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gerrit-public.fairphone.software / platform / external / clang / da90c77753f154014daca79e24e1bbabb4612dcf / . / docs / LanguageExtensions.html
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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>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]75 <li><a href="#c11">C11</a>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]76 <ul>
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]77 <li><a href="#c_alignas">C11 alignment specifiers</a></li>
78 <li><a href="#c_generic_selections">C11 generic selections</a></li>
79 <li><a href="#c_static_assert">C11 <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>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]106<li><a href="#dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</a>
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]107 <ul>
108 <li><a href="#address_sanitizer">AddressSanitizer</a></li>
109 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]110</li>
111<li><a href="#threadsafety">Thread Safety Annotation Checking</a>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]112 <ul>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]113 <li><a href="#ts_noanal"><tt>no_thread_safety_analysis</tt></a></li>
114 <li><a href="#ts_lockable"><tt>lockable</tt></a></li>
115 <li><a href="#ts_scopedlockable"><tt>scoped_lockable</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]116 <li><a href="#ts_guardedvar"><tt>guarded_var</tt></a></li>
117 <li><a href="#ts_ptguardedvar"><tt>pt_guarded_var</tt></a></li>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]118 <li><a href="#ts_guardedby"><tt>guarded_by(l)</tt></a></li>
119 <li><a href="#ts_ptguardedby"><tt>pt_guarded_by(l)</tt></a></li>
120 <li><a href="#ts_acquiredbefore"><tt>acquired_before(...)</tt></a></li>
121 <li><a href="#ts_acquiredafter"><tt>acquired_after(...)</tt></a></li>
122 <li><a href="#ts_elf"><tt>exclusive_lock_function(...)</tt></a></li>
123 <li><a href="#ts_slf"><tt>shared_lock_function(...)</tt></a></li>
124 <li><a href="#ts_etf"><tt>exclusive_trylock_function(...)</tt></a></li>
125 <li><a href="#ts_stf"><tt>shared_trylock_function(...)</tt></a></li>
126 <li><a href="#ts_uf"><tt>unlock_function(...)</tt></a></li>
127 <li><a href="#ts_lr"><tt>lock_returned(l)</tt></a></li>
128 <li><a href="#ts_le"><tt>locks_excluded(...)</tt></a></li>
129 <li><a href="#ts_elr"><tt>exclusive_locks_required(...)</tt></a></li>
130 <li><a href="#ts_slr"><tt>shared_locks_required(...)</tt></a></li>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]131 </ul>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]132</li>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]133</ul>
134
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]135<!-- ======================================================================= -->
136<h2 id="intro">Introduction</h2>
137<!-- ======================================================================= -->
138
139<p>This document describes the language extensions provided by Clang. In
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]140addition to the language extensions listed here, Clang aims to support a broad
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]141range of GCC extensions. Please see the <a
142href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for
143more information on these extensions.</p>
144
145<!-- ======================================================================= -->
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]146<h2 id="feature_check">Feature Checking Macros</h2>
147<!-- ======================================================================= -->
148
149<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]150on them. In order to allow fine-grain features checks, we support three builtin
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]151function-like macros. This allows you to directly test for a feature in your
152code without having to resort to something like autoconf or fragile "compiler
153version checks".</p>
154
155<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]156<h3><a name="__has_builtin">__has_builtin</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]157<!-- ======================================================================= -->
158
159<p>This function-like macro takes a single identifier argument that is the name
160of a builtin function. It evaluates to 1 if the builtin is supported or 0 if
161not. It can be used like this:</p>
162
163<blockquote>
164<pre>
165#ifndef __has_builtin // Optional of course.
166 #define __has_builtin(x) 0 // Compatibility with non-clang compilers.
167#endif
168
169...
170#if __has_builtin(__builtin_trap)
171 __builtin_trap();
172#else
173 abort();
174#endif
175...
176</pre>
177</blockquote>
178
179
180<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]181<h3><a name="__has_feature_extension"> __has_feature and __has_extension</a></h3>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]182<!-- ======================================================================= -->
183
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]184<p>These function-like macros take a single identifier argument that is the
185name of a feature. <code>__has_feature</code> evaluates to 1 if the feature
186is both supported by Clang and standardized in the current language standard
187or 0 if not (but see <a href="#has_feature_back_compat">below</a>), while
188<code>__has_extension</code> evaluates to 1 if the feature is supported by
189Clang in the current language (either as a language extension or a standard
190language feature) or 0 if not. They can be used like this:</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]191
192<blockquote>
193<pre>
194#ifndef __has_feature // Optional of course.
195 #define __has_feature(x) 0 // Compatibility with non-clang compilers.
196#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]197#ifndef __has_extension
198 #define __has_extension __has_feature // Compatibility with pre-3.0 compilers.
199#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]200
201...
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]202#if __has_feature(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]203// This code will only be compiled with the -std=c++11 and -std=gnu++11
204// options, because rvalue references are only standardized in C++11.
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]205#endif
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]206
207#if __has_extension(cxx_rvalue_references)
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]208// 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]209// and -std=gnu++98 options, because rvalue references are supported as a
210// language extension in C++98.
211#endif
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]212</pre>
213</blockquote>
214
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]215<p id="has_feature_back_compat">For backwards compatibility reasons,
216<code>__has_feature</code> can also be used to test for support for
217non-standardized features, i.e. features not prefixed <code>c_</code>,
218<code>cxx_</code> or <code>objc_</code>.</p>
219
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]220<p id="has_feature_for_non_language_features">
221Another use of <code>__has_feature</code> is to check for compiler features
222not related to the language standard, such as e.g.
223<a href="AddressSanitizer.html">AddressSanitizer</a>.
224
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]225<p>If the <code>-pedantic-errors</code> option is given,
226<code>__has_extension</code> is equivalent to <code>__has_feature</code>.</p>
227
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]228<p>The feature tag is described along with the language feature below.</p>
229
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]230<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]231<h3><a name="__has_attribute">__has_attribute</a></h3>
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]232<!-- ======================================================================= -->
233
234<p>This function-like macro takes a single identifier argument that is the name
235of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It
236can be used like this:</p>
237
238<blockquote>
239<pre>
240#ifndef __has_attribute // Optional of course.
241 #define __has_attribute(x) 0 // Compatibility with non-clang compilers.
242#endif
243
244...
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]245#if __has_attribute(always_inline)
246#define ALWAYS_INLINE __attribute__((always_inline))
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]247#else
Anders Carlsson961003d2011-01-24 03:54:51 +0000[diff] [blame]248#define ALWAYS_INLINE
Anders Carlssoncae50952010-10-20 02:31:43 +0000[diff] [blame]249#endif
250...
251</pre>
252</blockquote>
253
254<!-- ======================================================================= -->
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]255<h2 id="has_include">Include File Checking Macros</h2>
256<!-- ======================================================================= -->
257
258<p>Not all developments systems have the same include files.
259The <a href="#__has_include">__has_include</a> and
260<a href="#__has_include_next">__has_include_next</a> macros allow you to
261check for the existence of an include file before doing
262a possibly failing #include directive.</p>
263
264<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]265<h3><a name="__has_include">__has_include</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]266<!-- ======================================================================= -->
267
268<p>This function-like macro takes a single file name string argument that
269is the name of an include file. It evaluates to 1 if the file can
270be found using the include paths, or 0 otherwise:</p>
271
272<blockquote>
273<pre>
274// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]275#if __has_include("myinclude.h") &amp;&amp; __has_include(&lt;stdint.h&gt;)
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]276# include "myinclude.h"
277#endif
278
279// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]280#if defined(__has_include) &amp;&amp; __has_include("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]281# include "myinclude.h"
282#endif
283</pre>
284</blockquote>
285
286<p>To test for this feature, use #if defined(__has_include).</p>
287
288<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]289<h3><a name="__has_include_next">__has_include_next</a></h3>
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]290<!-- ======================================================================= -->
291
292<p>This function-like macro takes a single file name string argument that
293is the name of an include file. It is like __has_include except that it
294looks for the second instance of the given file found in the include
295paths. It evaluates to 1 if the second instance of the file can
296be found using the include paths, or 0 otherwise:</p>
297
298<blockquote>
299<pre>
300// Note the two possible file name string formats.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]301#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]302# include_next "myinclude.h"
303#endif
304
305// To avoid problem with non-clang compilers not having this macro.
