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| 17 | |
| 18 | <h1>Clang Language Extensions</h1> |
| 19 | |
| 20 | <ul> |
| 21 | <li><a href="#intro">Introduction</a></li> |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 22 | <li><a href="#feature_check">Feature Checking Macros</a></li> |
John Thompson | 92bd8c7 | 2009-11-02 22:28:12 +0000 | [diff] [blame] | 23 | <li><a href="#has_include">Include File Checking Macros</a></li> |
Chris Lattner | 81edc9f | 2009-04-13 02:45:46 +0000 | [diff] [blame] | 24 | <li><a href="#builtinmacros">Builtin Macros</a></li> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 25 | <li><a href="#vectors">Vectors and Extended Vectors</a></li> |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 26 | <li><a href="#deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> attributes</a></li> |
| 27 | <li><a href="#attributes-on-enumerators">Attributes on enumerators</a></li> |
Ted Kremenek | 87774fd | 2009-12-03 02:04:01 +0000 | [diff] [blame] | 28 | <li><a href="#checking_language_features">Checks for Standard Language Features</a></li> |
Ted Kremenek | 22c3410 | 2009-12-03 02:05:57 +0000 | [diff] [blame] | 29 | <ul> |
| 30 | <li><a href="#cxx_exceptions">C++ exceptions</a></li> |
| 31 | <li><a href="#cxx_rtti">C++ RTTI</a></li> |
| 32 | </ul> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 33 | <li><a href="#checking_upcoming_features">Checks for Upcoming Standard Language Features</a></li> |
| 34 | <ul> |
| 35 | <li><a href="#cxx_attributes">C++0x attributes</a></li> |
| 36 | <li><a href="#cxx_decltype">C++0x <tt>decltype()</tt></a></li> |
Douglas Gregor | 0750800 | 2011-02-05 20:35:30 +0000 | [diff] [blame] | 37 | <li><a href="#cxx_default_function_template_args">C++0x default template arguments in function templates</a></li> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 38 | <li><a href="#cxx_deleted_functions">C++0x deleted functions</a></li> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 39 | <li><a href="#cxx_lambdas">C++0x lambdas</a></li> |
| 40 | <li><a href="#cxx_nullptr">C++0x nullptr</a></li> |
| 41 | <li><a href="#cxx_rvalue_references">C++0x rvalue references</a></li> |
Douglas Gregor | 56209ff | 2011-01-26 21:25:54 +0000 | [diff] [blame] | 42 | <li><a href="#cxx_reference_qualified_functions">C++0x reference-qualified functions</a></li> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 43 | <li><a href="#cxx_static_assert">C++0x <tt>static_assert()</tt></a></li> |
| 44 | <li><a href="#cxx_auto_type">C++0x type inference</a></li> |
| 45 | <li><a href="#cxx_variadic_templates">C++0x variadic templates</a></li> |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 46 | <li><a href="#cxx_inline_namespaces">C++0x inline namespaces</a></li> |
Douglas Gregor | 1274ccd | 2010-10-08 23:50:27 +0000 | [diff] [blame] | 47 | <li><a href="#cxx_strong_enums">C++0x strongly-typed enumerations</a></li> |
Douglas Gregor | dab60ad | 2010-10-01 18:44:50 +0000 | [diff] [blame] | 48 | <li><a href="#cxx_trailing_return">C++0x trailing return type</a></li> |
Sebastian Redl | 4561ecd | 2011-03-15 21:17:12 +0000 | [diff] [blame] | 49 | <li><a href="#cxx_noexcept">C++0x noexcept specification</a></li> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 50 | </ul> |
Douglas Gregor | afdf137 | 2011-02-03 21:57:35 +0000 | [diff] [blame] | 51 | <li><a href="#checking_type_traits">Checks for Type Traits</a></li> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 52 | <li><a href="#blocks">Blocks</a></li> |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 53 | <li><a href="#overloading-in-c">Function Overloading in C</a></li> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 54 | <li><a href="#builtins">Builtin Functions</a> |
| 55 | <ul> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 56 | <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li> |
Chris Lattner | 21190d5 | 2009-09-21 03:09:59 +0000 | [diff] [blame] | 57 | <li><a href="#__builtin_unreachable">__builtin_unreachable</a></li> |
Douglas Gregor | afdf137 | 2011-02-03 21:57:35 +0000 | [diff] [blame] | 58 | </ul> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 59 | </li> |
Chris Lattner | 1177f91 | 2009-04-09 19:58:15 +0000 | [diff] [blame] | 60 | <li><a href="#targetspecific">Target-Specific Extensions</a> |
| 61 | <ul> |
| 62 | <li><a href="#x86-specific">X86/X86-64 Language Extensions</a></li> |
| 63 | </ul> |
| 64 | </li> |
John McCall | 8749401 | 2011-03-18 03:51:49 +0000 | [diff] [blame] | 65 | <li><a href="#analyzerspecific">Static Analysis-Specific Extensions</a></li> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 66 | </ul> |
| 67 | |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 68 | <!-- ======================================================================= --> |
