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16<div id="content">
17
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>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]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>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]33<li><a href="#general_features">Language and Target-Independent Features</a>
34 <ul>
35 <li><a href="#diagnostics">Controlling Errors and Warnings</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]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>
Chris Lattner67db8cd2010-05-30 23:42:51 +0000[diff] [blame]39 <li><a href="#diagnostics_categories">Diagnostic Categories</a></li>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]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 </ul>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]43 <li><a href="#precompiledheaders">Precompiled Headers</a></li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]44 <li><a href="#codegen">Controlling Code Generation</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]45 </ul>
46</li>
47<li><a href="#c">C Language Features</a>
48 <ul>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]49 <li><a href="#c_ext">Extensions supported by clang</a></li>
50 <li><a href="#c_modes">Differences between various standard modes</a></li>
51 <li><a href="#c_unimpl_gcc">GCC extensions not implemented yet</a></li>
52 <li><a href="#c_unsupp_gcc">Intentionally unsupported GCC extensions</a></li>
53 <li><a href="#c_ms">Microsoft extensions</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]54 </ul>
55</li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]56<li><a href="#target_features">Target-Specific Features and Limitations</a>
57 <ul>
58 <li><a href="#target_arch">CPU Architectures Features and Limitations</a>
59 <ul>
60 <li><a href="#target_arch_x86">X86</a></li>
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]61 <li><a href="#target_arch_arm">ARM</a></li>
62 <li><a href="#target_arch_other">Other platforms</a></li>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]63 </ul>
64 </li>
65 <li><a href="#target_os">Operating System Features and Limitations</a>
66 <ul>
67 <li><a href="#target_os_darwin">Darwin (Mac OS/X)</a></li>
68 <li>Linux, etc.</li>
69 </ul>
70
71 </li>
72 </ul>
73</li>
74</ul>
75
76
77<!-- ======================================================================= -->
78<h2 id="intro">Introduction</h2>
79<!-- ======================================================================= -->
80
81<p>The Clang Compiler is an open-source compiler for the C family of programming
82languages, aiming to be the best in class implementation of these languages.
83Clang builds on the LLVM optimizer and code generator, allowing it to provide
84high-quality optimization and code generation support for many targets. For
85more general information, please see the <a href="http://clang.llvm.org">Clang
86Web Site</a> or the <a href="http://llvm.org">LLVM Web Site</a>.</p>
87
88<p>This document describes important notes about using Clang as a compiler for
89an end-user, documenting the supported features, command line options, etc. If
90you are interested in using Clang to build a tool that processes code, please
91see <a href="InternalsManual.html">the Clang Internals Manual</a>. If you are
92interested in the <a href="http://clang.llvm.org/StaticAnalysis.html">Clang
93Static Analyzer</a>, please see its web page.</p>
94
95<p>Clang is designed to support the C family of programming languages, which
96includes <a href="#c">C</a>, <a href="#objc">Objective-C</a>, <a
97href="#cxx">C++</a>, and <a href="#objcxx">Objective-C++</a> as well as many
98dialects of those. For language-specific information, please see the
99corresponding language specific section:</p>
100
101<ul>
102<li><a href="#c">C Language</a>: K&amp;R C, ANSI C89, ISO C90, ISO C94
103 (C89+AMD1), ISO C99 (+TC1, TC2, TC3). </li>
104<li><a href="#objc">Objective-C Language</a>: ObjC 1, ObjC 2, ObjC 2.1, plus
105 variants depending on base language.</li>
106<li><a href="#cxx">C++ Language Features</a></li>
107<li><a href="#objcxx">Objective C++ Language</a></li>
108</ul>
109
110<p>In addition to these base languages and their dialects, Clang supports a
111broad variety of language extensions, which are documented in the corresponding
112language section. These extensions are provided to be compatible with the GCC,
113Microsoft, and other popular compilers as well as to improve functionality
114through Clang-specific features. The Clang driver and language features are
115intentionally designed to be as compatible with the GNU GCC compiler as
116reasonably possible, easing migration from GCC to Clang. In most cases, code
117"just works".</p>
118
119<p>In addition to language specific features, Clang has a variety of features
120that depend on what CPU architecture or operating system is being compiled for.
