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gerrit-public.fairphone.software / platform / external / clang / ce98c9b1a5719b2d0d2697696c9bacc28facc97c / . / docs / LanguageExtensions.html
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19
20<div id="content">
21
22<h1>Clang Language Extensions</h1>
23
24<ul>
25<li><a href="#intro">Introduction</a></li>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]26<li><a href="#feature_check">Feature Checking Macros</a></li>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]27<li><a href="#has_include">Include File Checking Macros</a></li>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]28<li><a href="#builtinmacros">Builtin Macros</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]29<li><a href="#vectors">Vectors and Extended Vectors</a></li>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]30<li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li>
31<li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]32<li><a href="#checking_language_features">Checks for Standard Language Features</a>
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]33 <ul>
34 <li><a href="#cxx_exceptions">C++ exceptions</a></li>
35 <li><a href="#cxx_rtti">C++ RTTI</a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]36 </ul></li>
37<li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]38 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]39 <li><a href="#cxx0x">C++11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]40 <ul>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]41 <li><a href="#cxx_access_control_sfinae">C++11 SFINAE includes
42 access control</a></li>
43 <li><a href="#cxx_alias_templates">C++11 alias templates</a></li>
44 <li><a href="#cxx_alignas">C++11 alignment specifiers</a></li>
45 <li><a href="#cxx_attributes">C++11 attributes</a></li>
46 <li><a href="#cxx_constexpr">C++11 generalized constant expressions</a></li>
47 <li><a href="#cxx_decltype">C++11 <tt>decltype()</tt></a></li>
48 <li><a href="#cxx_default_function_template_args">C++11 default template arguments in function templates</a></li>
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]49 <li><a href="#cxx_defaulted_functions">C++11 defaulted functions</a></li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]50 <li><a href="#cxx_delegating_constructor">C++11 delegating constructors</a></li>
51 <li><a href="#cxx_deleted_functions">C++11 deleted functions</a></li>
52 <li><a href="#cxx_explicit_conversions">C++11 explicit conversion functions</a></li>
53 <li><a href="#cxx_generalized_initializers">C++11 generalized initializers</a></li>
54 <li><a href="#cxx_implicit_moves">C++11 implicit move constructors/assignment operators</a></li>
55 <li><a href="#cxx_inheriting_constructors">C++11 inheriting constructors</a></li>
56 <li><a href="#cxx_inline_namespaces">C++11 inline namespaces</a></li>
57 <li><a href="#cxx_lambdas">C++11 lambdas</a></li>
58 <li><a href="#cxx_noexcept">C++11 noexcept specification</a></li>
59 <li><a href="#cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</a></li>
60 <li><a href="#cxx_nullptr">C++11 nullptr</a></li>
61 <li><a href="#cxx_override_control">C++11 override control</a></li>
62 <li><a href="#cxx_range_for">C++11 range-based for loop</a></li>
63 <li><a href="#cxx_raw_string_literals">C++11 raw string literals</a></li>
64 <li><a href="#cxx_rvalue_references">C++11 rvalue references</a></li>
65 <li><a href="#cxx_reference_qualified_functions">C++11 reference-qualified functions</a></li>
66 <li><a href="#cxx_static_assert">C++11 <tt>static_assert()</tt></a></li>
67 <li><a href="#cxx_auto_type">C++11 type inference</a></li>
68 <li><a href="#cxx_strong_enums">C++11 strongly-typed enumerations</a></li>
69 <li><a href="#cxx_trailing_return">C++11 trailing return type</a></li>
70 <li><a href="#cxx_unicode_literals">C++11 Unicode string literals</a></li>
71 <li><a href="#cxx_unrestricted_unions">C++11 unrestricted unions</a></li>
72 <li><a href="#cxx_user_literals">C++11 user-defined literals</a></li>
73 <li><a href="#cxx_variadic_templates">C++11 variadic templates</a></li>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]74 </ul></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]75 <li><a href="#c1x">C1X</a>
76 <ul>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]77 <li><a href="#c_alignas">C1X alignment specifiers</a></li>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]78 <li><a href="#c_generic_selections">C1X generic selections</a></li>
79 <li><a href="#c_static_assert">C1X <tt>_Static_assert()</tt></a></li>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]80 </ul></li>
81 </ul> </li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]82<li><a href="#checking_type_traits">Checks for Type Traits</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]83<li><a href="#blocks">Blocks</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]84<li><a href="#objc_features">Objective-C Features</a>
85 <ul>
86 <li><a href="#objc_instancetype">Related result types</a></li>
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]87 <li><a href="#objc_arc">Automatic reference counting</a></li>
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]88 <li><a href="#objc_fixed_enum">Enumerations with a fixed underlying type</a></li>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]89 </ul>
90</li>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]91<li><a href="#overloading-in-c">Function Overloading in C</a></li>
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]92<li><a href="#complex-list-init">Initializer lists for complex numbers in C</a></li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]93<li><a href="#builtins">Builtin Functions</a>
94 <ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]95 <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]96 <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]97 <li><a href="#__sync_swap">__sync_swap</a></li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]98 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]99</li>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]100<li><a href="#targetspecific">Target-Specific Extensions</a>
101 <ul>
102 <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li>
103 </ul>
104</li>
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]105<li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame^]106<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a></li>
107 <ul>
108 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
109 </ul>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]110<li><a href="#threadsafety">Thread Safety Annotation Checking</a></li>
111 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]112 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
113 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
114 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]115 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
116 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]117 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
118 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
119 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
120 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
121 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
122 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
123 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
124 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
125 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
126 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
127 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
128 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
129 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]130 </ul>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]131</ul>
132
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]133<!-- ======================================================================= -->
134<h2 id="intro">Introduction</h2>
135<!-- ======================================================================= -->
136
137<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]138addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]139range of GCC extensions. Please see the <a
140href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
141more information on these extensions.</p>
142
143<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]144<h2 id="feature_check">Feature Checking Macros</h2>
145<!-- ======================================================================= -->
146
147<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]148on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]149function-like macros. This allows you to directly test for a feature in your
150code without having to resort to something like autoconf or fragile "compiler
151version checks".</p>
152
153<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]154<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]155<!-- ======================================================================= -->
156
157<p>This function-like macro takes a single identifier argument that is the name
158of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
159not. It can be used like this:</p>
160
161<blockquote>
162<pre>
163#ifndef __has_builtin // Optional of course.
