Provided by: clang-6.0_6.0-1ubuntu2_amd64 bug


       clang - the Clang C, C++, and Objective-C compiler


       clang [options] filename 


       clang  is  a  C,  C++,  and Objective-C compiler which encompasses preprocessing, parsing,
       optimization, code generation, assembly, and linking.  Depending on which high-level  mode
       setting  is  passed,  Clang  will  stop  before  doing a full link.  While Clang is highly
       integrated, it is important to understand the stages of compilation, to understand how  to
       invoke it.  These stages are:

       Driver The  clang  executable  is  actually  a  small  driver  which  controls the overall
              execution of other tools such as the compiler, assembler and linker.  Typically you
              do  not  need  to interact with the driver, but you transparently use it to run the
              other tools.

              This stage handles tokenization of the input source file, macro expansion, #include
              expansion  and handling of other preprocessor directives.  The output of this stage
              is typically called a “.i” (for C), “.ii” (for C++), “.mi”  (for  Objective-C),  or
              “.mii” (for Objective-C++) file.

       Parsing and Semantic Analysis
              This  stage  parses  the  input  file, translating preprocessor tokens into a parse
              tree.  Once in the form of a parse tree, it applies semantic  analysis  to  compute
              types  for  expressions as well and determine whether the code is well formed. This
              stage is responsible for generating most of the compiler warnings as well as  parse
              errors. The output of this stage is an “Abstract Syntax Tree” (AST).

       Code Generation and Optimization
              This  stage translates an AST into low-level intermediate code (known as “LLVM IR”)
              and ultimately to machine code.  This  phase  is  responsible  for  optimizing  the
              generated  code  and  handling target-specific code generation.  The output of this
              stage is typically called a “.s” file or “assembly” file.

              Clang also supports the use of an integrated assembler, in which the code generator
              produces  object  files  directly.  This avoids the overhead of generating the “.s”
              file and of calling the target assembler.

              This stage runs the target assembler to translate the output of the compiler into a
              target  object  file.  The  output of this stage is typically called a “.o” file or
              “object” file.

       Linker This stage runs the target linker to merge multiple object files into an executable
              or  dynamic  library.  The  output  of  this  stage is typically called an “a.out”,
              “.dylib” or “.so” file.

       Clang Static Analyzer

       The Clang Static Analyzer is a tool that scans source code to try  to  find  bugs  through
       code  analysis.   This  tool  uses  many parts of Clang and is built into the same driver.
       Please see <> for more details on  how  to  use  the  static


   Stage Selection Options
       -E     Run the preprocessor stage.

              Run the preprocessor, parser and type checking stages.

       -S     Run  the  previous  stages  as  well as LLVM generation and optimization stages and
              target-specific code generation, producing an assembly file.

       -c     Run all of the above, plus the assembler, generating a target “.o” object file.

       no stage selection option
              If no stage selection option is specified, all stages above are run, and the linker
              is run to combine the results into an executable or shared library.

   Language Selection and Mode Options
       -x <language>
              Treat subsequent input files as having type language.

              Specify the language standard to compile for.

              Specify  the  C++  standard  library  to  use;  supported options are libstdc++ and
              libc++. If not specified, platform default will be used.

              Specify the compiler runtime library to  use;  supported  options  are  libgcc  and
              compiler-rt. If not specified, platform default will be used.

       -ansi  Same as -std=c89.

       -ObjC, -ObjC++
              Treat source input files as Objective-C and Object-C++ inputs respectively.

              Enable trigraphs.

              Indicate  that  the  file  should  be  compiled  for  a freestanding, not a hosted,

              Disable special handling and optimizations of builtin functions like  strlen()  and

              Indicate that math functions should be treated as updating errno.

              Enable support for Pascal-style strings with “\pfoo”.

              Enable support for Microsoft extensions.

              Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.

              Enable support for Borland extensions.

              Make  all  string  literals default to writable.  This disables uniquing of strings
              and other optimizations.

              Allow loose type checking rules for implicit vector conversions.

              Enable the “Blocks” language feature.

              Select the Objective-C ABI  version  to  use.  Available  versions  are  1  (legacy
              “fragile” ABI), 2 (non-fragile ABI 1), and 3 (non-fragile ABI 2).