Douglas Gregorcd5a5052009-11-09 15:15:41 +0000[diff] [blame]121Please see the <a href="#target_features">Target-Specific Features and
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]122Limitations</a> section for more details.</p>
123
124<p>The rest of the introduction introduces some basic <a
125href="#terminology">compiler terminology</a> that is used throughout this manual
126and contains a basic <a href="#basicusage">introduction to using Clang</a>
127as a command line compiler.</p>
128
129<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
130<h3 id="terminology">Terminology</h3>
131<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
132
133<p>Front end, parser, backend, preprocessor, undefined behavior, diagnostic,
134 optimizer</p>
135
136<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
137<h3 id="basicusage">Basic Usage</h3>
138<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
139
140<p>Intro to how to use a C compiler for newbies.</p>
141<p>
142compile + link
143
144compile then link
145
146debug info
147
148enabling optimizations
149
150picking a language to use, defaults to C99 by default. Autosenses based on
151extension.
152
153using a makefile
154</p>
155
156
157<!-- ======================================================================= -->
158<h2 id="commandline">Command Line Options</h2>
159<!-- ======================================================================= -->
160
161<p>
162This section is generally an index into other sections. It does not go into
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]163depth on the ones that are covered by other sections. However, the first part
164introduces the language selection and other high level options like -c, -g, etc.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]165</p>
166
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]167
168<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
169<h3 id="cl_diagnostics">Options to Control Error and Warning Messages</h3>
170<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
171
172<p><b>-Werror</b>: Turn warnings into errors.</p>
173<p><b>-Werror=foo</b>: Turn warning "foo" into an error.</p>
174<p><b>-Wno-error=foo</b>: Turn warning "foo" into an warning even if -Werror is
175 specified.</p>
176<p><b>-Wfoo</b>: Enable warning foo</p>
177<p><b>-Wno-foo</b>: Disable warning foo</p>
178<p><b>-w</b>: Disable all warnings.</p>
179<p><b>-pedantic</b>: Warn on language extensions.</p>
180<p><b>-pedantic-errors</b>: Error on language extensions.</p>
181<p><b>-Wsystem-headers</b>: Enable warnings from system headers.</p>
182
Chris Lattner0f0c9632010-04-07 20:49:23 +0000[diff] [blame]183<p><b>-ferror-limit=123</b>: Stop emitting diagnostics after 123 errors have
184 been produced. The default is 20, and the error limit can be disabled with
185 -ferror-limit=0.</p>
186
Douglas Gregor575cf372010-04-20 07:18:24 +0000[diff] [blame]187<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>
188
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]189<!-- ================================================= -->
190<h4 id="cl_diag_formatting">Formatting of Diagnostics</h4>
191<!-- ================================================= -->
192
193<p>Clang aims to produce beautiful diagnostics by default, particularly for new
194users that first come to Clang. However, different people have different
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]195preferences, and sometimes Clang is driven by another program that wants to
196parse simple and consistent output, not a person. For these cases, Clang
197provides a wide range of options to control the exact output format of the
198diagnostics that it generates.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]199
200<dl>
201
202<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
203<dt id="opt_fshow-column"><b>-f[no-]show-column</b>: Print column number in
204diagnostic.</dt>
205<dd>This option, which defaults to on, controls whether or not Clang prints the
206column number of a diagnostic. For example, when this is enabled, Clang will
207print something like:</p>
208
209<pre>
210 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
211 #endif bad
212 ^
213 //
214</pre>
215
216<p>When this is disabled, Clang will print "test.c:28: warning..." with no
217column number.</p>
218</dd>
219
220<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
221<dt id="opt_fshow-source-location"><b>-f[no-]show-source-location</b>: Print
222source file/line/column information in diagnostic.</dt>
223<dd>This option, which defaults to on, controls whether or not Clang prints the
224filename, line number and column number of a diagnostic. For example,
225when this is enabled, Clang will print something like:</p>
226
227<pre>
228 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
229 #endif bad
230 ^
231 //
232</pre>
233
234<p>When this is disabled, Clang will not print the "test.c:28:8: " part.</p>
235</dd>
236
237<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
238<dt id="opt_fcaret-diagnostics"><b>-f[no-]caret-diagnostics</b>: Print source
239line and ranges from source code in diagnostic.</dt>
240<dd>This option, which defaults to on, controls whether or not Clang prints the
241source line, source ranges, and caret when emitting a diagnostic. For example,
242when this is enabled, Clang will print something like:</p>
243
244<pre>
245 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
246 #endif bad
247 ^
248 //
249</pre>
250
251<p>When this is disabled, Clang will just print:</p>
252
253<pre>
254 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
255</pre>
256
257</dd>
258
259<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
260<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
261Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