164 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
165#endif
166
167...
168#if __has_builtin(__builtin_trap)
169 __builtin_trap();
170#else
171 abort();
172#endif
173...
174</pre>
175</blockquote>
176
177
178<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]179<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]180<!-- ======================================================================= -->
181
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]182<p>These function-like macros take a single identifier argument that is the
183name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
184is both supported by Clang and standardized in the current language standard
185or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
186<code>__has_extension</code> evaluates to 1 if the feature is supported by
187Clang in the current language (either as a language extension or a standard
188language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]189
190<blockquote>
191<pre>
192#ifndef __has_feature // Optional of course.
193 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
194#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]195#ifndef __has_extension
196 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
197#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]198
199...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]200#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]201// This code will only be compiled with the -std=c++11 and -std=gnu++11
202// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]203#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]204
205#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]206// This code will be compiled with the -std=c++11, -std=gnu++11, -std=c++98
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]207// and -std=gnu++98 options, because rvalue references are supported as a
208// language extension in C++98.
209#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]210</pre>
211</blockquote>
212
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]213<p id="has_feature_back_compat">For backwards compatibility reasons,
214<code>__has_feature</code> can also be used to test for support for
215non-standardized features, i.e. features not prefixed <code>c_</code>,
216<code>cxx_</code> or <code>objc_</code>.</p>
217
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame^]218<p id="has_feature_for_non_language_features">
219Another use of <code>__has_feature</code> is to check for compiler features
220not related to the language standard, such as e.g.
221<a href="AddressSanitizer.html">AddressSanitizer</a>.
222
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]223<p>If the <code>-pedantic-errors</code> option is given,
224<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
225
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]226<p>The feature tag is described along with the language feature below.</p>
227
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]228<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]229<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]230<!-- ======================================================================= -->
231
232<p>This function-like macro takes a single identifier argument that is the name
233of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
234can be used like this:</p>
235
236<blockquote>
237<pre>
238#ifndef __has_attribute // Optional of course.
239 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
240#endif
241
242...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]243#if __has_attribute(always_inline)
244#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]245#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]246#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]247#endif
248...
249</pre>
250</blockquote>
251
252<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]253<h2 id="has_include">Include File Checking Macros</h2>
254<!-- ======================================================================= -->
255
256<p>Not all developments systems have the same include files.
257The <a href="#__has_include">__has_include</a> and
258<a href="#__has_include_next">__has_include_next</a> macros allow you to
259check for the existence of an include file before doing
260a possibly failing #include directive.</p>
261
262<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]263<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]264<!-- ======================================================================= -->
265
266<p>This function-like macro takes a single file name string argument that
267is the name of an include file. It evaluates to 1 if the file can
268be found using the include paths, or 0 otherwise:</p>
269
270<blockquote>
271<pre>
272// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]273#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]274# include "myinclude.h"
275#endif
276
277// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]278#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]279# include "myinclude.h"
280#endif
281</pre>
282</blockquote>
283
284<p>To test for this feature, use #if defined(__has_include).</p>
285
286<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]287<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]288<!-- ======================================================================= -->
289
290<p>This function-like macro takes a single file name string argument that
291is the name of an include file. It is like __has_include except that it
292looks for the second instance of the given file found in the include
293paths. It evaluates to 1 if the second instance of the file can
294be found using the include paths, or 0 otherwise:</p>
295
296<blockquote>
297<pre>
298// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]299#if __has_include_next("myinclude.h") &amp;&amp; __has_include_next(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]300# include_next "myinclude.h"
301#endif
302
303// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]304#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]305# include_next "myinclude.h"
306#endif
307</pre>
308</blockquote>
309
310<p>Note that __has_include_next, like the GNU extension
311#include_next directive, is intended for use in headers only,
312and will issue a warning if used in the top-level compilation
313file. A warning will also be issued if an absolute path
314is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]315
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]316
317<!-- ======================================================================= -->
318<h3><a name="__has_warning">__has_warning</a></h3>
319<!-- ======================================================================= -->
320
321<p>This function-like macro takes a string literal that represents a command
322 line option for a warning and returns true if that is a valid warning
323 option.</p>
324
325<blockquote>
326<pre>
327#if __has_warning("-Wformat")
328...
