1CLANG(1) Clang CLANG(1)
2
6 clang - the Clang C, C++, and Objective-C compiler
7
9 clang [options] filename ...
10
12 clang is a C, C++, and Objective-C compiler which encompasses prepro‐
13 cessing, parsing, optimization, code generation, assembly, and linking.
14 Depending on which high-level mode setting is passed, Clang will stop
15 before doing a full link. While Clang is highly integrated, it is
16 important to understand the stages of compilation, to understand how to
17 invoke it. These stages are:
18 Driver The clang executable is actually a small driver which controls
20 the overall execution of other tools such as the compiler,
21 assembler and linker. Typically you do not need to interact
22 with the driver, but you transparently use it to run the other
23 tools.
24 Preprocessing
26 This stage handles tokenization of the input source file, macro
27 expansion, #include expansion and handling of other preprocessor
28 directives. The output of this stage is typically called a ".i"
29 (for C), ".ii" (for C++), ".mi" (for Objective-C), or ".mii"
30 (for Objective-C++) file.
31 Parsing and Semantic Analysis
33 This stage parses the input file, translating preprocessor
34 tokens into a parse tree. Once in the form of a parse tree, it
35 applies semantic analysis to compute types for expressions as
36 well and determine whether the code is well formed. This stage
37 is responsible for generating most of the compiler warnings as
38 well as parse errors. The output of this stage is an "Abstract
39 Syntax Tree" (AST).
40 Code Generation and Optimization
42 This stage translates an AST into low-level intermediate code
43 (known as "LLVM IR") and ultimately to machine code. This phase
44 is responsible for optimizing the generated code and handling
45 target-specific code generation. The output of this stage is
46 typically called a ".s" file or "assembly" file.
47 Clang also supports the use of an integrated assembler, in which
49 the code generator produces object files directly. This avoids
50 the overhead of generating the ".s" file and of calling the tar‐
51 get assembler.
52 Assembler
54 This stage runs the target assembler to translate the output of
55 the compiler into a target object file. The output of this stage
56 is typically called a ".o" file or "object" file.
57 Linker This stage runs the target linker to merge multiple object files
59 into an executable or dynamic library. The output of this stage
60 is typically called an "a.out", ".dylib" or ".so" file.
61 Clang Static Analyzer
63 The Clang Static Analyzer is a tool that scans source code to try to
65 find bugs through code analysis. This tool uses many parts of Clang
66 and is built into the same driver. Please see <‐
67 https://clang-analyzer.llvm.org> for more details on how to use the
68 static analyzer.
69
71 Stage Selection Options
72 -E Run the preprocessor stage.
73 -fsyntax-only
75 Run the preprocessor, parser and type checking stages.
76 -S Run the previous stages as well as LLVM generation and optimiza‐
78 tion stages and target-specific code generation, producing an
79 assembly file.
80 -c Run all of the above, plus the assembler, generating a target
82 ".o" object file.
83 no stage selection option
85 If no stage selection option is specified, all stages above are
86 run, and the linker is run to combine the results into an exe‐
87 cutable or shared library.
88 Language Selection and Mode Options
90 -x <language>
91 Treat subsequent input files as having type language.
92 -std=<standard>
94 Specify the language standard to compile for.
95 Supported values for the C language are:
97 c89
98 c90
99 iso9899:1990
100 ISO C 1990
102 iso9899:199409
103 ISO C 1990 with amendment 1
105 gnu89
106 gnu90
107 ISO C 1990 with GNU extensions
109 c99
110 iso9899:1999
111 ISO C 1999
113 gnu99
114 ISO C 1999 with GNU extensions
116 c11
117 iso9899:2011
118 ISO C 2011
120 gnu11
121 ISO C 2011 with GNU extensions
123 c17
124 iso9899:2017
125 ISO C 2017
127 gnu17
128 ISO C 2017 with GNU extensions
130 The default C language standard is gnu11, except on PS4, where
132 it is gnu99.
