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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>
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame^]254 <b><font color="black">test.c:28:8: <font color="magenta">warning</font>: extra tokens at end of #endif directive [-Wextra-tokens]</font></b>
255 #endif bad
256 <font color="green">^</font>
257 <font color="green">//</font>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]258</pre>
259
260</dd>
261
262<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Douglas Gregore8d44dd2010-07-09 16:31:58 +0000[diff] [blame^]263<dt id="opt_fcolor_diagnostics"><b>-f[no-]color-diagnostics</b>: </dt>
264<dd>This option, which defaults to on when a color-capable terminal is
265 detected, controls whether or not Clang prints diagnostics in color.
266 When this option is enabled, Clang will use colors to highlight
267 specific parts of the diagnostic, e.g.,
268
269<pre>
270<test.c:2:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
271#endif bad
272 ^
273 //
274</pre>
275</dd>'
276<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]277<dt id="opt_fdiagnostics-show-option"><b>-f[no-]diagnostics-show-option</b>:
278Enable <tt>[-Woption]</tt> information in diagnostic line.</dt>
279<dd>This option, which defaults to on,
280controls whether or not Clang prints the associated <A
281href="#cl_diag_warning_groups">warning group</a> option name when outputting
282a warning diagnostic. For example, in this output:</p>
283
284<pre>
285 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
286 #endif bad
287 ^
288 //
289</pre>
290
291<p>Passing <b>-fno-diagnostics-show-option</b> will prevent Clang from printing
292the [<a href="#opt_Wextra-tokens">-Wextra-tokens</a>] information in the
293diagnostic. This information tells you the flag needed to enable or disable the
294diagnostic, either from the command line or through <a
295href="#pragma_GCC_diagnostic">#pragma GCC diagnostic</a>.</dd>
296
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]297<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
298<dt id="opt_fdiagnostics-show-category"><b>-fdiagnostics-show-category=none/id/name</b>:
299Enable printing category information in diagnostic line.</dt>
300<dd>This option, which defaults to "none",
301controls whether or not Clang prints the category associated with a diagnostic
302when emitting it. Each diagnostic may or many not have an associated category,
303if it has one, it is listed in the diagnostic categorization field of the
304diagnostic line (in the []'s).</p>
305
306<p>For example, a format string warning will produce these three renditions
307based on the setting of this option:</p>
308
309<pre>
310 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat]
311 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,1</b>]
312 t.c:3:11: warning: conversion specifies type 'char *' but the argument has type 'int' [-Wformat<b>,Format String</b>]
313</pre>
314
315<p>This category can be used by clients that want to group diagnostics by
316category, so it should be a high level category. We want dozens of these, not
317hundreds or thousands of them.</p>
318</dd>
319
320
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]321
322<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
323<dt id="opt_fdiagnostics-fixit-info"><b>-f[no-]diagnostics-fixit-info</b>:
324Enable "FixIt" information in the diagnostics output.</dt>
325<dd>This option, which defaults to on, controls whether or not Clang prints the
326information on how to fix a specific diagnostic underneath it when it knows.