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]306#if defined(__has_include_next) &amp;&amp; __has_include_next("myinclude.h")
John Thompson92bd8c72009-11-02 22:28:12 +0000[diff] [blame]307# include_next "myinclude.h"
308#endif
309</pre>
310</blockquote>
311
312<p>Note that __has_include_next, like the GNU extension
313#include_next directive, is intended for use in headers only,
314and will issue a warning if used in the top-level compilation
315file. A warning will also be issued if an absolute path
316is used in the file argument.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]317
Ted Kremenekd7681502011-10-12 19:46:30 +0000[diff] [blame]318
319<!-- ======================================================================= -->
320<h3><a name="__has_warning">__has_warning</a></h3>
321<!-- ======================================================================= -->
322
323<p>This function-like macro takes a string literal that represents a command
324 line option for a warning and returns true if that is a valid warning
325 option.</p>
326
327<blockquote>
328<pre>
329#if __has_warning("-Wformat")
330...
331#endif
332</pre>
333</blockquote>
334
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]335<!-- ======================================================================= -->
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]336<h2 id="builtinmacros">Builtin Macros</h2>
337<!-- ======================================================================= -->
338
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]339<dl>
340 <dt><code>__BASE_FILE__</code></dt>
341 <dd>Defined to a string that contains the name of the main input
342 file passed to Clang.</dd>
343
344 <dt><code>__COUNTER__</code></dt>
345 <dd>Defined to an integer value that starts at zero and is
346 incremented each time the <code>__COUNTER__</code> macro is
347 expanded.</dd>
348
349 <dt><code>__INCLUDE_LEVEL__</code></dt>
350 <dd>Defined to an integral value that is the include depth of the
351 file currently being translated. For the main file, this value is
352 zero.</dd>
353
354 <dt><code>__TIMESTAMP__</code></dt>
355 <dd>Defined to the date and time of the last modification of the
356 current source file.</dd>
357
358 <dt><code>__clang__</code></dt>
359 <dd>Defined when compiling with Clang</dd>
360
361 <dt><code>__clang_major__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]362 <dd>Defined to the major marketing version number of Clang (e.g., the
363 2 in 2.0.1). Note that marketing version numbers should not be used to
364 check for language features, as different vendors use different numbering
365 schemes. Instead, use the <a href="#feature_check">feature checking
366 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]367
368 <dt><code>__clang_minor__</code></dt>
369 <dd>Defined to the minor version number of Clang (e.g., the 0 in
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]370 2.0.1). Note that marketing version numbers should not be used to
371 check for language features, as different vendors use different numbering
372 schemes. Instead, use the <a href="#feature_check">feature checking
373 macros</a>.</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]374
375 <dt><code>__clang_patchlevel__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]376 <dd>Defined to the marketing patch level of Clang (e.g., the 1 in 2.0.1).</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]377
378 <dt><code>__clang_version__</code></dt>
Chris Lattnerd4b66b92011-12-15 19:06:36 +0000[diff] [blame]379 <dd>Defined to a string that captures the Clang marketing version, including
380 the Subversion tag or revision number, e.g., "1.5 (trunk 102332)".</dd>
Douglas Gregor4290fbd2010-04-30 02:51:06 +0000[diff] [blame]381</dl>
Chris Lattner81edc9f2009-04-13 02:45:46 +0000[diff] [blame]382
383<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]384<h2 id="vectors">Vectors and Extended Vectors</h2>
385<!-- ======================================================================= -->
386
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame^]387<p>Supports the GCC, OpenCL, AltiVec and NEON vector extensions.</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]388
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame^]389OpenCL vector types are created using <tt>ext_vector_type</tt> attribute. It
390support for V.xyzw syntax and other tidbits as seen in OpenCL. An example
391is:</p>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]392
393<blockquote>
394<pre>
395typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>;
396typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>;
397
398float4 foo(float2 a, float2 b) {
399 float4 c;
400 c.xz = a;
401 c.yw = b;
402 return c;
403}
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]404</pre>
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]405</blockquote>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]406
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]407<p>Query for this feature with __has_extension(attribute_ext_vector_type).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]408
Anton Yartsevda90c772012-01-15 16:22:24 +0000[diff] [blame^]409<p>Giving -faltivec option to clang enables support for AltiVec vector syntax
410and functions. For example:</p>
411
412<blockquote>
413<pre>
414vector float foo(vector int a) {
415 vector int b;
416 b = vec_add(a, a) + a;
417 return (vector float)b;
418}
419</pre>
420</blockquote>
421
422<p>NEON vector types are created using <tt>neon_vector_type</tt> and
423<tt>neon_polyvector_type</tt> attributes. For example:</p>
424
425<blockquote>
426<pre>
427typedef <b>__attribute__((neon_vector_type(8)))</b> int8_t int8x8_t;
428typedef <b>__attribute__((neon_polyvector_type(16)))</b> poly8_t poly8x16_t;
429
430int8x8_t foo(int8x8_t a) {
431 int8x8_t v;
432 v = a;
433 return v;
434}
435</pre>
436</blockquote>
437
438<!-- ======================================================================= -->
439<h3><a name="vector_literals">Vector Literals</a></h3>
440<!-- ======================================================================= -->
441
442<p>Vector literals can be used to create vectors from a set of scalars, or
443vectors. Either parentheses or braces form can be used. In the parentheses form
444the number of literal values specified must be one, i.e. referring to a scalar
445value, or must match the size of the vector type being created. If a single
446scalar literal value is specified, the scalar literal value will be replicated
447to all the components of the vector type. In the brackets form any number of
448literals can be specified. For example:</p>
449
450<blockquote>
451<pre>
452typedef int v4si __attribute__((__vector_size__(16)));
453typedef float float4 __attribute__((ext_vector_type(4)));
454typedef float float2 __attribute__((ext_vector_type(2)));
455
456v4si vsi = (v4si){1, 2, 3, 4};
457float4 vf = (float4)(1.0f, 2.0f, 3.0f, 4.0f);
458vector int vi1 = (vector int)(1); // vi1 will be (1, 1, 1, 1).
459vector int vi2 = (vector int){1}; // vi2 will be (1, 0, 0, 0).
460vector int vi3 = (vector int)(1, 2); // error
461vector int vi4 = (vector int){1, 2}; // vi4 will be (1, 2, 0, 0).
462vector int vi5 = (vector int)(1, 2, 3, 4);
463float4 vf = (float4)((float2)(1.0f, 2.0f), (float2)(3.0f, 4.0f));
464</pre>
465</blockquote>
466
467<!-- ======================================================================= -->
468<h3><a name="vector_operations">Vector Operations</a></h3>
469<!-- ======================================================================= -->
470
471<p>The table below shows the support for each operation by vector extension.