133 Supported values for the C++ language are:
135 c++98
136 c++03
137 ISO C++ 1998 with amendments
139 gnu++98
140 gnu++03
141 ISO C++ 1998 with amendments and GNU extensions
143 c++11
144 ISO C++ 2011 with amendments
146 gnu++11
147 ISO C++ 2011 with amendments and GNU extensions
149 c++14
150 ISO C++ 2014 with amendments
152 gnu++14
153 ISO C++ 2014 with amendments and GNU extensions
155 c++17
156 ISO C++ 2017 with amendments
158 gnu++17
159 ISO C++ 2017 with amendments and GNU extensions
161 c++2a
162 Working draft for ISO C++ 2020
164 gnu++2a
165 Working draft for ISO C++ 2020 with GNU extensions
167 The default C++ language standard is gnu++14.
169 Supported values for the OpenCL language are:
171 cl1.0
172 OpenCL 1.0
174 cl1.1
175 OpenCL 1.1
177 cl1.2
178 OpenCL 1.2
180 cl2.0
181 OpenCL 2.0
183 The default OpenCL language standard is cl1.0.
185 Supported values for the CUDA language are:
187 cuda
188 NVIDIA CUDA(tm)
190 -stdlib=<library>
192 Specify the C++ standard library to use; supported options are
193 libstdc++ and libc++. If not specified, platform default will be
194 used.
195 -rtlib=<library>
197 Specify the compiler runtime library to use; supported options
198 are libgcc and compiler-rt. If not specified, platform default
199 will be used.
200 -ansi Same as -std=c89.
202 -ObjC, -ObjC++
204 Treat source input files as Objective-C and Object-C++ inputs
205 respectively.
206 -trigraphs
208 Enable trigraphs.
209 -ffreestanding
211 Indicate that the file should be compiled for a freestanding,
212 not a hosted, environment.
213 -fno-builtin
215 Disable special handling and optimizations of builtin functions
216 like strlen() and malloc().
217 -fmath-errno
219 Indicate that math functions should be treated as updating
220 errno.
221 -fpascal-strings
223 Enable support for Pascal-style strings with "\pfoo".
224 -fms-extensions
226 Enable support for Microsoft extensions.
227 -fmsc-version=
229 Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.
230 -fborland-extensions
232 Enable support for Borland extensions.
233 -fwritable-strings
235 Make all string literals default to writable. This disables
236 uniquing of strings and other optimizations.
237 -flax-vector-conversions
239 Allow loose type checking rules for implicit vector conversions.
240 -fblocks
242 Enable the "Blocks" language feature.
243 -fobjc-abi-version=version
245 Select the Objective-C ABI version to use. Available versions
246 are 1 (legacy "fragile" ABI), 2 (non-fragile ABI 1), and 3
247 (non-fragile ABI 2).
248 -fobjc-nonfragile-abi-version=<version>
250 Select the Objective-C non-fragile ABI version to use by
251 default. This will only be used as the Objective-C ABI when the
252 non-fragile ABI is enabled (either via -fobjc-nonfragile-abi, or
253 because it is the platform default).
254 -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
256 Enable use of the Objective-C non-fragile ABI. On platforms for
257 which this is the default ABI, it can be disabled with
258 -fno-objc-nonfragile-abi.
259 Target Selection Options
261 Clang fully supports cross compilation as an inherent part of its
262 design. Depending on how your version of Clang is configured, it may
263 have support for a number of cross compilers, or may only support a
264 native target.
265 -arch <architecture>
267 Specify the architecture to build for.
268 -mmacosx-version-min=<version>
270 When building for macOS, specify the minimum version supported
271 by your application.
272 -miphoneos-version-min
274 When building for iPhone OS, specify the minimum version sup‐
275 ported by your application.
276 --print-supported-cpus
278 Print out a list of supported processors for the given target
279 (specified through --target=<architecture> or -arch <architec‐
280 ture>). If no target is specified, the system default target
281 will be used.
282 -mcpu=?, -mtune=?
284 Aliases of --print-supported-cpus
285 -march=<cpu>
287 Specify that Clang should generate code for a specific processor
288 family member and later. For example, if you specify
289 -march=i486, the compiler is allowed to generate instructions
290 that are valid on i486 and later processors, but which may not
291 exist on earlier ones.
292 Code Generation Options
294 -O0, -O1, -O2, -O3, -Ofast, -Os, -Oz, -Og, -O, -O4
295 Specify which optimization level to use:
296 -O0 Means "no optimization": this level compiles the fastest
297 and generates the most debuggable code.
