast-string-functions
           Enables use of *_nobnd versions of string functions (not copying bounds) by Pointer
           Bounds Checker.  Disabled by default.

       -fchkp-use-nochk-string-functions
           Enables use of *_nochk versions of string functions (not checking bounds) by Pointer
           Bounds Checker.  Disabled by default.

       -fchkp-use-static-bounds
           Allow Pointer Bounds Checker to generate static bounds holding bounds of static
           variables.  Enabled by default.

       -fchkp-use-static-const-bounds
           Use statically-initialized bounds for constant bounds instead of generating them each
           time they are required.  By default enabled when -fchkp-use-static-bounds is enabled.

       -fchkp-treat-zero-dynamic-size-as-infinite
           With this option, objects with incomplete type whose dynamically-obtained size is zero
           are treated as having infinite size instead by Pointer Bounds Checker.  This option
           may be helpful if a program is linked with a library missing size information for some
           symbols.  Disabled by default.

       -fchkp-check-read
           Instructs Pointer Bounds Checker to generate checks for all read accesses to memory.
           Enabled by default.

       -fchkp-check-write
           Instructs Pointer Bounds Checker to generate checks for all write accesses to memory.
           Enabled by default.

       -fchkp-store-bounds
           Instructs Pointer Bounds Checker to generate bounds stores for pointer writes.
           Enabled by default.

       -fchkp-instrument-calls
           Instructs Pointer Bounds Checker to pass pointer bounds to calls.  Enabled by default.

       -fchkp-instrument-marked-only
           Instructs Pointer Bounds Checker to instrument only functions marked with the
           "bnd_instrument" attribute.  Disabled by default.

       -fchkp-use-wrappers
           Allows Pointer Bounds Checker to replace calls to built-in functions with calls to
           wrapper functions.  When -fchkp-use-wrappers is used to link a program, the GCC driver
           automatically links against libmpxwrappers.  See also -static-libmpxwrappers.  Enabled
           by default.

       -fcf-protection=[full|branch|return|none]
           Enable code instrumentation of control-flow transfers to increase program security by
           checking that target addresses of control-flow transfer instructions (such as indirect
           function call, function return, indirect jump) are valid.  This prevents diverting the
           flow of control to an unexpected target.  This is intended to protect against such
           threats as Return-oriented Programming (ROP), and similarly call/jmp-oriented
           programming (COP/JOP).

           The value "branch" tells the compiler to implement checking of validity of control-
           flow transfer at the point of indirect branch instructions, i.e. call/jmp
           instructions.  The value "return" implements checking of validity at the point of
           returning from a function.  The value "full" is an alias for specifying both "branch"
           and "return". The value "none" turns off instrumentation.

           The macro "__CET__" is defined when -fcf-protection is used.  The first bit of
           "__CET__" is set to 1 for the value "branch" and the second bit of "__CET__" is set to
           1 for the "return".

           You can also use the "nocf_check" attribute to identify which functions and calls
           should be skipped from instrumentation.

           Currently the x86 GNU/Linux target provides an implementation based on Intel Control-
           flow Enforcement Technology (CET).

           NOTE: In Ubuntu 19.10 and later versions, -fcf-protection is enabled by default for C,
           C++, ObjC, ObjC++, if none of -fno-cf-protection nor -fcf-protection=* are found.

       -fstack-protector
           Emit extra code to check for buffer overflows, such as stack smashing attacks.  This
           is done by adding a guard variable to functions with vulnerable objects.  This
           includes functions that call "alloca", and functions with buffers larger than 8 bytes.
           The guards are initialized when a function is entered and then checked when the
           function exits.  If a guard check fails, an error message is printed and the program
           exits.

       -fstack-protector-all
           Like -fstack-protector except that all functions are protected.

       -fstack-protector-strong
           Like -fstack-protector but includes additional functions to be protected --- those
           that have local array definitions, or have references to local frame addresses.

       -fstack-protector-explicit
           Like -fstack-protector but only protects those functions which have the
           "stack_protect" attribute.

       -fstack-check
           Generate code to verify that you do not go beyond the boundary of the stack.  You
           should specify this flag if you are running in an environment with multiple threads,
           but you only rarely need to specify it in a single-threaded environment since stack
           overflow is automatically detected on nearly all systems if there is only one stack.

           Note that this switch does not actually cause checking to be done; the operating
           system or the language runtime must do that.  The switch causes generation of code to
           ensure that they see the stack being extended.

           You can additionally specify a string parameter: no means no checking, generic means
           force the use of old-style checking, specific means use the best checking method and
           is equivalent to bare -fstack-check.

           Old-style checking is a generic mechanism that requires no specific target support in
           the compiler but comes with the following drawbacks:

           1.  Modified allocation strategy for large objects: they are always allocated
               dynamically if their size exceeds a fixed threshold.  Note this may change the
               semantics of some code.

           2.  Fixed limit on the size of the static frame of functions: when it is topped by a
               particular function, stack checking is not reliable and a warning is issued by the
               compiler.

           3.  Inefficiency: because of both the modified allocation strategy and the generic
               implementation, code performance is hampered.

           Note that old-style stack checking is also the fallback method for specific if no
           target support has been added in the compiler.

           -fstack-check= is designed for Ada's needs to detect infinite recursion and stack
           overflows.  specific is an excellent choice when compiling Ada code.  It is not
           generally sufficient to protect against stack-clash attacks.  To protect against those
           you want -fstack-clash-protection.

       -fstack-clash-protection
           Generate code to prevent stack clash style attacks.  When this option is enabled, the
           compiler will only allocate one page of stack space at a time and each page is
           accessed immediately after allocation.  Thus, it prevents allocations from jumping
           over any stack guard page provided by the operating system.

           Most targets do not fully support stack clash protection.  However, on those targets
           -fstack-clash-protection will protect dynamic stack allocations.
           -fstack-clash-protection may also provide limited protection for static stack
           allocations if the target supports -fstack-check=specific.

           NOTE: In Ubuntu 19.10 and later versions, -fstack-clash-protection is enabled by
           default for C, C++, ObjC, ObjC++, unless -fno-stack-clash-protection is found.

       -fstack-limit-register=reg
       -fstack-limit-symbol=sym
       -fno-stack-limit
           Generate code to ensure that the stack does not grow beyond a certain value, either
           the value of a register or the address of a symbol.  If a larger stack is required, a
           signal is raised at run time.  For most targets, the signal is raised before the stack
           overruns the boundary, so it is possible to catch the signal without taking special
           precautions.

           For instance, if the stack starts at absolute address 0x80000000 and grows downwards,
           you can use the flags -fstack-limit-symbol=__stack_limit and
           -Wl,--defsym,__stack_limit=0x7ffe0000 to enforce a stack limit of 128KB.  Note that
           this may only work with the GNU linker.

           You can locally override stack limit checking by using the "no_stack_limit" function
           attribute.

       -fsplit-stack
           Generate code to automatically split the stack before it overflows.  The resulting
           program has a discontiguous stack which can only overflow if the program is unable to
           allocate any more memory.  This is most useful when running threaded programs, as it
           is no longer necessary to calculate a good stack size to use for each thread.  This is
           currently only implemented for the x86 targets running GNU/Linux.

           When code compiled with -fsplit-stack calls code compiled without -fsplit-stack, there
           may not be much stack space available for the latter code to run.  If compiling all
           code, including library code, with -fsplit-stack is not an option, then the linker can
           fix up these calls so that the code compiled without -fsplit-stack always has a large
           stack.  Support for this is implemented in the gold linker in GNU binutils release
           2.21 and later.

       -fvtable-verify=[std|preinit|none]
           This option is only available when compiling C++ code.  It turns on (or off, if using
           -fvtable-verify=none) the security feature that verifies at run time, for every
           virtual call, that the vtable pointer through which the call is made is valid for the
           type of the object, and has not been corrupted or overwritten.  If an invalid vtable
           pointer is detected at run time, an error is reported and execution of the program is
           immediately halted.

           This option causes run-time data structures to be built at program startup, which are
           used for verifying the vtable pointers.  The options std and preinit control the
           timing of when these data structures are built.  In both cases the data structures are
           built before execution reaches "main".  Using -fvtable-verify=std causes the data
           structures to be built after shared libraries have been loaded and initialized.
           -fvtable-verify=preinit causes them to be built before shared libraries have been
           loaded and initialized.

           If this option appears multiple times in the command line with different values
           specified, none takes highest priority over both std and preinit; preinit takes
           priority over std.

       -fvtv-debug
           When used in conjunction with -fvtable-verify=std or -fvtable-verify=preinit, causes
           debug versions of the runtime functions for the vtable verification feature to be
           called.  This flag also causes the compiler to log information about which vtable
           pointers it finds for each class.  This information is written to a file named
           vtv_set_ptr_data.log in the directory named by the environment variable VTV_LOGS_DIR
           if that is defined or the current working directory otherwise.

           Note:  This feature appends data to the log file. If you want a fresh log file, be
           sure to delete any existing one.

       -fvtv-counts
           This is a debugging flag.  When used in conjunction with -fvtable-verify=std or
           -fvtable-verify=preinit, this causes the compiler to keep track of the total number of
           virtual calls it encounters and the number of verifications it inserts.  It also
           counts the number of calls to certain run-time library functions that it inserts and
           logs this information for each compilation unit.  The compiler writes this information
           to a file named vtv_count_data.log in the directory named by the environment variable
           VTV_LOGS_DIR if that is defined or the current working directory otherwise.  It also
           counts the size of the vtable pointer sets for each class, and writes this information
           to vtv_class_set_sizes.log in the same directory.

           Note:  This feature appends data to the log files.  To get fresh log files, be sure to
           delete any existing ones.

       -finstrument-functions
           Generate instrumentation calls for entry and exit to functions.  Just after function
           entry and just before function exit, the following profiling functions are called with
           the address of the current function and its call site.  (On some platforms,
           "__builtin_return_address" does not work beyond the current function, so the call site
           information may not be available to the profiling functions otherwise.)

                   void __cyg_profile_func_enter (void *this_fn,
                                                  void *call_site);
                   void __cyg_profile_func_exit  (void *this_fn,
                                                  void *call_site);

           The first argument is the address of the start of the current function, which may be
           looked up exactly in the symbol table.

           This instrumentation is also done for functions expanded inline in other functions.
           The profiling calls indicate where, conceptually, the inline function is entered and
           exited.  This means that addressable versions of such functions must be available.  If
           all your uses of a function are expanded inline, this may mean an additional expansion
           of code size.  If you use "extern inline" in your C code, an addressable version of
           such functions must be provided.  (This is normally the case anyway, but if you get
           lucky and the optimizer always expands the functions inline, you might have gotten
           away without providing static copies.)

           A function may be given the attribute "no_instrument_function", in which case this
           instrumentation is not done.  This can be used, for example, for the profiling
           functions listed above, high-priority interrupt routines, and any functions from which
           the profiling functions cannot safely be called (perhaps signal handlers, if the
           profiling routines generate output or allocate memory).

       -finstrument-functions-exclude-file-list=file,file,...
           Set the list of functions that are excluded from instrumentation (see the description
           of -finstrument-functions).  If the file that contains a function definition matches
           with one of file, then that function is not instrumented.  The match is done on
           substrings: if the file parameter is a substring of the file name, it is considered to
           be a match.

           For example:

                   -finstrument-functions-exclude-file-list=/bits/stl,include/sys

           excludes any inline function defined in files whose pathnames contain /bits/stl or
           include/sys.

           If, for some reason, you want to include letter , in one of sym, write ,. For example,
           -finstrument-functions-exclude-file-list=',,tmp' (note the single quote surrounding
           the option).

       -finstrument-functions-exclude-function-list=sym,sym,...
           This is similar to -finstrument-functions-exclude-file-list, but this option sets the
           list of function names to be excluded from instrumentation.  The function name to be
           matched is its user-visible name, such as "vector<int> blah(const vector<int> &)", not
           the internal mangled name (e.g., "_Z4blahRSt6vectorIiSaIiEE").  The match is done on
           substrings: if the sym parameter is a substring of the function name, it is considered
           to be a match.  For C99 and C++ extended identifiers, the function name must be given
           in UTF-8, not using universal character names.

       -fpatchable-function-entry=N[,M]
           Generate N NOPs right at the beginning of each function, with the function entry point
           before the Mth NOP.  If M is omitted, it defaults to 0 so the function entry points to
           the address just at the first NOP.  The NOP instructions reserve extra space which can
           be used to patch in any desired instrumentation at run time, provided that the code
           segment is writable.  The amount of space is controllable indirectly via the number of
           NOPs; the NOP instruction used corresponds to the instruction emitted by the internal
           GCC back-end interface "gen_nop".  This behavior is target-specific and may also
           depend on the architecture variant and/or other compilation options.

           For run-time identification, the starting addresses of these areas, which correspond
           to their respective function entries minus M, are additionally collected in the
           "__patchable_function_entries" section of the resulting binary.

           Note that the value of "__attribute__ ((patchable_function_entry (N,M)))" takes
           precedence over command-line option -fpatchable-function-entry=N,M.  This can be used
           to increase the area size or to remove it completely on a single function.  If "N=0",
           no pad location is recorded.

           The NOP instructions are inserted at---and maybe before, depending on M---the function
           entry address, even before the prologue.

   Options Controlling the Preprocessor
       These options control the C preprocessor, which is run on each C source file before actual
       compilation.

       If you use the -E option, nothing is done except preprocessing.  Some of these options
       make sense only together with -E because they cause the preprocessor output to be
       unsuitable for actual compilation.

       In addition to the options listed here, there are a number of options to control search
       paths for include files documented in Directory Options.  Options to control preprocessor
       diagnostics are listed in Warning Options.

       -D name
           Predefine name as a macro, with definition 1.

       -D name=definition
           The contents of definition are tokenized and processed as if they appeared during
           translation phase three in a #define directive.  In particular, the definition is
           truncated by embedded newline characters.

           If you are invoking the preprocessor from a shell or shell-like program you may need
           to use the shell's quoting syntax to protect characters such as spaces that have a
           meaning in the shell syntax.

           If you wish to define a function-like macro on the command line, write its argument
           list with surrounding parentheses before the equals sign (if any).  Parentheses are
           meaningful to most shells, so you should quote the option.  With sh and csh,
           -D'name(args...)=definition' works.

           -D and -U options are processed in the order they are given on the command line.  All
           -imacros file and -include file options are processed after all -D and -U options.

       -U name
           Cancel any previous definition of name, either built in or provided with a -D option.

       -include file
           Process file as if "#include "file"" appeared as the first line of the primary source
           file.  However, the first directory searched for file is the preprocessor's working
           directory instead of the directory containing the main source file.  If not found
           there, it is searched for in the remainder of the "#include "..."" search chain as
           normal.

           If multiple -include options are given, the files are included in the order they
           appear on the command line.

       -imacros file
           Exactly like -include, except that any output produced by scanning file is thrown
           away.  Macros it defines remain defined.  This allows you to acquire all the macros
           from a header without also processing its declarations.

           All files specified by -imacros are processed before all files specified by -include.

       -undef
           Do not predefine any system-specific or GCC-specific macros.  The standard predefined
           macros remain defined.

       -pthread
           Define additional macros required for using the POSIX threads library.  You should use
           this option consistently for both compilation and linking.  This option is supported
           on GNU/Linux targets, most other Unix derivatives, and also on x86 Cygwin and MinGW
           targets.

       -M  Instead of outputting the result of preprocessing, output a rule suitable for make
           describing the dependencies of the main source file.  The preprocessor outputs one
           make rule containing the object file name for that source file, a colon, and the names
           of all the included files, including those coming from -include or -imacros command-
           line options.

           Unless specified explicitly (with -MT or -MQ), the object file name consists of the
           name of the source file with any suffix replaced with object file suffix and with any
           leading directory parts removed.  If there are many included files then the rule is
           split into several lines using \-newline.  The rule has no commands.

           This option does not suppress the preprocessor's debug output, such as -dM.  To avoid
           mixing such debug output with the dependency rules you should explicitly specify the
           dependency output file with -MF, or use an environment variable like
           DEPENDENCIES_OUTPUT.  Debug output is still sent to the regular output stream as
           normal.

           Passing -M to the driver implies -E, and suppresses warnings with an implicit -w.

       -MM Like -M but do not mention header files that are found in system header directories,
           nor header files that are included, directly or indirectly, from such a header.

           This implies that the choice of angle brackets or double quotes in an #include
           directive does not in itself determine whether that header appears in -MM dependency
           output.

       -MF file
           When used with -M or -MM, specifies a file to write the dependencies to.  If no -MF
           switch is given the preprocessor sends the rules to the same place it would send
           preprocessed output.

           When used with the driver options -MD or -MMD, -MF overrides the default dependency
           output file.

           If file is -, then the dependencies are written to stdout.

       -MG In conjunction with an option such as -M requesting dependency generation, -MG assumes
           missing header files are generated files and adds them to the dependency list without
           raising an error.  The dependency filename is taken directly from the "#include"
           directive without prepending any path.  -MG also suppresses preprocessed output, as a
           missing header file renders this useless.

           This feature is used in automatic updating of makefiles.

       -MP This option instructs CPP to add a phony target for each dependency other than the
           main file, causing each to depend on nothing.  These dummy rules work around errors
           make gives if you remove header files without updating the Makefile to match.

           This is typical output:

                   test.o: test.c test.h

                   test.h:

       -MT target
           Change the target of the rule emitted by dependency generation.  By default CPP takes
           the name of the main input file, deletes any directory components and any file suffix
           such as .c, and appends the platform's usual object suffix.  The result is the target.

           An -MT option sets the target to be exactly the string you specify.  If you want
           multiple targets, you can specify them as a single argument to -MT, or use multiple
           -MT options.

           For example, -MT '$(objpfx)foo.o' might give

                   $(objpfx)foo.o: foo.c

       -MQ target
           Same as -MT, but it quotes any characters which are special to Make.
           -MQ '$(objpfx)foo.o' gives

                   $$(objpfx)foo.o: foo.c

           The default target is automatically quoted, as if it were given with -MQ.

       -MD -MD is equivalent to -M -MF file, except that -E is not implied.  The driver
           determines file based on whether an -o option is given.  If it is, the driver uses its
           argument but with a suffix of .d, otherwise it takes the name of the input file,
           removes any directory components and suffix, and applies a .d suffix.

           If -MD is used in conjunction with -E, any -o switch is understood to specify the
           dependency output file, but if used without -E, each -o is understood to specify a
           target object file.

           Since -E is not implied, -MD can be used to generate a dependency output file as a
           side effect of the compilation process.

       -MMD
           Like -MD except mention only user header files, not system header files.

       -fpreprocessed
           Indicate to the preprocessor that the input file has already been preprocessed.  This
           suppresses things like macro expansion, trigraph conversion, escaped newline splicing,
           and processing of most directives.  The preprocessor still recognizes and removes
           comments, so that you can pass a file preprocessed with -C to the compiler without
           problems.  In this mode the integrated preprocessor is little more than a tokenizer
           for the front ends.

           -fpreprocessed is implicit if the input file has one of the extensions .i, .ii or .mi.
           These are the extensions that GCC uses for preprocessed files created by -save-temps.

       -fdirectives-only
           When preprocessing, handle directives, but do not expand macros.

           The option's behavior depends on the -E and -fpreprocessed options.

           With -E, preprocessing is limited to the handling of directives such as "#define",
           "#ifdef", and "#error".  Other preprocessor operations, such as macro expansion and
           trigraph conversion are not performed.  In addition, the -dD option is implicitly
           enabled.

           With -fpreprocessed, predefinition of command line and most builtin macros is
           disabled.  Macros such as "__LINE__", which are contextually dependent, are handled
           normally.  This enables compilation of files previously preprocessed with "-E
           -fdirectives-only".

           With both -E and -fpreprocessed, the rules for -fpreprocessed take precedence.  This
           enables full preprocessing of files previously preprocessed with "-E
           -fdirectives-only".

       -fdollars-in-identifiers
           Accept $ in identifiers.

       -fextended-identifiers
           Accept universal character names in identifiers.  This option is enabled by default
           for C99 (and later C standard versions) and C++.

       -fno-canonical-system-headers
           When preprocessing, do not shorten system header paths with canonicalization.

       -ftabstop=width
           Set the distance between tab stops.  This helps the preprocessor report correct column
           numbers in warnings or errors, even if tabs appear on the line.  If the value is less
           than 1 or greater than 100, the option is ignored.  The default is 8.

       -ftrack-macro-expansion[=level]
           Track locations of tokens across macro expansions. This allows the compiler to emit
           diagnostic about the current macro expansion stack when a compilation error occurs in
           a macro expansion. Using this option makes the preprocessor and the compiler consume
           more memory. The level parameter can be used to choose the level of precision of token
           location tracking thus decreasing the memory consumption if necessary. Value 0 of
           level de-activates this option. Value 1 tracks tokens locations in a degraded mode for
           the sake of minimal memory overhead. In this mode all tokens resulting from the
           expansion of an argument of a function-like macro have the same location. Value 2
           tracks tokens locations completely. This value is the most memory hungry.  When this
           option is given no argument, the default parameter value is 2.

           Note that "-ftrack-macro-expansion=2" is activated by default.

       -fmacro-prefix-map=old=new
           When preprocessing files residing in directory old, expand the "__FILE__" and
           "__BASE_FILE__" macros as if the files resided in directory new instead.  This can be
           used to change an absolute path to a relative path by using . for new which can result
           in more reproducible builds that are location independent.  This option also affects
           "__builtin_FILE()" during compilation.  See also -ffile-prefix-map.

       -fexec-charset=charset
           Set the execution character set, used for string and character constants.  The default
           is UTF-8.  charset can be any encoding supported by the system's "iconv" library
           routine.

       -fwide-exec-charset=charset
           Set the wide execution character set, used for wide string and character constants.
           The default is UTF-32 or UTF-16, whichever corresponds to the width of "wchar_t".  As
           with -fexec-charset, charset can be any encoding supported by the system's "iconv"
           library routine; however, you will have problems with encodings that do not fit
           exactly in "wchar_t".

       -finput-charset=charset
           Set the input character set, used for translation from the character set of the input
           file to the source character set used by GCC.  If the locale does not specify, or GCC
           cannot get this information from the locale, the default is UTF-8.  This can be
           overridden by either the locale or this command-line option.  Currently the command-
           line option takes precedence if there's a conflict.  charset can be any encoding
           supported by the system's "iconv" library routine.

       -fpch-deps
           When using precompiled headers, this flag causes the dependency-output flags to also
           list the files from the precompiled header's dependencies.  If not specified, only the
           precompiled header are listed and not the files that were used to create it, because
           those files are not consulted when a precompiled header is used.

       -fpch-preprocess
           This option allows use of a precompiled header together with -E.  It inserts a special
           "#pragma", "#pragma GCC pch_preprocess "filename"" in the output to mark the place
           where the precompiled header was found, and its filename.  When -fpreprocessed is in
           use, GCC recognizes this "#pragma" and loads the PCH.

           This option is off by default, because the resulting preprocessed output is only
           really suitable as input to GCC.  It is switched on by -save-temps.

           You should not write this "#pragma" in your own code, but it is safe to edit the
           filename if the PCH file is available in a different location.  The filename may be
           absolute or it may be relative to GCC's current directory.

       -fworking-directory
           Enable generation of linemarkers in the preprocessor output that let the compiler know
           the current working directory at the time of preprocessing.  When this option is
           enabled, the preprocessor emits, after the initial linemarker, a second linemarker
           with the current working directory followed by two slashes.  GCC uses this directory,
           when it's present in the preprocessed input, as the directory emitted as the current
           working directory in some debugging information formats.  This option is implicitly
           enabled if debugging information is enabled, but this can be inhibited with the
           negated form -fno-working-directory.  If the -P flag is present in the command line,
           this option has no effect, since no "#line" directives are emitted whatsoever.

       -A predicate=answer
           Make an assertion with the predicate predicate and answer answer.  This form is
           preferred to the older form -A predicate(answer), which is still supported, because it
           does not use shell special characters.

       -A -predicate=answer
           Cancel an assertion with the predicate predicate and answer answer.

       -C  Do not discard comments.  All comments are passed through to the output file, except
           for comments in processed directives, which are deleted along with the directive.

           You should be prepared for side effects when using -C; it causes the preprocessor to
           treat comments as tokens in their own right.  For example, comments appearing at the
           start of what would be a directive line have the effect of turning that line into an
           ordinary source line, since the first token on the line is no longer a #.

       -CC Do not discard comments, including during macro expansion.  This is like -C, except
           that comments contained within macros are also passed through to the output file where
           the macro is expanded.

           In addition to the side effects of the -C option, the -CC option causes all C++-style
           comments inside a macro to be converted to C-style comments.  This is to prevent later
           use of that macro from inadvertently commenting out the remainder of the source line.

           The -CC option is generally used to support lint comments.

       -P  Inhibit generation of linemarkers in the output from the preprocessor.  This might be
           useful when running the preprocessor on something that is not C code, and will be sent
           to a program which might be confused by the linemarkers.

       -traditional
       -traditional-cpp
           Try to imitate the behavior of pre-standard C preprocessors, as opposed to ISO C
           preprocessors.  See the GNU CPP manual for details.

           Note that GCC does not otherwise attempt to emulate a pre-standard C compiler, and
           these options are only supported with the -E switch, or when invoking CPP explicitly.

       -trigraphs
           Support ISO C trigraphs.  These are three-character sequences, all starting with ??,
           that are defined by ISO C to stand for single characters.  For example, ??/ stands for
           \, so '??/n' is a character constant for a newline.

           The nine trigraphs and their replacements are

                   Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
                   Replacement:      [    ]    {    }    #    \    ^    |    ~

           By default, GCC ignores trigraphs, but in standard-conforming modes it converts them.
           See the -std and -ansi options.

       -remap
           Enable special code to work around file systems which only permit very short file
           names, such as MS-DOS.

       -H  Print the name of each header file used, in addition to other normal activities.  Each
           name is indented to show how deep in the #include stack it is.  Precompiled header
           files are also printed, even if they are found to be invalid; an invalid precompiled
           header file is printed with ...x and a valid one with ...! .

       -dletters
           Says to make debugging dumps during compilation as specified by letters.  The flags
           documented here are those relevant to the preprocessor.  Other letters are interpreted
           by the compiler proper, or reserved for future versions of GCC, and so are silently
           ignored.  If you specify letters whose behavior conflicts, the result is undefined.

           -dM Instead of the normal output, generate a list of #define directives for all the
               macros defined during the execution of the preprocessor, including predefined
               macros.  This gives you a way of finding out what is predefined in your version of
               the preprocessor.  Assuming you have no file foo.h, the command

                       touch foo.h; cpp -dM foo.h

               shows all the predefined macros.

               If you use -dM without the -E option, -dM is interpreted as a synonym for
               -fdump-rtl-mach.

           -dD Like -dM except in two respects: it does not include the predefined macros, and it
               outputs both the #define directives and the result of preprocessing.  Both kinds
               of output go to the standard output file.

           -dN Like -dD, but emit only the macro names, not their expansions.

           -dI Output #include directives in addition to the result of preprocessing.

           -dU Like -dD except that only macros that are expanded, or whose definedness is tested
               in preprocessor directives, are output; the output is delayed until the use or
               test of the macro; and #undef directives are also output for macros tested but
               undefined at the time.

       -fdebug-cpp
           This option is only useful for debugging GCC.  When used from CPP or with -E, it dumps
           debugging information about location maps.  Every token in the output is preceded by
           the dump of the map its location belongs to.

           When used from GCC without -E, this option has no effect.

       -Wp,option
           You can use -Wp,option to bypass the compiler driver and pass option directly through
           to the preprocessor.  If option contains commas, it is split into multiple options at
           the commas.  However, many options are modified, translated or interpreted by the
           compiler driver before being passed to the preprocessor, and -Wp forcibly bypasses
           this phase.  The preprocessor's direct interface is undocumented and subject to
           change, so whenever possible you should avoid using -Wp and let the driver handle the
           options instead.

       -Xpreprocessor option
           Pass option as an option to the preprocessor.  You can use this to supply system-
           specific preprocessor options that GCC does not recognize.

           If you want to pass an option that takes an argument, you must use -Xpreprocessor
           twice, once for the option and once for the argument.

       -no-integrated-cpp
           Perform preprocessing as a separate pass before compilation.  By default, GCC performs
           preprocessing as an integrated part of input tokenization and parsing.  If this option
           is provided, the appropriate language front end (cc1, cc1plus, or cc1obj for C, C++,
           and Objective-C, respectively) is instead invoked twice, once for preprocessing only
           and once for actual compilation of the preprocessed input.  This option may be useful
           in conjunction with the -B or -wrapper options to specify an alternate preprocessor or
           perform additional processing of the program source between normal preprocessing and
           compilation.

   Passing Options to the Assembler
       You can pass options to the assembler.

       -Wa,option
           Pass option as an option to the assembler.  If option contains commas, it is split
           into multiple options at the commas.

       -Xassembler option
           Pass option as an option to the assembler.  You can use this to supply system-specific
           assembler options that GCC does not recognize.

           If you want to pass an option that takes an argument, you must use -Xassembler twice,
           once for the option and once for the argument.

   Options for Linking
       These options come into play when the compiler links object files into an executable
       output file.  They are meaningless if the compiler is not doing a link step.

       object-file-name
           A file name that does not end in a special recognized suffix is considered to name an
           object file or library.  (Object files are distinguished from libraries by the linker
           according to the file contents.)  If linking is done, these object files are used as
           input to the linker.

       -c
       -S
       -E  If any of these options is used, then the linker is not run, and object file names
           should not be used as arguments.

       -fuse-ld=bfd
           Use the bfd linker instead of the default linker.

       -fuse-ld=gold
           Use the gold linker instead of the default linker.

       -fuse-ld=lld
           Use the LLVM lld linker instead of the default linker.

       -llibrary
       -l library
           Search the library named library when linking.  (The second alternative with the
           library as a separate argument is only for POSIX compliance and is not recommended.)

           It makes a difference where in the command you write this option; the linker searches
           and processes libraries and object files in the order they are specified.  Thus, foo.o
           -lz bar.o searches library z after file foo.o but before bar.o.  If bar.o refers to
           functions in z, those functions may not be loaded.

           The linker searches a standard list of directories for the library, which is actually
           a file named liblibrary.a.  The linker then uses this file as if it had been specified
           precisely by name.

           The directories searched include several standard system directories plus any that you
           specify with -L.

           Normally the files found this way are library files---archive files whose members are
           object files.  The linker handles an archive file by scanning through it for members
           which define symbols that have so far been referenced but not defined.  But if the
           file that is found is an ordinary object file, it is linked in the usual fashion.  The
           only difference between using an -l option and specifying a file name is that -l
           surrounds library with lib and .a and searches several directories.

       -lobjc
           You need this special case of the -l option in order to link an Objective-C or
           Objective-C++ program.

       -nostartfiles
           Do not use the standard system startup files when linking.  The standard system
           libraries are used normally, unless -nostdlib or -nodefaultlibs is used.

       -nodefaultlibs
           Do not use the standard system libraries when linking.  Only the libraries you specify
           are passed to the linker, and options specifying linkage of the system libraries, such
           as -static-libgcc or -shared-libgcc, are ignored.  The standard startup files are used
           normally, unless -nostartfiles is used.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and "memmove".  These
           entries are usually resolved by entries in libc.  These entry points should be
           supplied through some other mechanism when this option is specified.

       -nostdlib
           Do not use the standard system startup files or libraries when linking.  No startup
           files and only the libraries you specify are passed to the linker, and options
           specifying linkage of the system libraries, such as -static-libgcc or -shared-libgcc,
           are ignored.

           The compiler may generate calls to "memcmp", "memset", "memcpy" and "memmove".  These
           entries are usually resolved by entries in libc.  These entry points should be
           supplied through some other mechanism when this option is specified.

           One of the standard libraries bypassed by -nostdlib and -nodefaultlibs is libgcc.a, a
           library of internal subroutines which GCC uses to overcome shortcomings of particular
           machines, or special needs for some languages.

           In most cases, you need libgcc.a even when you want to avoid other standard libraries.
           In other words, when you specify -nostdlib or -nodefaultlibs you should usually
           specify -lgcc as well.  This ensures that you have no unresolved references to
           internal GCC library subroutines.  (An example of such an internal subroutine is
           "__main", used to ensure C++ constructors are called.)

       -pie
           Produce a dynamically linked position independent executable on targets that support
           it.  For predictable results, you must also specify the same set of options used for
           compilation (-fpie, -fPIE, or model suboptions) when you specify this linker option.

       -no-pie
           Don't produce a dynamically linked position independent executable.

       -static-pie
           Produce a static position independent executable on targets that support it.  A static
           position independent executable is similar to a static executable, but can be loaded
           at any address without a dynamic linker.  For predictable results, you must also
           specify the same set of options used for compilation (-fpie, -fPIE, or model
           suboptions) when you specify this linker option.

       -pthread
           Link with the POSIX threads library.  This option is supported on GNU/Linux targets,
           most other Unix derivatives, and also on x86 Cygwin and MinGW targets.  On some
           targets this option also sets flags for the preprocessor, so it should be used
           consistently for both compilation and linking.

       -rdynamic
           Pass the flag -export-dynamic to the ELF linker, on targets that support it. This
           instructs the linker to add all symbols, not only used ones, to the dynamic symbol
           table. This option is needed for some uses of "dlopen" or to allow obtaining
           backtraces from within a program.

       -s  Remove all symbol table and relocation information from the executable.

       -static
           On systems that support dynamic linking, this overrides -pie and prevents linking with
           the shared libraries.  On other systems, this option has no effect.

       -shared
           Produce a shared object which can then be linked with other objects to form an
           executable.  Not all systems support this option.  For predictable results, you must
           also specify the same set of options used for compilation (-fpic, -fPIC, or model
           suboptions) when you specify this linker option.[1]

       -shared-libgcc
       -static-libgcc
           On systems that provide libgcc as a shared library, these options force the use of
           either the shared or static version, respectively.  If no shared version of libgcc was
           built when the compiler was configured, these options have no effect.

           There are several situations in which an application should use the shared libgcc
           instead of the static version.  The most common of these is when the application
           wishes to throw and catch exceptions across different shared libraries.  In that case,
           each of the libraries as well as the application itself should use the shared libgcc.

           Therefore, the G++ driver automatically adds -shared-libgcc whenever you build a
           shared library or a main executable, because C++ programs typically use exceptions, so
           this is the right thing to do.

           If, instead, you use the GCC driver to create shared libraries, you may find that they
           are not always linked with the shared libgcc.  If GCC finds, at its configuration
           time, that you have a non-GNU linker or a GNU linker that does not support option
           --eh-frame-hdr, it links the shared version of libgcc into shared libraries by
           default.  Otherwise, it takes advantage of the linker and optimizes away the linking
           with the shared version of libgcc, linking with the static version of libgcc by
           default.  This allows exceptions to propagate through such shared libraries, without
           incurring relocation costs at library load time.

           However, if a library or main executable is supposed to throw or catch exceptions, you
           must link it using the G++ driver, or using the option -shared-libgcc, such that it is
           linked with the shared libgcc.

       -static-libasan
           When the -fsanitize=address option is used to link a program, the GCC driver
           automatically links against libasan.  If libasan is available as a shared library, and
           the -static option is not used, then this links against the shared version of libasan.
           The -static-libasan option directs the GCC driver to link libasan statically, without
           necessarily linking other libraries statically.

       -static-libtsan
           When the -fsanitize=thread option is used to link a program, the GCC driver
           automatically links against libtsan.  If libtsan is available as a shared library, and
           the -static option is not used, then this links against the shared version of libtsan.
           The -static-libtsan option directs the GCC driver to link libtsan statically, without
           necessarily linking other libraries statically.

       -static-liblsan
           When the -fsanitize=leak option is used to link a program, the GCC driver
           automatically links against liblsan.  If liblsan is available as a shared library, and
           the -static option is not used, then this links against the shared version of liblsan.
           The -static-liblsan option directs the GCC driver to link liblsan statically, without
           necessarily linking other libraries statically.

       -static-libubsan
           When the -fsanitize=undefined option is used to link a program, the GCC driver
           automatically links against libubsan.  If libubsan is available as a shared library,
           and the -static option is not used, then this links against the shared version of
           libubsan.  The -static-libubsan option directs the GCC driver to link libubsan
           statically, without necessarily linking other libraries statically.

       -static-libmpx
           When the -fcheck-pointer bounds and -mmpx options are used to link a program, the GCC
           driver automatically links against libmpx.  If libmpx is available as a shared
           library, and the -static option is not used, then this links against the shared
           version of libmpx.  The -static-libmpx option directs the GCC driver to link libmpx
           statically, without necessarily linking other libraries statically.

       -static-libmpxwrappers
           When the -fcheck-pointer bounds and -mmpx options are used to link a program without
           also using -fno-chkp-use-wrappers, the GCC driver automatically links against
           libmpxwrappers.  If libmpxwrappers is available as a shared library, and the -static
           option is not used, then this links against the shared version of libmpxwrappers.  The
           -static-libmpxwrappers option directs the GCC driver to link libmpxwrappers
           statically, without necessarily linking other libraries statically.

       -static-libstdc++
           When the g++ program is used to link a C++ program, it normally automatically links
           against libstdc++.  If libstdc++ is available as a shared library, and the -static
           option is not used, then this links against the shared version of libstdc++.  That is
           normally fine.  However, it is sometimes useful to freeze the version of libstdc++
           used by the program without going all the way to a fully static link.  The
           -static-libstdc++ option directs the g++ driver to link libstdc++ statically, without
           necessarily linking other libraries statically.

       -symbolic
           Bind references to global symbols when building a shared object.  Warn about any
           unresolved references (unless overridden by the link editor option -Xlinker -z
           -Xlinker defs).  Only a few systems support this option.

       -T script
           Use script as the linker script.  This option is supported by most systems using the
           GNU linker.  On some targets, such as bare-board targets without an operating system,
           the -T option may be required when linking to avoid references to undefined symbols.

       -Xlinker option
           Pass option as an option to the linker.  You can use this to supply system-specific
           linker options that GCC does not recognize.

           If you want to pass an option that takes a separate argument, you must use -Xlinker
           twice, once for the option and once for the argument.  For example, to pass -assert
           definitions, you must write -Xlinker -assert -Xlinker definitions.  It does not work
           to write -Xlinker "-assert definitions", because this passes the entire string as a
           single argument, which is not what the linker expects.

           When using the GNU linker, it is usually more convenient to pass arguments to linker
           options using the option=value syntax than as separate arguments.  For example, you
           can specify -Xlinker -Map=output.map rather than -Xlinker -Map -Xlinker output.map.
           Other linkers may not support this syntax for command-line options.

       -Wl,option
           Pass option as an option to the linker.  If option contains commas, it is split into
           multiple options at the commas.  You can use this syntax to pass an argument to the
           option.  For example, -Wl,-Map,output.map passes -Map output.map to the linker.  When
           using the GNU linker, you can also get the same effect with -Wl,-Map=output.map.

           NOTE: In Ubuntu 8.10 and later versions, for LDFLAGS, the option -Wl,-z,relro is used.
           To disable, use -Wl,-z,norelro.

       -u symbol
           Pretend the symbol symbol is undefined, to force linking of library modules to define
           it.  You can use -u multiple times with different symbols to force loading of
           additional library modules.

       -z keyword
           -z is passed directly on to the linker along with the keyword keyword. See the section
           in the documentation of your linker for permitted values and their meanings.

   Options for Directory Search
       These options specify directories to search for header files, for libraries and for parts
       of the compiler:

       -I dir
       -iquote dir
       -isystem dir
       -idirafter dir
           Add the directory dir to the list of directories to be searched for header files
           during preprocessing.  If dir begins with = or $SYSROOT, then the = or $SYSROOT is
           replaced by the sysroot prefix; see --sysroot and -isysroot.

           Directories specified with -iquote apply only to the quote form of the directive,
           "#include "file"".  Directories specified with -I, -isystem, or -idirafter apply to
           lookup for both the "#include "file"" and "#include <file>" directives.

           You can specify any number or combination of these options on the command line to
           search for header files in several directories.  The lookup order is as follows:

           1.  For the quote form of the include directive, the directory of the current file is
               searched first.

           2.  For the quote form of the include directive, the directories specified by -iquote
               options are searched in left-to-right order, as they appear on the command line.

           3.  Directories specified with -I options are scanned in left-to-right order.

           4.  Directories specified with -isystem options are scanned in left-to-right order.

           5.  Standard system directories are scanned.

           6.  Directories specified with -idirafter options are scanned in left-to-right order.

           You can use -I to override a system header file, substituting your own version, since
           these directories are searched before the standard system header file directories.
           However, you should not use this option to add directories that contain vendor-
           supplied system header files; use -isystem for that.

           The -isystem and -idirafter options also mark the directory as a system directory, so
           that it gets the same special treatment that is applied to the standard system
           directories.

           If a standard system include directory, or a directory specified with -isystem, is
           also specified with -I, the -I option is ignored.  The directory is still searched but
           as a system directory at its normal position in the system include chain.  This is to
           ensure that GCC's procedure to fix buggy system headers and the ordering for the
           "#include_next" directive are not inadvertently changed.  If you really need to change
           the search order for system directories, use the -nostdinc and/or -isystem options.

       -I- Split the include path.  This option has been deprecated.  Please use -iquote instead
           for -I directories before the -I- and remove the -I- option.

           Any directories specified with -I options before -I- are searched only for headers
           requested with "#include "file""; they are not searched for "#include <file>".  If
           additional directories are specified with -I options after the -I-, those directories
           are searched for all #include directives.

           In addition, -I- inhibits the use of the directory of the current file directory as
           the first search directory for "#include "file"".  There is no way to override this
           effect of -I-.

       -iprefix prefix
           Specify prefix as the prefix for subsequent -iwithprefix options.  If the prefix
           represents a directory, you should include the final /.

       -iwithprefix dir
       -iwithprefixbefore dir
           Append dir to the prefix specified previously with -iprefix, and add the resulting
           directory to the include search path.  -iwithprefixbefore puts it in the same place -I
           would; -iwithprefix puts it where -idirafter would.

       -isysroot dir
           This option is like the --sysroot option, but applies only to header files (except for
           Darwin targets, where it applies to both header files and libraries).  See the
           --sysroot option for more information.

       -imultilib dir
           Use dir as a subdirectory of the directory containing target-specific C++ headers.

       -nostdinc
           Do not search the standard system directories for header files.  Only the directories
           explicitly specified with -I, -iquote, -isystem, and/or -idirafter options (and the
           directory of the current file, if appropriate) are searched.

       -nostdinc++
           Do not search for header files in the C++-specific standard directories, but do still
           search the other standard directories.  (This option is used when building the C++
           library.)

       -iplugindir=dir
           Set the directory to search for plugins that are passed by -fplugin=name instead of
           -fplugin=path/name.so.  This option is not meant to be used by the user, but only
           passed by the driver.

       -Ldir
           Add directory dir to the list of directories to be searched for -l.

       -Bprefix
           This option specifies where to find the executables, libraries, include files, and
           data files of the compiler itself.

           The compiler driver program runs one or more of the subprograms cpp, cc1, as and ld.
           It tries prefix as a prefix for each program it tries to run, both with and without
           machine/version/ for the corresponding target machine and compiler version.

           For each subprogram to be run, the compiler driver first tries the -B prefix, if any.
           If that name is not found, or if -B is not specified, the driver tries two standard
           prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/.  If neither of those results in a
           file name that is found, the unmodified program name is searched for using the
           directories specified in your PATH environment variable.

           The compiler checks to see if the path provided by -B refers to a directory, and if
           necessary it adds a directory separator character at the end of the path.

           -B prefixes that effectively specify directory names also apply to libraries in the
           linker, because the compiler translates these options into -L options for the linker.
           They also apply to include files in the preprocessor, because the compiler translates
           these options into -isystem options for the preprocessor.  In this case, the compiler
           appends include to the prefix.

           The runtime support file libgcc.a can also be searched for using the -B prefix, if
           needed.  If it is not found there, the two standard prefixes above are tried, and that
           is all.  The file is left out of the link if it is not found by those means.

           Another way to specify a prefix much like the -B prefix is to use the environment
           variable GCC_EXEC_PREFIX.

           As a special kludge, if the path provided by -B is [dir/]stageN/, where N is a number
           in the range 0 to 9, then it is replaced by [dir/]include.  This is to help with boot-
           strapping the compiler.

       -no-canonical-prefixes
           Do not expand any symbolic links, resolve references to /../ or /./, or make the path
           absolute when generating a relative prefix.

       --sysroot=dir
           Use dir as the logical root directory for headers and libraries.  For example, if the
           compiler normally searches for headers in /usr/include and libraries in /usr/lib, it
           instead searches dir/usr/include and dir/usr/lib.

           If you use both this option and the -isysroot option, then the --sysroot option
           applies to libraries, but the -isysroot option applies to header files.