| 69 | <h2 id="intro">Introduction</h2> |
| 70 | <!-- ======================================================================= --> |
| 71 | |
| 72 | <p>This document describes the language extensions provided by Clang. In |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 73 | addition to the language extensions listed here, Clang aims to support a broad |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 74 | range of GCC extensions. Please see the <a |
| 75 | href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for |
| 76 | more information on these extensions.</p> |
| 77 | |
| 78 | <!-- ======================================================================= --> |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 79 | <h2 id="feature_check">Feature Checking Macros</h2> |
| 80 | <!-- ======================================================================= --> |
| 81 | |
| 82 | <p>Language extensions can be very useful, but only if you know you can depend |
Chris Lattner | c70e193 | 2011-03-21 16:25:11 +0000 | [diff] [blame^] | 83 | on them. In order to allow fine-grain features checks, we support three builtin |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 84 | function-like macros. This allows you to directly test for a feature in your |
| 85 | code without having to resort to something like autoconf or fragile "compiler |
| 86 | version checks".</p> |
| 87 | |
| 88 | <!-- ======================================================================= --> |
| 89 | <h3 id="__has_builtin">__has_builtin</h3> |
| 90 | <!-- ======================================================================= --> |
| 91 | |
| 92 | <p>This function-like macro takes a single identifier argument that is the name |
| 93 | of a builtin function. It evaluates to 1 if the builtin is supported or 0 if |
| 94 | not. It can be used like this:</p> |
| 95 | |
| 96 | <blockquote> |
| 97 | <pre> |
| 98 | #ifndef __has_builtin // Optional of course. |
| 99 | #define __has_builtin(x) 0 // Compatibility with non-clang compilers. |
| 100 | #endif |
| 101 | |
| 102 | ... |
| 103 | #if __has_builtin(__builtin_trap) |
| 104 | __builtin_trap(); |
| 105 | #else |
| 106 | abort(); |
| 107 | #endif |
| 108 | ... |
| 109 | </pre> |
| 110 | </blockquote> |
| 111 | |
| 112 | |
| 113 | <!-- ======================================================================= --> |
| 114 | <h3 id="__has_feature">__has_feature</h3> |
| 115 | <!-- ======================================================================= --> |
| 116 | |
| 117 | <p>This function-like macro takes a single identifier argument that is the name |
| 118 | of a feature. It evaluates to 1 if the feature is supported or 0 if not. It |
| 119 | can be used like this:</p> |
| 120 | |
| 121 | <blockquote> |
| 122 | <pre> |
| 123 | #ifndef __has_feature // Optional of course. |
| 124 | #define __has_feature(x) 0 // Compatibility with non-clang compilers. |
| 125 | #endif |
| 126 | |
| 127 | ... |
| 128 | #if __has_feature(attribute_overloadable) || \ |
| 129 | __has_feature(blocks) |
| 130 | ... |
| 131 | #endif |
| 132 | ... |
| 133 | </pre> |
| 134 | </blockquote> |
| 135 | |
| 136 | <p>The feature tag is described along with the language feature below.</p> |
| 137 | |
John Thompson | 92bd8c7 | 2009-11-02 22:28:12 +0000 | [diff] [blame] | 138 | <!-- ======================================================================= --> |
Anders Carlsson | cae5095 | 2010-10-20 02:31:43 +0000 | [diff] [blame] | 139 | <h3 id="__has_attribute">__has_attribute</h3> |
| 140 | <!-- ======================================================================= --> |
| 141 | |
| 142 | <p>This function-like macro takes a single identifier argument that is the name |
| 143 | of an attribute. It evaluates to 1 if the attribute is supported or 0 if not. It |
| 144 | can be used like this:</p> |
| 145 | |
| 146 | <blockquote> |
| 147 | <pre> |
| 148 | #ifndef __has_attribute // Optional of course. |
| 149 | #define __has_attribute(x) 0 // Compatibility with non-clang compilers. |
| 150 | #endif |
| 151 | |
| 152 | ... |
Anders Carlsson | 961003d | 2011-01-24 03:54:51 +0000 | [diff] [blame] | 153 | #if __has_attribute(always_inline) |
| 154 | #define ALWAYS_INLINE __attribute__((always_inline)) |
Anders Carlsson | cae5095 | 2010-10-20 02:31:43 +0000 | [diff] [blame] | 155 | #else |
Anders Carlsson | 961003d | 2011-01-24 03:54:51 +0000 | [diff] [blame] | 156 | #define ALWAYS_INLINE |
Anders Carlsson | cae5095 | 2010-10-20 02:31:43 +0000 | [diff] [blame] | 157 | #endif |
| 158 | ... |
| 159 | </pre> |
| 160 | </blockquote> |
| 161 | |
| 162 | <!-- ======================================================================= --> |
John Thompson | 92bd8c7 | 2009-11-02 22:28:12 +0000 | [diff] [blame] | 163 | <h2 id="has_include">Include File Checking Macros</h2> |
