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  18 <h1>Clang Compiler User's Manual</h1>
  19
  20 <ul>
  21 <li><a href="#intro">Introduction</a>
  22   <ul>
  23   <li><a href="#terminology">Terminology</a></li>
  24   <li><a href="#basicusage">Basic Usage</a></li>
  25   </ul>
  26 </li>
  27 <li><a href="#commandline">Command Line Options</a>
  28   <ul>
  29   <li><a href="#cl_diagnostics">Options to Control Error and Warning
  30       Messages</a></li>
  31   </ul>
  32 </li>
  33 <li><a href="#general_features">Language and Target-Independent Features</a>
  34  <ul>
  35   <li><a href="#diagnostics">Controlling Errors and Warnings</a>
  36    <ul>
  37    <li><a href="#diagnostics_display">Controlling How Clang Displays Diagnostics</a></li>
  38    <li><a href="#diagnostics_mappings">Diagnostic Mappings</a></li>
  39    <li><a href="#diagnostics_categories">Diagnostic Categories</a></li>
  40    <li><a href="#diagnostics_commandline">Controlling Diagnostics via Command Line Flags</a></li>
  41    <li><a href="#diagnostics_pragmas">Controlling Diagnostics via Pragmas</a></li>
  42    <li><a href="#analyzer_diagnositics">Controlling Static Analyzer Diagnostics</a></li>
  43    </ul>
  44   </li>
  45   <li><a href="#precompiledheaders">Precompiled Headers</a></li>
  46   <li><a href="#codegen">Controlling Code Generation</a></li>
  47  </ul>
  48 </li>
  49 <li><a href="#c">C Language Features</a>
  50   <ul>
  51   <li><a href="#c_ext">Extensions supported by clang</a></li>
  52   <li><a href="#c_modes">Differences between various standard modes</a></li>
  53   <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
  54   <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
  55   <li><a href="#c_ms">Microsoft extensions</a></li>
  56   </ul>
  57 </li>
  58 <li><a href="#target_features">Target-Specific Features and Limitations</a>
  59   <ul>
  60   <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
  61     <ul>
  62     <li><a href="#target_arch_x86">X86</a></li>
  63     <li><a href="#target_arch_arm">ARM</a></li>
  64     <li><a href="#target_arch_other">Other platforms</a></li>
  65     </ul>
  66   </li>
  67   <li><a href="#target_os">Operating System Features and Limitations</a>
  68     <ul>
  69     <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
  70     <li>Linux, etc.</li>
  71     <li><a href="#target_os_win32">Windows</a></li>
  72     </ul>
  73   </li>
  74   </ul>
  75 </li>
  76 </ul>
  77
  78
  79 <!-- ======================================================================= -->
  80 <h2 id="intro">Introduction</h2>
  81 <!-- ======================================================================= -->
  82
  83 <p>The Clang Compiler is an open-source compiler for the C family of programming
  84 languages, aiming to be the best in class implementation of these languages.
  85 Clang builds on the LLVM optimizer and code generator, allowing it to provide
  86 high-quality optimization and code generation support for many targets.  For
  87 more general information, please see the <a href="http://clang.llvm.org">Clang
  88 Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
  89
  90 <p>This document describes important notes about using Clang as a compiler for
  91 an end-user, documenting the supported features, command line options, etc.  If
  92 you are interested in using Clang to build a tool that processes code, please
  93 see <a href="InternalsManual.html">the Clang Internals Manual</a>.  If you are
  94 interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
  95 Static Analyzer</a>, please see its web page.</p>
  96
  97 <p>Clang is designed to support the C family of programming languages, which
  98 includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
  99 href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
 100 dialects of those.  For language-specific information, please see the
 101 corresponding language specific section:</p>
 102
 103 <ul>
 104 <li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
 105     (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
 106 <li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
 107     variants depending on base language.</li>
 108 <li><a href="#cxx">C++ Language Features</a></li>
 109 <li><a href="#objcxx">Objective C++ Language</a></li>
 110 </ul>
 111
 112 <p>In addition to these base languages and their dialects, Clang supports a
 113 broad variety of language extensions, which are documented in the corresponding
 114 language section.  These extensions are provided to be compatible with the GCC,
 115 Microsoft, and other popular compilers as well as to improve functionality
 116 through Clang-specific features.  The Clang driver and language features are
 117 intentionally designed to be as compatible with the GNU GCC compiler as
 118 reasonably possible, easing migration from GCC to Clang.  In most cases, code
 119 "just works".</p>
 120
 121 <p>In addition to language specific features, Clang has a variety of features
 122 that depend on what CPU architecture or operating system is being compiled for.
 123 Please see the <a href="#target_features">Target-Specific Features and
 124 Limitations</a> section for more details.</p>
 125
 126 <p>The rest of the introduction introduces some basic <a
 127 href="#terminology">compiler terminology</a> that is used throughout this manual
 128 and contains a basic <a href="#basicusage">introduction to using Clang</a>
 129 as a command line compiler.</p>
 130
 131 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 132 <h3 id="terminology">Terminology</h3>
 133 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 134
 135 <p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
 136  optimizer</p>
 137
 138 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 139 <h3 id="basicusage">Basic Usage</h3>
 140 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 141
 142 <p>Intro to how to use a C compiler for newbies.</p>
 143 <p>
 144 compile + link
 145
 146 compile then link
 147
 148 debug info
 149
 150 enabling optimizations
 151
 152 picking a language to use, defaults to C99 by default.  Autosenses based on
 153 extension.
