Provided by: clang-3.9_3.9.1-4ubuntu3~14.04.3_amd64 
NAME
clang - the Clang C, C++, and Objective-C compiler
SYNOPSIS
clang [options] filename ...
DESCRIPTION
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.
Preprocessing
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.
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 <‐
http://clang-analyzer.llvm.org> for more details on how to use the static analyzer.
OPTIONS
Stage Selection Options
-E Run the preprocessor stage.
-fsyntax-only
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.
-std=<language>
Specify the language standard to compile for.
-stdlib=<library>
Specify the C++ standard library to use; supported options are libstdc++ and libc++.
-ansi Same as -std=c89.
-ObjC, -ObjC++
Treat source input files as Objective-C and Object-C++ inputs respectively.
-trigraphs
Enable trigraphs.
-ffreestanding
Indicate that the file should be compiled for a freestanding, not a hosted, environment.
-fno-builtin
Disable special handling and optimizations of builtin functions like strlen() and malloc().
-fmath-errno
Indicate that math functions should be treated as updating errno.
-fpascal-strings
Enable support for Pascal-style strings with "\pfoo".
-fms-extensions
Enable support for Microsoft extensions.
-fmsc-version=
Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.
-fborland-extensions
Enable support for Borland extensions.
-fwritable-strings
Make all string literals default to writable. This disables uniquing of strings and other
optimizations.
-flax-vector-conversions
Allow loose type checking rules for implicit vector conversions.
-fblocks
Enable the "Blocks" language feature.
-fobjc-gc-only
Indicate that Objective-C code should be compiled in GC-only mode, which only works when
Objective-C Garbage Collection is enabled.
-fobjc-gc
Indicate that Objective-C code should be compiled in hybrid-GC mode, which works with both GC and
non-GC mode.
-fobjc-abi-version=version
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).
-fobjc-nonfragile-abi-version=<version>
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.
-mmacosx-version-min=<version>
When building for Mac OS X, specify the minimum version supported by your application.
-miphoneos-version-min
When building for iPhone OS, specify the minimum version supported by your application.
-march=<cpu>
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, -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.
-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.
-fexceptions
Enable generation of unwind information. This allows exceptions to be thrown through Clang
compiled stack frames. This is on by default in x86-64.
-ftrapv
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.
-fvisibility
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.
-ftls-model=<model>
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, -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).
Driver Options
-### Print (but do not run) the commands to run for this compilation.
--help Display available options.
-Qunused-arguments
Do not emit any warnings for unused driver arguments.
-Wa,<args>
Pass the comma separated arguments in args to the assembler.
-Wl,<args>
Pass the comma separated arguments in args to the linker.
-Wp,<args>
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-file-name=<file>
Print the full library path of file.
-print-libgcc-file-name
Print the library path for "libgcc.a".
-print-prog-name=<name>
Print the full program path of name.
-print-search-dirs
Print the paths used for finding libraries and programs.
-save-temps
Save intermediate compilation results.
-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.
-ftime-report
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
-D<macroname>=<value>
Adds an implicit #define into the predefines buffer which is read before the source file is
preprocessed.
-U<macroname>
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.
-I<directory>
Add the specified directory to the search path for include files.
-F<directory>
Add the specified directory to the search path for framework include files.
-nostdinc
Do not search the standard system directories or compiler builtin directories for include files.
-nostdlibinc
Do not search the standard system directories for include files, but do search compiler builtin
include directories.
-nobuiltininc
Do not search clang's builtin directory for include files.
ENVIRONMENT
TMPDIR, TEMP, TMP
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.
C_INCLUDE_PATH, OBJC_INCLUDE_PATH, CPLUS_INCLUDE_PATH, OBJCPLUS_INCLUDE_PATH
These environment variables specify additional paths, as for CPATH, which are only used when
processing the appropriate language.
MACOSX_DEPLOYMENT_TARGET
If -mmacosx-version-min is unspecified, the default deployment target is read from this
environment variable. This option only affects Darwin targets.
BUGS
To report bugs, please visit <http://llvm.org/bugs/>. Most bug reports should include preprocessed
source files (use the -E option) and the full output of the compiler, along with information to
reproduce.
SEE ALSO
as(1), ld(1)
AUTHOR
Maintained by the Clang / LLVM Team (<http://clang.llvm.org>)
COPYRIGHT
2007-2017, The Clang Team