| 164 | <!-- ======================================================================= --> |
| 165 | |
| 166 | <p>Not all developments systems have the same include files. |
| 167 | The <a href="#__has_include">__has_include</a> and |
| 168 | <a href="#__has_include_next">__has_include_next</a> macros allow you to |
| 169 | check for the existence of an include file before doing |
| 170 | a possibly failing #include directive.</p> |
| 171 | |
| 172 | <!-- ======================================================================= --> |
| 173 | <h3 id="__has_include">__has_include</h3> |
| 174 | <!-- ======================================================================= --> |
| 175 | |
| 176 | <p>This function-like macro takes a single file name string argument that |
| 177 | is the name of an include file. It evaluates to 1 if the file can |
| 178 | be found using the include paths, or 0 otherwise:</p> |
| 179 | |
| 180 | <blockquote> |
| 181 | <pre> |
| 182 | // Note the two possible file name string formats. |
| 183 | #if __has_include("myinclude.h") && __has_include(<stdint.h>) |
| 184 | # include "myinclude.h" |
| 185 | #endif |
| 186 | |
| 187 | // To avoid problem with non-clang compilers not having this macro. |
| 188 | #if defined(__has_include) && __has_include("myinclude.h") |
| 189 | # include "myinclude.h" |
| 190 | #endif |
| 191 | </pre> |
| 192 | </blockquote> |
| 193 | |
| 194 | <p>To test for this feature, use #if defined(__has_include).</p> |
| 195 | |
| 196 | <!-- ======================================================================= --> |
| 197 | <h3 id="__has_include_next">__has_include_next</h3> |
| 198 | <!-- ======================================================================= --> |
| 199 | |
| 200 | <p>This function-like macro takes a single file name string argument that |
| 201 | is the name of an include file. It is like __has_include except that it |
| 202 | looks for the second instance of the given file found in the include |
| 203 | paths. It evaluates to 1 if the second instance of the file can |
| 204 | be found using the include paths, or 0 otherwise:</p> |
| 205 | |
| 206 | <blockquote> |
| 207 | <pre> |
| 208 | // Note the two possible file name string formats. |
| 209 | #if __has_include_next("myinclude.h") && __has_include_next(<stdint.h>) |
| 210 | # include_next "myinclude.h" |
| 211 | #endif |
| 212 | |
| 213 | // To avoid problem with non-clang compilers not having this macro. |
| 214 | #if defined(__has_include_next) && __has_include_next("myinclude.h") |
| 215 | # include_next "myinclude.h" |
| 216 | #endif |
| 217 | </pre> |
| 218 | </blockquote> |
| 219 | |
| 220 | <p>Note that __has_include_next, like the GNU extension |
| 221 | #include_next directive, is intended for use in headers only, |
| 222 | and will issue a warning if used in the top-level compilation |
| 223 | file. A warning will also be issued if an absolute path |
| 224 | is used in the file argument.</p> |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 225 | |
| 226 | <!-- ======================================================================= --> |
Chris Lattner | 81edc9f | 2009-04-13 02:45:46 +0000 | [diff] [blame] | 227 | <h2 id="builtinmacros">Builtin Macros</h2> |
| 228 | <!-- ======================================================================= --> |
| 229 | |
Douglas Gregor | 4290fbd | 2010-04-30 02:51:06 +0000 | [diff] [blame] | 230 | <dl> |
| 231 | <dt><code>__BASE_FILE__</code></dt> |
| 232 | <dd>Defined to a string that contains the name of the main input |
| 233 | file passed to Clang.</dd> |
| 234 | |
| 235 | <dt><code>__COUNTER__</code></dt> |
| 236 | <dd>Defined to an integer value that starts at zero and is |
| 237 | incremented each time the <code>__COUNTER__</code> macro is |
| 238 | expanded.</dd> |
| 239 | |
| 240 | <dt><code>__INCLUDE_LEVEL__</code></dt> |
| 241 | <dd>Defined to an integral value that is the include depth of the |
| 242 | file currently being translated. For the main file, this value is |
| 243 | zero.</dd> |
| 244 | |
| 245 | <dt><code>__TIMESTAMP__</code></dt> |
| 246 | <dd>Defined to the date and time of the last modification of the |
| 247 | current source file.</dd> |
| 248 | |
| 249 | <dt><code>__clang__</code></dt> |
| 250 | <dd>Defined when compiling with Clang</dd> |
| 251 | |
| 252 | <dt><code>__clang_major__</code></dt> |
| 253 | <dd>Defined to the major version number of Clang (e.g., the 2 in |
| 254 | 2.0.1).</dd> |
| 255 | |
| 256 | <dt><code>__clang_minor__</code></dt> |
| 257 | <dd>Defined to the minor version number of Clang (e.g., the 0 in |
| 258 | 2.0.1).</dd> |
| 259 | |
| 260 | <dt><code>__clang_patchlevel__</code></dt> |
| 261 | <dd>Defined to the patch level of Clang (e.g., the 1 in 2.0.1).</dd> |
