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 im‐
16 portant 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, as‐
21 sembler and linker. Typically you do not need to interact with
22 the driver, but you transparently use it to run the other tools.
23 Preprocessing
25 This stage handles tokenization of the input source file, macro
26 expansion, #include expansion and handling of other preprocessor
27 directives. The output of this stage is typically called a ".i"
28 (for C), ".ii" (for C++), ".mi" (for Objective-C), or ".mii"
29 (for Objective-C++) file.
30 Parsing and Semantic Analysis
32 This stage parses the input file, translating preprocessor to‐
33 kens into a parse tree. Once in the form of a parse tree, it
34 applies semantic analysis to compute types for expressions as
35 well and determine whether the code is well formed. This stage
36 is responsible for generating most of the compiler warnings as
37 well as parse errors. The output of this stage is an "Abstract
38 Syntax Tree" (AST).
39 Code Generation and Optimization
41 This stage translates an AST into low-level intermediate code
42 (known as "LLVM IR") and ultimately to machine code. This phase
43 is responsible for optimizing the generated code and handling
44 target-specific code generation. The output of this stage is
45 typically called a ".s" file or "assembly" file.
46 Clang also supports the use of an integrated assembler, in which
48 the code generator produces object files directly. This avoids
49 the overhead of generating the ".s" file and of calling the tar‐
50 get assembler.
51 Assembler
53 This stage runs the target assembler to translate the output of
54 the compiler into a target object file. The output of this stage
55 is typically called a ".o" file or "object" file.
56 Linker This stage runs the target linker to merge multiple object files
58 into an executable or dynamic library. The output of this stage
59 is typically called an "a.out", ".dylib" or ".so" file.
60 Clang Static Analyzer
62 The Clang Static Analyzer is a tool that scans source code to try to
64 find bugs through code analysis. This tool uses many parts of Clang
65 and is built into the same driver. Please see <‐
66 https://clang-analyzer.llvm.org> for more details on how to use the
67 static analyzer.
68
70 Stage Selection Options
71 -E Run the preprocessor stage.
72 -fsyntax-only
74 Run the preprocessor, parser and semantic analysis stages.
75 -S Run the previous stages as well as LLVM generation and optimiza‐
77 tion stages and target-specific code generation, producing an
78 assembly file.
79 -c Run all of the above, plus the assembler, generating a target
81 ".o" object file.
82 no stage selection option
84 If no stage selection option is specified, all stages above are
85 run, and the linker is run to combine the results into an exe‐
86 cutable or shared library.
87 Language Selection and Mode Options
89 -x <language>
90 Treat subsequent input files as having type language.
91 -std=<standard>
93 Specify the language standard to compile for.
94 Supported values for the C language are:
96 c89
97 c90
98 iso9899:1990
99 ISO C 1990
101 iso9899:199409
102 ISO C 1990 with amendment 1
104 gnu89
105 gnu90
106 ISO C 1990 with GNU extensions
108 c99
109 iso9899:1999
110 ISO C 1999
112 gnu99
113 ISO C 1999 with GNU extensions
115 c11
116 iso9899:2011
117 ISO C 2011
119 gnu11
120 ISO C 2011 with GNU extensions
122 c17
123 iso9899:2017
124 ISO C 2017
126 gnu17
127 ISO C 2017 with GNU extensions
129 The default C language standard is gnu17, except on PS4, where
131 it is gnu99.
132 Supported values for the C++ language are:
134 c++98
135 c++03
136 ISO C++ 1998 with amendments
138 gnu++98
139 gnu++03
140 ISO C++ 1998 with amendments and GNU extensions
142 c++11
143 ISO C++ 2011 with amendments
145 gnu++11
146 ISO C++ 2011 with amendments and GNU extensions
148 c++14
149 ISO C++ 2014 with amendments
151 gnu++14
152 ISO C++ 2014 with amendments and GNU extensions
154 c++17
155 ISO C++ 2017 with amendments
157 gnu++17
158 ISO C++ 2017 with amendments and GNU extensions
160 c++20
161 ISO C++ 2020 with amendments
163 gnu++20
164 ISO C++ 2020 with amendments and GNU extensions
166 c++2b
167 Working draft for ISO C++ 2023
169 gnu++2b
170 Working draft for ISO C++ 2023 with GNU extensions
172 The default C++ language standard is gnu++17.
174 Supported values for the OpenCL language are:
176 cl1.0
177 OpenCL 1.0
179 cl1.1
180 OpenCL 1.1
182 cl1.2
183 OpenCL 1.2
185 cl2.0
186 OpenCL 2.0
188 The default OpenCL language standard is cl1.0.
190 Supported values for the CUDA language are:
192 cuda
193 NVIDIA CUDA(tm)
195 -stdlib=<library>
197 Specify the C++ standard library to use; supported options are
198 libstdc++ and libc++. If not specified, platform default will be
199 used.