472A dash indicates that an operation is not accepted according to a corresponding
473specification.</p>
474
475<table width="500" border="1" cellspacing="0">
476 <tr>
477 <th bgcolor="#ffddaa">Operator</th>
478 <th bgcolor="#ffddaa">OpenCL</th>
479 <th bgcolor="#ffddaa">AltiVec</th>
480 <th bgcolor="#ffddaa">GCC</th>
481 <th bgcolor="#ffddaa">NEON</th>
482 </tr>
483 <tr>
484 <td>[]</td>
485 <td align="center">yes</td>
486 <td align="center">yes</td>
487 <td align="center">yes</td>
488 <td align="center">-</td>
489 </tr>
490 <tr>
491 <td>unary operators +, -</td>
492 <td align="center">yes</td>
493 <td align="center">yes</td>
494 <td align="center">yes</td>
495 <td align="center">-</td>
496 </tr>
497 <tr>
498 <td>++, --</td>
499 <td align="center">yes</td>
500 <td align="center">yes</td>
501 <td align="center">-</td>
502 <td align="center">-</td>
503 </tr>
504 <tr>
505 <td>+, -, *, /, %</td>
506 <td align="center">yes</td>
507 <td align="center">yes</td>
508 <td align="center">yes</td>
509 <td align="center">-</td>
510 </tr>
511 <tr>
512 <td>bitwise operators &, |, ^, ~</td>
513 <td align="center">yes</td>
514 <td align="center">yes</td>
515 <td align="center">yes</td>
516 <td align="center">-</td>
517 </tr>
518 <tr>
519 <td>&gt&gt, &lt&lt</td>
520 <td align="center">yes</td>
521 <td align="center">yes</td>
522 <td align="center">yes</td>
523 <td align="center">-</td>
524 </tr>
525 <tr>
526 <td>!, &&,||</td>
527 <td align="center">no</td>
528 <td align="center">-</td>
529 <td align="center">-</td>
530 <td align="center">-</td>
531 </tr>
532 <tr>
533 <td>==,!=, >, <, >=, <=</td>
534 <td align="center">yes</td>
535 <td align="center">yes</td>
536 <td align="center">-</td>
537 <td align="center">-</td>
538 </tr>
539 <tr>
540 <td>=</td>
541 <td align="center">yes</td>
542 <td align="center">yes</td>
543 <td align="center">yes</td>
544 <td align="center">yes</td>
545 </tr>
546 <tr>
547 <td>:?</td>
548 <td align="center">yes</td>
549 <td align="center">-</td>
550 <td align="center">-</td>
551 <td align="center">-</td>
552 </tr>
553 <tr>
554 <td>sizeof</td>
555 <td align="center">yes</td>
556 <td align="center">yes</td>
557 <td align="center">yes</td>
558 <td align="center">yes</td>
559 </tr>
560</table>
561
Owen Andersond2bf0cd2010-01-27 01:22:36 +0000[diff] [blame]562<p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p>
563
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]564<!-- ======================================================================= -->
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]565<h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]566<!-- ======================================================================= -->
567
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]568<p>An optional string message can be added to the <tt>deprecated</tt>
569and <tt>unavailable</tt> attributes. For example:</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]570
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]571<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]572<pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]573</blockquote>
574
575<p>If the deprecated or unavailable declaration is used, the message
576will be incorporated into the appropriate diagnostic:</p>
577
578<blockquote>
Chris Lattner4836d6a2010-11-09 19:43:35 +0000[diff] [blame]579<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]580 explode();
581 ^</pre>
582</blockquote>
583
584<p>Query for this feature
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]585with <tt>__has_extension(attribute_deprecated_with_message)</tt>
586and <tt>__has_extension(attribute_unavailable_with_message)</tt>.</p>
John McCall48209082010-11-08 19:48:17 +0000[diff] [blame]587
588<!-- ======================================================================= -->
589<h2 id="attributes-on-enumerators">Attributes on Enumerators</h2>
590<!-- ======================================================================= -->
591
592<p>Clang allows attributes to be written on individual enumerators.
593This allows enumerators to be deprecated, made unavailable, etc. The
594attribute must appear after the enumerator name and before any
595initializer, like so:</p>
596
597<blockquote>
598<pre>enum OperationMode {
599 OM_Invalid,
600 OM_Normal,
601 OM_Terrified __attribute__((deprecated)),
602 OM_AbortOnError __attribute__((deprecated)) = 4
603};</pre>
604</blockquote>
605
606<p>Attributes on the <tt>enum</tt> declaration do not apply to
607individual enumerators.</p>
608
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]609<p>Query for this feature with <tt>__has_extension(enumerator_attributes)</tt>.</p>
Fariborz Jahanianc784dc12010-10-06 23:12:32 +0000[diff] [blame]610
611<!-- ======================================================================= -->
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]612<h2 id="checking_language_features">Checks for Standard Language Features</h2>
613<!-- ======================================================================= -->
614
615<p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are
616enabled. Those features are listed here.</p>
617
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]618<h3 id="cxx_exceptions">C++ exceptions</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]619
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]620<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]621example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]622
Ted Kremenek22c34102009-12-03 02:05:57 +0000[diff] [blame]623<h3 id="cxx_rtti">C++ RTTI</h3>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]624
Ted Kremenek0eb95602009-12-03 02:06:43 +0000[diff] [blame]625<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]626compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p>
Ted Kremenek87774fd2009-12-03 02:04:01 +0000[diff] [blame]627
628<!-- ======================================================================= -->
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]629<h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2>
630<!-- ======================================================================= -->
631
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]632<p>The <tt>__has_feature</tt> or <tt>__has_extension</tt> macros can be used
633to query if certain upcoming standard language features are enabled. Those
634features are listed here. Features that are not yet implemented will be
635noted.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]636
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]637<h3 id="cxx0x">C++11</h3>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]638
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]639<p>The features listed below are slated for inclusion in the upcoming
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]640C++11 standard. As a result, all these features are enabled
641with the <tt>-std=c++11</tt> option when compiling C++ code.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]642
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]643<h4 id="cxx_access_control_sfinae">C++11 SFINAE includes access control</h4>
Douglas Gregor7822ee32011-05-11 23:45:11 +0000[diff] [blame]644
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]645<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]646
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]647<h4 id="cxx_alias_templates">C++11 alias templates</h4>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]648
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]649<p>Use <tt>__has_feature(cxx_alias_templates)</tt> or
650<tt>__has_extension(cxx_alias_templates)</tt> to determine if support for
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]651C++11's alias declarations and alias templates is enabled.</p>
Richard Smith3e4c6c42011-05-05 21:57:07 +0000[diff] [blame]652
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]653<h4 id="cxx_alignas">C++11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]654
655<p>Use <tt>__has_feature(cxx_alignas)</tt> or
656<tt>__has_extension(cxx_alignas)</tt> to determine if support for alignment
657specifiers using <tt>alignas</tt> is enabled.</p>
658
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]659<h4 id="cxx_attributes">C++11 attributes</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]660
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]661<p>Use <tt>__has_feature(cxx_attributes)</tt> or
662<tt>__has_extension(cxx_attributes)</tt> to determine if support for attribute
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]663parsing with C++11's square bracket notation is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]664
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]665<h4 id="cxx_constexpr">C++11 generalized constant expressions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]666
667<p>Use <tt>__has_feature(cxx_constexpr)</tt> to determine if support
668for generalized constant expressions (e.g., <tt>constexpr</tt>) is
669enabled. Clang does not currently implement this feature.</p>
670
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]671<h4 id="cxx_decltype">C++11 <tt>decltype()</tt></h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]672
673<p>Use <tt>__has_feature(cxx_decltype)</tt> or
674<tt>__has_extension(cxx_decltype)</tt> to determine if support for the
675<tt>decltype()</tt> specifier is enabled.</p>
676
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]677<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]678
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]679<p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> or
680<tt>__has_extension(cxx_default_function_template_args)</tt> to determine
681if support for default template arguments in function templates is enabled.</p>
Douglas Gregor07508002011-02-05 20:35:30 +0000[diff] [blame]682
Douglas Gregorf695a692011-11-01 01:19:34 +0000[diff] [blame]683<h4 id="cxx_defaulted_functions">C++11 <tt>default</tt>ed functions</h4>
684
685<p>Use <tt>__has_feature(cxx_defaulted_functions)</tt> or
686<tt>__has_extension(cxx_defaulted_functions)</tt> to determine if support for
687defaulted function definitions (with <tt>= default</tt>) is enabled.</p>
688
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]689<h4 id="cxx_delegating_constructors">C++11 delegating constructors</h4>
Sean Huntd9624992011-06-23 06:11:37 +0000[diff] [blame]690
691<p>Use <tt>__has_feature(cxx_delegating_constructors)</tt> to determine if
