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gerrit-public.fairphone.software / platform / external / clang / 5e9392ba18f5925e26cc5714d1412eda0d219826 / . / 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>
Douglas Gregor5e9392b2011-12-03 18:14:24 +0000[diff] [blame^]727 <li><code>__is_final</code>: Determines whether the given type is declared with a <code>final</code> class-virt-specifier.</li>
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]728 <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]729</ul>
730
731<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]732<h2 id="blocks">Blocks</h2>
733<!-- ======================================================================= -->
734
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]735<p>The syntax and high level language feature description is in <a
736href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
737details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]738href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]739
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]740
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]741<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]742
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]743<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]744<h2 id="objc_features">Objective-C Features</h2>
745<!-- ======================================================================= -->
746
747<h3 id="objc_instancetype">Related result types</h3>
748
749<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>
750
751<blockquote>
752<pre>
753@interface NSObject
754+ (id)alloc;
755- (id)init;
756@end
757
758@interface NSArray : NSObject
759@end
760</pre>
761</blockquote>
762
763<p>and this common initialization pattern</p>
764
765<blockquote>
766<pre>
767NSArray *array = [[NSArray alloc] init];
768</pre>
769</blockquote>
770
771<p>the type of the expression <code>[NSArray alloc]</code> is
772<code>NSArray*</code> because <code>alloc</code> implicitly has a
773related result type. Similarly, the type of the expression
774<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
775<code>init</code> has a related result type and its receiver is known
776to 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>
777
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]778<p>A method with a related result type can be declared by using the
779type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
780is a contextual keyword that is only permitted in the result type of
781an Objective-C method, e.g.</p>
782
783<pre>
784@interface A
785+ (<b>instancetype</b>)constructAnA;
786@end
787</pre>
788
789<p>The related result type can also be inferred for some methods.
790To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]791word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]792considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]793type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]794
795<ul>
796
797 <li>the first word is "alloc" or "new", and the method is a class
798 method, or</li>
799
800 <li>the first word is "autorelease", "init", "retain", or "self",
801 and the method is an instance method.</li>
802
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]803</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]804
805<p>If a method with a related result type is overridden by a subclass
806method, the subclass method must also return a type that is compatible
807with the subclass type. For example:</p>
808
809<blockquote>
810<pre>
811@interface NSString : NSObject
812- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
813@end
814</pre>
815</blockquote>
816
817<p>Related result types only affect the type of a message send or
818property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]819with a related result type is treated the same way as method that
820returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]821
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]822<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
823the <tt>instancetype</tt> contextual keyword is available.</p>
824
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]825<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]826<h2 id="objc_arc">Automatic reference counting </h2>
827<!-- ======================================================================= -->
828
829<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>
830
831<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]832<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
833<!-- ======================================================================= -->
834
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]835<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]836underlying type within Objective-C. For example, one can write an
837enumeration type as:</p>
838
839<pre>
840typedef enum : unsigned char { Red, Green, Blue } Color;
841</pre>
842
843<p>This specifies that the underlying type, which is used to store the
844enumeration value, is <tt>unsigned char</tt>.</p>
845
846<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
847support for fixed underlying types is available in Objective-C.</p>
848
849<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]850<h2 id="overloading-in-c">Function Overloading in C</h2>
851<!-- ======================================================================= -->
852
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]853<p>Clang provides support for C++ function overloading in C. Function
854overloading in C is introduced using the <tt>overloadable</tt> attribute. For
855example, one might provide several overloaded versions of a <tt>tgsin</tt>
856function that invokes the appropriate standard function computing the sine of a
857value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
858precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]859
860<blockquote>
861<pre>
862#include &lt;math.h&gt;
863float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
864double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
865long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
866</pre>
867</blockquote>
868
869<p>Given these declarations, one can call <tt>tgsin</tt> with a
870<tt>float</tt> value to receive a <tt>float</tt> result, with a
871<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
872overloading in C follows the rules of C++ function overloading to pick
873the best overload given the call arguments, with a few C-specific
874semantics:</p>
875<ul>
876 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