329#endif
330</pre>
331</blockquote>
332
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]333<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]334<h2 id="builtinmacros">Builtin Macros</h2>
335<!-- ======================================================================= -->
336
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]337<dl>
338 <dt><code>__BASE_FILE__</code></dt>
339 <dd>Defined to a string that contains the name of the main input
340 file passed to Clang.</dd>
341
342 <dt><code>__COUNTER__</code></dt>
343 <dd>Defined to an integer value that starts at zero and is
344 incremented each time the <code>__COUNTER__</code> macro is
345 expanded.</dd>
346
347 <dt><code>__INCLUDE_LEVEL__</code></dt>
348 <dd>Defined to an integral value that is the include depth of the
349 file currently being translated. For the main file, this value is
350 zero.</dd>
351
352 <dt><code>__TIMESTAMP__</code></dt>
353 <dd>Defined to the date and time of the last modification of the
354 current source file.</dd>
355
356 <dt><code>__clang__</code></dt>
357 <dd>Defined when compiling with Clang</dd>
358
359 <dt><code>__clang_major__</code></dt>
360 <dd>Defined to the major version number of Clang (e.g., the 2 in
361 2.0.1).</dd>
362
363 <dt><code>__clang_minor__</code></dt>
364 <dd>Defined to the minor version number of Clang (e.g., the 0 in
365 2.0.1).</dd>
366
367 <dt><code>__clang_patchlevel__</code></dt>
368 <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd>
369
370 <dt><code>__clang_version__</code></dt>
371 <dd>Defined to a string that captures the Clang version, including
372 the Subversion tag or revision number, e.g., "1.5 (trunk
373 102332)".</dd>
374</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]375
376<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]377<h2 id="vectors">Vectors and Extended Vectors</h2>
378<!-- ======================================================================= -->
379
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]380<p>Supports the GCC vector extensions, plus some stuff like V[1].</p>
381
382<p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw
383syntax and other tidbits as seen in OpenCL. An example is:</p>
384
385<blockquote>
386<pre>
387typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
388typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
389
390float4 foo(float2 a, float2 b) {
391 float4 c;
392 c.xz = a;
393 c.yw = b;
394 return c;
395}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]396</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]397</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]398
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]399<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]400
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]401<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
402
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]403<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]404<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]405<!-- ======================================================================= -->
406
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]407<p>An optional string message can be added to the <tt>deprecated</tt>
408and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]409
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]410<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]411<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]412</blockquote>
413
414<p>If the deprecated or unavailable declaration is used, the message
415will be incorporated into the appropriate diagnostic:</p>
416
417<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]418<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]419 explode();
420 ^</pre>
421</blockquote>
422
423<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]424with <tt>__has_extension(attribute_deprecated_with_message)</tt>
425and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]426
427<!-- ======================================================================= -->
428<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
429<!-- ======================================================================= -->
430
431<p>Clang allows attributes to be written on individual enumerators.
432This allows enumerators to be deprecated, made unavailable, etc. The
433attribute must appear after the enumerator name and before any
434initializer, like so:</p>
435
436<blockquote>
437<pre>enum OperationMode {
438 OM_Invalid,
439 OM_Normal,
440 OM_Terrified __attribute__((deprecated)),
441 OM_AbortOnError __attribute__((deprecated)) = 4
442};</pre>
443</blockquote>
444
445<p>Attributes on the <tt>enum</tt> declaration do not apply to
446individual enumerators.</p>
447
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]448<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]449
450<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]451<h2 id="checking_language_features">Checks for Standard Language Features</h2>
452<!-- ======================================================================= -->
453
454<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
455enabled. Those features are listed here.</p>
456
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]457<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]458
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]459<p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For
Sean Hunt647ba1b2011-06-23 00:42:53 +0000[diff] [blame]460example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]461
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]462<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]463
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]464<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]465compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]466
467<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]468<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
469<!-- ======================================================================= -->
470
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]471<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
472to query if certain upcoming standard language features are enabled. Those
473features are listed here. Features that are not yet implemented will be
474noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]475
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]476<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]477
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]478<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]479C++11 standard. As a result, all these features are enabled
480with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]481
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]482<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]483
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]484<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]485
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]486<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]487
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]488<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
489<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]490C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]491
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]492<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]493
494<p>Use <tt>__has_feature(cxx_alignas)</tt> or
495<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
496specifiers using <tt>alignas</tt> is enabled.</p>
497
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]498<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]499
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]500<p>Use <tt>__has_feature(cxx_attributes)</tt> or
501<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]502parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]503
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]504<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]505
506<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
507for generalized constant expressions (e.g., <tt>constexpr</tt>) is
508enabled. Clang does not currently implement this feature.</p>
509
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]510<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]511
512<p>Use <tt>__has_feature(cxx_decltype)</tt> or
513<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
514<tt>decltype()</tt> specifier is enabled.</p>
515
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]516<h4 id="cxx_default_function_template_args">C++11 default template arguments in function templates</h4>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]517
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]518<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
519<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
520if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]521
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]522<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
523
524<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