           The GNU linker (beginning with version 2.16) has the necessary support for this
           option.  If your linker does not support this option, the header file aspect of
           --sysroot still works, but the library aspect does not.

       --no-sysroot-suffix
           For some targets, a suffix is added to the root directory specified with --sysroot,
           depending on the other options used, so that headers may for example be found in
           dir/suffix/usr/include instead of dir/usr/include.  This option disables the addition
           of such a suffix.

   Options for Code Generation Conventions
       These machine-independent options control the interface conventions used in code
       generation.

       Most of them have both positive and negative forms; the negative form of -ffoo is
       -fno-foo.  In the table below, only one of the forms is listed---the one that is not the
       default.  You can figure out the other form by either removing no- or adding it.

       -fstack-reuse=reuse-level
           This option controls stack space reuse for user declared local/auto variables and
           compiler generated temporaries.  reuse_level can be all, named_vars, or none. all
           enables stack reuse for all local variables and temporaries, named_vars enables the
           reuse only for user defined local variables with names, and none disables stack reuse
           completely. The default value is all. The option is needed when the program extends
           the lifetime of a scoped local variable or a compiler generated temporary beyond the
           end point defined by the language.  When a lifetime of a variable ends, and if the
           variable lives in memory, the optimizing compiler has the freedom to reuse its stack
           space with other temporaries or scoped local variables whose live range does not
           overlap with it. Legacy code extending local lifetime is likely to break with the
           stack reuse optimization.

           For example,

                      int *p;
                      {
                        int local1;

                        p = &local1;
                        local1 = 10;
                        ....
                      }
                      {
                         int local2;
                         local2 = 20;
                         ...
                      }

                      if (*p == 10)  // out of scope use of local1
                        {

                        }

           Another example:

                      struct A
                      {
                          A(int k) : i(k), j(k) { }
                          int i;
                          int j;
                      };

                      A *ap;

                      void foo(const A& ar)
                      {
                         ap = &ar;
                      }

                      void bar()
                      {
                         foo(A(10)); // temp object's lifetime ends when foo returns

                         {
                           A a(20);
                           ....
                         }
                         ap->i+= 10;  // ap references out of scope temp whose space
                                      // is reused with a. What is the value of ap->i?
                      }

           The lifetime of a compiler generated temporary is well defined by the C++ standard.
           When a lifetime of a temporary ends, and if the temporary lives in memory, the
           optimizing compiler has the freedom to reuse its stack space with other temporaries or
           scoped local variables whose live range does not overlap with it. However some of the
           legacy code relies on the behavior of older compilers in which temporaries' stack
           space is not reused, the aggressive stack reuse can lead to runtime errors. This
           option is used to control the temporary stack reuse optimization.

       -ftrapv
           This option generates traps for signed overflow on addition, subtraction,
           multiplication operations.  The options -ftrapv and -fwrapv override each other, so
           using -ftrapv -fwrapv on the command-line results in -fwrapv being effective.  Note
           that only active options override, so using -ftrapv -fwrapv -fno-wrapv on the command-
           line results in -ftrapv being effective.

       -fwrapv
           This option instructs the compiler to assume that signed arithmetic overflow of
           addition, subtraction and multiplication wraps around using twos-complement
           representation.  This flag enables some optimizations and disables others.  The
           options -ftrapv and -fwrapv override each other, so using -ftrapv -fwrapv on the
           command-line results in -fwrapv being effective.  Note that only active options
           override, so using -ftrapv -fwrapv -fno-wrapv on the command-line results in -ftrapv
           being effective.

       -fwrapv-pointer
           This option instructs the compiler to assume that pointer arithmetic overflow on
           addition and subtraction wraps around using twos-complement representation.  This flag
           disables some optimizations which assume pointer overflow is invalid.

       -fstrict-overflow
           This option implies -fno-wrapv -fno-wrapv-pointer and when negated implies -fwrapv
           -fwrapv-pointer.

       -fexceptions
           Enable exception handling.  Generates extra code needed to propagate exceptions.  For
           some targets, this implies GCC generates frame unwind information for all functions,
           which can produce significant data size overhead, although it does not affect
           execution.  If you do not specify this option, GCC enables it by default for languages
           like C++ that normally require exception handling, and disables it for languages like
           C that do not normally require it.  However, you may need to enable this option when
           compiling C code that needs to interoperate properly with exception handlers written
           in C++.  You may also wish to disable this option if you are compiling older C++
           programs that don't use exception handling.

       -fnon-call-exceptions
           Generate code that allows trapping instructions to throw exceptions.  Note that this
           requires platform-specific runtime support that does not exist everywhere.  Moreover,
           it only allows trapping instructions to throw exceptions, i.e. memory references or
           floating-point instructions.  It does not allow exceptions to be thrown from arbitrary
           signal handlers such as "SIGALRM".

       -fdelete-dead-exceptions
           Consider that instructions that may throw exceptions but don't otherwise contribute to
           the execution of the program can be optimized away.  This option is enabled by default
           for the Ada front end, as permitted by the Ada language specification.  Optimization
           passes that cause dead exceptions to be removed are enabled independently at different
           optimization levels.

       -funwind-tables
           Similar to -fexceptions, except that it just generates any needed static data, but
           does not affect the generated code in any other way.  You normally do not need to
           enable this option; instead, a language processor that needs this handling enables it
           on your behalf.

       -fasynchronous-unwind-tables
           Generate unwind table in DWARF format, if supported by target machine.  The table is
           exact at each instruction boundary, so it can be used for stack unwinding from
           asynchronous events (such as debugger or garbage collector).

       -fno-gnu-unique
           On systems with recent GNU assembler and C library, the C++ compiler uses the
           "STB_GNU_UNIQUE" binding to make sure that definitions of template static data members
           and static local variables in inline functions are unique even in the presence of
           "RTLD_LOCAL"; this is necessary to avoid problems with a library used by two different
           "RTLD_LOCAL" plugins depending on a definition in one of them and therefore
           disagreeing with the other one about the binding of the symbol.  But this causes
           "dlclose" to be ignored for affected DSOs; if your program relies on reinitialization
           of a DSO via "dlclose" and "dlopen", you can use -fno-gnu-unique.

       -fpcc-struct-return
           Return "short" "struct" and "union" values in memory like longer ones, rather than in
           registers.  This convention is less efficient, but it has the advantage of allowing
           intercallability between GCC-compiled files and files compiled with other compilers,
           particularly the Portable C Compiler (pcc).

           The precise convention for returning structures in memory depends on the target
           configuration macros.

           Short structures and unions are those whose size and alignment match that of some
           integer type.

           Warning: code compiled with the -fpcc-struct-return switch is not binary compatible
           with code compiled with the -freg-struct-return switch.  Use it to conform to a non-
           default application binary interface.

       -freg-struct-return
           Return "struct" and "union" values in registers when possible.  This is more efficient
           for small structures than -fpcc-struct-return.

           If you specify neither -fpcc-struct-return nor -freg-struct-return, GCC defaults to
           whichever convention is standard for the target.  If there is no standard convention,
           GCC defaults to -fpcc-struct-return, except on targets where GCC is the principal
           compiler.  In those cases, we can choose the standard, and we chose the more efficient
           register return alternative.

           Warning: code compiled with the -freg-struct-return switch is not binary compatible
           with code compiled with the -fpcc-struct-return switch.  Use it to conform to a non-
           default application binary interface.

       -fshort-enums
           Allocate to an "enum" type only as many bytes as it needs for the declared range of
           possible values.  Specifically, the "enum" type is equivalent to the smallest integer
           type that has enough room.

           Warning: the -fshort-enums switch causes GCC to generate code that is not binary
           compatible with code generated without that switch.  Use it to conform to a non-
           default application binary interface.

       -fshort-wchar
           Override the underlying type for "wchar_t" to be "short unsigned int" instead of the
           default for the target.  This option is useful for building programs to run under
           WINE.

           Warning: the -fshort-wchar switch causes GCC to generate code that is not binary
           compatible with code generated without that switch.  Use it to conform to a non-
           default application binary interface.

       -fno-common
           In C code, this option controls the placement of global variables defined without an
           initializer, known as tentative definitions in the C standard.  Tentative definitions
           are distinct from declarations of a variable with the "extern" keyword, which do not
           allocate storage.

           Unix C compilers have traditionally allocated storage for uninitialized global
           variables in a common block.  This allows the linker to resolve all tentative
           definitions of the same variable in different compilation units to the same object, or
           to a non-tentative definition.  This is the behavior specified by -fcommon, and is the
           default for GCC on most targets.  On the other hand, this behavior is not required by
           ISO C, and on some targets may carry a speed or code size penalty on variable
           references.

           The -fno-common option specifies that the compiler should instead place uninitialized
           global variables in the data section of the object file.  This inhibits the merging of
           tentative definitions by the linker so you get a multiple-definition error if the same
           variable is defined in more than one compilation unit.  Compiling with -fno-common is
           useful on targets for which it provides better performance, or if you wish to verify
           that the program will work on other systems that always treat uninitialized variable
           definitions this way.

       -fno-ident
           Ignore the "#ident" directive.

       -finhibit-size-directive
           Don't output a ".size" assembler directive, or anything else that would cause trouble
           if the function is split in the middle, and the two halves are placed at locations far
           apart in memory.  This option is used when compiling crtstuff.c; you should not need
           to use it for anything else.

       -fverbose-asm
           Put extra commentary information in the generated assembly code to make it more
           readable.  This option is generally only of use to those who actually need to read the
           generated assembly code (perhaps while debugging the compiler itself).

           -fno-verbose-asm, the default, causes the extra information to be omitted and is
           useful when comparing two assembler files.

           The added comments include:

           *   information on the compiler version and command-line options,

           *   the source code lines associated with the assembly instructions, in the form
               FILENAME:LINENUMBER:CONTENT OF LINE,

           *   hints on which high-level expressions correspond to the various assembly
               instruction operands.

           For example, given this C source file:

                   int test (int n)
                   {
                     int i;
                     int total = 0;

                     for (i = 0; i < n; i++)
                       total += i * i;

                     return total;
                   }

           compiling to (x86_64) assembly via -S and emitting the result direct to stdout via -o
           -

                   gcc -S test.c -fverbose-asm -Os -o -

           gives output similar to this:

                           .file   "test.c"
                   # GNU C11 (GCC) version 7.0.0 20160809 (experimental) (x86_64-pc-linux-gnu)
                     [...snip...]
                   # options passed:
                     [...snip...]

                           .text
                           .globl  test
                           .type   test, @function
                   test:
                   .LFB0:
                           .cfi_startproc
                   # test.c:4:   int total = 0;
                           xorl    %eax, %eax      # <retval>
                   # test.c:6:   for (i = 0; i < n; i++)
                           xorl    %edx, %edx      # i
                   .L2:
                   # test.c:6:   for (i = 0; i < n; i++)
                           cmpl    %edi, %edx      # n, i
                           jge     .L5     #,
                   # test.c:7:     total += i * i;
                           movl    %edx, %ecx      # i, tmp92
                           imull   %edx, %ecx      # i, tmp92
                   # test.c:6:   for (i = 0; i < n; i++)
                           incl    %edx    # i
                   # test.c:7:     total += i * i;
                           addl    %ecx, %eax      # tmp92, <retval>
                           jmp     .L2     #
                   .L5:
                   # test.c:10: }
                           ret
                           .cfi_endproc
                   .LFE0:
                           .size   test, .-test
                           .ident  "GCC: (GNU) 7.0.0 20160809 (experimental)"
                           .section        .note.GNU-stack,"",@progbits

           The comments are intended for humans rather than machines and hence the precise format
           of the comments is subject to change.

       -frecord-gcc-switches
           This switch causes the command line used to invoke the compiler to be recorded into
           the object file that is being created.  This switch is only implemented on some
           targets and the exact format of the recording is target and binary file format
           dependent, but it usually takes the form of a section containing ASCII text.  This
           switch is related to the -fverbose-asm switch, but that switch only records
           information in the assembler output file as comments, so it never reaches the object
           file.  See also -grecord-gcc-switches for another way of storing compiler options into
           the object file.

       -fpic
           Generate position-independent code (PIC) suitable for use in a shared library, if
           supported for the target machine.  Such code accesses all constant addresses through a
           global offset table (GOT).  The dynamic loader resolves the GOT entries when the
           program starts (the dynamic loader is not part of GCC; it is part of the operating
           system).  If the GOT size for the linked executable exceeds a machine-specific maximum
           size, you get an error message from the linker indicating that -fpic does not work; in
           that case, recompile with -fPIC instead.  (These maximums are 8k on the SPARC, 28k on
           AArch64 and 32k on the m68k and RS/6000.  The x86 has no such limit.)

           Position-independent code requires special support, and therefore works only on
           certain machines.  For the x86, GCC supports PIC for System V but not for the Sun
           386i.  Code generated for the IBM RS/6000 is always position-independent.

           When this flag is set, the macros "__pic__" and "__PIC__" are defined to 1.

       -fPIC
           If supported for the target machine, emit position-independent code, suitable for
           dynamic linking and avoiding any limit on the size of the global offset table.  This
           option makes a difference on AArch64, m68k, PowerPC and SPARC.

           Position-independent code requires special support, and therefore works only on
           certain machines.

           When this flag is set, the macros "__pic__" and "__PIC__" are defined to 2.

       -fpie
       -fPIE
           These options are similar to -fpic and -fPIC, but generated position independent code
           can be only linked into executables.  Usually these options are used when -pie GCC
           option is used during linking.

           -fpie and -fPIE both define the macros "__pie__" and "__PIE__".  The macros have the
           value 1 for -fpie and 2 for -fPIE.

       -fno-plt
           Do not use the PLT for external function calls in position-independent code.  Instead,
           load the callee address at call sites from the GOT and branch to it.  This leads to
           more efficient code by eliminating PLT stubs and exposing GOT loads to optimizations.
           On architectures such as 32-bit x86 where PLT stubs expect the GOT pointer in a
           specific register, this gives more register allocation freedom to the compiler.  Lazy
           binding requires use of the PLT; with -fno-plt all external symbols are resolved at
           load time.

           Alternatively, the function attribute "noplt" can be used to avoid calls through the
           PLT for specific external functions.

           In position-dependent code, a few targets also convert calls to functions that are
           marked to not use the PLT to use the GOT instead.

       -fno-jump-tables
           Do not use jump tables for switch statements even where it would be more efficient
           than other code generation strategies.  This option is of use in conjunction with
           -fpic or -fPIC for building code that forms part of a dynamic linker and cannot
           reference the address of a jump table.  On some targets, jump tables do not require a
           GOT and this option is not needed.

       -ffixed-reg
           Treat the register named reg as a fixed register; generated code should never refer to
           it (except perhaps as a stack pointer, frame pointer or in some other fixed role).

           reg must be the name of a register.  The register names accepted are machine-specific
           and are defined in the "REGISTER_NAMES" macro in the machine description macro file.

           This flag does not have a negative form, because it specifies a three-way choice.

       -fcall-used-reg
           Treat the register named reg as an allocable register that is clobbered by function
           calls.  It may be allocated for temporaries or variables that do not live across a
           call.  Functions compiled this way do not save and restore the register reg.

           It is an error to use this flag with the frame pointer or stack pointer.  Use of this
           flag for other registers that have fixed pervasive roles in the machine's execution
           model produces disastrous results.

           This flag does not have a negative form, because it specifies a three-way choice.

       -fcall-saved-reg
           Treat the register named reg as an allocable register saved by functions.  It may be
           allocated even for temporaries or variables that live across a call.  Functions
           compiled this way save and restore the register reg if they use it.

           It is an error to use this flag with the frame pointer or stack pointer.  Use of this
           flag for other registers that have fixed pervasive roles in the machine's execution
           model produces disastrous results.

           A different sort of disaster results from the use of this flag for a register in which
           function values may be returned.

           This flag does not have a negative form, because it specifies a three-way choice.

       -fpack-struct[=n]
           Without a value specified, pack all structure members together without holes.  When a
           value is specified (which must be a small power of two), pack structure members
           according to this value, representing the maximum alignment (that is, objects with
           default alignment requirements larger than this are output potentially unaligned at
           the next fitting location.

           Warning: the -fpack-struct switch causes GCC to generate code that is not binary
           compatible with code generated without that switch.  Additionally, it makes the code
           suboptimal.  Use it to conform to a non-default application binary interface.

       -fleading-underscore
           This option and its counterpart, -fno-leading-underscore, forcibly change the way C
           symbols are represented in the object file.  One use is to help link with legacy
           assembly code.

           Warning: the -fleading-underscore switch causes GCC to generate code that is not
           binary compatible with code generated without that switch.  Use it to conform to a
           non-default application binary interface.  Not all targets provide complete support
           for this switch.

       -ftls-model=model
           Alter the thread-local storage model to be used.  The model argument should be one of
           global-dynamic, local-dynamic, initial-exec or local-exec.  Note that the choice is
           subject to optimization: the compiler may use a more efficient model for symbols not
           visible outside of the translation unit, or if -fpic is not given on the command line.

           The default without -fpic is initial-exec; with -fpic the default is global-dynamic.

       -ftrampolines
           For targets that normally need trampolines for nested functions, always generate them
           instead of using descriptors.  Otherwise, for targets that do not need them, like for
           example HP-PA or IA-64, do nothing.

           A trampoline is a small piece of code that is created at run time on the stack when
           the address of a nested function is taken, and is used to call the nested function
           indirectly.  Therefore, it requires the stack to be made executable in order for the
           program to work properly.

           -fno-trampolines is enabled by default on a language by language basis to let the
           compiler avoid generating them, if it computes that this is safe, and replace them
           with descriptors.  Descriptors are made up of data only, but the generated code must
           be prepared to deal with them.  As of this writing, -fno-trampolines is enabled by
           default only for Ada.

           Moreover, code compiled with -ftrampolines and code compiled with -fno-trampolines are
           not binary compatible if nested functions are present.  This option must therefore be
           used on a program-wide basis and be manipulated with extreme care.

       -fvisibility=[default|internal|hidden|protected]
           Set the default ELF image symbol visibility to the specified option---all symbols are
           marked with this unless overridden within the code.  Using this feature can very
           substantially improve linking and load times of shared object libraries, produce more
           optimized code, provide near-perfect API export and prevent symbol clashes.  It is
           strongly recommended that you use this in any shared objects you distribute.

           Despite the nomenclature, default always means public; i.e., available to be linked
           against from outside the shared object.  protected and internal are pretty useless in
           real-world usage so the only other commonly used option is hidden.  The default if
           -fvisibility isn't specified is default, i.e., make every symbol public.

           A good explanation of the benefits offered by ensuring ELF symbols have the correct
           visibility is given by "How To Write Shared Libraries" by Ulrich Drepper (which can be
           found at <https://www.akkadia.org/drepper/>)---however a superior solution made
           possible by this option to marking things hidden when the default is public is to make
           the default hidden and mark things public.  This is the norm with DLLs on Windows and
           with -fvisibility=hidden and "__attribute__ ((visibility("default")))" instead of
           "__declspec(dllexport)" you get almost identical semantics with identical syntax.
           This is a great boon to those working with cross-platform projects.

           For those adding visibility support to existing code, you may find "#pragma GCC
           visibility" of use.  This works by you enclosing the declarations you wish to set
           visibility for with (for example) "#pragma GCC visibility push(hidden)" and "#pragma
           GCC visibility pop".  Bear in mind that symbol visibility should be viewed as part of
           the API interface contract and thus all new code should always specify visibility when
           it is not the default; i.e., declarations only for use within the local DSO should
           always be marked explicitly as hidden as so to avoid PLT indirection
           overheads---making this abundantly clear also aids readability and self-documentation
           of the code.  Note that due to ISO C++ specification requirements, "operator new" and
           "operator delete" must always be of default visibility.

           Be aware that headers from outside your project, in particular system headers and
           headers from any other library you use, may not be expecting to be compiled with
           visibility other than the default.  You may need to explicitly say "#pragma GCC
           visibility push(default)" before including any such headers.

           "extern" declarations are not affected by -fvisibility, so a lot of code can be
           recompiled with -fvisibility=hidden with no modifications.  However, this means that
           calls to "extern" functions with no explicit visibility use the PLT, so it is more
           effective to use "__attribute ((visibility))" and/or "#pragma GCC visibility" to tell
           the compiler which "extern" declarations should be treated as hidden.

           Note that -fvisibility does affect C++ vague linkage entities. This means that, for
           instance, an exception class that is be thrown between DSOs must be explicitly marked
           with default visibility so that the type_info nodes are unified between the DSOs.

           An overview of these techniques, their benefits and how to use them is at
           <http://gcc.gnu.org/wiki/Visibility>.

       -fstrict-volatile-bitfields
           This option should be used if accesses to volatile bit-fields (or other structure
           fields, although the compiler usually honors those types anyway) should use a single
           access of the width of the field's type, aligned to a natural alignment if possible.
           For example, targets with memory-mapped peripheral registers might require all such
           accesses to be 16 bits wide; with this flag you can declare all peripheral bit-fields
           as "unsigned short" (assuming short is 16 bits on these targets) to force GCC to use
           16-bit accesses instead of, perhaps, a more efficient 32-bit access.

           If this option is disabled, the compiler uses the most efficient instruction.  In the
           previous example, that might be a 32-bit load instruction, even though that accesses
           bytes that do not contain any portion of the bit-field, or memory-mapped registers
           unrelated to the one being updated.

           In some cases, such as when the "packed" attribute is applied to a structure field, it
           may not be possible to access the field with a single read or write that is correctly
           aligned for the target machine.  In this case GCC falls back to generating multiple
           accesses rather than code that will fault or truncate the result at run time.

           Note:  Due to restrictions of the C/C++11 memory model, write accesses are not allowed
           to touch non bit-field members.  It is therefore recommended to define all bits of the
           field's type as bit-field members.

           The default value of this option is determined by the application binary interface for
           the target processor.

       -fsync-libcalls
           This option controls whether any out-of-line instance of the "__sync" family of
           functions may be used to implement the C++11 "__atomic" family of functions.

           The default value of this option is enabled, thus the only useful form of the option
           is -fno-sync-libcalls.  This option is used in the implementation of the libatomic
           runtime library.

   GCC Developer Options
       This section describes command-line options that are primarily of interest to GCC
       developers, including options to support compiler testing and investigation of compiler
       bugs and compile-time performance problems.  This includes options that produce debug
       dumps at various points in the compilation; that print statistics such as memory use and
       execution time; and that print information about GCC's configuration, such as where it
       searches for libraries.  You should rarely need to use any of these options for ordinary
       compilation and linking tasks.

       -dletters
       -fdump-rtl-pass
       -fdump-rtl-pass=filename
           Says to make debugging dumps during compilation at times specified by letters.  This
           is used for debugging the RTL-based passes of the compiler.  The file names for most
           of the dumps are made by appending a pass number and a word to the dumpname, and the
           files are created in the directory of the output file.  In case of =filename option,
           the dump is output on the given file instead of the pass numbered dump files.  Note
           that the pass number is assigned as passes are registered into the pass manager.  Most
           passes are registered in the order that they will execute and for these passes the
           number corresponds to the pass execution order.  However, passes registered by
           plugins, passes specific to compilation targets, or passes that are otherwise
           registered after all the other passes are numbered higher than a pass named "final",
           even if they are executed earlier.  dumpname is generated from the name of the output
           file if explicitly specified and not an executable, otherwise it is the basename of
           the source file.

           Some -dletters switches have different meaning when -E is used for preprocessing.

           Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters.  Here
           are the possible letters for use in pass and letters, and their meanings:

           -fdump-rtl-alignments
               Dump after branch alignments have been computed.

           -fdump-rtl-asmcons
               Dump after fixing rtl statements that have unsatisfied in/out constraints.

           -fdump-rtl-auto_inc_dec
               Dump after auto-inc-dec discovery.  This pass is only run on architectures that
               have auto inc or auto dec instructions.

           -fdump-rtl-barriers
               Dump after cleaning up the barrier instructions.

           -fdump-rtl-bbpart
               Dump after partitioning hot and cold basic blocks.

           -fdump-rtl-bbro
               Dump after block reordering.

           -fdump-rtl-btl1
           -fdump-rtl-btl2
               -fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the two branch target
               load optimization passes.

           -fdump-rtl-bypass
               Dump after jump bypassing and control flow optimizations.

           -fdump-rtl-combine
               Dump after the RTL instruction combination pass.

           -fdump-rtl-compgotos
               Dump after duplicating the computed gotos.

           -fdump-rtl-ce1
           -fdump-rtl-ce2
           -fdump-rtl-ce3
               -fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable dumping after the three
               if conversion passes.

           -fdump-rtl-cprop_hardreg
               Dump after hard register copy propagation.

           -fdump-rtl-csa
               Dump after combining stack adjustments.

           -fdump-rtl-cse1
           -fdump-rtl-cse2
               -fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the two common
               subexpression elimination passes.

           -fdump-rtl-dce
               Dump after the standalone dead code elimination passes.

           -fdump-rtl-dbr
               Dump after delayed branch scheduling.

           -fdump-rtl-dce1
           -fdump-rtl-dce2
               -fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the two dead store
               elimination passes.

           -fdump-rtl-eh
               Dump after finalization of EH handling code.

           -fdump-rtl-eh_ranges
               Dump after conversion of EH handling range regions.

           -fdump-rtl-expand
               Dump after RTL generation.

           -fdump-rtl-fwprop1
           -fdump-rtl-fwprop2
               -fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after the two forward
               propagation passes.

           -fdump-rtl-gcse1
           -fdump-rtl-gcse2
               -fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after global common
               subexpression elimination.

           -fdump-rtl-init-regs
               Dump after the initialization of the registers.

           -fdump-rtl-initvals
               Dump after the computation of the initial value sets.

           -fdump-rtl-into_cfglayout
               Dump after converting to cfglayout mode.

           -fdump-rtl-ira
               Dump after iterated register allocation.

           -fdump-rtl-jump
               Dump after the second jump optimization.

           -fdump-rtl-loop2
               -fdump-rtl-loop2 enables dumping after the rtl loop optimization passes.

           -fdump-rtl-mach
               Dump after performing the machine dependent reorganization pass, if that pass
               exists.

           -fdump-rtl-mode_sw
               Dump after removing redundant mode switches.

           -fdump-rtl-rnreg
               Dump after register renumbering.

           -fdump-rtl-outof_cfglayout
               Dump after converting from cfglayout mode.

           -fdump-rtl-peephole2
               Dump after the peephole pass.

           -fdump-rtl-postreload
               Dump after post-reload optimizations.

           -fdump-rtl-pro_and_epilogue
               Dump after generating the function prologues and epilogues.

           -fdump-rtl-sched1
           -fdump-rtl-sched2
               -fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after the basic block
               scheduling passes.

           -fdump-rtl-ree
               Dump after sign/zero extension elimination.

           -fdump-rtl-seqabstr
               Dump after common sequence discovery.

           -fdump-rtl-shorten
               Dump after shortening branches.

           -fdump-rtl-sibling
               Dump after sibling call optimizations.

           -fdump-rtl-split1
           -fdump-rtl-split2
           -fdump-rtl-split3
           -fdump-rtl-split4
           -fdump-rtl-split5
               These options enable dumping after five rounds of instruction splitting.

           -fdump-rtl-sms
               Dump after modulo scheduling.  This pass is only run on some architectures.

           -fdump-rtl-stack
               Dump after conversion from GCC's "flat register file" registers to the x87's
               stack-like registers.  This pass is only run on x86 variants.

           -fdump-rtl-subreg1
           -fdump-rtl-subreg2
               -fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after the two subreg
               expansion passes.

           -fdump-rtl-unshare
               Dump after all rtl has been unshared.

           -fdump-rtl-vartrack
               Dump after variable tracking.

           -fdump-rtl-vregs
               Dump after converting virtual registers to hard registers.

           -fdump-rtl-web
               Dump after live range splitting.

           -fdump-rtl-regclass
           -fdump-rtl-subregs_of_mode_init
           -fdump-rtl-subregs_of_mode_finish
           -fdump-rtl-dfinit
           -fdump-rtl-dfinish
               These dumps are defined but always produce empty files.

           -da
           -fdump-rtl-all
               Produce all the dumps listed above.

           -dA Annotate the assembler output with miscellaneous debugging information.

           -dD Dump all macro definitions, at the end of preprocessing, in addition to normal
               output.

           -dH Produce a core dump whenever an error occurs.

           -dp Annotate the assembler output with a comment indicating which pattern and
               alternative is used.  The length and cost of each instruction are also printed.

           -dP Dump the RTL in the assembler output as a comment before each instruction.  Also
               turns on -dp annotation.

           -dx Just generate RTL for a function instead of compiling it.  Usually used with
               -fdump-rtl-expand.

       -fdump-noaddr
           When doing debugging dumps, suppress address output.  This makes it more feasible to
           use diff on debugging dumps for compiler invocations with different compiler binaries
           and/or different text / bss / data / heap / stack / dso start locations.

       -freport-bug
           Collect and dump debug information into a temporary file if an internal compiler error
           (ICE) occurs.

       -fdump-unnumbered
           When doing debugging dumps, suppress instruction numbers and address output.  This
           makes it more feasible to use diff on debugging dumps for compiler invocations with
           different options, in particular with and without -g.

       -fdump-unnumbered-links
           When doing debugging dumps (see -d option above), suppress instruction numbers for the
           links to the previous and next instructions in a sequence.

       -fdump-ipa-switch
           Control the dumping at various stages of inter-procedural analysis language tree to a
           file.  The file name is generated by appending a switch specific suffix to the source
           file name, and the file is created in the same directory as the output file.  The
           following dumps are possible:

           all Enables all inter-procedural analysis dumps.

           cgraph
               Dumps information about call-graph optimization, unused function removal, and
               inlining decisions.

           inline
               Dump after function inlining.

       -fdump-lang-all
       -fdump-lang-switch
       -fdump-lang-switch-options
       -fdump-lang-switch-options=filename
           Control the dumping of language-specific information.  The options and filename
           portions behave as described in the -fdump-tree option.  The following switch values
           are accepted:

           all Enable all language-specific dumps.

           class
               Dump class hierarchy information.  Virtual table information is emitted unless
               'slim' is specified.  This option is applicable to C++ only.

           raw Dump the raw internal tree data.  This option is applicable to C++ only.

       -fdump-passes
           Print on stderr the list of optimization passes that are turned on and off by the
           current command-line options.

       -fdump-statistics-option
           Enable and control dumping of pass statistics in a separate file.  The file name is
           generated by appending a suffix ending in .statistics to the source file name, and the
           file is created in the same directory as the output file.  If the -option form is
           used, -stats causes counters to be summed over the whole compilation unit while
           -details dumps every event as the passes generate them.  The default with no option is
           to sum counters for each function compiled.

       -fdump-tree-all
       -fdump-tree-switch
       -fdump-tree-switch-options
       -fdump-tree-switch-options=filename
           Control the dumping at various stages of processing the intermediate language tree to
           a file.  The file name is generated by appending a switch-specific suffix to the
           source file name, and the file is created in the same directory as the output file. In
           case of =filename option, the dump is output on the given file instead of the auto
           named dump files.  If the -options form is used, options is a list of - separated
           options which control the details of the dump.  Not all options are applicable to all
           dumps; those that are not meaningful are ignored.  The following options are available

           address
               Print the address of each node.  Usually this is not meaningful as it changes
               according to the environment and source file.  Its primary use is for tying up a
               dump file with a debug environment.

           asmname
               If "DECL_ASSEMBLER_NAME" has been set for a given decl, use that in the dump
               instead of "DECL_NAME".  Its primary use is ease of use working backward from
               mangled names in the assembly file.

           slim
               When dumping front-end intermediate representations, inhibit dumping of members of
               a scope or body of a function merely because that scope has been reached.  Only
               dump such items when they are directly reachable by some other path.

               When dumping pretty-printed trees, this option inhibits dumping the bodies of
               control structures.

               When dumping RTL, print the RTL in slim (condensed) form instead of the default
               LISP-like representation.

           raw Print a raw representation of the tree.  By default, trees are pretty-printed into
               a C-like representation.

           details
               Enable more detailed dumps (not honored by every dump option). Also include
               information from the optimization passes.

           stats
               Enable dumping various statistics about the pass (not honored by every dump
               option).

           blocks
               Enable showing basic block boundaries (disabled in raw dumps).

           graph
               For each of the other indicated dump files (-fdump-rtl-pass), dump a
               representation of the control flow graph suitable for viewing with GraphViz to
               file.passid.pass.dot.  Each function in the file is pretty-printed as a subgraph,
               so that GraphViz can render them all in a single plot.

               This option currently only works for RTL dumps, and the RTL is always dumped in
               slim form.

           vops
               Enable showing virtual operands for every statement.

           lineno
               Enable showing line numbers for statements.

           uid Enable showing the unique ID ("DECL_UID") for each variable.

           verbose
               Enable showing the tree dump for each statement.

           eh  Enable showing the EH region number holding each statement.

           scev
               Enable showing scalar evolution analysis details.

           optimized
               Enable showing optimization information (only available in certain passes).

           missed
               Enable showing missed optimization information (only available in certain passes).

           note
               Enable other detailed optimization information (only available in certain passes).

           =filename
               Instead of an auto named dump file, output into the given file name. The file
               names stdout and stderr are treated specially and are considered already open
               standard streams. For example,

                       gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
                            -fdump-tree-pre=/dev/stderr file.c

               outputs vectorizer dump into foo.dump, while the PRE dump is output on to stderr.
               If two conflicting dump filenames are given for the same pass, then the latter
               option overrides the earlier one.

           all Turn on all options, except raw, slim, verbose and lineno.

           optall
               Turn on all optimization options, i.e., optimized, missed, and note.

           To determine what tree dumps are available or find the dump for a pass of interest
           follow the steps below.

           1.  Invoke GCC with -fdump-passes and in the stderr output look for a code that
               corresponds to the pass you are interested in.  For example, the codes
               "tree-evrp", "tree-vrp1", and "tree-vrp2" correspond to the three Value Range
               Propagation passes.  The number at the end distinguishes distinct invocations of
               the same pass.

           2.  To enable the creation of the dump file, append the pass code to the -fdump-
               option prefix and invoke GCC with it.  For example, to enable the dump from the
               Early Value Range Propagation pass, invoke GCC with the -fdump-tree-evrp option.
               Optionally, you may specify the name of the dump file.  If you don't specify one,
               GCC creates as described below.

           3.  Find the pass dump in a file whose name is composed of three components separated
               by a period: the name of the source file GCC was invoked to compile, a numeric
               suffix indicating the pass number followed by the letter t for tree passes (and
               the letter r for RTL passes), and finally the pass code.  For example, the Early
               VRP pass dump might be in a file named myfile.c.038t.evrp in the current working
               directory.  Note that the numeric codes are not stable and may change from one
               version of GCC to another.

       -fopt-info
       -fopt-info-options
       -fopt-info-options=filename
           Controls optimization dumps from various optimization passes. If the -options form is
           used, options is a list of - separated option keywords to select the dump details and
           optimizations.

           The options can be divided into two groups: options describing the verbosity of the
           dump, and options describing which optimizations should be included. The options from
           both the groups can be freely mixed as they are non-overlapping. However, in case of
           any conflicts, the later options override the earlier options on the command line.

           The following options control the dump verbosity:

           optimized
               Print information when an optimization is successfully applied. It is up to a pass
               to decide which information is relevant. For example, the vectorizer passes print
               the source location of loops which are successfully vectorized.

           missed
               Print information about missed optimizations. Individual passes control which
               information to include in the output.

           note
               Print verbose information about optimizations, such as certain transformations,
               more detailed messages about decisions etc.

           all Print detailed optimization information. This includes optimized, missed, and
               note.

           One or more of the following option keywords can be used to describe a group of
           optimizations:

           ipa Enable dumps from all interprocedural optimizations.

           loop
               Enable dumps from all loop optimizations.

           inline
               Enable dumps from all inlining optimizations.

           omp Enable dumps from all OMP (Offloading and Multi Processing) optimizations.

           vec Enable dumps from all vectorization optimizations.

           optall
               Enable dumps from all optimizations. This is a superset of the optimization groups
               listed above.

           If options is omitted, it defaults to optimized-optall, which means to dump all info
           about successful optimizations from all the passes.

           If the filename is provided, then the dumps from all the applicable optimizations are
           concatenated into the filename.  Otherwise the dump is output onto stderr. Though
           multiple -fopt-info options are accepted, only one of them can include a filename. If
           other filenames are provided then all but the first such option are ignored.

           Note that the output filename is overwritten in case of multiple translation units. If
           a combined output from multiple translation units is desired, stderr should be used
           instead.

           In the following example, the optimization info is output to stderr:

                   gcc -O3 -fopt-info

           This example:

                   gcc -O3 -fopt-info-missed=missed.all

           outputs missed optimization report from all the passes into missed.all, and this one:

                   gcc -O2 -ftree-vectorize -fopt-info-vec-missed

           prints information about missed optimization opportunities from vectorization passes
           on stderr.  Note that -fopt-info-vec-missed is equivalent to -fopt-info-missed-vec.
           The order of the optimization group names and message types listed after -fopt-info
           does not matter.

           As another example,

                   gcc -O3 -fopt-info-inline-optimized-missed=inline.txt

           outputs information about missed optimizations as well as optimized locations from all
           the inlining passes into inline.txt.

           Finally, consider:

                   gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt

           Here the two output filenames vec.miss and loop.opt are in conflict since only one
           output file is allowed. In this case, only the first option takes effect and the
           subsequent options are ignored. Thus only vec.miss is produced which contains dumps
           from the vectorizer about missed opportunities.

       -fsched-verbose=n
           On targets that use instruction scheduling, this option controls the amount of
           debugging output the scheduler prints to the dump files.

           For n greater than zero, -fsched-verbose outputs the same information as
           -fdump-rtl-sched1 and -fdump-rtl-sched2.  For n greater than one, it also output basic
           block probabilities, detailed ready list information and unit/insn info.  For n
           greater than two, it includes RTL at abort point, control-flow and regions info.  And
           for n over four, -fsched-verbose also includes dependence info.

       -fenable-kind-pass
       -fdisable-kind-pass=range-list
           This is a set of options that are used to explicitly disable/enable optimization
           passes.  These options are intended for use for debugging GCC.  Compiler users should
           use regular options for enabling/disabling passes instead.

           -fdisable-ipa-pass
               Disable IPA pass pass. pass is the pass name.  If the same pass is statically
               invoked in the compiler multiple times, the pass name should be appended with a
               sequential number starting from 1.

           -fdisable-rtl-pass
           -fdisable-rtl-pass=range-list
               Disable RTL pass pass.  pass is the pass name.  If the same pass is statically
               invoked in the compiler multiple times, the pass name should be appended with a
               sequential number starting from 1.  range-list is a comma-separated list of
               function ranges or assembler names.  Each range is a number pair separated by a
               colon.  The range is inclusive in both ends.  If the range is trivial, the number
               pair can be simplified as a single number.  If the function's call graph node's
               uid falls within one of the specified ranges, the pass is disabled for that
               function.  The uid is shown in the function header of a dump file, and the pass
               names can be dumped by using option -fdump-passes.

           -fdisable-tree-pass
           -fdisable-tree-pass=range-list
               Disable tree pass pass.  See -fdisable-rtl for the description of option
               arguments.

           -fenable-ipa-pass
               Enable IPA pass pass.  pass is the pass name.  If the same pass is statically
               invoked in the compiler multiple times, the pass name should be appended with a
               sequential number starting from 1.

           -fenable-rtl-pass
           -fenable-rtl-pass=range-list
               Enable RTL pass pass.  See -fdisable-rtl for option argument description and
               examples.

           -fenable-tree-pass
           -fenable-tree-pass=range-list
               Enable tree pass pass.  See -fdisable-rtl for the description of option arguments.

           Here are some examples showing uses of these options.

                   # disable ccp1 for all functions
                      -fdisable-tree-ccp1
                   # disable complete unroll for function whose cgraph node uid is 1
                      -fenable-tree-cunroll=1
                   # disable gcse2 for functions at the following ranges [1,1],
                   # [300,400], and [400,1000]
                   # disable gcse2 for functions foo and foo2
                      -fdisable-rtl-gcse2=foo,foo2
                   # disable early inlining
                      -fdisable-tree-einline
                   # disable ipa inlining
                      -fdisable-ipa-inline
                   # enable tree full unroll
                      -fenable-tree-unroll

       -fchecking
       -fchecking=n
           Enable internal consistency checking.  The default depends on the compiler
           configuration.  -fchecking=2 enables further internal consistency checking that might
           affect code generation.

       -frandom-seed=string
           This option provides a seed that GCC uses in place of random numbers in generating
           certain symbol names that have to be different in every compiled file.  It is also
           used to place unique stamps in coverage data files and the object files that produce
           them.  You can use the -frandom-seed option to produce reproducibly identical object
           files.

           The string can either be a number (decimal, octal or hex) or an arbitrary string (in
           which case it's converted to a number by computing CRC32).

           The string should be different for every file you compile.

       -save-temps
       -save-temps=cwd
           Store the usual "temporary" intermediate files permanently; place them in the current
           directory and name them based on the source file.  Thus, compiling foo.c with -c
           -save-temps produces files foo.i and foo.s, as well as foo.o.  This creates a
           preprocessed foo.i output file even though the compiler now normally uses an
           integrated preprocessor.

           When used in combination with the -x command-line option, -save-temps is sensible
           enough to avoid over writing an input source file with the same extension as an
           intermediate file.  The corresponding intermediate file may be obtained by renaming
           the source file before using -save-temps.

           If you invoke GCC in parallel, compiling several different source files that share a
           common base name in different subdirectories or the same source file compiled for
           multiple output destinations, it is likely that the different parallel compilers will
           interfere with each other, and overwrite the temporary files.  For instance:

                   gcc -save-temps -o outdir1/foo.o indir1/foo.c&
                   gcc -save-temps -o outdir2/foo.o indir2/foo.c&

           may result in foo.i and foo.o being written to simultaneously by both compilers.

       -save-temps=obj
           Store the usual "temporary" intermediate files permanently.  If the -o option is used,
           the temporary files are based on the object file.  If the -o option is not used, the
           -save-temps=obj switch behaves like -save-temps.

           For example:

                   gcc -save-temps=obj -c foo.c
                   gcc -save-temps=obj -c bar.c -o dir/xbar.o
                   gcc -save-temps=obj foobar.c -o dir2/yfoobar

           creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i, dir2/yfoobar.s, and
           dir2/yfoobar.o.

       -time[=file]
           Report the CPU time taken by each subprocess in the compilation sequence.  For C
           source files, this is the compiler proper and assembler (plus the linker if linking is
           done).

           Without the specification of an output file, the output looks like this:

                   # cc1 0.12 0.01
                   # as 0.00 0.01

           The first number on each line is the "user time", that is time spent executing the
           program itself.  The second number is "system time", time spent executing operating
           system routines on behalf of the program.  Both numbers are in seconds.

           With the specification of an output file, the output is appended to the named file,
           and it looks like this:

                   0.12 0.01 cc1 <options>
                   0.00 0.01 as <options>

           The "user time" and the "system time" are moved before the program name, and the
           options passed to the program are displayed, so that one can later tell what file was
           being compiled, and with which options.

       -fdump-final-insns[=file]
           Dump the final internal representation (RTL) to file.  If the optional argument is
           omitted (or if file is "."), the name of the dump file is determined by appending
           ".gkd" to the compilation output file name.

       -fcompare-debug[=opts]
           If no error occurs during compilation, run the compiler a second time, adding opts and
           -fcompare-debug-second to the arguments passed to the second compilation.  Dump the
           final internal representation in both compilations, and print an error if they differ.

           If the equal sign is omitted, the default -gtoggle is used.

           The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and nonzero,
           implicitly enables -fcompare-debug.  If GCC_COMPARE_DEBUG is defined to a string
           starting with a dash, then it is used for opts, otherwise the default -gtoggle is
           used.

           -fcompare-debug=, with the equal sign but without opts, is equivalent to
           -fno-compare-debug, which disables the dumping of the final representation and the
           second compilation, preventing even GCC_COMPARE_DEBUG from taking effect.

           To verify full coverage during -fcompare-debug testing, set GCC_COMPARE_DEBUG to say
           -fcompare-debug-not-overridden, which GCC rejects as an invalid option in any actual
           compilation (rather than preprocessing, assembly or linking).  To get just a warning,
           setting GCC_COMPARE_DEBUG to -w%n-fcompare-debug not overridden will do.

       -fcompare-debug-second
           This option is implicitly passed to the compiler for the second compilation requested
           by -fcompare-debug, along with options to silence warnings, and omitting other options
           that would cause the compiler to produce output to files or to standard output as a
           side effect.  Dump files and preserved temporary files are renamed so as to contain
           the ".gk" additional extension during the second compilation, to avoid overwriting
           those generated by the first.

           When this option is passed to the compiler driver, it causes the first compilation to
           be skipped, which makes it useful for little other than debugging the compiler proper.