877 double</tt> is ranked as a floating-point promotion (per C99) rather
878 than as a floating-point conversion (as in C++).</li>
879
880 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
881 <tt>U*</tt> is considered a pointer conversion (with conversion
882 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
883
884 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
885 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
886 conversion is given "conversion" rank.</li>
887</ul>
888
889<p>The declaration of <tt>overloadable</tt> functions is restricted to
890function declarations and definitions. Most importantly, if any
891function with a given name is given the <tt>overloadable</tt>
892attribute, then all function declarations and definitions with that
893name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]894attribute. This rule even applies to redeclarations of functions whose original
895declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]896
897<blockquote>
898<pre>
899int f(int) __attribute__((overloadable));
900float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
901
902int g(int) __attribute__((overloadable));
903int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
904</pre>
905</blockquote>
906
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]907<p>Functions marked <tt>overloadable</tt> must have
908prototypes. Therefore, the following code is ill-formed:</p>
909
910<blockquote>
911<pre>
912int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
913</pre>
914</blockquote>
915
916<p>However, <tt>overloadable</tt> functions are allowed to use a
917ellipsis 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>
918
919<blockquote>
920<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]921void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]922</pre>
923</blockquote>
924
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]925<p>Functions declared with the <tt>overloadable</tt> attribute have
926their names mangled according to the same rules as C++ function
927names. For example, the three <tt>tgsin</tt> functions in our
928motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]929<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]930caveats to this use of name mangling:</p>
931
932<ul>
933
934 <li>Future versions of Clang may change the name mangling of
935 functions overloaded in C, so you should not depend on an specific
936 mangling. To be completely safe, we strongly urge the use of
937 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
938
939 <li>The <tt>overloadable</tt> attribute has almost no meaning when
940 used in C++, because names will already be mangled and functions are
941 already overloadable. However, when an <tt>overloadable</tt>
942 function occurs within an <tt>extern "C"</tt> linkage specification,
943 it's name <i>will</i> be mangled in the same way as it would in
944 C.</li>
945</ul>
946
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]947<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]948
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]949<!-- ======================================================================= -->
950<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
951<!-- ======================================================================= -->
952
953<p>clang supports an extension which allows the following in C:</p>
954
955<blockquote>
956<pre>
957#include &lt;math.h&gt;
958#include &lt;complex.h&gt;
959complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
960</pre>
961</blockquote>
962
963<p>This construct is useful because there is no way to separately
964initialize the real and imaginary parts of a complex variable in
965standard C, given that clang does not support <code>_Imaginary</code>.
966(clang also supports the <code>__real__</code> and <code>__imag__</code>
967extensions from gcc, which help in some cases, but are not usable in
968static initializers.)
969
970<p>Note that this extension does not allow eliding the braces; the
971meaning of the following two lines is different:</p>
972
973<blockquote>
974<pre>
975complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
976complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
977</pre>
978</blockquote>
979
980<p>This extension also works in C++ mode, as far as that goes, but does not
981 apply to the C++ <code>std::complex</code>. (In C++11, list
982 initialization allows the same syntax to be used with
983 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]984
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]985<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]986<h2 id="builtins">Builtin Functions</h2>
987<!-- ======================================================================= -->
988
989<p>Clang supports a number of builtin library functions with the same syntax as
990GCC, including things like <tt>__builtin_nan</tt>,
991<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
992<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
993addition to the GCC builtins, Clang supports a number of builtins that GCC does
994not, which are listed here.</p>
995
996<p>Please note that Clang does not and will not support all of the GCC builtins
997for vector operations. Instead of using builtins, you should use the functions
998defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
999define portable wrappers for these. Many of the Clang versions of these
1000functions are implemented directly in terms of <a href="#vectors">extended
1001vector support</a> instead of builtins, in order to reduce the number of
1002builtins that we need to implement.</p>
1003
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1004<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1005<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1006<!-- ======================================================================= -->
1007
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1008<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1009permutation/shuffle/swizzle operations. This builtin is also very important for
1010the implementation of various target-specific header files like
1011<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1012</p>
1013
1014<p><b>Syntax:</b></p>
1015
1016<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1017__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1018</pre>
1019
1020<p><b>Examples:</b></p>
1021
1022<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1023 // Identity operation - return 4-element vector V1.