262<dd>This option, which defaults to on,
263controls whether or not Clang prints the associated <A
264href="#cl_diag_warning_groups">warning group</a> option name when outputting
265a warning diagnostic. For example, in this output:</p>
266
267<pre>
268 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
269 #endif bad
270 ^
271 //
272</pre>
273
274<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
275the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
276diagnostic. This information tells you the flag needed to enable or disable the
277diagnostic, either from the command line or through <a
278href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
279
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]280<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
281<dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
282Enable printing category information in diagnostic line.</dt>
283<dd>This option, which defaults to "none",
284controls whether or not Clang prints the category associated with a diagnostic
285when emitting it. Each diagnostic may or many not have an associated category,
286if it has one, it is listed in the diagnostic categorization field of the
287diagnostic line (in the []'s).</p>
288
289<p>For example, a format string warning will produce these three renditions
290based on the setting of this option:</p>
291
292<pre>
293 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
294 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
295 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
296</pre>
297
298<p>This category can be used by clients that want to group diagnostics by
299category, so it should be a high level category. We want dozens of these, not
300hundreds or thousands of them.</p>
301</dd>
302
303
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]304
305<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
306<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
307Enable "FixIt" information in the diagnostics output.</dt>
308<dd>This option, which defaults to on, controls whether or not Clang prints the
309information on how to fix a specific diagnostic underneath it when it knows.
310For example, in this output:</p>
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-fixit-info</b> will prevent Clang from printing
320the "//" line at the end of the message. This information is useful for users
321who may not understand what is wrong, but can be confusing for machine
322parsing.</p>
323</dd>
324
325<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]326<dt id="opt_fdiagnostics-print-source-range-info">
327<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]328Print machine parsable information about source ranges.</dt>
329<dd>This option, which defaults to off, controls whether or not Clang prints
330information about source ranges in a machine parsable format after the
331file/line/column number information. The information is a simple sequence of
332brace enclosed ranges, where each range lists the start and end line/column
333locations. For example, in this output:</p>
334
335<pre>
336exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
337 P = (P-42) + Gamma*4;
338 ~~~~~~ ^ ~~~~~~~
339</pre>
340
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]341<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]342</dd>
343
344
345</dl>
346
347
348
349
350<!-- ===================================================== -->
351<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
352<!-- ===================================================== -->
353
354<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
355
356
357<dl>
358
359
360<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
361<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
362 the end of a preprocessor directive.</dt>
363<dd>This option, which defaults to on, enables warnings about extra tokens at
364the end of preprocessor directives. For example:</p>
365
366<pre>
367 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
368 #endif bad
369 ^
370</pre>
371
372<p>These extra tokens are not strictly conforming, and are usually best handled
373by commenting them out.</p>
374
375<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
376 and <a href="">-Wbaz</a>.</p>
377</dd>
378
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]379<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
380<dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
381Warn about unqualified uses of a member template whose name resolves
382to another template at the location of the use.</dt>
383<dd>This option, which defaults to on, enables a warning in the
384following code:</p>
385
386<pre>
387template&lt;typename T> struct set{};
388template&lt;typename T> struct trait { typedef const T& type; };
389struct Value {
390 template&lt;typename T> void set(typename trait&lt;T>::type value) {}
391};
392void foo() {
393 Value v;
394 v.set&lt;double>(3.2);
395}
396</pre>
397
398<p>C++ [basic.lookup.classref] requires this to be an error, but,
399because it's hard to work around, Clang downgrades it to a warning as
400an extension.</p>
401</dd>
402
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]403<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
404<dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
405an unusable copy constructor when binding a reference to a temporary.</dt>
406<dd>This option, which defaults to on, enables warnings about binding a
407reference to a temporary when the temporary doesn't have a usable copy
408constructor. For example:</p>
409
410<pre>
411 struct NonCopyable {
412 NonCopyable();
413 private:
414 NonCopyable(const NonCopyable&);
415 };
416 void foo(const NonCopyable&);
417 void bar() {
418 foo(NonCopyable()); // Disallowed in C++98; allowed in C++0x.