692support for delegating constructors is enabled.</p>
693
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]694<h4 id="cxx_deleted_functions">C++11 <tt>delete</tt>d functions</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]695
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]696<p>Use <tt>__has_feature(cxx_deleted_functions)</tt> or
697<tt>__has_extension(cxx_deleted_functions)</tt> to determine if support for
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]698deleted function definitions (with <tt>= delete</tt>) is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]699
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]700<h4 id="cxx_explicit_conversions">C++11 explicit conversion functions</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]701<p>Use <tt>__has_feature(cxx_explicit_conversions)</tt> to determine if support for <tt>explicit</tt> conversion functions is enabled.</p>
702
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]703<h4 id="cxx_generalized_initializers">C++11 generalized initializers</h4>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]704
705<p>Use <tt>__has_feature(cxx_generalized_initializers)</tt> to determine if
706support for generalized initializers (using braced lists and
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]707<tt>std::initializer_list</tt>) is enabled. Clang does not currently implement
708this feature.</p>
709
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]710<h4 id="cxx_implicit_moves">C++11 implicit move constructors/assignment operators</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]711
Sebastian Redl72a81d22011-10-10 18:10:00 +0000[diff] [blame]712<p>Use <tt>__has_feature(cxx_implicit_moves)</tt> to determine if Clang will
713implicitly generate move constructors and move assignment operators where needed.</p>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]714
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]715<h4 id="cxx_inheriting_constructors">C++11 inheriting constructors</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]716
717<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>
718
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]719<h4 id="cxx_inline_namespaces">C++11 inline namespaces</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]720
721<p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> or
722<tt>__has_extension(cxx_inline_namespaces)</tt> to determine if support for
723inline namespaces is enabled.</p>
Sean Hunte1f6dea2011-08-07 00:34:32 +0000[diff] [blame]724
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]725<h4 id="cxx_lambdas">C++11 lambdas</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]726
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]727<p>Use <tt>__has_feature(cxx_lambdas)</tt> or
728<tt>__has_extension(cxx_lambdas)</tt> to determine if support for lambdas
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]729is enabled. Clang does not currently implement this feature.</p>
730
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]731<h4 id="cxx_noexcept">C++11 noexcept</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]732
733<p>Use <tt>__has_feature(cxx_noexcept)</tt> or
734<tt>__has_extension(cxx_noexcept)</tt> to determine if support for noexcept
735exception specifications is enabled.</p>
736
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]737<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]738
739<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]740
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]741<h4 id="cxx_nullptr">C++11 <tt>nullptr</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]742
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]743<p>Use <tt>__has_feature(cxx_nullptr)</tt> or
744<tt>__has_extension(cxx_nullptr)</tt> to determine if support for
Douglas Gregor84ee2ee2011-05-21 23:15:46 +0000[diff] [blame]745<tt>nullptr</tt> is enabled.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]746
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]747<h4 id="cxx_override_control">C++11 <tt>override control</tt></h4>
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]748
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]749<p>Use <tt>__has_feature(cxx_override_control)</tt> or
750<tt>__has_extension(cxx_override_control)</tt> to determine if support for
Anders Carlssonc8b9f792011-03-25 15:04:23 +0000[diff] [blame]751the override control keywords is enabled.</p>
752
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]753<h4 id="cxx_reference_qualified_functions">C++11 reference-qualified functions</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]754<p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> or
755<tt>__has_extension(cxx_reference_qualified_functions)</tt> to determine
756if support for reference-qualified functions (e.g., member functions with
757<code>&amp;</code> or <code>&amp;&amp;</code> applied to <code>*this</code>)
758is enabled.</p>
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]759
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]760<h4 id="cxx_range_for">C++11 range-based <tt>for</tt> loop</h4>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]761
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]762<p>Use <tt>__has_feature(cxx_range_for)</tt> or
763<tt>__has_extension(cxx_range_for)</tt> to determine if support for the
764range-based for loop is enabled. </p>
Richard Smitha391a462011-04-15 15:14:40 +0000[diff] [blame]765
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]766<h4 id="cxx_raw_string_literals">C++11 raw string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]767<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>
768
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]769<h4 id="cxx_rvalue_references">C++11 rvalue references</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]770
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]771<p>Use <tt>__has_feature(cxx_rvalue_references)</tt> or
772<tt>__has_extension(cxx_rvalue_references)</tt> to determine if support for
Douglas Gregor56209ff2011-01-26 21:25:54 +0000[diff] [blame]773rvalue references is enabled. </p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]774
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]775<h4 id="cxx_static_assert">C++11 <tt>static_assert()</tt></h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]776
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]777<p>Use <tt>__has_feature(cxx_static_assert)</tt> or
778<tt>__has_extension(cxx_static_assert)</tt> to determine if support for
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]779compile-time assertions using <tt>static_assert</tt> is enabled.</p>
780
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]781<h4 id="cxx_auto_type">C++11 type inference</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]782
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]783<p>Use <tt>__has_feature(cxx_auto_type)</tt> or
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]784<tt>__has_extension(cxx_auto_type)</tt> to determine C++11 type inference is
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]785supported using the <tt>auto</tt> specifier. If this is disabled, <tt>auto</tt>
786will instead be a storage class specifier, as in C or C++98.</p>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]787
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]788<h4 id="cxx_strong_enums">C++11 strongly typed enumerations</h4>
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]789
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]790<p>Use <tt>__has_feature(cxx_strong_enums)</tt> or
791<tt>__has_extension(cxx_strong_enums)</tt> to determine if support for
792strongly typed, scoped enumerations is enabled.</p>
Sebastian Redlf6c09772010-08-31 23:28:47 +0000[diff] [blame]793
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]794<h4 id="cxx_trailing_return">C++11 trailing return type</h4>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]795
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]796<p>Use <tt>__has_feature(cxx_trailing_return)</tt> or
797<tt>__has_extension(cxx_trailing_return)</tt> to determine if support for the
798alternate function declaration syntax with trailing return type is enabled.</p>
Douglas Gregordab60ad2010-10-01 18:44:50 +0000[diff] [blame]799
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]800<h4 id="cxx_unicode_literals">C++11 Unicode string literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]801<p>Use <tt>__has_feature(cxx_unicode_literals)</tt> to determine if
802support for Unicode string literals is enabled.</p>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]803
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]804<h4 id="cxx_unrestricted_unions">C++11 unrestricted unions</h4>
Sebastian Redl4561ecd2011-03-15 21:17:12 +0000[diff] [blame]805
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]806<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]807
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]808<h4 id="cxx_user_literals">C++11 user-defined literals</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]809
810<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>
811
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]812<h4 id="cxx_variadic_templates">C++11 variadic templates</h4>
Douglas Gregorece38942011-08-29 17:28:38 +0000[diff] [blame]813
814<p>Use <tt>__has_feature(cxx_variadic_templates)</tt> or
815<tt>__has_extension(cxx_variadic_templates)</tt> to determine if support
816for variadic templates is enabled.</p>
Douglas Gregor1274ccd2010-10-08 23:50:27 +0000[diff] [blame]817
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]818<h3 id="c11">C11</h3>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]819
820<p>The features listed below are slated for inclusion in the upcoming
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]821C11 standard. As a result, all these features are enabled
822with the <tt>-std=c11</tt> option when compiling C code.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]823
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]824<h4 id="c_alignas">C11 alignment specifiers</h4>
Peter Collingbournefd5f6862011-10-14 23:44:46 +0000[diff] [blame]825
826<p>Use <tt>__has_feature(c_alignas)</tt> or <tt>__has_extension(c_alignas)</tt>
827to determine if support for alignment specifiers using <tt>_Alignas</tt>
828is enabled.</p>