327For example, in this output:</p>
328
329<pre>
330 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
331 #endif bad
332 ^
333 //
334</pre>
335
336<p>Passing <b>-fno-diagnostics-fixit-info</b> will prevent Clang from printing
337the "//" line at the end of the message. This information is useful for users
338who may not understand what is wrong, but can be confusing for machine
339parsing.</p>
340</dd>
341
342<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]343<dt id="opt_fdiagnostics-print-source-range-info">
344<b>-f[no-]diagnostics-print-source-range-info</b>:
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]345Print machine parsable information about source ranges.</dt>
346<dd>This option, which defaults to off, controls whether or not Clang prints
347information about source ranges in a machine parsable format after the
348file/line/column number information. The information is a simple sequence of
349brace enclosed ranges, where each range lists the start and end line/column
350locations. For example, in this output:</p>
351
352<pre>
353exprs.c:47:15:{47:8-47:14}{47:17-47:24}: error: invalid operands to binary expression ('int *' and '_Complex float')
354 P = (P-42) + Gamma*4;
355 ~~~~~~ ^ ~~~~~~~
356</pre>
357
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]358<p>The {}'s are generated by -fdiagnostics-print-source-range-info.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]359</dd>
360
361
362</dl>
363
364
365
366
367<!-- ===================================================== -->
368<h4 id="cl_diag_warning_groups">Individual Warning Groups</h4>
369<!-- ===================================================== -->
370
371<p>TODO: Generate this from tblgen. Define one anchor per warning group.</p>
372
373
374<dl>
375
376
377<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
378<dt id="opt_Wextra-tokens"><b>-Wextra-tokens</b>: Warn about excess tokens at
379 the end of a preprocessor directive.</dt>
380<dd>This option, which defaults to on, enables warnings about extra tokens at
381the end of preprocessor directives. For example:</p>
382
383<pre>
384 test.c:28:8: warning: extra tokens at end of #endif directive [-Wextra-tokens]
385 #endif bad
386 ^
387</pre>
388
389<p>These extra tokens are not strictly conforming, and are usually best handled
390by commenting them out.</p>
391
392<p>This option is also enabled by <a href="">-Wfoo</a>, <a href="">-Wbar</a>,
393 and <a href="">-Wbaz</a>.</p>
394</dd>
395
Jeffrey Yasskin21d07e42010-06-05 01:39:57 +0000[diff] [blame]396<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
397<dt id="opt_Wambiguous-member-template"><b>-Wambiguous-member-template</b>:
398Warn about unqualified uses of a member template whose name resolves
399to another template at the location of the use.</dt>
400<dd>This option, which defaults to on, enables a warning in the
401following code:</p>
402
403<pre>
404template&lt;typename T> struct set{};
405template&lt;typename T> struct trait { typedef const T& type; };
406struct Value {
407 template&lt;typename T> void set(typename trait&lt;T>::type value) {}
408};
409void foo() {
410 Value v;
411 v.set&lt;double>(3.2);
412}
413</pre>
414
415<p>C++ [basic.lookup.classref] requires this to be an error, but,
416because it's hard to work around, Clang downgrades it to a warning as
417an extension.</p>
418</dd>
419
Jeffrey Yasskin57d12fd2010-06-07 15:58:05 +0000[diff] [blame]420<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
421<dt id="opt_Wbind-to-temporary-copy"><b>-Wbind-to-temporary-copy</b>: Warn about
422an unusable copy constructor when binding a reference to a temporary.</dt>
423<dd>This option, which defaults to on, enables warnings about binding a
424reference to a temporary when the temporary doesn't have a usable copy
425constructor. For example:</p>
426
427<pre>
428 struct NonCopyable {
429 NonCopyable();
430 private:
431 NonCopyable(const NonCopyable&);
432 };
433 void foo(const NonCopyable&);
434 void bar() {
435 foo(NonCopyable()); // Disallowed in C++98; allowed in C++0x.
436 }
437</pre>
438<pre>
439 struct NonCopyable2 {
440 NonCopyable2();
441 NonCopyable2(NonCopyable2&);
442 };
443 void foo(const NonCopyable2&);
444 void bar() {
445 foo(NonCopyable2()); // Disallowed in C++98; allowed in C++0x.