419 }
420</pre>
421<pre>
422 struct NonCopyable2 {
423 NonCopyable2();
424 NonCopyable2(NonCopyable2&);
425 };
426 void foo(const NonCopyable2&);
427 void bar() {
428 foo(NonCopyable2()); // Disallowed in C++98; allowed in C++0x.
429 }
430</pre>
431
432<p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
433argument whose instantiation produces a compile error, that error will
434still be a hard error in C++98 mode even if this warning is turned
435off.</p>
436
437</dd>
438
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]439</dl>
440
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]441<!-- ======================================================================= -->
442<h2 id="general_features">Language and Target-Independent Features</h2>
443<!-- ======================================================================= -->
444
445
446<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
447<h3 id="diagnostics">Controlling Errors and Warnings</h3>
448<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
449
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]450<p>Clang provides a number of ways to control which code constructs cause it to
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]451emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]452
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]453<h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]454
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]455<p>When Clang emits a diagnostic, it includes rich information in the output,
456and gives you fine-grain control over which information is printed. Clang has
457the ability to print this information, and these are the options that control
458it:</p>
459
460<p>
461<ol>
462<li>A file/line/column indicator that shows exactly where the diagnostic occurs
463 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
464 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
465<li>A categorization of the diagnostic as a note, warning, error, or fatal
466 error.</li>
467<li>A text string that describes what the problem is.</li>
468<li>An option that indicates how to control the diagnostic (for diagnostics that
469 support it) [<a
470 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]471<li>A <a href="#diagnostics_categories">high-level category</a> for the
472 diagnostic for clients that want to group diagnostics by class (for
473 diagnostics that support it) [<a
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]474 href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]475<li>The line of source code that the issue occurs on, along with a caret and
476 ranges that indicate the important locations [<a
477 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
478<li>"FixIt" information, which is a concise explanation of how to fix the
479 problem (when Clang is certain it knows) [<a
480 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
481<li>A machine-parsable representation of the ranges involved (off by
482 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]483 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]484</ol></p>
485
486<p>For more information please see <a href="#cl_diag_formatting">Formatting of
487Diagnostics</a>.</p>
488
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]489
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]490<h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]491
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]492<p>All diagnostics are mapped into one of these 5 classes:</p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]493
494<p>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]495<ul>
496<li>Ignored</li>
497<li>Note</li>
498<li>Warning</li>
499<li>Error</li>
500<li>Fatal</li>
501</ul></p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]502
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]503<h4 id="diagnostics_categories">Diagnostic Categories</h4>
504
505<p>Though not shown by default, diagnostics may each be associated with a
506 high-level category. This category is intended to make it possible to triage
507 builds that produce a large number of errors or warnings in a grouped way.
508</p>
509
510<p>Categories are not shown by default, but they can be turned on with the
511<a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
512When set to "<tt>name</tt>", the category is printed textually in the diagnostic
513output. When it is set to "<tt>id</tt>", a category number is printed. The
514mapping of category names to category id's can be obtained by running '<tt>clang
515 --print-diagnostic-categories</tt>'.
516</p>
517
518<h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
519 Flags</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]520
521<p>-W flags, -pedantic, etc</p>
522
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]523<h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
524
525<p>Clang can also control what diagnostics are enabled through the use of
526pragmas in the source code. This is useful for turning off specific warnings
527in a section of source code. Clang supports GCC's pragma for compatibility
528with existing source code, as well as several extensions. </p>
529
530<p>The pragma may control any warning that can be used from the command line.
531Warnings may be set to ignored, warning, error, or fatal. The following
532example code will tell Clang or GCC to ignore the -Wall warnings:</p>
533
534<pre>
535#pragma GCC diagnostic ignored "-Wall"
536</pre>
537
538<p>In addition to all of the functionality of provided by GCC's pragma, Clang
539also allows you to push and pop the current warning state. This is particularly
540useful when writing a header file that will be compiled by other people, because
541you don't know what warning flags they build with.</p>
542
543<p>In the below example
544-Wmultichar is ignored for only a single line of code, after which the
545diagnostics return to whatever state had previously existed.</p>
546
547<pre>
548#pragma clang diagnostic push
549#pragma clang diagnostic ignored "-Wmultichar"
550
551char b = 'df'; // no warning.
