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17
18<h1>Clang Language Extensions</h1>
19
20<ul>
21<li><a href="#intro">Introduction</a></li>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]22<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]23<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]24<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]25<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]26<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
27<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]28<li><a href="#checking_language_features">Checks for Standard Language Features</a></li>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]29 <ul>
30 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
31 <li><a href="#cxx_rtti">C++ RTTI</a></li>
32 </ul>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]33<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a></li>
34 <ul>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]35 <li><a href="#cxx0x">C++0x</a>
36 <ul>
37 <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li>
38 <li><a href="#cxx_access_control_sfinae">C++0x SFINAE includes access control</a></li>
39 <li><a href="#cxx_alias_templates">C++0x alias templates</a></li>
40 <li><a href="#cxx_attributes">C++0x attributes</a></li>
41 <li><a href="#cxx_default_function_template_args">C++0x default template arguments in function templates</a></li>
42 <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li>
43 <li><a href="#cxx_lambdas">C++0x lambdas</a></li>
44 <li><a href="#cxx_nullptr">C++0x nullptr</a></li>
45 <li><a href="#cxx_override_control">C++0x override control</a></li>
46 <li><a href="#cxx_range_for">C++0x range-based for loop</a></li>
47 <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li>
48 <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li>
49 <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li>
50 <li><a href="#cxx_auto_type">C++0x type inference</a></li>
51 <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li>
52 <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li>
53 <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li>
54 <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li>
55 <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li>
56 </ul>
57 <li><a href="#c1x">C1X</a>
58 <ul>
59 <li><a href="#c_generic_selections">C1X generic selections</a></li>
60 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
61 </ul>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]62 </ul>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]63<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]64<li><a href="#blocks">Blocks</a></li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]65<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]66<li><a href="#builtins">Builtin Functions</a>
67 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]68 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]69 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]70 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]71 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]72</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]73<li><a href="#targetspecific">Target-Specific Extensions</a>
74 <ul>
75 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
76 </ul>
77</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]78<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]79</ul>
80
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]81<!-- ======================================================================= -->
82<h2 id="intro">Introduction</h2>
83<!-- ======================================================================= -->
84
85<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]86addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]87range of GCC extensions. Please see the <a
88href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
89more information on these extensions.</p>
90
91<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]92<h2 id="feature_check">Feature Checking Macros</h2>
93<!-- ======================================================================= -->
94
95<p>Language extensions can be very useful, but only if you know you can depend
Chris Lattnerc70e1932011-03-21 16:25:11 +0000[diff] [blame]96on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]97function-like macros. This allows you to directly test for a feature in your
98code without having to resort to something like autoconf or fragile "compiler
99version checks".</p>
100
101<!-- ======================================================================= -->
102<h3 id="__has_builtin">__has_builtin</h3>
103<!-- ======================================================================= -->
104
105<p>This function-like macro takes a single identifier argument that is the name
106of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
107not. It can be used like this:</p>
108
109<blockquote>
110<pre>
111#ifndef __has_builtin // Optional of course.
112 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
113#endif
114
115...
116#if __has_builtin(__builtin_trap)
117 __builtin_trap();
118#else
119 abort();
120#endif
121...
122</pre>
123</blockquote>
124
125
126<!-- ======================================================================= -->
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]127<h3 id="__has_feature_extension">__has_feature and __has_extension</h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]128<!-- ======================================================================= -->
129
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]130<p>These function-like macros take a single identifier argument that is the
131name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
132is both supported by Clang and standardized in the current language standard
133or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
134<code>__has_extension</code> evaluates to 1 if the feature is supported by
135Clang in the current language (either as a language extension or a standard
136language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]137
138<blockquote>
139<pre>
140#ifndef __has_feature // Optional of course.
141 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
142#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]143#ifndef __has_extension
144 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
145#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]146
147...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]148#if __has_feature(cxx_rvalue_references)
149// This code will only be compiled with the -std=c++0x and -std=gnu++0x
150// options, because rvalue references are only standardized in C++0x.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]151#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]152
153#if __has_extension(cxx_rvalue_references)
154// This code will be compiled with the -std=c++0x, -std=gnu++0x, -std=c++98
155// and -std=gnu++98 options, because rvalue references are supported as a
156// language extension in C++98.