       -gtoggle
           Turn off generation of debug info, if leaving out this option generates it, or turn it
           on at level 2 otherwise.  The position of this argument in the command line does not
           matter; it takes effect after all other options are processed, and it does so only
           once, no matter how many times it is given.  This is mainly intended to be used with
           -fcompare-debug.

       -fvar-tracking-assignments-toggle
           Toggle -fvar-tracking-assignments, in the same way that -gtoggle toggles -g.

       -Q  Makes the compiler print out each function name as it is compiled, and print some
           statistics about each pass when it finishes.

       -ftime-report
           Makes the compiler print some statistics about the time consumed by each pass when it
           finishes.

       -ftime-report-details
           Record the time consumed by infrastructure parts separately for each pass.

       -fira-verbose=n
           Control the verbosity of the dump file for the integrated register allocator.  The
           default value is 5.  If the value n is greater or equal to 10, the dump output is sent
           to stderr using the same format as n minus 10.

       -flto-report
           Prints a report with internal details on the workings of the link-time optimizer.  The
           contents of this report vary from version to version.  It is meant to be useful to GCC
           developers when processing object files in LTO mode (via -flto).

           Disabled by default.

       -flto-report-wpa
           Like -flto-report, but only print for the WPA phase of Link Time Optimization.

       -fmem-report
           Makes the compiler print some statistics about permanent memory allocation when it
           finishes.

       -fmem-report-wpa
           Makes the compiler print some statistics about permanent memory allocation for the WPA
           phase only.

       -fpre-ipa-mem-report
       -fpost-ipa-mem-report
           Makes the compiler print some statistics about permanent memory allocation before or
           after interprocedural optimization.

       -fprofile-report
           Makes the compiler print some statistics about consistency of the (estimated) profile
           and effect of individual passes.

       -fstack-usage
           Makes the compiler output stack usage information for the program, on a per-function
           basis.  The filename for the dump is made by appending .su to the auxname.  auxname is
           generated from the name of the output file, if explicitly specified and it is not an
           executable, otherwise it is the basename of the source file.  An entry is made up of
           three fields:

           *   The name of the function.

           *   A number of bytes.

           *   One or more qualifiers: "static", "dynamic", "bounded".

           The qualifier "static" means that the function manipulates the stack statically: a
           fixed number of bytes are allocated for the frame on function entry and released on
           function exit; no stack adjustments are otherwise made in the function.  The second
           field is this fixed number of bytes.

           The qualifier "dynamic" means that the function manipulates the stack dynamically: in
           addition to the static allocation described above, stack adjustments are made in the
           body of the function, for example to push/pop arguments around function calls.  If the
           qualifier "bounded" is also present, the amount of these adjustments is bounded at
           compile time and the second field is an upper bound of the total amount of stack used
           by the function.  If it is not present, the amount of these adjustments is not bounded
           at compile time and the second field only represents the bounded part.

       -fstats
           Emit statistics about front-end processing at the end of the compilation.  This option
           is supported only by the C++ front end, and the information is generally only useful
           to the G++ development team.

       -fdbg-cnt-list
           Print the name and the counter upper bound for all debug counters.

       -fdbg-cnt=counter-value-list
           Set the internal debug counter upper bound.  counter-value-list is a comma-separated
           list of name:value pairs which sets the upper bound of each debug counter name to
           value.  All debug counters have the initial upper bound of "UINT_MAX"; thus "dbg_cnt"
           returns true always unless the upper bound is set by this option.  For example, with
           -fdbg-cnt=dce:10,tail_call:0, "dbg_cnt(dce)" returns true only for first 10
           invocations.

       -print-file-name=library
           Print the full absolute name of the library file library that would be used when
           linking---and don't do anything else.  With this option, GCC does not compile or link
           anything; it just prints the file name.

       -print-multi-directory
           Print the directory name corresponding to the multilib selected by any other switches
           present in the command line.  This directory is supposed to exist in GCC_EXEC_PREFIX.

       -print-multi-lib
           Print the mapping from multilib directory names to compiler switches that enable them.
           The directory name is separated from the switches by ;, and each switch starts with an
           @ instead of the -, without spaces between multiple switches.  This is supposed to
           ease shell processing.

       -print-multi-os-directory
           Print the path to OS libraries for the selected multilib, relative to some lib
           subdirectory.  If OS libraries are present in the lib subdirectory and no multilibs
           are used, this is usually just ., if OS libraries are present in libsuffix sibling
           directories this prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are
           present in lib/subdir subdirectories it prints e.g. amd64, sparcv9 or ev6.

       -print-multiarch
           Print the path to OS libraries for the selected multiarch, relative to some lib
           subdirectory.

       -print-prog-name=program
           Like -print-file-name, but searches for a program such as cpp.

       -print-libgcc-file-name
           Same as -print-file-name=libgcc.a.

           This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with
           libgcc.a.  You can do:

                   gcc -nostdlib <files>... `gcc -print-libgcc-file-name`

       -print-search-dirs
           Print the name of the configured installation directory and a list of program and
           library directories gcc searches---and don't do anything else.

           This is useful when gcc prints the error message installation problem, cannot exec
           cpp0: No such file or directory.  To resolve this you either need to put cpp0 and the
           other compiler components where gcc expects to find them, or you can set the
           environment variable GCC_EXEC_PREFIX to the directory where you installed them.  Don't
           forget the trailing /.

       -print-sysroot
           Print the target sysroot directory that is used during compilation.  This is the
           target sysroot specified either at configure time or using the --sysroot option,
           possibly with an extra suffix that depends on compilation options.  If no target
           sysroot is specified, the option prints nothing.

       -print-sysroot-headers-suffix
           Print the suffix added to the target sysroot when searching for headers, or give an
           error if the compiler is not configured with such a suffix---and don't do anything
           else.

       -dumpmachine
           Print the compiler's target machine (for example, i686-pc-linux-gnu)---and don't do
           anything else.

       -dumpversion
           Print the compiler version (for example, 3.0, 6.3.0 or 7)---and don't do anything
           else.  This is the compiler version used in filesystem paths, specs, can be depending
           on how the compiler has been configured just a single number (major version), two
           numbers separated by dot (major and minor version) or three numbers separated by dots
           (major, minor and patchlevel version).

       -dumpfullversion
           Print the full compiler version, always 3 numbers separated by dots, major, minor and
           patchlevel version.

       -dumpspecs
           Print the compiler's built-in specs---and don't do anything else.  (This is used when
           GCC itself is being built.)

   Machine-Dependent Options
       Each target machine supported by GCC can have its own options---for example, to allow you
       to compile for a particular processor variant or ABI, or to control optimizations specific
       to that machine.  By convention, the names of machine-specific options start with -m.

       Some configurations of the compiler also support additional target-specific options,
       usually for compatibility with other compilers on the same platform.

       AArch64 Options

       These options are defined for AArch64 implementations:

       -mabi=name
           Generate code for the specified data model.  Permissible values are ilp32 for SysV-
           like data model where int, long int and pointers are 32 bits, and lp64 for SysV-like
           data model where int is 32 bits, but long int and pointers are 64 bits.

           The default depends on the specific target configuration.  Note that the LP64 and
           ILP32 ABIs are not link-compatible; you must compile your entire program with the same
           ABI, and link with a compatible set of libraries.

       -mbig-endian
           Generate big-endian code.  This is the default when GCC is configured for an
           aarch64_be-*-* target.

       -mgeneral-regs-only
           Generate code which uses only the general-purpose registers.  This will prevent the
           compiler from using floating-point and Advanced SIMD registers but will not impose any
           restrictions on the assembler.

       -mlittle-endian
           Generate little-endian code.  This is the default when GCC is configured for an
           aarch64-*-* but not an aarch64_be-*-* target.

       -mcmodel=tiny
           Generate code for the tiny code model.  The program and its statically defined symbols
           must be within 1MB of each other.  Programs can be statically or dynamically linked.

       -mcmodel=small
           Generate code for the small code model.  The program and its statically defined
           symbols must be within 4GB of each other.  Programs can be statically or dynamically
           linked.  This is the default code model.

       -mcmodel=large
           Generate code for the large code model.  This makes no assumptions about addresses and
           sizes of sections.  Programs can be statically linked only.

       -mstrict-align
           Avoid generating memory accesses that may not be aligned on a natural object boundary
           as described in the architecture specification.

       -momit-leaf-frame-pointer
       -mno-omit-leaf-frame-pointer
           Omit or keep the frame pointer in leaf functions.  The former behavior is the default.

       -mtls-dialect=desc
           Use TLS descriptors as the thread-local storage mechanism for dynamic accesses of TLS
           variables.  This is the default.

       -mtls-dialect=traditional
           Use traditional TLS as the thread-local storage mechanism for dynamic accesses of TLS
           variables.

       -mtls-size=size
           Specify bit size of immediate TLS offsets.  Valid values are 12, 24, 32, 48.  This
           option requires binutils 2.26 or newer.

       -mfix-cortex-a53-835769
       -mno-fix-cortex-a53-835769
           Enable or disable the workaround for the ARM Cortex-A53 erratum number 835769.  This
           involves inserting a NOP instruction between memory instructions and 64-bit integer
           multiply-accumulate instructions.

       -mfix-cortex-a53-843419
       -mno-fix-cortex-a53-843419
           Enable or disable the workaround for the ARM Cortex-A53 erratum number 843419.  This
           erratum workaround is made at link time and this will only pass the corresponding flag
           to the linker.

       -mlow-precision-recip-sqrt
       -mno-low-precision-recip-sqrt
           Enable or disable the reciprocal square root approximation.  This option only has an
           effect if -ffast-math or -funsafe-math-optimizations is used as well.  Enabling this
           reduces precision of reciprocal square root results to about 16 bits for single
           precision and to 32 bits for double precision.

       -mlow-precision-sqrt
       -mno-low-precision-sqrt
           Enable or disable the square root approximation.  This option only has an effect if
           -ffast-math or -funsafe-math-optimizations is used as well.  Enabling this reduces
           precision of square root results to about 16 bits for single precision and to 32 bits
           for double precision.  If enabled, it implies -mlow-precision-recip-sqrt.

       -mlow-precision-div
       -mno-low-precision-div
           Enable or disable the division approximation.  This option only has an effect if
           -ffast-math or -funsafe-math-optimizations is used as well.  Enabling this reduces
           precision of division results to about 16 bits for single precision and to 32 bits for
           double precision.

       -march=name
           Specify the name of the target architecture and, optionally, one or more feature
           modifiers.  This option has the form -march=arch{+[no]feature}*.

           The permissible values for arch are armv8-a, armv8.1-a, armv8.2-a, armv8.3-a or
           armv8.4-a or native.

           The value armv8.4-a implies armv8.3-a and enables compiler support for the ARMv8.4-A
           architecture extensions.

           The value armv8.3-a implies armv8.2-a and enables compiler support for the ARMv8.3-A
           architecture extensions.

           The value armv8.2-a implies armv8.1-a and enables compiler support for the ARMv8.2-A
           architecture extensions.

           The value armv8.1-a implies armv8-a and enables compiler support for the ARMv8.1-A
           architecture extension.  In particular, it enables the +crc, +lse, and +rdma features.

           The value native is available on native AArch64 GNU/Linux and causes the compiler to
           pick the architecture of the host system.  This option has no effect if the compiler
           is unable to recognize the architecture of the host system,

           The permissible values for feature are listed in the sub-section on
           aarch64-feature-modifiers,,-march and -mcpu Feature Modifiers.  Where conflicting
           feature modifiers are specified, the right-most feature is used.

           GCC uses name to determine what kind of instructions it can emit when generating
           assembly code.  If -march is specified without either of -mtune or -mcpu also being
           specified, the code is tuned to perform well across a range of target processors
           implementing the target architecture.

       -mtune=name
           Specify the name of the target processor for which GCC should tune the performance of
           the code.  Permissible values for this option are: generic, cortex-a35, cortex-a53,
           cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, exynos-m1, falkor,
           qdf24xx, saphira, xgene1, vulcan, thunderx, thunderxt88, thunderxt88p1, thunderxt81,
           thunderxt83, thunderx2t99, cortex-a57.cortex-a53, cortex-a72.cortex-a53,
           cortex-a73.cortex-a35, cortex-a73.cortex-a53, cortex-a75.cortex-a55, native.

           The values cortex-a57.cortex-a53, cortex-a72.cortex-a53, cortex-a73.cortex-a35,
           cortex-a73.cortex-a53, cortex-a75.cortex-a55 specify that GCC should tune for a
           big.LITTLE system.

           Additionally on native AArch64 GNU/Linux systems the value native tunes performance to
           the host system.  This option has no effect if the compiler is unable to recognize the
           processor of the host system.

           Where none of -mtune=, -mcpu= or -march= are specified, the code is tuned to perform
           well across a range of target processors.

           This option cannot be suffixed by feature modifiers.

       -mcpu=name
           Specify the name of the target processor, optionally suffixed by one or more feature
           modifiers.  This option has the form -mcpu=cpu{+[no]feature}*, where the permissible
           values for cpu are the same as those available for -mtune.  The permissible values for
           feature are documented in the sub-section on aarch64-feature-modifiers,,-march and
           -mcpu Feature Modifiers.  Where conflicting feature modifiers are specified, the
           right-most feature is used.

           GCC uses name to determine what kind of instructions it can emit when generating
           assembly code (as if by -march) and to determine the target processor for which to
           tune for performance (as if by -mtune).  Where this option is used in conjunction with
           -march or -mtune, those options take precedence over the appropriate part of this
           option.

       -moverride=string
           Override tuning decisions made by the back-end in response to a -mtune= switch.  The
           syntax, semantics, and accepted values for string in this option are not guaranteed to
           be consistent across releases.

           This option is only intended to be useful when developing GCC.

       -mverbose-cost-dump
           Enable verbose cost model dumping in the debug dump files.  This option is provided
           for use in debugging the compiler.

       -mpc-relative-literal-loads
       -mno-pc-relative-literal-loads
           Enable or disable PC-relative literal loads.  With this option literal pools are
           accessed using a single instruction and emitted after each function.  This limits the
           maximum size of functions to 1MB.  This is enabled by default for -mcmodel=tiny.

       -msign-return-address=scope
           Select the function scope on which return address signing will be applied.
           Permissible values are none, which disables return address signing, non-leaf, which
           enables pointer signing for functions which are not leaf functions, and all, which
           enables pointer signing for all functions.  The default value is none.

       -msve-vector-bits=bits
           Specify the number of bits in an SVE vector register.  This option only has an effect
           when SVE is enabled.

           GCC supports two forms of SVE code generation: "vector-length agnostic" output that
           works with any size of vector register and "vector-length specific" output that allows
           GCC to make assumptions about the vector length when it is useful for optimization
           reasons.  The possible values of bits are: scalable, 128, 256, 512, 1024 and 2048.
           Specifying scalable selects vector-length agnostic output.  At present
           -msve-vector-bits=128 also generates vector-length agnostic output.  All other values
           generate vector-length specific code.  The behavior of these values may change in
           future releases and no value except scalable should be relied on for producing code
           that is portable across different hardware SVE vector lengths.

           The default is -msve-vector-bits=scalable, which produces vector-length agnostic code.

       -march and -mcpu Feature Modifiers

       Feature modifiers used with -march and -mcpu can be any of the following and their
       inverses nofeature:

       crc Enable CRC extension.  This is on by default for -march=armv8.1-a.

       crypto
           Enable Crypto extension.  This also enables Advanced SIMD and floating-point
           instructions.

       fp  Enable floating-point instructions.  This is on by default for all possible values for
           options -march and -mcpu.

       simd
           Enable Advanced SIMD instructions.  This also enables floating-point instructions.
           This is on by default for all possible values for options -march and -mcpu.

       sve Enable Scalable Vector Extension instructions.  This also enables Advanced SIMD and
           floating-point instructions.

       lse Enable Large System Extension instructions.  This is on by default for
           -march=armv8.1-a.

       rdma
           Enable Round Double Multiply Accumulate instructions.  This is on by default for
           -march=armv8.1-a.

       fp16
           Enable FP16 extension.  This also enables floating-point instructions.

       fp16fml
           Enable FP16 fmla extension.  This also enables FP16 extensions and floating-point
           instructions. This option is enabled by default for -march=armv8.4-a. Use of this
           option with architectures prior to Armv8.2-A is not supported.

       rcpc
           Enable the RcPc extension.  This does not change code generation from GCC, but is
           passed on to the assembler, enabling inline asm statements to use instructions from
           the RcPc extension.

       dotprod
           Enable the Dot Product extension.  This also enables Advanced SIMD instructions.

       aes Enable the Armv8-a aes and pmull crypto extension.  This also enables Advanced SIMD
           instructions.

       sha2
           Enable the Armv8-a sha2 crypto extension.  This also enables Advanced SIMD
           instructions.

       sha3
           Enable the sha512 and sha3 crypto extension.  This also enables Advanced SIMD
           instructions. Use of this option with architectures prior to Armv8.2-A is not
           supported.

       sm4 Enable the sm3 and sm4 crypto extension.  This also enables Advanced SIMD
           instructions.  Use of this option with architectures prior to Armv8.2-A is not
           supported.

       Feature crypto implies aes, sha2, and simd, which implies fp.  Conversely, nofp implies
       nosimd, which implies nocrypto, noaes and nosha2.

       Adapteva Epiphany Options

       These -m options are defined for Adapteva Epiphany:

       -mhalf-reg-file
           Don't allocate any register in the range "r32"..."r63".  That allows code to run on
           hardware variants that lack these registers.

       -mprefer-short-insn-regs
           Preferentially allocate registers that allow short instruction generation.  This can
           result in increased instruction count, so this may either reduce or increase overall
           code size.

       -mbranch-cost=num
           Set the cost of branches to roughly num "simple" instructions.  This cost is only a
           heuristic and is not guaranteed to produce consistent results across releases.

       -mcmove
           Enable the generation of conditional moves.

       -mnops=num
           Emit num NOPs before every other generated instruction.

       -mno-soft-cmpsf
           For single-precision floating-point comparisons, emit an "fsub" instruction and test
           the flags.  This is faster than a software comparison, but can get incorrect results
           in the presence of NaNs, or when two different small numbers are compared such that
           their difference is calculated as zero.  The default is -msoft-cmpsf, which uses
           slower, but IEEE-compliant, software comparisons.

       -mstack-offset=num
           Set the offset between the top of the stack and the stack pointer.  E.g., a value of 8
           means that the eight bytes in the range "sp+0...sp+7" can be used by leaf functions
           without stack allocation.  Values other than 8 or 16 are untested and unlikely to
           work.  Note also that this option changes the ABI; compiling a program with a
           different stack offset than the libraries have been compiled with generally does not
           work.  This option can be useful if you want to evaluate if a different stack offset
           would give you better code, but to actually use a different stack offset to build
           working programs, it is recommended to configure the toolchain with the appropriate
           --with-stack-offset=num option.

       -mno-round-nearest
           Make the scheduler assume that the rounding mode has been set to truncating.  The
           default is -mround-nearest.

       -mlong-calls
           If not otherwise specified by an attribute, assume all calls might be beyond the
           offset range of the "b" / "bl" instructions, and therefore load the function address
           into a register before performing a (otherwise direct) call.  This is the default.

       -mshort-calls
           If not otherwise specified by an attribute, assume all direct calls are in the range
           of the "b" / "bl" instructions, so use these instructions for direct calls.  The
           default is -mlong-calls.

       -msmall16
           Assume addresses can be loaded as 16-bit unsigned values.  This does not apply to
           function addresses for which -mlong-calls semantics are in effect.

       -mfp-mode=mode
           Set the prevailing mode of the floating-point unit.  This determines the floating-
           point mode that is provided and expected at function call and return time.  Making
           this mode match the mode you predominantly need at function start can make your
           programs smaller and faster by avoiding unnecessary mode switches.

           mode can be set to one the following values:

           caller
               Any mode at function entry is valid, and retained or restored when the function
               returns, and when it calls other functions.  This mode is useful for compiling
               libraries or other compilation units you might want to incorporate into different
               programs with different prevailing FPU modes, and the convenience of being able to
               use a single object file outweighs the size and speed overhead for any extra mode
               switching that might be needed, compared with what would be needed with a more
               specific choice of prevailing FPU mode.

           truncate
               This is the mode used for floating-point calculations with truncating (i.e. round
               towards zero) rounding mode.  That includes conversion from floating point to
               integer.

           round-nearest
               This is the mode used for floating-point calculations with round-to-nearest-or-
               even rounding mode.

           int This is the mode used to perform integer calculations in the FPU, e.g.  integer
               multiply, or integer multiply-and-accumulate.

           The default is -mfp-mode=caller

       -mnosplit-lohi
       -mno-postinc
       -mno-postmodify
           Code generation tweaks that disable, respectively, splitting of 32-bit loads,
           generation of post-increment addresses, and generation of post-modify addresses.  The
           defaults are msplit-lohi, -mpost-inc, and -mpost-modify.

       -mnovect-double
           Change the preferred SIMD mode to SImode.  The default is -mvect-double, which uses
           DImode as preferred SIMD mode.

       -max-vect-align=num
           The maximum alignment for SIMD vector mode types.  num may be 4 or 8.  The default is
           8.  Note that this is an ABI change, even though many library function interfaces are
           unaffected if they don't use SIMD vector modes in places that affect size and/or
           alignment of relevant types.

       -msplit-vecmove-early
           Split vector moves into single word moves before reload.  In theory this can give
           better register allocation, but so far the reverse seems to be generally the case.

       -m1reg-reg
           Specify a register to hold the constant -1, which makes loading small negative
           constants and certain bitmasks faster.  Allowable values for reg are r43 and r63,
           which specify use of that register as a fixed register, and none, which means that no
           register is used for this purpose.  The default is -m1reg-none.

       ARC Options

       The following options control the architecture variant for which code is being compiled:

       -mbarrel-shifter
           Generate instructions supported by barrel shifter.  This is the default unless
           -mcpu=ARC601 or -mcpu=ARCEM is in effect.

       -mjli-always
           Force to call a function using jli_s instruction.  This option is valid only for ARCv2
           architecture.

       -mcpu=cpu
           Set architecture type, register usage, and instruction scheduling parameters for cpu.
           There are also shortcut alias options available for backward compatibility and
           convenience.  Supported values for cpu are

           arc600
               Compile for ARC600.  Aliases: -mA6, -mARC600.

           arc601
               Compile for ARC601.  Alias: -mARC601.

           arc700
               Compile for ARC700.  Aliases: -mA7, -mARC700.  This is the default when configured
               with --with-cpu=arc700.

           arcem
               Compile for ARC EM.

           archs
               Compile for ARC HS.

           em  Compile for ARC EM CPU with no hardware extensions.

           em4 Compile for ARC EM4 CPU.

           em4_dmips
               Compile for ARC EM4 DMIPS CPU.

           em4_fpus
               Compile for ARC EM4 DMIPS CPU with the single-precision floating-point extension.

           em4_fpuda
               Compile for ARC EM4 DMIPS CPU with single-precision floating-point and double
               assist instructions.

           hs  Compile for ARC HS CPU with no hardware extensions except the atomic instructions.

           hs34
               Compile for ARC HS34 CPU.

           hs38
               Compile for ARC HS38 CPU.

           hs38_linux
               Compile for ARC HS38 CPU with all hardware extensions on.

           arc600_norm
               Compile for ARC 600 CPU with "norm" instructions enabled.

           arc600_mul32x16
               Compile for ARC 600 CPU with "norm" and 32x16-bit multiply instructions enabled.

           arc600_mul64
               Compile for ARC 600 CPU with "norm" and "mul64"-family instructions enabled.

           arc601_norm
               Compile for ARC 601 CPU with "norm" instructions enabled.

           arc601_mul32x16
               Compile for ARC 601 CPU with "norm" and 32x16-bit multiply instructions enabled.

           arc601_mul64
               Compile for ARC 601 CPU with "norm" and "mul64"-family instructions enabled.

           nps400
               Compile for ARC 700 on NPS400 chip.

           em_mini
               Compile for ARC EM minimalist configuration featuring reduced register set.

       -mdpfp
       -mdpfp-compact
           Generate double-precision FPX instructions, tuned for the compact implementation.

       -mdpfp-fast
           Generate double-precision FPX instructions, tuned for the fast implementation.

       -mno-dpfp-lrsr
           Disable "lr" and "sr" instructions from using FPX extension aux registers.

       -mea
           Generate extended arithmetic instructions.  Currently only "divaw", "adds", "subs",
           and "sat16" are supported.  This is always enabled for -mcpu=ARC700.

       -mno-mpy
           Do not generate "mpy"-family instructions for ARC700.  This option is deprecated.

       -mmul32x16
           Generate 32x16-bit multiply and multiply-accumulate instructions.

       -mmul64
           Generate "mul64" and "mulu64" instructions.  Only valid for -mcpu=ARC600.

       -mnorm
           Generate "norm" instructions.  This is the default if -mcpu=ARC700 is in effect.

       -mspfp
       -mspfp-compact
           Generate single-precision FPX instructions, tuned for the compact implementation.

       -mspfp-fast
           Generate single-precision FPX instructions, tuned for the fast implementation.

       -msimd
           Enable generation of ARC SIMD instructions via target-specific builtins.  Only valid
           for -mcpu=ARC700.

       -msoft-float
           This option ignored; it is provided for compatibility purposes only.  Software
           floating-point code is emitted by default, and this default can overridden by FPX
           options; -mspfp, -mspfp-compact, or -mspfp-fast for single precision, and -mdpfp,
           -mdpfp-compact, or -mdpfp-fast for double precision.

       -mswap
           Generate "swap" instructions.

       -matomic
           This enables use of the locked load/store conditional extension to implement atomic
           memory built-in functions.  Not available for ARC 6xx or ARC EM cores.

       -mdiv-rem
           Enable "div" and "rem" instructions for ARCv2 cores.

       -mcode-density
           Enable code density instructions for ARC EM.  This option is on by default for ARC HS.

       -mll64
           Enable double load/store operations for ARC HS cores.

       -mtp-regno=regno
           Specify thread pointer register number.

       -mmpy-option=multo
           Compile ARCv2 code with a multiplier design option.  You can specify the option using
           either a string or numeric value for multo.  wlh1 is the default value.  The
           recognized values are:

           0
           none
               No multiplier available.

           1
           w   16x16 multiplier, fully pipelined.  The following instructions are enabled: "mpyw"
               and "mpyuw".

           2
           wlh1
               32x32 multiplier, fully pipelined (1 stage).  The following instructions are
               additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           3
           wlh2
               32x32 multiplier, fully pipelined (2 stages).  The following instructions are
               additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           4
           wlh3
               Two 16x16 multipliers, blocking, sequential.  The following instructions are
               additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           5
           wlh4
               One 16x16 multiplier, blocking, sequential.  The following instructions are
               additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           6
           wlh5
               One 32x4 multiplier, blocking, sequential.  The following instructions are
               additionally enabled: "mpy", "mpyu", "mpym", "mpymu", and "mpy_s".

           7
           plus_dmpy
               ARC HS SIMD support.

           8
           plus_macd
               ARC HS SIMD support.

           9
           plus_qmacw
               ARC HS SIMD support.

           This option is only available for ARCv2 cores.

       -mfpu=fpu
           Enables support for specific floating-point hardware extensions for ARCv2 cores.
           Supported values for fpu are:

           fpus
               Enables support for single-precision floating-point hardware extensions.

           fpud
               Enables support for double-precision floating-point hardware extensions.  The
               single-precision floating-point extension is also enabled.  Not available for ARC
               EM.

           fpuda
               Enables support for double-precision floating-point hardware extensions using
               double-precision assist instructions.  The single-precision floating-point
               extension is also enabled.  This option is only available for ARC EM.

           fpuda_div
               Enables support for double-precision floating-point hardware extensions using
               double-precision assist instructions.  The single-precision floating-point,
               square-root, and divide extensions are also enabled.  This option is only
               available for ARC EM.

           fpuda_fma
               Enables support for double-precision floating-point hardware extensions using
               double-precision assist instructions.  The single-precision floating-point and
               fused multiply and add hardware extensions are also enabled.  This option is only
               available for ARC EM.

           fpuda_all
               Enables support for double-precision floating-point hardware extensions using
               double-precision assist instructions.  All single-precision floating-point
               hardware extensions are also enabled.  This option is only available for ARC EM.

           fpus_div
               Enables support for single-precision floating-point, square-root and divide
               hardware extensions.

           fpud_div
               Enables support for double-precision floating-point, square-root and divide
               hardware extensions.  This option includes option fpus_div. Not available for ARC
               EM.

           fpus_fma
               Enables support for single-precision floating-point and fused multiply and add
               hardware extensions.

           fpud_fma
               Enables support for double-precision floating-point and fused multiply and add
               hardware extensions.  This option includes option fpus_fma.  Not available for ARC
               EM.

           fpus_all
               Enables support for all single-precision floating-point hardware extensions.

           fpud_all
               Enables support for all single- and double-precision floating-point hardware
               extensions.  Not available for ARC EM.

       -mirq-ctrl-saved=register-range, blink, lp_count
           Specifies general-purposes registers that the processor automatically saves/restores
           on interrupt entry and exit.  register-range is specified as two registers separated
           by a dash.  The register range always starts with "r0", the upper limit is "fp"
           register.  blink and lp_count are optional.  This option is only valid for ARC EM and
           ARC HS cores.

       -mrgf-banked-regs=number
           Specifies the number of registers replicated in second register bank on entry to fast
           interrupt.  Fast interrupts are interrupts with the highest priority level P0.  These
           interrupts save only PC and STATUS32 registers to avoid memory transactions during
           interrupt entry and exit sequences.  Use this option when you are using fast
           interrupts in an ARC V2 family processor.  Permitted values are 4, 8, 16, and 32.

       -mlpc-width=width
           Specify the width of the "lp_count" register.  Valid values for width are 8, 16, 20,
           24, 28 and 32 bits.  The default width is fixed to 32 bits.  If the width is less than
           32, the compiler does not attempt to transform loops in your program to use the zero-
           delay loop mechanism unless it is known that the "lp_count" register can hold the
           required loop-counter value.  Depending on the width specified, the compiler and run-
           time library might continue to use the loop mechanism for various needs.  This option
           defines macro "__ARC_LPC_WIDTH__" with the value of width.

       -mrf16
           This option instructs the compiler to generate code for a 16-entry register file.
           This option defines the "__ARC_RF16__" preprocessor macro.

       The following options are passed through to the assembler, and also define preprocessor
       macro symbols.

       -mdsp-packa
           Passed down to the assembler to enable the DSP Pack A extensions.  Also sets the
           preprocessor symbol "__Xdsp_packa".  This option is deprecated.

       -mdvbf
           Passed down to the assembler to enable the dual Viterbi butterfly extension.  Also
           sets the preprocessor symbol "__Xdvbf".  This option is deprecated.

       -mlock
           Passed down to the assembler to enable the locked load/store conditional extension.
           Also sets the preprocessor symbol "__Xlock".

       -mmac-d16
           Passed down to the assembler.  Also sets the preprocessor symbol "__Xxmac_d16".  This
           option is deprecated.

       -mmac-24
           Passed down to the assembler.  Also sets the preprocessor symbol "__Xxmac_24".  This
           option is deprecated.

       -mrtsc
           Passed down to the assembler to enable the 64-bit time-stamp counter extension
           instruction.  Also sets the preprocessor symbol "__Xrtsc".  This option is deprecated.

       -mswape
           Passed down to the assembler to enable the swap byte ordering extension instruction.
           Also sets the preprocessor symbol "__Xswape".

       -mtelephony
           Passed down to the assembler to enable dual- and single-operand instructions for
           telephony.  Also sets the preprocessor symbol "__Xtelephony".  This option is
           deprecated.

       -mxy
           Passed down to the assembler to enable the XY memory extension.  Also sets the
           preprocessor symbol "__Xxy".

       The following options control how the assembly code is annotated:

       -misize
           Annotate assembler instructions with estimated addresses.

       -mannotate-align
           Explain what alignment considerations lead to the decision to make an instruction
           short or long.

       The following options are passed through to the linker:

       -marclinux
           Passed through to the linker, to specify use of the "arclinux" emulation.  This option
           is enabled by default in tool chains built for "arc-linux-uclibc" and
           "arceb-linux-uclibc" targets when profiling is not requested.

       -marclinux_prof
           Passed through to the linker, to specify use of the "arclinux_prof" emulation.  This
           option is enabled by default in tool chains built for "arc-linux-uclibc" and
           "arceb-linux-uclibc" targets when profiling is requested.

       The following options control the semantics of generated code:

       -mlong-calls
           Generate calls as register indirect calls, thus providing access to the full 32-bit
           address range.

       -mmedium-calls
           Don't use less than 25-bit addressing range for calls, which is the offset available
           for an unconditional branch-and-link instruction.  Conditional execution of function
           calls is suppressed, to allow use of the 25-bit range, rather than the 21-bit range
           with conditional branch-and-link.  This is the default for tool chains built for
           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.

       -G num
           Put definitions of externally-visible data in a small data section if that data is no
           bigger than num bytes.  The default value of num is 4 for any ARC configuration, or 8
           when we have double load/store operations.

       -mno-sdata
           Do not generate sdata references.  This is the default for tool chains built for
           "arc-linux-uclibc" and "arceb-linux-uclibc" targets.

       -mvolatile-cache
           Use ordinarily cached memory accesses for volatile references.  This is the default.

       -mno-volatile-cache
           Enable cache bypass for volatile references.

       The following options fine tune code generation:

       -malign-call
           Do alignment optimizations for call instructions.

       -mauto-modify-reg
           Enable the use of pre/post modify with register displacement.

       -mbbit-peephole
           Enable bbit peephole2.

       -mno-brcc
           This option disables a target-specific pass in arc_reorg to generate compare-and-
           branch ("brcc") instructions.  It has no effect on generation of these instructions
           driven by the combiner pass.

       -mcase-vector-pcrel
           Use PC-relative switch case tables to enable case table shortening.  This is the
           default for -Os.

       -mcompact-casesi
           Enable compact "casesi" pattern.  This is the default for -Os, and only available for
           ARCv1 cores.

       -mno-cond-exec
           Disable the ARCompact-specific pass to generate conditional execution instructions.

           Due to delay slot scheduling and interactions between operand numbers, literal sizes,
           instruction lengths, and the support for conditional execution, the target-independent
           pass to generate conditional execution is often lacking, so the ARC port has kept a
           special pass around that tries to find more conditional execution generation
           opportunities after register allocation, branch shortening, and delay slot scheduling
           have been done.  This pass generally, but not always, improves performance and code
           size, at the cost of extra compilation time, which is why there is an option to switch
           it off.  If you have a problem with call instructions exceeding their allowable offset
           range because they are conditionalized, you should consider using -mmedium-calls
           instead.

       -mearly-cbranchsi
           Enable pre-reload use of the "cbranchsi" pattern.

       -mexpand-adddi
           Expand "adddi3" and "subdi3" at RTL generation time into "add.f", "adc" etc.  This
           option is deprecated.

       -mindexed-loads
           Enable the use of indexed loads.  This can be problematic because some optimizers then
           assume that indexed stores exist, which is not the case.

       -mlra
           Enable Local Register Allocation.  This is still experimental for ARC, so by default
           the compiler uses standard reload (i.e. -mno-lra).

       -mlra-priority-none
           Don't indicate any priority for target registers.

       -mlra-priority-compact
           Indicate target register priority for r0..r3 / r12..r15.

       -mlra-priority-noncompact
           Reduce target register priority for r0..r3 / r12..r15.

       -mno-millicode
           When optimizing for size (using -Os), prologues and epilogues that have to save or
           restore a large number of registers are often shortened by using call to a special
           function in libgcc; this is referred to as a millicode call.  As these calls can pose
           performance issues, and/or cause linking issues when linking in a nonstandard way,
           this option is provided to turn off millicode call generation.

       -mmixed-code
           Tweak register allocation to help 16-bit instruction generation.  This generally has
           the effect of decreasing the average instruction size while increasing the instruction
           count.

       -mq-class
           Enable q instruction alternatives.  This is the default for -Os.

       -mRcq
           Enable Rcq constraint handling.  Most short code generation depends on this.  This is
           the default.

       -mRcw
           Enable Rcw constraint handling.  Most ccfsm condexec mostly depends on this.  This is
           the default.

       -msize-level=level
           Fine-tune size optimization with regards to instruction lengths and alignment.  The
           recognized values for level are:

           0   No size optimization.  This level is deprecated and treated like 1.

           1   Short instructions are used opportunistically.

           2   In addition, alignment of loops and of code after barriers are dropped.

           3   In addition, optional data alignment is dropped, and the option Os is enabled.

           This defaults to 3 when -Os is in effect.  Otherwise, the behavior when this is not
           set is equivalent to level 1.

       -mtune=cpu
           Set instruction scheduling parameters for cpu, overriding any implied by -mcpu=.

           Supported values for cpu are

           ARC600
               Tune for ARC600 CPU.

           ARC601
               Tune for ARC601 CPU.

           ARC700
               Tune for ARC700 CPU with standard multiplier block.

           ARC700-xmac
               Tune for ARC700 CPU with XMAC block.

           ARC725D
               Tune for ARC725D CPU.

           ARC750D
               Tune for ARC750D CPU.

       -mmultcost=num
           Cost to assume for a multiply instruction, with 4 being equal to a normal instruction.

       -munalign-prob-threshold=probability
           Set probability threshold for unaligning branches.  When tuning for ARC700 and
           optimizing for speed, branches without filled delay slot are preferably emitted
           unaligned and long, unless profiling indicates that the probability for the branch to
           be taken is below probability.  The default is (REG_BR_PROB_BASE/2), i.e. 5000.

       The following options are maintained for backward compatibility, but are now deprecated
       and will be removed in a future release:

       -margonaut
           Obsolete FPX.

       -mbig-endian
       -EB Compile code for big-endian targets.  Use of these options is now deprecated.  Big-
           endian code is supported by configuring GCC to build "arceb-elf32" and
           "arceb-linux-uclibc" targets, for which big endian is the default.

       -mlittle-endian
       -EL Compile code for little-endian targets.  Use of these options is now deprecated.
           Little-endian code is supported by configuring GCC to build "arc-elf32" and
           "arc-linux-uclibc" targets, for which little endian is the default.

       -mbarrel_shifter
           Replaced by -mbarrel-shifter.

       -mdpfp_compact
           Replaced by -mdpfp-compact.

       -mdpfp_fast
           Replaced by -mdpfp-fast.

       -mdsp_packa
           Replaced by -mdsp-packa.

       -mEA
           Replaced by -mea.

       -mmac_24
           Replaced by -mmac-24.

       -mmac_d16
           Replaced by -mmac-d16.

       -mspfp_compact
           Replaced by -mspfp-compact.

       -mspfp_fast
           Replaced by -mspfp-fast.

       -mtune=cpu
           Values arc600, arc601, arc700 and arc700-xmac for cpu are replaced by ARC600, ARC601,
           ARC700 and ARC700-xmac respectively.

       -multcost=num
           Replaced by -mmultcost.

       ARM Options

       These -m options are defined for the ARM port:

       -mabi=name
           Generate code for the specified ABI.  Permissible values are: apcs-gnu, atpcs, aapcs,
           aapcs-linux and iwmmxt.

       -mapcs-frame
           Generate a stack frame that is compliant with the ARM Procedure Call Standard for all
           functions, even if this is not strictly necessary for correct execution of the code.
           Specifying -fomit-frame-pointer with this option causes the stack frames not to be
           generated for leaf functions.  The default is -mno-apcs-frame.  This option is
           deprecated.

       -mapcs
           This is a synonym for -mapcs-frame and is deprecated.

       -mthumb-interwork
           Generate code that supports calling between the ARM and Thumb instruction sets.
           Without this option, on pre-v5 architectures, the two instruction sets cannot be
           reliably used inside one program.  The default is -mno-thumb-interwork, since slightly
           larger code is generated when -mthumb-interwork is specified.  In AAPCS configurations
           this option is meaningless.

       -mno-sched-prolog
           Prevent the reordering of instructions in the function prologue, or the merging of
           those instruction with the instructions in the function's body.  This means that all
           functions start with a recognizable set of instructions (or in fact one of a choice
           from a small set of different function prologues), and this information can be used to
           locate the start of functions inside an executable piece of code.  The default is
           -msched-prolog.

       -mfloat-abi=name
           Specifies which floating-point ABI to use.  Permissible values are: soft, softfp and
           hard.

           Specifying soft causes GCC to generate output containing library calls for floating-
           point operations.  softfp allows the generation of code using hardware floating-point
           instructions, but still uses the soft-float calling conventions.  hard allows
           generation of floating-point instructions and uses FPU-specific calling conventions.

           The default depends on the specific target configuration.  Note that the hard-float
           and soft-float ABIs are not link-compatible; you must compile your entire program with
           the same ABI, and link with a compatible set of libraries.

       -mlittle-endian
           Generate code for a processor running in little-endian mode.  This is the default for
           all standard configurations.

       -mbig-endian
           Generate code for a processor running in big-endian mode; the default is to compile
           code for a little-endian processor.

       -mbe8
       -mbe32
           When linking a big-endian image select between BE8 and BE32 formats.  The option has
           no effect for little-endian images and is ignored.  The default is dependent on the
           selected target architecture.  For ARMv6 and later architectures the default is BE8,
           for older architectures the default is BE32.  BE32 format has been deprecated by ARM.

       -march=name[+extension...]
           This specifies the name of the target ARM architecture.  GCC uses this name to
           determine what kind of instructions it can emit when generating assembly code.  This
           option can be used in conjunction with or instead of the -mcpu= option.

           Permissible names are: armv4t, armv5t, armv5te, armv6, armv6j, armv6k, armv6kz,
           armv6t2, armv6z, armv6zk, armv7, armv7-a, armv7ve, armv8-a, armv8.1-a, armv8.2-a,
           armv8.3-a, armv8.4-a, armv7-r, armv8-r, armv6-m, armv6s-m, armv7-m, armv7e-m,
           armv8-m.base, armv8-m.main, iwmmxt and iwmmxt2.

           Additionally, the following architectures, which lack support for the Thumb execution
           state, are recognized but support is deprecated: armv2, armv2a, armv3, armv3m, armv4,
           armv5 and armv5e.

           Many of the architectures support extensions.  These can be added by appending
           +extension to the architecture name.  Extension options are processed in order and
           capabilities accumulate.  An extension will also enable any necessary base extensions
           upon which it depends.  For example, the +crypto extension will always enable the
           +simd extension.  The exception to the additive construction is for extensions that
           are prefixed with +no...: these extensions disable the specified option and any other
           extensions that may depend on the presence of that extension.

           For example, -march=armv7-a+simd+nofp+vfpv4 is equivalent to writing
           -march=armv7-a+vfpv4 since the +simd option is entirely disabled by the +nofp option
           that follows it.

           Most extension names are generically named, but have an effect that is dependent upon
           the architecture to which it is applied.  For example, the +simd option can be applied
           to both armv7-a and armv8-a architectures, but will enable the original ARMv7-A
           Advanced SIMD (Neon) extensions for armv7-a and the ARMv8-A variant for armv8-a.

           The table below lists the supported extensions for each architecture.  Architectures
           not mentioned do not support any extensions.

           armv5e
           armv5te
           armv6
           armv6j
           armv6k
           armv6kz
           armv6t2
           armv6z
           armv6zk
               +fp The VFPv2 floating-point instructions.  The extension +vfpv2 can be used as an
                   alias for this extension.

               +nofp
                   Disable the floating-point instructions.

           armv7
               The common subset of the ARMv7-A, ARMv7-R and ARMv7-M architectures.

               +fp The VFPv3 floating-point instructions, with 16 double-precision registers.
                   The extension +vfpv3-d16 can be used as an alias for this extension.  Note
                   that floating-point is not supported by the base ARMv7-M architecture, but is
                   compatible with both the ARMv7-A and ARMv7-R architectures.

               +nofp
                   Disable the floating-point instructions.

           armv7-a
               +mp The multiprocessing extension.

               +sec
                   The security extension.

               +fp The VFPv3 floating-point instructions, with 16 double-precision registers.
                   The extension +vfpv3-d16 can be used as an alias for this extension.

               +simd
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions.  The
                   extensions +neon and +neon-vfpv3 can be used as aliases for this extension.

               +vfpv3
                   The VFPv3 floating-point instructions, with 32 double-precision registers.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions, with 16 double-precision registers and
                   the half-precision floating-point conversion operations.

               +vfpv3-fp16
                   The VFPv3 floating-point instructions, with 32 double-precision registers and
                   the half-precision floating-point conversion operations.

               +vfpv4-d16
                   The VFPv4 floating-point instructions, with 16 double-precision registers.

               +vfpv4
                   The VFPv4 floating-point instructions, with 32 double-precision registers.

               +neon-fp16
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with
                   the half-precision floating-point conversion operations.

               +neon-vfpv4
                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions.

               +nosimd
                   Disable the Advanced SIMD instructions (does not disable floating point).

