CLANG(1)                             Clang                            CLANG(1)

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

       clang [options] filename

       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.

              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.

              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 analyzer.

   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 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.

              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

              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

              Enable trigraphs.

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

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

              Indicate that math functions should be treated as  updating  er-

              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  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

   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.

              When building for Mac OS X, specify  the  minimum  version  sup-
              ported by your application.

              When  building  for  iPhone OS, specify the minimum version sup-
              ported by your application.

              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-

                 -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 -O2.

                 -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.

              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 gener-
              ated 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 com-
              mon 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", "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-

   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  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.

              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
              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

              Add the specified directory to the search path for framework in-
              clude 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 loca-
              tion to  write  temporary  files  used  during  the  compilation

       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.

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

              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

4                                May 23, 2018                         CLANG(1)

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