 154
 155 using a makefile
 156 </p>
 157
 158
 159 <!-- ======================================================================= -->
 160 <h2 id="commandline">Command Line Options</h2>
 161 <!-- ======================================================================= -->
 162
 163 <p>
 164 This section is generally an index into other sections.  It does not go into
 165 depth on the ones that are covered by other sections.  However, the first part
 166 introduces the language selection and other high level options like -c, -g, etc.
 167 </p>
 168
 169
 170 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 171 <h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
 172 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 173
 174 <p><b>-Werror</b>: Turn warnings into errors.</p>
 175 <p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
 176 <p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
 177    specified.</p>
 178 <p><b>-Wfoo</b>: Enable warning foo</p>
 179 <p><b>-Wno-foo</b>: Disable warning foo</p>
 180 <p><b>-w</b>: Disable all warnings.</p>
 181 <p><b>-pedantic</b>: Warn on language extensions.</p>
 182 <p><b>-pedantic-errors</b>: Error on language extensions.</p>
 183 <p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
 184
 185 <p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
 186    been produced.  The default is 20, and the error limit can be disabled with
 187    -ferror-limit=0.</p>
 188
 189 <p><b>-ftemplate-backtrace-limit=123</b>: Only emit up to 123 template instantiation notes within the template instantiation backtrace for a single warning or error. The default is 10, and the limit can be disabled with -ftemplate-backtrace-limit=0.</p>
 190
 191 <!-- ================================================= -->
 192 <h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
 193 <!-- ================================================= -->
 194
 195 <p>Clang aims to produce beautiful diagnostics by default, particularly for new
 196 users that first come to Clang.  However, different people have different
 197 preferences, and sometimes Clang is driven by another program that wants to
 198 parse simple and consistent output, not a person. For these cases, Clang
 199 provides a wide range of options to control the exact output format of the
 200 diagnostics that it generates.</p>
 201
 202 <dl>
 203
 204 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 205 <dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
 206 diagnostic.</dt>
 207 <dd>This option, which defaults to on, controls whether or not Clang prints the
 208 column number of a diagnostic.  For example, when this is enabled, Clang will
 209 print something like:
 210
 211 <pre>
 212   test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 213   #endif bad
 214          ^
 215          //
 216 </pre>
 217
 218 <p>When this is disabled, Clang will print "test.c:28: warning..." with no
 219 column number.</p>
 220 </dd>
 221
 222 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 223 <dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
 224 source file/line/column information in diagnostic.</dt>
 225 <dd>This option, which defaults to on, controls whether or not Clang prints the
 226 filename, line number and column number of a diagnostic.  For example,
 227 when this is enabled, Clang will print something like:
 228
 229 <pre>
 230   test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 231   #endif bad
 232          ^
 233          //
 234 </pre>
 235
 236 <p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
 237 </dd>
 238
 239 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 240 <dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
 241 line and ranges from source code in diagnostic.</dt>
 242 <dd>This option, which defaults to on, controls whether or not Clang prints the
 243 source line, source ranges, and caret when emitting a diagnostic.  For example,
 244 when this is enabled, Clang will print something like:
 245
 246 <pre>
 247   test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 248   #endif bad
 249          ^
 250          //
 251 </pre>
 252 </dd>
 253 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 254 <dt id="opt_fcolor_diagnostics"><b>-f[no-]color-diagnostics</b>: </dt>
 255 <dd>This option, which defaults to on when a color-capable terminal is
 256   detected, controls whether or not Clang prints diagnostics in color.
 257   When this option is enabled, Clang will use colors to highlight
 258   specific parts of the diagnostic, e.g.,
 259  <pre>
 260   <b><font color="black">test.c:28:8: <font color="magenta">warning</font>: extra tokens at end of #endif directive [-Wextra-tokens]</font></b>
 261   #endif bad
 262          <font color="green">^</font>
 263          <font color="green">//</font>
 264 </pre>
 265
 266 <p>When this is disabled, Clang will just print:</p>
 267
 268 <pre>
 269   test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 270   #endif bad
 271          ^
 272          //
 273 </pre>
 274 </dd>
 275 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 276 <dt id="opt_fdiagnostics-format"><b>-fdiagnostics-format=clang/msvc/vi</b>:
 277 Changes diagnostic output format to better match IDEs and command line tools.</dt>
 278 <dd>This option controls the output format of the filename, line number, and column printed in diagnostic messages. The options, and their affect on formatting a simple conversion diagnostic, follow:
 279
 280   <dl>
 281     <dt><b>clang</b> (default)</dt>
 282     <dd>
 283       <pre>t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
 284     </dd>
 285
 286     <dt><b>msvc</b></dt>
 287     <dd>
 288       <pre>t.c(3,11) : warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
 289     </dd>
 290
 291     <dt><b>vi</b></dt>
 292     <dd>
 293       <pre>t.c +3:11: warning: conversion specifies type 'char *' but the argument has type 'int'</pre>
 294     </dd>
 295   </dl>
 296 </dd>
 297
 298 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 299 <dt id="opt_fdiagnostics-show-name"><b>-f[no-]diagnostics-show-name</b>:
 300 Enable the display of the diagnostic name.</dt>
 301 <dd>This option, which defaults to off, controls whether or not
 302 Clang prints the associated name.</dd>
 303 <br>
 304 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 305 <dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
 306 Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
 307 <dd>This option, which defaults to on,
 308 controls whether or not Clang prints the associated <A
 309 href="#cl_diag_warning_groups">warning group</a> option name when outputting
 310 a warning diagnostic.  For example, in this output:
 311
 312 <pre>
 313   test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 314   #endif bad
 315          ^
 316          //
 317 </pre>
 318
 319 <p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
 320 the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
 321 diagnostic.  This information tells you the flag needed to enable or disable the
 322 diagnostic, either from the command line or through <a
 323 href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
 324
 325 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 326 <dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
 327 Enable printing category information in diagnostic line.</dt>
 328 <dd>This option, which defaults to "none",
 329 controls whether or not Clang prints the category associated with a diagnostic
 330 when emitting it.  Each diagnostic may or many not have an associated category,
 331 if it has one, it is listed in the diagnostic categorization field of the
 332 diagnostic line (in the []'s).