               +nofp
                   Disable the floating-point and Advanced SIMD instructions.

           armv7ve
               The extended version of the ARMv7-A architecture with support for virtualization.

               +fp The VFPv4 floating-point instructions, with 16 double-precision registers.
                   The extension +vfpv4-d16 can be used as an alias for this extension.

               +simd
                   The Advanced SIMD (Neon) v2 and the VFPv4 floating-point instructions.  The
                   extension +neon-vfpv4 can be used as an alias for this extension.

               +vfpv3-d16
                   The VFPv3 floating-point instructions, with 16 double-precision registers.

               +vfpv3
                   The VFPv3 floating-point instructions, with 32 double-precision registers.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions, with 16 double-precision registers and
                   the half-precision floating-point conversion operations.

               +vfpv3-fp16
                   The VFPv3 floating-point instructions, with 32 double-precision registers and
                   the half-precision floating-point conversion operations.

               +vfpv4-d16
                   The VFPv4 floating-point instructions, with 16 double-precision registers.

               +vfpv4
                   The VFPv4 floating-point instructions, with 32 double-precision registers.

               +neon
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions.  The
                   extension +neon-vfpv3 can be used as an alias for this extension.

               +neon-fp16
                   The Advanced SIMD (Neon) v1 and the VFPv3 floating-point instructions, with
                   the half-precision floating-point conversion operations.

               +nosimd
                   Disable the Advanced SIMD instructions (does not disable floating point).

               +nofp
                   Disable the floating-point and Advanced SIMD instructions.

           armv8-a
               +crc
                   The Cyclic Redundancy Check (CRC) instructions.

               +simd
                   The ARMv8-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

           armv8.1-a
               +simd
                   The ARMv8.1-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.  This also enables the Advanced SIMD and
                   floating-point instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

           armv8.2-a
           armv8.3-a
               +fp16
                   The half-precision floating-point data processing instructions.  This also
                   enables the Advanced SIMD and floating-point instructions.

               +fp16fml
                   The half-precision floating-point fmla extension.  This also enables the half-
                   precision floating-point extension and Advanced SIMD and floating-point
                   instructions.

               +simd
                   The ARMv8.1-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.  This also enables the Advanced SIMD and
                   floating-point instructions.

               +dotprod
                   Enable the Dot Product extension.  This also enables Advanced SIMD
                   instructions.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

           armv8.4-a
               +fp16
                   The half-precision floating-point data processing instructions.  This also
                   enables the Advanced SIMD and floating-point instructions as well as the Dot
                   Product extension and the half-precision floating-point fmla extension.

               +simd
                   The ARMv8.3-A Advanced SIMD and floating-point instructions as well as the Dot
                   Product extension.

               +crypto
                   The cryptographic instructions.  This also enables the Advanced SIMD and
                   floating-point instructions as well as the Dot Product extension.

               +nocrypto
                   Disable the cryptographic extension.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

           armv7-r
               +fp.sp
                   The single-precision VFPv3 floating-point instructions.  The extension
                   +vfpv3xd can be used as an alias for this extension.

               +fp The VFPv3 floating-point instructions with 16 double-precision registers.  The
                   extension +vfpv3-d16 can be used as an alias for this extension.

               +vfpv3xd-d16-fp16
                   The single-precision VFPv3 floating-point instructions with 16 double-
                   precision registers and the half-precision floating-point conversion
                   operations.

               +vfpv3-d16-fp16
                   The VFPv3 floating-point instructions, with 16 double-precision registers and
                   the half-precision floating-point conversion operations.

               +nofp
                   Disable the floating-point extension.

               +idiv
                   The ARM-state integer division instructions.

               +noidiv
                   Disable the ARM-state integer division extension.

           armv7e-m
               +fp The single-precision VFPv4 floating-point instructions.

               +fpv5
                   The single-precision FPv5 floating-point instructions.

               +fp.dp
                   The single- and double-precision FPv5 floating-point instructions.

               +nofp
                   Disable the floating-point extensions.

           armv8-m.main
               +dsp
                   The DSP instructions.

               +nodsp
                   Disable the DSP extension.

               +fp The single-precision floating-point instructions.

               +fp.dp
                   The single- and double-precision floating-point instructions.

               +nofp
                   Disable the floating-point extension.

           armv8-r
               +crc
                   The Cyclic Redundancy Check (CRC) instructions.

               +fp.sp
                   The single-precision FPv5 floating-point instructions.

               +simd
                   The ARMv8-A Advanced SIMD and floating-point instructions.

               +crypto
                   The cryptographic instructions.

               +nocrypto
                   Disable the cryptographic instructions.

               +nofp
                   Disable the floating-point, Advanced SIMD and cryptographic instructions.

           -march=native causes the compiler to auto-detect the architecture of the build
           computer.  At present, this feature is only supported on GNU/Linux, and not all
           architectures are recognized.  If the auto-detect is unsuccessful the option has no
           effect.

       -mtune=name
           This option specifies the name of the target ARM processor for which GCC should tune
           the performance of the code.  For some ARM implementations better performance can be
           obtained by using this option.  Permissible names are: arm2, arm250, arm3, arm6,
           arm60, arm600, arm610, arm620, arm7, arm7m, arm7d, arm7dm, arm7di, arm7dmi, arm70,
           arm700, arm700i, arm710, arm710c, arm7100, arm720, arm7500, arm7500fe, arm7tdmi,
           arm7tdmi-s, arm710t, arm720t, arm740t, strongarm, strongarm110, strongarm1100,
           strongarm1110, arm8, arm810, arm9, arm9e, arm920, arm920t, arm922t, arm946e-s,
           arm966e-s, arm968e-s, arm926ej-s, arm940t, arm9tdmi, arm10tdmi, arm1020t, arm1026ej-s,
           arm10e, arm1020e, arm1022e, arm1136j-s, arm1136jf-s, mpcore, mpcorenovfp, arm1156t2-s,
           arm1156t2f-s, arm1176jz-s, arm1176jzf-s, generic-armv7-a, cortex-a5, cortex-a7,
           cortex-a8, cortex-a9, cortex-a12, cortex-a15, cortex-a17, cortex-a32, cortex-a35,
           cortex-a53, cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, cortex-r4,
           cortex-r4f, cortex-r5, cortex-r7, cortex-r8, cortex-r52, cortex-m33, cortex-m23,
           cortex-m7, cortex-m4, cortex-m3, cortex-m1, cortex-m0, cortex-m0plus,
           cortex-m1.small-multiply, cortex-m0.small-multiply, cortex-m0plus.small-multiply,
           exynos-m1, marvell-pj4, xscale, iwmmxt, iwmmxt2, ep9312, fa526, fa626, fa606te,
           fa626te, fmp626, fa726te, xgene1.

           Additionally, this option can specify that GCC should tune the performance of the code
           for a big.LITTLE system.  Permissible names are: cortex-a15.cortex-a7,
           cortex-a17.cortex-a7, cortex-a57.cortex-a53, cortex-a72.cortex-a53,
           cortex-a72.cortex-a35, cortex-a73.cortex-a53, cortex-a75.cortex-a55.

           -mtune=generic-arch specifies that GCC should tune the performance for a blend of
           processors within architecture arch.  The aim is to generate code that run well on the
           current most popular processors, balancing between optimizations that benefit some
           CPUs in the range, and avoiding performance pitfalls of other CPUs.  The effects of
           this option may change in future GCC versions as CPU models come and go.

           -mtune permits the same extension options as -mcpu, but the extension options do not
           affect the tuning of the generated code.

           -mtune=native causes the compiler to auto-detect the CPU of the build computer.  At
           present, this feature is only supported on GNU/Linux, and not all architectures are
           recognized.  If the auto-detect is unsuccessful the option has no effect.

       -mcpu=name[+extension...]
           This specifies the name of the target ARM processor.  GCC uses this name to derive the
           name of the target ARM architecture (as if specified by -march) and the ARM processor
           type for which to tune for performance (as if specified by -mtune).  Where this option
           is used in conjunction with -march or -mtune, those options take precedence over the
           appropriate part of this option.

           Many of the supported CPUs implement optional architectural extensions.  Where this is
           so the architectural extensions are normally enabled by default.  If implementations
           that lack the extension exist, then the extension syntax can be used to disable those
           extensions that have been omitted.  For floating-point and Advanced SIMD (Neon)
           instructions, the settings of the options -mfloat-abi and -mfpu must also be
           considered: floating-point and Advanced SIMD instructions will only be used if
           -mfloat-abi is not set to soft; and any setting of -mfpu other than auto will override
           the available floating-point and SIMD extension instructions.

           For example, cortex-a9 can be found in three major configurations: integer only, with
           just a floating-point unit or with floating-point and Advanced SIMD.  The default is
           to enable all the instructions, but the extensions +nosimd and +nofp can be used to
           disable just the SIMD or both the SIMD and floating-point instructions respectively.

           Permissible names for this option are the same as those for -mtune.

           The following extension options are common to the listed CPUs:

           +nodsp
               Disable the DSP instructions on cortex-m33.

           +nofp
               Disables the floating-point instructions on arm9e, arm946e-s, arm966e-s,
               arm968e-s, arm10e, arm1020e, arm1022e, arm926ej-s, arm1026ej-s, cortex-r5,
               cortex-r7, cortex-r8, cortex-m4, cortex-m7 and cortex-m33.  Disables the floating-
               point and SIMD instructions on generic-armv7-a, cortex-a5, cortex-a7, cortex-a8,
               cortex-a9, cortex-a12, cortex-a15, cortex-a17, cortex-a15.cortex-a7,
               cortex-a17.cortex-a7, cortex-a32, cortex-a35, cortex-a53 and cortex-a55.

           +nofp.dp
               Disables the double-precision component of the floating-point instructions on
               cortex-r5, cortex-r7, cortex-r8, cortex-r52 and cortex-m7.

           +nosimd
               Disables the SIMD (but not floating-point) instructions on generic-armv7-a,
               cortex-a5, cortex-a7 and cortex-a9.

           +crypto
               Enables the cryptographic instructions on cortex-a32, cortex-a35, cortex-a53,
               cortex-a55, cortex-a57, cortex-a72, cortex-a73, cortex-a75, exynos-m1, xgene1,
               cortex-a57.cortex-a53, cortex-a72.cortex-a53, cortex-a73.cortex-a35,
               cortex-a73.cortex-a53 and cortex-a75.cortex-a55.

           Additionally the generic-armv7-a pseudo target defaults to VFPv3 with 16 double-
           precision registers.  It supports the following extension options: mp, sec, vfpv3-d16,
           vfpv3, vfpv3-d16-fp16, vfpv3-fp16, vfpv4-d16, vfpv4, neon, neon-vfpv3, neon-fp16,
           neon-vfpv4.  The meanings are the same as for the extensions to -march=armv7-a.

           -mcpu=generic-arch is also permissible, and is equivalent to -march=arch
           -mtune=generic-arch.  See -mtune for more information.

           -mcpu=native causes the compiler to auto-detect the CPU of the build computer.  At
           present, this feature is only supported on GNU/Linux, and not all architectures are
           recognized.  If the auto-detect is unsuccessful the option has no effect.

       -mfpu=name
           This specifies what floating-point hardware (or hardware emulation) is available on
           the target.  Permissible names are: auto, vfpv2, vfpv3, vfpv3-fp16, vfpv3-d16,
           vfpv3-d16-fp16, vfpv3xd, vfpv3xd-fp16, neon-vfpv3, neon-fp16, vfpv4, vfpv4-d16,
           fpv4-sp-d16, neon-vfpv4, fpv5-d16, fpv5-sp-d16, fp-armv8, neon-fp-armv8 and
           crypto-neon-fp-armv8.  Note that neon is an alias for neon-vfpv3 and vfp is an alias
           for vfpv2.

           The setting auto is the default and is special.  It causes the compiler to select the
           floating-point and Advanced SIMD instructions based on the settings of -mcpu and
           -march.

           If the selected floating-point hardware includes the NEON extension (e.g. -mfpu=neon),
           note that floating-point operations are not generated by GCC's auto-vectorization pass
           unless -funsafe-math-optimizations is also specified.  This is because NEON hardware
           does not fully implement the IEEE 754 standard for floating-point arithmetic (in
           particular denormal values are treated as zero), so the use of NEON instructions may
           lead to a loss of precision.

           You can also set the fpu name at function level by using the "target("fpu=")" function
           attributes or pragmas.

       -mfp16-format=name
           Specify the format of the "__fp16" half-precision floating-point type.  Permissible
           names are none, ieee, and alternative; the default is none, in which case the "__fp16"
           type is not defined.

       -mstructure-size-boundary=n
           The sizes of all structures and unions are rounded up to a multiple of the number of
           bits set by this option.  Permissible values are 8, 32 and 64.  The default value
           varies for different toolchains.  For the COFF targeted toolchain the default value is
           8.  A value of 64 is only allowed if the underlying ABI supports it.

           Specifying a larger number can produce faster, more efficient code, but can also
           increase the size of the program.  Different values are potentially incompatible.
           Code compiled with one value cannot necessarily expect to work with code or libraries
           compiled with another value, if they exchange information using structures or unions.

           This option is deprecated.

       -mabort-on-noreturn
           Generate a call to the function "abort" at the end of a "noreturn" function.  It is
           executed if the function tries to return.

       -mlong-calls
       -mno-long-calls
           Tells the compiler to perform function calls by first loading the address of the
           function into a register and then performing a subroutine call on this register.  This
           switch is needed if the target function lies outside of the 64-megabyte addressing
           range of the offset-based version of subroutine call instruction.

           Even if this switch is enabled, not all function calls are turned into long calls.
           The heuristic is that static functions, functions that have the "short_call"
           attribute, functions that are inside the scope of a "#pragma no_long_calls" directive,
           and functions whose definitions have already been compiled within the current
           compilation unit are not turned into long calls.  The exceptions to this rule are that
           weak function definitions, functions with the "long_call" attribute or the "section"
           attribute, and functions that are within the scope of a "#pragma long_calls" directive
           are always turned into long calls.

           This feature is not enabled by default.  Specifying -mno-long-calls restores the
           default behavior, as does placing the function calls within the scope of a "#pragma
           long_calls_off" directive.  Note these switches have no effect on how the compiler
           generates code to handle function calls via function pointers.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather than loading it in the
           prologue for each function.  The runtime system is responsible for initializing this
           register with an appropriate value before execution begins.

       -mpic-register=reg
           Specify the register to be used for PIC addressing.  For standard PIC base case, the
           default is any suitable register determined by compiler.  For single PIC base case,
           the default is R9 if target is EABI based or stack-checking is enabled, otherwise the
           default is R10.

       -mpic-data-is-text-relative
           Assume that the displacement between the text and data segments is fixed at static
           link time.  This permits using PC-relative addressing operations to access data known
           to be in the data segment.  For non-VxWorks RTP targets, this option is enabled by
           default.  When disabled on such targets, it will enable -msingle-pic-base by default.

       -mpoke-function-name
           Write the name of each function into the text section, directly preceding the function
           prologue.  The generated code is similar to this:

                        t0
                            .ascii "arm_poke_function_name", 0
                            .align
                        t1
                            .word 0xff000000 + (t1 - t0)
                        arm_poke_function_name
                            mov     ip, sp
                            stmfd   sp!, {fp, ip, lr, pc}
                            sub     fp, ip, #4

           When performing a stack backtrace, code can inspect the value of "pc" stored at "fp +
           0".  If the trace function then looks at location "pc - 12" and the top 8 bits are
           set, then we know that there is a function name embedded immediately preceding this
           location and has length "((pc[-3]) & 0xff000000)".

       -mthumb
       -marm
           Select between generating code that executes in ARM and Thumb states.  The default for
           most configurations is to generate code that executes in ARM state, but the default
           can be changed by configuring GCC with the --with-mode=state configure option.

           You can also override the ARM and Thumb mode for each function by using the
           "target("thumb")" and "target("arm")" function attributes or pragmas.

       -mflip-thumb
           Switch ARM/Thumb modes on alternating functions.  This option is provided for
           regression testing of mixed Thumb/ARM code generation, and is not intended for
           ordinary use in compiling code.

       -mtpcs-frame
           Generate a stack frame that is compliant with the Thumb Procedure Call Standard for
           all non-leaf functions.  (A leaf function is one that does not call any other
           functions.)  The default is -mno-tpcs-frame.

       -mtpcs-leaf-frame
           Generate a stack frame that is compliant with the Thumb Procedure Call Standard for
           all leaf functions.  (A leaf function is one that does not call any other functions.)
           The default is -mno-apcs-leaf-frame.

       -mcallee-super-interworking
           Gives all externally visible functions in the file being compiled an ARM instruction
           set header which switches to Thumb mode before executing the rest of the function.
           This allows these functions to be called from non-interworking code.  This option is
           not valid in AAPCS configurations because interworking is enabled by default.

       -mcaller-super-interworking
           Allows calls via function pointers (including virtual functions) to execute correctly
           regardless of whether the target code has been compiled for interworking or not.
           There is a small overhead in the cost of executing a function pointer if this option
           is enabled.  This option is not valid in AAPCS configurations because interworking is
           enabled by default.

       -mtp=name
           Specify the access model for the thread local storage pointer.  The valid models are
           soft, which generates calls to "__aeabi_read_tp", cp15, which fetches the thread
           pointer from "cp15" directly (supported in the arm6k architecture), and auto, which
           uses the best available method for the selected processor.  The default setting is
           auto.

       -mtls-dialect=dialect
           Specify the dialect to use for accessing thread local storage.  Two dialects are
           supported---gnu and gnu2.  The gnu dialect selects the original GNU scheme for
           supporting local and global dynamic TLS models.  The gnu2 dialect selects the GNU
           descriptor scheme, which provides better performance for shared libraries.  The GNU
           descriptor scheme is compatible with the original scheme, but does require new
           assembler, linker and library support.  Initial and local exec TLS models are
           unaffected by this option and always use the original scheme.

       -mword-relocations
           Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32).  This is
           enabled by default on targets (uClinux, SymbianOS) where the runtime loader imposes
           this restriction, and when -fpic or -fPIC is specified.

       -mfix-cortex-m3-ldrd
           Some Cortex-M3 cores can cause data corruption when "ldrd" instructions with
           overlapping destination and base registers are used.  This option avoids generating
           these instructions.  This option is enabled by default when -mcpu=cortex-m3 is
           specified.

       -munaligned-access
       -mno-unaligned-access
           Enables (or disables) reading and writing of 16- and 32- bit values from addresses
           that are not 16- or 32- bit aligned.  By default unaligned access is disabled for all
           pre-ARMv6, all ARMv6-M and for ARMv8-M Baseline architectures, and enabled for all
           other architectures.  If unaligned access is not enabled then words in packed data
           structures are accessed a byte at a time.

           The ARM attribute "Tag_CPU_unaligned_access" is set in the generated object file to
           either true or false, depending upon the setting of this option.  If unaligned access
           is enabled then the preprocessor symbol "__ARM_FEATURE_UNALIGNED" is also defined.

       -mneon-for-64bits
           Enables using Neon to handle scalar 64-bits operations. This is disabled by default
           since the cost of moving data from core registers to Neon is high.

       -mslow-flash-data
           Assume loading data from flash is slower than fetching instruction.  Therefore literal
           load is minimized for better performance.  This option is only supported when
           compiling for ARMv7 M-profile and off by default.

       -masm-syntax-unified
           Assume inline assembler is using unified asm syntax.  The default is currently off
           which implies divided syntax.  This option has no impact on Thumb2. However, this may
           change in future releases of GCC.  Divided syntax should be considered deprecated.

       -mrestrict-it
           Restricts generation of IT blocks to conform to the rules of ARMv8-A.  IT blocks can
           only contain a single 16-bit instruction from a select set of instructions. This
           option is on by default for ARMv8-A Thumb mode.

       -mprint-tune-info
           Print CPU tuning information as comment in assembler file.  This is an option used
           only for regression testing of the compiler and not intended for ordinary use in
           compiling code.  This option is disabled by default.

       -mverbose-cost-dump
           Enable verbose cost model dumping in the debug dump files.  This option is provided
           for use in debugging the compiler.

       -mpure-code
           Do not allow constant data to be placed in code sections.  Additionally, when
           compiling for ELF object format give all text sections the ELF processor-specific
           section attribute "SHF_ARM_PURECODE".  This option is only available when generating
           non-pic code for M-profile targets with the MOVT instruction.

       -mcmse
           Generate secure code as per the "ARMv8-M Security Extensions: Requirements on
           Development Tools Engineering Specification", which can be found on
           <http://infocenter.arm.com/help/topic/com.arm.doc.ecm0359818/ECM0359818_armv8m_security_extensions_reqs_on_dev_tools_1_0.pdf>.

       AVR Options

       These options are defined for AVR implementations:

       -mmcu=mcu
           Specify Atmel AVR instruction set architectures (ISA) or MCU type.

           The default for this option is@tie{}avr2.

           GCC supports the following AVR devices and ISAs:

           "avr2"
               "Classic" devices with up to 8@tie{}KiB of program memory.  mcu@tie{}= "attiny22",
               "attiny26", "at90c8534", "at90s2313", "at90s2323", "at90s2333", "at90s2343",
               "at90s4414", "at90s4433", "at90s4434", "at90s8515", "at90s8535".

           "avr25"
               "Classic" devices with up to 8@tie{}KiB of program memory and with the "MOVW"
               instruction.  mcu@tie{}= "ata5272", "ata6616c", "attiny13", "attiny13a",
               "attiny2313", "attiny2313a", "attiny24", "attiny24a", "attiny25", "attiny261",
               "attiny261a", "attiny43u", "attiny4313", "attiny44", "attiny44a", "attiny441",
               "attiny45", "attiny461", "attiny461a", "attiny48", "attiny828", "attiny84",
               "attiny84a", "attiny841", "attiny85", "attiny861", "attiny861a", "attiny87",
               "attiny88", "at86rf401".

           "avr3"
               "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of  program memory.
               mcu@tie{}= "at43usb355", "at76c711".

           "avr31"
               "Classic" devices with 128@tie{}KiB of program memory.  mcu@tie{}= "atmega103",
               "at43usb320".

           "avr35"
               "Classic" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory and with
               the "MOVW" instruction.  mcu@tie{}= "ata5505", "ata6617c", "ata664251",
               "atmega16u2", "atmega32u2", "atmega8u2", "attiny1634", "attiny167", "at90usb162",
               "at90usb82".

           "avr4"
               "Enhanced" devices with up to 8@tie{}KiB of program memory.  mcu@tie{}= "ata6285",
               "ata6286", "ata6289", "ata6612c", "atmega48", "atmega48a", "atmega48p",
               "atmega48pa", "atmega48pb", "atmega8", "atmega8a", "atmega8hva", "atmega8515",
               "atmega8535", "atmega88", "atmega88a", "atmega88p", "atmega88pa", "atmega88pb",
               "at90pwm1", "at90pwm2", "at90pwm2b", "at90pwm3", "at90pwm3b", "at90pwm81".

           "avr5"
               "Enhanced" devices with 16@tie{}KiB up to 64@tie{}KiB of program memory.
               mcu@tie{}= "ata5702m322", "ata5782", "ata5790", "ata5790n", "ata5791", "ata5795",
               "ata5831", "ata6613c", "ata6614q", "ata8210", "ata8510", "atmega16", "atmega16a",
               "atmega16hva", "atmega16hva2", "atmega16hvb", "atmega16hvbrevb", "atmega16m1",
               "atmega16u4", "atmega161", "atmega162", "atmega163", "atmega164a", "atmega164p",
               "atmega164pa", "atmega165", "atmega165a", "atmega165p", "atmega165pa",
               "atmega168", "atmega168a", "atmega168p", "atmega168pa", "atmega168pb",
               "atmega169", "atmega169a", "atmega169p", "atmega169pa", "atmega32", "atmega32a",
               "atmega32c1", "atmega32hvb", "atmega32hvbrevb", "atmega32m1", "atmega32u4",
               "atmega32u6", "atmega323", "atmega324a", "atmega324p", "atmega324pa", "atmega325",
               "atmega325a", "atmega325p", "atmega325pa", "atmega3250", "atmega3250a",
               "atmega3250p", "atmega3250pa", "atmega328", "atmega328p", "atmega328pb",
               "atmega329", "atmega329a", "atmega329p", "atmega329pa", "atmega3290",
               "atmega3290a", "atmega3290p", "atmega3290pa", "atmega406", "atmega64",
               "atmega64a", "atmega64c1", "atmega64hve", "atmega64hve2", "atmega64m1",
               "atmega64rfr2", "atmega640", "atmega644", "atmega644a", "atmega644p",
               "atmega644pa", "atmega644rfr2", "atmega645", "atmega645a", "atmega645p",
               "atmega6450", "atmega6450a", "atmega6450p", "atmega649", "atmega649a",
               "atmega649p", "atmega6490", "atmega6490a", "atmega6490p", "at90can32",
               "at90can64", "at90pwm161", "at90pwm216", "at90pwm316", "at90scr100", "at90usb646",
               "at90usb647", "at94k", "m3000".

           "avr51"
               "Enhanced" devices with 128@tie{}KiB of program memory.  mcu@tie{}= "atmega128",
               "atmega128a", "atmega128rfa1", "atmega128rfr2", "atmega1280", "atmega1281",
               "atmega1284", "atmega1284p", "atmega1284rfr2", "at90can128", "at90usb1286",
               "at90usb1287".

           "avr6"
               "Enhanced" devices with 3-byte PC, i.e. with more than 128@tie{}KiB of program
               memory.  mcu@tie{}= "atmega256rfr2", "atmega2560", "atmega2561", "atmega2564rfr2".

           "avrxmega2"
               "XMEGA" devices with more than 8@tie{}KiB and up to 64@tie{}KiB of program memory.
               mcu@tie{}= "atxmega16a4", "atxmega16a4u", "atxmega16c4", "atxmega16d4",
               "atxmega16e5", "atxmega32a4", "atxmega32a4u", "atxmega32c3", "atxmega32c4",
               "atxmega32d3", "atxmega32d4", "atxmega32e5", "atxmega8e5".

           "avrxmega3"
               "XMEGA" devices with up to 64@tie{}KiB of combined program memory and RAM, and
               with program memory visible in the RAM address space.  mcu@tie{}= "attiny1614",
               "attiny1616", "attiny1617", "attiny212", "attiny214", "attiny3214", "attiny3216",
               "attiny3217", "attiny412", "attiny414", "attiny416", "attiny417", "attiny814",
               "attiny816", "attiny817".

           "avrxmega4"
               "XMEGA" devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program
               memory.  mcu@tie{}= "atxmega64a3", "atxmega64a3u", "atxmega64a4u", "atxmega64b1",
               "atxmega64b3", "atxmega64c3", "atxmega64d3", "atxmega64d4".

           "avrxmega5"
               "XMEGA" devices with more than 64@tie{}KiB and up to 128@tie{}KiB of program
               memory and more than 64@tie{}KiB of RAM.  mcu@tie{}= "atxmega64a1",
               "atxmega64a1u".

           "avrxmega6"
               "XMEGA" devices with more than 128@tie{}KiB of program memory.  mcu@tie{}=
               "atxmega128a3", "atxmega128a3u", "atxmega128b1", "atxmega128b3", "atxmega128c3",
               "atxmega128d3", "atxmega128d4", "atxmega192a3", "atxmega192a3u", "atxmega192c3",
               "atxmega192d3", "atxmega256a3", "atxmega256a3b", "atxmega256a3bu",
               "atxmega256a3u", "atxmega256c3", "atxmega256d3", "atxmega384c3", "atxmega384d3".

           "avrxmega7"
               "XMEGA" devices with more than 128@tie{}KiB of program memory and more than
               64@tie{}KiB of RAM.  mcu@tie{}= "atxmega128a1", "atxmega128a1u", "atxmega128a4u".

           "avrtiny"
               "TINY" Tiny core devices with 512@tie{}B up to 4@tie{}KiB of program memory.
               mcu@tie{}= "attiny10", "attiny20", "attiny4", "attiny40", "attiny5", "attiny9".

           "avr1"
               This ISA is implemented by the minimal AVR core and supported for assembler only.
               mcu@tie{}= "attiny11", "attiny12", "attiny15", "attiny28", "at90s1200".

       -mabsdata
           Assume that all data in static storage can be accessed by LDS / STS instructions.
           This option has only an effect on reduced Tiny devices like ATtiny40.  See also the
           "absdata" AVR Variable Attributes,variable attribute.

       -maccumulate-args
           Accumulate outgoing function arguments and acquire/release the needed stack space for
           outgoing function arguments once in function prologue/epilogue.  Without this option,
           outgoing arguments are pushed before calling a function and popped afterwards.

           Popping the arguments after the function call can be expensive on AVR so that
           accumulating the stack space might lead to smaller executables because arguments need
           not be removed from the stack after such a function call.

           This option can lead to reduced code size for functions that perform several calls to
           functions that get their arguments on the stack like calls to printf-like functions.

       -mbranch-cost=cost
           Set the branch costs for conditional branch instructions to cost.  Reasonable values
           for cost are small, non-negative integers. The default branch cost is 0.

       -mcall-prologues
           Functions prologues/epilogues are expanded as calls to appropriate subroutines.  Code
           size is smaller.

       -mgas-isr-prologues
           Interrupt service routines (ISRs) may use the "__gcc_isr" pseudo instruction supported
           by GNU Binutils.  If this option is on, the feature can still be disabled for
           individual ISRs by means of the AVR Function Attributes,,"no_gccisr" function
           attribute.  This feature is activated per default if optimization is on (but not with
           -Og, @pxref{Optimize Options}), and if GNU Binutils support PR21683
           ("https://sourceware.org/PR21683").

       -mint8
           Assume "int" to be 8-bit integer.  This affects the sizes of all types: a "char" is 1
           byte, an "int" is 1 byte, a "long" is 2 bytes, and "long long" is 4 bytes.  Please
           note that this option does not conform to the C standards, but it results in smaller
           code size.

       -mmain-is-OS_task
           Do not save registers in "main".  The effect is the same like attaching attribute AVR
           Function Attributes,,"OS_task" to "main". It is activated per default if optimization
           is on.

       -mn-flash=num
           Assume that the flash memory has a size of num times 64@tie{}KiB.

       -mno-interrupts
           Generated code is not compatible with hardware interrupts.  Code size is smaller.

       -mrelax
           Try to replace "CALL" resp. "JMP" instruction by the shorter "RCALL" resp. "RJMP"
           instruction if applicable.  Setting -mrelax just adds the --mlink-relax option to the
           assembler's command line and the --relax option to the linker's command line.

           Jump relaxing is performed by the linker because jump offsets are not known before
           code is located. Therefore, the assembler code generated by the compiler is the same,
           but the instructions in the executable may differ from instructions in the assembler
           code.

           Relaxing must be turned on if linker stubs are needed, see the section on "EIND" and
           linker stubs below.

       -mrmw
           Assume that the device supports the Read-Modify-Write instructions "XCH", "LAC", "LAS"
           and "LAT".

       -mshort-calls
           Assume that "RJMP" and "RCALL" can target the whole program memory.

           This option is used internally for multilib selection.  It is not an optimization
           option, and you don't need to set it by hand.

       -msp8
           Treat the stack pointer register as an 8-bit register, i.e. assume the high byte of
           the stack pointer is zero.  In general, you don't need to set this option by hand.

           This option is used internally by the compiler to select and build multilibs for
           architectures "avr2" and "avr25".  These architectures mix devices with and without
           "SPH".  For any setting other than -mmcu=avr2 or -mmcu=avr25 the compiler driver adds
           or removes this option from the compiler proper's command line, because the compiler
           then knows if the device or architecture has an 8-bit stack pointer and thus no "SPH"
           register or not.

       -mstrict-X
           Use address register "X" in a way proposed by the hardware.  This means that "X" is
           only used in indirect, post-increment or pre-decrement addressing.

           Without this option, the "X" register may be used in the same way as "Y" or "Z" which
           then is emulated by additional instructions.  For example, loading a value with
           "X+const" addressing with a small non-negative "const < 64" to a register Rn is
           performed as

                   adiw r26, const   ; X += const
                   ld   <Rn>, X        ; <Rn> = *X
                   sbiw r26, const   ; X -= const

       -mtiny-stack
           Only change the lower 8@tie{}bits of the stack pointer.

       -mfract-convert-truncate
           Allow to use truncation instead of rounding towards zero for fractional fixed-point
           types.

       -nodevicelib
           Don't link against AVR-LibC's device specific library "lib<mcu>.a".

       -Waddr-space-convert
           Warn about conversions between address spaces in the case where the resulting address
           space is not contained in the incoming address space.

       -Wmisspelled-isr
           Warn if the ISR is misspelled, i.e. without __vector prefix.  Enabled by default.

       "EIND" and Devices with More Than 128 Ki Bytes of Flash

       Pointers in the implementation are 16@tie{}bits wide.  The address of a function or label
       is represented as word address so that indirect jumps and calls can target any code
       address in the range of 64@tie{}Ki words.

       In order to facilitate indirect jump on devices with more than 128@tie{}Ki bytes of
       program memory space, there is a special function register called "EIND" that serves as
       most significant part of the target address when "EICALL" or "EIJMP" instructions are
       used.

       Indirect jumps and calls on these devices are handled as follows by the compiler and are
       subject to some limitations:

       *   The compiler never sets "EIND".

       *   The compiler uses "EIND" implicitly in "EICALL"/"EIJMP" instructions or might read
           "EIND" directly in order to emulate an indirect call/jump by means of a "RET"
           instruction.

       *   The compiler assumes that "EIND" never changes during the startup code or during the
           application. In particular, "EIND" is not saved/restored in function or interrupt
           service routine prologue/epilogue.

       *   For indirect calls to functions and computed goto, the linker generates stubs. Stubs
           are jump pads sometimes also called trampolines. Thus, the indirect call/jump jumps to
           such a stub.  The stub contains a direct jump to the desired address.

       *   Linker relaxation must be turned on so that the linker generates the stubs correctly
           in all situations. See the compiler option -mrelax and the linker option --relax.
           There are corner cases where the linker is supposed to generate stubs but aborts
           without relaxation and without a helpful error message.

       *   The default linker script is arranged for code with "EIND = 0".  If code is supposed
           to work for a setup with "EIND != 0", a custom linker script has to be used in order
           to place the sections whose name start with ".trampolines" into the segment where
           "EIND" points to.

       *   The startup code from libgcc never sets "EIND".  Notice that startup code is a blend
           of code from libgcc and AVR-LibC.  For the impact of AVR-LibC on "EIND", see the AVR-
           LibC user manual ("http://nongnu.org/avr-libc/user-manual/").

       *   It is legitimate for user-specific startup code to set up "EIND" early, for example by
           means of initialization code located in section ".init3". Such code runs prior to
           general startup code that initializes RAM and calls constructors, but after the bit of
           startup code from AVR-LibC that sets "EIND" to the segment where the vector table is
           located.

                   #include <avr/io.h>

                   static void
                   __attribute__((section(".init3"),naked,used,no_instrument_function))
                   init3_set_eind (void)
                   {
                     __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t"
                                     "out %i0,r24" :: "n" (&EIND) : "r24","memory");
                   }

           The "__trampolines_start" symbol is defined in the linker script.

       *   Stubs are generated automatically by the linker if the following two conditions are
           met:

           -<The address of a label is taken by means of the "gs" modifier>
               (short for generate stubs) like so:

                       LDI r24, lo8(gs(<func>))
                       LDI r25, hi8(gs(<func>))

           -<The final location of that label is in a code segment>
               outside the segment where the stubs are located.

       *   The compiler emits such "gs" modifiers for code labels in the following situations:

           -<Taking address of a function or code label.>
           -<Computed goto.>
           -<If prologue-save function is used, see -mcall-prologues>
               command-line option.

           -<Switch/case dispatch tables. If you do not want such dispatch>
               tables you can specify the -fno-jump-tables command-line option.

           -<C and C++ constructors/destructors called during startup/shutdown.>
           -<If the tools hit a "gs()" modifier explained above.>
       *   Jumping to non-symbolic addresses like so is not supported:

                   int main (void)
                   {
                       /* Call function at word address 0x2 */
                       return ((int(*)(void)) 0x2)();
                   }

           Instead, a stub has to be set up, i.e. the function has to be called through a symbol
           ("func_4" in the example):

                   int main (void)
                   {
                       extern int func_4 (void);

                       /* Call function at byte address 0x4 */
                       return func_4();
                   }

           and the application be linked with -Wl,--defsym,func_4=0x4.  Alternatively, "func_4"
           can be defined in the linker script.

       Handling of the "RAMPD", "RAMPX", "RAMPY" and "RAMPZ" Special Function Registers

       Some AVR devices support memories larger than the 64@tie{}KiB range that can be accessed
       with 16-bit pointers.  To access memory locations outside this 64@tie{}KiB range, the
       content of a "RAMP" register is used as high part of the address: The "X", "Y", "Z"
       address register is concatenated with the "RAMPX", "RAMPY", "RAMPZ" special function
       register, respectively, to get a wide address. Similarly, "RAMPD" is used together with
       direct addressing.

       *   The startup code initializes the "RAMP" special function registers with zero.

       *   If a AVR Named Address Spaces,named address space other than generic or "__flash" is
           used, then "RAMPZ" is set as needed before the operation.

       *   If the device supports RAM larger than 64@tie{}KiB and the compiler needs to change
           "RAMPZ" to accomplish an operation, "RAMPZ" is reset to zero after the operation.

       *   If the device comes with a specific "RAMP" register, the ISR prologue/epilogue
           saves/restores that SFR and initializes it with zero in case the ISR code might
           (implicitly) use it.

       *   RAM larger than 64@tie{}KiB is not supported by GCC for AVR targets.  If you use
           inline assembler to read from locations outside the 16-bit address range and change
           one of the "RAMP" registers, you must reset it to zero after the access.

       AVR Built-in Macros

       GCC defines several built-in macros so that the user code can test for the presence or
       absence of features.  Almost any of the following built-in macros are deduced from device
       capabilities and thus triggered by the -mmcu= command-line option.

       For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in
       Functions.

       "__AVR_ARCH__"
           Build-in macro that resolves to a decimal number that identifies the architecture and
           depends on the -mmcu=mcu option.  Possible values are:

           2, 25, 3, 31, 35, 4, 5, 51, 6

           for mcu="avr2", "avr25", "avr3", "avr31", "avr35", "avr4", "avr5", "avr51", "avr6",

           respectively and

           100, 102, 103, 104, 105, 106, 107

           for mcu="avrtiny", "avrxmega2", "avrxmega3", "avrxmega4", "avrxmega5", "avrxmega6",
           "avrxmega7", respectively.  If mcu specifies a device, this built-in macro is set
           accordingly. For example, with -mmcu=atmega8 the macro is defined to 4.

       "__AVR_Device__"
           Setting -mmcu=device defines this built-in macro which reflects the device's name. For
           example, -mmcu=atmega8 defines the built-in macro "__AVR_ATmega8__", -mmcu=attiny261a
           defines "__AVR_ATtiny261A__", etc.

           The built-in macros' names follow the scheme "__AVR_Device__" where Device is the
           device name as from the AVR user manual. The difference between Device in the built-in
           macro and device in -mmcu=device is that the latter is always lowercase.

           If device is not a device but only a core architecture like avr51, this macro is not
           defined.

       "__AVR_DEVICE_NAME__"
           Setting -mmcu=device defines this built-in macro to the device's name. For example,
           with -mmcu=atmega8 the macro is defined to "atmega8".

           If device is not a device but only a core architecture like avr51, this macro is not
           defined.

       "__AVR_XMEGA__"
           The device / architecture belongs to the XMEGA family of devices.

       "__AVR_HAVE_ELPM__"
           The device has the "ELPM" instruction.

       "__AVR_HAVE_ELPMX__"
           The device has the "ELPM Rn,Z" and "ELPM Rn,Z+" instructions.

       "__AVR_HAVE_MOVW__"
           The device has the "MOVW" instruction to perform 16-bit register-register moves.

       "__AVR_HAVE_LPMX__"
           The device has the "LPM Rn,Z" and "LPM Rn,Z+" instructions.

       "__AVR_HAVE_MUL__"
           The device has a hardware multiplier.

       "__AVR_HAVE_JMP_CALL__"
           The device has the "JMP" and "CALL" instructions.  This is the case for devices with
           more than 8@tie{}KiB of program memory.

       "__AVR_HAVE_EIJMP_EICALL__"
       "__AVR_3_BYTE_PC__"
           The device has the "EIJMP" and "EICALL" instructions.  This is the case for devices
           with more than 128@tie{}KiB of program memory.  This also means that the program
           counter (PC) is 3@tie{}bytes wide.

       "__AVR_2_BYTE_PC__"
           The program counter (PC) is 2@tie{}bytes wide. This is the case for devices with up to
           128@tie{}KiB of program memory.

       "__AVR_HAVE_8BIT_SP__"
       "__AVR_HAVE_16BIT_SP__"
           The stack pointer (SP) register is treated as 8-bit respectively 16-bit register by
           the compiler.  The definition of these macros is affected by -mtiny-stack.

       "__AVR_HAVE_SPH__"
       "__AVR_SP8__"
           The device has the SPH (high part of stack pointer) special function register or has
           an 8-bit stack pointer, respectively.  The definition of these macros is affected by
           -mmcu= and in the cases of -mmcu=avr2 and -mmcu=avr25 also by -msp8.

       "__AVR_HAVE_RAMPD__"
       "__AVR_HAVE_RAMPX__"
       "__AVR_HAVE_RAMPY__"
       "__AVR_HAVE_RAMPZ__"
           The device has the "RAMPD", "RAMPX", "RAMPY", "RAMPZ" special function register,
           respectively.

       "__NO_INTERRUPTS__"
           This macro reflects the -mno-interrupts command-line option.

       "__AVR_ERRATA_SKIP__"
       "__AVR_ERRATA_SKIP_JMP_CALL__"
           Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit instructions because of a
           hardware erratum.  Skip instructions are "SBRS", "SBRC", "SBIS", "SBIC" and "CPSE".
           The second macro is only defined if "__AVR_HAVE_JMP_CALL__" is also set.

       "__AVR_ISA_RMW__"
           The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).

       "__AVR_SFR_OFFSET__=offset"
           Instructions that can address I/O special function registers directly like "IN",
           "OUT", "SBI", etc. may use a different address as if addressed by an instruction to
           access RAM like "LD" or "STS". This offset depends on the device architecture and has
           to be subtracted from the RAM address in order to get the respective I/O@tie{}address.

       "__AVR_SHORT_CALLS__"
           The -mshort-calls command line option is set.

       "__AVR_PM_BASE_ADDRESS__=addr"
           Some devices support reading from flash memory by means of "LD*" instructions.  The
           flash memory is seen in the data address space at an offset of
           "__AVR_PM_BASE_ADDRESS__".  If this macro is not defined, this feature is not
           available.  If defined, the address space is linear and there is no need to put
           ".rodata" into RAM.  This is handled by the default linker description file, and is
           currently available for "avrtiny" and "avrxmega3".  Even more convenient, there is no
           need to use address spaces like "__flash" or features like attribute "progmem" and
           "pgm_read_*".

       "__WITH_AVRLIBC__"
           The compiler is configured to be used together with AVR-Libc.  See the --with-avrlibc
           configure option.

       Blackfin Options

       -mcpu=cpu[-sirevision]
           Specifies the name of the target Blackfin processor.  Currently, cpu can be one of
           bf512, bf514, bf516, bf518, bf522, bf523, bf524, bf525, bf526, bf527, bf531, bf532,
           bf533, bf534, bf536, bf537, bf538, bf539, bf542, bf544, bf547, bf548, bf549, bf542m,
           bf544m, bf547m, bf548m, bf549m, bf561, bf592.

           The optional sirevision specifies the silicon revision of the target Blackfin
           processor.  Any workarounds available for the targeted silicon revision are enabled.
           If sirevision is none, no workarounds are enabled.  If sirevision is any, all
           workarounds for the targeted processor are enabled.  The "__SILICON_REVISION__" macro
           is defined to two hexadecimal digits representing the major and minor numbers in the
           silicon revision.  If sirevision is none, the "__SILICON_REVISION__" is not defined.
           If sirevision is any, the "__SILICON_REVISION__" is defined to be 0xffff.  If this
           optional sirevision is not used, GCC assumes the latest known silicon revision of the
           targeted Blackfin processor.

           GCC defines a preprocessor macro for the specified cpu.  For the bfin-elf toolchain,
           this option causes the hardware BSP provided by libgloss to be linked in if -msim is
           not given.

           Without this option, bf532 is used as the processor by default.

           Note that support for bf561 is incomplete.  For bf561, only the preprocessor macro is
           defined.

       -msim
           Specifies that the program will be run on the simulator.  This causes the simulator
           BSP provided by libgloss to be linked in.  This option has effect only for bfin-elf
           toolchain.  Certain other options, such as -mid-shared-library and -mfdpic, imply
           -msim.