829
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]830<h4 id="c_generic_selections">C11 generic selections</h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]831
832<p>Use <tt>__has_feature(c_generic_selections)</tt> or
833<tt>__has_extension(c_generic_selections)</tt> to determine if support for
834generic selections is enabled.</p>
835
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]836<p>As an extension, the C11 generic selection expression is available in all
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]837languages supported by Clang. The syntax is the same as that given in the
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]838C11 standard.</p>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]839
840<p>In C, type compatibility is decided according to the rules given in the
841appropriate standard, but in C++, which lacks the type compatibility rules
842used in C, types are considered compatible only if they are equivalent.</p>
843
Benjamin Kramerffbe9b92011-12-23 17:00:35 +0000[diff] [blame]844<h4 id="c_static_assert">C11 <tt>_Static_assert()</tt></h4>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]845
846<p>Use <tt>__has_feature(c_static_assert)</tt> or
847<tt>__has_extension(c_static_assert)</tt> to determine if support for
848compile-time assertions using <tt>_Static_assert</tt> is enabled.</p>
849
Sean Hunt4ef4c6b2010-01-13 08:31:49 +0000[diff] [blame]850<!-- ======================================================================= -->
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]851<h2 id="checking_type_traits">Checks for Type Traits</h2>
852<!-- ======================================================================= -->
853
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]854<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]855<blockquote>
856<pre>
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]857#if __has_extension(is_convertible_to)
Douglas Gregorafdf1372011-02-03 21:57:35 +0000[diff] [blame]858template&lt;typename From, typename To&gt;
859struct is_convertible_to {
860 static const bool value = __is_convertible_to(From, To);
861};
862#else
863// Emulate type trait
864#endif
865</pre>
866</blockquote>
867
868<p>The following type traits are supported by Clang:</p>
869<ul>
870 <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li>
871 <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li>
872 <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li>
873 <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li>
874 <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li>
875 <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li>
876 <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li>
877 <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li>
878 <li><code>__is_abstract</code> (GNU, Microsoft)</li>
879 <li><code>__is_base_of</code> (GNU, Microsoft)</li>
880 <li><code>__is_class</code> (GNU, Microsoft)</li>
881 <li><code>__is_convertible_to</code> (Microsoft)</li>
882 <li><code>__is_empty</code> (GNU, Microsoft)</li>
883 <li><code>__is_enum</code> (GNU, Microsoft)</li>
884 <li><code>__is_pod</code> (GNU, Microsoft)</li>
885 <li><code>__is_polymorphic</code> (GNU, Microsoft)</li>
886 <li><code>__is_union</code> (GNU, Microsoft)</li>
887 <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]888 <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]889 <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]890</ul>
891
892<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]893<h2 id="blocks">Blocks</h2>
894<!-- ======================================================================= -->
895
Chris Lattnera7dbdf52009-03-09 07:03:22 +0000[diff] [blame]896<p>The syntax and high level language feature description is in <a
897href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI
898details for the clang implementation are in <a
Chris Lattner5d7650b2010-03-16 21:43:03 +0000[diff] [blame]899href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]900
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]901
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]902<p>Query for this feature with __has_extension(blocks).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]903
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]904<!-- ======================================================================= -->
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]905<h2 id="objc_features">Objective-C Features</h2>
906<!-- ======================================================================= -->
907
908<h3 id="objc_instancetype">Related result types</h3>
909
910<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>
911
912<blockquote>
913<pre>
914@interface NSObject
915+ (id)alloc;
916- (id)init;
917@end
918
919@interface NSArray : NSObject
920@end
921</pre>
922</blockquote>
923
924<p>and this common initialization pattern</p>
925
926<blockquote>
927<pre>
928NSArray *array = [[NSArray alloc] init];
929</pre>
930</blockquote>
931
932<p>the type of the expression <code>[NSArray alloc]</code> is
933<code>NSArray*</code> because <code>alloc</code> implicitly has a
934related result type. Similarly, the type of the expression
935<code>[[NSArray alloc] init]</code> is <code>NSArray*</code>, since
936<code>init</code> has a related result type and its receiver is known
937to 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>
938
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]939<p>A method with a related result type can be declared by using the
940type <tt>instancetype</tt> as its result type. <tt>instancetype</tt>
941is a contextual keyword that is only permitted in the result type of
942an Objective-C method, e.g.</p>
943
944<pre>
945@interface A
946+ (<b>instancetype</b>)constructAnA;
947@end
948</pre>
949
950<p>The related result type can also be inferred for some methods.
951To determine whether a method has an inferred related result type, the first
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]952word in the camel-case selector (e.g., "init" in "initWithObjects") is
Douglas Gregor8a0ace62011-11-03 18:33:01 +0000[diff] [blame]953considered, and the method will have a related result type if its return
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]954type is compatible with the type of its class and if</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]955
956<ul>
957
958 <li>the first word is "alloc" or "new", and the method is a class
959 method, or</li>
960
961 <li>the first word is "autorelease", "init", "retain", or "self",
962 and the method is an instance method.</li>
963
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]964</ul>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]965
966<p>If a method with a related result type is overridden by a subclass
967method, the subclass method must also return a type that is compatible
968with the subclass type. For example:</p>
969
970<blockquote>
971<pre>
972@interface NSString : NSObject
973- (NSUnrelated *)init; // incorrect usage: NSUnrelated is not NSString or a superclass of NSString
974@end
975</pre>
976</blockquote>
977
978<p>Related result types only affect the type of a message send or
979property access via the given method. In all other respects, a method
Douglas Gregore97179c2011-09-08 01:46:34 +0000[diff] [blame]980with a related result type is treated the same way as method that
981returns <tt>id</tt>.</p>
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]982
Douglas Gregoraebb6532011-09-08 17:19:31 +0000[diff] [blame]983<p>Use <tt>__has_feature(objc_instancetype)</tt> to determine whether
984the <tt>instancetype</tt> contextual keyword is available.</p>
985
Douglas Gregor926df6c2011-06-11 01:09:30 +0000[diff] [blame]986<!-- ======================================================================= -->
John McCallf85e1932011-06-15 23:02:42 +0000[diff] [blame]987<h2 id="objc_arc">Automatic reference counting </h2>
988<!-- ======================================================================= -->
989
990<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>
991
992<!-- ======================================================================= -->
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]993<h2 id="objc_fixed_enum">Enumerations with a fixed underlying type</h2>
994<!-- ======================================================================= -->
995
David Blaikie5090e9f2011-10-18 05:49:30 +0000[diff] [blame]996<p>Clang provides support for C++11 enumerations with a fixed
Douglas Gregor5471bc82011-09-08 17:18:35 +0000[diff] [blame]997underlying type within Objective-C. For example, one can write an
998enumeration type as:</p>
999
1000<pre>
1001typedef enum : unsigned char { Red, Green, Blue } Color;
1002</pre>
1003
1004<p>This specifies that the underlying type, which is used to store the
1005enumeration value, is <tt>unsigned char</tt>.</p>
1006
1007<p>Use <tt>__has_feature(objc_fixed_enum)</tt> to determine whether
1008support for fixed underlying types is available in Objective-C.</p>
1009
1010<!-- ======================================================================= -->
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1011<h2 id="overloading-in-c">Function Overloading in C</h2>
1012<!-- ======================================================================= -->
1013
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1014<p>Clang provides support for C++ function overloading in C. Function
1015overloading in C is introduced using the <tt>overloadable</tt> attribute. For
1016example, one might provide several overloaded versions of a <tt>tgsin</tt>
1017function that invokes the appropriate standard function computing the sine of a
1018value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt>
1019precision:</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1020
1021<blockquote>
1022<pre>
1023#include &lt;math.h&gt;
1024float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); }
1025double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); }
1026long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); }
1027</pre>
1028</blockquote>
1029
1030<p>Given these declarations, one can call <tt>tgsin</tt> with a
1031<tt>float</tt> value to receive a <tt>float</tt> result, with a
1032<tt>double</tt> to receive a <tt>double</tt> result, etc. Function
1033overloading in C follows the rules of C++ function overloading to pick
1034the best overload given the call arguments, with a few C-specific