 333
 334 <p>For example, a format string warning will produce these three renditions
 335 based on the setting of this option:</p>
 336
 337 <pre>
 338   t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
 339   t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
 340   t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
 341 </pre>
 342
 343 <p>This category can be used by clients that want to group diagnostics by
 344 category, so it should be a high level category.  We want dozens of these, not
 345 hundreds or thousands of them.</p>
 346 </dd>
 347
 348
 349
 350 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 351 <dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
 352 Enable "FixIt" information in the diagnostics output.</dt>
 353 <dd>This option, which defaults to on, controls whether or not Clang prints the
 354 information on how to fix a specific diagnostic underneath it when it knows.
 355 For example, in this output:
 356
 357 <pre>
 358   test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 359   #endif bad
 360          ^
 361          //
 362 </pre>
 363
 364 <p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
 365 the "//" line at the end of the message.  This information is useful for users
 366 who may not understand what is wrong, but can be confusing for machine
 367 parsing.</p>
 368 </dd>
 369
 370 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 371 <dt id="opt_fdiagnostics-print-source-range-info">
 372 <b>-f[no-]diagnostics-print-source-range-info</b>:
 373 Print machine parsable information about source ranges.</dt>
 374 <dd>This option, which defaults to off, controls whether or not Clang prints
 375 information about source ranges in a machine parsable format after the
 376 file/line/column number information.  The information is a simple sequence of
 377 brace enclosed ranges, where each range lists the start and end line/column
 378 locations.  For example, in this output:
 379
 380 <pre>
 381 exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
 382    P = (P-42) + Gamma*4;
 383        ~~~~~~ ^ ~~~~~~~
 384 </pre>
 385
 386 <p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
 387 </dd>
 388
 389 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 390 <dt id="opt_fdiagnostics-parseable-fixits">
 391 <b>-fdiagnostics-parseable-fixits</b>:
 392 Print Fix-Its in a machine parseable form.</dt>
 393 <dd><p>This option makes Clang print available Fix-Its in a machine parseable format at the end of diagnostics. The following example illustrates the format:</p>
 394
 395 <pre>
 396  fix-it:"t.cpp":{7:25-7:29}:"Gamma"
 397 </pre>
 398
 399 <p>The range printed is a half-open range, so in this example the characters at
 400 column 25 up to but not including column 29 on line 7 in t.cpp should be
 401 replaced with the string &quot;Gamma&quot;. Either the range or the replacement
 402 string may be empty (representing strict insertions and strict erasures,
 403 respectively). Both the file name and the insertion string escape backslash (as
 404 &quot;\\&quot;), tabs (as &quot;\t&quot;), newlines (as &quot;\n&quot;), double
 405 quotes(as &quot;\&quot;&quot;) and non-printable characters (as octal
 406 &quot;\xxx&quot;).</p>
 407 </dd>
 408
 409 </dl>
 410
 411
 412
 413
 414 <!-- ===================================================== -->
 415 <h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
 416 <!-- ===================================================== -->
 417
 418 <p>TODO: Generate this from tblgen.  Define one anchor per warning group.</p>
 419
 420
 421 <dl>
 422
 423
 424 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 425 <dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
 426     the end of a preprocessor directive.</dt>
 427 <dd>This option, which defaults to on, enables warnings about extra tokens at
 428 the end of preprocessor directives.  For example:
 429
 430 <pre>
 431   test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
 432   #endif bad
 433          ^
 434 </pre>
 435
 436 <p>These extra tokens are not strictly conforming, and are usually best handled
 437 by commenting them out.</p>
 438
 439 <p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
 440  and <a href="">-Wbaz</a>.</p>
 441 </dd>
 442
 443 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 444 <dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
 445 Warn about unqualified uses of a member template whose name resolves
 446 to another template at the location of the use.</dt>
 447 <dd>This option, which defaults to on, enables a warning in the
 448 following code:
 449
 450 <pre>
 451 template&lt;typename T> struct set{};
 452 template&lt;typename T> struct trait { typedef const T& type; };
 453 struct Value {
 454   template&lt;typename T> void set(typename trait&lt;T>::type value) {}
 455 };
 456 void foo() {
 457   Value v;
 458   v.set&lt;double>(3.2);
 459 }
 460 </pre>
 461
 462 <p>C++ [basic.lookup.classref] requires this to be an error, but,
 463 because it's hard to work around, Clang downgrades it to a warning as
 464 an extension.</p>
 465 </dd>
 466
 467 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 468 <dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
 469 an unusable copy constructor when binding a reference to a temporary.</dt>
 470 <dd>This option, which defaults to on, enables warnings about binding a
 471 reference to a temporary when the temporary doesn't have a usable copy
 472 constructor.  For example:
 473
 474 <pre>
 475   struct NonCopyable {
 476     NonCopyable();
 477   private:
 478     NonCopyable(const NonCopyable&);
 479   };
 480   void foo(const NonCopyable&);
 481   void bar() {
 482     foo(NonCopyable());  // Disallowed in C++98; allowed in C++0x.