       -momit-leaf-frame-pointer
           Don't keep the frame pointer in a register for leaf functions.  This avoids the
           instructions to save, set up and restore frame pointers and makes an extra register
           available in leaf functions.

       -mspecld-anomaly
           When enabled, the compiler ensures that the generated code does not contain
           speculative loads after jump instructions. If this option is used,
           "__WORKAROUND_SPECULATIVE_LOADS" is defined.

       -mno-specld-anomaly
           Don't generate extra code to prevent speculative loads from occurring.

       -mcsync-anomaly
           When enabled, the compiler ensures that the generated code does not contain CSYNC or
           SSYNC instructions too soon after conditional branches.  If this option is used,
           "__WORKAROUND_SPECULATIVE_SYNCS" is defined.

       -mno-csync-anomaly
           Don't generate extra code to prevent CSYNC or SSYNC instructions from occurring too
           soon after a conditional branch.

       -mlow-64k
           When enabled, the compiler is free to take advantage of the knowledge that the entire
           program fits into the low 64k of memory.

       -mno-low-64k
           Assume that the program is arbitrarily large.  This is the default.

       -mstack-check-l1
           Do stack checking using information placed into L1 scratchpad memory by the uClinux
           kernel.

       -mid-shared-library
           Generate code that supports shared libraries via the library ID method.  This allows
           for execute in place and shared libraries in an environment without virtual memory
           management.  This option implies -fPIC.  With a bfin-elf target, this option implies
           -msim.

       -mno-id-shared-library
           Generate code that doesn't assume ID-based shared libraries are being used.  This is
           the default.

       -mleaf-id-shared-library
           Generate code that supports shared libraries via the library ID method, but assumes
           that this library or executable won't link against any other ID shared libraries.
           That allows the compiler to use faster code for jumps and calls.

       -mno-leaf-id-shared-library
           Do not assume that the code being compiled won't link against any ID shared libraries.
           Slower code is generated for jump and call insns.

       -mshared-library-id=n
           Specifies the identification number of the ID-based shared library being compiled.
           Specifying a value of 0 generates more compact code; specifying other values forces
           the allocation of that number to the current library but is no more space- or time-
           efficient than omitting this option.

       -msep-data
           Generate code that allows the data segment to be located in a different area of memory
           from the text segment.  This allows for execute in place in an environment without
           virtual memory management by eliminating relocations against the text section.

       -mno-sep-data
           Generate code that assumes that the data segment follows the text segment.  This is
           the default.

       -mlong-calls
       -mno-long-calls
           Tells the compiler to perform function calls by first loading the address of the
           function into a register and then performing a subroutine call on this register.  This
           switch is needed if the target function lies outside of the 24-bit addressing range of
           the offset-based version of subroutine call instruction.

           This feature is not enabled by default.  Specifying -mno-long-calls restores the
           default behavior.  Note these switches have no effect on how the compiler generates
           code to handle function calls via function pointers.

       -mfast-fp
           Link with the fast floating-point library. This library relaxes some of the IEEE
           floating-point standard's rules for checking inputs against Not-a-Number (NAN), in the
           interest of performance.

       -minline-plt
           Enable inlining of PLT entries in function calls to functions that are not known to
           bind locally.  It has no effect without -mfdpic.

       -mmulticore
           Build a standalone application for multicore Blackfin processors.  This option causes
           proper start files and link scripts supporting multicore to be used, and defines the
           macro "__BFIN_MULTICORE".  It can only be used with -mcpu=bf561[-sirevision].

           This option can be used with -mcorea or -mcoreb, which selects the one-application-
           per-core programming model.  Without -mcorea or -mcoreb, the
           single-application/dual-core programming model is used. In this model, the main
           function of Core B should be named as "coreb_main".

           If this option is not used, the single-core application programming model is used.

       -mcorea
           Build a standalone application for Core A of BF561 when using the one-application-per-
           core programming model. Proper start files and link scripts are used to support Core
           A, and the macro "__BFIN_COREA" is defined.  This option can only be used in
           conjunction with -mmulticore.

       -mcoreb
           Build a standalone application for Core B of BF561 when using the one-application-per-
           core programming model. Proper start files and link scripts are used to support Core
           B, and the macro "__BFIN_COREB" is defined. When this option is used, "coreb_main"
           should be used instead of "main".  This option can only be used in conjunction with
           -mmulticore.

       -msdram
           Build a standalone application for SDRAM. Proper start files and link scripts are used
           to put the application into SDRAM, and the macro "__BFIN_SDRAM" is defined.  The
           loader should initialize SDRAM before loading the application.

       -micplb
           Assume that ICPLBs are enabled at run time.  This has an effect on certain anomaly
           workarounds.  For Linux targets, the default is to assume ICPLBs are enabled; for
           standalone applications the default is off.

       C6X Options

       -march=name
           This specifies the name of the target architecture.  GCC uses this name to determine
           what kind of instructions it can emit when generating assembly code.  Permissible
           names are: c62x, c64x, c64x+, c67x, c67x+, c674x.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default.

       -msim
           Choose startup files and linker script suitable for the simulator.

       -msdata=default
           Put small global and static data in the ".neardata" section, which is pointed to by
           register "B14".  Put small uninitialized global and static data in the ".bss" section,
           which is adjacent to the ".neardata" section.  Put small read-only data into the
           ".rodata" section.  The corresponding sections used for large pieces of data are
           ".fardata", ".far" and ".const".

       -msdata=all
           Put all data, not just small objects, into the sections reserved for small data, and
           use addressing relative to the "B14" register to access them.

       -msdata=none
           Make no use of the sections reserved for small data, and use absolute addresses to
           access all data.  Put all initialized global and static data in the ".fardata"
           section, and all uninitialized data in the ".far" section.  Put all constant data into
           the ".const" section.

       CRIS Options

       These options are defined specifically for the CRIS ports.

       -march=architecture-type
       -mcpu=architecture-type
           Generate code for the specified architecture.  The choices for architecture-type are
           v3, v8 and v10 for respectively ETRAX 4, ETRAX 100, and ETRAX 100 LX.  Default is v0
           except for cris-axis-linux-gnu, where the default is v10.

       -mtune=architecture-type
           Tune to architecture-type everything applicable about the generated code, except for
           the ABI and the set of available instructions.  The choices for architecture-type are
           the same as for -march=architecture-type.

       -mmax-stack-frame=n
           Warn when the stack frame of a function exceeds n bytes.

       -metrax4
       -metrax100
           The options -metrax4 and -metrax100 are synonyms for -march=v3 and -march=v8
           respectively.

       -mmul-bug-workaround
       -mno-mul-bug-workaround
           Work around a bug in the "muls" and "mulu" instructions for CPU models where it
           applies.  This option is active by default.

       -mpdebug
           Enable CRIS-specific verbose debug-related information in the assembly code.  This
           option also has the effect of turning off the #NO_APP formatted-code indicator to the
           assembler at the beginning of the assembly file.

       -mcc-init
           Do not use condition-code results from previous instruction; always emit compare and
           test instructions before use of condition codes.

       -mno-side-effects
           Do not emit instructions with side effects in addressing modes other than post-
           increment.

       -mstack-align
       -mno-stack-align
       -mdata-align
       -mno-data-align
       -mconst-align
       -mno-const-align
           These options (no- options) arrange (eliminate arrangements) for the stack frame,
           individual data and constants to be aligned for the maximum single data access size
           for the chosen CPU model.  The default is to arrange for 32-bit alignment.  ABI
           details such as structure layout are not affected by these options.

       -m32-bit
       -m16-bit
       -m8-bit
           Similar to the stack- data- and const-align options above, these options arrange for
           stack frame, writable data and constants to all be 32-bit, 16-bit or 8-bit aligned.
           The default is 32-bit alignment.

       -mno-prologue-epilogue
       -mprologue-epilogue
           With -mno-prologue-epilogue, the normal function prologue and epilogue which set up
           the stack frame are omitted and no return instructions or return sequences are
           generated in the code.  Use this option only together with visual inspection of the
           compiled code: no warnings or errors are generated when call-saved registers must be
           saved, or storage for local variables needs to be allocated.

       -mno-gotplt
       -mgotplt
           With -fpic and -fPIC, don't generate (do generate) instruction sequences that load
           addresses for functions from the PLT part of the GOT rather than (traditional on other
           architectures) calls to the PLT.  The default is -mgotplt.

       -melf
           Legacy no-op option only recognized with the cris-axis-elf and cris-axis-linux-gnu
           targets.

       -mlinux
           Legacy no-op option only recognized with the cris-axis-linux-gnu target.

       -sim
           This option, recognized for the cris-axis-elf, arranges to link with input-output
           functions from a simulator library.  Code, initialized data and zero-initialized data
           are allocated consecutively.

       -sim2
           Like -sim, but pass linker options to locate initialized data at 0x40000000 and zero-
           initialized data at 0x80000000.

       CR16 Options

       These options are defined specifically for the CR16 ports.

       -mmac
           Enable the use of multiply-accumulate instructions. Disabled by default.

       -mcr16cplus
       -mcr16c
           Generate code for CR16C or CR16C+ architecture. CR16C+ architecture is default.

       -msim
           Links the library libsim.a which is in compatible with simulator. Applicable to ELF
           compiler only.

       -mint32
           Choose integer type as 32-bit wide.

       -mbit-ops
           Generates "sbit"/"cbit" instructions for bit manipulations.

       -mdata-model=model
           Choose a data model. The choices for model are near, far or medium. medium is default.
           However, far is not valid with -mcr16c, as the CR16C architecture does not support the
           far data model.

       Darwin Options

       These options are defined for all architectures running the Darwin operating system.

       FSF GCC on Darwin does not create "fat" object files; it creates an object file for the
       single architecture that GCC was built to target.  Apple's GCC on Darwin does create "fat"
       files if multiple -arch options are used; it does so by running the compiler or linker
       multiple times and joining the results together with lipo.

       The subtype of the file created (like ppc7400 or ppc970 or i686) is determined by the
       flags that specify the ISA that GCC is targeting, like -mcpu or -march.  The
       -force_cpusubtype_ALL option can be used to override this.

       The Darwin tools vary in their behavior when presented with an ISA mismatch.  The
       assembler, as, only permits instructions to be used that are valid for the subtype of the
       file it is generating, so you cannot put 64-bit instructions in a ppc750 object file.  The
       linker for shared libraries, /usr/bin/libtool, fails and prints an error if asked to
       create a shared library with a less restrictive subtype than its input files (for
       instance, trying to put a ppc970 object file in a ppc7400 library).  The linker for
       executables, ld, quietly gives the executable the most restrictive subtype of any of its
       input files.

       -Fdir
           Add the framework directory dir to the head of the list of directories to be searched
           for header files.  These directories are interleaved with those specified by -I
           options and are scanned in a left-to-right order.

           A framework directory is a directory with frameworks in it.  A framework is a
           directory with a Headers and/or PrivateHeaders directory contained directly in it that
           ends in .framework.  The name of a framework is the name of this directory excluding
           the .framework.  Headers associated with the framework are found in one of those two
           directories, with Headers being searched first.  A subframework is a framework
           directory that is in a framework's Frameworks directory.  Includes of subframework
           headers can only appear in a header of a framework that contains the subframework, or
           in a sibling subframework header.  Two subframeworks are siblings if they occur in the
           same framework.  A subframework should not have the same name as a framework; a
           warning is issued if this is violated.  Currently a subframework cannot have
           subframeworks; in the future, the mechanism may be extended to support this.  The
           standard frameworks can be found in /System/Library/Frameworks and
           /Library/Frameworks.  An example include looks like "#include <Framework/header.h>",
           where Framework denotes the name of the framework and header.h is found in the
           PrivateHeaders or Headers directory.

       -iframeworkdir
           Like -F except the directory is a treated as a system directory.  The main difference
           between this -iframework and -F is that with -iframework the compiler does not warn
           about constructs contained within header files found via dir.  This option is valid
           only for the C family of languages.

       -gused
           Emit debugging information for symbols that are used.  For stabs debugging format,
           this enables -feliminate-unused-debug-symbols.  This is by default ON.

       -gfull
           Emit debugging information for all symbols and types.

       -mmacosx-version-min=version
           The earliest version of MacOS X that this executable will run on is version.  Typical
           values of version include 10.1, 10.2, and 10.3.9.

           If the compiler was built to use the system's headers by default, then the default for
           this option is the system version on which the compiler is running, otherwise the
           default is to make choices that are compatible with as many systems and code bases as
           possible.

       -mkernel
           Enable kernel development mode.  The -mkernel option sets -static, -fno-common,
           -fno-use-cxa-atexit, -fno-exceptions, -fno-non-call-exceptions, -fapple-kext,
           -fno-weak and -fno-rtti where applicable.  This mode also sets -mno-altivec,
           -msoft-float, -fno-builtin and -mlong-branch for PowerPC targets.

       -mone-byte-bool
           Override the defaults for "bool" so that "sizeof(bool)==1".  By default "sizeof(bool)"
           is 4 when compiling for Darwin/PowerPC and 1 when compiling for Darwin/x86, so this
           option has no effect on x86.

           Warning: The -mone-byte-bool switch causes GCC to generate code that is not binary
           compatible with code generated without that switch.  Using this switch may require
           recompiling all other modules in a program, including system libraries.  Use this
           switch to conform to a non-default data model.

       -mfix-and-continue
       -ffix-and-continue
       -findirect-data
           Generate code suitable for fast turnaround development, such as to allow GDB to
           dynamically load .o files into already-running programs.  -findirect-data and
           -ffix-and-continue are provided for backwards compatibility.

       -all_load
           Loads all members of static archive libraries.  See man ld(1) for more information.

       -arch_errors_fatal
           Cause the errors having to do with files that have the wrong architecture to be fatal.

       -bind_at_load
           Causes the output file to be marked such that the dynamic linker will bind all
           undefined references when the file is loaded or launched.

       -bundle
           Produce a Mach-o bundle format file.  See man ld(1) for more information.

       -bundle_loader executable
           This option specifies the executable that will load the build output file being
           linked.  See man ld(1) for more information.

       -dynamiclib
           When passed this option, GCC produces a dynamic library instead of an executable when
           linking, using the Darwin libtool command.

       -force_cpusubtype_ALL
           This causes GCC's output file to have the ALL subtype, instead of one controlled by
           the -mcpu or -march option.

       -allowable_client  client_name
       -client_name
       -compatibility_version
       -current_version
       -dead_strip
       -dependency-file
       -dylib_file
       -dylinker_install_name
       -dynamic
       -exported_symbols_list
       -filelist
       -flat_namespace
       -force_flat_namespace
       -headerpad_max_install_names
       -image_base
       -init
       -install_name
       -keep_private_externs
       -multi_module
       -multiply_defined
       -multiply_defined_unused
       -noall_load
       -no_dead_strip_inits_and_terms
       -nofixprebinding
       -nomultidefs
       -noprebind
       -noseglinkedit
       -pagezero_size
       -prebind
       -prebind_all_twolevel_modules
       -private_bundle
       -read_only_relocs
       -sectalign
       -sectobjectsymbols
       -whyload
       -seg1addr
       -sectcreate
       -sectobjectsymbols
       -sectorder
       -segaddr
       -segs_read_only_addr
       -segs_read_write_addr
       -seg_addr_table
       -seg_addr_table_filename
       -seglinkedit
       -segprot
       -segs_read_only_addr
       -segs_read_write_addr
       -single_module
       -static
       -sub_library
       -sub_umbrella
       -twolevel_namespace
       -umbrella
       -undefined
       -unexported_symbols_list
       -weak_reference_mismatches
       -whatsloaded
           These options are passed to the Darwin linker.  The Darwin linker man page describes
           them in detail.

       DEC Alpha Options

       These -m options are defined for the DEC Alpha implementations:

       -mno-soft-float
       -msoft-float
           Use (do not use) the hardware floating-point instructions for floating-point
           operations.  When -msoft-float is specified, functions in libgcc.a are used to perform
           floating-point operations.  Unless they are replaced by routines that emulate the
           floating-point operations, or compiled in such a way as to call such emulations
           routines, these routines issue floating-point operations.   If you are compiling for
           an Alpha without floating-point operations, you must ensure that the library is built
           so as not to call them.

           Note that Alpha implementations without floating-point operations are required to have
           floating-point registers.

       -mfp-reg
       -mno-fp-regs
           Generate code that uses (does not use) the floating-point register set.  -mno-fp-regs
           implies -msoft-float.  If the floating-point register set is not used, floating-point
           operands are passed in integer registers as if they were integers and floating-point
           results are passed in $0 instead of $f0.  This is a non-standard calling sequence, so
           any function with a floating-point argument or return value called by code compiled
           with -mno-fp-regs must also be compiled with that option.

           A typical use of this option is building a kernel that does not use, and hence need
           not save and restore, any floating-point registers.

       -mieee
           The Alpha architecture implements floating-point hardware optimized for maximum
           performance.  It is mostly compliant with the IEEE floating-point standard.  However,
           for full compliance, software assistance is required.  This option generates code
           fully IEEE-compliant code except that the inexact-flag is not maintained (see below).
           If this option is turned on, the preprocessor macro "_IEEE_FP" is defined during
           compilation.  The resulting code is less efficient but is able to correctly support
           denormalized numbers and exceptional IEEE values such as not-a-number and plus/minus
           infinity.  Other Alpha compilers call this option -ieee_with_no_inexact.

       -mieee-with-inexact
           This is like -mieee except the generated code also maintains the IEEE inexact-flag.
           Turning on this option causes the generated code to implement fully-compliant IEEE
           math.  In addition to "_IEEE_FP", "_IEEE_FP_EXACT" is defined as a preprocessor macro.
           On some Alpha implementations the resulting code may execute significantly slower than
           the code generated by default.  Since there is very little code that depends on the
           inexact-flag, you should normally not specify this option.  Other Alpha compilers call
           this option -ieee_with_inexact.

       -mfp-trap-mode=trap-mode
           This option controls what floating-point related traps are enabled.  Other Alpha
           compilers call this option -fptm trap-mode.  The trap mode can be set to one of four
           values:

           n   This is the default (normal) setting.  The only traps that are enabled are the
               ones that cannot be disabled in software (e.g., division by zero trap).

           u   In addition to the traps enabled by n, underflow traps are enabled as well.

           su  Like u, but the instructions are marked to be safe for software completion (see
               Alpha architecture manual for details).

           sui Like su, but inexact traps are enabled as well.

       -mfp-rounding-mode=rounding-mode
           Selects the IEEE rounding mode.  Other Alpha compilers call this option -fprm
           rounding-mode.  The rounding-mode can be one of:

           n   Normal IEEE rounding mode.  Floating-point numbers are rounded towards the nearest
               machine number or towards the even machine number in case of a tie.

           m   Round towards minus infinity.

           c   Chopped rounding mode.  Floating-point numbers are rounded towards zero.

           d   Dynamic rounding mode.  A field in the floating-point control register (fpcr, see
               Alpha architecture reference manual) controls the rounding mode in effect.  The C
               library initializes this register for rounding towards plus infinity.  Thus,
               unless your program modifies the fpcr, d corresponds to round towards plus
               infinity.

       -mtrap-precision=trap-precision
           In the Alpha architecture, floating-point traps are imprecise.  This means without
           software assistance it is impossible to recover from a floating trap and program
           execution normally needs to be terminated.  GCC can generate code that can assist
           operating system trap handlers in determining the exact location that caused a
           floating-point trap.  Depending on the requirements of an application, different
           levels of precisions can be selected:

           p   Program precision.  This option is the default and means a trap handler can only
               identify which program caused a floating-point exception.

           f   Function precision.  The trap handler can determine the function that caused a
               floating-point exception.

           i   Instruction precision.  The trap handler can determine the exact instruction that
               caused a floating-point exception.

           Other Alpha compilers provide the equivalent options called -scope_safe and
           -resumption_safe.

       -mieee-conformant
           This option marks the generated code as IEEE conformant.  You must not use this option
           unless you also specify -mtrap-precision=i and either -mfp-trap-mode=su or
           -mfp-trap-mode=sui.  Its only effect is to emit the line .eflag 48 in the function
           prologue of the generated assembly file.

       -mbuild-constants
           Normally GCC examines a 32- or 64-bit integer constant to see if it can construct it
           from smaller constants in two or three instructions.  If it cannot, it outputs the
           constant as a literal and generates code to load it from the data segment at run time.

           Use this option to require GCC to construct all integer constants using code, even if
           it takes more instructions (the maximum is six).

           You typically use this option to build a shared library dynamic loader.  Itself a
           shared library, it must relocate itself in memory before it can find the variables and
           constants in its own data segment.

       -mbwx
       -mno-bwx
       -mcix
       -mno-cix
       -mfix
       -mno-fix
       -mmax
       -mno-max
           Indicate whether GCC should generate code to use the optional BWX, CIX, FIX and MAX
           instruction sets.  The default is to use the instruction sets supported by the CPU
           type specified via -mcpu= option or that of the CPU on which GCC was built if none is
           specified.

       -mfloat-vax
       -mfloat-ieee
           Generate code that uses (does not use) VAX F and G floating-point arithmetic instead
           of IEEE single and double precision.

       -mexplicit-relocs
       -mno-explicit-relocs
           Older Alpha assemblers provided no way to generate symbol relocations except via
           assembler macros.  Use of these macros does not allow optimal instruction scheduling.
           GNU binutils as of version 2.12 supports a new syntax that allows the compiler to
           explicitly mark which relocations should apply to which instructions.  This option is
           mostly useful for debugging, as GCC detects the capabilities of the assembler when it
           is built and sets the default accordingly.

       -msmall-data
       -mlarge-data
           When -mexplicit-relocs is in effect, static data is accessed via gp-relative
           relocations.  When -msmall-data is used, objects 8 bytes long or smaller are placed in
           a small data area (the ".sdata" and ".sbss" sections) and are accessed via 16-bit
           relocations off of the $gp register.  This limits the size of the small data area to
           64KB, but allows the variables to be directly accessed via a single instruction.

           The default is -mlarge-data.  With this option the data area is limited to just below
           2GB.  Programs that require more than 2GB of data must use "malloc" or "mmap" to
           allocate the data in the heap instead of in the program's data segment.

           When generating code for shared libraries, -fpic implies -msmall-data and -fPIC
           implies -mlarge-data.

       -msmall-text
       -mlarge-text
           When -msmall-text is used, the compiler assumes that the code of the entire program
           (or shared library) fits in 4MB, and is thus reachable with a branch instruction.
           When -msmall-data is used, the compiler can assume that all local symbols share the
           same $gp value, and thus reduce the number of instructions required for a function
           call from 4 to 1.

           The default is -mlarge-text.

       -mcpu=cpu_type
           Set the instruction set and instruction scheduling parameters for machine type
           cpu_type.  You can specify either the EV style name or the corresponding chip number.
           GCC supports scheduling parameters for the EV4, EV5 and EV6 family of processors and
           chooses the default values for the instruction set from the processor you specify.  If
           you do not specify a processor type, GCC defaults to the processor on which the
           compiler was built.

           Supported values for cpu_type are

           ev4
           ev45
           21064
               Schedules as an EV4 and has no instruction set extensions.

           ev5
           21164
               Schedules as an EV5 and has no instruction set extensions.

           ev56
           21164a
               Schedules as an EV5 and supports the BWX extension.

           pca56
           21164pc
           21164PC
               Schedules as an EV5 and supports the BWX and MAX extensions.

           ev6
           21264
               Schedules as an EV6 and supports the BWX, FIX, and MAX extensions.

           ev67
           21264a
               Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions.

           Native toolchains also support the value native, which selects the best architecture
           option for the host processor.  -mcpu=native has no effect if GCC does not recognize
           the processor.

       -mtune=cpu_type
           Set only the instruction scheduling parameters for machine type cpu_type.  The
           instruction set is not changed.

           Native toolchains also support the value native, which selects the best architecture
           option for the host processor.  -mtune=native has no effect if GCC does not recognize
           the processor.

       -mmemory-latency=time
           Sets the latency the scheduler should assume for typical memory references as seen by
           the application.  This number is highly dependent on the memory access patterns used
           by the application and the size of the external cache on the machine.

           Valid options for time are

           number
               A decimal number representing clock cycles.

           L1
           L2
           L3
           main
               The compiler contains estimates of the number of clock cycles for "typical" EV4 &
               EV5 hardware for the Level 1, 2 & 3 caches (also called Dcache, Scache, and
               Bcache), as well as to main memory.  Note that L3 is only valid for EV5.

       FR30 Options

       These options are defined specifically for the FR30 port.

       -msmall-model
           Use the small address space model.  This can produce smaller code, but it does assume
           that all symbolic values and addresses fit into a 20-bit range.

       -mno-lsim
           Assume that runtime support has been provided and so there is no need to include the
           simulator library (libsim.a) on the linker command line.

       FT32 Options

       These options are defined specifically for the FT32 port.

       -msim
           Specifies that the program will be run on the simulator.  This causes an alternate
           runtime startup and library to be linked.  You must not use this option when
           generating programs that will run on real hardware; you must provide your own runtime
           library for whatever I/O functions are needed.

       -mlra
           Enable Local Register Allocation.  This is still experimental for FT32, so by default
           the compiler uses standard reload.

       -mnodiv
           Do not use div and mod instructions.

       -mft32b
           Enable use of the extended instructions of the FT32B processor.

       -mcompress
           Compress all code using the Ft32B code compression scheme.

       -mnopm
           Do not generate code that reads program memory.

       FRV Options

       -mgpr-32
           Only use the first 32 general-purpose registers.

       -mgpr-64
           Use all 64 general-purpose registers.

       -mfpr-32
           Use only the first 32 floating-point registers.

       -mfpr-64
           Use all 64 floating-point registers.

       -mhard-float
           Use hardware instructions for floating-point operations.

       -msoft-float
           Use library routines for floating-point operations.

       -malloc-cc
           Dynamically allocate condition code registers.

       -mfixed-cc
           Do not try to dynamically allocate condition code registers, only use "icc0" and
           "fcc0".

       -mdword
           Change ABI to use double word insns.

       -mno-dword
           Do not use double word instructions.

       -mdouble
           Use floating-point double instructions.

       -mno-double
           Do not use floating-point double instructions.

       -mmedia
           Use media instructions.

       -mno-media
           Do not use media instructions.

       -mmuladd
           Use multiply and add/subtract instructions.

       -mno-muladd
           Do not use multiply and add/subtract instructions.

       -mfdpic
           Select the FDPIC ABI, which uses function descriptors to represent pointers to
           functions.  Without any PIC/PIE-related options, it implies -fPIE.  With -fpic or
           -fpie, it assumes GOT entries and small data are within a 12-bit range from the GOT
           base address; with -fPIC or -fPIE, GOT offsets are computed with 32 bits.  With a
           bfin-elf target, this option implies -msim.

       -minline-plt
           Enable inlining of PLT entries in function calls to functions that are not known to
           bind locally.  It has no effect without -mfdpic.  It's enabled by default if
           optimizing for speed and compiling for shared libraries (i.e., -fPIC or -fpic), or
           when an optimization option such as -O3 or above is present in the command line.

       -mTLS
           Assume a large TLS segment when generating thread-local code.

       -mtls
           Do not assume a large TLS segment when generating thread-local code.

       -mgprel-ro
           Enable the use of "GPREL" relocations in the FDPIC ABI for data that is known to be in
           read-only sections.  It's enabled by default, except for -fpic or -fpie: even though
           it may help make the global offset table smaller, it trades 1 instruction for 4.  With
           -fPIC or -fPIE, it trades 3 instructions for 4, one of which may be shared by multiple
           symbols, and it avoids the need for a GOT entry for the referenced symbol, so it's
           more likely to be a win.  If it is not, -mno-gprel-ro can be used to disable it.

       -multilib-library-pic
           Link with the (library, not FD) pic libraries.  It's implied by -mlibrary-pic, as well
           as by -fPIC and -fpic without -mfdpic.  You should never have to use it explicitly.

       -mlinked-fp
           Follow the EABI requirement of always creating a frame pointer whenever a stack frame
           is allocated.  This option is enabled by default and can be disabled with
           -mno-linked-fp.

       -mlong-calls
           Use indirect addressing to call functions outside the current compilation unit.  This
           allows the functions to be placed anywhere within the 32-bit address space.

       -malign-labels
           Try to align labels to an 8-byte boundary by inserting NOPs into the previous packet.
           This option only has an effect when VLIW packing is enabled.  It doesn't create new
           packets; it merely adds NOPs to existing ones.

       -mlibrary-pic
           Generate position-independent EABI code.

       -macc-4
           Use only the first four media accumulator registers.

       -macc-8
           Use all eight media accumulator registers.

       -mpack
           Pack VLIW instructions.

       -mno-pack
           Do not pack VLIW instructions.

       -mno-eflags
           Do not mark ABI switches in e_flags.

       -mcond-move
           Enable the use of conditional-move instructions (default).

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mno-cond-move
           Disable the use of conditional-move instructions.

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mscc
           Enable the use of conditional set instructions (default).

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mno-scc
           Disable the use of conditional set instructions.

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mcond-exec
           Enable the use of conditional execution (default).

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mno-cond-exec
           Disable the use of conditional execution.

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mvliw-branch
           Run a pass to pack branches into VLIW instructions (default).

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mno-vliw-branch
           Do not run a pass to pack branches into VLIW instructions.

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mmulti-cond-exec
           Enable optimization of "&&" and "||" in conditional execution (default).

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mno-multi-cond-exec
           Disable optimization of "&&" and "||" in conditional execution.

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mnested-cond-exec
           Enable nested conditional execution optimizations (default).

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -mno-nested-cond-exec
           Disable nested conditional execution optimizations.

           This switch is mainly for debugging the compiler and will likely be removed in a
           future version.

       -moptimize-membar
           This switch removes redundant "membar" instructions from the compiler-generated code.
           It is enabled by default.

       -mno-optimize-membar
           This switch disables the automatic removal of redundant "membar" instructions from the
           generated code.

       -mtomcat-stats
           Cause gas to print out tomcat statistics.

       -mcpu=cpu
           Select the processor type for which to generate code.  Possible values are frv, fr550,
           tomcat, fr500, fr450, fr405, fr400, fr300 and simple.

       GNU/Linux Options

       These -m options are defined for GNU/Linux targets:

       -mglibc
           Use the GNU C library.  This is the default except on *-*-linux-*uclibc*,
           *-*-linux-*musl* and *-*-linux-*android* targets.

       -muclibc
           Use uClibc C library.  This is the default on *-*-linux-*uclibc* targets.

       -mmusl
           Use the musl C library.  This is the default on *-*-linux-*musl* targets.

       -mbionic
           Use Bionic C library.  This is the default on *-*-linux-*android* targets.

       -mandroid
           Compile code compatible with Android platform.  This is the default on
           *-*-linux-*android* targets.

           When compiling, this option enables -mbionic, -fPIC, -fno-exceptions and -fno-rtti by
           default.  When linking, this option makes the GCC driver pass Android-specific options
           to the linker.  Finally, this option causes the preprocessor macro "__ANDROID__" to be
           defined.

       -tno-android-cc
           Disable compilation effects of -mandroid, i.e., do not enable -mbionic, -fPIC,
           -fno-exceptions and -fno-rtti by default.

       -tno-android-ld
           Disable linking effects of -mandroid, i.e., pass standard Linux linking options to the
           linker.

       H8/300 Options

       These -m options are defined for the H8/300 implementations:

       -mrelax
           Shorten some address references at link time, when possible; uses the linker option
           -relax.

       -mh Generate code for the H8/300H.

       -ms Generate code for the H8S.

       -mn Generate code for the H8S and H8/300H in the normal mode.  This switch must be used
           either with -mh or -ms.

       -ms2600
           Generate code for the H8S/2600.  This switch must be used with -ms.

       -mexr
           Extended registers are stored on stack before execution of function with monitor
           attribute. Default option is -mexr.  This option is valid only for H8S targets.

       -mno-exr
           Extended registers are not stored on stack before execution of function with monitor
           attribute. Default option is -mno-exr.  This option is valid only for H8S targets.

       -mint32
           Make "int" data 32 bits by default.

       -malign-300
           On the H8/300H and H8S, use the same alignment rules as for the H8/300.  The default
           for the H8/300H and H8S is to align longs and floats on 4-byte boundaries.
           -malign-300 causes them to be aligned on 2-byte boundaries.  This option has no effect
           on the H8/300.

       HPPA Options

       These -m options are defined for the HPPA family of computers:

       -march=architecture-type
           Generate code for the specified architecture.  The choices for architecture-type are
           1.0 for PA 1.0, 1.1 for PA 1.1, and 2.0 for PA 2.0 processors.  Refer to
           /usr/lib/sched.models on an HP-UX system to determine the proper architecture option
           for your machine.  Code compiled for lower numbered architectures runs on higher
           numbered architectures, but not the other way around.

       -mpa-risc-1-0
       -mpa-risc-1-1
       -mpa-risc-2-0
           Synonyms for -march=1.0, -march=1.1, and -march=2.0 respectively.

       -mcaller-copies
           The caller copies function arguments passed by hidden reference.  This option should
           be used with care as it is not compatible with the default 32-bit runtime.  However,
           only aggregates larger than eight bytes are passed by hidden reference and the option
           provides better compatibility with OpenMP.

       -mjump-in-delay
           This option is ignored and provided for compatibility purposes only.

       -mdisable-fpregs
           Prevent floating-point registers from being used in any manner.  This is necessary for
           compiling kernels that perform lazy context switching of floating-point registers.  If
           you use this option and attempt to perform floating-point operations, the compiler
           aborts.

       -mdisable-indexing
           Prevent the compiler from using indexing address modes.  This avoids some rather
           obscure problems when compiling MIG generated code under MACH.

       -mno-space-regs
           Generate code that assumes the target has no space registers.  This allows GCC to
           generate faster indirect calls and use unscaled index address modes.

           Such code is suitable for level 0 PA systems and kernels.

       -mfast-indirect-calls
           Generate code that assumes calls never cross space boundaries.  This allows GCC to
           emit code that performs faster indirect calls.

           This option does not work in the presence of shared libraries or nested functions.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.  A fixed register
           is one that the register allocator cannot use.  This is useful when compiling kernel
           code.  A register range is specified as two registers separated by a dash.  Multiple
           register ranges can be specified separated by a comma.

       -mlong-load-store
           Generate 3-instruction load and store sequences as sometimes required by the HP-UX 10
           linker.  This is equivalent to the +k option to the HP compilers.

       -mportable-runtime
           Use the portable calling conventions proposed by HP for ELF systems.

       -mgas
           Enable the use of assembler directives only GAS understands.

       -mschedule=cpu-type
           Schedule code according to the constraints for the machine type cpu-type.  The choices
           for cpu-type are 700 7100, 7100LC, 7200, 7300 and 8000.  Refer to
           /usr/lib/sched.models on an HP-UX system to determine the proper scheduling option for
           your machine.  The default scheduling is 8000.

       -mlinker-opt
           Enable the optimization pass in the HP-UX linker.  Note this makes symbolic debugging
           impossible.  It also triggers a bug in the HP-UX 8 and HP-UX 9 linkers in which they
           give bogus error messages when linking some programs.

       -msoft-float
           Generate output containing library calls for floating point.  Warning: the requisite
           libraries are not available for all HPPA targets.  Normally the facilities of the
           machine's usual C compiler are used, but this cannot be done directly in cross-
           compilation.  You must make your own arrangements to provide suitable library
           functions for cross-compilation.

           -msoft-float changes the calling convention in the output file; therefore, it is only
           useful if you compile all of a program with this option.  In particular, you need to
           compile libgcc.a, the library that comes with GCC, with -msoft-float in order for this
           to work.

       -msio
           Generate the predefine, "_SIO", for server IO.  The default is -mwsio.  This generates
           the predefines, "__hp9000s700", "__hp9000s700__" and "_WSIO", for workstation IO.
           These options are available under HP-UX and HI-UX.

       -mgnu-ld
           Use options specific to GNU ld.  This passes -shared to ld when building a shared
           library.  It is the default when GCC is configured, explicitly or implicitly, with the
           GNU linker.  This option does not affect which ld is called; it only changes what
           parameters are passed to that ld.  The ld that is called is determined by the
           --with-ld configure option, GCC's program search path, and finally by the user's PATH.
           The linker used by GCC can be printed using which `gcc -print-prog-name=ld`.  This
           option is only available on the 64-bit HP-UX GCC, i.e. configured with
           hppa*64*-*-hpux*.

       -mhp-ld
           Use options specific to HP ld.  This passes -b to ld when building a shared library
           and passes +Accept TypeMismatch to ld on all links.  It is the default when GCC is
           configured, explicitly or implicitly, with the HP linker.  This option does not affect
           which ld is called; it only changes what parameters are passed to that ld.  The ld
           that is called is determined by the --with-ld configure option, GCC's program search
           path, and finally by the user's PATH.  The linker used by GCC can be printed using
           which `gcc -print-prog-name=ld`.  This option is only available on the 64-bit HP-UX
           GCC, i.e. configured with hppa*64*-*-hpux*.

       -mlong-calls
           Generate code that uses long call sequences.  This ensures that a call is always able
           to reach linker generated stubs.  The default is to generate long calls only when the
           distance from the call site to the beginning of the function or translation unit, as
           the case may be, exceeds a predefined limit set by the branch type being used.  The
           limits for normal calls are 7,600,000 and 240,000 bytes, respectively for the PA 2.0
           and PA 1.X architectures.  Sibcalls are always limited at 240,000 bytes.

           Distances are measured from the beginning of functions when using the
           -ffunction-sections option, or when using the -mgas and -mno-portable-runtime options
           together under HP-UX with the SOM linker.

           It is normally not desirable to use this option as it degrades performance.  However,
           it may be useful in large applications, particularly when partial linking is used to
           build the application.

           The types of long calls used depends on the capabilities of the assembler and linker,
           and the type of code being generated.  The impact on systems that support long
           absolute calls, and long pic symbol-difference or pc-relative calls should be
           relatively small.  However, an indirect call is used on 32-bit ELF systems in pic code
           and it is quite long.

       -munix=unix-std
           Generate compiler predefines and select a startfile for the specified UNIX standard.
           The choices for unix-std are 93, 95 and 98.  93 is supported on all HP-UX versions.
           95 is available on HP-UX 10.10 and later.  98 is available on HP-UX 11.11 and later.
           The default values are 93 for HP-UX 10.00, 95 for HP-UX 10.10 though to 11.00, and 98
           for HP-UX 11.11 and later.

           -munix=93 provides the same predefines as GCC 3.3 and 3.4.  -munix=95 provides
           additional predefines for "XOPEN_UNIX" and "_XOPEN_SOURCE_EXTENDED", and the startfile
           unix95.o.  -munix=98 provides additional predefines for "_XOPEN_UNIX",
           "_XOPEN_SOURCE_EXTENDED", "_INCLUDE__STDC_A1_SOURCE" and "_INCLUDE_XOPEN_SOURCE_500",
           and the startfile unix98.o.

           It is important to note that this option changes the interfaces for various library
           routines.  It also affects the operational behavior of the C library.  Thus, extreme
           care is needed in using this option.

           Library code that is intended to operate with more than one UNIX standard must test,
           set and restore the variable "__xpg4_extended_mask" as appropriate.  Most GNU software
           doesn't provide this capability.

       -nolibdld
           Suppress the generation of link options to search libdld.sl when the -static option is
           specified on HP-UX 10 and later.

       -static
           The HP-UX implementation of setlocale in libc has a dependency on libdld.sl.  There
           isn't an archive version of libdld.sl.  Thus, when the -static option is specified,
           special link options are needed to resolve this dependency.

           On HP-UX 10 and later, the GCC driver adds the necessary options to link with
           libdld.sl when the -static option is specified.  This causes the resulting binary to
           be dynamic.  On the 64-bit port, the linkers generate dynamic binaries by default in
           any case.  The -nolibdld option can be used to prevent the GCC driver from adding
           these link options.

       -threads
           Add support for multithreading with the dce thread library under HP-UX.  This option
           sets flags for both the preprocessor and linker.

       IA-64 Options

       These are the -m options defined for the Intel IA-64 architecture.

       -mbig-endian
           Generate code for a big-endian target.  This is the default for HP-UX.

       -mlittle-endian
           Generate code for a little-endian target.  This is the default for AIX5 and GNU/Linux.

       -mgnu-as
       -mno-gnu-as
           Generate (or don't) code for the GNU assembler.  This is the default.

       -mgnu-ld
       -mno-gnu-ld
           Generate (or don't) code for the GNU linker.  This is the default.

       -mno-pic
           Generate code that does not use a global pointer register.  The result is not position
           independent code, and violates the IA-64 ABI.

       -mvolatile-asm-stop
       -mno-volatile-asm-stop
           Generate (or don't) a stop bit immediately before and after volatile asm statements.

       -mregister-names
       -mno-register-names
           Generate (or don't) in, loc, and out register names for the stacked registers.  This
           may make assembler output more readable.

       -mno-sdata
       -msdata
           Disable (or enable) optimizations that use the small data section.  This may be useful
           for working around optimizer bugs.

       -mconstant-gp
           Generate code that uses a single constant global pointer value.  This is useful when
           compiling kernel code.

       -mauto-pic
           Generate code that is self-relocatable.  This implies -mconstant-gp.  This is useful
           when compiling firmware code.

       -minline-float-divide-min-latency
           Generate code for inline divides of floating-point values using the minimum latency
           algorithm.

       -minline-float-divide-max-throughput
           Generate code for inline divides of floating-point values using the maximum throughput
           algorithm.

       -mno-inline-float-divide
           Do not generate inline code for divides of floating-point values.

       -minline-int-divide-min-latency
           Generate code for inline divides of integer values using the minimum latency
           algorithm.

       -minline-int-divide-max-throughput
           Generate code for inline divides of integer values using the maximum throughput
           algorithm.

       -mno-inline-int-divide
           Do not generate inline code for divides of integer values.

       -minline-sqrt-min-latency
           Generate code for inline square roots using the minimum latency algorithm.

       -minline-sqrt-max-throughput
           Generate code for inline square roots using the maximum throughput algorithm.

       -mno-inline-sqrt
           Do not generate inline code for "sqrt".

       -mfused-madd
       -mno-fused-madd
           Do (don't) generate code that uses the fused multiply/add or multiply/subtract
           instructions.  The default is to use these instructions.

       -mno-dwarf2-asm
       -mdwarf2-asm
           Don't (or do) generate assembler code for the DWARF line number debugging info.  This
           may be useful when not using the GNU assembler.

       -mearly-stop-bits
       -mno-early-stop-bits
           Allow stop bits to be placed earlier than immediately preceding the instruction that
           triggered the stop bit.  This can improve instruction scheduling, but does not always
           do so.

       -mfixed-range=register-range
           Generate code treating the given register range as fixed registers.  A fixed register
           is one that the register allocator cannot use.  This is useful when compiling kernel
           code.  A register range is specified as two registers separated by a dash.  Multiple
           register ranges can be specified separated by a comma.

       -mtls-size=tls-size
           Specify bit size of immediate TLS offsets.  Valid values are 14, 22, and 64.

       -mtune=cpu-type
           Tune the instruction scheduling for a particular CPU, Valid values are itanium,
           itanium1, merced, itanium2, and mckinley.

       -milp32
       -mlp64
           Generate code for a 32-bit or 64-bit environment.  The 32-bit environment sets int,
           long and pointer to 32 bits.  The 64-bit environment sets int to 32 bits and long and
           pointer to 64 bits.  These are HP-UX specific flags.

       -mno-sched-br-data-spec
       -msched-br-data-spec
           (Dis/En)able data speculative scheduling before reload.  This results in generation of
           "ld.a" instructions and the corresponding check instructions ("ld.c" / "chk.a").  The
           default setting is disabled.

       -msched-ar-data-spec
       -mno-sched-ar-data-spec
           (En/Dis)able data speculative scheduling after reload.  This results in generation of
           "ld.a" instructions and the corresponding check instructions ("ld.c" / "chk.a").  The
           default setting is enabled.

       -mno-sched-control-spec
       -msched-control-spec
           (Dis/En)able control speculative scheduling.  This feature is available only during
           region scheduling (i.e. before reload).  This results in generation of the "ld.s"
           instructions and the corresponding check instructions "chk.s".  The default setting is
           disabled.

       -msched-br-in-data-spec
       -mno-sched-br-in-data-spec
           (En/Dis)able speculative scheduling of the instructions that are dependent on the data
           speculative loads before reload.  This is effective only with -msched-br-data-spec
           enabled.  The default setting is enabled.

       -msched-ar-in-data-spec
       -mno-sched-ar-in-data-spec
           (En/Dis)able speculative scheduling of the instructions that are dependent on the data
           speculative loads after reload.  This is effective only with -msched-ar-data-spec
           enabled.  The default setting is enabled.

       -msched-in-control-spec
       -mno-sched-in-control-spec
           (En/Dis)able speculative scheduling of the instructions that are dependent on the
           control speculative loads.  This is effective only with -msched-control-spec enabled.
           The default setting is enabled.