446 }
447</pre>
448
449<p>Note that if <tt>NonCopyable2::NonCopyable2()</tt> has a default
450argument whose instantiation produces a compile error, that error will
451still be a hard error in C++98 mode even if this warning is turned
452off.</p>
453
454</dd>
455
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]456</dl>
457
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]458<!-- ======================================================================= -->
459<h2 id="general_features">Language and Target-Independent Features</h2>
460<!-- ======================================================================= -->
461
462
463<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
464<h3 id="diagnostics">Controlling Errors and Warnings</h3>
465<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
466
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]467<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]468emit errors and warning messages, and how they are displayed to the console.</p>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]469
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]470<h4 id="diagnostics_display">Controlling How Clang Displays Diagnostics</h4>
Chris Lattner65a795b2009-04-20 06:00:23 +0000[diff] [blame]471
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]472<p>When Clang emits a diagnostic, it includes rich information in the output,
473and gives you fine-grain control over which information is printed. Clang has
474the ability to print this information, and these are the options that control
475it:</p>
476
477<p>
478<ol>
479<li>A file/line/column indicator that shows exactly where the diagnostic occurs
480 in your code [<a href="#opt_fshow-column">-fshow-column</a>, <a
481 href="#opt_fshow-source-location">-fshow-source-location</a>].</li>
482<li>A categorization of the diagnostic as a note, warning, error, or fatal
483 error.</li>
484<li>A text string that describes what the problem is.</li>
485<li>An option that indicates how to control the diagnostic (for diagnostics that
486 support it) [<a
487 href="#opt_fdiagnostics-show-option">-fdiagnostics-show-option</a>].</li>
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]488<li>A <a href="#diagnostics_categories">high-level category</a> for the
489 diagnostic for clients that want to group diagnostics by class (for
490 diagnostics that support it) [<a
Chris Lattner28a43a42010-05-05 01:35:28 +0000[diff] [blame]491 href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]492<li>The line of source code that the issue occurs on, along with a caret and
493 ranges that indicate the important locations [<a
494 href="opt_fcaret-diagnostics">-fcaret-diagnostics</a>].</li>
495<li>"FixIt" information, which is a concise explanation of how to fix the
496 problem (when Clang is certain it knows) [<a
497 href="opt_fdiagnostics-fixit-info">-fdiagnostics-fixit-info</a>].</li>
498<li>A machine-parsable representation of the ranges involved (off by
499 default) [<a
Chris Lattner2a9cc232009-04-21 05:35:32 +0000[diff] [blame]500 href="opt_fdiagnostics-print-source-range-info">-fdiagnostics-print-source-range-info</a>].</li>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]501</ol></p>
502
503<p>For more information please see <a href="#cl_diag_formatting">Formatting of
504Diagnostics</a>.</p>
505
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]506
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]507<h4 id="diagnostics_mappings">Diagnostic Mappings</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]508
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]509<p>All diagnostics are mapped into one of these 5 classes:</p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]510
511<p>
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]512<ul>
513<li>Ignored</li>
514<li>Note</li>
515<li>Warning</li>
516<li>Error</li>
517<li>Fatal</li>
518</ul></p>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]519
Chris Lattner3f145382010-05-24 21:35:18 +0000[diff] [blame]520<h4 id="diagnostics_categories">Diagnostic Categories</h4>
521
522<p>Though not shown by default, diagnostics may each be associated with a
523 high-level category. This category is intended to make it possible to triage
524 builds that produce a large number of errors or warnings in a grouped way.
525</p>
526
527<p>Categories are not shown by default, but they can be turned on with the
528<a href="#opt_fdiagnostics-show-category">-fdiagnostics-show-category</a> option.
529When set to "<tt>name</tt>", the category is printed textually in the diagnostic
530output. When it is set to "<tt>id</tt>", a category number is printed. The
531mapping of category names to category id's can be obtained by running '<tt>clang
532 --print-diagnostic-categories</tt>'.