525<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
526defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
527
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]528<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]529
530<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
531support for delegating constructors is enabled.</p>
532
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]533<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]534
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]535<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
536<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]537deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]538
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]539<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h3>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]540<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
541
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]542<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]543
544<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
545support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]546<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
547this feature.</p>
548
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]549<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]550
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]551<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
552implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]553
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]554<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]555
556<p>Use <tt>__has_feature(cxx_inheriting_constructors)</tt> to determine if support for inheriting constructors is enabled. Clang does not currently implement this feature.</p>
557
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]558<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]559
560<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
561<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
562inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]563
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]564<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]565
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]566<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
567<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]568is enabled. Clang does not currently implement this feature.</p>
569
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]570<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]571
572<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
573<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
574exception specifications is enabled.</p>
575
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]576<h4 id="cxx_nonstatic_member_init">C++11 in-class non-static data member initialization</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]577
578<p>Use <tt>__has_feature(cxx_nonstatic_member_init)</tt> to determine whether in-class initialization of non-static data members is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]579
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]580<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]581
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]582<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
583<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]584<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]585
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]586<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]587
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]588<p>Use <tt>__has_feature(cxx_override_control)</tt> or
589<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]590the override control keywords is enabled.</p>
591
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]592<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]593<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
594<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
595if support for reference-qualified functions (e.g., member functions with
596<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
597is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]598
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]599<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]600
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]601<p>Use <tt>__has_feature(cxx_range_for)</tt> or
602<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
603range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]604
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]605<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]606<p>Use <tt>__has_feature(cxx_raw_string_literals)</tt> to determine if support for raw string literals (e.g., <tt>R"foo\bar"</tt>) is enabled.</p>
607
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]608<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]609
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]610<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
611<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]612rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]613
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]614<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]615
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]616<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
617<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]618compile-time assertions using <tt>static_assert</tt> is enabled.</p>
619
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]620<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]621
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]622<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]623<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]624supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
625will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]626
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]627<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]628
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]629<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
630<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
631strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]632
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]633<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]634
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]635<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
636<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
637alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]638
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]639<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]640<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
641support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]642
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]643<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]644
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]645<p>Use <tt>__has_feature(cxx_unrestricted_unions)</tt> to determine if support for unrestricted unions is enabled. Clang does not currently support this feature.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]646
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]647<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]648
649<p>Use <tt>__has_feature(cxx_user_literals)</tt> to determine if support for user-defined literals is enabled. Clang does not currently support this feature.</p>
650
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]651<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]652
653<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
654<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
655for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]656
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]657<h3 id="c1x">C1X</h3>
658
659<p>The features listed below are slated for inclusion in the upcoming
660C1X standard. As a result, all these features are enabled
661with the <tt>-std=c1x</tt> option when compiling C code.</p>
662
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]663<h4 id="c_alignas">C1X alignment specifiers</h4>
664
665<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
666to determine if support for alignment specifiers using <tt>_Alignas</tt>
667is enabled.</p>
668
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]669<h4 id="c_generic_selections">C1X generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]670
671<p>Use <tt>__has_feature(c_generic_selections)</tt> or
672<tt>__has_extension(c_generic_selections)</tt> to determine if support for
673generic selections is enabled.</p>
674
675<p>As an extension, the C1X generic selection expression is available in all
676languages supported by Clang. The syntax is the same as that given in the
677C1X draft standard.</p>
678
679<p>In C, type compatibility is decided according to the rules given in the
680appropriate standard, but in C++, which lacks the type compatibility rules