       -mno-sched-prefer-non-data-spec-insns
       -msched-prefer-non-data-spec-insns
           If enabled, data-speculative instructions are chosen for schedule only if there are no
           other choices at the moment.  This makes the use of the data speculation much more
           conservative.  The default setting is disabled.

       -mno-sched-prefer-non-control-spec-insns
       -msched-prefer-non-control-spec-insns
           If enabled, control-speculative instructions are chosen for schedule only if there are
           no other choices at the moment.  This makes the use of the control speculation much
           more conservative.  The default setting is disabled.

       -mno-sched-count-spec-in-critical-path
       -msched-count-spec-in-critical-path
           If enabled, speculative dependencies are considered during computation of the
           instructions priorities.  This makes the use of the speculation a bit more
           conservative.  The default setting is disabled.

       -msched-spec-ldc
           Use a simple data speculation check.  This option is on by default.

       -msched-control-spec-ldc
           Use a simple check for control speculation.  This option is on by default.

       -msched-stop-bits-after-every-cycle
           Place a stop bit after every cycle when scheduling.  This option is on by default.

       -msched-fp-mem-deps-zero-cost
           Assume that floating-point stores and loads are not likely to cause a conflict when
           placed into the same instruction group.  This option is disabled by default.

       -msel-sched-dont-check-control-spec
           Generate checks for control speculation in selective scheduling.  This flag is
           disabled by default.

       -msched-max-memory-insns=max-insns
           Limit on the number of memory insns per instruction group, giving lower priority to
           subsequent memory insns attempting to schedule in the same instruction group.
           Frequently useful to prevent cache bank conflicts.  The default value is 1.

       -msched-max-memory-insns-hard-limit
           Makes the limit specified by msched-max-memory-insns a hard limit, disallowing more
           than that number in an instruction group.  Otherwise, the limit is "soft", meaning
           that non-memory operations are preferred when the limit is reached, but memory
           operations may still be scheduled.

       LM32 Options

       These -m options are defined for the LatticeMico32 architecture:

       -mbarrel-shift-enabled
           Enable barrel-shift instructions.

       -mdivide-enabled
           Enable divide and modulus instructions.

       -mmultiply-enabled
           Enable multiply instructions.

       -msign-extend-enabled
           Enable sign extend instructions.

       -muser-enabled
           Enable user-defined instructions.

       M32C Options

       -mcpu=name
           Select the CPU for which code is generated.  name may be one of r8c for the R8C/Tiny
           series, m16c for the M16C (up to /60) series, m32cm for the M16C/80 series, or m32c
           for the M32C/80 series.

       -msim
           Specifies that the program will be run on the simulator.  This causes an alternate
           runtime library to be linked in which supports, for example, file I/O.  You must not
           use this option when generating programs that will run on real hardware; you must
           provide your own runtime library for whatever I/O functions are needed.

       -memregs=number
           Specifies the number of memory-based pseudo-registers GCC uses during code generation.
           These pseudo-registers are used like real registers, so there is a tradeoff between
           GCC's ability to fit the code into available registers, and the performance penalty of
           using memory instead of registers.  Note that all modules in a program must be
           compiled with the same value for this option.  Because of that, you must not use this
           option with GCC's default runtime libraries.

       M32R/D Options

       These -m options are defined for Renesas M32R/D architectures:

       -m32r2
           Generate code for the M32R/2.

       -m32rx
           Generate code for the M32R/X.

       -m32r
           Generate code for the M32R.  This is the default.

       -mmodel=small
           Assume all objects live in the lower 16MB of memory (so that their addresses can be
           loaded with the "ld24" instruction), and assume all subroutines are reachable with the
           "bl" instruction.  This is the default.

           The addressability of a particular object can be set with the "model" attribute.

       -mmodel=medium
           Assume objects may be anywhere in the 32-bit address space (the compiler generates
           "seth/add3" instructions to load their addresses), and assume all subroutines are
           reachable with the "bl" instruction.

       -mmodel=large
           Assume objects may be anywhere in the 32-bit address space (the compiler generates
           "seth/add3" instructions to load their addresses), and assume subroutines may not be
           reachable with the "bl" instruction (the compiler generates the much slower
           "seth/add3/jl" instruction sequence).

       -msdata=none
           Disable use of the small data area.  Variables are put into one of ".data", ".bss", or
           ".rodata" (unless the "section" attribute has been specified).  This is the default.

           The small data area consists of sections ".sdata" and ".sbss".  Objects may be
           explicitly put in the small data area with the "section" attribute using one of these
           sections.

       -msdata=sdata
           Put small global and static data in the small data area, but do not generate special
           code to reference them.

       -msdata=use
           Put small global and static data in the small data area, and generate special
           instructions to reference them.

       -G num
           Put global and static objects less than or equal to num bytes into the small data or
           BSS sections instead of the normal data or BSS sections.  The default value of num is
           8.  The -msdata option must be set to one of sdata or use for this option to have any
           effect.

           All modules should be compiled with the same -G num value.  Compiling with different
           values of num may or may not work; if it doesn't the linker gives an error
           message---incorrect code is not generated.

       -mdebug
           Makes the M32R-specific code in the compiler display some statistics that might help
           in debugging programs.

       -malign-loops
           Align all loops to a 32-byte boundary.

       -mno-align-loops
           Do not enforce a 32-byte alignment for loops.  This is the default.

       -missue-rate=number
           Issue number instructions per cycle.  number can only be 1 or 2.

       -mbranch-cost=number
           number can only be 1 or 2.  If it is 1 then branches are preferred over conditional
           code, if it is 2, then the opposite applies.

       -mflush-trap=number
           Specifies the trap number to use to flush the cache.  The default is 12.  Valid
           numbers are between 0 and 15 inclusive.

       -mno-flush-trap
           Specifies that the cache cannot be flushed by using a trap.

       -mflush-func=name
           Specifies the name of the operating system function to call to flush the cache.  The
           default is _flush_cache, but a function call is only used if a trap is not available.

       -mno-flush-func
           Indicates that there is no OS function for flushing the cache.

       M680x0 Options

       These are the -m options defined for M680x0 and ColdFire processors.  The default settings
       depend on which architecture was selected when the compiler was configured; the defaults
       for the most common choices are given below.

       -march=arch
           Generate code for a specific M680x0 or ColdFire instruction set architecture.
           Permissible values of arch for M680x0 architectures are: 68000, 68010, 68020, 68030,
           68040, 68060 and cpu32.  ColdFire architectures are selected according to Freescale's
           ISA classification and the permissible values are: isaa, isaaplus, isab and isac.

           GCC defines a macro "__mcfarch__" whenever it is generating code for a ColdFire
           target.  The arch in this macro is one of the -march arguments given above.

           When used together, -march and -mtune select code that runs on a family of similar
           processors but that is optimized for a particular microarchitecture.

       -mcpu=cpu
           Generate code for a specific M680x0 or ColdFire processor.  The M680x0 cpus are:
           68000, 68010, 68020, 68030, 68040, 68060, 68302, 68332 and cpu32.  The ColdFire cpus
           are given by the table below, which also classifies the CPUs into families:

           Family : -mcpu arguments
           51 : 51 51ac 51ag 51cn 51em 51je 51jf 51jg 51jm 51mm 51qe 51qm
           5206 : 5202 5204 5206
           5206e : 5206e
           5208 : 5207 5208
           5211a : 5210a 5211a
           5213 : 5211 5212 5213
           5216 : 5214 5216
           52235 : 52230 52231 52232 52233 52234 52235
           5225 : 5224 5225
           52259 : 52252 52254 52255 52256 52258 52259
           5235 : 5232 5233 5234 5235 523x
           5249 : 5249
           5250 : 5250
           5271 : 5270 5271
           5272 : 5272
           5275 : 5274 5275
           5282 : 5280 5281 5282 528x
           53017 : 53011 53012 53013 53014 53015 53016 53017
           5307 : 5307
           5329 : 5327 5328 5329 532x
           5373 : 5372 5373 537x
           5407 : 5407
           5475 : 5470 5471 5472 5473 5474 5475 547x 5480 5481 5482 5483 5484 5485

           -mcpu=cpu overrides -march=arch if arch is compatible with cpu.  Other combinations of
           -mcpu and -march are rejected.

           GCC defines the macro "__mcf_cpu_cpu" when ColdFire target cpu is selected.  It also
           defines "__mcf_family_family", where the value of family is given by the table above.

       -mtune=tune
           Tune the code for a particular microarchitecture within the constraints set by -march
           and -mcpu.  The M680x0 microarchitectures are: 68000, 68010, 68020, 68030, 68040,
           68060 and cpu32.  The ColdFire microarchitectures are: cfv1, cfv2, cfv3, cfv4 and
           cfv4e.

           You can also use -mtune=68020-40 for code that needs to run relatively well on 68020,
           68030 and 68040 targets.  -mtune=68020-60 is similar but includes 68060 targets as
           well.  These two options select the same tuning decisions as -m68020-40 and -m68020-60
           respectively.

           GCC defines the macros "__mcarch" and "__mcarch__" when tuning for 680x0 architecture
           arch.  It also defines "mcarch" unless either -ansi or a non-GNU -std option is used.
           If GCC is tuning for a range of architectures, as selected by -mtune=68020-40 or
           -mtune=68020-60, it defines the macros for every architecture in the range.

           GCC also defines the macro "__muarch__" when tuning for ColdFire microarchitecture
           uarch, where uarch is one of the arguments given above.

       -m68000
       -mc68000
           Generate output for a 68000.  This is the default when the compiler is configured for
           68000-based systems.  It is equivalent to -march=68000.

           Use this option for microcontrollers with a 68000 or EC000 core, including the 68008,
           68302, 68306, 68307, 68322, 68328 and 68356.

       -m68010
           Generate output for a 68010.  This is the default when the compiler is configured for
           68010-based systems.  It is equivalent to -march=68010.

       -m68020
       -mc68020
           Generate output for a 68020.  This is the default when the compiler is configured for
           68020-based systems.  It is equivalent to -march=68020.

       -m68030
           Generate output for a 68030.  This is the default when the compiler is configured for
           68030-based systems.  It is equivalent to -march=68030.

       -m68040
           Generate output for a 68040.  This is the default when the compiler is configured for
           68040-based systems.  It is equivalent to -march=68040.

           This option inhibits the use of 68881/68882 instructions that have to be emulated by
           software on the 68040.  Use this option if your 68040 does not have code to emulate
           those instructions.

       -m68060
           Generate output for a 68060.  This is the default when the compiler is configured for
           68060-based systems.  It is equivalent to -march=68060.

           This option inhibits the use of 68020 and 68881/68882 instructions that have to be
           emulated by software on the 68060.  Use this option if your 68060 does not have code
           to emulate those instructions.

       -mcpu32
           Generate output for a CPU32.  This is the default when the compiler is configured for
           CPU32-based systems.  It is equivalent to -march=cpu32.

           Use this option for microcontrollers with a CPU32 or CPU32+ core, including the 68330,
           68331, 68332, 68333, 68334, 68336, 68340, 68341, 68349 and 68360.

       -m5200
           Generate output for a 520X ColdFire CPU.  This is the default when the compiler is
           configured for 520X-based systems.  It is equivalent to -mcpu=5206, and is now
           deprecated in favor of that option.

           Use this option for microcontroller with a 5200 core, including the MCF5202, MCF5203,
           MCF5204 and MCF5206.

       -m5206e
           Generate output for a 5206e ColdFire CPU.  The option is now deprecated in favor of
           the equivalent -mcpu=5206e.

       -m528x
           Generate output for a member of the ColdFire 528X family.  The option is now
           deprecated in favor of the equivalent -mcpu=528x.

       -m5307
           Generate output for a ColdFire 5307 CPU.  The option is now deprecated in favor of the
           equivalent -mcpu=5307.

       -m5407
           Generate output for a ColdFire 5407 CPU.  The option is now deprecated in favor of the
           equivalent -mcpu=5407.

       -mcfv4e
           Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).  This includes use of
           hardware floating-point instructions.  The option is equivalent to -mcpu=547x, and is
           now deprecated in favor of that option.

       -m68020-40
           Generate output for a 68040, without using any of the new instructions.  This results
           in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a
           68040.  The generated code does use the 68881 instructions that are emulated on the
           68040.

           The option is equivalent to -march=68020 -mtune=68020-40.

       -m68020-60
           Generate output for a 68060, without using any of the new instructions.  This results
           in code that can run relatively efficiently on either a 68020/68881 or a 68030 or a
           68040.  The generated code does use the 68881 instructions that are emulated on the
           68060.

           The option is equivalent to -march=68020 -mtune=68020-60.

       -mhard-float
       -m68881
           Generate floating-point instructions.  This is the default for 68020 and above, and
           for ColdFire devices that have an FPU.  It defines the macro "__HAVE_68881__" on
           M680x0 targets and "__mcffpu__" on ColdFire targets.

       -msoft-float
           Do not generate floating-point instructions; use library calls instead.  This is the
           default for 68000, 68010, and 68832 targets.  It is also the default for ColdFire
           devices that have no FPU.

       -mdiv
       -mno-div
           Generate (do not generate) ColdFire hardware divide and remainder instructions.  If
           -march is used without -mcpu, the default is "on" for ColdFire architectures and "off"
           for M680x0 architectures.  Otherwise, the default is taken from the target CPU (either
           the default CPU, or the one specified by -mcpu).  For example, the default is "off"
           for -mcpu=5206 and "on" for -mcpu=5206e.

           GCC defines the macro "__mcfhwdiv__" when this option is enabled.

       -mshort
           Consider type "int" to be 16 bits wide, like "short int".  Additionally, parameters
           passed on the stack are also aligned to a 16-bit boundary even on targets whose API
           mandates promotion to 32-bit.

       -mno-short
           Do not consider type "int" to be 16 bits wide.  This is the default.

       -mnobitfield
       -mno-bitfield
           Do not use the bit-field instructions.  The -m68000, -mcpu32 and -m5200 options imply
           -mnobitfield.

       -mbitfield
           Do use the bit-field instructions.  The -m68020 option implies -mbitfield.  This is
           the default if you use a configuration designed for a 68020.

       -mrtd
           Use a different function-calling convention, in which functions that take a fixed
           number of arguments return with the "rtd" instruction, which pops their arguments
           while returning.  This saves one instruction in the caller since there is no need to
           pop the arguments there.

           This calling convention is incompatible with the one normally used on Unix, so you
           cannot use it if you need to call libraries compiled with the Unix compiler.

           Also, you must provide function prototypes for all functions that take variable
           numbers of arguments (including "printf"); otherwise incorrect code is generated for
           calls to those functions.

           In addition, seriously incorrect code results if you call a function with too many
           arguments.  (Normally, extra arguments are harmlessly ignored.)

           The "rtd" instruction is supported by the 68010, 68020, 68030, 68040, 68060 and CPU32
           processors, but not by the 68000 or 5200.

       -mno-rtd
           Do not use the calling conventions selected by -mrtd.  This is the default.

       -malign-int
       -mno-align-int
           Control whether GCC aligns "int", "long", "long long", "float", "double", and "long
           double" variables on a 32-bit boundary (-malign-int) or a 16-bit boundary
           (-mno-align-int).  Aligning variables on 32-bit boundaries produces code that runs
           somewhat faster on processors with 32-bit busses at the expense of more memory.

           Warning: if you use the -malign-int switch, GCC aligns structures containing the above
           types differently than most published application binary interface specifications for
           the m68k.

       -mpcrel
           Use the pc-relative addressing mode of the 68000 directly, instead of using a global
           offset table.  At present, this option implies -fpic, allowing at most a 16-bit offset
           for pc-relative addressing.  -fPIC is not presently supported with -mpcrel, though
           this could be supported for 68020 and higher processors.

       -mno-strict-align
       -mstrict-align
           Do not (do) assume that unaligned memory references are handled by the system.

       -msep-data
           Generate code that allows the data segment to be located in a different area of memory
           from the text segment.  This allows for execute-in-place in an environment without
           virtual memory management.  This option implies -fPIC.

       -mno-sep-data
           Generate code that assumes that the data segment follows the text segment.  This is
           the default.

       -mid-shared-library
           Generate code that supports shared libraries via the library ID method.  This allows
           for execute-in-place and shared libraries in an environment without virtual memory
           management.  This option implies -fPIC.

       -mno-id-shared-library
           Generate code that doesn't assume ID-based shared libraries are being used.  This is
           the default.

       -mshared-library-id=n
           Specifies the identification number of the ID-based shared library being compiled.
           Specifying a value of 0 generates more compact code; specifying other values forces
           the allocation of that number to the current library, but is no more space- or time-
           efficient than omitting this option.

       -mxgot
       -mno-xgot
           When generating position-independent code for ColdFire, generate code that works if
           the GOT has more than 8192 entries.  This code is larger and slower than code
           generated without this option.  On M680x0 processors, this option is not needed; -fPIC
           suffices.

           GCC normally uses a single instruction to load values from the GOT.  While this is
           relatively efficient, it only works if the GOT is smaller than about 64k.  Anything
           larger causes the linker to report an error such as:

                   relocation truncated to fit: R_68K_GOT16O foobar

           If this happens, you should recompile your code with -mxgot.  It should then work with
           very large GOTs.  However, code generated with -mxgot is less efficient, since it
           takes 4 instructions to fetch the value of a global symbol.

           Note that some linkers, including newer versions of the GNU linker, can create
           multiple GOTs and sort GOT entries.  If you have such a linker, you should only need
           to use -mxgot when compiling a single object file that accesses more than 8192 GOT
           entries.  Very few do.

           These options have no effect unless GCC is generating position-independent code.

       -mlong-jump-table-offsets
           Use 32-bit offsets in "switch" tables.  The default is to use 16-bit offsets.

       MCore Options

       These are the -m options defined for the Motorola M*Core processors.

       -mhardlit
       -mno-hardlit
           Inline constants into the code stream if it can be done in two instructions or less.

       -mdiv
       -mno-div
           Use the divide instruction.  (Enabled by default).

       -mrelax-immediate
       -mno-relax-immediate
           Allow arbitrary-sized immediates in bit operations.

       -mwide-bitfields
       -mno-wide-bitfields
           Always treat bit-fields as "int"-sized.

       -m4byte-functions
       -mno-4byte-functions
           Force all functions to be aligned to a 4-byte boundary.

       -mcallgraph-data
       -mno-callgraph-data
           Emit callgraph information.

       -mslow-bytes
       -mno-slow-bytes
           Prefer word access when reading byte quantities.

       -mlittle-endian
       -mbig-endian
           Generate code for a little-endian target.

       -m210
       -m340
           Generate code for the 210 processor.

       -mno-lsim
           Assume that runtime support has been provided and so omit the simulator library
           (libsim.a) from the linker command line.

       -mstack-increment=size
           Set the maximum amount for a single stack increment operation.  Large values can
           increase the speed of programs that contain functions that need a large amount of
           stack space, but they can also trigger a segmentation fault if the stack is extended
           too much.  The default value is 0x1000.

       MeP Options

       -mabsdiff
           Enables the "abs" instruction, which is the absolute difference between two registers.

       -mall-opts
           Enables all the optional instructions---average, multiply, divide, bit operations,
           leading zero, absolute difference, min/max, clip, and saturation.

       -maverage
           Enables the "ave" instruction, which computes the average of two registers.

       -mbased=n
           Variables of size n bytes or smaller are placed in the ".based" section by default.
           Based variables use the $tp register as a base register, and there is a 128-byte limit
           to the ".based" section.

       -mbitops
           Enables the bit operation instructions---bit test ("btstm"), set ("bsetm"), clear
           ("bclrm"), invert ("bnotm"), and test-and-set ("tas").

       -mc=name
           Selects which section constant data is placed in.  name may be tiny, near, or far.

       -mclip
           Enables the "clip" instruction.  Note that -mclip is not useful unless you also
           provide -mminmax.

       -mconfig=name
           Selects one of the built-in core configurations.  Each MeP chip has one or more
           modules in it; each module has a core CPU and a variety of coprocessors, optional
           instructions, and peripherals.  The "MeP-Integrator" tool, not part of GCC, provides
           these configurations through this option; using this option is the same as using all
           the corresponding command-line options.  The default configuration is default.

       -mcop
           Enables the coprocessor instructions.  By default, this is a 32-bit coprocessor.  Note
           that the coprocessor is normally enabled via the -mconfig= option.

       -mcop32
           Enables the 32-bit coprocessor's instructions.

       -mcop64
           Enables the 64-bit coprocessor's instructions.

       -mivc2
           Enables IVC2 scheduling.  IVC2 is a 64-bit VLIW coprocessor.

       -mdc
           Causes constant variables to be placed in the ".near" section.

       -mdiv
           Enables the "div" and "divu" instructions.

       -meb
           Generate big-endian code.

       -mel
           Generate little-endian code.

       -mio-volatile
           Tells the compiler that any variable marked with the "io" attribute is to be
           considered volatile.

       -ml Causes variables to be assigned to the ".far" section by default.

       -mleadz
           Enables the "leadz" (leading zero) instruction.

       -mm Causes variables to be assigned to the ".near" section by default.

       -mminmax
           Enables the "min" and "max" instructions.

       -mmult
           Enables the multiplication and multiply-accumulate instructions.

       -mno-opts
           Disables all the optional instructions enabled by -mall-opts.

       -mrepeat
           Enables the "repeat" and "erepeat" instructions, used for low-overhead looping.

       -ms Causes all variables to default to the ".tiny" section.  Note that there is a
           65536-byte limit to this section.  Accesses to these variables use the %gp base
           register.

       -msatur
           Enables the saturation instructions.  Note that the compiler does not currently
           generate these itself, but this option is included for compatibility with other tools,
           like "as".

       -msdram
           Link the SDRAM-based runtime instead of the default ROM-based runtime.

       -msim
           Link the simulator run-time libraries.

       -msimnovec
           Link the simulator runtime libraries, excluding built-in support for reset and
           exception vectors and tables.

       -mtf
           Causes all functions to default to the ".far" section.  Without this option, functions
           default to the ".near" section.

       -mtiny=n
           Variables that are n bytes or smaller are allocated to the ".tiny" section.  These
           variables use the $gp base register.  The default for this option is 4, but note that
           there's a 65536-byte limit to the ".tiny" section.

       MicroBlaze Options

       -msoft-float
           Use software emulation for floating point (default).

       -mhard-float
           Use hardware floating-point instructions.

       -mmemcpy
           Do not optimize block moves, use "memcpy".

       -mno-clearbss
           This option is deprecated.  Use -fno-zero-initialized-in-bss instead.

       -mcpu=cpu-type
           Use features of, and schedule code for, the given CPU.  Supported values are in the
           format vX.YY.Z, where X is a major version, YY is the minor version, and Z is
           compatibility code.  Example values are v3.00.a, v4.00.b, v5.00.a, v5.00.b, v6.00.a.

       -mxl-soft-mul
           Use software multiply emulation (default).

       -mxl-soft-div
           Use software emulation for divides (default).

       -mxl-barrel-shift
           Use the hardware barrel shifter.

       -mxl-pattern-compare
           Use pattern compare instructions.

       -msmall-divides
           Use table lookup optimization for small signed integer divisions.

       -mxl-stack-check
           This option is deprecated.  Use -fstack-check instead.

       -mxl-gp-opt
           Use GP-relative ".sdata"/".sbss" sections.

       -mxl-multiply-high
           Use multiply high instructions for high part of 32x32 multiply.

       -mxl-float-convert
           Use hardware floating-point conversion instructions.

       -mxl-float-sqrt
           Use hardware floating-point square root instruction.

       -mbig-endian
           Generate code for a big-endian target.

       -mlittle-endian
           Generate code for a little-endian target.

       -mxl-reorder
           Use reorder instructions (swap and byte reversed load/store).

       -mxl-mode-app-model
           Select application model app-model.  Valid models are

           executable
               normal executable (default), uses startup code crt0.o.

           xmdstub
               for use with Xilinx Microprocessor Debugger (XMD) based software intrusive debug
               agent called xmdstub. This uses startup file crt1.o and sets the start address of
               the program to 0x800.

           bootstrap
               for applications that are loaded using a bootloader.  This model uses startup file
               crt2.o which does not contain a processor reset vector handler. This is suitable
               for transferring control on a processor reset to the bootloader rather than the
               application.

           novectors
               for applications that do not require any of the MicroBlaze vectors. This option
               may be useful for applications running within a monitoring application. This model
               uses crt3.o as a startup file.

           Option -xl-mode-app-model is a deprecated alias for -mxl-mode-app-model.

       MIPS Options

       -EB Generate big-endian code.

       -EL Generate little-endian code.  This is the default for mips*el-*-* configurations.

       -march=arch
           Generate code that runs on arch, which can be the name of a generic MIPS ISA, or the
           name of a particular processor.  The ISA names are: mips1, mips2, mips3, mips4,
           mips32, mips32r2, mips32r3, mips32r5, mips32r6, mips64, mips64r2, mips64r3, mips64r5
           and mips64r6.  The processor names are: 4kc, 4km, 4kp, 4ksc, 4kec, 4kem, 4kep, 4ksd,
           5kc, 5kf, 20kc, 24kc, 24kf2_1, 24kf1_1, 24kec, 24kef2_1, 24kef1_1, 34kc, 34kf2_1,
           34kf1_1, 34kn, 74kc, 74kf2_1, 74kf1_1, 74kf3_2, 1004kc, 1004kf2_1, 1004kf1_1, i6400,
           interaptiv, loongson2e, loongson2f, loongson3a, m4k, m14k, m14kc, m14ke, m14kec,
           m5100, m5101, octeon, octeon+, octeon2, octeon3, orion, p5600, r2000, r3000, r3900,
           r4000, r4400, r4600, r4650, r4700, r6000, r8000, rm7000, rm9000, r10000, r12000,
           r14000, r16000, sb1, sr71000, vr4100, vr4111, vr4120, vr4130, vr4300, vr5000, vr5400,
           vr5500, xlr and xlp.  The special value from-abi selects the most compatible
           architecture for the selected ABI (that is, mips1 for 32-bit ABIs and mips3 for 64-bit
           ABIs).

           The native Linux/GNU toolchain also supports the value native, which selects the best
           architecture option for the host processor.  -march=native has no effect if GCC does
           not recognize the processor.

           In processor names, a final 000 can be abbreviated as k (for example, -march=r2k).
           Prefixes are optional, and vr may be written r.

           Names of the form nf2_1 refer to processors with FPUs clocked at half the rate of the
           core, names of the form nf1_1 refer to processors with FPUs clocked at the same rate
           as the core, and names of the form nf3_2 refer to processors with FPUs clocked a ratio
           of 3:2 with respect to the core.  For compatibility reasons, nf is accepted as a
           synonym for nf2_1 while nx and bfx are accepted as synonyms for nf1_1.

           GCC defines two macros based on the value of this option.  The first is "_MIPS_ARCH",
           which gives the name of target architecture, as a string.  The second has the form
           "_MIPS_ARCH_foo", where foo is the capitalized value of "_MIPS_ARCH".  For example,
           -march=r2000 sets "_MIPS_ARCH" to "r2000" and defines the macro "_MIPS_ARCH_R2000".

           Note that the "_MIPS_ARCH" macro uses the processor names given above.  In other
           words, it has the full prefix and does not abbreviate 000 as k.  In the case of from-
           abi, the macro names the resolved architecture (either "mips1" or "mips3").  It names
           the default architecture when no -march option is given.

       -mtune=arch
           Optimize for arch.  Among other things, this option controls the way instructions are
           scheduled, and the perceived cost of arithmetic operations.  The list of arch values
           is the same as for -march.

           When this option is not used, GCC optimizes for the processor specified by -march.  By
           using -march and -mtune together, it is possible to generate code that runs on a
           family of processors, but optimize the code for one particular member of that family.

           -mtune defines the macros "_MIPS_TUNE" and "_MIPS_TUNE_foo", which work in the same
           way as the -march ones described above.

       -mips1
           Equivalent to -march=mips1.

       -mips2
           Equivalent to -march=mips2.

       -mips3
           Equivalent to -march=mips3.

       -mips4
           Equivalent to -march=mips4.

       -mips32
           Equivalent to -march=mips32.

       -mips32r3
           Equivalent to -march=mips32r3.

       -mips32r5
           Equivalent to -march=mips32r5.

       -mips32r6
           Equivalent to -march=mips32r6.

       -mips64
           Equivalent to -march=mips64.

       -mips64r2
           Equivalent to -march=mips64r2.

       -mips64r3
           Equivalent to -march=mips64r3.

       -mips64r5
           Equivalent to -march=mips64r5.

       -mips64r6
           Equivalent to -march=mips64r6.

       -mips16
       -mno-mips16
           Generate (do not generate) MIPS16 code.  If GCC is targeting a MIPS32 or MIPS64
           architecture, it makes use of the MIPS16e ASE.

           MIPS16 code generation can also be controlled on a per-function basis by means of
           "mips16" and "nomips16" attributes.

       -mflip-mips16
           Generate MIPS16 code on alternating functions.  This option is provided for regression
           testing of mixed MIPS16/non-MIPS16 code generation, and is not intended for ordinary
           use in compiling user code.

       -minterlink-compressed
       -mno-interlink-compressed
           Require (do not require) that code using the standard (uncompressed) MIPS ISA be link-
           compatible with MIPS16 and microMIPS code, and vice versa.

           For example, code using the standard ISA encoding cannot jump directly to MIPS16 or
           microMIPS code; it must either use a call or an indirect jump.  -minterlink-compressed
           therefore disables direct jumps unless GCC knows that the target of the jump is not
           compressed.

       -minterlink-mips16
       -mno-interlink-mips16
           Aliases of -minterlink-compressed and -mno-interlink-compressed.  These options
           predate the microMIPS ASE and are retained for backwards compatibility.

       -mabi=32
       -mabi=o64
       -mabi=n32
       -mabi=64
       -mabi=eabi
           Generate code for the given ABI.

           Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally generates 64-bit
           code when you select a 64-bit architecture, but you can use -mgp32 to get 32-bit code
           instead.

           For information about the O64 ABI, see <http://gcc.gnu.org/projects/mipso64-abi.html>.

           GCC supports a variant of the o32 ABI in which floating-point registers are 64 rather
           than 32 bits wide.  You can select this combination with -mabi=32 -mfp64.  This ABI
           relies on the "mthc1" and "mfhc1" instructions and is therefore only supported for
           MIPS32R2, MIPS32R3 and MIPS32R5 processors.

           The register assignments for arguments and return values remain the same, but each
           scalar value is passed in a single 64-bit register rather than a pair of 32-bit
           registers.  For example, scalar floating-point values are returned in $f0 only, not a
           $f0/$f1 pair.  The set of call-saved registers also remains the same in that the even-
           numbered double-precision registers are saved.

           Two additional variants of the o32 ABI are supported to enable a transition from
           32-bit to 64-bit registers.  These are FPXX (-mfpxx) and FP64A (-mfp64
           -mno-odd-spreg).  The FPXX extension mandates that all code must execute correctly
           when run using 32-bit or 64-bit registers.  The code can be interlinked with either
           FP32 or FP64, but not both.  The FP64A extension is similar to the FP64 extension but
           forbids the use of odd-numbered single-precision registers.  This can be used in
           conjunction with the "FRE" mode of FPUs in MIPS32R5 processors and allows both FP32
           and FP64A code to interlink and run in the same process without changing FPU modes.

       -mabicalls
       -mno-abicalls
           Generate (do not generate) code that is suitable for SVR4-style dynamic objects.
           -mabicalls is the default for SVR4-based systems.

       -mshared
       -mno-shared
           Generate (do not generate) code that is fully position-independent, and that can
           therefore be linked into shared libraries.  This option only affects -mabicalls.

           All -mabicalls code has traditionally been position-independent, regardless of options
           like -fPIC and -fpic.  However, as an extension, the GNU toolchain allows executables
           to use absolute accesses for locally-binding symbols.  It can also use shorter GP
           initialization sequences and generate direct calls to locally-defined functions.  This
           mode is selected by -mno-shared.

           -mno-shared depends on binutils 2.16 or higher and generates objects that can only be
           linked by the GNU linker.  However, the option does not affect the ABI of the final
           executable; it only affects the ABI of relocatable objects.  Using -mno-shared
           generally makes executables both smaller and quicker.

           -mshared is the default.

       -mplt
       -mno-plt
           Assume (do not assume) that the static and dynamic linkers support PLTs and copy
           relocations.  This option only affects -mno-shared -mabicalls.  For the n64 ABI, this
           option has no effect without -msym32.

           You can make -mplt the default by configuring GCC with --with-mips-plt.  The default
           is -mno-plt otherwise.

       -mxgot
       -mno-xgot
           Lift (do not lift) the usual restrictions on the size of the global offset table.

           GCC normally uses a single instruction to load values from the GOT.  While this is
           relatively efficient, it only works if the GOT is smaller than about 64k.  Anything
           larger causes the linker to report an error such as:

                   relocation truncated to fit: R_MIPS_GOT16 foobar

           If this happens, you should recompile your code with -mxgot.  This works with very
           large GOTs, although the code is also less efficient, since it takes three
           instructions to fetch the value of a global symbol.

           Note that some linkers can create multiple GOTs.  If you have such a linker, you
           should only need to use -mxgot when a single object file accesses more than 64k's
           worth of GOT entries.  Very few do.

           These options have no effect unless GCC is generating position independent code.

       -mgp32
           Assume that general-purpose registers are 32 bits wide.

       -mgp64
           Assume that general-purpose registers are 64 bits wide.

       -mfp32
           Assume that floating-point registers are 32 bits wide.

       -mfp64
           Assume that floating-point registers are 64 bits wide.

       -mfpxx
           Do not assume the width of floating-point registers.

       -mhard-float
           Use floating-point coprocessor instructions.

       -msoft-float
           Do not use floating-point coprocessor instructions.  Implement floating-point
           calculations using library calls instead.

       -mno-float
           Equivalent to -msoft-float, but additionally asserts that the program being compiled
           does not perform any floating-point operations.  This option is presently supported
           only by some bare-metal MIPS configurations, where it may select a special set of
           libraries that lack all floating-point support (including, for example, the floating-
           point "printf" formats).  If code compiled with -mno-float accidentally contains
           floating-point operations, it is likely to suffer a link-time or run-time failure.

       -msingle-float
           Assume that the floating-point coprocessor only supports single-precision operations.

       -mdouble-float
           Assume that the floating-point coprocessor supports double-precision operations.  This
           is the default.

       -modd-spreg
       -mno-odd-spreg
           Enable the use of odd-numbered single-precision floating-point registers for the o32
           ABI.  This is the default for processors that are known to support these registers.
           When using the o32 FPXX ABI, -mno-odd-spreg is set by default.

       -mabs=2008
       -mabs=legacy
           These options control the treatment of the special not-a-number (NaN) IEEE 754
           floating-point data with the "abs.fmt" and "neg.fmt" machine instructions.

           By default or when -mabs=legacy is used the legacy treatment is selected.  In this
           case these instructions are considered arithmetic and avoided where correct operation
           is required and the input operand might be a NaN.  A longer sequence of instructions
           that manipulate the sign bit of floating-point datum manually is used instead unless
           the -ffinite-math-only option has also been specified.

           The -mabs=2008 option selects the IEEE 754-2008 treatment.  In this case these
           instructions are considered non-arithmetic and therefore operating correctly in all
           cases, including in particular where the input operand is a NaN.  These instructions
           are therefore always used for the respective operations.

       -mnan=2008
       -mnan=legacy
           These options control the encoding of the special not-a-number (NaN) IEEE 754
           floating-point data.

           The -mnan=legacy option selects the legacy encoding.  In this case quiet NaNs (qNaNs)
           are denoted by the first bit of their trailing significand field being 0, whereas
           signaling NaNs (sNaNs) are denoted by the first bit of their trailing significand
           field being 1.

           The -mnan=2008 option selects the IEEE 754-2008 encoding.  In this case qNaNs are
           denoted by the first bit of their trailing significand field being 1, whereas sNaNs
           are denoted by the first bit of their trailing significand field being 0.

           The default is -mnan=legacy unless GCC has been configured with --with-nan=2008.

       -mllsc
       -mno-llsc
           Use (do not use) ll, sc, and sync instructions to implement atomic memory built-in
           functions.  When neither option is specified, GCC uses the instructions if the target
           architecture supports them.

           -mllsc is useful if the runtime environment can emulate the instructions and -mno-llsc
           can be useful when compiling for nonstandard ISAs.  You can make either option the
           default by configuring GCC with --with-llsc and --without-llsc respectively.
           --with-llsc is the default for some configurations; see the installation documentation
           for details.

       -mdsp
       -mno-dsp
           Use (do not use) revision 1 of the MIPS DSP ASE.
             This option defines the preprocessor macro "__mips_dsp".  It also defines
           "__mips_dsp_rev" to 1.

       -mdspr2
       -mno-dspr2
           Use (do not use) revision 2 of the MIPS DSP ASE.
             This option defines the preprocessor macros "__mips_dsp" and "__mips_dspr2".  It
           also defines "__mips_dsp_rev" to 2.

       -msmartmips
       -mno-smartmips
           Use (do not use) the MIPS SmartMIPS ASE.

       -mpaired-single
       -mno-paired-single
           Use (do not use) paired-single floating-point instructions.
             This option requires hardware floating-point support to be enabled.

       -mdmx
       -mno-mdmx
           Use (do not use) MIPS Digital Media Extension instructions.  This option can only be
           used when generating 64-bit code and requires hardware floating-point support to be
           enabled.

       -mips3d
       -mno-mips3d
           Use (do not use) the MIPS-3D ASE.  The option -mips3d implies -mpaired-single.

       -mmicromips
       -mno-micromips
           Generate (do not generate) microMIPS code.

           MicroMIPS code generation can also be controlled on a per-function basis by means of
           "micromips" and "nomicromips" attributes.

       -mmt
       -mno-mt
           Use (do not use) MT Multithreading instructions.

       -mmcu
       -mno-mcu
           Use (do not use) the MIPS MCU ASE instructions.

       -meva
       -mno-eva
           Use (do not use) the MIPS Enhanced Virtual Addressing instructions.

       -mvirt
       -mno-virt
           Use (do not use) the MIPS Virtualization (VZ) instructions.

       -mxpa
       -mno-xpa
           Use (do not use) the MIPS eXtended Physical Address (XPA) instructions.

       -mlong64
           Force "long" types to be 64 bits wide.  See -mlong32 for an explanation of the default
           and the way that the pointer size is determined.

       -mlong32
           Force "long", "int", and pointer types to be 32 bits wide.

           The default size of "int"s, "long"s and pointers depends on the ABI.  All the
           supported ABIs use 32-bit "int"s.  The n64 ABI uses 64-bit "long"s, as does the 64-bit
           EABI; the others use 32-bit "long"s.  Pointers are the same size as "long"s, or the
           same size as integer registers, whichever is smaller.

       -msym32
       -mno-sym32
           Assume (do not assume) that all symbols have 32-bit values, regardless of the selected
           ABI.  This option is useful in combination with -mabi=64 and -mno-abicalls because it
           allows GCC to generate shorter and faster references to symbolic addresses.

       -G num
           Put definitions of externally-visible data in a small data section if that data is no
           bigger than num bytes.  GCC can then generate more efficient accesses to the data; see
           -mgpopt for details.

           The default -G option depends on the configuration.

       -mlocal-sdata
       -mno-local-sdata
           Extend (do not extend) the -G behavior to local data too, such as to static variables
           in C.  -mlocal-sdata is the default for all configurations.

           If the linker complains that an application is using too much small data, you might
           want to try rebuilding the less performance-critical parts with -mno-local-sdata.  You
           might also want to build large libraries with -mno-local-sdata, so that the libraries
           leave more room for the main program.

       -mextern-sdata
       -mno-extern-sdata
           Assume (do not assume) that externally-defined data is in a small data section if the
           size of that data is within the -G limit.  -mextern-sdata is the default for all
           configurations.

           If you compile a module Mod with -mextern-sdata -G num -mgpopt, and Mod references a
           variable Var that is no bigger than num bytes, you must make sure that Var is placed
           in a small data section.  If Var is defined by another module, you must either compile
           that module with a high-enough -G setting or attach a "section" attribute to Var's
           definition.  If Var is common, you must link the application with a high-enough -G
           setting.

           The easiest way of satisfying these restrictions is to compile and link every module
           with the same -G option.  However, you may wish to build a library that supports
           several different small data limits.  You can do this by compiling the library with
           the highest supported -G setting and additionally using -mno-extern-sdata to stop the
           library from making assumptions about externally-defined data.

       -mgpopt
       -mno-gpopt
           Use (do not use) GP-relative accesses for symbols that are known to be in a small data
           section; see -G, -mlocal-sdata and -mextern-sdata.  -mgpopt is the default for all
           configurations.

           -mno-gpopt is useful for cases where the $gp register might not hold the value of
           "_gp".  For example, if the code is part of a library that might be used in a boot
           monitor, programs that call boot monitor routines pass an unknown value in $gp.  (In
           such situations, the boot monitor itself is usually compiled with -G0.)

           -mno-gpopt implies -mno-local-sdata and -mno-extern-sdata.

       -membedded-data
       -mno-embedded-data
           Allocate variables to the read-only data section first if possible, then next in the
           small data section if possible, otherwise in data.  This gives slightly slower code
           than the default, but reduces the amount of RAM required when executing, and thus may
           be preferred for some embedded systems.

       -muninit-const-in-rodata
       -mno-uninit-const-in-rodata
           Put uninitialized "const" variables in the read-only data section.  This option is
           only meaningful in conjunction with -membedded-data.

       -mcode-readable=setting
           Specify whether GCC may generate code that reads from executable sections.  There are
           three possible settings:

           -mcode-readable=yes
               Instructions may freely access executable sections.  This is the default setting.

           -mcode-readable=pcrel
               MIPS16 PC-relative load instructions can access executable sections, but other
               instructions must not do so.  This option is useful on 4KSc and 4KSd processors
               when the code TLBs have the Read Inhibit bit set.  It is also useful on processors
               that can be configured to have a dual instruction/data SRAM interface and that,
               like the M4K, automatically redirect PC-relative loads to the instruction RAM.

           -mcode-readable=no
               Instructions must not access executable sections.  This option can be useful on
               targets that are configured to have a dual instruction/data SRAM interface but
               that (unlike the M4K) do not automatically redirect PC-relative loads to the
               instruction RAM.

       -msplit-addresses
       -mno-split-addresses
           Enable (disable) use of the "%hi()" and "%lo()" assembler relocation operators.  This
           option has been superseded by -mexplicit-relocs but is retained for backwards
           compatibility.

       -mexplicit-relocs
       -mno-explicit-relocs
           Use (do not use) assembler relocation operators when dealing with symbolic addresses.
           The alternative, selected by -mno-explicit-relocs, is to use assembler macros instead.

           -mexplicit-relocs is the default if GCC was configured to use an assembler that
           supports relocation operators.

       -mcheck-zero-division
       -mno-check-zero-division
           Trap (do not trap) on integer division by zero.

           The default is -mcheck-zero-division.

       -mdivide-traps
       -mdivide-breaks
           MIPS systems check for division by zero by generating either a conditional trap or a
           break instruction.  Using traps results in smaller code, but is only supported on MIPS
           II and later.  Also, some versions of the Linux kernel have a bug that prevents trap
           from generating the proper signal ("SIGFPE").  Use -mdivide-traps to allow conditional
           traps on architectures that support them and -mdivide-breaks to force the use of
           breaks.

           The default is usually -mdivide-traps, but this can be overridden at configure time
           using --with-divide=breaks.  Divide-by-zero checks can be completely disabled using
           -mno-check-zero-division.

       -mload-store-pairs
       -mno-load-store-pairs
           Enable (disable) an optimization that pairs consecutive load or store instructions to
           enable load/store bonding.  This option is enabled by default but only takes effect
           when the selected architecture is known to support bonding.

       -mmemcpy
       -mno-memcpy
           Force (do not force) the use of "memcpy" for non-trivial block moves.  The default is
           -mno-memcpy, which allows GCC to inline most constant-sized copies.

       -mlong-calls
       -mno-long-calls
           Disable (do not disable) use of the "jal" instruction.  Calling functions using "jal"
           is more efficient but requires the caller and callee to be in the same 256 megabyte
           segment.

           This option has no effect on abicalls code.  The default is -mno-long-calls.

       -mmad
       -mno-mad
           Enable (disable) use of the "mad", "madu" and "mul" instructions, as provided by the
           R4650 ISA.

       -mimadd
       -mno-imadd
           Enable (disable) use of the "madd" and "msub" integer instructions.  The default is
           -mimadd on architectures that support "madd" and "msub" except for the 74k
           architecture where it was found to generate slower code.

       -mfused-madd
       -mno-fused-madd
           Enable (disable) use of the floating-point multiply-accumulate instructions, when they
           are available.  The default is -mfused-madd.

           On the R8000 CPU when multiply-accumulate instructions are used, the intermediate
           product is calculated to infinite precision and is not subject to the FCSR Flush to
           Zero bit.  This may be undesirable in some circumstances.  On other processors the
           result is numerically identical to the equivalent computation using separate multiply,
           add, subtract and negate instructions.

