clang-3.8(1)



CLANG(1)                             Clang                            CLANG(1)

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 prepro-
       cessing, 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  im-
       portant  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, as-
              sembler 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 to-
              kens 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 tar-
              get 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 optimiza-
              tion  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  exe-
              cutable 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 er-
              rno.

       -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  de-
              fault.  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
              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 de-
       sign.  Depending on how your version of Clang  is  configured,  it  may
       have support for a number of cross compilers, or may only support a na-
       tive target.

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

       -mmacosx-version-min=<version>
              When building for Mac OS X, specify  the  minimum  version  sup-
              ported by your application.

       -miphoneos-version-min
              When  building  for  iPhone OS, specify the minimum version sup-
              ported 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 opti-
                 mizations.

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

                 -Ofast Enables all the  optimizations  from  -O3  along  with
                 other  aggressive  optimizations that may violate strict com-
                 pliance 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     Generate debug information.  Note that Clang  debug  information
              works best at -O0.

       -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 implies -fmodule-format=obj.

              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  assump-
              tion that the debug type information can be spread out over mul-
              tiple 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 gener-
              ated to detect this and abort when it happens.

       -fvisibility
              This flag sets the default visibility level.

       -fcommon
              This flag specifies that variables without initializers get com-
              mon 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", "lo-
              cal-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 ef-
              ficient model if possible.

       -flto, -emit-llvm
              Generate output files in LLVM formats, suitable  for  link  time
              optimization.   When used with -S this generates LLVM intermedi-
              ate language assembly files, otherwise this generates LLVM  bit-
              code  format object files (which may be passed to the linker de-
              pending 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  inte-
              grated  assembler. Whether the integrated assembler is on by de-
              fault 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,  -fdiagnos-
       tics-fixit-info,       -fdiagnostics-parseable-fixits,       -fdiagnos-
       tics-print-source-range-info,   -fprint-source-range-info,   -fdiagnos-
       tics-show-option, -fmessage-length
              These options control how Clang prints out information about di-
              agnostics (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 in-
              clude 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 loca-
              tion  to  write  temporary  files  used  during  the compilation
              process.

       CPATH  If this environment variable is present, it is treated as a  de-
              limited  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_IN-
       CLUDE_PATH
              These environment variables specify  additional  paths,  as  for
              CPATH,  which are only used when processing the appropriate lan-
              guage.

       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

3.8                              Dec 23, 2017                         CLANG(1)

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