1024 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1025
1026 // "Splat" element 0 of V1 into a 4-element result.
1027 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1028
1029 // Reverse 4-element vector V1.
1030 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1031
1032 // Concatenate every other element of 4-element vectors V1 and V2.
1033 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1034
1035 // Concatenate every other element of 8-element vectors V1 and V2.
1036 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1037</pre>
1038
1039<p><b>Description:</b></p>
1040
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1041<p>The first two arguments to __builtin_shufflevector are vectors that have the
1042same element type. The remaining arguments are a list of integers that specify
1043the elements indices of the first two vectors that should be extracted and
1044returned in a new vector. These element indices are numbered sequentially
1045starting with the first vector, continuing into the second vector. Thus, if
1046vec1 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]1047</p>
1048
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1049<p>The result of __builtin_shufflevector is a vector
1050with the same element type as vec1/vec2 but that has an element count equal to
1051the number of indices specified.
1052</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1053
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1054<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1055
1056<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1057<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1058<!-- ======================================================================= -->
1059
1060<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1061the program cannot be reached, even if the compiler might otherwise think it
1062can. This is useful to improve optimization and eliminates certain warnings.
1063For example, without the <tt>__builtin_unreachable</tt> in the example below,
1064the compiler assumes that the inline asm can fall through and prints a "function
1065declared 'noreturn' should not return" warning.
1066</p>
1067
1068<p><b>Syntax:</b></p>
1069
1070<pre>
1071__builtin_unreachable()
1072</pre>
1073
1074<p><b>Example of Use:</b></p>
1075
1076<pre>
1077void myabort(void) __attribute__((noreturn));
1078void myabort(void) {
1079 asm("int3");
1080 __builtin_unreachable();
1081}
1082</pre>
1083
1084<p><b>Description:</b></p>
1085
1086<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1087it has undefined behavior, it is a statement that it is never reached and the
1088optimizer can take advantage of this to produce better code. This builtin takes
1089no arguments and produces a void result.
1090</p>
1091
1092<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1093
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1094<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1095<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1096<!-- ======================================================================= -->
1097
1098<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1099memory.
1100</p>
1101
1102<p><b>Syntax:</b></p>
1103
1104<pre>
1105<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1106</pre>
1107
1108<p><b>Example of Use:</b></p>
1109
1110<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1111int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1112</pre>
1113
1114<p><b>Description:</b></p>
1115
1116<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1117intrinsics to allow code to atomically swap the current value with the new
1118value. More importantly, it helps developers write more efficient and correct
1119code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1120relying on the platform specific implementation details of
1121__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1122</p>
1123
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1124
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1125<!-- ======================================================================= -->
1126<h2 id="targetspecific">Target-Specific Extensions</h2>
1127<!-- ======================================================================= -->
1128
1129<p>Clang supports some language features conditionally on some targets.</p>
1130
1131<!-- ======================================================================= -->
1132<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1133<!-- ======================================================================= -->
1134
1135<p>The X86 backend has these language extensions:</p>
1136
1137<!-- ======================================================================= -->
1138<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1139<!-- ======================================================================= -->
1140
1141<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1142relative to the X86 GS segment register, and address space #257 causes it to be
1143relative to the X86 FS segment. Note that this is a very very low-level
1144feature that should only be used if you know what you're doing (for example in
1145an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1146
1147<p>Here is an example:</p>
1148
1149<pre>
1150#define GS_RELATIVE __attribute__((address_space(256)))
1151int foo(int GS_RELATIVE *P) {
1152 return *P;
1153}
1154</pre>
1155
1156<p>Which compiles to (on X86-32):</p>
1157
1158<pre>
1159_foo:
1160 movl 4(%esp), %eax
1161 movl %gs:(%eax), %eax
1162 ret
1163</pre>
1164
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1165<!-- ======================================================================= -->
1166<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1167<!-- ======================================================================= -->
1168
1169<p>Clang supports additional attributes that are useful for documenting program
1170invariants and rules for static analysis tools. The extensions documented here
1171are used by the <a
1172href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1173engine</a> that is part of Clang's Analysis library.</p>
1174
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1175<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1176
1177<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1178attribute. This attribute, which is typically affixed to a function prototype,
1179indicates that a call to a given function never returns. Function prototypes for
1180common functions like <tt>exit</tt> are typically annotated with this attribute,
1181as well as a variety of common assertion handlers. Users can educate the static
1182analyzer about their own custom assertion handles (thus cutting down on false
1183positives due to false paths) by marking their own &quot;panic&quot; functions
1184with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1185
1186<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1187there are special functions that for all intents and purposes should be
1188considered panic functions (i.e., they are only called when an internal program
1189error occurs) but may actually return so that the program can fail gracefully.