681used in C, types are considered compatible only if they are equivalent.</p>
682
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]683<h4 id="c_static_assert">C1X <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]684
685<p>Use <tt>__has_feature(c_static_assert)</tt> or
686<tt>__has_extension(c_static_assert)</tt> to determine if support for
687compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
688
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]689<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]690<h2 id="checking_type_traits">Checks for Type Traits</h2>
691<!-- ======================================================================= -->
692
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]693<p>Clang supports the <a href="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]694<blockquote>
695<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]696#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]697template&lt;typename From, typename To&gt;
698struct is_convertible_to {
699 static const bool value = __is_convertible_to(From, To);
700};
701#else
702// Emulate type trait
703#endif
704</pre>
705</blockquote>
706
707<p>The following type traits are supported by Clang:</p>
708<ul>
709 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
710 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
711 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
712 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
713 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
714 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
715 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
716 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
717 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
718 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
719 <li><code>__is_class</code> (GNU, Microsoft)</li>
720 <li><code>__is_convertible_to</code> (Microsoft)</li>
721 <li><code>__is_empty</code> (GNU, Microsoft)</li>
722 <li><code>__is_enum</code> (GNU, Microsoft)</li>
723 <li><code>__is_pod</code> (GNU, Microsoft)</li>
724 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
725 <li><code>__is_union</code> (GNU, Microsoft)</li>
726 <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]727 <li><code>__underlying_type(type)</code>: Retrieves the underlying type for a given <code>enum</code> type. This trait is required to implement the C++11 standard library.</li>
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]728</ul>
729
730<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]731<h2 id="blocks">Blocks</h2>
732<!-- ======================================================================= -->
733
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]734<p>The syntax and high level language feature description is in <a
735href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
736details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]737href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]738
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]739
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]740<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]741
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]742<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]743<h2 id="objc_features">Objective-C Features</h2>
744<!-- ======================================================================= -->
745
746<h3 id="objc_instancetype">Related result types</h3>
747
748<p>According to Cocoa conventions, Objective-C methods with certain names ("init", "alloc", etc.) always return objects that are an instance of the receiving class's type. Such methods are said to have a "related result type", meaning that a message send to one of these methods will have the same static type as an instance of the receiver class. For example, given the following classes:</p>
749
750<blockquote>
751<pre>
752@interface NSObject
753+ (id)alloc;
754- (id)init;
755@end
756
757@interface NSArray : NSObject
758@end
759</pre>
760</blockquote>
761
762<p>and this common initialization pattern</p>
763
764<blockquote>
765<pre>
766NSArray *array = [[NSArray alloc] init];
767</pre>
768</blockquote>
769
770<p>the type of the expression <code>[NSArray alloc]</code> is
771<code>NSArray*</code> because <code>alloc</code> implicitly has a
772related result type. Similarly, the type of the expression
773<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
774<code>init</code> has a related result type and its receiver is known
775to have the type <code>NSArray *</code>. If neither <code>alloc</code> nor <code>init</code> had a related result type, the expressions would have had type <code>id</code>, as declared in the method signature.</p>
776
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]777<p>A method with a related result type can be declared by using the
778type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
779is a contextual keyword that is only permitted in the result type of
780an Objective-C method, e.g.</p>
781
782<pre>
783@interface A
784+ (<b>instancetype</b>)constructAnA;
785@end
786</pre>
787
788<p>The related result type can also be inferred for some methods.
789To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]790word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]791considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]792type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]793
794<ul>
795
796 <li>the first word is "alloc" or "new", and the method is a class
797 method, or</li>
798
799 <li>the first word is "autorelease", "init", "retain", or "self",
800 and the method is an instance method.</li>
801
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]802</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]803
804<p>If a method with a related result type is overridden by a subclass
805method, the subclass method must also return a type that is compatible
806with the subclass type. For example:</p>
807
808<blockquote>
809<pre>
810@interface NSString : NSObject
811- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
812@end
813</pre>
814</blockquote>
815
816<p>Related result types only affect the type of a message send or
817property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]818with a related result type is treated the same way as method that
819returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]820
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]821<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
822the <tt>instancetype</tt> contextual keyword is available.</p>
823
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]824<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]825<h2 id="objc_arc">Automatic reference counting </h2>
826<!-- ======================================================================= -->
827
828<p>Clang provides support for <a href="AutomaticReferenceCounting.html">automated reference counting</a> in Objective-C, which eliminates the need for manual retain/release/autorelease message sends. There are two feature macros associated with automatic reference counting: <code>__has_feature(objc_arc)</code> indicates the availability of automated reference counting in general, while <code>__has_feature(objc_arc_weak)</code> indicates that automated reference counting also includes support for <code>__weak</code> pointers to Objective-C objects.</p>
829
830<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]831<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
832<!-- ======================================================================= -->
833
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]834<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]835underlying type within Objective-C. For example, one can write an
836enumeration type as:</p>
837
838<pre>
839typedef enum : unsigned char { Red, Green, Blue } Color;
840</pre>
841
842<p>This specifies that the underlying type, which is used to store the
843enumeration value, is <tt>unsigned char</tt>.</p>
844
845<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
846support for fixed underlying types is available in Objective-C.</p>
847
848<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]849<h2 id="overloading-in-c">Function Overloading in C</h2>
850<!-- ======================================================================= -->
851
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]852<p>Clang provides support for C++ function overloading in C. Function
853overloading in C is introduced using the <tt>overloadable</tt> attribute. For
854example, one might provide several overloaded versions of a <tt>tgsin</tt>
855function that invokes the appropriate standard function computing the sine of a
856value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
857precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]858
859<blockquote>
860<pre>
861#include &lt;math.h&gt;
862float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
863double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
864long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
865</pre>
866</blockquote>
867
