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, -flax-vector-conversions=<kind>,
239 -fno-lax-vector-conversions
240 Allow loose type checking rules for implicit vector conversions.
241 Possible values of <kind>:
242 · none: allow no implicit conversions between vectors
244 · integer: allow implicit bitcasts between integer vectors of
246 the same overall bit-width
247 · all: allow implicit bitcasts between any vectors of the same
249 overall bit-width
250 <kind> defaults to integer if unspecified.
252 -fblocks
254 Enable the "Blocks" language feature.
255 -fobjc-abi-version=version
257 Select the Objective-C ABI version to use. Available versions
258 are 1 (legacy "fragile" ABI), 2 (non-fragile ABI 1), and 3
259 (non-fragile ABI 2).
260 -fobjc-nonfragile-abi-version=<version>
262 Select the Objective-C non-fragile ABI version to use by
263 default. This will only be used as the Objective-C ABI when the
264 non-fragile ABI is enabled (either via -fobjc-nonfragile-abi, or
265 because it is the platform default).
266 -fobjc-nonfragile-abi, -fno-objc-nonfragile-abi
268 Enable use of the Objective-C non-fragile ABI. On platforms for
269 which this is the default ABI, it can be disabled with
270 -fno-objc-nonfragile-abi.
271 Target Selection Options
273 Clang fully supports cross compilation as an inherent part of its
274 design. Depending on how your version of Clang is configured, it may
275 have support for a number of cross compilers, or may only support a
276 native target.
277 -arch <architecture>
279 Specify the architecture to build for.
280 -mmacosx-version-min=<version>
282 When building for macOS, specify the minimum version supported
283 by your application.
284 -miphoneos-version-min
286 When building for iPhone OS, specify the minimum version sup‐
287 ported by your application.
288 --print-supported-cpus
290 Print out a list of supported processors for the given target
291 (specified through --target=<architecture> or -arch <architec‐
292 ture>). If no target is specified, the system default target
293 will be used.
294 -mcpu=?, -mtune=?
296 Aliases of --print-supported-cpus
297 -march=<cpu>
299 Specify that Clang should generate code for a specific processor
300 family member and later. For example, if you specify
301 -march=i486, the compiler is allowed to generate instructions
302 that are valid on i486 and later processors, but which may not
303 exist on earlier ones.
304 Code Generation Options
306 -O0, -O1, -O2, -O3, -Ofast, -Os, -Oz, -Og, -O, -O4
307 Specify which optimization level to use:
308 -O0 Means "no optimization": this level compiles the fastest
309 and generates the most debuggable code.
310 -O1 Somewhere between -O0 and -O2.
312 -O2 Moderate level of optimization which enables most opti‐
314 mizations.
315 -O3 Like -O2, except that it enables optimizations that take
317 longer to perform or that may generate larger code (in an
318 attempt to make the program run faster).
319 -Ofast Enables all the optimizations from -O3 along with
321 other aggressive optimizations that may violate strict com‐
322 pliance with language standards.
323 -Os Like -O2 with extra optimizations to reduce code size.
325 -Oz Like -Os (and thus -O2), but reduces code size further.
327 -Og Like -O1. In future versions, this option might disable
329 different optimizations in order to improve debuggability.
330 -O Equivalent to -O2.
332 -O4 and higher
334 Currently equivalent to -O3
335 -g, -gline-tables-only, -gmodules
337 Control debug information output. Note that Clang debug infor‐
338 mation works best at -O0. When more than one option starting
339 with -g is specified, the last one wins:
340 -g Generate debug information.
341 -gline-tables-only Generate only line table debug informa‐
343 tion. This allows for symbolicated backtraces with inlining
344 information, but does not include any information about vari‐
345 ables, their locations or types.
346 -gmodules Generate debug information that contains external
348 references to types defined in Clang modules or precompiled
349 headers instead of emitting redundant debug type information
350 into every object file. This option transparently switches
351 the Clang module format to object file containers that hold
352 the Clang module together with the debug information. When
353 compiling a program that uses Clang modules or precompiled
354 headers, this option produces complete debug information with
355 faster compile times and much smaller object files.
356 This option should not be used when building static libraries
358 for distribution to other machines because the debug info
359 will contain references to the module cache on the machine
360 the object files in the library were built on.
361 -fstandalone-debug -fno-standalone-debug
363 Clang supports a number of optimizations to reduce the size of
364 debug information in the binary. They work based on the assump‐
365 tion that the debug type information can be spread out over mul‐
366 tiple compilation units. For instance, Clang will not emit type
367 definitions for types that are not needed by a module and could
368 be replaced with a forward declaration. Further, Clang will
369 only emit type info for a dynamic C++ class in the module that
370 contains the vtable for the class.
371 The -fstandalone-debug option turns off these optimizations.
373 This is useful when working with 3rd-party libraries that don't
374 come with debug information. This is the default on Darwin.
375 Note that Clang will never emit type information for types that
376 are not referenced at all by the program.
377 -fexceptions
379 Enable generation of unwind information. This allows exceptions
380 to be thrown through Clang compiled stack frames. This is on by
381 default in x86-64.
382 -ftrapv
384 Generate code to catch integer overflow errors. Signed integer
385 overflow is undefined in C. With this flag, extra code is gener‐
386 ated to detect this and abort when it happens.
387 -fvisibility
389 This flag sets the default visibility level.
390 -fcommon, -fno-common
392 This flag specifies that variables without initializers get com‐
393 mon linkage. It can be disabled with -fno-common.