533</p>
534
535<h4 id="diagnostics_commandline">Controlling Diagnostics via Command Line
536 Flags</h4>
Chris Lattner8217f4e2009-04-20 06:26:18 +0000[diff] [blame]537
538<p>-W flags, -pedantic, etc</p>
539
Chris Lattner3401cf82009-07-12 21:22:10 +0000[diff] [blame]540<h4 id="diagnostics_pragmas">Controlling Diagnostics via Pragmas</h4>
541
542<p>Clang can also control what diagnostics are enabled through the use of
543pragmas in the source code. This is useful for turning off specific warnings
544in a section of source code. Clang supports GCC's pragma for compatibility
545with existing source code, as well as several extensions. </p>
546
547<p>The pragma may control any warning that can be used from the command line.
548Warnings may be set to ignored, warning, error, or fatal. The following
549example code will tell Clang or GCC to ignore the -Wall warnings:</p>
550
551<pre>
552#pragma GCC diagnostic ignored "-Wall"
553</pre>
554
555<p>In addition to all of the functionality of provided by GCC's pragma, Clang
556also allows you to push and pop the current warning state. This is particularly
557useful when writing a header file that will be compiled by other people, because
558you don't know what warning flags they build with.</p>
559
560<p>In the below example
561-Wmultichar is ignored for only a single line of code, after which the
562diagnostics return to whatever state had previously existed.</p>
563
564<pre>
565#pragma clang diagnostic push
566#pragma clang diagnostic ignored "-Wmultichar"
567
568char b = 'df'; // no warning.
569
570#pragma clang diagnostic pop
571</pre>
572
573<p>The push and pop pragmas will save and restore the full diagnostic state of
574the compiler, regardless of how it was set. That means that it is possible to
575use push and pop around GCC compatible diagnostics and Clang will push and pop
576them appropriately, while GCC will ignore the pushes and pops as unknown
577pragmas. It should be noted that while Clang supports the GCC pragma, Clang and
578GCC do not support the exact same set of warnings, so even when using GCC
579compatible #pragmas there is no guarantee that they will have identical behaviour
580on both compilers. </p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]581
582<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
583<h3 id="precompiledheaders">Precompiled Headers</h3>
584<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
585
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]586<p><a href="http://en.wikipedia.org/wiki/Precompiled_header">Precompiled
587headers</a> are a general approach employed by many compilers to reduce
588compilation time. The underlying motivation of the approach is that it is
589common for the same (and often large) header files to be included by
590multiple source files. Consequently, compile times can often be greatly improved
591by caching some of the (redundant) work done by a compiler to process headers.
592Precompiled header files, which represent one of many ways to implement
593this optimization, are literally files that represent an on-disk cache that
594contains the vital information necessary to reduce some of the work
595needed to process a corresponding header file. While details of precompiled
596headers vary between compilers, precompiled headers have been shown to be a
597highly effective at speeding up program compilation on systems with very large
598system headers (e.g., Mac OS/X).</p>
599
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]600<h4>Generating a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]601
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]602<p>To generate a PCH file using Clang, one invokes Clang with
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]603the <b><tt>-x <i>&lt;language&gt;</i>-header</tt></b> option. This mirrors the
604interface in GCC for generating PCH files:</p>
605
606<pre>
607 $ gcc -x c-header test.h -o test.h.gch
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]608 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]609</pre>
610
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]611<h4>Using a PCH File</h4>
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]612
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]613<p>A PCH file can then be used as a prefix header when a
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]614<b><tt>-include</tt></b> option is passed to <tt>clang</tt>:</p>
615
616<pre>
617 $ clang -include test.h test.c -o test
618</pre>
619
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]620<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]621is 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]622will be processed from the PCH file. Otherwise, Clang falls back to
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]623directly processing the content of <tt>test.h</tt>. This mirrors the behavior of
624GCC.</p>
625
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]626<p><b>NOTE:</b> Clang does <em>not</em> automatically use PCH files