| 262 | |
| 263 | <dt><code>__clang_version__</code></dt> |
| 264 | <dd>Defined to a string that captures the Clang version, including |
| 265 | the Subversion tag or revision number, e.g., "1.5 (trunk |
| 266 | 102332)".</dd> |
| 267 | </dl> |
Chris Lattner | 81edc9f | 2009-04-13 02:45:46 +0000 | [diff] [blame] | 268 | |
| 269 | <!-- ======================================================================= --> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 270 | <h2 id="vectors">Vectors and Extended Vectors</h2> |
| 271 | <!-- ======================================================================= --> |
| 272 | |
Owen Anderson | d2bf0cd | 2010-01-27 01:22:36 +0000 | [diff] [blame] | 273 | <p>Supports the GCC vector extensions, plus some stuff like V[1].</p> |
| 274 | |
| 275 | <p>Also supports <tt>ext_vector</tt>, which additionally support for V.xyzw |
| 276 | syntax and other tidbits as seen in OpenCL. An example is:</p> |
| 277 | |
| 278 | <blockquote> |
| 279 | <pre> |
| 280 | typedef float float4 <b>__attribute__((ext_vector_type(4)))</b>; |
| 281 | typedef float float2 <b>__attribute__((ext_vector_type(2)))</b>; |
| 282 | |
| 283 | float4 foo(float2 a, float2 b) { |
| 284 | float4 c; |
| 285 | c.xz = a; |
| 286 | c.yw = b; |
| 287 | return c; |
| 288 | } |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 289 | </pre> |
Owen Anderson | d2bf0cd | 2010-01-27 01:22:36 +0000 | [diff] [blame] | 290 | </blockquote> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 291 | |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 292 | <p>Query for this feature with __has_feature(attribute_ext_vector_type).</p> |
| 293 | |
Owen Anderson | d2bf0cd | 2010-01-27 01:22:36 +0000 | [diff] [blame] | 294 | <p>See also <a href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p> |
| 295 | |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 296 | <!-- ======================================================================= --> |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 297 | <h2 id="deprecated">Messages on <tt>deprecated</tt> and <tt>unavailable</tt> Attributes</h2> |
Fariborz Jahanian | c784dc1 | 2010-10-06 23:12:32 +0000 | [diff] [blame] | 298 | <!-- ======================================================================= --> |
| 299 | |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 300 | <p>An optional string message can be added to the <tt>deprecated</tt> |
| 301 | and <tt>unavailable</tt> attributes. For example:</p> |
Fariborz Jahanian | c784dc1 | 2010-10-06 23:12:32 +0000 | [diff] [blame] | 302 | |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 303 | <blockquote> |
Chris Lattner | 4836d6a | 2010-11-09 19:43:35 +0000 | [diff] [blame] | 304 | <pre>void explode(void) __attribute__((deprecated("extremely unsafe, use 'combust' instead!!!")));</pre> |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 305 | </blockquote> |
| 306 | |
| 307 | <p>If the deprecated or unavailable declaration is used, the message |
| 308 | will be incorporated into the appropriate diagnostic:</p> |
| 309 | |
| 310 | <blockquote> |
Chris Lattner | 4836d6a | 2010-11-09 19:43:35 +0000 | [diff] [blame] | 311 | <pre>harmless.c:4:3: warning: 'explode' is deprecated: extremely unsafe, use 'combust' instead!!! [-Wdeprecated-declarations] |
John McCall | 4820908 | 2010-11-08 19:48:17 +0000 | [diff] [blame] | 312 | explode(); |
| 313 | ^</pre> |
| 314 | </blockquote> |
| 315 | |
| 316 | <p>Query for this feature |
| 317 | with <tt>__has_feature(attribute_deprecated_with_message)</tt> |
| 318 | and <tt>__has_feature(attribute_unavailable_with_message)</tt>.</p> |
| 319 | |
| 320 | <!-- ======================================================================= --> |
| 321 | <h2 id="attributes-on-enumerators">Attributes on Enumerators</h2> |
| 322 | <!-- ======================================================================= --> |
| 323 | |
| 324 | <p>Clang allows attributes to be written on individual enumerators. |
| 325 | This allows enumerators to be deprecated, made unavailable, etc. The |
| 326 | attribute must appear after the enumerator name and before any |
| 327 | initializer, like so:</p> |
| 328 | |
| 329 | <blockquote> |
| 330 | <pre>enum OperationMode { |
| 331 | OM_Invalid, |
| 332 | OM_Normal, |
| 333 | OM_Terrified __attribute__((deprecated)), |
| 334 | OM_AbortOnError __attribute__((deprecated)) = 4 |
| 335 | };</pre> |
| 336 | </blockquote> |
| 337 | |
| 338 | <p>Attributes on the <tt>enum</tt> declaration do not apply to |
| 339 | individual enumerators.</p> |
| 340 | |
| 341 | <p>Query for this feature with <tt>__has_feature(enumerator_attributes)</tt>.</p> |
Fariborz Jahanian | c784dc1 | 2010-10-06 23:12:32 +0000 | [diff] [blame] | 342 | |