              Select the Objective-C non-fragile ABI version to use by default. This will only be
              used as the Objective-C ABI  when  the  non-fragile  ABI  is  enabled  (either  via
              -fobjc-nonfragile-abi, or because it is the platform default).

       -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
              Enable  use  of the Objective-C non-fragile ABI. On platforms for which this is the
              default ABI, it can be disabled with -fno-objc-nonfragile-abi.

   Target Selection Options
       Clang fully supports cross compilation as an inherent part of its  design.   Depending  on
       how  your  version  of  Clang  is  configured,  it  may have support for a number of cross
       compilers, or may only support a native target.

       -arch <architecture>
              Specify the architecture to build for.

              When building for  Mac  OS  X,  specify  the  minimum  version  supported  by  your

              When  building  for  iPhone  OS,  specify  the  minimum  version  supported by your

              Specify that Clang should generate code for a specific processor family member  and
              later.   For  example,  if  you  specify  -march=i486,  the  compiler is allowed to
              generate instructions that are valid on i486 and later processors,  but  which  may
              not exist on earlier ones.

   Code Generation Options
       -O0, -O1, -O2, -O3, -Ofast, -Os, -Oz, -Og, -O, -O4
              Specify which optimization level to use:
                 -O0  Means  “no optimization”: this level compiles the fastest and generates the
                 most debuggable code.

                 -O1 Somewhere between -O0 and -O2.

                 -O2 Moderate level of optimization which enables most optimizations.

                 -O3 Like -O2, except that it enables optimizations that take longer  to  perform
                 or that may generate larger code (in an attempt to make the program run faster).

                 -Ofast  Enables  all  the  optimizations  from  -O3  along with other aggressive
                 optimizations that may violate strict compliance with language standards.

                 -Os Like -O2 with extra optimizations to reduce code size.

                 -Oz Like -Os (and thus -O2), but reduces code size further.

                 -Og  Like  -O1.  In  future  versions,  this  option  might  disable   different
                 optimizations in order to improve debuggability.

                 -O Equivalent to -O2.

                 -O4 and higher
                     Currently equivalent to -O3

       -g, -gline-tables-only, -gmodules
              Control  debug information output.  Note that Clang debug information works best at
              -O0.  When more than one option starting with -g is specified, the last one wins:
                 -g Generate debug information.

                 -gline-tables-only Generate only line table debug information. This  allows  for
                 symbolicated  backtraces  with  inlining  information,  but does not include any
                 information about variables, their locations or types.

                 -gmodules Generate debug information that contains external references to  types
                 defined  in  Clang  modules or precompiled headers instead of emitting redundant
                 debug type information  into  every  object  file.   This  option  transparently
                 switches  the  Clang module format to object file containers that hold the Clang
                 module together with the debug information.  When compiling a program that  uses
                 Clang  modules  or  precompiled  headers,  this  option  produces complete debug
                 information with faster compile times and much smaller object files.

                 This option should not be used when building static libraries  for  distribution
                 to  other  machines because the debug info will contain references to the module
                 cache on the machine the object files in the library were built on.

       -fstandalone-debug -fno-standalone-debug
              Clang supports a number of optimizations to reduce the size of debug information in
              the  binary.  They work based on the assumption that the debug type information can
              be spread out over multiple compilation units.  For instance, Clang will  not  emit
              type  definitions  for  types that are not needed by a module and could be replaced
              with a forward declaration.  Further, Clang will only emit type info for a  dynamic
              C++ class in the module that contains the vtable for the class.

              The  -fstandalone-debug  option turns off these optimizations.  This is useful when
              working with 3rd-party libraries that don’t come with debug information.   This  is
              the  default on Darwin.  Note that Clang will never emit type information for types
              that are not referenced at all by the program.

              Enable generation of unwind  information.  This  allows  exceptions  to  be  thrown
              through Clang compiled stack frames.  This is on by default in x86-64.

              Generate  code  to  catch  integer  overflow  errors.   Signed  integer overflow is
              undefined in C. With this flag, extra code is generated to detect  this  and  abort
              when it happens.

              This flag sets the default visibility level.

       -fcommon, -fno-common
              This flag specifies that variables without initializers get common linkage.  It can
              be disabled with -fno-common.