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]627for headers that are directly included within a source file. For example:</p>
628
629<pre>
Chris Lattnere42ec542009-06-13 20:35:58 +0000[diff] [blame]630 $ clang -x c-header test.h -o test.h.pch
Chris Lattner5c3074f2009-04-20 04:37:38 +0000[diff] [blame]631 $ cat test.c
632 #include "test.h"
633 $ clang test.c -o test
634</pre>
635
Douglas Gregorf4d59532009-06-03 22:37:00 +0000[diff] [blame]636<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]637<tt>test.h</tt> since <tt>test.h</tt> was included directly in the source file
638and not specified on the command line using <tt>-include</tt>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]639
Douglas Gregore650c8c2009-07-07 00:12:59 +0000[diff] [blame]640<h4>Relocatable PCH Files</h4>
641<p>It is sometimes necessary to build a precompiled header from headers that
642are not yet in their final, installed locations. For example, one might build a
643precompiled header within the build tree that is then meant to be installed
644alongside the headers. Clang permits the creation of "relocatable" precompiled
645headers, which are built with a given path (into the build directory) and can
646later be used from an installed location.</p>
647
648<p>To build a relocatable precompiled header, place your headers into a
649subdirectory whose structure mimics the installed location. For example, if you
650want to build a precompiled header for the header <code>mylib.h</code> that
651will be installed into <code>/usr/include</code>, create a subdirectory
652<code>build/usr/include</code> and place the header <code>mylib.h</code> into
653that subdirectory. If <code>mylib.h</code> depends on other headers, then
654they can be stored within <code>build/usr/include</code> in a way that mimics
655the installed location.</p>
656
657<p>Building a relocatable precompiled header requires two additional arguments.
658First, pass the <code>--relocatable-pch</code> flag to indicate that the
659resulting PCH file should be relocatable. Second, pass
660<code>-isysroot /path/to/build</code>, which makes all includes for your
661library relative to the build directory. For example:</p>
662
663<pre>
664 # clang -x c-header --relocatable-pch -isysroot /path/to/build /path/to/build/mylib.h mylib.h.pch
665</pre>
666
667<p>When loading the relocatable PCH file, the various headers used in the PCH
668file are found from the system header root. For example, <code>mylib.h</code>
669can be found in <code>/usr/include/mylib.h</code>. If the headers are installed
670in some other system root, the <code>-isysroot</code> option can be used provide
671a different system root from which the headers will be based. For example,
672<code>-isysroot /Developer/SDKs/MacOSX10.4u.sdk</code> will look for
673<code>mylib.h</code> in
674<code>/Developer/SDKs/MacOSX10.4u.sdk/usr/include/mylib.h</code>.</p>
675
676<p>Relocatable precompiled headers are intended to be used in a limited number
677of cases where the compilation environment is tightly controlled and the
678precompiled header cannot be generated after headers have been installed.
679Relocatable precompiled headers also have some performance impact, because
680the difference in location between the header locations at PCH build time vs.
681at the time of PCH use requires one of the PCH optimizations,
682<code>stat()</code> caching, to be disabled. However, this change is only
683likely to affect PCH files that reference a large number of headers.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]684
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]685<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
686<h3 id="codegen">Controlling Code Generation</h3>
687<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
688
689<p>Clang provides a number of ways to control code generation. The options are listed below.</p>
690
691<!-- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -->
692<dt id="opt_fcatch-undefined-behavior"><b>-fcatch-undefined-behavior</b>: Turn
693on runtime code generation to check for undefined behavior.</dt>
694
695<dd>This option, which defaults to off, controls whether or not Clang
696adds runtime checks for undefined runtime behavior. If the check fails,
697<tt>__builtin_trap()</tt> is used to indicate failure.
698The checks are:
699<p>
Mike Stump88b2a172009-12-16 03:25:12 +0000[diff] [blame]700<li>Subscripting where the static type of one operand is variable
701 which is decayed from an array type and the other operand is
702 greater than the size of the array or less than zero.</li>
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]703<li>Shift operators where the amount shifted is greater or equal to the
704 promoted bit-width of the left-hand-side or less than zero.</li>
Mike Stump8f6a3ed2009-12-16 03:18:14 +0000[diff] [blame]705<li>If control flow reaches __builtin_unreachable.