| 343 | <!-- ======================================================================= --> |
Ted Kremenek | 87774fd | 2009-12-03 02:04:01 +0000 | [diff] [blame] | 344 | <h2 id="checking_language_features">Checks for Standard Language Features</h2> |
| 345 | <!-- ======================================================================= --> |
| 346 | |
| 347 | <p>The <tt>__has_feature</tt> macro can be used to query if certain standard language features are |
| 348 | enabled. Those features are listed here.</p> |
| 349 | |
Ted Kremenek | 22c3410 | 2009-12-03 02:05:57 +0000 | [diff] [blame] | 350 | <h3 id="cxx_exceptions">C++ exceptions</h3> |
Ted Kremenek | 87774fd | 2009-12-03 02:04:01 +0000 | [diff] [blame] | 351 | |
Ted Kremenek | 22c3410 | 2009-12-03 02:05:57 +0000 | [diff] [blame] | 352 | <p>Use <tt>__has_feature(cxx_exceptions)</tt> to determine if C++ exceptions have been enabled. For |
| 353 | example, compiling code with <tt>-fexceptions</tt> enables C++ exceptions.</p> |
Ted Kremenek | 87774fd | 2009-12-03 02:04:01 +0000 | [diff] [blame] | 354 | |
Ted Kremenek | 22c3410 | 2009-12-03 02:05:57 +0000 | [diff] [blame] | 355 | <h3 id="cxx_rtti">C++ RTTI</h3> |
Ted Kremenek | 87774fd | 2009-12-03 02:04:01 +0000 | [diff] [blame] | 356 | |
Ted Kremenek | 0eb9560 | 2009-12-03 02:06:43 +0000 | [diff] [blame] | 357 | <p>Use <tt>__has_feature(cxx_rtti)</tt> to determine if C++ RTTI has been enabled. For example, |
Ted Kremenek | 22c3410 | 2009-12-03 02:05:57 +0000 | [diff] [blame] | 358 | compiling code with <tt>-fno-rtti</tt> disables the use of RTTI.</p> |
Ted Kremenek | 87774fd | 2009-12-03 02:04:01 +0000 | [diff] [blame] | 359 | |
| 360 | <!-- ======================================================================= --> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 361 | <h2 id="checking_upcoming_features">Checks for Upcoming Standard Language Features</h2> |
| 362 | <!-- ======================================================================= --> |
| 363 | |
| 364 | <p>The <tt>__has_feature</tt> macro can be used to query if certain upcoming |
| 365 | standard language features are enabled. Those features are listed here.</p> |
| 366 | |
| 367 | <p>Currently, all features listed here are slated for inclusion in the upcoming |
| 368 | C++0x standard. As a result, all the features that clang supports are enabled |
| 369 | with the <tt>-std=c++0x</tt> option when compiling C++ code. Features that are |
| 370 | not yet implemented will be noted.</p> |
| 371 | |
| 372 | <h3 id="cxx_decltype">C++0x <tt>decltype()</tt></h3> |
| 373 | |
| 374 | <p>Use <tt>__has_feature(cxx_decltype)</tt> to determine if support for the |
| 375 | <tt>decltype()</tt> specifier is enabled.</p> |
| 376 | |
| 377 | <h3 id="cxx_attributes">C++0x attributes</h3> |
| 378 | |
| 379 | <p>Use <tt>__has_feature(cxx_attributes)</tt> to determine if support for |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 380 | attribute parsing with C++0x's square bracket notation is enabled.</p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 381 | |
Douglas Gregor | 0750800 | 2011-02-05 20:35:30 +0000 | [diff] [blame] | 382 | <h3 id="cxx_default_function_template_args">C++0x default template arguments in function templates</h3> |
| 383 | |
| 384 | <p>Use <tt>__has_feature(cxx_default_function_template_args)</tt> to determine if support for default template arguments in function templates is enabled.</p> |
| 385 | |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 386 | <h3 id="cxx_deleted_functions">C++0x deleted functions</tt></h3> |
| 387 | |
| 388 | <p>Use <tt>__has_feature(cxx_deleted_functions)</tt> to determine if support for |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 389 | deleted function definitions (with <tt>= delete</tt>) is enabled.</p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 390 | |
Douglas Gregor | 9cc90a3 | 2010-01-13 16:27:49 +0000 | [diff] [blame] | 391 | <h3 id="cxx_lambdas">C++0x lambdas</h3> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 392 | |
| 393 | <p>Use <tt>__has_feature(cxx_lambdas)</tt> to determine if support for |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 394 | lambdas is enabled. clang does not currently implement this feature.</p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 395 | |
| 396 | <h3 id="cxx_nullptr">C++0x <tt>nullptr</tt></h3> |
| 397 | |
| 398 | <p>Use <tt>__has_feature(cxx_nullptr)</tt> to determine if support for |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 399 | <tt>nullptr</tt> is enabled. clang does not yet fully implement this |
| 400 | feature.</p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 401 | |
Douglas Gregor | 56209ff | 2011-01-26 21:25:54 +0000 | [diff] [blame] | 402 | <h3 id="cxx_reference_qualified_functions">C++0x reference-qualified functions</h3> |