298 -O1 Somewhere between -O0 and -O2.
300 -O2 Moderate level of optimization which enables most opti‐
302 mizations.
303 -O3 Like -O2, except that it enables optimizations that take
305 longer to perform or that may generate larger code (in an
306 attempt to make the program run faster).
307 -Ofast Enables all the optimizations from -O3 along with
309 other aggressive optimizations that may violate strict com‐
310 pliance with language standards.
311 -Os Like -O2 with extra optimizations to reduce code size.
313 -Oz Like -Os (and thus -O2), but reduces code size further.
315 -Og Like -O1. In future versions, this option might disable
317 different optimizations in order to improve debuggability.
318 -O Equivalent to -O2.
320 -O4 and higher
322 Currently equivalent to -O3
323 -g, -gline-tables-only, -gmodules
325 Control debug information output. Note that Clang debug infor‐
326 mation works best at -O0. When more than one option starting
327 with -g is specified, the last one wins:
328 -g Generate debug information.
329 -gline-tables-only Generate only line table debug informa‐
331 tion. This allows for symbolicated backtraces with inlining
332 information, but does not include any information about vari‐
333 ables, their locations or types.
334 -gmodules Generate debug information that contains external
336 references to types defined in Clang modules or precompiled
337 headers instead of emitting redundant debug type information
338 into every object file. This option transparently switches
339 the Clang module format to object file containers that hold
340 the Clang module together with the debug information. When
341 compiling a program that uses Clang modules or precompiled
342 headers, this option produces complete debug information with
343 faster compile times and much smaller object files.
344 This option should not be used when building static libraries
346 for distribution to other machines because the debug info
347 will contain references to the module cache on the machine
348 the object files in the library were built on.
349 -fstandalone-debug -fno-standalone-debug
351 Clang supports a number of optimizations to reduce the size of
352 debug information in the binary. They work based on the assump‐
353 tion that the debug type information can be spread out over mul‐
354 tiple compilation units. For instance, Clang will not emit type
355 definitions for types that are not needed by a module and could
356 be replaced with a forward declaration. Further, Clang will
357 only emit type info for a dynamic C++ class in the module that
358 contains the vtable for the class.
359 The -fstandalone-debug option turns off these optimizations.
361 This is useful when working with 3rd-party libraries that don't
362 come with debug information. This is the default on Darwin.
363 Note that Clang will never emit type information for types that
364 are not referenced at all by the program.
365 -fexceptions
367 Enable generation of unwind information. This allows exceptions
368 to be thrown through Clang compiled stack frames. This is on by
369 default in x86-64.
370 -ftrapv
372 Generate code to catch integer overflow errors. Signed integer
373 overflow is undefined in C. With this flag, extra code is gener‐
374 ated to detect this and abort when it happens.
375 -fvisibility
377 This flag sets the default visibility level.
378 -fcommon, -fno-common
380 This flag specifies that variables without initializers get com‐
381 mon linkage. It can be disabled with -fno-common.
382 -ftls-model=<model>
384 Set the default thread-local storage (TLS) model to use for
385 thread-local variables. Valid values are: "global-dynamic",
386 "local-dynamic", "initial-exec" and "local-exec". The default is
387 "global-dynamic". The default model can be overridden with the
388 tls_model attribute. The compiler will try to choose a more
389 efficient model if possible.
390 -flto, -flto=full, -flto=thin, -emit-llvm
392 Generate output files in LLVM formats, suitable for link time
393 optimization. When used with -S this generates LLVM intermedi‐
394 ate language assembly files, otherwise this generates LLVM bit‐
395 code format object files (which may be passed to the linker
396 depending on the stage selection options).
397 The default for -flto is "full", in which the LLVM bitcode is
399 suitable for monolithic Link Time Optimization (LTO), where the
400 linker merges all such modules into a single combined module for
401 optimization. With "thin", ThinLTO compilation is invoked
402 instead.
403 Driver Options
405 -### Print (but do not run) the commands to run for this compilation.
406 --help Display available options.