              Set the default thread-local storage (TLS) model to use for thread-local variables.
              Valid   values   are:   “global-dynamic”,   “local-dynamic”,   “initial-exec”   and
              “local-exec”. The default is “global-dynamic”. The default model can be  overridden
              with  the  tls_model  attribute.  The  compiler will try to choose a more efficient
              model if possible.

       -flto, -flto=full, -flto=thin, -emit-llvm
              Generate output files in LLVM formats, suitable for link time  optimization.   When
              used  with  -S  this generates LLVM intermediate language assembly files, otherwise
              this generates LLVM bitcode format object files (which may be passed to the  linker
              depending on the stage selection options).

              The  default  for  -flto  is  “full”,  in  which  the  LLVM bitcode is suitable for
              monolithic Link Time Optimization (LTO), where the linker merges all  such  modules
              into a single combined module for optimization. With “thin”, ThinLTO compilation is
              invoked instead.

   Driver Options
       -###   Print (but do not run) the commands to run for this compilation.

       --help Display available options.

              Do not emit any warnings for unused driver arguments.

              Pass the comma separated arguments in args to the assembler.

              Pass the comma separated arguments in args to the linker.

              Pass the comma separated arguments in args to the preprocessor.

       -Xanalyzer <arg>
              Pass arg to the static analyzer.

       -Xassembler <arg>
              Pass arg to the assembler.

       -Xlinker <arg>
              Pass arg to the linker.

       -Xpreprocessor <arg>
              Pass arg to the preprocessor.

       -o <file>
              Write output to file.

              Print the full library path of file.

              Print the library path for the currently used compiler runtime library  (“libgcc.a”
              or “libclang_rt.builtins.*.a”).

              Print the full program path of name.

              Print the paths used for finding libraries and programs.

              Save intermediate compilation results.

       -save-stats, -save-stats=cwd, -save-stats=obj
              Save  internal code generation (LLVM) statistics to a file in the current directory
              (-save-stats/”-save-stats=cwd”)   or   the   directory   of   the    output    file

       -integrated-as, -no-integrated-as
              Used  to  enable  and  disable,  respectively, the use of the integrated assembler.
              Whether the integrated assembler is on by default is target dependent.

       -time  Time individual commands.

              Print timing summary of each stage of compilation.

       -v     Show commands to run and use verbose output.

   Diagnostics Options
       -fshow-column,  -fshow-source-location,   -fcaret-diagnostics,   -fdiagnostics-fixit-info,
       -fdiagnostics-parseable-fixits,                     -fdiagnostics-print-source-range-info,
       -fprint-source-range-info, -fdiagnostics-show-option, -fmessage-length
              These options control how Clang prints out information  about  diagnostics  (errors
              and warnings). Please see the Clang User’s Manual for more information.

   Preprocessor Options
              Adds an implicit #define into the predefines buffer which is read before the source
              file is preprocessed.

              Adds an implicit #undef into the predefines buffer which is read before the  source
              file is preprocessed.

       -include <filename>
              Adds  an  implicit  #include  into  the  predefines buffer which is read before the
              source file is preprocessed.

              Add the specified directory to the search path for include files.

              Add the specified directory to the search path for framework include files.

              Do not search the standard system directories or compiler builtin  directories  for
              include files.

              Do  not  search  the  standard  system directories for include files, but do search
              compiler builtin include directories.

              Do not search clang’s builtin directory for include files.


              These environment variables are checked,  in  order,  for  the  location  to  write
              temporary files used during the compilation process.

       CPATH  If this environment variable is present, it is treated as a delimited list of paths
              to be added to the default system include path list. The delimiter is the  platform
              dependent delimiter, as used in the PATH environment variable.

              Empty components in the environment variable are ignored.

              These  environment variables specify additional paths, as for CPATH, which are only
              used when processing the appropriate language.

              If -mmacosx-version-min is unspecified, the default deployment target is read  from
              this environment variable. This option only affects Darwin targets.


       To  report  bugs,  please  visit <>.  Most bug reports should include
       preprocessed source files (use the -E option) and the full output of the  compiler,  along
       with information to reproduce.


       as(1), ld(1)


       Maintained by the Clang / LLVM Team (<>)


       2007-2018, The Clang Team