 483   }
 484 </pre>
 485 <pre>
 486   struct NonCopyable2 {
 487     NonCopyable2();
 488     NonCopyable2(NonCopyable2&);
 489   };
 490   void foo(const NonCopyable2&);
 491   void bar() {
 492     foo(NonCopyable2());  // Disallowed in C++98; allowed in C++0x.
 493   }
 494 </pre>
 495
 496 <p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
 497 argument whose instantiation produces a compile error, that error will
 498 still be a hard error in C++98 mode even if this warning is turned
 499 off.</p>
 500
 501 </dd>
 502
 503 </dl>
 504
 505 <!-- ======================================================================= -->
 506 <h2 id="general_features">Language and Target-Independent Features</h2>
 507 <!-- ======================================================================= -->
 508
 509
 510 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 511 <h3 id="diagnostics">Controlling Errors and Warnings</h3>
 512 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 513
 514 <p>Clang provides a number of ways to control which code constructs cause it to
 515 emit errors and warning messages, and how they are displayed to the console.</p>
 516
 517 <h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
 518
 519 <p>When Clang emits a diagnostic, it includes rich information in the output,
 520 and gives you fine-grain control over which information is printed.  Clang has
 521 the ability to print this information, and these are the options that control
 522 it:</p>
 523
 524 <ol>
 525 <li>A file/line/column indicator that shows exactly where the diagnostic occurs
 526     in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
 527     href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
 528 <li>A categorization of the diagnostic as a note, warning, error, or fatal
 529     error.</li>
 530 <li>A text string that describes what the problem is.</li>
 531 <li>An option that indicates whether to print the diagnostic name [<a
 532     href="#opt_fdiagnostics-show-name">-fdiagnostics-show-name</a>].</li>
 533 <li>An option that indicates how to control the diagnostic (for diagnostics that
 534     support it) [<a
 535    href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
 536 <li>A <a href="#diagnostics_categories">high-level category</a> for the
 537     diagnostic for clients that want to group diagnostics by class (for
 538     diagnostics that support it) [<a
 539    href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
 540 <li>The line of source code that the issue occurs on, along with a caret and
 541     ranges that indicate the important locations [<a
 542     href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
 543 <li>"FixIt" information, which is a concise explanation of how to fix the
 544     problem (when Clang is certain it knows) [<a
 545     href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
 546 <li>A machine-parsable representation of the ranges involved (off by
 547     default) [<a
 548       href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
 549 </ol>
 550
 551 <p>For more information please see <a href="#cl_diag_formatting">Formatting of
 552 Diagnostics</a>.</p>
 553
 554
 555 <h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
 556
 557 <p>All diagnostics are mapped into one of these 5 classes:</p>
 558
 559 <ul>
 560 <li>Ignored</li>
 561 <li>Note</li>
 562 <li>Warning</li>
 563 <li>Error</li>
 564 <li>Fatal</li>
 565 </ul>
 566
 567 <h4 id="diagnostics_categories">Diagnostic Categories</h4>
 568
 569 <p>Though not shown by default, diagnostics may each be associated with a
 570    high-level category.  This category is intended to make it possible to triage
 571    builds that produce a large number of errors or warnings in a grouped way.
 572 </p>
 573
 574 <p>Categories are not shown by default, but they can be turned on with the
 575 <a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
 576 When set to "<tt>name</tt>", the category is printed textually in the diagnostic
 577 output.  When it is set to "<tt>id</tt>", a category number is printed.  The
 578 mapping of category names to category id's can be obtained by running '<tt>clang
 579   --print-diagnostic-categories</tt>'.
 580 </p>
 581
 582 <h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
 583  Flags</h4>
 584
 585 <p>-W flags, -pedantic, etc</p>
 586
 587 <h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
 588
 589 <p>Clang can also control what diagnostics are enabled through the use of
 590 pragmas in the source code. This is useful for turning off specific warnings
 591 in a section of source code. Clang supports GCC's pragma for compatibility
 592 with existing source code, as well as several extensions. </p>
 593
 594 <p>The pragma may control any warning that can be used from the command line.