157#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]158</pre>
159</blockquote>
160
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]161<p id="has_feature_back_compat">For backwards compatibility reasons,
162<code>__has_feature</code> can also be used to test for support for
163non-standardized features, i.e. features not prefixed <code>c_</code>,
164<code>cxx_</code> or <code>objc_</code>.</p>
165
166<p>If the <code>-pedantic-errors</code> option is given,
167<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
168
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]169<p>The feature tag is described along with the language feature below.</p>
170
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]171<!-- ======================================================================= -->
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]172<h3 id="__has_attribute">__has_attribute</h3>
173<!-- ======================================================================= -->
174
175<p>This function-like macro takes a single identifier argument that is the name
176of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
177can be used like this:</p>
178
179<blockquote>
180<pre>
181#ifndef __has_attribute // Optional of course.
182 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
183#endif
184
185...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]186#if __has_attribute(always_inline)
187#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]188#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]189#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]190#endif
191...
192</pre>
193</blockquote>
194
195<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]196<h2 id="has_include">Include File Checking Macros</h2>
197<!-- ======================================================================= -->
198
199<p>Not all developments systems have the same include files.
200The <a href="#__has_include">__has_include</a> and
201<a href="#__has_include_next">__has_include_next</a> macros allow you to
202check for the existence of an include file before doing
203a possibly failing #include directive.</p>
204
205<!-- ======================================================================= -->
206<h3 id="__has_include">__has_include</h3>
207<!-- ======================================================================= -->
208
209<p>This function-like macro takes a single file name string argument that
210is the name of an include file. It evaluates to 1 if the file can
211be found using the include paths, or 0 otherwise:</p>
212
213<blockquote>
214<pre>
215// Note the two possible file name string formats.
216#if __has_include("myinclude.h") && __has_include(&lt;stdint.h&gt;)
217# include "myinclude.h"
218#endif
219
220// To avoid problem with non-clang compilers not having this macro.
221#if defined(__has_include) && __has_include("myinclude.h")
222# include "myinclude.h"
223#endif
224</pre>
225</blockquote>
226
227<p>To test for this feature, use #if defined(__has_include).</p>
228
229<!-- ======================================================================= -->
230<h3 id="__has_include_next">__has_include_next</h3>
231<!-- ======================================================================= -->
232
233<p>This function-like macro takes a single file name string argument that
234is the name of an include file. It is like __has_include except that it
235looks for the second instance of the given file found in the include
236paths. It evaluates to 1 if the second instance of the file can
237be found using the include paths, or 0 otherwise:</p>
238
239<blockquote>
240<pre>
241// Note the two possible file name string formats.
242#if __has_include_next("myinclude.h") && __has_include_next(&lt;stdint.h&gt;)
243# include_next "myinclude.h"
244#endif
245
246// To avoid problem with non-clang compilers not having this macro.
247#if defined(__has_include_next) && __has_include_next("myinclude.h")
248# include_next "myinclude.h"
249#endif
250</pre>
251</blockquote>
252
253<p>Note that __has_include_next, like the GNU extension
254#include_next directive, is intended for use in headers only,
255and will issue a warning if used in the top-level compilation
256file. A warning will also be issued if an absolute path
257is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]258
259<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]260<h2 id="builtinmacros">Builtin Macros</h2>
261<!-- ======================================================================= -->
262
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]263<dl>
264 <dt><code>__BASE_FILE__</code></dt>
265 <dd>Defined to a string that contains the name of the main input
266 file passed to Clang.</dd>
267
268 <dt><code>__COUNTER__</code></dt>
269 <dd>Defined to an integer value that starts at zero and is
270 incremented each time the <code>__COUNTER__</code> macro is
271 expanded.</dd>
272
273 <dt><code>__INCLUDE_LEVEL__</code></dt>
274 <dd>Defined to an integral value that is the include depth of the
275 file currently being translated. For the main file, this value is
276 zero.</dd>
277
278 <dt><code>__TIMESTAMP__</code></dt>
279 <dd>Defined to the date and time of the last modification of the
280 current source file.</dd>
281
282 <dt><code>__clang__</code></dt>
283 <dd>Defined when compiling with Clang</dd>
284
285 <dt><code>__clang_major__</code></dt>
286 <dd>Defined to the major version number of Clang (e.g., the 2 in
287 2.0.1).</dd>
288
289 <dt><code>__clang_minor__</code></dt>
290 <dd>Defined to the minor version number of Clang (e.g., the 0 in
291 2.0.1).</dd>
292
293 <dt><code>__clang_patchlevel__</code></dt>
294 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
295
296 <dt><code>__clang_version__</code></dt>
297 <dd>Defined to a string that captures the Clang version, including
298 the Subversion tag or revision number, e.g., "1.5 (trunk
299 102332)".</dd>
300</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]301
302<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]303<h2 id="vectors">Vectors and Extended Vectors</h2>
304<!-- ======================================================================= -->
305
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]306<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
307
308<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
309syntax and other tidbits as seen in OpenCL. An example is:</p>
310
311<blockquote>
312<pre>
313typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
314typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
315
316float4 foo(float2 a, float2 b) {
317 float4 c;
318 c.xz = a;
319 c.yw = b;
320 return c;
321}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]322</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]323</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]324
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]325<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]326
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]327<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
328
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]329<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]330<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]331<!-- ======================================================================= -->
332
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]333<p>An optional string message can be added to the <tt>deprecated</tt>
334and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]335