1035semantics:</p>
1036<ul>
1037 <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long
1038 double</tt> is ranked as a floating-point promotion (per C99) rather
1039 than as a floating-point conversion (as in C++).</li>
1040
1041 <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type
1042 <tt>U*</tt> is considered a pointer conversion (with conversion
1043 rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li>
1044
1045 <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt>
1046 is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This
1047 conversion is given "conversion" rank.</li>
1048</ul>
1049
1050<p>The declaration of <tt>overloadable</tt> functions is restricted to
1051function declarations and definitions. Most importantly, if any
1052function with a given name is given the <tt>overloadable</tt>
1053attribute, then all function declarations and definitions with that
1054name (and in that scope) must have the <tt>overloadable</tt>
Chris Lattnerf161d412009-02-13 21:51:45 +0000[diff] [blame]1055attribute. This rule even applies to redeclarations of functions whose original
1056declaration had the <tt>overloadable</tt> attribute, e.g.,</p>
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1057
1058<blockquote>
1059<pre>
1060int f(int) __attribute__((overloadable));
1061float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i>
1062
1063int g(int) __attribute__((overloadable));
1064int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i>
1065</pre>
1066</blockquote>
1067
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1068<p>Functions marked <tt>overloadable</tt> must have
1069prototypes. Therefore, the following code is ill-formed:</p>
1070
1071<blockquote>
1072<pre>
1073int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i>
1074</pre>
1075</blockquote>
1076
1077<p>However, <tt>overloadable</tt> functions are allowed to use a
1078ellipsis 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>
1079
1080<blockquote>
1081<pre>
Chris Lattner02246802009-02-18 22:27:46 +0000[diff] [blame]1082void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i>
Douglas Gregor965acbb2009-02-18 07:07:28 +0000[diff] [blame]1083</pre>
1084</blockquote>
1085
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1086<p>Functions declared with the <tt>overloadable</tt> attribute have
1087their names mangled according to the same rules as C++ function
1088names. For example, the three <tt>tgsin</tt> functions in our
1089motivating example get the mangled names <tt>_Z5tgsinf</tt>,
Chris Lattner71b48d62010-11-28 18:19:13 +0000[diff] [blame]1090<tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1091caveats to this use of name mangling:</p>
1092
1093<ul>
1094
1095 <li>Future versions of Clang may change the name mangling of
1096 functions overloaded in C, so you should not depend on an specific
1097 mangling. To be completely safe, we strongly urge the use of
1098 <tt>static inline</tt> with <tt>overloadable</tt> functions.</li>
1099
1100 <li>The <tt>overloadable</tt> attribute has almost no meaning when
1101 used in C++, because names will already be mangled and functions are
1102 already overloadable. However, when an <tt>overloadable</tt>
1103 function occurs within an <tt>extern "C"</tt> linkage specification,
1104 it's name <i>will</i> be mangled in the same way as it would in
1105 C.</li>
1106</ul>
1107
Peter Collingbournec1b5fa42011-05-13 20:54:45 +0000[diff] [blame]1108<p>Query for this feature with __has_extension(attribute_overloadable).</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1109
Eli Friedman0c706c22011-09-19 23:17:44 +0000[diff] [blame]1110<!-- ======================================================================= -->
1111<h2 id="complex-list-init">Initializer lists for complex numbers in C</h2>
1112<!-- ======================================================================= -->
1113
1114<p>clang supports an extension which allows the following in C:</p>
1115
1116<blockquote>
1117<pre>
1118#include &lt;math.h&gt;
1119#include &lt;complex.h&gt;
1120complex float x = { 1.0f, INFINITY }; // Init to (1, Inf)
1121</pre>
1122</blockquote>
1123
1124<p>This construct is useful because there is no way to separately
1125initialize the real and imaginary parts of a complex variable in
1126standard C, given that clang does not support <code>_Imaginary</code>.
1127(clang also supports the <code>__real__</code> and <code>__imag__</code>
1128extensions from gcc, which help in some cases, but are not usable in
1129static initializers.)
1130
1131<p>Note that this extension does not allow eliding the braces; the
1132meaning of the following two lines is different:</p>
1133
1134<blockquote>
1135<pre>
1136complex float x[] = { { 1.0f, 1.0f } }; // [0] = (1, 1)
1137complex float x[] = { 1.0f, 1.0f }; // [0] = (1, 0), [1] = (1, 0)
1138</pre>
1139</blockquote>
1140
1141<p>This extension also works in C++ mode, as far as that goes, but does not
1142 apply to the C++ <code>std::complex</code>. (In C++11, list
1143 initialization allows the same syntax to be used with
1144 <code>std::complex</code> with the same meaning.)
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1145
Douglas Gregorcb54d432009-02-13 00:57:04 +0000[diff] [blame]1146<!-- ======================================================================= -->
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1147<h2 id="builtins">Builtin Functions</h2>
1148<!-- ======================================================================= -->
1149
1150<p>Clang supports a number of builtin library functions with the same syntax as
1151GCC, including things like <tt>__builtin_nan</tt>,
1152<tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>,
1153<tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In
1154addition to the GCC builtins, Clang supports a number of builtins that GCC does
1155not, which are listed here.</p>
1156
1157<p>Please note that Clang does not and will not support all of the GCC builtins
1158for vector operations. Instead of using builtins, you should use the functions
1159defined in target-specific header files like <tt>&lt;xmmintrin.h&gt;</tt>, which
1160define portable wrappers for these. Many of the Clang versions of these
1161functions are implemented directly in terms of <a href="#vectors">extended
1162vector support</a> instead of builtins, in order to reduce the number of
1163builtins that we need to implement.</p>
1164
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1165<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1166<h3><a name="__builtin_shufflevector">__builtin_shufflevector</a></h3>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1167<!-- ======================================================================= -->
1168
Chris Lattneraad826b2009-09-16 18:56:12 +0000[diff] [blame]1169<p><tt>__builtin_shufflevector</tt> is used to express generic vector
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1170permutation/shuffle/swizzle operations. This builtin is also very important for
1171the implementation of various target-specific header files like
1172<tt>&lt;xmmintrin.h&gt;</tt>.
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1173</p>
1174
1175<p><b>Syntax:</b></p>
1176
1177<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1178__builtin_shufflevector(vec1, vec2, index1, index2, ...)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1179</pre>
1180
1181<p><b>Examples:</b></p>
1182
1183<pre>
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1184 // Identity operation - return 4-element vector V1.
1185 __builtin_shufflevector(V1, V1, 0, 1, 2, 3)
1186
1187 // "Splat" element 0 of V1 into a 4-element result.
1188 __builtin_shufflevector(V1, V1, 0, 0, 0, 0)
1189
1190 // Reverse 4-element vector V1.
1191 __builtin_shufflevector(V1, V1, 3, 2, 1, 0)
1192
1193 // Concatenate every other element of 4-element vectors V1 and V2.
1194 __builtin_shufflevector(V1, V2, 0, 2, 4, 6)
1195
1196 // Concatenate every other element of 8-element vectors V1 and V2.
1197 __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14)
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1198</pre>
1199
1200<p><b>Description:</b></p>
1201
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1202<p>The first two arguments to __builtin_shufflevector are vectors that have the
1203same element type. The remaining arguments are a list of integers that specify
1204the elements indices of the first two vectors that should be extracted and
1205returned in a new vector. These element indices are numbered sequentially
1206starting with the first vector, continuing into the second vector. Thus, if
1207vec1 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]1208</p>
1209
Chris Lattner6f72da52009-02-13 20:00:20 +0000[diff] [blame]1210<p>The result of __builtin_shufflevector is a vector
1211with the same element type as vec1/vec2 but that has an element count equal to
1212the number of indices specified.
1213</p>
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1214
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1215<p>Query for this feature with __has_builtin(__builtin_shufflevector).</p>
1216
1217<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1218<h3><a name="__builtin_unreachable">__builtin_unreachable</a></h3>
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1219<!-- ======================================================================= -->
1220
1221<p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in
1222the program cannot be reached, even if the compiler might otherwise think it
1223can. This is useful to improve optimization and eliminates certain warnings.
1224For example, without the <tt>__builtin_unreachable</tt> in the example below,
1225the compiler assumes that the inline asm can fall through and prints a "function
1226declared 'noreturn' should not return" warning.
1227</p>
1228
1229<p><b>Syntax:</b></p>
1230
1231<pre>
1232__builtin_unreachable()
1233</pre>
1234
1235<p><b>Example of Use:</b></p>
1236
1237<pre>
1238void myabort(void) __attribute__((noreturn));
1239void myabort(void) {
1240 asm("int3");
1241 __builtin_unreachable();
1242}
1243</pre>
1244
1245<p><b>Description:</b></p>
1246
1247<p>The __builtin_unreachable() builtin has completely undefined behavior. Since
1248it has undefined behavior, it is a statement that it is never reached and the
1249optimizer can take advantage of this to produce better code. This builtin takes
1250no arguments and produces a void result.