706<li>When llvm implements more __builtin_object_size support, reads and
707 writes for objects that __builtin_object_size indicates we aren't
708 accessing valid memory. Bit-fields and vectors are not yet checked.
Mike Stump53664ca2009-12-14 23:53:10 +0000[diff] [blame]709</p>
710</dd>
711
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]712<dt id="opt_fno-assume-sane-operator-new"><b>-fno-assume-sane-operator-new</b>:
713Don't assume that the C++'s new operator is sane.</dt>
Nuno Lopesb23f20d2009-12-17 10:15:49 +0000[diff] [blame]714<dd>This option tells the compiler to do not assume that C++'s global new
715operator will always return a pointer that do not
Nuno Lopesaa526242009-12-17 10:00:52 +0000[diff] [blame]716alias any other pointer when the function returns.</dd>
717
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]718<!-- ======================================================================= -->
719<h2 id="c">C Language Features</h2>
720<!-- ======================================================================= -->
721
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]722<p>The support for standard C in clang is feature-complete except for the C99
723floating-point pragmas.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]724
725<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]726<h3 id="c_ext">Extensions supported by clang</h3>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]727<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
728
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]729<p>See <a href="LanguageExtensions.html">clang language extensions</a>.</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]730
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]731<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
732<h3 id="c_modes">Differences between various standard modes</h3>
733<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]734
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]735<p>clang supports the -std option, which changes what language mode clang uses.
736The supported modes for C are c89, gnu89, c94, c99, gnu99 and various aliases
737for those modes. If no -std option is specified, clang defaults to gnu99 mode.
738</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]739
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]740<p>Differences between all c* and gnu* modes:</p>
741<ul>
742<li>c* modes define "__STRICT_ANSI__".</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]743<li>Target-specific defines not prefixed by underscores, like "linux", are
744defined in gnu* modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]745<li>Trigraphs default to being off in gnu* modes; they can be enabled by the
746-trigraphs option.</li>
747<li>The parser recognizes "asm" and "typeof" as keywords in gnu* modes; the
748variants "__asm__" and "__typeof__" are recognized in all modes.</li>
Eli Friedmanb0ac5452009-05-16 23:17:30 +0000[diff] [blame]749<li>The Apple "blocks" extension is recognized by default in gnu* modes
750on some platforms; it can be enabled in any mode with the "-fblocks"
751option.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]752</ul>
753
754<p>Differences between *89 and *99 modes:</p>
755<ul>
756<li>The *99 modes default to implementing "inline" as specified in C99, while
757the *89 modes implement the GNU version. This can be overridden for individual
758functions with the __gnu_inline__ attribute.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]759<li>Digraphs are not recognized in c89 mode.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]760<li>The scope of names defined inside a "for", "if", "switch", "while", or "do"
761statement is different. (example: "if ((struct x {int x;}*)0) {}".)</li>
762<li>__STDC_VERSION__ is not defined in *89 modes.</li>
Eli Friedman26fa0ed2009-05-27 23:02:57 +0000[diff] [blame]763<li>"inline" is not recognized as a keyword in c89 mode.</li>
764<li>"restrict" is not recognized as a keyword in *89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]765<li>Commas are allowed in integer constant expressions in *99 modes.</li>
766<li>Arrays which are not lvalues are not implicitly promoted to pointers in
767*89 modes.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]768<li>Some warnings are different.</li>
769</ul>
770
771<p>c94 mode is identical to c89 mode except that digraphs are enabled in
772c94 mode (FIXME: And __STDC_VERSION__ should be defined!).</p>
773
774<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
775<h3 id="c_unimpl_gcc">GCC extensions not implemented yet</h3>
776<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
777
778<p>clang tries to be compatible with gcc as much as possible, but some gcc
779extensions are not implemented yet:</p>
780
781<ul>
782<li>clang does not support __label__
783(<a href="http://llvm.org/bugs/show_bug.cgi?id=3429">bug 3429</a>). This is
784a relatively small feature, so it is likely to be implemented relatively
785soon.</li>
786
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]787<li>clang does not support #pragma weak
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]788(<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]789the uses described in the bug, this is likely to be implemented at some
790point, at least partially.</li>
791
792<li>clang does not support #pragma align
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]793(<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]794relatively small feature, so it is likely to be implemented relatively
795soon.</li>
796
Eli Friedman4da92552009-06-02 08:21:31 +0000[diff] [blame]797<li>clang does not support code generation for local variables pinned to
798registers (<a href="http://llvm.org/bugs/show_bug.cgi?id=3933">bug 3933</a>).