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]336<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]337<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]338</blockquote>
339
340<p>If the deprecated or unavailable declaration is used, the message
341will be incorporated into the appropriate diagnostic:</p>
342
343<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]344<pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! [-Wdeprecated-declarations]
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]345 explode();
346 ^</pre>
347</blockquote>
348
349<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]350with <tt>__has_extension(attribute_deprecated_with_message)</tt>
351and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]352
353<!-- ======================================================================= -->
354<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
355<!-- ======================================================================= -->
356
357<p>Clang allows attributes to be written on individual enumerators.
358This allows enumerators to be deprecated, made unavailable, etc. The
359attribute must appear after the enumerator name and before any
360initializer, like so:</p>
361
362<blockquote>
363<pre>enum OperationMode {
364 OM_Invalid,
365 OM_Normal,
366 OM_Terrified __attribute__((deprecated)),
367 OM_AbortOnError __attribute__((deprecated)) = 4
368};</pre>
369</blockquote>
370
371<p>Attributes on the <tt>enum</tt> declaration do not apply to
372individual enumerators.</p>
373
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]374<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]375
376<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]377<h2 id="checking_language_features">Checks for Standard Language Features</h2>
378<!-- ======================================================================= -->
379
380<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
381enabled. Those features are listed here.</p>
382
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]383<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]384
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]385<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For
386example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]387
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]388<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]389
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]390<p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example,
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]391compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]392
393<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]394<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
395<!-- ======================================================================= -->
396
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]397<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
398to query if certain upcoming standard language features are enabled. Those
399features are listed here. Features that are not yet implemented will be
400noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]401
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]402<h3 id="cxx0x">C++0x</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]403
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]404<p>The features listed below are slated for inclusion in the upcoming
405C++0x standard. As a result, all these features are enabled
406with the <tt>-std=c++0x</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]407
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]408<h4 id="cxx_decltype">C++0x <tt>decltype()</tt></h3>
409
410<p>Use <tt>__has_feature(cxx_decltype)</tt> or
411<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]412<tt>decltype()</tt> specifier is enabled.</p>
413
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]414<h4 id="cxx_access_control_sfinae">C++0x SFINAE includes access control</h3>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]415
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]416<p>Use <tt>__has_feature(cxx_access_control_sfinae)</tt> or <tt>__has_extension(cxx_access_control_sfinae)</tt> to determine whether access-control errors (e.g., calling a private constructor) are considered to be template argument deduction errors (aka SFINAE errors), per <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1170">C++ DR1170</a>.</p>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]417
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]418<h4 id="cxx_alias_templates">C++0x alias templates</h3>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]419
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]420<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
421<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]422C++0x's alias declarations and alias templates is enabled.</p>
423
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]424<h4 id="cxx_attributes">C++0x attributes</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]425
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]426<p>Use <tt>__has_feature(cxx_attributes)</tt> or
427<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
428parsing with C++0x's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]429
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]430<h4 id="cxx_default_function_template_args">C++0x default template arguments in function templates</h3>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]431
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]432<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
433<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
434if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]435
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]436<h4 id="cxx_deleted_functions">C++0x deleted functions</tt></h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]437
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]438<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
439<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]440deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]441
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]442<h4 id="cxx_lambdas">C++0x lambdas</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]443
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]444<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
445<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
446is enabled. clang does not currently implement this feature.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]447
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]448<h4 id="cxx_nullptr">C++0x <tt>nullptr</tt></h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]449
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]450<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
451<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]452<tt>nullptr</tt> is enabled. clang does not yet fully implement this
453feature.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]454
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]455<h4 id="cxx_override_control">C++0x <tt>override control</tt></h3>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]456
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]457<p>Use <tt>__has_feature(cxx_override_control)</tt> or
458<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]459the override control keywords is enabled.</p>