868<p>Given these declarations, one can call <tt>tgsin</tt> with a
869<tt>float</tt> value to receive a <tt>float</tt> result, with a
870<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
871overloading in C follows the rules of C++ function overloading to pick
872the best overload given the call arguments, with a few C-specific
873semantics:</p>
874<ul>
875 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
876 double</tt> is ranked as a floating-point promotion (per C99) rather
877 than as a floating-point conversion (as in C++).</li>
878
879 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
880 <tt>U*</tt> is considered a pointer conversion (with conversion
881 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
882
883 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
884 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
885 conversion is given "conversion" rank.</li>
886</ul>
887
888<p>The declaration of <tt>overloadable</tt> functions is restricted to
889function declarations and definitions. Most importantly, if any
890function with a given name is given the <tt>overloadable</tt>
891attribute, then all function declarations and definitions with that
892name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]893attribute. This rule even applies to redeclarations of functions whose original
894declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]895
896<blockquote>
897<pre>
898int f(int) __attribute__((overloadable));
899float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
900
901int g(int) __attribute__((overloadable));
902int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
903</pre>
904</blockquote>
905
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]906<p>Functions marked <tt>overloadable</tt> must have
907prototypes. Therefore, the following code is ill-formed:</p>
908
909<blockquote>
910<pre>
911int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
912</pre>
913</blockquote>
914
915<p>However, <tt>overloadable</tt> functions are allowed to use a
916ellipsis 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>
917
918<blockquote>
919<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]920void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]921</pre>
922</blockquote>
923
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]924<p>Functions declared with the <tt>overloadable</tt> attribute have
925their names mangled according to the same rules as C++ function
926names. For example, the three <tt>tgsin</tt> functions in our
927motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]928<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]929caveats to this use of name mangling:</p>
930
931<ul>
932
933 <li>Future versions of Clang may change the name mangling of
934 functions overloaded in C, so you should not depend on an specific
935 mangling. To be completely safe, we strongly urge the use of
936 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
937
938 <li>The <tt>overloadable</tt> attribute has almost no meaning when
939 used in C++, because names will already be mangled and functions are
940 already overloadable. However, when an <tt>overloadable</tt>
941 function occurs within an <tt>extern "C"</tt> linkage specification,
942 it's name <i>will</i> be mangled in the same way as it would in
943 C.</li>
944</ul>
945
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]946<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]947
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]948<!-- ======================================================================= -->
949<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
950<!-- ======================================================================= -->
951
952<p>clang supports an extension which allows the following in C:</p>
953
954<blockquote>
955<pre>
956#include &lt;math.h&gt;
957#include &lt;complex.h&gt;
958complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
959</pre>
960</blockquote>
961
962<p>This construct is useful because there is no way to separately
963initialize the real and imaginary parts of a complex variable in
964standard C, given that clang does not support <code>_Imaginary</code>.
965(clang also supports the <code>__real__</code> and <code>__imag__</code>
966extensions from gcc, which help in some cases, but are not usable in
967static initializers.)
968
969<p>Note that this extension does not allow eliding the braces; the
970meaning of the following two lines is different:</p>
971
972<blockquote>
973<pre>
974complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
975complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
976</pre>
977</blockquote>
978
979<p>This extension also works in C++ mode, as far as that goes, but does not
980 apply to the C++ <code>std::complex</code>. (In C++11, list
981 initialization allows the same syntax to be used with
982 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]983
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]984<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]985<h2 id="builtins">Builtin Functions</h2>
986<!-- ======================================================================= -->
987
988<p>Clang supports a number of builtin library functions with the same syntax as
989GCC, including things like <tt>__builtin_nan</tt>,
990<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
991<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
992addition to the GCC builtins, Clang supports a number of builtins that GCC does
993not, which are listed here.</p>
994
995<p>Please note that Clang does not and will not support all of the GCC builtins
996for vector operations. Instead of using builtins, you should use the functions
997defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
998define portable wrappers for these. Many of the Clang versions of these
999functions are implemented directly in terms of <a href="#vectors">extended
1000vector support</a> instead of builtins, in order to reduce the number of
1001builtins that we need to implement.</p>
1002
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1003<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1004<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1005<!-- ======================================================================= -->
1006
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1007<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1008permutation/shuffle/swizzle operations. This builtin is also very important for
1009the implementation of various target-specific header files like
1010<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1011</p>
1012
1013<p><b>Syntax:</b></p>
1014
1015<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1016__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1017</pre>
1018
1019<p><b>Examples:</b></p>
1020
1021<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1022 // Identity operation - return 4-element vector V1.
1023 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1024
1025 // "Splat" element 0 of V1 into a 4-element result.
1026 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1027
1028 // Reverse 4-element vector V1.
1029 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1030
1031 // Concatenate every other element of 4-element vectors V1 and V2.
1032 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1033
1034 // Concatenate every other element of 8-element vectors V1 and V2.
1035 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1036</pre>
1037
1038<p><b>Description:</b></p>
1039
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1040<p>The first two arguments to __builtin_shufflevector are vectors that have the
1041same element type. The remaining arguments are a list of integers that specify
1042the elements indices of the first two vectors that should be extracted and
1043returned in a new vector. These element indices are numbered sequentially
1044starting with the first vector, continuing into the second vector. Thus, if
1045vec1 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]1046</p>
1047
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1048<p>The result of __builtin_shufflevector is a vector
1049with the same element type as vec1/vec2 but that has an element count equal to
1050the number of indices specified.
1051</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1052
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1053<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1054
1055<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1056<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1057<!-- ======================================================================= -->
1058
1059<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1060the program cannot be reached, even if the compiler might otherwise think it
1061can. This is useful to improve optimization and eliminates certain warnings.
1062For example, without the <tt>__builtin_unreachable</tt> in the example below,
1063the compiler assumes that the inline asm can fall through and prints a "function
1064declared 'noreturn' should not return" warning.