 595 Warnings may be set to ignored, warning, error, or fatal. The following
 596 example code will tell Clang or GCC to ignore the -Wall warnings:</p>
 597
 598 <pre>
 599 #pragma GCC diagnostic ignored "-Wall"
 600 </pre>
 601
 602 <p>In addition to all of the functionality provided by GCC's pragma, Clang
 603 also allows you to push and pop the current warning state.  This is particularly
 604 useful when writing a header file that will be compiled by other people, because
 605 you don't know what warning flags they build with.</p>
 606
 607 <p>In the below example
 608 -Wmultichar is ignored for only a single line of code, after which the
 609 diagnostics return to whatever state had previously existed.</p>
 610
 611 <pre>
 612 #pragma clang diagnostic push
 613 #pragma clang diagnostic ignored "-Wmultichar"
 614
 615 char b = 'df'; // no warning.
 616
 617 #pragma clang diagnostic pop
 618 </pre>
 619
 620 <p>The push and pop pragmas will save and restore the full diagnostic state of
 621 the compiler, regardless of how it was set. That means that it is possible to
 622 use push and pop around GCC compatible diagnostics and Clang will push and pop
 623 them appropriately, while GCC will ignore the pushes and pops as unknown
 624 pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
 625 GCC do not support the exact same set of warnings, so even when using GCC
 626 compatible #pragmas there is no guarantee that they will have identical behaviour
 627 on both compilers. </p>
 628
 629 <h4 id="analyzer_diagnositics">Controlling Static Analyzer Diagnostics</h4>
 630
 631 <p>While not strictly part of the compiler, the diagnostics from Clang's <a
 632 href="http://clang-analyzer.llvm.org">static analyzer</a> can also be influenced
 633 by the user via changes to the source code.  This can be done in two ways:
 634
 635 <ul>
 636
 637 <li id="analyzer_annotations"><b>Annotations</b>: The static analyzer recognizes various GCC-style
 638 attributes (e.g., <tt>__attribute__((nonnull)))</tt>) that can either suppress
 639 static analyzer warnings or teach the analyzer about code invariants which
 640 enable it to find more bugs. While many of these attributes are standard GCC
 641 attributes, additional ones have been added to Clang to specifically support the
 642 static analyzer. Detailed information on these annotations can be found in the
 643 <a href="http://clang-analyzer.llvm.org/annotations.html">analyzer's
 644 documentation</a>.</li>
 645
 646 <li><b><tt>__clang_analyzer__</tt></b>: When the static analyzer is using Clang
 647 to parse source files, it implicitly defines the preprocessor macro
 648 <tt>__clang_analyzer__</tt>. While discouraged, code can use this macro to
 649 selectively exclude code the analyzer examines.  Here is an example:
 650
 651 <pre>
 652 #ifndef __clang_analyzer__
 653 // Code not to be analyzed
 654 #endif
 655 </pre>
 656
 657 In general, this usage is discouraged. Instead, we prefer that users file bugs
 658 against the analyzer when it flags false positives. There is also active
 659 discussion of allowing users in the future to selectively silence specific
 660 analyzer warnings (some of which can already be done using <a
 661 href="analyzer_annotations">annotations</a>).</li>
 662
 663 </ul>
 664
 665 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 666 <h3 id="precompiledheaders">Precompiled Headers</h3>
 667 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 668
 669 <p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
 670 headers</a> are a general approach employed by many compilers to reduce
 671 compilation time. The underlying motivation of the approach is that it is
 672 common for the same (and often large) header files to be included by
 673 multiple source files. Consequently, compile times can often be greatly improved
 674 by caching some of the (redundant) work done by a compiler to process headers.
 675 Precompiled header files, which represent one of many ways to implement
 676 this optimization, are literally files that represent an on-disk cache that
 677 contains the vital information necessary to reduce some of the work
 678 needed to process a corresponding header file. While details of precompiled
 679 headers vary between compilers, precompiled headers have been shown to be
 680 highly effective at speeding up program compilation on systems with very large
 681 system headers (e.g., Mac OS/X).</p>
 682
 683 <h4>Generating a PCH File</h4>
 684
 685 <p>To generate a PCH file using Clang, one invokes Clang with
 686 the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
 687 interface in GCC for generating PCH files:</p>
 688
 689 <pre>
 690   $ gcc -x c-header test.h -o test.h.gch
 691   $ clang -x c-header test.h -o test.h.pch
 692 </pre>
 693
 694 <h4>Using a PCH File</h4>
 695
 696 <p>A PCH file can then be used as a prefix header when a
 697 <b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
 698
 699 <pre>
 700   $ clang -include test.h test.c -o test
 701 </pre>
 702
 703 <p>The <tt>clang</tt> driver will first check if a PCH file for <tt>test.h</tt>
 704 is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
 705 will be processed from the PCH file. Otherwise, Clang falls back to
 706 directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
 707 GCC.</p>
 708
 709 <p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
 710 for headers that are directly included within a source file. For example:</p>
 711
 712 <pre>
 713   $ clang -x c-header test.h -o test.h.pch
 714   $ cat test.c
 715   #include "test.h"
 716   $ clang test.c -o test
 717 </pre>
 718
 719 <p>In this example, <tt>clang</tt> will not automatically use the PCH file for
 720 <tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
 721 and not specified on the command line using <tt>-include</tt>.</p>
 722
 723 <h4>Relocatable PCH Files</h4>
 724 <p>It is sometimes necessary to build a precompiled header from headers that
 725 are not yet in their final, installed locations. For example, one might build a
 726 precompiled header within the build tree that is then meant to be installed
 727 alongside the headers. Clang permits the creation of "relocatable" precompiled
 728 headers, which are built with a given path (into the build directory) and can
 729 later be used from an installed location.</p>
 730
 731 <p>To build a relocatable precompiled header, place your headers into a
 732 subdirectory whose structure mimics the installed location. For example, if you
 733 want to build a precompiled header for the header <code>mylib.h</code> that
 734 will be installed into <code>/usr/include</code>, create a subdirectory
 735 <code>build/usr/include</code> and place the header <code>mylib.h</code> into
 736 that subdirectory. If <code>mylib.h</code> depends on other headers, then
 737 they can be stored within <code>build/usr/include</code> in a way that mimics
 738 the installed location.</p>
 739
 740 <p>Building a relocatable precompiled header requires two additional arguments.