200 -rtlib=<library>
202 Specify the compiler runtime library to use; supported options
203 are libgcc and compiler-rt. If not specified, platform default
204 will be used.
205 -ansi Same as -std=c89.
207 -ObjC, -ObjC++
209 Treat source input files as Objective-C and Object-C++ inputs
210 respectively.
211 -trigraphs
213 Enable trigraphs.
214 -ffreestanding
216 Indicate that the file should be compiled for a freestanding,
217 not a hosted, environment. Note that it is assumed that a free‐
218 standing environment will additionally provide memcpy, memmove,
219 memset and memcmp implementations, as these are needed for effi‐
220 cient codegen for many programs.
221 -fno-builtin
223 Disable special handling and optimizations of well-known library
224 functions, like strlen() and malloc().
225 -fno-builtin-<function>
227 Disable special handling and optimizations for the specific li‐
228 brary function. For example, -fno-builtin-strlen removes any
229 special handling for the strlen() library function.
230 -fno-builtin-std-<function>
232 Disable special handling and optimizations for the specific C++
233 standard library function in namespace std. For example,
234 -fno-builtin-std-move_if_noexcept removes any special handling
235 for the std::move_if_noexcept() library function.
236 For C standard library functions that the C++ standard library
238 also provides in namespace std, use -fno-builtin-<function> in‐
239 stead.
240 -fmath-errno
242 Indicate that math functions should be treated as updating er‐
243 rno.
244 -fpascal-strings
246 Enable support for Pascal-style strings with "\pfoo".
247 -fms-extensions
249 Enable support for Microsoft extensions.
250 -fmsc-version=
252 Set _MSC_VER. Defaults to 1300 on Windows. Not set otherwise.
253 -fborland-extensions
255 Enable support for Borland extensions.
256 -fwritable-strings
258 Make all string literals default to writable. This disables
259 uniquing of strings and other optimizations.
260 -flax-vector-conversions, -flax-vector-conversions=<kind>,
262 -fno-lax-vector-conversions
263 Allow loose type checking rules for implicit vector conversions.
264 Possible values of <kind>:
265 • none: allow no implicit conversions between vectors
267 • integer: allow implicit bitcasts between integer vectors of
269 the same overall bit-width
270 • all: allow implicit bitcasts between any vectors of the same
272 overall bit-width
273 <kind> defaults to integer if unspecified.
275 -fblocks
277 Enable the "Blocks" language feature.
278 -fobjc-abi-version=version
280 Select the Objective-C ABI version to use. Available versions
281 are 1 (legacy "fragile" ABI), 2 (non-fragile ABI 1), and 3
282 (non-fragile ABI 2).
283 -fobjc-nonfragile-abi-version=<version>
285 Select the Objective-C non-fragile ABI version to use by de‐
286 fault. This will only be used as the Objective-C ABI when the
287 non-fragile ABI is enabled (either via -fobjc-nonfragile-abi, or
288 because it is the platform default).
289 -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
291 Enable use of the Objective-C non-fragile ABI. On platforms for
292 which this is the default ABI, it can be disabled with
293 -fno-objc-nonfragile-abi.
294 Target Selection Options
296 Clang fully supports cross compilation as an inherent part of its de‐
297 sign. Depending on how your version of Clang is configured, it may
298 have support for a number of cross compilers, or may only support a na‐
299 tive target.
300 -arch <architecture>
302 Specify the architecture to build for (Mac OS X specific).
303 -target <architecture>
305 Specify the architecture to build for (all platforms).
306 -mmacosx-version-min=<version>
308 When building for macOS, specify the minimum version supported
309 by your application.
310 -miphoneos-version-min
312 When building for iPhone OS, specify the minimum version sup‐
313 ported by your application.
314 --print-supported-cpus
316 Print out a list of supported processors for the given target
317 (specified through --target=<architecture> or -arch <architec‐
318 ture>). If no target is specified, the system default target
319 will be used.
320 -mcpu=?, -mtune=?
322 Acts as an alias for --print-supported-cpus.
323 -march=<cpu>
325 Specify that Clang should generate code for a specific processor
326 family member and later. For example, if you specify
327 -march=i486, the compiler is allowed to generate instructions
328 that are valid on i486 and later processors, but which may not
329 exist on earlier ones.