1065</p>
1066
1067<p><b>Syntax:</b></p>
1068
1069<pre>
1070__builtin_unreachable()
1071</pre>
1072
1073<p><b>Example of Use:</b></p>
1074
1075<pre>
1076void myabort(void) __attribute__((noreturn));
1077void myabort(void) {
1078 asm("int3");
1079 __builtin_unreachable();
1080}
1081</pre>
1082
1083<p><b>Description:</b></p>
1084
1085<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1086it has undefined behavior, it is a statement that it is never reached and the
1087optimizer can take advantage of this to produce better code. This builtin takes
1088no arguments and produces a void result.
1089</p>
1090
1091<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1092
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1093<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1094<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1095<!-- ======================================================================= -->
1096
1097<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1098memory.
1099</p>
1100
1101<p><b>Syntax:</b></p>
1102
1103<pre>
1104<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1105</pre>
1106
1107<p><b>Example of Use:</b></p>
1108
1109<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1110int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1111</pre>
1112
1113<p><b>Description:</b></p>
1114
1115<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1116intrinsics to allow code to atomically swap the current value with the new
1117value. More importantly, it helps developers write more efficient and correct
1118code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1119relying on the platform specific implementation details of
1120__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1121</p>
1122
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1123
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1124<!-- ======================================================================= -->
1125<h2 id="targetspecific">Target-Specific Extensions</h2>
1126<!-- ======================================================================= -->
1127
1128<p>Clang supports some language features conditionally on some targets.</p>
1129
1130<!-- ======================================================================= -->
1131<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1132<!-- ======================================================================= -->
1133
1134<p>The X86 backend has these language extensions:</p>
1135
1136<!-- ======================================================================= -->
1137<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1138<!-- ======================================================================= -->
1139
1140<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1141relative to the X86 GS segment register, and address space #257 causes it to be
1142relative to the X86 FS segment. Note that this is a very very low-level
1143feature that should only be used if you know what you're doing (for example in
1144an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1145
1146<p>Here is an example:</p>
1147
1148<pre>
1149#define GS_RELATIVE __attribute__((address_space(256)))
1150int foo(int GS_RELATIVE *P) {
1151 return *P;
1152}
1153</pre>
1154
1155<p>Which compiles to (on X86-32):</p>
1156
1157<pre>
1158_foo:
1159 movl 4(%esp), %eax
1160 movl %gs:(%eax), %eax
1161 ret
1162</pre>
1163
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1164<!-- ======================================================================= -->
1165<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1166<!-- ======================================================================= -->
1167
1168<p>Clang supports additional attributes that are useful for documenting program
1169invariants and rules for static analysis tools. The extensions documented here
1170are used by the <a
1171href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1172engine</a> that is part of Clang's Analysis library.</p>
1173
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1174<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1175
1176<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1177attribute. This attribute, which is typically affixed to a function prototype,
1178indicates that a call to a given function never returns. Function prototypes for
1179common functions like <tt>exit</tt> are typically annotated with this attribute,
1180as well as a variety of common assertion handlers. Users can educate the static
1181analyzer about their own custom assertion handles (thus cutting down on false
1182positives due to false paths) by marking their own &quot;panic&quot; functions
1183with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1184
1185<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1186there are special functions that for all intents and purposes should be
1187considered panic functions (i.e., they are only called when an internal program
1188error occurs) but may actually return so that the program can fail gracefully.
1189The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1190as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1191pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1192<tt>noreturn</tt>).</p>
1193
1194<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]1195same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1196placed at the end of function prototypes:</p>
1197
1198<pre>
1199 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1200</pre>
1201
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1202<p>Query for this feature with
1203<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1204
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1205<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1206
1207<p>Many methods in Objective-C have conventional meanings determined
1208by their selectors. For the purposes of static analysis, it is
1209sometimes useful to be able to mark a method as having a particular
1210conventional meaning despite not having the right selector, or as not
1211having the conventional meaning that its selector would suggest.
1212For these use cases, we provide an attribute to specifically describe
1213the <q>method family</q> that a method belongs to.</p>
1214
1215<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1216where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1217<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1218can only be placed at the end of a method declaration:</p>
1219
1220<pre>
1221 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1222</pre>
1223
1224<p>Users who do not wish to change the conventional meaning of a
1225method, and who merely want to document its non-standard retain and
1226release semantics, should use the
1227<a href="#attr_retain_release">retaining behavior attributes</a>
1228described below.</p>
1229
1230<p>Query for this feature with
1231<tt>__has_attribute(objc_method_family)</tt>.</p>
1232
1233<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1234
1235<p>In Objective-C, functions and methods are generally assumed to take
1236and return objects with +0 retain counts, with some exceptions for
1237special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1238there are exceptions, and so Clang provides attributes to allow these
1239exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1240ignore non-leaks). Some exceptions may be better described using
1241the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1242attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1243
1244<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1245<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1246and <tt>cf_returns_not_retained</tt> attributes can be placed on
1247methods and functions that return Objective-C or CoreFoundation
1248objects. They are commonly placed at the end of a function prototype
1249or method declaration:</p>
1250
1251<pre>
1252 id foo() <b>__attribute__((ns_returns_retained))</b>;
1253
1254 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1255</pre>
1256
1257<p>The <tt>*_returns_retained</tt> attributes specify that the
1258returned object has a +1 retain count.