 741 First, pass the <code>--relocatable-pch</code> flag to indicate that the
 742 resulting PCH file should be relocatable. Second, pass
 743 <code>-isysroot /path/to/build</code>, which makes all includes for your
 744 library relative to the build directory. For example:</p>
 745
 746 <pre>
 747   # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
 748 </pre>
 749
 750 <p>When loading the relocatable PCH file, the various headers used in the PCH
 751 file are found from the system header root. For example, <code>mylib.h</code>
 752 can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
 753 in some other system root, the <code>-isysroot</code> option can be used provide
 754 a different system root from which the headers will be based. For example,
 755 <code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
 756 <code>mylib.h</code> in
 757 <code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
 758
 759 <p>Relocatable precompiled headers are intended to be used in a limited number
 760 of cases where the compilation environment is tightly controlled and the
 761 precompiled header cannot be generated after headers have been installed.
 762 Relocatable precompiled headers also have some performance impact, because
 763 the difference in location between the header locations at PCH build time vs.
 764 at the time of PCH use requires one of the PCH optimizations,
 765 <code>stat()</code> caching, to be disabled. However, this change is only
 766 likely to affect PCH files that reference a large number of headers.</p>
 767
 768 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 769 <h3 id="codegen">Controlling Code Generation</h3>
 770 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 771
 772 <p>Clang provides a number of ways to control code generation.  The options are listed below.</p>
 773
 774 <!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
 775 <dl>
 776 <dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
 777 on runtime code generation to check for undefined behavior.</dt>
 778
 779 <dd>This option, which defaults to off, controls whether or not Clang
 780 adds runtime checks for undefined runtime behavior.  If a check fails,
 781 <tt>__builtin_trap()</tt> is used to indicate failure.
 782 The checks are:
 783 <ul>
 784 <li>Subscripting where the static type of one operand is a variable
 785     which is decayed from an array type and the other operand is
 786     greater than the size of the array or less than zero.</li>
 787 <li>Shift operators where the amount shifted is greater or equal to the
 788     promoted bit-width of the left-hand-side or less than zero.</li>
 789 <li>If control flow reaches __builtin_unreachable.
 790 <li>When llvm implements more __builtin_object_size support, reads and
 791     writes for objects that __builtin_object_size indicates we aren't
 792     accessing valid memory.  Bit-fields and vectors are not yet checked.
 793 </ul>
 794 </dd>
 795
 796 <dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
 797 Don't assume that the C++'s new operator is sane.</dt>
 798 <dd>This option tells the compiler to do not assume that C++'s global new
 799 operator will always return a pointer that does not
 800 alias any other pointer when the function returns.</dd>
 801
 802 <dt id="opt_ftrap-function"><b>-ftrap-function=[name]</b>: Instruct code
 803 generator to emit a function call to the specified function name for
 804 <tt>__builtin_trap()</tt>.</dt>
 805
 806 <dd>LLVM code generator translates <tt>__builtin_trap()</tt> to a trap
 807 instruction if it is supported by the target ISA. Otherwise, the builtin is
 808 translated into a call to <tt>abort</tt>. If this option is set, then the code
 809 generator will always lower the builtin to a call to the specified function
 810 regardless of whether the target ISA has a trap instruction. This option is
 811 useful for environments (e.g. deeply embedded) where a trap cannot be properly
 812 handled, or when some custom behavior is desired.</dd>
 813 </dl>
 814
 815 <!-- ======================================================================= -->
 816 <h2 id="c">C Language Features</h2>
 817 <!-- ======================================================================= -->
 818
 819 <p>The support for standard C in clang is feature-complete except for the C99
 820 floating-point pragmas.</p>
 821
 822 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 823 <h3 id="c_ext">Extensions supported by clang</h3>
 824 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 825
 826 <p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
 827
 828 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 829 <h3 id="c_modes">Differences between various standard modes</h3>
 830 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 831
 832 <p>clang supports the -std option, which changes what language mode clang uses.
 833 The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
 834 for those modes.  If no -std option is specified, clang defaults to gnu99 mode.