460
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]461<h4 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h3>
462<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
463<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
464if support for reference-qualified functions (e.g., member functions with
465<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
466is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]467
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]468<h4 id="cxx_range_for">C++0x range-based for loop</tt></h3>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]469
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]470<p>Use <tt>__has_feature(cxx_range_for)</tt> or
471<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
472range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]473
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]474<h4 id="cxx_rvalue_references">C++0x rvalue references</tt></h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]475
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]476<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
477<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]478rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]479
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]480<h4 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]481
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]482<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
483<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]484compile-time assertions using <tt>static_assert</tt> is enabled.</p>
485
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]486<h4 id="cxx_auto_type">C++0x type inference</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]487
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]488<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
489<tt>__has_extension(cxx_auto_type)</tt> to determine C++0x type inference is
490supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
491will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]492
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]493<h4 id="cxx_variadic_templates">C++0x variadic templates</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]494
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]495<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
496<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
Douglas Gregor83d77812011-01-19 23:15:20 +0000[diff] [blame]497for variadic templates is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]498
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]499<h4 id="cxx_inline_namespaces">C++0x inline namespaces</h3>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]500
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]501<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
502<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]503inline namespaces is enabled.</p>
504
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]505<h4 id="cxx_trailing_return">C++0x trailing return type</h3>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]506
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]507<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
508<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
509alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]510
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]511<h4 id="cxx_noexcept">C++0x noexcept</h3>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]512
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]513<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
514<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
515exception specifications is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]516
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]517<h4 id="cxx_strong_enums">C++0x strongly typed enumerations</h3>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]518
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]519<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
520<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]521strongly typed, scoped enumerations is enabled.</p>
522
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]523<h3 id="c1x">C1X</h3>
524
525<p>The features listed below are slated for inclusion in the upcoming
526C1X standard. As a result, all these features are enabled
527with the <tt>-std=c1x</tt> option when compiling C code.</p>
528
529<h4 id="c_generic_selections">C1X generic selections</h2>
530
531<p>Use <tt>__has_feature(c_generic_selections)</tt> or
532<tt>__has_extension(c_generic_selections)</tt> to determine if support for
533generic selections is enabled.</p>
534
535<p>As an extension, the C1X generic selection expression is available in all
536languages supported by Clang. The syntax is the same as that given in the
537C1X draft standard.</p>
538
539<p>In C, type compatibility is decided according to the rules given in the
540appropriate standard, but in C++, which lacks the type compatibility rules
541used in C, types are considered compatible only if they are equivalent.</p>
542
543<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h3>
544
545<p>Use <tt>__has_feature(c_static_assert)</tt> or
546<tt>__has_extension(c_static_assert)</tt> to determine if support for
547compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
548
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]549<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]550<h2 id="checking_type_traits">Checks for Type Traits</h2>
551<!-- ======================================================================= -->
552
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]553<p>Clang supports the <a hef="http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html">GNU C++ type traits</a> and a subset of the <a href="http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx">Microsoft Visual C++ Type traits</a>. For each supported type trait <code>__X</code>, <code>__has_extension(X)</code> indicates the presence of the type trait. For example:
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]554<blockquote>
555<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]556#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]557template&lt;typename From, typename To&gt;
558struct is_convertible_to {
559 static const bool value = __is_convertible_to(From, To);
560};
561#else
562// Emulate type trait
563#endif
564</pre>
565</blockquote>
566
567<p>The following type traits are supported by Clang:</p>
568<ul>
569 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
570 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
571 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
572 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
573 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
574 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
575 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
576 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
577 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
578 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
579 <li><code>__is_class</code> (GNU, Microsoft)</li>
580 <li><code>__is_convertible_to</code> (Microsoft)</li>
581 <li><code>__is_empty</code> (GNU, Microsoft)</li>
582 <li><code>__is_enum</code> (GNU, Microsoft)</li>
583 <li><code>__is_pod</code> (GNU, Microsoft)</li>
584 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