552
553#pragma clang diagnostic pop
554</pre>
555
556<p>The push and pop pragmas will save and restore the full diagnostic state of
557the compiler, regardless of how it was set. That means that it is possible to
558use push and pop around GCC compatible diagnostics and Clang will push and pop
559them appropriately, while GCC will ignore the pushes and pops as unknown
560pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
561GCC do not support the exact same set of warnings, so even when using GCC
562compatible #pragmas there is no guarantee that they will have identical behaviour
563on both compilers. </p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]564
565<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
566<h3 id="precompiledheaders">Precompiled Headers</h3>
567<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
568
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]569<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
570headers</a> are a general approach employed by many compilers to reduce
571compilation time. The underlying motivation of the approach is that it is
572common for the same (and often large) header files to be included by
573multiple source files. Consequently, compile times can often be greatly improved
574by caching some of the (redundant) work done by a compiler to process headers.
575Precompiled header files, which represent one of many ways to implement
576this optimization, are literally files that represent an on-disk cache that
577contains the vital information necessary to reduce some of the work
578needed to process a corresponding header file. While details of precompiled
579headers vary between compilers, precompiled headers have been shown to be a
580highly effective at speeding up program compilation on systems with very large
581system headers (e.g., Mac OS/X).</p>
582
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]583<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]584
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]585<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]586the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
587interface in GCC for generating PCH files:</p>
588
589<pre>
590 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]591 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]592</pre>
593
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]594<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]595
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]596<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]597<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
598
599<pre>
600 $ clang -include test.h test.c -o test
601</pre>
602
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]603<p>The <tt>clang</tt> driver will first check if a PCH file for <tt>test.h</tt>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]604is available; if so, the contents of <tt>test.h</tt> (and the files it includes)
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]605will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]606directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
607GCC.</p>
608
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]609<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]610for headers that are directly included within a source file. For example:</p>
611
612<pre>
Chris Lattnere42ec542009-06-13 20:35:58 +0000[diff] [blame]613 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]614 $ cat test.c
615 #include "test.h"
616 $ clang test.c -o test
617</pre>
618
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]619<p>In this example, <tt>clang</tt> will not automatically use the PCH file for
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]620<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
621and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]622
Douglas Gregore650c8c2009-07-07 00:12:59 +0000[diff] [blame]623<h4>Relocatable PCH Files</h4>
624<p>It is sometimes necessary to build a precompiled header from headers that
625are not yet in their final, installed locations. For example, one might build a
626precompiled header within the build tree that is then meant to be installed
627alongside the headers. Clang permits the creation of "relocatable" precompiled
628headers, which are built with a given path (into the build directory) and can
629later be used from an installed location.</p>
630
631<p>To build a relocatable precompiled header, place your headers into a
632subdirectory whose structure mimics the installed location. For example, if you
633want to build a precompiled header for the header <code>mylib.h</code> that
634will be installed into <code>/usr/include</code>, create a subdirectory
635<code>build/usr/include</code> and place the header <code>mylib.h</code> into
636that subdirectory. If <code>mylib.h</code> depends on other headers, then
637they can be stored within <code>build/usr/include</code> in a way that mimics
638the installed location.</p>
639
640<p>Building a relocatable precompiled header requires two additional arguments.
641First, pass the <code>--relocatable-pch</code> flag to indicate that the
642resulting PCH file should be relocatable. Second, pass
643<code>-isysroot /path/to/build</code>, which makes all includes for your
644library relative to the build directory. For example:</p>
645
646<pre>
647 # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
648</pre>
649
650<p>When loading the relocatable PCH file, the various headers used in the PCH
651file are found from the system header root. For example, <code>mylib.h</code>
652can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
653in some other system root, the <code>-isysroot</code> option can be used provide
654a different system root from which the headers will be based. For example,
655<code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
656<code>mylib.h</code> in
657<code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
658
659<p>Relocatable precompiled headers are intended to be used in a limited number
660of cases where the compilation environment is tightly controlled and the
661precompiled header cannot be generated after headers have been installed.
662Relocatable precompiled headers also have some performance impact, because
663the difference in location between the header locations at PCH build time vs.
664at the time of PCH use requires one of the PCH optimizations,
665<code>stat()</code> caching, to be disabled. However, this change is only
666likely to affect PCH files that reference a large number of headers.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]667
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]668<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
669<h3 id="codegen">Controlling Code Generation</h3>
670<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
671
672<p>Clang provides a number of ways to control code generation. The options are listed below.</p>
673
674<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
675<dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
676on runtime code generation to check for undefined behavior.</dt>
677
678<dd>This option, which defaults to off, controls whether or not Clang
679adds runtime checks for undefined runtime behavior. If the check fails,
680<tt>__builtin_trap()</tt> is used to indicate failure.