 835 </p>
 836
 837 <p>Differences between all c* and gnu* modes:</p>
 838 <ul>
 839 <li>c* modes define "__STRICT_ANSI__".</li>
 840 <li>Target-specific defines not prefixed by underscores, like "linux", are
 841 defined in gnu* modes.</li>
 842 <li>Trigraphs default to being off in gnu* modes; they can be enabled by the
 843 -trigraphs option.</li>
 844 <li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
 845 variants "__asm__" and "__typeof__" are recognized in all modes.</li>
 846 <li>The Apple "blocks" extension is recognized by default in gnu* modes
 847 on some platforms; it can be enabled in any mode with the "-fblocks"
 848 option.</li>
 849 <li>Arrays that are VLA's according to the standard, but which can be constant
 850     folded by the frontend are treated as fixed size arrays.  This occurs for
 851     things like "int X[(1, 2)];", which is technically a VLA.  c* modes are
 852     strictly compliant and treat these as VLAs.</li>
 853 </ul>
 854
 855 <p>Differences between *89 and *99 modes:</p>
 856 <ul>
 857 <li>The *99 modes default to implementing "inline" as specified in C99, while
 858 the *89 modes implement the GNU version.  This can be overridden for individual
 859 functions with the __gnu_inline__ attribute.</li>
 860 <li>Digraphs are not recognized in c89 mode.</li>
 861 <li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
 862 statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
 863 <li>__STDC_VERSION__ is not defined in *89 modes.</li>
 864 <li>"inline" is not recognized as a keyword in c89 mode.</li>
 865 <li>"restrict" is not recognized as a keyword in *89 modes.</li>
 866 <li>Commas are allowed in integer constant expressions in *99 modes.</li>
 867 <li>Arrays which are not lvalues are not implicitly promoted to pointers in
 868 *89 modes.</li>
 869 <li>Some warnings are different.</li>
 870 </ul>
 871
 872 <p>c94 mode is identical to c89 mode except that digraphs are enabled in
 873 c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
 874
 875 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 876 <h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
 877 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 878
 879 <p>clang tries to be compatible with gcc as much as possible, but some gcc
 880 extensions are not implemented yet:</p>
 881
 882 <ul>
 883
 884 <li>clang does not support #pragma weak
 885 (<a href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug 3679</a>). Due to
 886 the uses described in the bug, this is likely to be implemented at some
 887 point, at least partially.</li>
 888
 889 <li>clang does not support decimal floating point types (_Decimal32 and
 890 friends) or fixed-point types (_Fract and friends); nobody has expressed
 891 interest in these features yet, so it's hard to say when they will be
 892 implemented.</li>
 893
 894 <li>clang does not support nested functions; this is a complex feature which
 895 is infrequently used, so it is unlikely to be implemented anytime soon.</li>
 896
 897 <li>clang does not support global register variables, this is unlikely
 898 to be implemented soon because it requires additional LLVM backend support.
 899 </li>
 900
 901 <li>clang does not support static initialization of flexible array
 902 members. This appears to be a rarely used extension, but could be
 903 implemented pending user demand.</li>
 904
 905 <li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
 906 This is used rarely, but in some potentially interesting places, like the
 907 glibc headers, so it may be implemented pending user demand.  Note that
 908 because clang pretends to be like GCC 4.2, and this extension was introduced
 909 in 4.3, the glibc headers will not try to use this extension with clang at
 910 the moment.</li>
 911
 912 <li>clang does not support the gcc extension for forward-declaring function
 913 parameters; this has not showed up in any real-world code yet, though, so it
 914 might never be implemented.</li>
 915
 916 </ul>
 917
 918 <p>This is not a complete list; if you find an unsupported extension
 919 missing from this list, please send an e-mail to cfe-dev.  This list
 920 currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
 921 Also, this list does not include bugs in mostly-implemented features; please
 922 see the <a href="http://llvm.org/bugs/buglist.cgi?quicksearch=product%3Aclang+component%3A-New%2BBugs%2CAST%2CBasic%2CDriver%2CHeaders%2CLLVM%2BCodeGen%2Cparser%2Cpreprocessor%2CSemantic%2BAnalyzer">
 923 bug tracker</a> for known existing bugs (FIXME: Is there a section for
 924 bug-reporting guidelines somewhere?).</p>
 925
 926 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 927 <h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
 928 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 929
 930 <ul>
 931
 932 <li>clang does not support the gcc extension that allows variable-length arrays
 933 in structures.  This is for a few reasons: one, it is tricky
 934 to implement, two, the extension is completely undocumented, and three, the
 935 extension appears to be rarely used.  Note that clang <em>does</em> support
 936 flexible array members (arrays with a zero or unspecified size at the end of
 937 a structure).</li>
 938
 939 <li>clang does not have an equivalent to gcc's "fold"; this means that
 940 clang doesn't accept some constructs gcc might accept in contexts where a
 941 constant expression is required, like "x-x" where x is a variable.</li>
 942
 943 <li>clang does not support multiple alternative constraints in inline asm; this
 944 is an extremely obscure feature which would be complicated to implement
 945 correctly.</li>
 946
 947 <li>clang does not support __builtin_apply and friends; this extension is
 948 extremely obscure and difficult to implement reliably.</li>
 949
 950 </ul>
 951
 952 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 953 <h3 id="c_ms">Microsoft extensions</h3>
 954 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 955
 956 <p>clang has some experimental support for extensions from
 957 Microsoft Visual C++; to enable it, use the -fms-extensions command-line
 958 option.  This is the default for Windows targets.  Note that the
 959 support is incomplete; enabling Microsoft extensions will silently drop
 960 certain constructs (including __declspec and Microsoft-style asm statements).