585 <li><code>__is_union</code> (GNU, Microsoft)</li>
586 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
587</ul>
588
589<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]590<h2 id="blocks">Blocks</h2>
591<!-- ======================================================================= -->
592
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]593<p>The syntax and high level language feature description is in <a
594href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
595details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]596href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]597
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]598
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]599<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]600
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]601<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]602<h2 id="overloading-in-c">Function Overloading in C</h2>
603<!-- ======================================================================= -->
604
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]605<p>Clang provides support for C++ function overloading in C. Function
606overloading in C is introduced using the <tt>overloadable</tt> attribute. For
607example, one might provide several overloaded versions of a <tt>tgsin</tt>
608function that invokes the appropriate standard function computing the sine of a
609value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
610precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]611
612<blockquote>
613<pre>
614#include &lt;math.h&gt;
615float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
616double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
617long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
618</pre>
619</blockquote>
620
621<p>Given these declarations, one can call <tt>tgsin</tt> with a
622<tt>float</tt> value to receive a <tt>float</tt> result, with a
623<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
624overloading in C follows the rules of C++ function overloading to pick
625the best overload given the call arguments, with a few C-specific
626semantics:</p>
627<ul>
628 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
629 double</tt> is ranked as a floating-point promotion (per C99) rather
630 than as a floating-point conversion (as in C++).</li>
631
632 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
633 <tt>U*</tt> is considered a pointer conversion (with conversion
634 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
635
636 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
637 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
638 conversion is given "conversion" rank.</li>
639</ul>
640
641<p>The declaration of <tt>overloadable</tt> functions is restricted to
642function declarations and definitions. Most importantly, if any
643function with a given name is given the <tt>overloadable</tt>
644attribute, then all function declarations and definitions with that
645name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]646attribute. This rule even applies to redeclarations of functions whose original
647declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]648
649<blockquote>
650<pre>
651int f(int) __attribute__((overloadable));
652float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
653
654int g(int) __attribute__((overloadable));
655int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
656</pre>
657</blockquote>
658
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]659<p>Functions marked <tt>overloadable</tt> must have
660prototypes. Therefore, the following code is ill-formed:</p>
661
662<blockquote>
663<pre>
664int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
665</pre>
666</blockquote>
667
668<p>However, <tt>overloadable</tt> functions are allowed to use a
669ellipsis even if there are no named parameters (as is permitted in C++). This feature is particularly useful when combined with the <tt>unavailable</tt> attribute:</p>
670
671<blockquote>
672<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]673void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]674</pre>
675</blockquote>
676
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]677<p>Functions declared with the <tt>overloadable</tt> attribute have
678their names mangled according to the same rules as C++ function
679names. For example, the three <tt>tgsin</tt> functions in our
680motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]681<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]682caveats to this use of name mangling:</p>
683
684<ul>
685
686 <li>Future versions of Clang may change the name mangling of
687 functions overloaded in C, so you should not depend on an specific
688 mangling. To be completely safe, we strongly urge the use of
689 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
690
691 <li>The <tt>overloadable</tt> attribute has almost no meaning when
692 used in C++, because names will already be mangled and functions are
693 already overloadable. However, when an <tt>overloadable</tt>
694 function occurs within an <tt>extern "C"</tt> linkage specification,
695 it's name <i>will</i> be mangled in the same way as it would in
696 C.</li>
697</ul>
698
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame^]699<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]700
701
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]702<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]703<h2 id="builtins">Builtin Functions</h2>
704<!-- ======================================================================= -->
705
706<p>Clang supports a number of builtin library functions with the same syntax as
707GCC, including things like <tt>__builtin_nan</tt>,
708<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
709<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
710addition to the GCC builtins, Clang supports a number of builtins that GCC does
711not, which are listed here.</p>
712
713<p>Please note that Clang does not and will not support all of the GCC builtins
714for vector operations. Instead of using builtins, you should use the functions
715defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
716define portable wrappers for these. Many of the Clang versions of these
717functions are implemented directly in terms of <a href="#vectors">extended
718vector support</a> instead of builtins, in order to reduce the number of
719builtins that we need to implement.</p>
720
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]721<!-- ======================================================================= -->
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]722<h3 id="__builtin_shufflevector">__builtin_shufflevector</h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]723<!-- ======================================================================= -->
724
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]725<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]726permutation/shuffle/swizzle operations. This builtin is also very important for
727the implementation of various target-specific header files like
728<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]729</p>
730
731<p><b>Syntax:</b></p>
732
733<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]734__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]735</pre>
736
737<p><b>Examples:</b></p>
738
739<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]740 // Identity operation - return 4-element vector V1.