681The checks are:
682<p>
Mike Stump88b2a172009-12-16 03:25:12 +0000[diff] [blame]683<li>Subscripting where the static type of one operand is variable
684 which is decayed from an array type and the other operand is
685 greater than the size of the array or less than zero.</li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]686<li>Shift operators where the amount shifted is greater or equal to the
687 promoted bit-width of the left-hand-side or less than zero.</li>
Mike Stump8f6a3ed2009-12-16 03:18:14 +0000[diff] [blame]688<li>If control flow reaches __builtin_unreachable.
689<li>When llvm implements more __builtin_object_size support, reads and
690 writes for objects that __builtin_object_size indicates we aren't
691 accessing valid memory. Bit-fields and vectors are not yet checked.
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]692</p>
693</dd>
694
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]695<dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
696Don't assume that the C++'s new operator is sane.</dt>
Nuno Lopesb23f20d2009-12-17 10:15:49 +0000[diff] [blame]697<dd>This option tells the compiler to do not assume that C++'s global new
698operator will always return a pointer that do not
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]699alias any other pointer when the function returns.</dd>
700
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]701<!-- ======================================================================= -->
702<h2 id="c">C Language Features</h2>
703<!-- ======================================================================= -->
704
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]705<p>The support for standard C in clang is feature-complete except for the C99
706floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]707
708<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]709<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]710<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
711
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]712<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]713
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]714<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
715<h3 id="c_modes">Differences between various standard modes</h3>
716<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]717
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]718<p>clang supports the -std option, which changes what language mode clang uses.
719The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
720for those modes. If no -std option is specified, clang defaults to gnu99 mode.
721</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]722
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]723<p>Differences between all c* and gnu* modes:</p>
724<ul>
725<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]726<li>Target-specific defines not prefixed by underscores, like "linux", are
727defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]728<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
729-trigraphs option.</li>
730<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
731variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]732<li>The Apple "blocks" extension is recognized by default in gnu* modes
733on some platforms; it can be enabled in any mode with the "-fblocks"
734option.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]735</ul>
736
737<p>Differences between *89 and *99 modes:</p>
738<ul>
739<li>The *99 modes default to implementing "inline" as specified in C99, while
740the *89 modes implement the GNU version. This can be overridden for individual
741functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]742<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]743<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
744statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
745<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]746<li>"inline" is not recognized as a keyword in c89 mode.</li>
747<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]748<li>Commas are allowed in integer constant expressions in *99 modes.</li>
749<li>Arrays which are not lvalues are not implicitly promoted to pointers in
750*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]751<li>Some warnings are different.</li>
752</ul>
753
754<p>c94 mode is identical to c89 mode except that digraphs are enabled in
755c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
756
757<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
758<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
759<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
760
761<p>clang tries to be compatible with gcc as much as possible, but some gcc
762extensions are not implemented yet:</p>
763
764<ul>
765<li>clang does not support __label__
766(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
767a relatively small feature, so it is likely to be implemented relatively
768soon.</li>
769
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]770<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]771(<a href="http://llvm.org/bugs/show_bug.cgi?id=3679">bug 3679</a>). Due to
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]772the uses described in the bug, this is likely to be implemented at some
773point, at least partially.</li>
774
775<li>clang does not support #pragma align
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]776(<a href="http://llvm.org/bugs/show_bug.cgi?id=3811">bug 3811</a>). This is a
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]777relatively small feature, so it is likely to be implemented relatively
778soon.</li>
779
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]780<li>clang does not support code generation for local variables pinned to
781registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
782This is a relatively small feature, so it is likely to be implemented
783relatively soon.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]784
785<li>clang does not support decimal floating point types (_Decimal32 and
786friends) or fixed-point types (_Fract and friends); nobody has expressed
787interest in these features yet, so it's hard to say when they will be
788implemented.</li>
789
790<li>clang does not support nested functions; this is a complex feature which
791is infrequently used, so it is unlikely to be implemented anytime soon.</li>
792
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]793<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]794to be implemented soon because it requires additional LLVM backend support.