1190The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1191as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1192pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1193<tt>noreturn</tt>).</p>
1194
1195<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]1196same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1197placed at the end of function prototypes:</p>
1198
1199<pre>
1200 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1201</pre>
1202
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1203<p>Query for this feature with
1204<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1205
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1206<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1207
1208<p>Many methods in Objective-C have conventional meanings determined
1209by their selectors. For the purposes of static analysis, it is
1210sometimes useful to be able to mark a method as having a particular
1211conventional meaning despite not having the right selector, or as not
1212having the conventional meaning that its selector would suggest.
1213For these use cases, we provide an attribute to specifically describe
1214the <q>method family</q> that a method belongs to.</p>
1215
1216<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1217where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1218<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1219can only be placed at the end of a method declaration:</p>
1220
1221<pre>
1222 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1223</pre>
1224
1225<p>Users who do not wish to change the conventional meaning of a
1226method, and who merely want to document its non-standard retain and
1227release semantics, should use the
1228<a href="#attr_retain_release">retaining behavior attributes</a>
1229described below.</p>
1230
1231<p>Query for this feature with
1232<tt>__has_attribute(objc_method_family)</tt>.</p>
1233
1234<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1235
1236<p>In Objective-C, functions and methods are generally assumed to take
1237and return objects with +0 retain counts, with some exceptions for
1238special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1239there are exceptions, and so Clang provides attributes to allow these
1240exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1241ignore non-leaks). Some exceptions may be better described using
1242the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1243attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1244
1245<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1246<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1247and <tt>cf_returns_not_retained</tt> attributes can be placed on
1248methods and functions that return Objective-C or CoreFoundation
1249objects. They are commonly placed at the end of a function prototype
1250or method declaration:</p>
1251
1252<pre>
1253 id foo() <b>__attribute__((ns_returns_retained))</b>;
1254
1255 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1256</pre>
1257
1258<p>The <tt>*_returns_retained</tt> attributes specify that the
1259returned object has a +1 retain count.
1260The <tt>*_returns_not_retained</tt> attributes specify that the return
1261object has a +0 retain count, even if the normal convention for its
1262selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1263returned object is +0, but is guaranteed to live at least as long as the
1264next flush of an autorelease pool.</p>
1265
1266<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1267attributes can be placed on an parameter declaration; they specify
1268that the argument is expected to have a +1 retain count, which will be
1269balanced in some way by the function or method.
1270The <tt>ns_consumes_self</tt> attribute can only be placed on an
1271Objective-C method; it specifies that the method expects
1272its <tt>self</tt> parameter to have a +1 retain count, which it will
1273balance in some way.</p>
1274
1275<pre>
1276 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1277
1278 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1279 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1280</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1281
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1282<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1283<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1284
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1285<!-- ======================================================================= -->
1286<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1287<!-- ======================================================================= -->
1288<h3 id="address_sanitizer">AddressSanitizer</h3>
1289<p> Use <code>__has_feature(address_sanitizer)</code>
1290to check if the code is being built with <a
1291 href="AddressSanitizer.html">AddressSanitizer</a>.