799This is a relatively small feature, so it is likely to be implemented
800relatively soon.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]801
802<li>clang does not support decimal floating point types (_Decimal32 and
803friends) or fixed-point types (_Fract and friends); nobody has expressed
804interest in these features yet, so it's hard to say when they will be
805implemented.</li>
806
807<li>clang does not support nested functions; this is a complex feature which
808is infrequently used, so it is unlikely to be implemented anytime soon.</li>
809
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]810<li>clang does not support global register variables, this is unlikely
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]811to be implemented soon because it requires additional LLVM backend support.
812</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]813
814<li>clang does not support static initialization of flexible array
815members. This appears to be a rarely used extension, but could be
816implemented pending user demand.</li>
817
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]818<li>clang does not support __builtin_va_arg_pack/__builtin_va_arg_pack_len.
819This is used rarely, but in some potentially interesting places, like the
820glibc headers, so it may be implemented pending user demand. Note that
821because clang pretends to be like GCC 4.2, and this extension was introduced
822in 4.3, the glibc headers will not try to use this extension with clang at
823the moment.</li>
824
825<li>clang does not support the gcc extension for forward-declaring function
826parameters; this has not showed up in any real-world code yet, though, so it
827might never be implemented.</li>
828
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]829</ul>
830
831<p>This is not a complete list; if you find an unsupported extension
832missing from this list, please send an e-mail to cfe-dev. This list
833currently excludes C++; see <a href="#cxx">C++ Language Features</a>.
834Also, this list does not include bugs in mostly-implemented features; please
835see 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">
836bug tracker</a> for known existing bugs (FIXME: Is there a section for
837bug-reporting guidelines somewhere?).</p>
838
839<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
840<h3 id="c_unsupp_gcc">Intentionally unsupported GCC extensions</h3>
841<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
842
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]843<ul>
844
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]845<li>clang does not support the gcc extension that allows variable-length arrays
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]846in structures. This is for a few of reasons: one, it is tricky
847to implement, two, the extension is completely undocumented, and three, the
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]848extension appears to be rarely used.</li>
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]849
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]850<li>clang does not support duplicate definitions of a function where one is
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]851inline. This complicates clients of the AST which normally can expect there is
852at most one definition for each function. Source code using this feature should
853be changed to define the inline and out-of-line definitions in separate
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]854translation units.</li>
Daniel Dunbarc5f928c2009-06-04 18:37:52 +0000[diff] [blame]855
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]856<li>clang does not have an equivalent to gcc's "fold"; this means that
857clang doesn't accept some constructs gcc might accept in contexts where a
858constant expression is required, like "x-x" where x is a variable, or calls
859to C library functions like strlen.</li>
860
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]861<li>clang does not support multiple alternative constraints in inline asm; this
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]862is an extremely obscure feature which would be complicated to implement
Eli Friedman2f3fca02009-06-12 20:08:48 +0000[diff] [blame]863correctly.</li>
Eli Friedmanca130bd2009-06-12 20:04:25 +0000[diff] [blame]864
865<li>clang does not support __builtin_apply and friends; this extension is
866extremely obscure and difficult to implement reliably.</li>
867
Eli Friedman0b326002009-06-12 20:11:05 +0000[diff] [blame]868</ul>
869
Eli Friedman660a5ac2009-04-28 18:48:34 +0000[diff] [blame]870<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
871<h3 id="c_ms">Microsoft extensions</h3>
872<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
873
874<p>clang has some experimental support for extensions from
875Microsoft Visual C++; to enable it, use the -fms-extensions command-line
Eli Friedmana1821b52009-06-08 06:21:03 +0000[diff] [blame]876option. This is the default for Windows targets. Note that the
877support is incomplete; enabling Microsoft extensions will silently drop
878certain constructs (including __declspec and Microsoft-style asm statements).