       -nocpp
           Tell the MIPS assembler to not run its preprocessor over user assembler files (with a
           .s suffix) when assembling them.

       -mfix-24k
       -mno-fix-24k
           Work around the 24K E48 (lost data on stores during refill) errata.  The workarounds
           are implemented by the assembler rather than by GCC.

       -mfix-r4000
       -mno-fix-r4000
           Work around certain R4000 CPU errata:

           -   A double-word or a variable shift may give an incorrect result if executed
               immediately after starting an integer division.

           -   A double-word or a variable shift may give an incorrect result if executed while
               an integer multiplication is in progress.

           -   An integer division may give an incorrect result if started in a delay slot of a
               taken branch or a jump.

       -mfix-r4400
       -mno-fix-r4400
           Work around certain R4400 CPU errata:

           -   A double-word or a variable shift may give an incorrect result if executed
               immediately after starting an integer division.

       -mfix-r10000
       -mno-fix-r10000
           Work around certain R10000 errata:

           -   "ll"/"sc" sequences may not behave atomically on revisions prior to 3.0.  They may
               deadlock on revisions 2.6 and earlier.

           This option can only be used if the target architecture supports branch-likely
           instructions.  -mfix-r10000 is the default when -march=r10000 is used; -mno-fix-r10000
           is the default otherwise.

       -mfix-rm7000
       -mno-fix-rm7000
           Work around the RM7000 "dmult"/"dmultu" errata.  The workarounds are implemented by
           the assembler rather than by GCC.

       -mfix-vr4120
       -mno-fix-vr4120
           Work around certain VR4120 errata:

           -   "dmultu" does not always produce the correct result.

           -   "div" and "ddiv" do not always produce the correct result if one of the operands
               is negative.

           The workarounds for the division errata rely on special functions in libgcc.a.  At
           present, these functions are only provided by the "mips64vr*-elf" configurations.

           Other VR4120 errata require a NOP to be inserted between certain pairs of
           instructions.  These errata are handled by the assembler, not by GCC itself.

       -mfix-vr4130
           Work around the VR4130 "mflo"/"mfhi" errata.  The workarounds are implemented by the
           assembler rather than by GCC, although GCC avoids using "mflo" and "mfhi" if the
           VR4130 "macc", "macchi", "dmacc" and "dmacchi" instructions are available instead.

       -mfix-sb1
       -mno-fix-sb1
           Work around certain SB-1 CPU core errata.  (This flag currently works around the SB-1
           revision 2 "F1" and "F2" floating-point errata.)

       -mr10k-cache-barrier=setting
           Specify whether GCC should insert cache barriers to avoid the side effects of
           speculation on R10K processors.

           In common with many processors, the R10K tries to predict the outcome of a conditional
           branch and speculatively executes instructions from the "taken" branch.  It later
           aborts these instructions if the predicted outcome is wrong.  However, on the R10K,
           even aborted instructions can have side effects.

           This problem only affects kernel stores and, depending on the system, kernel loads.
           As an example, a speculatively-executed store may load the target memory into cache
           and mark the cache line as dirty, even if the store itself is later aborted.  If a DMA
           operation writes to the same area of memory before the "dirty" line is flushed, the
           cached data overwrites the DMA-ed data.  See the R10K processor manual for a full
           description, including other potential problems.

           One workaround is to insert cache barrier instructions before every memory access that
           might be speculatively executed and that might have side effects even if aborted.
           -mr10k-cache-barrier=setting controls GCC's implementation of this workaround.  It
           assumes that aborted accesses to any byte in the following regions does not have side
           effects:

           1.  the memory occupied by the current function's stack frame;

           2.  the memory occupied by an incoming stack argument;

           3.  the memory occupied by an object with a link-time-constant address.

           It is the kernel's responsibility to ensure that speculative accesses to these regions
           are indeed safe.

           If the input program contains a function declaration such as:

                   void foo (void);

           then the implementation of "foo" must allow "j foo" and "jal foo" to be executed
           speculatively.  GCC honors this restriction for functions it compiles itself.  It
           expects non-GCC functions (such as hand-written assembly code) to do the same.

           The option has three forms:

           -mr10k-cache-barrier=load-store
               Insert a cache barrier before a load or store that might be speculatively executed
               and that might have side effects even if aborted.

           -mr10k-cache-barrier=store
               Insert a cache barrier before a store that might be speculatively executed and
               that might have side effects even if aborted.

           -mr10k-cache-barrier=none
               Disable the insertion of cache barriers.  This is the default setting.

       -mflush-func=func
       -mno-flush-func
           Specifies the function to call to flush the I and D caches, or to not call any such
           function.  If called, the function must take the same arguments as the common
           "_flush_func", that is, the address of the memory range for which the cache is being
           flushed, the size of the memory range, and the number 3 (to flush both caches).  The
           default depends on the target GCC was configured for, but commonly is either
           "_flush_func" or "__cpu_flush".

       mbranch-cost=num
           Set the cost of branches to roughly num "simple" instructions.  This cost is only a
           heuristic and is not guaranteed to produce consistent results across releases.  A zero
           cost redundantly selects the default, which is based on the -mtune setting.

       -mbranch-likely
       -mno-branch-likely
           Enable or disable use of Branch Likely instructions, regardless of the default for the
           selected architecture.  By default, Branch Likely instructions may be generated if
           they are supported by the selected architecture.  An exception is for the MIPS32 and
           MIPS64 architectures and processors that implement those architectures; for those,
           Branch Likely instructions are not be generated by default because the MIPS32 and
           MIPS64 architectures specifically deprecate their use.

       -mcompact-branches=never
       -mcompact-branches=optimal
       -mcompact-branches=always
           These options control which form of branches will be generated.  The default is
           -mcompact-branches=optimal.

           The -mcompact-branches=never option ensures that compact branch instructions will
           never be generated.

           The -mcompact-branches=always option ensures that a compact branch instruction will be
           generated if available.  If a compact branch instruction is not available, a delay
           slot form of the branch will be used instead.

           This option is supported from MIPS Release 6 onwards.

           The -mcompact-branches=optimal option will cause a delay slot branch to be used if one
           is available in the current ISA and the delay slot is successfully filled.  If the
           delay slot is not filled, a compact branch will be chosen if one is available.

       -mfp-exceptions
       -mno-fp-exceptions
           Specifies whether FP exceptions are enabled.  This affects how FP instructions are
           scheduled for some processors.  The default is that FP exceptions are enabled.

           For instance, on the SB-1, if FP exceptions are disabled, and we are emitting 64-bit
           code, then we can use both FP pipes.  Otherwise, we can only use one FP pipe.

       -mvr4130-align
       -mno-vr4130-align
           The VR4130 pipeline is two-way superscalar, but can only issue two instructions
           together if the first one is 8-byte aligned.  When this option is enabled, GCC aligns
           pairs of instructions that it thinks should execute in parallel.

           This option only has an effect when optimizing for the VR4130.  It normally makes code
           faster, but at the expense of making it bigger.  It is enabled by default at
           optimization level -O3.

       -msynci
       -mno-synci
           Enable (disable) generation of "synci" instructions on architectures that support it.
           The "synci" instructions (if enabled) are generated when "__builtin___clear_cache" is
           compiled.

           This option defaults to -mno-synci, but the default can be overridden by configuring
           GCC with --with-synci.

           When compiling code for single processor systems, it is generally safe to use "synci".
           However, on many multi-core (SMP) systems, it does not invalidate the instruction
           caches on all cores and may lead to undefined behavior.

       -mrelax-pic-calls
       -mno-relax-pic-calls
           Try to turn PIC calls that are normally dispatched via register $25 into direct calls.
           This is only possible if the linker can resolve the destination at link time and if
           the destination is within range for a direct call.

           -mrelax-pic-calls is the default if GCC was configured to use an assembler and a
           linker that support the ".reloc" assembly directive and -mexplicit-relocs is in
           effect.  With -mno-explicit-relocs, this optimization can be performed by the
           assembler and the linker alone without help from the compiler.

       -mmcount-ra-address
       -mno-mcount-ra-address
           Emit (do not emit) code that allows "_mcount" to modify the calling function's return
           address.  When enabled, this option extends the usual "_mcount" interface with a new
           ra-address parameter, which has type "intptr_t *" and is passed in register $12.
           "_mcount" can then modify the return address by doing both of the following:

           *   Returning the new address in register $31.

           *   Storing the new address in "*ra-address", if ra-address is nonnull.

           The default is -mno-mcount-ra-address.

       -mframe-header-opt
       -mno-frame-header-opt
           Enable (disable) frame header optimization in the o32 ABI.  When using the o32 ABI,
           calling functions will allocate 16 bytes on the stack for the called function to write
           out register arguments.  When enabled, this optimization will suppress the allocation
           of the frame header if it can be determined that it is unused.

           This optimization is off by default at all optimization levels.

       -mlxc1-sxc1
       -mno-lxc1-sxc1
           When applicable, enable (disable) the generation of "lwxc1", "swxc1", "ldxc1", "sdxc1"
           instructions.  Enabled by default.

       -mmadd4
       -mno-madd4
           When applicable, enable (disable) the generation of 4-operand "madd.s", "madd.d" and
           related instructions.  Enabled by default.

       MMIX Options

       These options are defined for the MMIX:

       -mlibfuncs
       -mno-libfuncs
           Specify that intrinsic library functions are being compiled, passing all values in
           registers, no matter the size.

       -mepsilon
       -mno-epsilon
           Generate floating-point comparison instructions that compare with respect to the "rE"
           epsilon register.

       -mabi=mmixware
       -mabi=gnu
           Generate code that passes function parameters and return values that (in the called
           function) are seen as registers $0 and up, as opposed to the GNU ABI which uses global
           registers $231 and up.

       -mzero-extend
       -mno-zero-extend
           When reading data from memory in sizes shorter than 64 bits, use (do not use) zero-
           extending load instructions by default, rather than sign-extending ones.

       -mknuthdiv
       -mno-knuthdiv
           Make the result of a division yielding a remainder have the same sign as the divisor.
           With the default, -mno-knuthdiv, the sign of the remainder follows the sign of the
           dividend.  Both methods are arithmetically valid, the latter being almost exclusively
           used.

       -mtoplevel-symbols
       -mno-toplevel-symbols
           Prepend (do not prepend) a : to all global symbols, so the assembly code can be used
           with the "PREFIX" assembly directive.

       -melf
           Generate an executable in the ELF format, rather than the default mmo format used by
           the mmix simulator.

       -mbranch-predict
       -mno-branch-predict
           Use (do not use) the probable-branch instructions, when static branch prediction
           indicates a probable branch.

       -mbase-addresses
       -mno-base-addresses
           Generate (do not generate) code that uses base addresses.  Using a base address
           automatically generates a request (handled by the assembler and the linker) for a
           constant to be set up in a global register.  The register is used for one or more base
           address requests within the range 0 to 255 from the value held in the register.  The
           generally leads to short and fast code, but the number of different data items that
           can be addressed is limited.  This means that a program that uses lots of static data
           may require -mno-base-addresses.

       -msingle-exit
       -mno-single-exit
           Force (do not force) generated code to have a single exit point in each function.

       MN10300 Options

       These -m options are defined for Matsushita MN10300 architectures:

       -mmult-bug
           Generate code to avoid bugs in the multiply instructions for the MN10300 processors.
           This is the default.

       -mno-mult-bug
           Do not generate code to avoid bugs in the multiply instructions for the MN10300
           processors.

       -mam33
           Generate code using features specific to the AM33 processor.

       -mno-am33
           Do not generate code using features specific to the AM33 processor.  This is the
           default.

       -mam33-2
           Generate code using features specific to the AM33/2.0 processor.

       -mam34
           Generate code using features specific to the AM34 processor.

       -mtune=cpu-type
           Use the timing characteristics of the indicated CPU type when scheduling instructions.
           This does not change the targeted processor type.  The CPU type must be one of
           mn10300, am33, am33-2 or am34.

       -mreturn-pointer-on-d0
           When generating a function that returns a pointer, return the pointer in both "a0" and
           "d0".  Otherwise, the pointer is returned only in "a0", and attempts to call such
           functions without a prototype result in errors.  Note that this option is on by
           default; use -mno-return-pointer-on-d0 to disable it.

       -mno-crt0
           Do not link in the C run-time initialization object file.

       -mrelax
           Indicate to the linker that it should perform a relaxation optimization pass to
           shorten branches, calls and absolute memory addresses.  This option only has an effect
           when used on the command line for the final link step.

           This option makes symbolic debugging impossible.

       -mliw
           Allow the compiler to generate Long Instruction Word instructions if the target is the
           AM33 or later.  This is the default.  This option defines the preprocessor macro
           "__LIW__".

       -mnoliw
           Do not allow the compiler to generate Long Instruction Word instructions.  This option
           defines the preprocessor macro "__NO_LIW__".

       -msetlb
           Allow the compiler to generate the SETLB and Lcc instructions if the target is the
           AM33 or later.  This is the default.  This option defines the preprocessor macro
           "__SETLB__".

       -mnosetlb
           Do not allow the compiler to generate SETLB or Lcc instructions.  This option defines
           the preprocessor macro "__NO_SETLB__".

       Moxie Options

       -meb
           Generate big-endian code.  This is the default for moxie-*-* configurations.

       -mel
           Generate little-endian code.

       -mmul.x
           Generate mul.x and umul.x instructions.  This is the default for moxiebox-*-*
           configurations.

       -mno-crt0
           Do not link in the C run-time initialization object file.

       MSP430 Options

       These options are defined for the MSP430:

       -masm-hex
           Force assembly output to always use hex constants.  Normally such constants are signed
           decimals, but this option is available for testsuite and/or aesthetic purposes.

       -mmcu=
           Select the MCU to target.  This is used to create a C preprocessor symbol based upon
           the MCU name, converted to upper case and pre- and post-fixed with __.  This in turn
           is used by the msp430.h header file to select an MCU-specific supplementary header
           file.

           The option also sets the ISA to use.  If the MCU name is one that is known to only
           support the 430 ISA then that is selected, otherwise the 430X ISA is selected.  A
           generic MCU name of msp430 can also be used to select the 430 ISA.  Similarly the
           generic msp430x MCU name selects the 430X ISA.

           In addition an MCU-specific linker script is added to the linker command line.  The
           script's name is the name of the MCU with .ld appended.  Thus specifying -mmcu=xxx on
           the gcc command line defines the C preprocessor symbol "__XXX__" and cause the linker
           to search for a script called xxx.ld.

           This option is also passed on to the assembler.

       -mwarn-mcu
       -mno-warn-mcu
           This option enables or disables warnings about conflicts between the MCU name
           specified by the -mmcu option and the ISA set by the -mcpu option and/or the hardware
           multiply support set by the -mhwmult option.  It also toggles warnings about
           unrecognized MCU names.  This option is on by default.

       -mcpu=
           Specifies the ISA to use.  Accepted values are msp430, msp430x and msp430xv2.  This
           option is deprecated.  The -mmcu= option should be used to select the ISA.

       -msim
           Link to the simulator runtime libraries and linker script.  Overrides any scripts that
           would be selected by the -mmcu= option.

       -mlarge
           Use large-model addressing (20-bit pointers, 32-bit "size_t").

       -msmall
           Use small-model addressing (16-bit pointers, 16-bit "size_t").

       -mrelax
           This option is passed to the assembler and linker, and allows the linker to perform
           certain optimizations that cannot be done until the final link.

       mhwmult=
           Describes the type of hardware multiply supported by the target.  Accepted values are
           none for no hardware multiply, 16bit for the original 16-bit-only multiply supported
           by early MCUs.  32bit for the 16/32-bit multiply supported by later MCUs and f5series
           for the 16/32-bit multiply supported by F5-series MCUs.  A value of auto can also be
           given.  This tells GCC to deduce the hardware multiply support based upon the MCU name
           provided by the -mmcu option.  If no -mmcu option is specified or if the MCU name is
           not recognized then no hardware multiply support is assumed.  "auto" is the default
           setting.

           Hardware multiplies are normally performed by calling a library routine.  This saves
           space in the generated code.  When compiling at -O3 or higher however the hardware
           multiplier is invoked inline.  This makes for bigger, but faster code.

           The hardware multiply routines disable interrupts whilst running and restore the
           previous interrupt state when they finish.  This makes them safe to use inside
           interrupt handlers as well as in normal code.

       -minrt
           Enable the use of a minimum runtime environment - no static initializers or
           constructors.  This is intended for memory-constrained devices.  The compiler includes
           special symbols in some objects that tell the linker and runtime which code fragments
           are required.

       -mcode-region=
       -mdata-region=
           These options tell the compiler where to place functions and data that do not have one
           of the "lower", "upper", "either" or "section" attributes.  Possible values are
           "lower", "upper", "either" or "any".  The first three behave like the corresponding
           attribute.  The fourth possible value - "any" - is the default.  It leaves placement
           entirely up to the linker script and how it assigns the standard sections (".text",
           ".data", etc) to the memory regions.

       -msilicon-errata=
           This option passes on a request to assembler to enable the fixes for the named silicon
           errata.

       -msilicon-errata-warn=
           This option passes on a request to the assembler to enable warning messages when a
           silicon errata might need to be applied.

       NDS32 Options

       These options are defined for NDS32 implementations:

       -mbig-endian
           Generate code in big-endian mode.

       -mlittle-endian
           Generate code in little-endian mode.

       -mreduced-regs
           Use reduced-set registers for register allocation.

       -mfull-regs
           Use full-set registers for register allocation.

       -mcmov
           Generate conditional move instructions.

       -mno-cmov
           Do not generate conditional move instructions.

       -mext-perf
           Generate performance extension instructions.

       -mno-ext-perf
           Do not generate performance extension instructions.

       -mext-perf2
           Generate performance extension 2 instructions.

       -mno-ext-perf2
           Do not generate performance extension 2 instructions.

       -mext-string
           Generate string extension instructions.

       -mno-ext-string
           Do not generate string extension instructions.

       -mv3push
           Generate v3 push25/pop25 instructions.

       -mno-v3push
           Do not generate v3 push25/pop25 instructions.

       -m16-bit
           Generate 16-bit instructions.

       -mno-16-bit
           Do not generate 16-bit instructions.

       -misr-vector-size=num
           Specify the size of each interrupt vector, which must be 4 or 16.

       -mcache-block-size=num
           Specify the size of each cache block, which must be a power of 2 between 4 and 512.

       -march=arch
           Specify the name of the target architecture.

       -mcmodel=code-model
           Set the code model to one of

           small
               All the data and read-only data segments must be within 512KB addressing space.
               The text segment must be within 16MB addressing space.

           medium
               The data segment must be within 512KB while the read-only data segment can be
               within 4GB addressing space.  The text segment should be still within 16MB
               addressing space.

           large
               All the text and data segments can be within 4GB addressing space.

       -mctor-dtor
           Enable constructor/destructor feature.

       -mrelax
           Guide linker to relax instructions.

       Nios II Options

       These are the options defined for the Altera Nios II processor.

       -G num
           Put global and static objects less than or equal to num bytes into the small data or
           BSS sections instead of the normal data or BSS sections.  The default value of num is
           8.

       -mgpopt=option
       -mgpopt
       -mno-gpopt
           Generate (do not generate) GP-relative accesses.  The following option names are
           recognized:

           none
               Do not generate GP-relative accesses.

           local
               Generate GP-relative accesses for small data objects that are not external, weak,
               or uninitialized common symbols.  Also use GP-relative addressing for objects that
               have been explicitly placed in a small data section via a "section" attribute.

           global
               As for local, but also generate GP-relative accesses for small data objects that
               are external, weak, or common.  If you use this option, you must ensure that all
               parts of your program (including libraries) are compiled with the same -G setting.

           data
               Generate GP-relative accesses for all data objects in the program.  If you use
               this option, the entire data and BSS segments of your program must fit in 64K of
               memory and you must use an appropriate linker script to allocate them within the
               addressable range of the global pointer.

           all Generate GP-relative addresses for function pointers as well as data pointers.  If
               you use this option, the entire text, data, and BSS segments of your program must
               fit in 64K of memory and you must use an appropriate linker script to allocate
               them within the addressable range of the global pointer.

           -mgpopt is equivalent to -mgpopt=local, and -mno-gpopt is equivalent to -mgpopt=none.

           The default is -mgpopt except when -fpic or -fPIC is specified to generate position-
           independent code.  Note that the Nios II ABI does not permit GP-relative accesses from
           shared libraries.

           You may need to specify -mno-gpopt explicitly when building programs that include
           large amounts of small data, including large GOT data sections.  In this case, the
           16-bit offset for GP-relative addressing may not be large enough to allow access to
           the entire small data section.

       -mgprel-sec=regexp
           This option specifies additional section names that can be accessed via GP-relative
           addressing.  It is most useful in conjunction with "section" attributes on variable
           declarations and a custom linker script.  The regexp is a POSIX Extended Regular
           Expression.

           This option does not affect the behavior of the -G option, and the specified sections
           are in addition to the standard ".sdata" and ".sbss" small-data sections that are
           recognized by -mgpopt.

       -mr0rel-sec=regexp
           This option specifies names of sections that can be accessed via a 16-bit offset from
           "r0"; that is, in the low 32K or high 32K of the 32-bit address space.  It is most
           useful in conjunction with "section" attributes on variable declarations and a custom
           linker script.  The regexp is a POSIX Extended Regular Expression.

           In contrast to the use of GP-relative addressing for small data, zero-based addressing
           is never generated by default and there are no conventional section names used in
           standard linker scripts for sections in the low or high areas of memory.

       -mel
       -meb
           Generate little-endian (default) or big-endian (experimental) code, respectively.

       -march=arch
           This specifies the name of the target Nios II architecture.  GCC uses this name to
           determine what kind of instructions it can emit when generating assembly code.
           Permissible names are: r1, r2.

           The preprocessor macro "__nios2_arch__" is available to programs, with value 1 or 2,
           indicating the targeted ISA level.

       -mbypass-cache
       -mno-bypass-cache
           Force all load and store instructions to always bypass cache by using I/O variants of
           the instructions. The default is not to bypass the cache.

       -mno-cache-volatile
       -mcache-volatile
           Volatile memory access bypass the cache using the I/O variants of the load and store
           instructions. The default is not to bypass the cache.

       -mno-fast-sw-div
       -mfast-sw-div
           Do not use table-based fast divide for small numbers. The default is to use the fast
           divide at -O3 and above.

       -mno-hw-mul
       -mhw-mul
       -mno-hw-mulx
       -mhw-mulx
       -mno-hw-div
       -mhw-div
           Enable or disable emitting "mul", "mulx" and "div" family of instructions by the
           compiler. The default is to emit "mul" and not emit "div" and "mulx".

       -mbmx
       -mno-bmx
       -mcdx
       -mno-cdx
           Enable or disable generation of Nios II R2 BMX (bit manipulation) and CDX (code
           density) instructions.  Enabling these instructions also requires -march=r2.  Since
           these instructions are optional extensions to the R2 architecture, the default is not
           to emit them.

       -mcustom-insn=N
       -mno-custom-insn
           Each -mcustom-insn=N option enables use of a custom instruction with encoding N when
           generating code that uses insn.  For example, -mcustom-fadds=253 generates custom
           instruction 253 for single-precision floating-point add operations instead of the
           default behavior of using a library call.

           The following values of insn are supported.  Except as otherwise noted, floating-point
           operations are expected to be implemented with normal IEEE 754 semantics and
           correspond directly to the C operators or the equivalent GCC built-in functions.

           Single-precision floating point:

           fadds, fsubs, fdivs, fmuls
               Binary arithmetic operations.

           fnegs
               Unary negation.

           fabss
               Unary absolute value.

           fcmpeqs, fcmpges, fcmpgts, fcmples, fcmplts, fcmpnes
               Comparison operations.

           fmins, fmaxs
               Floating-point minimum and maximum.  These instructions are only generated if
               -ffinite-math-only is specified.

           fsqrts
               Unary square root operation.

           fcoss, fsins, ftans, fatans, fexps, flogs
               Floating-point trigonometric and exponential functions.  These instructions are
               only generated if -funsafe-math-optimizations is also specified.

           Double-precision floating point:

           faddd, fsubd, fdivd, fmuld
               Binary arithmetic operations.

           fnegd
               Unary negation.

           fabsd
               Unary absolute value.

           fcmpeqd, fcmpged, fcmpgtd, fcmpled, fcmpltd, fcmpned
               Comparison operations.

           fmind, fmaxd
               Double-precision minimum and maximum.  These instructions are only generated if
               -ffinite-math-only is specified.

           fsqrtd
               Unary square root operation.

           fcosd, fsind, ftand, fatand, fexpd, flogd
               Double-precision trigonometric and exponential functions.  These instructions are
               only generated if -funsafe-math-optimizations is also specified.

           Conversions:

           fextsd
               Conversion from single precision to double precision.

           ftruncds
               Conversion from double precision to single precision.

           fixsi, fixsu, fixdi, fixdu
               Conversion from floating point to signed or unsigned integer types, with
               truncation towards zero.

           round
               Conversion from single-precision floating point to signed integer, rounding to the
               nearest integer and ties away from zero.  This corresponds to the
               "__builtin_lroundf" function when -fno-math-errno is used.

           floatis, floatus, floatid, floatud
               Conversion from signed or unsigned integer types to floating-point types.

           In addition, all of the following transfer instructions for internal registers X and Y
           must be provided to use any of the double-precision floating-point instructions.
           Custom instructions taking two double-precision source operands expect the first
           operand in the 64-bit register X.  The other operand (or only operand of a unary
           operation) is given to the custom arithmetic instruction with the least significant
           half in source register src1 and the most significant half in src2.  A custom
           instruction that returns a double-precision result returns the most significant 32
           bits in the destination register and the other half in 32-bit register Y.  GCC
           automatically generates the necessary code sequences to write register X and/or read
           register Y when double-precision floating-point instructions are used.

           fwrx
               Write src1 into the least significant half of X and src2 into the most significant
               half of X.

           fwry
               Write src1 into Y.

           frdxhi, frdxlo
               Read the most or least (respectively) significant half of X and store it in dest.

           frdy
               Read the value of Y and store it into dest.

           Note that you can gain more local control over generation of Nios II custom
           instructions by using the "target("custom-insn=N")" and "target("no-custom-insn")"
           function attributes or pragmas.

       -mcustom-fpu-cfg=name
           This option enables a predefined, named set of custom instruction encodings (see
           -mcustom-insn above).  Currently, the following sets are defined:

           -mcustom-fpu-cfg=60-1 is equivalent to: -mcustom-fmuls=252 -mcustom-fadds=253
           -mcustom-fsubs=254 -fsingle-precision-constant

           -mcustom-fpu-cfg=60-2 is equivalent to: -mcustom-fmuls=252 -mcustom-fadds=253
           -mcustom-fsubs=254 -mcustom-fdivs=255 -fsingle-precision-constant

           -mcustom-fpu-cfg=72-3 is equivalent to: -mcustom-floatus=243 -mcustom-fixsi=244
           -mcustom-floatis=245 -mcustom-fcmpgts=246 -mcustom-fcmples=249 -mcustom-fcmpeqs=250
           -mcustom-fcmpnes=251 -mcustom-fmuls=252 -mcustom-fadds=253 -mcustom-fsubs=254
           -mcustom-fdivs=255 -fsingle-precision-constant

           Custom instruction assignments given by individual -mcustom-insn= options override
           those given by -mcustom-fpu-cfg=, regardless of the order of the options on the
           command line.

           Note that you can gain more local control over selection of a FPU configuration by
           using the "target("custom-fpu-cfg=name")" function attribute or pragma.

       These additional -m options are available for the Altera Nios II ELF (bare-metal) target:

       -mhal
           Link with HAL BSP.  This suppresses linking with the GCC-provided C runtime startup
           and termination code, and is typically used in conjunction with -msys-crt0= to specify
           the location of the alternate startup code provided by the HAL BSP.

       -msmallc
           Link with a limited version of the C library, -lsmallc, rather than Newlib.

       -msys-crt0=startfile
           startfile is the file name of the startfile (crt0) to use when linking.  This option
           is only useful in conjunction with -mhal.

       -msys-lib=systemlib
           systemlib is the library name of the library that provides low-level system calls
           required by the C library, e.g. "read" and "write".  This option is typically used to
           link with a library provided by a HAL BSP.

       Nvidia PTX Options

       These options are defined for Nvidia PTX:

       -m32
       -m64
           Generate code for 32-bit or 64-bit ABI.

       -mmainkernel
           Link in code for a __main kernel.  This is for stand-alone instead of offloading
           execution.

       -moptimize
           Apply partitioned execution optimizations.  This is the default when any level of
           optimization is selected.

       -msoft-stack
           Generate code that does not use ".local" memory directly for stack storage. Instead, a
           per-warp stack pointer is maintained explicitly. This enables variable-length stack
           allocation (with variable-length arrays or "alloca"), and when global memory is used
           for underlying storage, makes it possible to access automatic variables from other
           threads, or with atomic instructions. This code generation variant is used for OpenMP
           offloading, but the option is exposed on its own for the purpose of testing the
           compiler; to generate code suitable for linking into programs using OpenMP offloading,
           use option -mgomp.

       -muniform-simt
           Switch to code generation variant that allows to execute all threads in each warp,
           while maintaining memory state and side effects as if only one thread in each warp was
           active outside of OpenMP SIMD regions.  All atomic operations and calls to runtime
           (malloc, free, vprintf) are conditionally executed (iff current lane index equals the
           master lane index), and the register being assigned is copied via a shuffle
           instruction from the master lane.  Outside of SIMD regions lane 0 is the master;
           inside, each thread sees itself as the master.  Shared memory array "int
           __nvptx_uni[]" stores all-zeros or all-ones bitmasks for each warp, indicating current
           mode (0 outside of SIMD regions).  Each thread can bitwise-and the bitmask at position
           "tid.y" with current lane index to compute the master lane index.

       -mgomp
           Generate code for use in OpenMP offloading: enables -msoft-stack and -muniform-simt
           options, and selects corresponding multilib variant.

       PDP-11 Options

       These options are defined for the PDP-11:

       -mfpu
           Use hardware FPP floating point.  This is the default.  (FIS floating point on the
           PDP-11/40 is not supported.)

       -msoft-float
           Do not use hardware floating point.

       -mac0
           Return floating-point results in ac0 (fr0 in Unix assembler syntax).

       -mno-ac0
           Return floating-point results in memory.  This is the default.

       -m40
           Generate code for a PDP-11/40.

       -m45
           Generate code for a PDP-11/45.  This is the default.

       -m10
           Generate code for a PDP-11/10.

       -mbcopy-builtin
           Use inline "movmemhi" patterns for copying memory.  This is the default.

       -mbcopy
           Do not use inline "movmemhi" patterns for copying memory.

       -mint16
       -mno-int32
           Use 16-bit "int".  This is the default.

       -mint32
       -mno-int16
           Use 32-bit "int".

       -mfloat64
       -mno-float32
           Use 64-bit "float".  This is the default.

       -mfloat32
       -mno-float64
           Use 32-bit "float".

       -mabshi
           Use "abshi2" pattern.  This is the default.

       -mno-abshi
           Do not use "abshi2" pattern.

       -mbranch-expensive
           Pretend that branches are expensive.  This is for experimenting with code generation
           only.

       -mbranch-cheap
           Do not pretend that branches are expensive.  This is the default.

       -munix-asm
           Use Unix assembler syntax.  This is the default when configured for pdp11-*-bsd.

       -mdec-asm
           Use DEC assembler syntax.  This is the default when configured for any PDP-11 target
           other than pdp11-*-bsd.

       picoChip Options

       These -m options are defined for picoChip implementations:

       -mae=ae_type
           Set the instruction set, register set, and instruction scheduling parameters for array
           element type ae_type.  Supported values for ae_type are ANY, MUL, and MAC.

           -mae=ANY selects a completely generic AE type.  Code generated with this option runs
           on any of the other AE types.  The code is not as efficient as it would be if compiled
           for a specific AE type, and some types of operation (e.g., multiplication) do not work
           properly on all types of AE.

           -mae=MUL selects a MUL AE type.  This is the most useful AE type for compiled code,
           and is the default.

           -mae=MAC selects a DSP-style MAC AE.  Code compiled with this option may suffer from
           poor performance of byte (char) manipulation, since the DSP AE does not provide
           hardware support for byte load/stores.

       -msymbol-as-address
           Enable the compiler to directly use a symbol name as an address in a load/store
           instruction, without first loading it into a register.  Typically, the use of this
           option generates larger programs, which run faster than when the option isn't used.
           However, the results vary from program to program, so it is left as a user option,
           rather than being permanently enabled.

       -mno-inefficient-warnings
           Disables warnings about the generation of inefficient code.  These warnings can be
           generated, for example, when compiling code that performs byte-level memory operations
           on the MAC AE type.  The MAC AE has no hardware support for byte-level memory
           operations, so all byte load/stores must be synthesized from word load/store
           operations.  This is inefficient and a warning is generated to indicate that you
           should rewrite the code to avoid byte operations, or to target an AE type that has the
           necessary hardware support.  This option disables these warnings.

       PowerPC Options

       These are listed under

       PowerPC SPE Options

       These -m options are defined for PowerPC SPE:

       -mmfcrf
       -mno-mfcrf
       -mpopcntb
       -mno-popcntb
           You use these options to specify which instructions are available on the processor you
           are using.  The default value of these options is determined when configuring GCC.
           Specifying the -mcpu=cpu_type overrides the specification of these options.  We
           recommend you use the -mcpu=cpu_type option rather than the options listed above.

           The -mmfcrf option allows GCC to generate the move from condition register field
           instruction implemented on the POWER4 processor and other processors that support the
           PowerPC V2.01 architecture.  The -mpopcntb option allows GCC to generate the popcount
           and double-precision FP reciprocal estimate instruction implemented on the POWER5
           processor and other processors that support the PowerPC V2.02 architecture.

       -mcpu=cpu_type
           Set architecture type, register usage, and instruction scheduling parameters for
           machine type cpu_type.  Supported values for cpu_type are 8540, 8548, and native.

           -mcpu=powerpc specifies pure 32-bit PowerPC (either endian), with an appropriate,
           generic processor model assumed for scheduling purposes.

           Specifying native as cpu type detects and selects the architecture option that
           corresponds to the host processor of the system performing the compilation.
           -mcpu=native has no effect if GCC does not recognize the processor.

           The other options specify a specific processor.  Code generated under those options
           runs best on that processor, and may not run at all on others.

           The -mcpu options automatically enable or disable the following options:

           -mhard-float  -mmfcrf  -mmultiple -mpopcntb -mpopcntd -msingle-float -mdouble-float
           -mfloat128

           The particular options set for any particular CPU varies between compiler versions,
           depending on what setting seems to produce optimal code for that CPU; it doesn't
           necessarily reflect the actual hardware's capabilities.  If you wish to set an
           individual option to a particular value, you may specify it after the -mcpu option,
           like -mcpu=8548.

       -mtune=cpu_type
           Set the instruction scheduling parameters for machine type cpu_type, but do not set
           the architecture type or register usage, as -mcpu=cpu_type does.  The same values for
           cpu_type are used for -mtune as for -mcpu.  If both are specified, the code generated
           uses the architecture and registers set by -mcpu, but the scheduling parameters set by
           -mtune.

       -msecure-plt
           Generate code that allows ld and ld.so to build executables and shared libraries with
           non-executable ".plt" and ".got" sections.  This is a PowerPC 32-bit SYSV ABI option.

       -mbss-plt
           Generate code that uses a BSS ".plt" section that ld.so fills in, and requires ".plt"
           and ".got" sections that are both writable and executable.  This is a PowerPC 32-bit
           SYSV ABI option.

       -misel
       -mno-isel
           This switch enables or disables the generation of ISEL instructions.

       -misel=yes/no
           This switch has been deprecated.  Use -misel and -mno-isel instead.

       -mspe
       -mno-spe
           This switch enables or disables the generation of SPE simd instructions.

       -mspe=yes/no
           This option has been deprecated.  Use -mspe and -mno-spe instead.

       -mfloat128
       -mno-float128
           Enable/disable the __float128 keyword for IEEE 128-bit floating point and use either
           software emulation for IEEE 128-bit floating point or hardware instructions.

       -mfloat-gprs=yes/single/double/no
       -mfloat-gprs
           This switch enables or disables the generation of floating-point operations on the
           general-purpose registers for architectures that support it.

           The argument yes or single enables the use of single-precision floating-point
           operations.

           The argument double enables the use of single and double-precision floating-point
           operations.

           The argument no disables floating-point operations on the general-purpose registers.

           This option is currently only available on the MPC854x.

       -mfull-toc
       -mno-fp-in-toc
       -mno-sum-in-toc
       -mminimal-toc
           Modify generation of the TOC (Table Of Contents), which is created for every
           executable file.  The -mfull-toc option is selected by default.  In that case, GCC
           allocates at least one TOC entry for each unique non-automatic variable reference in
           your program.  GCC also places floating-point constants in the TOC.  However, only
           16,384 entries are available in the TOC.

           If you receive a linker error message that saying you have overflowed the available
           TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and
           -mno-sum-in-toc options.  -mno-fp-in-toc prevents GCC from putting floating-point
           constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the
           sum of an address and a constant at run time instead of putting that sum into the TOC.
           You may specify one or both of these options.  Each causes GCC to produce very
           slightly slower and larger code at the expense of conserving TOC space.

           If you still run out of space in the TOC even when you specify both of these options,
           specify -mminimal-toc instead.  This option causes GCC to make only one TOC entry for
           every file.  When you specify this option, GCC produces code that is slower and larger
           but which uses extremely little TOC space.  You may wish to use this option only on
           files that contain less frequently-executed code.

       -maix32
           Disables the 64-bit ABI.  GCC defaults to -maix32.

       -mxl-compat
       -mno-xl-compat
           Produce code that conforms more closely to IBM XL compiler semantics when using AIX-
           compatible ABI.  Pass floating-point arguments to prototyped functions beyond the
           register save area (RSA) on the stack in addition to argument FPRs.  Do not assume
           that most significant double in 128-bit long double value is properly rounded when
           comparing values and converting to double.  Use XL symbol names for long double
           support routines.

           The AIX calling convention was extended but not initially documented to handle an
           obscure K&R C case of calling a function that takes the address of its arguments with
           fewer arguments than declared.  IBM XL compilers access floating-point arguments that
           do not fit in the RSA from the stack when a subroutine is compiled without
           optimization.  Because always storing floating-point arguments on the stack is
           inefficient and rarely needed, this option is not enabled by default and only is
           necessary when calling subroutines compiled by IBM XL compilers without optimization.

       -malign-natural
       -malign-power
           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural
           overrides the ABI-defined alignment of larger types, such as floating-point doubles,
           on their natural size-based boundary.  The option -malign-power instructs GCC to
           follow the ABI-specified alignment rules.  GCC defaults to the standard alignment
           defined in the ABI.

           On 64-bit Darwin, natural alignment is the default, and -malign-power is not
           supported.

       -msoft-float
       -mhard-float
           Generate code that does not use (uses) the floating-point register set.  Software
           floating-point emulation is provided if you use the -msoft-float option, and pass the
           option to GCC when linking.

       -msingle-float
       -mdouble-float
           Generate code for single- or double-precision floating-point operations.
           -mdouble-float implies -msingle-float.

       -mmultiple
       -mno-multiple
           Generate code that uses (does not use) the load multiple word instructions and the
           store multiple word instructions.  These instructions are generated by default on
           POWER systems, and not generated on PowerPC systems.  Do not use -mmultiple on little-
           endian PowerPC systems, since those instructions do not work when the processor is in
           little-endian mode.  The exceptions are PPC740 and PPC750 which permit these
           instructions in little-endian mode.

       -mupdate
       -mno-update
           Generate code that uses (does not use) the load or store instructions that update the
           base register to the address of the calculated memory location.  These instructions
           are generated by default.  If you use -mno-update, there is a small window between the
           time that the stack pointer is updated and the address of the previous frame is
           stored, which means code that walks the stack frame across interrupts or signals may
           get corrupted data.

       -mavoid-indexed-addresses
       -mno-avoid-indexed-addresses
           Generate code that tries to avoid (not avoid) the use of indexed load or store
           instructions. These instructions can incur a performance penalty on Power6 processors
           in certain situations, such as when stepping through large arrays that cross a 16M
           boundary.  This option is enabled by default when targeting Power6 and disabled
           otherwise.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use) the floating-point multiply and accumulate
           instructions.  These instructions are generated by default if hardware floating point
           is used.  The machine-dependent -mfused-madd option is now mapped to the machine-
           independent -ffp-contract=fast option, and -mno-fused-madd is mapped to
           -ffp-contract=off.

       -mno-strict-align
       -mstrict-align
           On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory
           references are handled by the system.

       -mrelocatable
       -mno-relocatable
           Generate code that allows (does not allow) a static executable to be relocated to a
           different address at run time.  A simple embedded PowerPC system loader should
           relocate the entire contents of ".got2" and 4-byte locations listed in the ".fixup"
           section, a table of 32-bit addresses generated by this option.  For this to work, all
           objects linked together must be compiled with -mrelocatable or -mrelocatable-lib.
           -mrelocatable code aligns the stack to an 8-byte boundary.

       -mrelocatable-lib
       -mno-relocatable-lib
           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section to allow static
           executables to be relocated at run time, but -mrelocatable-lib does not use the
           smaller stack alignment of -mrelocatable.  Objects compiled with -mrelocatable-lib may
           be linked with objects compiled with any combination of the -mrelocatable options.

       -mno-toc
       -mtoc
           On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains
           a pointer to a global area pointing to the addresses used in the program.

       -mlittle
       -mlittle-endian
           On System V.4 and embedded PowerPC systems compile code for the processor in little-
           endian mode.  The -mlittle-endian option is the same as -mlittle.

       -mbig
       -mbig-endian
           On System V.4 and embedded PowerPC systems compile code for the processor in big-
           endian mode.  The -mbig-endian option is the same as -mbig.

       -mdynamic-no-pic
           On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that
           its external references are relocatable.  The resulting code is suitable for
           applications, but not shared libraries.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather than loading it in the
           prologue for each function.  The runtime system is responsible for initializing this
           register with an appropriate value before execution begins.

       -mprioritize-restricted-insns=priority
           This option controls the priority that is assigned to dispatch-slot restricted
           instructions during the second scheduling pass.  The argument priority takes the value
           0, 1, or 2 to assign no, highest, or second-highest (respectively) priority to
           dispatch-slot restricted instructions.

       -msched-costly-dep=dependence_type
           This option controls which dependences are considered costly by the target during
           instruction scheduling.  The argument dependence_type takes one of the following
           values:

           no  No dependence is costly.

           all All dependences are costly.

           true_store_to_load
               A true dependence from store to load is costly.

           store_to_load
               Any dependence from store to load is costly.

           number
               Any dependence for which the latency is greater than or equal to number is costly.

       -minsert-sched-nops=scheme
           This option controls which NOP insertion scheme is used during the second scheduling
           pass.  The argument scheme takes one of the following values:

           no  Don't insert NOPs.

           pad Pad with NOPs any dispatch group that has vacant issue slots, according to the
               scheduler's grouping.

           regroup_exact
               Insert NOPs to force costly dependent insns into separate groups.  Insert exactly
               as many NOPs as needed to force an insn to a new group, according to the estimated
               processor grouping.

           number
               Insert NOPs to force costly dependent insns into separate groups.  Insert number
               NOPs to force an insn to a new group.

       -mcall-sysv
           On System V.4 and embedded PowerPC systems compile code using calling conventions that
           adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC
           processor supplement.  This is the default unless you configured GCC using
           powerpc-*-eabiaix.

       -mcall-sysv-eabi
       -mcall-eabi
           Specify both -mcall-sysv and -meabi options.

       -mcall-sysv-noeabi
           Specify both -mcall-sysv and -mno-eabi options.

       -mcall-aixdesc
           On System V.4 and embedded PowerPC systems compile code for the AIX operating system.

       -mcall-linux
           On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU
           system.

       -mcall-freebsd
           On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating
           system.

       -mcall-netbsd
           On System V.4 and embedded PowerPC systems compile code for the NetBSD operating
           system.

       -mcall-openbsd
           On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating
           system.

       -maix-struct-return
           Return all structures in memory (as specified by the AIX ABI).

       -msvr4-struct-return
           Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI).

       -mabi=abi-type
           Extend the current ABI with a particular extension, or remove such extension.  Valid
           values are altivec, no-altivec, spe, no-spe, ibmlongdouble, ieeelongdouble, elfv1,
           elfv2.

       -mabi=spe
           Extend the current ABI with SPE ABI extensions.  This does not change the default ABI,
           instead it adds the SPE ABI extensions to the current ABI.

       -mabi=no-spe
           Disable Book-E SPE ABI extensions for the current ABI.