1259The <tt>*_returns_not_retained</tt> attributes specify that the return
1260object has a +0 retain count, even if the normal convention for its
1261selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1262returned object is +0, but is guaranteed to live at least as long as the
1263next flush of an autorelease pool.</p>
1264
1265<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1266attributes can be placed on an parameter declaration; they specify
1267that the argument is expected to have a +1 retain count, which will be
1268balanced in some way by the function or method.
1269The <tt>ns_consumes_self</tt> attribute can only be placed on an
1270Objective-C method; it specifies that the method expects
1271its <tt>self</tt> parameter to have a +1 retain count, which it will
1272balance in some way.</p>
1273
1274<pre>
1275 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1276
1277 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1278 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1279</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1280
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1281<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1282<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1283
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame^]1284<!-- ======================================================================= -->
1285<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1286<!-- ======================================================================= -->
1287<h3 id="address_sanitizer">AddressSanitizer</h3>
1288<p> Use <code>__has_feature(address_sanitizer)</code>
1289to check if the code is being built with <a
1290 href="AddressSanitizer.html">AddressSanitizer</a>.
1291</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1292
1293<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1294<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1295<!-- ======================================================================= -->
1296
1297<p>Clang supports additional attributes for checking basic locking policies in
1298multithreaded programs.
1299Clang currently parses the following list of attributes, although
1300<b>the implementation for these annotations is currently in development.</b>
1301For more details, see the
1302<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1303</p>
1304
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1305<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1306
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1307<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1308declaration to specify that the thread safety analysis should not be run on that
1309function. This attribute provides an escape hatch (e.g. for situations when it
1310is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1311
1312<h4 id="ts_lockable">lockable</h4>
1313
1314<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1315that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1316used to check consistency.</p>
1317
1318<h4 id="ts_scopedlockable">scoped_lockable</h4>
1319
1320<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1321specify that it has a "scoped" lockable type. Objects of this type will acquire
1322the lock upon construction and release it upon going out of scope.
1323 This annotation is primarily used to check
1324consistency.</p>
1325
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1326<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1327
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1328<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1329specify that the variable must be accessed while holding some lock.</p>
1330
1331<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1332
1333<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1334specify that the pointer must be dereferenced while holding some lock.</p>
1335
1336<h4 id="ts_guardedby">guarded_by(l)</h4>
1337
1338<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1339specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1340
1341<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1342
1343<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1344specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1345
1346<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1347
1348<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1349of a lockable variable to specify that the lock must be acquired before all
1350attribute arguments. Arguments must be lockable type, and there must be at
1351least one argument.</p>
1352
1353<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1354
1355<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1356of a lockable variable to specify that the lock must be acquired after all
1357attribute arguments. Arguments must be lockable type, and there must be at
1358least one argument.</p>
1359
1360<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1361
1362<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1363declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1364exclusively. This attribute takes zero or more arguments: either of lockable
1365type or integers indexing into function parameters of lockable type. If no
1366arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1367enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1368
1369<h4 id="ts_slf">shared_lock_function(...)</h4>
1370
1371<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1372declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1373 the locks may be shared (e.g. read locks). This attribute takes zero or more
1374arguments: either of lockable type or integers indexing into function
1375parameters of lockable type. If no arguments are given, the acquired lock is
1376implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1377
1378<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1379
1380<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1381declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1382all listed locks exclusively. This attribute takes one or more arguments. The
1383first argument is an integer or boolean value specifying the return value of a
1384successful lock acquisition. The remaining arugments are either of lockable type
1385or integers indexing into function parameters of lockable type. If only one
1386argument is given, the acquired lock is implicitly <tt>this</tt> of the
1387enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1388
1389<h4 id="ts_stf">shared_trylock_function(...)</h4>
1390
1391<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1392declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1393all listed locks, although the locks may be shared (e.g. read locks). This
1394attribute takes one or more arguments. The first argument is an integer or
1395boolean value specifying the return value of a successful lock acquisition. The
1396remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1397function parameters of lockable type. If only one argument is given, the
1398acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1399
1400<h4 id="ts_uf">unlock_function(...)</h4>
1401
1402<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1403declaration to specify that the function release all listed locks. This
1404attribute takes zero or more arguments: either of lockable type or integers
1405indexing into function parameters of lockable type. If no arguments are given,
1406the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1407
1408<h4 id="ts_lr">lock_returned(l)</h4>
1409
1410<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1411declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1412must be of lockable type). This annotation is used to aid in resolving lock
1413expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1414
1415<h4 id="ts_le">locks_excluded(...)</h4>
1416
1417<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1418to specify that the function must not be called with the listed locks. Arguments
1419must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1420
1421<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1422
1423<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1424declaration to specify that the function must be called while holding the listed
1425exclusive locks. Arguments must be lockable type, and there must be at
1426least one argument.</p>
1427
1428<h4 id="ts_slr">shared_locks_required(...)</h4>
1429
1430<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1431declaration to specify that the function must be called while holding the listed
1432shared locks. Arguments must be lockable type, and there must be at
1433least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1434
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1435</div>
1436</body>
1437</html>