| 403 | <p>Use <tt>__has_feature(cxx_reference_qualified_functions)</tt> to determine if support for reference-qualified functions (e.g., member functions with <code>&</code> or <code>&&</code> applied to <code>*this</code>) is enabled.</p> |
| 404 | |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 405 | <h3 id="cxx_rvalue_references">C++0x rvalue references</tt></h3> |
| 406 | |
| 407 | <p>Use <tt>__has_feature(cxx_rvalue_references)</tt> to determine if support for |
Douglas Gregor | 56209ff | 2011-01-26 21:25:54 +0000 | [diff] [blame] | 408 | rvalue references is enabled. </p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 409 | |
| 410 | <h3 id="cxx_static_assert">C++0x <tt>static_assert()</tt></h3> |
| 411 | |
| 412 | <p>Use <tt>__has_feature(cxx_static_assert)</tt> to determine if support for |
| 413 | compile-time assertions using <tt>static_assert</tt> is enabled.</p> |
| 414 | |
| 415 | <h3 id="cxx_auto_type">C++0x type inference</h3> |
| 416 | |
| 417 | <p>Use <tt>__has_feature(cxx_auto_type)</tt> to determine C++0x type inference |
| 418 | is supported using the <tt>auto</tt> specifier. If this is disabled, |
Richard Smith | fd405ef | 2011-02-23 00:41:16 +0000 | [diff] [blame] | 419 | <tt>auto</tt> will instead be a storage class specifier, as in C or C++98.</p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 420 | |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 421 | <h3 id="cxx_variadic_templates">C++0x variadic templates</h3> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 422 | |
| 423 | <p>Use <tt>__has_feature(cxx_variadic_templates)</tt> to determine if support |
Douglas Gregor | 83d7781 | 2011-01-19 23:15:20 +0000 | [diff] [blame] | 424 | for variadic templates is enabled.</p> |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 425 | |
Sebastian Redl | f6c0977 | 2010-08-31 23:28:47 +0000 | [diff] [blame] | 426 | <h3 id="cxx_inline_namespaces">C++0x inline namespaces</h3> |
| 427 | |
| 428 | <p>Use <tt>__has_feature(cxx_inline_namespaces)</tt> to determine if support for |
| 429 | inline namespaces is enabled.</p> |
| 430 | |
Douglas Gregor | dab60ad | 2010-10-01 18:44:50 +0000 | [diff] [blame] | 431 | <h3 id="cxx_trailing_return">C++0x trailing return type</h3> |
| 432 | |
| 433 | <p>Use <tt>__has_feature(cxx_trailing_return)</tt> to determine if support for |
| 434 | the alternate function declaration syntax with trailing return type is enabled.</p> |
| 435 | |
Sebastian Redl | 4561ecd | 2011-03-15 21:17:12 +0000 | [diff] [blame] | 436 | <h3 id="cxx_noexcept">C++0x noexcept</h3> |
| 437 | |
| 438 | <p>Use <tt>__has_feature(cxx_noexcept)</tt> to determine if support for |
| 439 | noexcept exception specifications is enabled.</p> |
| 440 | |
Douglas Gregor | 1274ccd | 2010-10-08 23:50:27 +0000 | [diff] [blame] | 441 | <h3 id="cxx_strong_enums">C++0x strongly typed enumerations</h3> |
| 442 | |
| 443 | <p>Use <tt>__has_feature(cxx_strong_enums)</tt> to determine if support for |
| 444 | strongly typed, scoped enumerations is enabled.</p> |
| 445 | |
Sean Hunt | 4ef4c6b | 2010-01-13 08:31:49 +0000 | [diff] [blame] | 446 | <!-- ======================================================================= --> |
Douglas Gregor | afdf137 | 2011-02-03 21:57:35 +0000 | [diff] [blame] | 447 | <h2 id="checking_type_traits">Checks for Type Traits</h2> |
| 448 | <!-- ======================================================================= --> |
| 449 | |
| 450 | <p>Clang supports the <a hef="http://gcc.gnu.org/onlinedocs/gcc/Type-Traits.html">GNU C++ type traits</a> and a subset of the <a href="http://msdn.microsoft.com/en-us/library/ms177194(v=VS.100).aspx">Microsoft Visual C++ Type traits</a>. For each supported type trait <code>__X</code>, <code>__has_feature(X)</code> indicates the presence of the type trait. For example: |
| 451 | <blockquote> |
| 452 | <pre> |
| 453 | #if __has_feature(is_convertible_to) |
| 454 | template<typename From, typename To> |
| 455 | struct is_convertible_to { |
| 456 | static const bool value = __is_convertible_to(From, To); |
| 457 | }; |
| 458 | #else |
| 459 | // Emulate type trait |
| 460 | #endif |
| 461 | </pre> |
| 462 | </blockquote> |
| 463 | |
| 464 | <p>The following type traits are supported by Clang:</p> |
| 465 | <ul> |
| 466 | <li><code>__has_nothrow_assign</code> (GNU, Microsoft)</li> |
| 467 | <li><code>__has_nothrow_copy</code> (GNU, Microsoft)</li> |
| 468 | <li><code>__has_nothrow_constructor</code> (GNU, Microsoft)</li> |
| 469 | <li><code>__has_trivial_assign</code> (GNU, Microsoft)</li> |
| 470 | <li><code>__has_trivial_copy</code> (GNU, Microsoft)</li> |
| 471 | <li><code>__has_trivial_constructor</code> (GNU, Microsoft)</li> |
| 472 | <li><code>__has_trivial_destructor</code> (GNU, Microsoft)</li> |