1251</p>
1252
1253<p>Query for this feature with __has_builtin(__builtin_unreachable).</p>
1254
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1255<!-- ======================================================================= -->
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1256<h3><a name="__sync_swap">__sync_swap</a></h3>
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1257<!-- ======================================================================= -->
1258
1259<p><tt>__sync_swap</tt> is used to atomically swap integers or pointers in
1260memory.
1261</p>
1262
1263<p><b>Syntax:</b></p>
1264
1265<pre>
1266<i>type</i> __sync_swap(<i>type</i> *ptr, <i>type</i> value, ...)
1267</pre>
1268
1269<p><b>Example of Use:</b></p>
1270
1271<pre>
Sean Hunt7e98b472011-06-23 01:21:01 +0000[diff] [blame]1272int old_value = __sync_swap(&amp;value, new_value);
Chris Lattner23aa9c82011-04-09 03:57:26 +0000[diff] [blame]1273</pre>
1274
1275<p><b>Description:</b></p>
1276
1277<p>The __sync_swap() builtin extends the existing __sync_*() family of atomic
1278intrinsics to allow code to atomically swap the current value with the new
1279value. More importantly, it helps developers write more efficient and correct
1280code by avoiding expensive loops around __sync_bool_compare_and_swap() or
1281relying on the platform specific implementation details of
1282__sync_lock_test_and_set(). The __sync_swap() builtin is a full barrier.
1283</p>
1284
Chris Lattner21190d52009-09-21 03:09:59 +0000[diff] [blame]1285
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1286<!-- ======================================================================= -->
1287<h2 id="targetspecific">Target-Specific Extensions</h2>
1288<!-- ======================================================================= -->
1289
1290<p>Clang supports some language features conditionally on some targets.</p>
1291
1292<!-- ======================================================================= -->
1293<h3 id="x86-specific">X86/X86-64 Language Extensions</h3>
1294<!-- ======================================================================= -->
1295
1296<p>The X86 backend has these language extensions:</p>
1297
1298<!-- ======================================================================= -->
1299<h4 id="x86-gs-segment">Memory references off the GS segment</h4>
1300<!-- ======================================================================= -->
1301
1302<p>Annotating a pointer with address space #256 causes it to be code generated
Chris Lattnera021e7c2009-05-05 18:54:47 +0000[diff] [blame]1303relative to the X86 GS segment register, and address space #257 causes it to be
1304relative to the X86 FS segment. Note that this is a very very low-level
1305feature that should only be used if you know what you're doing (for example in
1306an OS kernel).</p>
Chris Lattner1177f912009-04-09 19:58:15 +0000[diff] [blame]1307
1308<p>Here is an example:</p>
1309
1310<pre>
1311#define GS_RELATIVE __attribute__((address_space(256)))
1312int foo(int GS_RELATIVE *P) {
1313 return *P;
1314}
1315</pre>
1316
1317<p>Which compiles to (on X86-32):</p>
1318
1319<pre>
1320_foo:
1321 movl 4(%esp), %eax
1322 movl %gs:(%eax), %eax
1323 ret
1324</pre>
1325
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1326<!-- ======================================================================= -->
1327<h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2>
1328<!-- ======================================================================= -->
1329
1330<p>Clang supports additional attributes that are useful for documenting program
1331invariants and rules for static analysis tools. The extensions documented here
1332are used by the <a
1333href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer
1334engine</a> that is part of Clang's Analysis library.</p>
1335
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1336<h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1337
1338<p>Clang's static analysis engine understands the standard <tt>noreturn</tt>
Ted Kremenek4df21142009-04-10 05:04:22 +0000[diff] [blame]1339attribute. This attribute, which is typically affixed to a function prototype,
1340indicates that a call to a given function never returns. Function prototypes for
1341common functions like <tt>exit</tt> are typically annotated with this attribute,
1342as well as a variety of common assertion handlers. Users can educate the static
1343analyzer about their own custom assertion handles (thus cutting down on false
1344positives due to false paths) by marking their own &quot;panic&quot; functions
1345with this attribute.</p>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1346
1347<p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes
Nick Lewycky625b5862009-06-14 04:08:08 +0000[diff] [blame]1348there are special functions that for all intents and purposes should be
1349considered panic functions (i.e., they are only called when an internal program
1350error occurs) but may actually return so that the program can fail gracefully.
1351The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions
1352as being interpreted as &quot;no return&quot; functions by the analyzer (thus
Chris Lattner28935892009-04-10 05:54:56 +0000[diff] [blame]1353pruning bogus paths) but will not affect compilation (as in the case of
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1354<tt>noreturn</tt>).</p>
1355
1356<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]1357same places where the <tt>noreturn</tt> attribute can be placed. It is commonly
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1358placed at the end of function prototypes:</p>
1359
1360<pre>
1361 void foo() <b>__attribute__((analyzer_noreturn))</b>;
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1362</pre>
1363
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1364<p>Query for this feature with
1365<tt>__has_attribute(analyzer_noreturn)</tt>.</p>
Chris Lattner148772a2009-06-13 07:13:28 +0000[diff] [blame]1366
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1367<h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3>
1368
1369<p>Many methods in Objective-C have conventional meanings determined
1370by their selectors. For the purposes of static analysis, it is
1371sometimes useful to be able to mark a method as having a particular
1372conventional meaning despite not having the right selector, or as not
1373having the conventional meaning that its selector would suggest.
1374For these use cases, we provide an attribute to specifically describe
1375the <q>method family</q> that a method belongs to.</p>
1376
1377<p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>,
1378where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>,
1379<tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute
1380can only be placed at the end of a method declaration:</p>
1381
1382<pre>
1383 - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>;
1384</pre>
1385
1386<p>Users who do not wish to change the conventional meaning of a
1387method, and who merely want to document its non-standard retain and
1388release semantics, should use the
1389<a href="#attr_retain_release">retaining behavior attributes</a>
1390described below.</p>
1391
1392<p>Query for this feature with
1393<tt>__has_attribute(objc_method_family)</tt>.</p>
1394
1395<h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1396
1397<p>In Objective-C, functions and methods are generally assumed to take
1398and return objects with +0 retain counts, with some exceptions for
1399special methods like <tt>+alloc</tt> and <tt>init</tt>. However,
1400there are exceptions, and so Clang provides attributes to allow these
1401exceptions to be documented, which helps the analyzer find leaks (and
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1402ignore non-leaks). Some exceptions may be better described using
1403the <a href="#attr_method_family"><tt>objc_method_family</tt></a>
1404attribute instead.</p>
John McCall630b7ae2011-01-25 04:26:21 +0000[diff] [blame]1405
1406<p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>,
1407<tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>,
1408and <tt>cf_returns_not_retained</tt> attributes can be placed on
1409methods and functions that return Objective-C or CoreFoundation
1410objects. They are commonly placed at the end of a function prototype
1411or method declaration:</p>
1412
1413<pre>
1414 id foo() <b>__attribute__((ns_returns_retained))</b>;
1415
1416 - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>;
1417</pre>
1418
1419<p>The <tt>*_returns_retained</tt> attributes specify that the
1420returned object has a +1 retain count.
1421The <tt>*_returns_not_retained</tt> attributes specify that the return
1422object has a +0 retain count, even if the normal convention for its
1423selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the
1424returned object is +0, but is guaranteed to live at least as long as the
1425next flush of an autorelease pool.</p>
1426
1427<p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt>
1428attributes can be placed on an parameter declaration; they specify
1429that the argument is expected to have a +1 retain count, which will be
1430balanced in some way by the function or method.