879</p>
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]880
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]881<li>clang does not support the Microsoft extension where anonymous
Daniel Dunbar869e0542009-05-13 00:23:53 +0000[diff] [blame]882record members can be declared using user defined typedefs.</li>
Daniel Dunbar05fa6292009-05-12 23:12:07 +0000[diff] [blame]883
Daniel Dunbar9375ed12009-05-13 21:40:49 +0000[diff] [blame]884<li>clang supports the Microsoft "#pragma pack" feature for
885controlling record layout. GCC also contains support for this feature,
886however where MSVC and GCC are incompatible clang follows the MSVC
887definition.</li>
888
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]889<!-- ======================================================================= -->
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]890<h2 id="target_features">Target-Specific Features and Limitations</h2>
891<!-- ======================================================================= -->
892
893
894<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
895<h3 id="target_arch">CPU Architectures Features and Limitations</h3>
896<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
897
898<!-- ======================== -->
899<h4 id="target_arch_x86">X86</h4>
900<!-- ======================== -->
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]901<p>The support for X86 (both 32-bit and 64-bit) is considered stable
902on Darwin (Mac OS/X), Linux, FreeBSD, and Dragonfly BSD: it has been tested to
903correctly compile large C and Objective-C codebases. (FIXME: Anything specific
904we want to say here? Possibly mention some LLVM x86 limitations?)
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]905
Eli Friedman3b658d32009-06-08 05:12:39 +0000[diff] [blame]906<!-- ======================== -->
907<h4 id="target_arch_arm">ARM</h4>
908<!-- ======================== -->
909ARM support is mostly feature-complete, but still experimental; it hasn't
910undergone significant testing.
911
912<!-- ======================== -->
913<h4 id="target_arch_other">Other platforms</h4>
914<!-- ======================== -->
915clang currently contains some support for PPC and Sparc; however, significant
916pieces of code generation are still missing, and they haven't undergone
917significant testing.
918
919<p>clang contains some support for the embedded PIC16 processor
920(FIXME: I haven't been keeping track of this; what should this say?).
921
922<p>clang contains limited support for the MSP430 embedded processor, but both
923the clang support and the LLVM backend support are highly experimental.
924
925<p>Other platforms are completely unsupported at the moment. Adding the
926minimal support needed for parsing and semantic analysis on a new platform
927is quite easy; see lib/Basic/Targets.cpp in the clang source tree. This level
928of support is also sufficient for conversion to LLVM IR for simple programs.
929Proper support for conversion to LLVM IR requires adding code to
930lib/CodeGen/CGCall.cpp at the moment; this is likely to change soon, though.
931Generating assembly requires a suitable LLVM backend.
Chris Lattnercf17d9d2009-04-20 04:23:09 +0000[diff] [blame]932
933<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
934<h3 id="target_os">Operating System Features and Limitations</h3>
935<!-- = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = -->
936
937<!-- ======================================= -->
938<h4 id="target_os_darwin">Darwin (Mac OS/X)</h4>
939<!-- ======================================= -->
940
941<p>No __thread support, 64-bit ObjC support requires SL tools.</p>
942
943</div>
944</body>
945</html>