394 -ftls-model=<model>
396 Set the default thread-local storage (TLS) model to use for
397 thread-local variables. Valid values are: "global-dynamic",
398 "local-dynamic", "initial-exec" and "local-exec". The default is
399 "global-dynamic". The default model can be overridden with the
400 tls_model attribute. The compiler will try to choose a more
401 efficient model if possible.
402 -flto, -flto=full, -flto=thin, -emit-llvm
404 Generate output files in LLVM formats, suitable for link time
405 optimization. When used with -S this generates LLVM intermedi‐
406 ate language assembly files, otherwise this generates LLVM bit‐
407 code format object files (which may be passed to the linker
408 depending on the stage selection options).
409 The default for -flto is "full", in which the LLVM bitcode is
411 suitable for monolithic Link Time Optimization (LTO), where the
412 linker merges all such modules into a single combined module for
413 optimization. With "thin", ThinLTO compilation is invoked
414 instead.
415 Driver Options
417 -### Print (but do not run) the commands to run for this compilation.
418 --help Display available options.
420 -Qunused-arguments
422 Do not emit any warnings for unused driver arguments.
423 -Wa,<args>
425 Pass the comma separated arguments in args to the assembler.
426 -Wl,<args>
428 Pass the comma separated arguments in args to the linker.
429 -Wp,<args>
431 Pass the comma separated arguments in args to the preprocessor.
432 -Xanalyzer <arg>
434 Pass arg to the static analyzer.
435 -Xassembler <arg>
437 Pass arg to the assembler.
438 -Xlinker <arg>
440 Pass arg to the linker.
441 -Xpreprocessor <arg>
443 Pass arg to the preprocessor.
444 -o <file>
446 Write output to file.
447 -print-file-name=<file>
449 Print the full library path of file.
450 -print-libgcc-file-name
452 Print the library path for the currently used compiler runtime
453 library ("libgcc.a" or "libclang_rt.builtins.*.a").
454 -print-prog-name=<name>
456 Print the full program path of name.
457 -print-search-dirs
459 Print the paths used for finding libraries and programs.
460 -save-temps
462 Save intermediate compilation results.
463 -save-stats, -save-stats=cwd, -save-stats=obj
465 Save internal code generation (LLVM) statistics to a file in the
466 current directory (-save-stats/"-save-stats=cwd") or the direc‐
467 tory of the output file ("-save-state=obj").
468 -integrated-as, -no-integrated-as
470 Used to enable and disable, respectively, the use of the inte‐
471 grated assembler. Whether the integrated assembler is on by
472 default is target dependent.
473 -time Time individual commands.
475 -ftime-report
477 Print timing summary of each stage of compilation.
478 -v Show commands to run and use verbose output.
480 Diagnostics Options
482 -fshow-column, -fshow-source-location, -fcaret-diagnostics, -fdiagnos‐
483 tics-fixit-info, -fdiagnostics-parseable-fixits, -fdiagnos‐
484 tics-print-source-range-info, -fprint-source-range-info, -fdiagnos‐
485 tics-show-option, -fmessage-length
486 These options control how Clang prints out information about
487 diagnostics (errors and warnings). Please see the Clang User's
488 Manual for more information.
489 Preprocessor Options
491 -D<macroname>=<value>
492 Adds an implicit #define into the predefines buffer which is
493 read before the source file is preprocessed.
494 -U<macroname>
496 Adds an implicit #undef into the predefines buffer which is read
497 before the source file is preprocessed.
498 -include <filename>
500 Adds an implicit #include into the predefines buffer which is
501 read before the source file is preprocessed.
502 -I<directory>
504 Add the specified directory to the search path for include
505 files.
506 -F<directory>
508 Add the specified directory to the search path for framework
509 include files.
510 -nostdinc
512 Do not search the standard system directories or compiler
513 builtin directories for include files.
514 -nostdlibinc
516 Do not search the standard system directories for include files,
517 but do search compiler builtin include directories.
518 -nobuiltininc
520 Do not search clang's builtin directory for include files.
521
523 TMPDIR, TEMP, TMP
524 These environment variables are checked, in order, for the loca‐
525 tion to write temporary files used during the compilation
526 process.
527 CPATH If this environment variable is present, it is treated as a
529 delimited list of paths to be added to the default system
530 include path list. The delimiter is the platform dependent
531 delimiter, as used in the PATH environment variable.
532 Empty components in the environment variable are ignored.
534 C_INCLUDE_PATH, OBJC_INCLUDE_PATH, CPLUS_INCLUDE_PATH, OBJC‐
536 PLUS_INCLUDE_PATH
537 These environment variables specify additional paths, as for
538 CPATH, which are only used when processing the appropriate lan‐
539 guage.
540 MACOSX_DEPLOYMENT_TARGET
542 If -mmacosx-version-min is unspecified, the default deployment
543 target is read from this environment variable. This option only
544 affects Darwin targets.
545
547 To report bugs, please visit <https://bugs.llvm.org/>. Most bug
548 reports should include preprocessed source files (use the -E option)
549 and the full output of the compiler, along with information to repro‐
550 duce.
551
553 as(1), ld(1)
554
556 Maintained by the Clang / LLVM Team (<http://clang.llvm.org>)
557
559 2007-2020, The Clang Team
56010 Apr 03, 2020 CLANG(1)