741 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
742
743 // "Splat" element 0 of V1 into a 4-element result.
744 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
745
746 // Reverse 4-element vector V1.
747 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
748
749 // Concatenate every other element of 4-element vectors V1 and V2.
750 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
751
752 // Concatenate every other element of 8-element vectors V1 and V2.
753 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]754</pre>
755
756<p><b>Description:</b></p>
757
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]758<p>The first two arguments to __builtin_shufflevector are vectors that have the
759same element type. The remaining arguments are a list of integers that specify
760the elements indices of the first two vectors that should be extracted and
761returned in a new vector. These element indices are numbered sequentially
762starting with the first vector, continuing into the second vector. Thus, if
763vec1 is a 4-element vector, index 5 would refer to the second element of vec2.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]764</p>
765
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]766<p>The result of __builtin_shufflevector is a vector
767with the same element type as vec1/vec2 but that has an element count equal to
768the number of indices specified.
769</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]770
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]771<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
772
773<!-- ======================================================================= -->
774<h3 id="__builtin_unreachable">__builtin_unreachable</h3>
775<!-- ======================================================================= -->
776
777<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
778the program cannot be reached, even if the compiler might otherwise think it
779can. This is useful to improve optimization and eliminates certain warnings.
780For example, without the <tt>__builtin_unreachable</tt> in the example below,
781the compiler assumes that the inline asm can fall through and prints a "function
782declared 'noreturn' should not return" warning.
783</p>
784
785<p><b>Syntax:</b></p>
786
787<pre>
788__builtin_unreachable()
789</pre>
790
791<p><b>Example of Use:</b></p>
792
793<pre>
794void myabort(void) __attribute__((noreturn));
795void myabort(void) {
796 asm("int3");
797 __builtin_unreachable();
798}
799</pre>
800
801<p><b>Description:</b></p>
802
803<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
804it has undefined behavior, it is a statement that it is never reached and the
805optimizer can take advantage of this to produce better code. This builtin takes
806no arguments and produces a void result.
807</p>
808
809<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
810
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]811<!-- ======================================================================= -->
812<h3 id="__sync_swap">__sync_swap</h3>
813<!-- ======================================================================= -->
814
815<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
816memory.