       -mabi=ibmlongdouble
           Change the current ABI to use IBM extended-precision long double.  This is not likely
           to work if your system defaults to using IEEE extended-precision long double.  If you
           change the long double type from IEEE extended-precision, the compiler will issue a
           warning unless you use the -Wno-psabi option.  Requires -mlong-double-128 to be
           enabled.

       -mabi=ieeelongdouble
           Change the current ABI to use IEEE extended-precision long double.  This is not likely
           to work if your system defaults to using IBM extended-precision long double.  If you
           change the long double type from IBM extended-precision, the compiler will issue a
           warning unless you use the -Wno-psabi option.  Requires -mlong-double-128 to be
           enabled.

       -mabi=elfv1
           Change the current ABI to use the ELFv1 ABI.  This is the default ABI for big-endian
           PowerPC 64-bit Linux.  Overriding the default ABI requires special system support and
           is likely to fail in spectacular ways.

       -mabi=elfv2
           Change the current ABI to use the ELFv2 ABI.  This is the default ABI for little-
           endian PowerPC 64-bit Linux.  Overriding the default ABI requires special system
           support and is likely to fail in spectacular ways.

       -mgnu-attribute
       -mno-gnu-attribute
           Emit .gnu_attribute assembly directives to set tag/value pairs in a .gnu.attributes
           section that specify ABI variations in function parameters or return values.

       -mprototype
       -mno-prototype
           On System V.4 and embedded PowerPC systems assume that all calls to variable argument
           functions are properly prototyped.  Otherwise, the compiler must insert an instruction
           before every non-prototyped call to set or clear bit 6 of the condition code register
           ("CR") to indicate whether floating-point values are passed in the floating-point
           registers in case the function takes variable arguments.  With -mprototype, only calls
           to prototyped variable argument functions set or clear the bit.

       -msim
           On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and
           that the standard C libraries are libsim.a and libc.a.  This is the default for
           powerpc-*-eabisim configurations.

       -mmvme
           On embedded PowerPC systems, assume that the startup module is called crt0.o and the
           standard C libraries are libmvme.a and libc.a.

       -mads
           On embedded PowerPC systems, assume that the startup module is called crt0.o and the
           standard C libraries are libads.a and libc.a.

       -myellowknife
           On embedded PowerPC systems, assume that the startup module is called crt0.o and the
           standard C libraries are libyk.a and libc.a.

       -mvxworks
           On System V.4 and embedded PowerPC systems, specify that you are compiling for a
           VxWorks system.

       -memb
           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags header to indicate
           that eabi extended relocations are used.

       -meabi
       -mno-eabi
           On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded
           Applications Binary Interface (EABI), which is a set of modifications to the System
           V.4 specifications.  Selecting -meabi means that the stack is aligned to an 8-byte
           boundary, a function "__eabi" is called from "main" to set up the EABI environment,
           and the -msdata option can use both "r2" and "r13" to point to two separate small data
           areas.  Selecting -mno-eabi means that the stack is aligned to a 16-byte boundary, no
           EABI initialization function is called from "main", and the -msdata option only uses
           "r13" to point to a single small data area.  The -meabi option is on by default if you
           configured GCC using one of the powerpc*-*-eabi* options.

       -msdata=eabi
           On System V.4 and embedded PowerPC systems, put small initialized "const" global and
           static data in the ".sdata2" section, which is pointed to by register "r2".  Put small
           initialized non-"const" global and static data in the ".sdata" section, which is
           pointed to by register "r13".  Put small uninitialized global and static data in the
           ".sbss" section, which is adjacent to the ".sdata" section.  The -msdata=eabi option
           is incompatible with the -mrelocatable option.  The -msdata=eabi option also sets the
           -memb option.

       -msdata=sysv
           On System V.4 and embedded PowerPC systems, put small global and static data in the
           ".sdata" section, which is pointed to by register "r13".  Put small uninitialized
           global and static data in the ".sbss" section, which is adjacent to the ".sdata"
           section.  The -msdata=sysv option is incompatible with the -mrelocatable option.

       -msdata=default
       -msdata
           On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same
           as -msdata=eabi, otherwise compile code the same as -msdata=sysv.

       -msdata=data
           On System V.4 and embedded PowerPC systems, put small global data in the ".sdata"
           section.  Put small uninitialized global data in the ".sbss" section.  Do not use
           register "r13" to address small data however.  This is the default behavior unless
           other -msdata options are used.

       -msdata=none
       -mno-sdata
           On embedded PowerPC systems, put all initialized global and static data in the ".data"
           section, and all uninitialized data in the ".bss" section.

       -mblock-move-inline-limit=num
           Inline all block moves (such as calls to "memcpy" or structure copies) less than or
           equal to num bytes.  The minimum value for num is 32 bytes on 32-bit targets and 64
           bytes on 64-bit targets.  The default value is target-specific.

       -G num
           On embedded PowerPC systems, put global and static items less than or equal to num
           bytes into the small data or BSS sections instead of the normal data or BSS section.
           By default, num is 8.  The -G num switch is also passed to the linker.  All modules
           should be compiled with the same -G num value.

       -mregnames
       -mno-regnames
           On System V.4 and embedded PowerPC systems do (do not) emit register names in the
           assembly language output using symbolic forms.

       -mlongcall
       -mno-longcall
           By default assume that all calls are far away so that a longer and more expensive
           calling sequence is required.  This is required for calls farther than 32 megabytes
           (33,554,432 bytes) from the current location.  A short call is generated if the
           compiler knows the call cannot be that far away.  This setting can be overridden by
           the "shortcall" function attribute, or by "#pragma longcall(0)".

           Some linkers are capable of detecting out-of-range calls and generating glue code on
           the fly.  On these systems, long calls are unnecessary and generate slower code.  As
           of this writing, the AIX linker can do this, as can the GNU linker for PowerPC/64.  It
           is planned to add this feature to the GNU linker for 32-bit PowerPC systems as well.

           In the future, GCC may ignore all longcall specifications when the linker is known to
           generate glue.

       -mtls-markers
       -mno-tls-markers
           Mark (do not mark) calls to "__tls_get_addr" with a relocation specifying the function
           argument.  The relocation allows the linker to reliably associate function call with
           argument setup instructions for TLS optimization, which in turn allows GCC to better
           schedule the sequence.

       -mrecip
       -mno-recip
           This option enables use of the reciprocal estimate and reciprocal square root estimate
           instructions with additional Newton-Raphson steps to increase precision instead of
           doing a divide or square root and divide for floating-point arguments.  You should use
           the -ffast-math option when using -mrecip (or at least -funsafe-math-optimizations,
           -ffinite-math-only, -freciprocal-math and -fno-trapping-math).  Note that while the
           throughput of the sequence is generally higher than the throughput of the non-
           reciprocal instruction, the precision of the sequence can be decreased by up to 2 ulp
           (i.e. the inverse of 1.0 equals 0.99999994) for reciprocal square roots.

       -mrecip=opt
           This option controls which reciprocal estimate instructions may be used.  opt is a
           comma-separated list of options, which may be preceded by a "!" to invert the option:

           all Enable all estimate instructions.

           default
               Enable the default instructions, equivalent to -mrecip.

           none
               Disable all estimate instructions, equivalent to -mno-recip.

           div Enable the reciprocal approximation instructions for both single and double
               precision.

           divf
               Enable the single-precision reciprocal approximation instructions.

           divd
               Enable the double-precision reciprocal approximation instructions.

           rsqrt
               Enable the reciprocal square root approximation instructions for both single and
               double precision.

           rsqrtf
               Enable the single-precision reciprocal square root approximation instructions.

           rsqrtd
               Enable the double-precision reciprocal square root approximation instructions.

           So, for example, -mrecip=all,!rsqrtd enables all of the reciprocal estimate
           instructions, except for the "FRSQRTE", "XSRSQRTEDP", and "XVRSQRTEDP" instructions
           which handle the double-precision reciprocal square root calculations.

       -mrecip-precision
       -mno-recip-precision
           Assume (do not assume) that the reciprocal estimate instructions provide higher-
           precision estimates than is mandated by the PowerPC ABI.  Selecting -mcpu=power6,
           -mcpu=power7 or -mcpu=power8 automatically selects -mrecip-precision.  The double-
           precision square root estimate instructions are not generated by default on low-
           precision machines, since they do not provide an estimate that converges after three
           steps.

       -mpointers-to-nested-functions
       -mno-pointers-to-nested-functions
           Generate (do not generate) code to load up the static chain register ("r11") when
           calling through a pointer on AIX and 64-bit Linux systems where a function pointer
           points to a 3-word descriptor giving the function address, TOC value to be loaded in
           register "r2", and static chain value to be loaded in register "r11".  The
           -mpointers-to-nested-functions is on by default.  You cannot call through pointers to
           nested functions or pointers to functions compiled in other languages that use the
           static chain if you use -mno-pointers-to-nested-functions.

       -msave-toc-indirect
       -mno-save-toc-indirect
           Generate (do not generate) code to save the TOC value in the reserved stack location
           in the function prologue if the function calls through a pointer on AIX and 64-bit
           Linux systems.  If the TOC value is not saved in the prologue, it is saved just before
           the call through the pointer.  The -mno-save-toc-indirect option is the default.

       -mcompat-align-parm
       -mno-compat-align-parm
           Generate (do not generate) code to pass structure parameters with a maximum alignment
           of 64 bits, for compatibility with older versions of GCC.

           Older versions of GCC (prior to 4.9.0) incorrectly did not align a structure parameter
           on a 128-bit boundary when that structure contained a member requiring 128-bit
           alignment.  This is corrected in more recent versions of GCC.  This option may be used
           to generate code that is compatible with functions compiled with older versions of
           GCC.

           The -mno-compat-align-parm option is the default.

       -mstack-protector-guard=guard
       -mstack-protector-guard-reg=reg
       -mstack-protector-guard-offset=offset
       -mstack-protector-guard-symbol=symbol
           Generate stack protection code using canary at guard.  Supported locations are global
           for global canary or tls for per-thread canary in the TLS block (the default with GNU
           libc version 2.4 or later).

           With the latter choice the options -mstack-protector-guard-reg=reg and
           -mstack-protector-guard-offset=offset furthermore specify which register to use as
           base register for reading the canary, and from what offset from that base register.
           The default for those is as specified in the relevant ABI.
           -mstack-protector-guard-symbol=symbol overrides the offset with a symbol reference to
           a canary in the TLS block.

       RISC-V Options

       These command-line options are defined for RISC-V targets:

       -mbranch-cost=n
           Set the cost of branches to roughly n instructions.

       -mplt
       -mno-plt
           When generating PIC code, do or don't allow the use of PLTs. Ignored for non-PIC.  The
           default is -mplt.

       -mabi=ABI-string
           Specify integer and floating-point calling convention.  ABI-string contains two parts:
           the size of integer types and the registers used for floating-point types.  For
           example -march=rv64ifd -mabi=lp64d means that long and pointers are 64-bit (implicitly
           defining int to be 32-bit), and that floating-point values up to 64 bits wide are
           passed in F registers.  Contrast this with -march=rv64ifd -mabi=lp64f, which still
           allows the compiler to generate code that uses the F and D extensions but only allows
           floating-point values up to 32 bits long to be passed in registers; or -march=rv64ifd
           -mabi=lp64, in which no floating-point arguments will be passed in registers.

           The default for this argument is system dependent, users who want a specific calling
           convention should specify one explicitly.  The valid calling conventions are: ilp32,
           ilp32f, ilp32d, lp64, lp64f, and lp64d.  Some calling conventions are impossible to
           implement on some ISAs: for example, -march=rv32if -mabi=ilp32d is invalid because the
           ABI requires 64-bit values be passed in F registers, but F registers are only 32 bits
           wide.

       -mfdiv
       -mno-fdiv
           Do or don't use hardware floating-point divide and square root instructions.  This
           requires the F or D extensions for floating-point registers.  The default is to use
           them if the specified architecture has these instructions.

       -mdiv
       -mno-div
           Do or don't use hardware instructions for integer division.  This requires the M
           extension.  The default is to use them if the specified architecture has these
           instructions.

       -march=ISA-string
           Generate code for given RISC-V ISA (e.g. rv64im).  ISA strings must be lower-case.
           Examples include rv64i, rv32g, and rv32imaf.

       -mtune=processor-string
           Optimize the output for the given processor, specified by microarchitecture name.

       -mpreferred-stack-boundary=num
           Attempt to keep the stack boundary aligned to a 2 raised to num byte boundary.  If
           -mpreferred-stack-boundary is not specified, the default is 4 (16 bytes or 128-bits).

           Warning: If you use this switch, then you must build all modules with the same value,
           including any libraries.  This includes the system libraries and startup modules.

       -msmall-data-limit=n
           Put global and static data smaller than n bytes into a special section (on some
           targets).

       -msave-restore
       -mno-save-restore
           Do or don't use smaller but slower prologue and epilogue code that uses library
           function calls.  The default is to use fast inline prologues and epilogues.

       -mstrict-align
       -mno-strict-align
           Do not or do generate unaligned memory accesses.  The default is set depending on
           whether the processor we are optimizing for supports fast unaligned access or not.

       -mcmodel=medlow
           Generate code for the medium-low code model. The program and its statically defined
           symbols must lie within a single 2 GiB address range and must lie between absolute
           addresses -2 GiB and +2 GiB. Programs can be statically or dynamically linked. This is
           the default code model.

       -mcmodel=medany
           Generate code for the medium-any code model. The program and its statically defined
           symbols must be within any single 2 GiB address range. Programs can be statically or
           dynamically linked.

       -mexplicit-relocs
       -mno-exlicit-relocs
           Use or do not use assembler relocation operators when dealing with symbolic addresses.
           The alternative is to use assembler macros instead, which may limit optimization.

       -mrelax
       -mno-relax
           Take advantage of linker relaxations to reduce the number of instructions required to
           materialize symbol addresses. The default is to take advantage of linker relaxations.

       RL78 Options

       -msim
           Links in additional target libraries to support operation within a simulator.

       -mmul=none
       -mmul=g10
       -mmul=g13
       -mmul=g14
       -mmul=rl78
           Specifies the type of hardware multiplication and division support to be used.  The
           simplest is "none", which uses software for both multiplication and division.  This is
           the default.  The "g13" value is for the hardware multiply/divide peripheral found on
           the RL78/G13 (S2 core) targets.  The "g14" value selects the use of the multiplication
           and division instructions supported by the RL78/G14 (S3 core) parts.  The value "rl78"
           is an alias for "g14" and the value "mg10" is an alias for "none".

           In addition a C preprocessor macro is defined, based upon the setting of this option.
           Possible values are: "__RL78_MUL_NONE__", "__RL78_MUL_G13__" or "__RL78_MUL_G14__".

       -mcpu=g10
       -mcpu=g13
       -mcpu=g14
       -mcpu=rl78
           Specifies the RL78 core to target.  The default is the G14 core, also known as an S3
           core or just RL78.  The G13 or S2 core does not have multiply or divide instructions,
           instead it uses a hardware peripheral for these operations.  The G10 or S1 core does
           not have register banks, so it uses a different calling convention.

           If this option is set it also selects the type of hardware multiply support to use,
           unless this is overridden by an explicit -mmul=none option on the command line.  Thus
           specifying -mcpu=g13 enables the use of the G13 hardware multiply peripheral and
           specifying -mcpu=g10 disables the use of hardware multiplications altogether.

           Note, although the RL78/G14 core is the default target, specifying -mcpu=g14 or
           -mcpu=rl78 on the command line does change the behavior of the toolchain since it also
           enables G14 hardware multiply support.  If these options are not specified on the
           command line then software multiplication routines will be used even though the code
           targets the RL78 core.  This is for backwards compatibility with older toolchains
           which did not have hardware multiply and divide support.

           In addition a C preprocessor macro is defined, based upon the setting of this option.
           Possible values are: "__RL78_G10__", "__RL78_G13__" or "__RL78_G14__".

       -mg10
       -mg13
       -mg14
       -mrl78
           These are aliases for the corresponding -mcpu= option.  They are provided for
           backwards compatibility.

       -mallregs
           Allow the compiler to use all of the available registers.  By default registers
           "r24..r31" are reserved for use in interrupt handlers.  With this option enabled these
           registers can be used in ordinary functions as well.

       -m64bit-doubles
       -m32bit-doubles
           Make the "double" data type be 64 bits (-m64bit-doubles) or 32 bits (-m32bit-doubles)
           in size.  The default is -m32bit-doubles.

       -msave-mduc-in-interrupts
       -mno-save-mduc-in-interrupts
           Specifies that interrupt handler functions should preserve the MDUC registers.  This
           is only necessary if normal code might use the MDUC registers, for example because it
           performs multiplication and division operations.  The default is to ignore the MDUC
           registers as this makes the interrupt handlers faster.  The target option -mg13 needs
           to be passed for this to work as this feature is only available on the G13 target (S2
           core).  The MDUC registers will only be saved if the interrupt handler performs a
           multiplication or division operation or it calls another function.

       IBM RS/6000 and PowerPC Options

       These -m options are defined for the IBM RS/6000 and PowerPC:

       -mpowerpc-gpopt
       -mno-powerpc-gpopt
       -mpowerpc-gfxopt
       -mno-powerpc-gfxopt
       -mpowerpc64
       -mno-powerpc64
       -mmfcrf
       -mno-mfcrf
       -mpopcntb
       -mno-popcntb
       -mpopcntd
       -mno-popcntd
       -mfprnd
       -mno-fprnd
       -mcmpb
       -mno-cmpb
       -mmfpgpr
       -mno-mfpgpr
       -mhard-dfp
       -mno-hard-dfp
           You use these options to specify which instructions are available on the processor you
           are using.  The default value of these options is determined when configuring GCC.
           Specifying the -mcpu=cpu_type overrides the specification of these options.  We
           recommend you use the -mcpu=cpu_type option rather than the options listed above.

           Specifying -mpowerpc-gpopt allows GCC to use the optional PowerPC architecture
           instructions in the General Purpose group, including floating-point square root.
           Specifying -mpowerpc-gfxopt allows GCC to use the optional PowerPC architecture
           instructions in the Graphics group, including floating-point select.

           The -mmfcrf option allows GCC to generate the move from condition register field
           instruction implemented on the POWER4 processor and other processors that support the
           PowerPC V2.01 architecture.  The -mpopcntb option allows GCC to generate the popcount
           and double-precision FP reciprocal estimate instruction implemented on the POWER5
           processor and other processors that support the PowerPC V2.02 architecture.  The
           -mpopcntd option allows GCC to generate the popcount instruction implemented on the
           POWER7 processor and other processors that support the PowerPC V2.06 architecture.
           The -mfprnd option allows GCC to generate the FP round to integer instructions
           implemented on the POWER5+ processor and other processors that support the PowerPC
           V2.03 architecture.  The -mcmpb option allows GCC to generate the compare bytes
           instruction implemented on the POWER6 processor and other processors that support the
           PowerPC V2.05 architecture.  The -mmfpgpr option allows GCC to generate the FP move
           to/from general-purpose register instructions implemented on the POWER6X processor and
           other processors that support the extended PowerPC V2.05 architecture.  The -mhard-dfp
           option allows GCC to generate the decimal floating-point instructions implemented on
           some POWER processors.

           The -mpowerpc64 option allows GCC to generate the additional 64-bit instructions that
           are found in the full PowerPC64 architecture and to treat GPRs as 64-bit, doubleword
           quantities.  GCC defaults to -mno-powerpc64.

       -mcpu=cpu_type
           Set architecture type, register usage, and instruction scheduling parameters for
           machine type cpu_type.  Supported values for cpu_type are 401, 403, 405, 405fp, 440,
           440fp, 464, 464fp, 476, 476fp, 505, 601, 602, 603, 603e, 604, 604e, 620, 630, 740,
           7400, 7450, 750, 801, 821, 823, 860, 970, 8540, a2, e300c2, e300c3, e500mc, e500mc64,
           e5500, e6500, ec603e, G3, G4, G5, titan, power3, power4, power5, power5+, power6,
           power6x, power7, power8, power9, powerpc, powerpc64, powerpc64le, rs64, and native.

           -mcpu=powerpc, -mcpu=powerpc64, and -mcpu=powerpc64le specify pure 32-bit PowerPC
           (either endian), 64-bit big endian PowerPC and 64-bit little endian PowerPC
           architecture machine types, with an appropriate, generic processor model assumed for
           scheduling purposes.

           Specifying native as cpu type detects and selects the architecture option that
           corresponds to the host processor of the system performing the compilation.
           -mcpu=native has no effect if GCC does not recognize the processor.

           The other options specify a specific processor.  Code generated under those options
           runs best on that processor, and may not run at all on others.

           The -mcpu options automatically enable or disable the following options:

           -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple -mpopcntb -mpopcntd  -mpowerpc64
           -mpowerpc-gpopt  -mpowerpc-gfxopt  -msingle-float -mdouble-float -msimple-fpu  -mmulhw
           -mdlmzb  -mmfpgpr -mvsx -mcrypto -mhtm -mpower8-fusion -mpower8-vector -mquad-memory
           -mquad-memory-atomic -mfloat128 -mfloat128-hardware

           The particular options set for any particular CPU varies between compiler versions,
           depending on what setting seems to produce optimal code for that CPU; it doesn't
           necessarily reflect the actual hardware's capabilities.  If you wish to set an
           individual option to a particular value, you may specify it after the -mcpu option,
           like -mcpu=970 -mno-altivec.

           On AIX, the -maltivec and -mpowerpc64 options are not enabled or disabled by the -mcpu
           option at present because AIX does not have full support for these options.  You may
           still enable or disable them individually if you're sure it'll work in your
           environment.

       -mtune=cpu_type
           Set the instruction scheduling parameters for machine type cpu_type, but do not set
           the architecture type or register usage, as -mcpu=cpu_type does.  The same values for
           cpu_type are used for -mtune as for -mcpu.  If both are specified, the code generated
           uses the architecture and registers set by -mcpu, but the scheduling parameters set by
           -mtune.

       -mcmodel=small
           Generate PowerPC64 code for the small model: The TOC is limited to 64k.

       -mcmodel=medium
           Generate PowerPC64 code for the medium model: The TOC and other static data may be up
           to a total of 4G in size.  This is the default for 64-bit Linux.

       -mcmodel=large
           Generate PowerPC64 code for the large model: The TOC may be up to 4G in size.  Other
           data and code is only limited by the 64-bit address space.

       -maltivec
       -mno-altivec
           Generate code that uses (does not use) AltiVec instructions, and also enable the use
           of built-in functions that allow more direct access to the AltiVec instruction set.
           You may also need to set -mabi=altivec to adjust the current ABI with AltiVec ABI
           enhancements.

           When -maltivec is used, rather than -maltivec=le or -maltivec=be, the element order
           for AltiVec intrinsics such as "vec_splat", "vec_extract", and "vec_insert" match
           array element order corresponding to the endianness of the target.  That is, element
           zero identifies the leftmost element in a vector register when targeting a big-endian
           platform, and identifies the rightmost element in a vector register when targeting a
           little-endian platform.

       -maltivec=be
           Generate AltiVec instructions using big-endian element order, regardless of whether
           the target is big- or little-endian.  This is the default when targeting a big-endian
           platform.  Using this option is currently deprecated.  Support for this feature will
           be removed in GCC 9.

           The element order is used to interpret element numbers in AltiVec intrinsics such as
           "vec_splat", "vec_extract", and "vec_insert".  By default, these match array element
           order corresponding to the endianness for the target.

       -maltivec=le
           Generate AltiVec instructions using little-endian element order, regardless of whether
           the target is big- or little-endian.  This is the default when targeting a little-
           endian platform.  This option is currently ignored when targeting a big-endian
           platform.

           The element order is used to interpret element numbers in AltiVec intrinsics such as
           "vec_splat", "vec_extract", and "vec_insert".  By default, these match array element
           order corresponding to the endianness for the target.

       -mvrsave
       -mno-vrsave
           Generate VRSAVE instructions when generating AltiVec code.

       -msecure-plt
           Generate code that allows ld and ld.so to build executables and shared libraries with
           non-executable ".plt" and ".got" sections.  This is a PowerPC 32-bit SYSV ABI option.

       -mbss-plt
           Generate code that uses a BSS ".plt" section that ld.so fills in, and requires ".plt"
           and ".got" sections that are both writable and executable.  This is a PowerPC 32-bit
           SYSV ABI option.

       -misel
       -mno-isel
           This switch enables or disables the generation of ISEL instructions.

       -misel=yes/no
           This switch has been deprecated.  Use -misel and -mno-isel instead.

       -mpaired
       -mno-paired
           This switch enables or disables the generation of PAIRED simd instructions.

       -mvsx
       -mno-vsx
           Generate code that uses (does not use) vector/scalar (VSX) instructions, and also
           enable the use of built-in functions that allow more direct access to the VSX
           instruction set.

       -mcrypto
       -mno-crypto
           Enable the use (disable) of the built-in functions that allow direct access to the
           cryptographic instructions that were added in version 2.07 of the PowerPC ISA.

       -mhtm
       -mno-htm
           Enable (disable) the use of the built-in functions that allow direct access to the
           Hardware Transactional Memory (HTM) instructions that were added in version 2.07 of
           the PowerPC ISA.

       -mpower8-fusion
       -mno-power8-fusion
           Generate code that keeps (does not keeps) some integer operations adjacent so that the
           instructions can be fused together on power8 and later processors.

       -mpower8-vector
       -mno-power8-vector
           Generate code that uses (does not use) the vector and scalar instructions that were
           added in version 2.07 of the PowerPC ISA.  Also enable the use of built-in functions
           that allow more direct access to the vector instructions.

       -mquad-memory
       -mno-quad-memory
           Generate code that uses (does not use) the non-atomic quad word memory instructions.
           The -mquad-memory option requires use of 64-bit mode.

       -mquad-memory-atomic
       -mno-quad-memory-atomic
           Generate code that uses (does not use) the atomic quad word memory instructions.  The
           -mquad-memory-atomic option requires use of 64-bit mode.

       -mfloat128
       -mno-float128
           Enable/disable the __float128 keyword for IEEE 128-bit floating point and use either
           software emulation for IEEE 128-bit floating point or hardware instructions.

           The VSX instruction set (-mvsx, -mcpu=power7, -mcpu=power8), or -mcpu=power9 must be
           enabled to use the IEEE 128-bit floating point support.  The IEEE 128-bit floating
           point support only works on PowerPC Linux systems.

           The default for -mfloat128 is enabled on PowerPC Linux systems using the VSX
           instruction set, and disabled on other systems.

           If you use the ISA 3.0 instruction set (-mpower9-vector or -mcpu=power9) on a 64-bit
           system, the IEEE 128-bit floating point support will also enable the generation of ISA
           3.0 IEEE 128-bit floating point instructions.  Otherwise, if you do not specify to
           generate ISA 3.0 instructions or you are targeting a 32-bit big endian system, IEEE
           128-bit floating point will be done with software emulation.

       -mfloat128-hardware
       -mno-float128-hardware
           Enable/disable using ISA 3.0 hardware instructions to support the __float128 data
           type.

           The default for -mfloat128-hardware is enabled on PowerPC Linux systems using the ISA
           3.0 instruction set, and disabled on other systems.

       -m32
       -m64
           Generate code for 32-bit or 64-bit environments of Darwin and SVR4 targets (including
           GNU/Linux).  The 32-bit environment sets int, long and pointer to 32 bits and
           generates code that runs on any PowerPC variant.  The 64-bit environment sets int to
           32 bits and long and pointer to 64 bits, and generates code for PowerPC64, as for
           -mpowerpc64.

       -mfull-toc
       -mno-fp-in-toc
       -mno-sum-in-toc
       -mminimal-toc
           Modify generation of the TOC (Table Of Contents), which is created for every
           executable file.  The -mfull-toc option is selected by default.  In that case, GCC
           allocates at least one TOC entry for each unique non-automatic variable reference in
           your program.  GCC also places floating-point constants in the TOC.  However, only
           16,384 entries are available in the TOC.

           If you receive a linker error message that saying you have overflowed the available
           TOC space, you can reduce the amount of TOC space used with the -mno-fp-in-toc and
           -mno-sum-in-toc options.  -mno-fp-in-toc prevents GCC from putting floating-point
           constants in the TOC and -mno-sum-in-toc forces GCC to generate code to calculate the
           sum of an address and a constant at run time instead of putting that sum into the TOC.
           You may specify one or both of these options.  Each causes GCC to produce very
           slightly slower and larger code at the expense of conserving TOC space.

           If you still run out of space in the TOC even when you specify both of these options,
           specify -mminimal-toc instead.  This option causes GCC to make only one TOC entry for
           every file.  When you specify this option, GCC produces code that is slower and larger
           but which uses extremely little TOC space.  You may wish to use this option only on
           files that contain less frequently-executed code.

       -maix64
       -maix32
           Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit "long" type, and
           the infrastructure needed to support them.  Specifying -maix64 implies -mpowerpc64,
           while -maix32 disables the 64-bit ABI and implies -mno-powerpc64.  GCC defaults to
           -maix32.

       -mxl-compat
       -mno-xl-compat
           Produce code that conforms more closely to IBM XL compiler semantics when using AIX-
           compatible ABI.  Pass floating-point arguments to prototyped functions beyond the
           register save area (RSA) on the stack in addition to argument FPRs.  Do not assume
           that most significant double in 128-bit long double value is properly rounded when
           comparing values and converting to double.  Use XL symbol names for long double
           support routines.

           The AIX calling convention was extended but not initially documented to handle an
           obscure K&R C case of calling a function that takes the address of its arguments with
           fewer arguments than declared.  IBM XL compilers access floating-point arguments that
           do not fit in the RSA from the stack when a subroutine is compiled without
           optimization.  Because always storing floating-point arguments on the stack is
           inefficient and rarely needed, this option is not enabled by default and only is
           necessary when calling subroutines compiled by IBM XL compilers without optimization.

       -mpe
           Support IBM RS/6000 SP Parallel Environment (PE).  Link an application written to use
           message passing with special startup code to enable the application to run.  The
           system must have PE installed in the standard location (/usr/lpp/ppe.poe/), or the
           specs file must be overridden with the -specs= option to specify the appropriate
           directory location.  The Parallel Environment does not support threads, so the -mpe
           option and the -pthread option are incompatible.

       -malign-natural
       -malign-power
           On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option -malign-natural
           overrides the ABI-defined alignment of larger types, such as floating-point doubles,
           on their natural size-based boundary.  The option -malign-power instructs GCC to
           follow the ABI-specified alignment rules.  GCC defaults to the standard alignment
           defined in the ABI.

           On 64-bit Darwin, natural alignment is the default, and -malign-power is not
           supported.

       -msoft-float
       -mhard-float
           Generate code that does not use (uses) the floating-point register set.  Software
           floating-point emulation is provided if you use the -msoft-float option, and pass the
           option to GCC when linking.

       -msingle-float
       -mdouble-float
           Generate code for single- or double-precision floating-point operations.
           -mdouble-float implies -msingle-float.

       -msimple-fpu
           Do not generate "sqrt" and "div" instructions for hardware floating-point unit.

       -mfpu=name
           Specify type of floating-point unit.  Valid values for name are sp_lite (equivalent to
           -msingle-float -msimple-fpu), dp_lite (equivalent to -mdouble-float -msimple-fpu),
           sp_full (equivalent to -msingle-float), and dp_full (equivalent to -mdouble-float).

       -mxilinx-fpu
           Perform optimizations for the floating-point unit on Xilinx PPC 405/440.

       -mmultiple
       -mno-multiple
           Generate code that uses (does not use) the load multiple word instructions and the
           store multiple word instructions.  These instructions are generated by default on
           POWER systems, and not generated on PowerPC systems.  Do not use -mmultiple on little-
           endian PowerPC systems, since those instructions do not work when the processor is in
           little-endian mode.  The exceptions are PPC740 and PPC750 which permit these
           instructions in little-endian mode.

       -mupdate
       -mno-update
           Generate code that uses (does not use) the load or store instructions that update the
           base register to the address of the calculated memory location.  These instructions
           are generated by default.  If you use -mno-update, there is a small window between the
           time that the stack pointer is updated and the address of the previous frame is
           stored, which means code that walks the stack frame across interrupts or signals may
           get corrupted data.

       -mavoid-indexed-addresses
       -mno-avoid-indexed-addresses
           Generate code that tries to avoid (not avoid) the use of indexed load or store
           instructions. These instructions can incur a performance penalty on Power6 processors
           in certain situations, such as when stepping through large arrays that cross a 16M
           boundary.  This option is enabled by default when targeting Power6 and disabled
           otherwise.

       -mfused-madd
       -mno-fused-madd
           Generate code that uses (does not use) the floating-point multiply and accumulate
           instructions.  These instructions are generated by default if hardware floating point
           is used.  The machine-dependent -mfused-madd option is now mapped to the machine-
           independent -ffp-contract=fast option, and -mno-fused-madd is mapped to
           -ffp-contract=off.

       -mmulhw
       -mno-mulhw
           Generate code that uses (does not use) the half-word multiply and multiply-accumulate
           instructions on the IBM 405, 440, 464 and 476 processors.  These instructions are
           generated by default when targeting those processors.

       -mdlmzb
       -mno-dlmzb
           Generate code that uses (does not use) the string-search dlmzb instruction on the IBM
           405, 440, 464 and 476 processors.  This instruction is generated by default when
           targeting those processors.

       -mno-bit-align
       -mbit-align
           On System V.4 and embedded PowerPC systems do not (do) force structures and unions
           that contain bit-fields to be aligned to the base type of the bit-field.

           For example, by default a structure containing nothing but 8 "unsigned" bit-fields of
           length 1 is aligned to a 4-byte boundary and has a size of 4 bytes.  By using
           -mno-bit-align, the structure is aligned to a 1-byte boundary and is 1 byte in size.

       -mno-strict-align
       -mstrict-align
           On System V.4 and embedded PowerPC systems do not (do) assume that unaligned memory
           references are handled by the system.

       -mrelocatable
       -mno-relocatable
           Generate code that allows (does not allow) a static executable to be relocated to a
           different address at run time.  A simple embedded PowerPC system loader should
           relocate the entire contents of ".got2" and 4-byte locations listed in the ".fixup"
           section, a table of 32-bit addresses generated by this option.  For this to work, all
           objects linked together must be compiled with -mrelocatable or -mrelocatable-lib.
           -mrelocatable code aligns the stack to an 8-byte boundary.

       -mrelocatable-lib
       -mno-relocatable-lib
           Like -mrelocatable, -mrelocatable-lib generates a ".fixup" section to allow static
           executables to be relocated at run time, but -mrelocatable-lib does not use the
           smaller stack alignment of -mrelocatable.  Objects compiled with -mrelocatable-lib may
           be linked with objects compiled with any combination of the -mrelocatable options.

       -mno-toc
       -mtoc
           On System V.4 and embedded PowerPC systems do not (do) assume that register 2 contains
           a pointer to a global area pointing to the addresses used in the program.

       -mlittle
       -mlittle-endian
           On System V.4 and embedded PowerPC systems compile code for the processor in little-
           endian mode.  The -mlittle-endian option is the same as -mlittle.

       -mbig
       -mbig-endian
           On System V.4 and embedded PowerPC systems compile code for the processor in big-
           endian mode.  The -mbig-endian option is the same as -mbig.

       -mdynamic-no-pic
           On Darwin and Mac OS X systems, compile code so that it is not relocatable, but that
           its external references are relocatable.  The resulting code is suitable for
           applications, but not shared libraries.

       -msingle-pic-base
           Treat the register used for PIC addressing as read-only, rather than loading it in the
           prologue for each function.  The runtime system is responsible for initializing this
           register with an appropriate value before execution begins.

       -mprioritize-restricted-insns=priority
           This option controls the priority that is assigned to dispatch-slot restricted
           instructions during the second scheduling pass.  The argument priority takes the value
           0, 1, or 2 to assign no, highest, or second-highest (respectively) priority to
           dispatch-slot restricted instructions.

       -msched-costly-dep=dependence_type
           This option controls which dependences are considered costly by the target during
           instruction scheduling.  The argument dependence_type takes one of the following
           values:

           no  No dependence is costly.

           all All dependences are costly.

           true_store_to_load
               A true dependence from store to load is costly.

           store_to_load
               Any dependence from store to load is costly.

           number
               Any dependence for which the latency is greater than or equal to number is costly.

       -minsert-sched-nops=scheme
           This option controls which NOP insertion scheme is used during the second scheduling
           pass.  The argument scheme takes one of the following values:

           no  Don't insert NOPs.

           pad Pad with NOPs any dispatch group that has vacant issue slots, according to the
               scheduler's grouping.

           regroup_exact
               Insert NOPs to force costly dependent insns into separate groups.  Insert exactly
               as many NOPs as needed to force an insn to a new group, according to the estimated
               processor grouping.

           number
               Insert NOPs to force costly dependent insns into separate groups.  Insert number
               NOPs to force an insn to a new group.

       -mcall-sysv
           On System V.4 and embedded PowerPC systems compile code using calling conventions that
           adhere to the March 1995 draft of the System V Application Binary Interface, PowerPC
           processor supplement.  This is the default unless you configured GCC using
           powerpc-*-eabiaix.

       -mcall-sysv-eabi
       -mcall-eabi
           Specify both -mcall-sysv and -meabi options.

       -mcall-sysv-noeabi
           Specify both -mcall-sysv and -mno-eabi options.

       -mcall-aixdesc
           On System V.4 and embedded PowerPC systems compile code for the AIX operating system.

       -mcall-linux
           On System V.4 and embedded PowerPC systems compile code for the Linux-based GNU
           system.

       -mcall-freebsd
           On System V.4 and embedded PowerPC systems compile code for the FreeBSD operating
           system.

       -mcall-netbsd
           On System V.4 and embedded PowerPC systems compile code for the NetBSD operating
           system.

       -mcall-openbsd
           On System V.4 and embedded PowerPC systems compile code for the OpenBSD operating
           system.

       -mtraceback=traceback_type
           Select the type of traceback table. Valid values for traceback_type are full, part,
           and no.

       -maix-struct-return
           Return all structures in memory (as specified by the AIX ABI).

       -msvr4-struct-return
           Return structures smaller than 8 bytes in registers (as specified by the SVR4 ABI).

       -mabi=abi-type
           Extend the current ABI with a particular extension, or remove such extension.  Valid
           values are altivec, no-altivec, spe, no-spe, ibmlongdouble, ieeelongdouble, elfv1,
           elfv2.

       -mabi=ibmlongdouble
           Change the current ABI to use IBM extended-precision long double.  This is not likely
           to work if your system defaults to using IEEE extended-precision long double.  If you
           change the long double type from IEEE extended-precision, the compiler will issue a
           warning unless you use the -Wno-psabi option.  Requires -mlong-double-128 to be
           enabled.

       -mabi=ieeelongdouble
           Change the current ABI to use IEEE extended-precision long double.  This is not likely
           to work if your system defaults to using IBM extended-precision long double.  If you
           change the long double type from IBM extended-precision, the compiler will issue a
           warning unless you use the -Wno-psabi option.  Requires -mlong-double-128 to be
           enabled.

       -mabi=elfv1
           Change the current ABI to use the ELFv1 ABI.  This is the default ABI for big-endian
           PowerPC 64-bit Linux.  Overriding the default ABI requires special system support and
           is likely to fail in spectacular ways.

       -mabi=elfv2
           Change the current ABI to use the ELFv2 ABI.  This is the default ABI for little-
           endian PowerPC 64-bit Linux.  Overriding the default ABI requires special system
           support and is likely to fail in spectacular ways.

       -mgnu-attribute
       -mno-gnu-attribute
           Emit .gnu_attribute assembly directives to set tag/value pairs in a .gnu.attributes
           section that specify ABI variations in function parameters or return values.

       -mprototype
       -mno-prototype
           On System V.4 and embedded PowerPC systems assume that all calls to variable argument
           functions are properly prototyped.  Otherwise, the compiler must insert an instruction
           before every non-prototyped call to set or clear bit 6 of the condition code register
           ("CR") to indicate whether floating-point values are passed in the floating-point
           registers in case the function takes variable arguments.  With -mprototype, only calls
           to prototyped variable argument functions set or clear the bit.

       -msim
           On embedded PowerPC systems, assume that the startup module is called sim-crt0.o and
           that the standard C libraries are libsim.a and libc.a.  This is the default for
           powerpc-*-eabisim configurations.

       -mmvme
           On embedded PowerPC systems, assume that the startup module is called crt0.o and the
           standard C libraries are libmvme.a and libc.a.

       -mads
           On embedded PowerPC systems, assume that the startup module is called crt0.o and the
           standard C libraries are libads.a and libc.a.

       -myellowknife
           On embedded PowerPC systems, assume that the startup module is called crt0.o and the
           standard C libraries are libyk.a and libc.a.

       -mvxworks
           On System V.4 and embedded PowerPC systems, specify that you are compiling for a
           VxWorks system.

       -memb
           On embedded PowerPC systems, set the "PPC_EMB" bit in the ELF flags header to indicate
           that eabi extended relocations are used.

       -meabi
       -mno-eabi
           On System V.4 and embedded PowerPC systems do (do not) adhere to the Embedded
           Applications Binary Interface (EABI), which is a set of modifications to the System
           V.4 specifications.  Selecting -meabi means that the stack is aligned to an 8-byte
           boundary, a function "__eabi" is called from "main" to set up the EABI environment,
           and the -msdata option can use both "r2" and "r13" to point to two separate small data
           areas.  Selecting -mno-eabi means that the stack is aligned to a 16-byte boundary, no
           EABI initialization function is called from "main", and the -msdata option only uses
           "r13" to point to a single small data area.  The -meabi option is on by default if you
           configured GCC using one of the powerpc*-*-eabi* options.

       -msdata=eabi
           On System V.4 and embedded PowerPC systems, put small initialized "const" global and
           static data in the ".sdata2" section, which is pointed to by register "r2".  Put small
           initialized non-"const" global and static data in the ".sdata" section, which is
           pointed to by register "r13".  Put small uninitialized global and static data in the
           ".sbss" section, which is adjacent to the ".sdata" section.  The -msdata=eabi option
           is incompatible with the -mrelocatable option.  The -msdata=eabi option also sets the
           -memb option.

       -msdata=sysv
           On System V.4 and embedded PowerPC systems, put small global and static data in the
           ".sdata" section, which is pointed to by register "r13".  Put small uninitialized
           global and static data in the ".sbss" section, which is adjacent to the ".sdata"
           section.  The -msdata=sysv option is incompatible with the -mrelocatable option.

       -msdata=default
       -msdata
           On System V.4 and embedded PowerPC systems, if -meabi is used, compile code the same
           as -msdata=eabi, otherwise compile code the same as -msdata=sysv.

       -msdata=data
           On System V.4 and embedded PowerPC systems, put small global data in the ".sdata"
           section.  Put small uninitialized global data in the ".sbss" section.  Do not use
           register "r13" to address small data however.  This is the default behavior unless
           other -msdata options are used.

       -msdata=none
       -mno-sdata
           On embedded PowerPC systems, put all initialized global and static data in the ".data"
           section, and all uninitialized data in the ".bss" section.

       -mreadonly-in-sdata
       -mreadonly-in-sdata
           Put read-only objects in the ".sdata" section as well.  This is the default.

       -mblock-move-inline-limit=num
           Inline all block moves (such as calls to "memcpy" or structure copies) less than or
           equal to num bytes.  The minimum value for num is 32 bytes on 32-bit targets and 64
           bytes on 64-bit targets.  The default value is target-specific.

       -mblock-compare-inline-limit=num
           Generate non-looping inline code for all block compares (such as calls to "memcmp" or
           structure compares) less than or equal to num bytes. If num is 0, all inline expansion
           (non-loop and loop) of block compare is disabled. The default value is target-
           specific.

       -mblock-compare-inline-loop-limit=num
           Generate an inline expansion using loop code for all block compares that are less than
           or equal to num bytes, but greater than the limit for non-loop inline block compare
           expansion. If the block length is not constant, at most num bytes will be compared
           before "memcmp" is called to compare the remainder of the block. The default value is
           target-specific.

       -mstring-compare-inline-limit=num
           Generate at most num pairs of load instructions to compare the string inline. If the
           difference or end of string is not found at the end of the inline compare a call to
           "strcmp" or "strncmp" will take care of the rest of the comparison. The default is 8
           pairs of loads, which will compare 64 bytes on a 64-bit target and 32 bytes on a
           32-bit target.

       -G num
           On embedded PowerPC systems, put global and static items less than or equal to num
           bytes into the small data or BSS sections instead of the normal data or BSS section.
           By default, num is 8.  The -G num switch is also passed to the linker.  All modules
           should be compiled with the same -G num value.

       -mregnames
       -mno-regnames
           On System V.4 and embedded PowerPC systems do (do not) emit register names in the
           assembly language output using symbolic forms.

       -mlongcall
       -mno-longcall
           By default assume that all calls are far away so that a longer and more expensive
           calling sequence is required.  This is required for calls farther than 32 meg