330 Code Generation Options
332 -O0, -O1, -O2, -O3, -Ofast, -Os, -Oz, -Og, -O, -O4
333 Specify which optimization level to use:
334 -O0 Means "no optimization": this level compiles the fastest
335 and generates the most debuggable code.
336 -O1 Somewhere between -O0 and -O2.
338 -O2 Moderate level of optimization which enables most opti‐
340 mizations.
341 -O3 Like -O2, except that it enables optimizations that take
343 longer to perform or that may generate larger code (in an at‐
344 tempt to make the program run faster).
345 -Ofast Enables all the optimizations from -O3 along with
347 other aggressive optimizations that may violate strict com‐
348 pliance with language standards.
349 -Os Like -O2 with extra optimizations to reduce code size.
351 -Oz Like -Os (and thus -O2), but reduces code size further.
353 -Og Like -O1. In future versions, this option might disable
355 different optimizations in order to improve debuggability.
356 -O Equivalent to -O1.
358 -O4 and higher
360 Currently equivalent to -O3
361 -g, -gline-tables-only, -gmodules
363 Control debug information output. Note that Clang debug infor‐
364 mation works best at -O0. When more than one option starting
365 with -g is specified, the last one wins:
366 -g Generate debug information.
367 -gline-tables-only Generate only line table debug informa‐
369 tion. This allows for symbolicated backtraces with inlining
370 information, but does not include any information about vari‐
371 ables, their locations or types.
372 -gmodules Generate debug information that contains external
374 references to types defined in Clang modules or precompiled
375 headers instead of emitting redundant debug type information
376 into every object file. This option transparently switches
377 the Clang module format to object file containers that hold
378 the Clang module together with the debug information. When
379 compiling a program that uses Clang modules or precompiled
380 headers, this option produces complete debug information with
381 faster compile times and much smaller object files.
382 This option should not be used when building static libraries
384 for distribution to other machines because the debug info
385 will contain references to the module cache on the machine
386 the object files in the library were built on.
387 -fstandalone-debug -fno-standalone-debug
389 Clang supports a number of optimizations to reduce the size of
390 debug information in the binary. They work based on the assump‐
391 tion that the debug type information can be spread out over mul‐
392 tiple compilation units. For instance, Clang will not emit type
393 definitions for types that are not needed by a module and could
394 be replaced with a forward declaration. Further, Clang will
395 only emit type info for a dynamic C++ class in the module that
396 contains the vtable for the class.
397 The -fstandalone-debug option turns off these optimizations.
399 This is useful when working with 3rd-party libraries that don't
400 come with debug information. This is the default on Darwin.
401 Note that Clang will never emit type information for types that
402 are not referenced at all by the program.
403 -feliminate-unused-debug-types
405 By default, Clang does not emit type information for types that
406 are defined but not used in a program. To retain the debug info
407 for these unused types, the negation -fno-eliminate-unused-de‐
408 bug-types can be used.
409 -fexceptions
411 Enable generation of unwind information. This allows exceptions
412 to be thrown through Clang compiled stack frames. This is on by
413 default in x86-64.
414 -ftrapv
416 Generate code to catch integer overflow errors. Signed integer
417 overflow is undefined in C. With this flag, extra code is gener‐
418 ated to detect this and abort when it happens.
419 -fvisibility
421 This flag sets the default visibility level.
422 -fcommon, -fno-common
424 This flag specifies that variables without initializers get com‐
425 mon linkage. It can be disabled with -fno-common.
426 -ftls-model=<model>
428 Set the default thread-local storage (TLS) model to use for
429 thread-local variables. Valid values are: "global-dynamic", "lo‐
430 cal-dynamic", "initial-exec" and "local-exec". The default is
431 "global-dynamic". The default model can be overridden with the
432 tls_model attribute. The compiler will try to choose a more ef‐
433 ficient model if possible.
434 -flto, -flto=full, -flto=thin, -emit-llvm
436 Generate output files in LLVM formats, suitable for link time
437 optimization. When used with -S this generates LLVM intermedi‐
438 ate language assembly files, otherwise this generates LLVM bit‐
439 code format object files (which may be passed to the linker de‐
440 pending on the stage selection options).
441 The default for -flto is "full", in which the LLVM bitcode is
443 suitable for monolithic Link Time Optimization (LTO), where the
444 linker merges all such modules into a single combined module for
445 optimization. With "thin", ThinLTO compilation is invoked in‐
446 stead.
447 NOTE:
449 On Darwin, when using -flto along with -g and compiling and
450 linking in separate steps, you also need to pass -Wl,-ob‐
451 ject_path_lto,<lto-filename>.o at the linking step to in‐
452 struct the ld64 linker not to delete the temporary object
453 file generated during Link Time Optimization (this flag is
454 automatically passed to the linker by Clang if compilation
455 and linking are done in a single step). This allows debugging
456 the executable as well as generating the .dSYM bundle using
457 dsymutil(1).