817</p>
818
819<p><b>Syntax:</b></p>
820
821<pre>
822<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
823</pre>
824
825<p><b>Example of Use:</b></p>
826
827<pre>
828int old_value = __sync_swap(&value, new_value);
829</pre>
830
831<p><b>Description:</b></p>
832
833<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
834intrinsics to allow code to atomically swap the current value with the new
835value. More importantly, it helps developers write more efficient and correct
836code by avoiding expensive loops around __sync_bool_compare_and_swap() or
837relying on the platform specific implementation details of
838__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
839</p>
840
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]841
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]842<!-- ======================================================================= -->
843<h2 id="targetspecific">Target-Specific Extensions</h2>
844<!-- ======================================================================= -->
845
846<p>Clang supports some language features conditionally on some targets.</p>
847
848<!-- ======================================================================= -->
849<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
850<!-- ======================================================================= -->
851
852<p>The X86 backend has these language extensions:</p>
853
854<!-- ======================================================================= -->
855<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
856<!-- ======================================================================= -->
857
858<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]859relative to the X86 GS segment register, and address space #257 causes it to be
860relative to the X86 FS segment. Note that this is a very very low-level
861feature that should only be used if you know what you're doing (for example in
862an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]863
864<p>Here is an example:</p>
865
866<pre>
867#define GS_RELATIVE __attribute__((address_space(256)))
868int foo(int GS_RELATIVE *P) {
869 return *P;
870}
871</pre>
872
873<p>Which compiles to (on X86-32):</p>
874
875<pre>
876_foo:
877 movl 4(%esp), %eax
878 movl %gs:(%eax), %eax
879 ret
880</pre>
881
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]882<!-- ======================================================================= -->
883<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
884<!-- ======================================================================= -->
885
886<p>Clang supports additional attributes that are useful for documenting program
887invariants and rules for static analysis tools. The extensions documented here
888are used by the <a
889href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
890engine</a> that is part of Clang's Analysis library.</p>
891
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]892<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]893
894<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]895attribute. This attribute, which is typically affixed to a function prototype,
896indicates that a call to a given function never returns. Function prototypes for
897common functions like <tt>exit</tt> are typically annotated with this attribute,
898as well as a variety of common assertion handlers. Users can educate the static
899analyzer about their own custom assertion handles (thus cutting down on false
900positives due to false paths) by marking their own &quot;panic&quot; functions
901with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]902
903<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]904there are special functions that for all intents and purposes should be
905considered panic functions (i.e., they are only called when an internal program
906error occurs) but may actually return so that the program can fail gracefully.
907The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
908as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]909pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]910<tt>noreturn</tt>).</p>
911
912<p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]913same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]914placed at the end of function prototypes:</p>
915
916<pre>
917 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]918</pre>
919
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]920<p>Query for this feature with
921<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]922
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]923<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
924
925<p>Many methods in Objective-C have conventional meanings determined
926by their selectors. For the purposes of static analysis, it is
927sometimes useful to be able to mark a method as having a particular
928conventional meaning despite not having the right selector, or as not
929having the conventional meaning that its selector would suggest.
930For these use cases, we provide an attribute to specifically describe
931the <q>method family</q> that a method belongs to.</p>
932
933<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
934where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
935<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
936can only be placed at the end of a method declaration:</p>
937
938<pre>
939 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
940</pre>
941
942<p>Users who do not wish to change the conventional meaning of a
943method, and who merely want to document its non-standard retain and
944release semantics, should use the
945<a href="#attr_retain_release">retaining behavior attributes</a>
946described below.</p>
947
948<p>Query for this feature with
949<tt>__has_attribute(objc_method_family)</tt>.</p>
950
951<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]952
953<p>In Objective-C, functions and methods are generally assumed to take
954and return objects with +0 retain counts, with some exceptions for
955special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
956there are exceptions, and so Clang provides attributes to allow these
957exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]958ignore non-leaks). Some exceptions may be better described using
959the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
960attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]961
962<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
963<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
964and <tt>cf_returns_not_retained</tt> attributes can be placed on
965methods and functions that return Objective-C or CoreFoundation
966objects. They are commonly placed at the end of a function prototype
967or method declaration:</p>
968
969<pre>
970 id foo() <b>__attribute__((ns_returns_retained))</b>;
971
972 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
973</pre>
974
975<p>The <tt>*_returns_retained</tt> attributes specify that the
976returned object has a +1 retain count.
977The <tt>*_returns_not_retained</tt> attributes specify that the return
978object has a +0 retain count, even if the normal convention for its
979selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
980returned object is +0, but is guaranteed to live at least as long as the
981next flush of an autorelease pool.</p>
982
983<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
984attributes can be placed on an parameter declaration; they specify
985that the argument is expected to have a +1 retain count, which will be
986balanced in some way by the function or method.
987The <tt>ns_consumes_self</tt> attribute can only be placed on an
988Objective-C method; it specifies that the method expects
989its <tt>self</tt> parameter to have a +1 retain count, which it will
990balance in some way.</p>
991
992<pre>
993 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
994
995 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
996 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
997</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]998
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]999<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1000<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1001
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1002</div>
1003</body>
1004</html>