1292</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1293
1294<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1295<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1296<!-- ======================================================================= -->
1297
1298<p>Clang supports additional attributes for checking basic locking policies in
1299multithreaded programs.
1300Clang currently parses the following list of attributes, although
1301<b>the implementation for these annotations is currently in development.</b>
1302For more details, see the
1303<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1304</p>
1305
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1306<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1307
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1308<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1309declaration to specify that the thread safety analysis should not be run on that
1310function. This attribute provides an escape hatch (e.g. for situations when it
1311is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1312
1313<h4 id="ts_lockable">lockable</h4>
1314
1315<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1316that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1317used to check consistency.</p>
1318
1319<h4 id="ts_scopedlockable">scoped_lockable</h4>
1320
1321<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1322specify that it has a "scoped" lockable type. Objects of this type will acquire
1323the lock upon construction and release it upon going out of scope.
1324 This annotation is primarily used to check
1325consistency.</p>
1326
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1327<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1328
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1329<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1330specify that the variable must be accessed while holding some lock.</p>
1331
1332<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1333
1334<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1335specify that the pointer must be dereferenced while holding some lock.</p>
1336
1337<h4 id="ts_guardedby">guarded_by(l)</h4>
1338
1339<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1340specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1341
1342<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1343
1344<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1345specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1346
1347<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1348
1349<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1350of a lockable variable to specify that the lock must be acquired before all
1351attribute arguments. Arguments must be lockable type, and there must be at
1352least one argument.</p>
1353
1354<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1355
1356<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1357of a lockable variable to specify that the lock must be acquired after all
1358attribute arguments. Arguments must be lockable type, and there must be at
1359least one argument.</p>
1360
1361<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1362
1363<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1364declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1365exclusively. This attribute takes zero or more arguments: either of lockable
1366type or integers indexing into function parameters of lockable type. If no
1367arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1368enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1369
1370<h4 id="ts_slf">shared_lock_function(...)</h4>
1371
1372<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1373declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1374 the locks may be shared (e.g. read locks). This attribute takes zero or more
1375arguments: either of lockable type or integers indexing into function
1376parameters of lockable type. If no arguments are given, the acquired lock is
1377implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1378
1379<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1380
1381<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1382declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1383all listed locks exclusively. This attribute takes one or more arguments. The
1384first argument is an integer or boolean value specifying the return value of a
1385successful lock acquisition. The remaining arugments are either of lockable type
1386or integers indexing into function parameters of lockable type. If only one
1387argument is given, the acquired lock is implicitly <tt>this</tt> of the
1388enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1389
1390<h4 id="ts_stf">shared_trylock_function(...)</h4>
1391
1392<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1393declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1394all listed locks, although the locks may be shared (e.g. read locks). This
1395attribute takes one or more arguments. The first argument is an integer or
1396boolean value specifying the return value of a successful lock acquisition. The
1397remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1398function parameters of lockable type. If only one argument is given, the
1399acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1400
1401<h4 id="ts_uf">unlock_function(...)</h4>
1402
1403<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1404declaration to specify that the function release all listed locks. This
1405attribute takes zero or more arguments: either of lockable type or integers
1406indexing into function parameters of lockable type. If no arguments are given,
1407the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1408
1409<h4 id="ts_lr">lock_returned(l)</h4>
1410
1411<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1412declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1413must be of lockable type). This annotation is used to aid in resolving lock
1414expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1415
1416<h4 id="ts_le">locks_excluded(...)</h4>
1417
1418<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1419to specify that the function must not be called with the listed locks. Arguments
1420must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1421
1422<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1423
1424<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1425declaration to specify that the function must be called while holding the listed
1426exclusive locks. Arguments must be lockable type, and there must be at
1427least one argument.</p>
1428
1429<h4 id="ts_slr">shared_locks_required(...)</h4>
1430
1431<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1432declaration to specify that the function must be called while holding the listed
1433shared locks. Arguments must be lockable type, and there must be at
1434least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1435
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1436</div>
1437</body>
1438</html>