458 Driver Options
460 -### Print (but do not run) the commands to run for this compilation.
461 --help Display available options.
463 -Qunused-arguments
465 Do not emit any warnings for unused driver arguments.
466 -Wa,<args>
468 Pass the comma separated arguments in args to the assembler.
469 -Wl,<args>
471 Pass the comma separated arguments in args to the linker.
472 -Wp,<args>
474 Pass the comma separated arguments in args to the preprocessor.
475 -Xanalyzer <arg>
477 Pass arg to the static analyzer.
478 -Xassembler <arg>
480 Pass arg to the assembler.
481 -Xlinker <arg>
483 Pass arg to the linker.
484 -Xpreprocessor <arg>
486 Pass arg to the preprocessor.
487 -o <file>
489 Write output to file.
490 -print-file-name=<file>
492 Print the full library path of file.
493 -print-libgcc-file-name
495 Print the library path for the currently used compiler runtime
496 library ("libgcc.a" or "libclang_rt.builtins.*.a").
497 -print-prog-name=<name>
499 Print the full program path of name.
500 -print-search-dirs
502 Print the paths used for finding libraries and programs.
503 -save-temps
505 Save intermediate compilation results.
506 -save-stats, -save-stats=cwd, -save-stats=obj
508 Save internal code generation (LLVM) statistics to a file in the
509 current directory (-save-stats/"-save-stats=cwd") or the direc‐
510 tory of the output file ("-save-state=obj").
511 -integrated-as, -no-integrated-as
513 Used to enable and disable, respectively, the use of the inte‐
514 grated assembler. Whether the integrated assembler is on by de‐
515 fault is target dependent.
516 -time Time individual commands.
518 -ftime-report
520 Print timing summary of each stage of compilation.
521 -v Show commands to run and use verbose output.
523 Diagnostics Options
525 -fshow-column, -fshow-source-location, -fcaret-diagnostics, -fdiagnos‐
526 tics-fixit-info, -fdiagnostics-parseable-fixits, -fdiagnos‐
527 tics-print-source-range-info, -fprint-source-range-info, -fdiagnos‐
528 tics-show-option, -fmessage-length
529 These options control how Clang prints out information about di‐
530 agnostics (errors and warnings). Please see the Clang User's
531 Manual for more information.
532 Preprocessor Options
534 -D<macroname>=<value>
535 Adds an implicit #define into the predefines buffer which is
536 read before the source file is preprocessed.
537 -U<macroname>
539 Adds an implicit #undef into the predefines buffer which is read
540 before the source file is preprocessed.
541 -include <filename>
543 Adds an implicit #include into the predefines buffer which is
544 read before the source file is preprocessed.
545 -I<directory>
547 Add the specified directory to the search path for include
548 files.
549 -F<directory>
551 Add the specified directory to the search path for framework in‐
552 clude files.
553 -nostdinc
555 Do not search the standard system directories or compiler
556 builtin directories for include files.
557 -nostdlibinc
559 Do not search the standard system directories for include files,
560 but do search compiler builtin include directories.
561 -nobuiltininc
563 Do not search clang's builtin directory for include files.
564
566 TMPDIR, TEMP, TMP
567 These environment variables are checked, in order, for the loca‐
568 tion to write temporary files used during the compilation
569 process.
570 CPATH If this environment variable is present, it is treated as a de‐
572 limited list of paths to be added to the default system include
573 path list. The delimiter is the platform dependent delimiter, as
574 used in the PATH environment variable.
575 Empty components in the environment variable are ignored.
577 C_INCLUDE_PATH, OBJC_INCLUDE_PATH, CPLUS_INCLUDE_PATH, OBJCPLUS_IN‐
579 CLUDE_PATH
580 These environment variables specify additional paths, as for
581 CPATH, which are only used when processing the appropriate lan‐
582 guage.
583 MACOSX_DEPLOYMENT_TARGET
585 If -mmacosx-version-min is unspecified, the default deployment
586 target is read from this environment variable. This option only
587 affects Darwin targets.
588
590 To report bugs, please visit <‐
591 https://github.com/llvm/llvm-project/issues/>. Most bug reports should
592 include preprocessed source files (use the -E option) and the full out‐
593 put of the compiler, along with information to reproduce.
594
596 as(1), ld(1)
597
599 Maintained by the Clang / LLVM Team (<http://clang.llvm.org>)
600
602 2007-2023, The Clang Team
60316 Aug 24, 2023 CLANG(1)