408 -Qunused-arguments
410 Do not emit any warnings for unused driver arguments.
411 -Wa,<args>
413 Pass the comma separated arguments in args to the assembler.
414 -Wl,<args>
416 Pass the comma separated arguments in args to the linker.
417 -Wp,<args>
419 Pass the comma separated arguments in args to the preprocessor.
420 -Xanalyzer <arg>
422 Pass arg to the static analyzer.
423 -Xassembler <arg>
425 Pass arg to the assembler.
426 -Xlinker <arg>
428 Pass arg to the linker.
429 -Xpreprocessor <arg>
431 Pass arg to the preprocessor.
432 -o <file>
434 Write output to file.
435 -print-file-name=<file>
437 Print the full library path of file.
438 -print-libgcc-file-name
440 Print the library path for the currently used compiler runtime
441 library ("libgcc.a" or "libclang_rt.builtins.*.a").
442 -print-prog-name=<name>
444 Print the full program path of name.
445 -print-search-dirs
447 Print the paths used for finding libraries and programs.
448 -save-temps
450 Save intermediate compilation results.
451 -save-stats, -save-stats=cwd, -save-stats=obj
453 Save internal code generation (LLVM) statistics to a file in the
454 current directory (-save-stats/"-save-stats=cwd") or the direc‐
455 tory of the output file ("-save-state=obj").
456 -integrated-as, -no-integrated-as
458 Used to enable and disable, respectively, the use of the inte‐
459 grated assembler. Whether the integrated assembler is on by
460 default is target dependent.
461 -time Time individual commands.
463 -ftime-report
465 Print timing summary of each stage of compilation.
466 -v Show commands to run and use verbose output.
468 Diagnostics Options
470 -fshow-column, -fshow-source-location, -fcaret-diagnostics, -fdiagnos‐
471 tics-fixit-info, -fdiagnostics-parseable-fixits, -fdiagnos‐
472 tics-print-source-range-info, -fprint-source-range-info, -fdiagnos‐
473 tics-show-option, -fmessage-length
474 These options control how Clang prints out information about
475 diagnostics (errors and warnings). Please see the Clang User's
476 Manual for more information.
477 Preprocessor Options
479 -D<macroname>=<value>
480 Adds an implicit #define into the predefines buffer which is
481 read before the source file is preprocessed.
482 -U<macroname>
484 Adds an implicit #undef into the predefines buffer which is read
485 before the source file is preprocessed.
486 -include <filename>
488 Adds an implicit #include into the predefines buffer which is
489 read before the source file is preprocessed.
490 -I<directory>
492 Add the specified directory to the search path for include
493 files.
494 -F<directory>
496 Add the specified directory to the search path for framework
497 include files.
498 -nostdinc
500 Do not search the standard system directories or compiler
501 builtin directories for include files.
502 -nostdlibinc
504 Do not search the standard system directories for include files,
505 but do search compiler builtin include directories.
506 -nobuiltininc
508 Do not search clang's builtin directory for include files.
509
511 TMPDIR, TEMP, TMP
512 These environment variables are checked, in order, for the loca‐
513 tion to write temporary files used during the compilation
514 process.
515 CPATH If this environment variable is present, it is treated as a
517 delimited list of paths to be added to the default system
518 include path list. The delimiter is the platform dependent
519 delimiter, as used in the PATH environment variable.
520 Empty components in the environment variable are ignored.
522 C_INCLUDE_PATH, OBJC_INCLUDE_PATH, CPLUS_INCLUDE_PATH, OBJC‐
524 PLUS_INCLUDE_PATH
525 These environment variables specify additional paths, as for
526 CPATH, which are only used when processing the appropriate lan‐
527 guage.
528 MACOSX_DEPLOYMENT_TARGET
530 If -mmacosx-version-min is unspecified, the default deployment
531 target is read from this environment variable. This option only
532 affects Darwin targets.
533
535 To report bugs, please visit <https://bugs.llvm.org/>. Most bug
536 reports should include preprocessed source files (use the -E option)
537 and the full output of the compiler, along with information to repro‐
538 duce.
539
541 as(1), ld(1)
542
544 Maintained by the Clang / LLVM Team (<http://clang.llvm.org>)
545
547 2007-2019, The Clang Team
5489 Sep 19, 2019 CLANG(1)