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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    <-
       https://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=<standard>
              Specify the language standard to compile for.

              Supported values for the C language are:
                 c89
                 c90
                 iso9899:1990

                     ISO C 1990
                 iso9899:199409

                     ISO C 1990 with amendment 1
                 gnu89
                 gnu90

                     ISO C 1990 with GNU extensions
                 c99
                 iso9899:1999

                     ISO C 1999
                 gnu99

                     ISO C 1999 with GNU extensions
                 c11
                 iso9899:2011

                     ISO C 2011
                 gnu11

                     ISO C 2011 with GNU extensions
                 c17
                 iso9899:2017

                     ISO C 2017
                 gnu17

                     ISO C 2017 with GNU extensions

              The  default  C language standard is gnu17, except on PS4, where
              it is gnu99.

              Supported values for the C++ language are:
                 c++98
                 c++03

                     ISO C++ 1998 with amendments
                 gnu++98
                 gnu++03

                     ISO C++ 1998 with amendments and GNU extensions
                 c++11

                     ISO C++ 2011 with amendments
                 gnu++11

                     ISO C++ 2011 with amendments and GNU extensions
                 c++14

                     ISO C++ 2014 with amendments
                 gnu++14

                     ISO C++ 2014 with amendments and GNU extensions
                 c++17

                     ISO C++ 2017 with amendments
                 gnu++17

                     ISO C++ 2017 with amendments and GNU extensions
                 c++2a

                     Working draft for ISO C++ 2020
                 gnu++2a

                     Working draft for ISO C++ 2020 with GNU extensions

              The default C++ language standard is gnu++14.

              Supported values for the OpenCL language are:
                 cl1.0

                     OpenCL 1.0
                 cl1.1

                     OpenCL 1.1
                 cl1.2

                     OpenCL 1.2
                 cl2.0

                     OpenCL 2.0

              The default OpenCL language standard is cl1.0.

              Supported values for the CUDA language are:
                 cuda

                     NVIDIA CUDA(tm)

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

       -rtlib=<library>
              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.

       -trigraphs
              Enable trigraphs.

       -ffreestanding
              Indicate  that  the  file should be compiled for a freestanding,
              not a hosted, environment. Note that it is assumed that a  free-
              standing  environment will additionally provide memcpy, memmove,
              memset and memcmp implementations, as these are needed for effi-
              cient codegen for many programs.

       -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,              -flax-vector-conversions=<kind>,
       -fno-lax-vector-conversions
              Allow loose type checking rules for implicit vector conversions.
              Possible values of <kind>:

              • none: allow no implicit conversions between vectors

              • integer: allow implicit bitcasts between  integer  vectors  of
                the same overall bit-width

              • all:  allow  implicit bitcasts between any vectors of the same
                overall bit-width

              <kind> defaults to integer if unspecified.

       -fblocks
              Enable the “Blocks” language feature.

       -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, -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 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.

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

       --print-supported-cpus
              Print out a list of supported processors for  the  given  target
              (specified  through  --target=<architecture> or -arch <architec-
              ture>). If no target is specified,  the  system  default  target
              will be used.

       -mcpu=?, -mtune=?
              Acts as an alias for --print-supported-cpus.

       -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, -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  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.

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

                 -O Equivalent to -O1.

                 -O4 and higher
                     Currently equivalent to -O3

       -g, -gline-tables-only, -gmodules
              Control debug information output.  Note that Clang debug  infor-
              mation  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  informa-
                 tion.  This  allows for symbolicated backtraces with inlining
                 information, but does not include any information about vari-
                 ables, 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 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.

       -feliminate-unused-debug-types
              By  default, Clang does not emit type information for types that
              are defined but not used in a program. To retain the debug  info
              for  these  unused types, the negation -fno-eliminate-unused-de-
              bug-types can be used.

       -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, -fno-common
              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, -flto=full, -flto=thin, -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).

              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 in-
              stead.

              NOTE:
                 On Darwin, when using -flto along with -g and  compiling  and
                 linking  in  separate  steps,  you also need to pass -Wl,-ob-
                 ject_path_lto,<lto-filename>.o at the  linking  step  to  in-
                 struct  the  ld64  linker  not to delete the temporary object
                 file generated during Link Time Optimization  (this  flag  is
                 automatically  passed  to  the linker by Clang if compilation
                 and linking are done in a single step). This allows debugging
                 the  executable  as well as generating the .dSYM bundle using
                 dsymutil(1).

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

       -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  direc-
              tory of the output file (“-save-state=obj”).

       -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.

BUGS
       To         report         bugs,         please         visit         <-
       https://github.com/llvm/llvm-project/issues/>.  Most bug reports should
       include preprocessed source files (use the -E option) and the full out-
       put 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
       2007-2023, The Clang Team

14                               Feb 17, 2023                         CLANG(1)

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