1431The <tt>ns_consumes_self</tt> attribute can only be placed on an
1432Objective-C method; it specifies that the method expects
1433its <tt>self</tt> parameter to have a +1 retain count, which it will
1434balance in some way.</p>
1435
1436<pre>
1437 void <b>foo(__attribute__((ns_consumed))</b> NSString *string);
1438
1439 - (void) bar <b>__attribute__((ns_consumes_self))</b>;
1440 - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x;
1441</pre>
Ted Kremeneked869312009-04-10 05:03:33 +0000[diff] [blame]1442
John McCall87494012011-03-18 03:51:49 +0000[diff] [blame]1443<p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>,
1444<tt>__has_attribute(ns_returns_retained)</tt>, etc.</p>
1445
Kostya Serebryanyce98c9b2011-11-28 20:51:02 +0000[diff] [blame]1446<!-- ======================================================================= -->
1447<h2 id="dynamicanalyzerspecific">Dynamic Analysis-Specific Extensions</h2>
1448<!-- ======================================================================= -->
1449<h3 id="address_sanitizer">AddressSanitizer</h3>
1450<p> Use <code>__has_feature(address_sanitizer)</code>
1451to check if the code is being built with <a
1452 href="AddressSanitizer.html">AddressSanitizer</a>.
1453</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1454
1455<!-- ======================================================================= -->
Caitlin Sadowski73cbbc82011-07-28 18:38:36 +0000[diff] [blame]1456<h2 id="threadsafety">Thread-Safety Annotation Checking</h2>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1457<!-- ======================================================================= -->
1458
1459<p>Clang supports additional attributes for checking basic locking policies in
1460multithreaded programs.
1461Clang currently parses the following list of attributes, although
1462<b>the implementation for these annotations is currently in development.</b>
1463For more details, see the
1464<a href="http://gcc.gnu.org/wiki/ThreadSafetyAnnotation">GCC implementation</a>.
1465</p>
1466
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1467<h4 id="ts_noanal">no_thread_safety_analysis</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1468
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1469<p>Use <tt>__attribute__((no_thread_safety_analysis))</tt> on a function
1470declaration to specify that the thread safety analysis should not be run on that
1471function. This attribute provides an escape hatch (e.g. for situations when it
1472is difficult to annotate the locking policy). </p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1473
1474<h4 id="ts_lockable">lockable</h4>
1475
1476<p>Use <tt>__attribute__((lockable))</tt> on a class definition to specify
1477that it has a lockable type (e.g. a Mutex class). This annotation is primarily
1478used to check consistency.</p>
1479
1480<h4 id="ts_scopedlockable">scoped_lockable</h4>
1481
1482<p>Use <tt>__attribute__((scoped_lockable))</tt> on a class definition to
1483specify that it has a "scoped" lockable type. Objects of this type will acquire
1484the lock upon construction and release it upon going out of scope.
1485 This annotation is primarily used to check
1486consistency.</p>
1487
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1488<h4 id="ts_guardedvar">guarded_var</h4>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1489
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1490<p>Use <tt>__attribute__((guarded_var))</tt> on a variable declaration to
1491specify that the variable must be accessed while holding some lock.</p>
1492
1493<h4 id="ts_ptguardedvar">pt_guarded_var</h4>
1494
1495<p>Use <tt>__attribute__((pt_guarded_var))</tt> on a pointer declaration to
1496specify that the pointer must be dereferenced while holding some lock.</p>
1497
1498<h4 id="ts_guardedby">guarded_by(l)</h4>
1499
1500<p>Use <tt>__attribute__((guarded_by(l)))</tt> on a variable declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1501specify that the variable must be accessed while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1502
1503<h4 id="ts_ptguardedby">pt_guarded_by(l)</h4>
1504
1505<p>Use <tt>__attribute__((pt_guarded_by(l)))</tt> on a pointer declaration to
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1506specify that the pointer must be dereferenced while holding lock <tt>l</tt>.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1507
1508<h4 id="ts_acquiredbefore">acquired_before(...)</h4>
1509
1510<p>Use <tt>__attribute__((acquired_before(...)))</tt> on a declaration
1511of a lockable variable to specify that the lock must be acquired before all
1512attribute arguments. Arguments must be lockable type, and there must be at
1513least one argument.</p>
1514
1515<h4 id="ts_acquiredafter">acquired_after(...)</h4>
1516
1517<p>Use <tt>__attribute__((acquired_after(...)))</tt> on a declaration
1518of a lockable variable to specify that the lock must be acquired after all
1519attribute arguments. Arguments must be lockable type, and there must be at
1520least one argument.</p>
1521
1522<h4 id="ts_elf">exclusive_lock_function(...)</h4>
1523
1524<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1525declaration to specify that the function acquires all listed locks
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1526exclusively. This attribute takes zero or more arguments: either of lockable
1527type or integers indexing into function parameters of lockable type. If no
1528arguments are given, the acquired lock is implicitly <tt>this</tt> of the
1529enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1530
1531<h4 id="ts_slf">shared_lock_function(...)</h4>
1532
1533<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1534declaration to specify that the function acquires all listed locks, although
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1535 the locks may be shared (e.g. read locks). This attribute takes zero or more
1536arguments: either of lockable type or integers indexing into function
1537parameters of lockable type. If no arguments are given, the acquired lock is
1538implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1539
1540<h4 id="ts_etf">exclusive_trylock_function(...)</h4>
1541
1542<p>Use <tt>__attribute__((exclusive_lock_function(...)))</tt> on a function
1543declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1544all listed locks exclusively. This attribute takes one or more arguments. The
1545first argument is an integer or boolean value specifying the return value of a
1546successful lock acquisition. The remaining arugments are either of lockable type
1547or integers indexing into function parameters of lockable type. If only one
1548argument is given, the acquired lock is implicitly <tt>this</tt> of the
1549enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1550
1551<h4 id="ts_stf">shared_trylock_function(...)</h4>
1552
1553<p>Use <tt>__attribute__((shared_lock_function(...)))</tt> on a function
1554declaration to specify that the function will try (without blocking) to acquire
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1555all listed locks, although the locks may be shared (e.g. read locks). This
1556attribute takes one or more arguments. The first argument is an integer or
1557boolean value specifying the return value of a successful lock acquisition. The
1558remaining arugments are either of lockable type or integers indexing into
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1559function parameters of lockable type. If only one argument is given, the
1560acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
1561
1562<h4 id="ts_uf">unlock_function(...)</h4>
1563
1564<p>Use <tt>__attribute__((unlock_function(...)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1565declaration to specify that the function release all listed locks. This
1566attribute takes zero or more arguments: either of lockable type or integers
1567indexing into function parameters of lockable type. If no arguments are given,
1568the acquired lock is implicitly <tt>this</tt> of the enclosing object.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1569
1570<h4 id="ts_lr">lock_returned(l)</h4>
1571
1572<p>Use <tt>__attribute__((lock_returned(l)))</tt> on a function
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1573declaration to specify that the function returns lock <tt>l</tt> (<tt>l</tt>
1574must be of lockable type). This annotation is used to aid in resolving lock
1575expressions.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1576
1577<h4 id="ts_le">locks_excluded(...)</h4>
1578
1579<p>Use <tt>__attribute__((locks_excluded(...)))</tt> on a function declaration
Caitlin Sadowskib51e0312011-08-09 17:59:31 +0000[diff] [blame]1580to specify that the function must not be called with the listed locks. Arguments
1581must be lockable type, and there must be at least one argument.</p>
Caitlin Sadowskidb33e142011-07-28 20:12:35 +0000[diff] [blame]1582
1583<h4 id="ts_elr">exclusive_locks_required(...)</h4>
1584
1585<p>Use <tt>__attribute__((exclusive_locks_required(...)))</tt> on a function
1586declaration to specify that the function must be called while holding the listed
1587exclusive locks. Arguments must be lockable type, and there must be at
1588least one argument.</p>
1589
1590<h4 id="ts_slr">shared_locks_required(...)</h4>
1591
1592<p>Use <tt>__attribute__((shared_locks_required(...)))</tt> on a function
1593declaration to specify that the function must be called while holding the listed
1594shared locks. Arguments must be lockable type, and there must be at
1595least one argument.</p>
Caitlin Sadowskifdde9e72011-07-28 17:21:07 +0000[diff] [blame]1596
Chris Lattner5ce933f2009-02-09 08:46:11 +0000[diff] [blame]1597</div>
1598</body>
1599</html>