| 473 | <li><code>__has_virtual_destructor</code> (GNU, Microsoft)</li> |
| 474 | <li><code>__is_abstract</code> (GNU, Microsoft)</li> |
| 475 | <li><code>__is_base_of</code> (GNU, Microsoft)</li> |
| 476 | <li><code>__is_class</code> (GNU, Microsoft)</li> |
| 477 | <li><code>__is_convertible_to</code> (Microsoft)</li> |
| 478 | <li><code>__is_empty</code> (GNU, Microsoft)</li> |
| 479 | <li><code>__is_enum</code> (GNU, Microsoft)</li> |
| 480 | <li><code>__is_pod</code> (GNU, Microsoft)</li> |
| 481 | <li><code>__is_polymorphic</code> (GNU, Microsoft)</li> |
| 482 | <li><code>__is_union</code> (GNU, Microsoft)</li> |
| 483 | <li><code>__is_literal(type)</code>: Determines whether the given type is a literal type</li> |
| 484 | </ul> |
| 485 | |
| 486 | <!-- ======================================================================= --> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 487 | <h2 id="blocks">Blocks</h2> |
| 488 | <!-- ======================================================================= --> |
| 489 | |
Chris Lattner | a7dbdf5 | 2009-03-09 07:03:22 +0000 | [diff] [blame] | 490 | <p>The syntax and high level language feature description is in <a |
| 491 | href="BlockLanguageSpec.txt">BlockLanguageSpec.txt</a>. Implementation and ABI |
| 492 | details for the clang implementation are in <a |
Chris Lattner | 5d7650b | 2010-03-16 21:43:03 +0000 | [diff] [blame] | 493 | href="Block-ABI-Apple.txt">Block-ABI-Apple.txt</a>.</p> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 494 | |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 495 | |
| 496 | <p>Query for this feature with __has_feature(blocks).</p> |
| 497 | |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 498 | <!-- ======================================================================= --> |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 499 | <h2 id="overloading-in-c">Function Overloading in C</h2> |
| 500 | <!-- ======================================================================= --> |
| 501 | |
Chris Lattner | f161d41 | 2009-02-13 21:51:45 +0000 | [diff] [blame] | 502 | <p>Clang provides support for C++ function overloading in C. Function |
| 503 | overloading in C is introduced using the <tt>overloadable</tt> attribute. For |
| 504 | example, one might provide several overloaded versions of a <tt>tgsin</tt> |
| 505 | function that invokes the appropriate standard function computing the sine of a |
| 506 | value with <tt>float</tt>, <tt>double</tt>, or <tt>long double</tt> |
| 507 | precision:</p> |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 508 | |
| 509 | <blockquote> |
| 510 | <pre> |
| 511 | #include <math.h> |
| 512 | float <b>__attribute__((overloadable))</b> tgsin(float x) { return sinf(x); } |
| 513 | double <b>__attribute__((overloadable))</b> tgsin(double x) { return sin(x); } |
| 514 | long double <b>__attribute__((overloadable))</b> tgsin(long double x) { return sinl(x); } |
| 515 | </pre> |
| 516 | </blockquote> |
| 517 | |
| 518 | <p>Given these declarations, one can call <tt>tgsin</tt> with a |
| 519 | <tt>float</tt> value to receive a <tt>float</tt> result, with a |
| 520 | <tt>double</tt> to receive a <tt>double</tt> result, etc. Function |
| 521 | overloading in C follows the rules of C++ function overloading to pick |
| 522 | the best overload given the call arguments, with a few C-specific |
| 523 | semantics:</p> |
| 524 | <ul> |
| 525 | <li>Conversion from <tt>float</tt> or <tt>double</tt> to <tt>long |
| 526 | double</tt> is ranked as a floating-point promotion (per C99) rather |
| 527 | than as a floating-point conversion (as in C++).</li> |
| 528 | |
| 529 | <li>A conversion from a pointer of type <tt>T*</tt> to a pointer of type |
| 530 | <tt>U*</tt> is considered a pointer conversion (with conversion |
| 531 | rank) if <tt>T</tt> and <tt>U</tt> are compatible types.</li> |
| 532 | |
| 533 | <li>A conversion from type <tt>T</tt> to a value of type <tt>U</tt> |
| 534 | is permitted if <tt>T</tt> and <tt>U</tt> are compatible types. This |
| 535 | conversion is given "conversion" rank.</li> |
| 536 | </ul> |
| 537 | |
| 538 | <p>The declaration of <tt>overloadable</tt> functions is restricted to |
| 539 | function declarations and definitions. Most importantly, if any |
| 540 | function with a given name is given the <tt>overloadable</tt> |
| 541 | attribute, then all function declarations and definitions with that |
| 542 | name (and in that scope) must have the <tt>overloadable</tt> |
Chris Lattner | f161d41 | 2009-02-13 21:51:45 +0000 | [diff] [blame] | 543 | attribute. This rule even applies to redeclarations of functions whose original |
| 544 | declaration had the <tt>overloadable</tt> attribute, e.g.,</p> |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 545 | |