795</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]796
797<li>clang does not support static initialization of flexible array
798members. This appears to be a rarely used extension, but could be
799implemented pending user demand.</li>
800
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]801<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
802This is used rarely, but in some potentially interesting places, like the
803glibc headers, so it may be implemented pending user demand. Note that
804because clang pretends to be like GCC 4.2, and this extension was introduced
805in 4.3, the glibc headers will not try to use this extension with clang at
806the moment.</li>
807
808<li>clang does not support the gcc extension for forward-declaring function
809parameters; this has not showed up in any real-world code yet, though, so it
810might never be implemented.</li>
811
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]812</ul>
813
814<p>This is not a complete list; if you find an unsupported extension
815missing from this list, please send an e-mail to cfe-dev. This list
816currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
817Also, this list does not include bugs in mostly-implemented features; please
818see 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">
819bug tracker</a> for known existing bugs (FIXME: Is there a section for
820bug-reporting guidelines somewhere?).</p>
821
822<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
823<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
824<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
825
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]826<ul>
827
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]828<li>clang does not support the gcc extension that allows variable-length arrays
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]829in structures. This is for a few of reasons: one, it is tricky
830to implement, two, the extension is completely undocumented, and three, the
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]831extension appears to be rarely used.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]832
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]833<li>clang does not support duplicate definitions of a function where one is
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]834inline. This complicates clients of the AST which normally can expect there is
835at most one definition for each function. Source code using this feature should
836be changed to define the inline and out-of-line definitions in separate
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]837translation units.</li>
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]838
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]839<li>clang does not have an equivalent to gcc's "fold"; this means that
840clang doesn't accept some constructs gcc might accept in contexts where a
841constant expression is required, like "x-x" where x is a variable, or calls
842to C library functions like strlen.</li>
843
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]844<li>clang does not support multiple alternative constraints in inline asm; this
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]845is an extremely obscure feature which would be complicated to implement
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]846correctly.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]847
848<li>clang does not support __builtin_apply and friends; this extension is
849extremely obscure and difficult to implement reliably.</li>
850
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]851</ul>
852
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]853<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
854<h3 id="c_ms">Microsoft extensions</h3>
855<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
856
857<p>clang has some experimental support for extensions from
858Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]859option. This is the default for Windows targets. Note that the
860support is incomplete; enabling Microsoft extensions will silently drop
861certain constructs (including __declspec and Microsoft-style asm statements).
862</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]863
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]864<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]865record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]866
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]867<li>clang supports the Microsoft "#pragma pack" feature for
868controlling record layout. GCC also contains support for this feature,
869however where MSVC and GCC are incompatible clang follows the MSVC
870definition.</li>
871
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]872<!-- ======================================================================= -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]873<h2 id="target_features">Target-Specific Features and Limitations</h2>
874<!-- ======================================================================= -->
875
876
877<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
878<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
879<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
880
881<!-- ======================== -->
882<h4 id="target_arch_x86">X86</h4>
883<!-- ======================== -->
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]884<p>The support for X86 (both 32-bit and 64-bit) is considered stable
885on Darwin (Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to
886correctly compile large C and Objective-C codebases. (FIXME: Anything specific
887we want to say here? Possibly mention some LLVM x86 limitations?)
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]888
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]889<!-- ======================== -->
890<h4 id="target_arch_arm">ARM</h4>
891<!-- ======================== -->
892ARM support is mostly feature-complete, but still experimental; it hasn't
893undergone significant testing.
894
895<!-- ======================== -->
896<h4 id="target_arch_other">Other platforms</h4>
897<!-- ======================== -->
898clang currently contains some support for PPC and Sparc; however, significant
899pieces of code generation are still missing, and they haven't undergone
900significant testing.
901
902<p>clang contains some support for the embedded PIC16 processor
903(FIXME: I haven't been keeping track of this; what should this say?).
904
905<p>clang contains limited support for the MSP430 embedded processor, but both
906the clang support and the LLVM backend support are highly experimental.
907
908<p>Other platforms are completely unsupported at the moment. Adding the
909minimal support needed for parsing and semantic analysis on a new platform
910is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
911of support is also sufficient for conversion to LLVM IR for simple programs.
912Proper support for conversion to LLVM IR requires adding code to
913lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
914Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]915
916<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
917<h3 id="target_os">Operating System Features and Limitations</h3>
918<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
919
920<!-- ======================================= -->
921<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
922<!-- ======================================= -->
923
924<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
925
926</div>
927</body>
928</html>