 961 </p>
 962
 963 <ul>
 964 <li>clang allows setting _MSC_VER with -fmsc-version=. It defaults to 1300 which
 965 is the same as Visual C/C++ 2003. Any number is supported and can greatly affect
 966 what Windows SDK and c++stdlib headers clang can compile. This option will be
 967 removed when clang supports the full set of MS extensions required for these
 968 headers.</li>
 969
 970 <li>clang does not support the Microsoft extension where anonymous
 971 record members can be declared using user defined typedefs.</li>
 972
 973 <li>clang supports the Microsoft "#pragma pack" feature for
 974 controlling record layout. GCC also contains support for this feature,
 975 however where MSVC and GCC are incompatible clang follows the MSVC
 976 definition.</li>
 977 </ul>
 978
 979 <!-- ======================================================================= -->
 980 <h2 id="target_features">Target-Specific Features and Limitations</h2>
 981 <!-- ======================================================================= -->
 982
 983
 984 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 985 <h3 id="target_arch">CPU Architectures Features and Limitations</h3>
 986 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
 987
 988 <!-- ======================== -->
 989 <h4 id="target_arch_x86">X86</h4>
 990 <!-- ======================== -->
 991
 992 <p>The support for X86 (both 32-bit and 64-bit) is considered stable on Darwin
 993 (Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to correctly
 994 compile many large C, C++, Objective-C, and Objective-C++ codebases.</p>
 995
 996 <p>On x86_64-mingw32, passing i128(by value) is incompatible to Microsoft x64
 997 calling conversion. You might need to tweak WinX86_64ABIInfo::classify()
 998 in lib/CodeGen/TargetInfo.cpp.</p>
 999
1000 <!-- ======================== -->
1001 <h4 id="target_arch_arm">ARM</h4>
1002 <!-- ======================== -->
1003
1004 <p>The support for ARM (specifically ARMv6 and ARMv7) is considered stable on
1005 Darwin (iOS): it has been tested to correctly compile many large C, C++,
1006 Objective-C, and Objective-C++ codebases.  Clang only supports a limited number
1007 of ARM architectures. It does not yet fully support ARMv5, for example.</p>
1008
1009 <!-- ======================== -->
1010 <h4 id="target_arch_other">Other platforms</h4>
1011 <!-- ======================== -->
1012 clang currently contains some support for PPC and Sparc; however, significant
1013 pieces of code generation are still missing, and they haven't undergone
1014 significant testing.
1015
1016 <p>clang contains limited support for the MSP430 embedded processor, but both
1017 the clang support and the LLVM backend support are highly experimental.
1018
1019 <p>Other platforms are completely unsupported at the moment.  Adding the
1020 minimal support needed for parsing and semantic analysis on a new platform
1021 is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
1022 of support is also sufficient for conversion to LLVM IR for simple programs.
1023 Proper support for conversion to LLVM IR requires adding code to
1024 lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
1025 Generating assembly requires a suitable LLVM backend.
1026
1027 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1028 <h3 id="target_os">Operating System Features and Limitations</h3>
1029 <!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
1030
1031 <!-- ======================================= -->
1032 <h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
1033 <!-- ======================================= -->
1034
1035 <p>No __thread support, 64-bit ObjC support requires SL tools.</p>
1036
1037 <!-- ======================================= -->
1038 <h4 id="target_os_win32">Windows</h4>
1039 <!-- ======================================= -->
1040
1041 <p>Experimental supports are on Cygming.</p>
1042
1043 <h5>Cygwin</h5>
1044
1045 <p>Clang works on Cygwin-1.7.</p>
1046
1047 <h5>MinGW32</h5>
1048
1049 <p>Clang works on some mingw32 distributions.
1050 Clang assumes directories as below;</p>
1051
1052 <ul>
1053 <li><tt>C:/mingw/include</tt></li>
1054 <li><tt>C:/mingw/lib</tt></li>
1055 <li><tt>C:/mingw/lib/gcc/mingw32/4.[3-5].0/include/c++</tt></li>
1056 </ul>
1057
1058 <p>On MSYS, a few tests might fail. It is due to <a href="http://llvm.org/bugs/show_bug.cgi?id=8520">Bug 8520</a> and is fixed in <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110314/118106.html">LLVM's r127724</a>.</p>
1059
1060 <h5>MinGW-w64</h5>
1061
1062 <p>For x32(i686-w64-mingw32), it is not supported yet.</p>
1063
1064 <p>For x64(x86_64-w64-mingw32), <a href="http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20110321/118499.html">an essential patch(LLVM's r128206)</a> would be needed. It is incompatible to <a href="http://tdm-gcc.tdragon.net/development">TDM-GCC</a> due to the definition of symbol &quot;<code>___chkstk</code>&quot;. Clang assumes as below;<p>
1065
1066 <ul>
1067 <li><tt>C:/mingw/x86_64-w64-mingw32/include</tt></li>
1068 <li><tt>C:/mingw/x86_64-w64-mingw32/include/c++/4.5.[23]</tt></li>
1069 <li>GCC driver &quot;gcc.exe&quot; to build x86_64-w64-mingw32 binary.</li>
1070 </ul>
1071
1072 <p><a href="http://llvm.org/bugs/show_bug.cgi?id=8833">Some tests might fail</a>
1073 on x64.</p>
1074
1075 </div>
1076 </body>
1077 </html>