| 546 | <blockquote> |
| 547 | <pre> |
| 548 | int f(int) __attribute__((overloadable)); |
| 549 | float f(float); <i>// error: declaration of "f" must have the "overloadable" attribute</i> |
| 550 | |
| 551 | int g(int) __attribute__((overloadable)); |
| 552 | int g(int) { } <i>// error: redeclaration of "g" must also have the "overloadable" attribute</i> |
| 553 | </pre> |
| 554 | </blockquote> |
| 555 | |
Douglas Gregor | 965acbb | 2009-02-18 07:07:28 +0000 | [diff] [blame] | 556 | <p>Functions marked <tt>overloadable</tt> must have |
| 557 | prototypes. Therefore, the following code is ill-formed:</p> |
| 558 | |
| 559 | <blockquote> |
| 560 | <pre> |
| 561 | int h() __attribute__((overloadable)); <i>// error: h does not have a prototype</i> |
| 562 | </pre> |
| 563 | </blockquote> |
| 564 | |
| 565 | <p>However, <tt>overloadable</tt> functions are allowed to use a |
| 566 | ellipsis 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> |
| 567 | |
| 568 | <blockquote> |
| 569 | <pre> |
Chris Lattner | 0224680 | 2009-02-18 22:27:46 +0000 | [diff] [blame] | 570 | void honeypot(...) __attribute__((overloadable, unavailable)); <i>// calling me is an error</i> |
Douglas Gregor | 965acbb | 2009-02-18 07:07:28 +0000 | [diff] [blame] | 571 | </pre> |
| 572 | </blockquote> |
| 573 | |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 574 | <p>Functions declared with the <tt>overloadable</tt> attribute have |
| 575 | their names mangled according to the same rules as C++ function |
| 576 | names. For example, the three <tt>tgsin</tt> functions in our |
| 577 | motivating example get the mangled names <tt>_Z5tgsinf</tt>, |
Chris Lattner | 71b48d6 | 2010-11-28 18:19:13 +0000 | [diff] [blame] | 578 | <tt>_Z5tgsind</tt>, and <tt>_Z5tgsine</tt>, respectively. There are two |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 579 | caveats to this use of name mangling:</p> |
| 580 | |
| 581 | <ul> |
| 582 | |
| 583 | <li>Future versions of Clang may change the name mangling of |
| 584 | functions overloaded in C, so you should not depend on an specific |
| 585 | mangling. To be completely safe, we strongly urge the use of |
| 586 | <tt>static inline</tt> with <tt>overloadable</tt> functions.</li> |
| 587 | |
| 588 | <li>The <tt>overloadable</tt> attribute has almost no meaning when |
| 589 | used in C++, because names will already be mangled and functions are |
| 590 | already overloadable. However, when an <tt>overloadable</tt> |
| 591 | function occurs within an <tt>extern "C"</tt> linkage specification, |
| 592 | it's name <i>will</i> be mangled in the same way as it would in |
| 593 | C.</li> |
| 594 | </ul> |
| 595 | |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 596 | <p>Query for this feature with __has_feature(attribute_overloadable).</p> |
| 597 | |
| 598 | |
Douglas Gregor | cb54d43 | 2009-02-13 00:57:04 +0000 | [diff] [blame] | 599 | <!-- ======================================================================= --> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 600 | <h2 id="builtins">Builtin Functions</h2> |
| 601 | <!-- ======================================================================= --> |
| 602 | |
| 603 | <p>Clang supports a number of builtin library functions with the same syntax as |
| 604 | GCC, including things like <tt>__builtin_nan</tt>, |
| 605 | <tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>, |
| 606 | <tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In |
| 607 | addition to the GCC builtins, Clang supports a number of builtins that GCC does |
| 608 | not, which are listed here.</p> |
| 609 | |
| 610 | <p>Please note that Clang does not and will not support all of the GCC builtins |
| 611 | for vector operations. Instead of using builtins, you should use the functions |
| 612 | defined in target-specific header files like <tt><xmmintrin.h></tt>, which |
| 613 | define portable wrappers for these. Many of the Clang versions of these |
| 614 | functions are implemented directly in terms of <a href="#vectors">extended |
| 615 | vector support</a> instead of builtins, in order to reduce the number of |
| 616 | builtins that we need to implement.</p> |
| 617 | |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 618 | <!-- ======================================================================= --> |
Chris Lattner | 6f72da5 | 2009-02-13 20:00:20 +0000 | [diff] [blame] | 619 | <h3 id="__builtin_shufflevector">__builtin_shufflevector</h3> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 620 | <!-- ======================================================================= --> |
| 621 | |
Chris Lattner | aad826b | 2009-09-16 18:56:12 +0000 | [diff] [blame] | 622 | <p><tt>__builtin_shufflevector</tt> is used to express generic vector |
Chris Lattner | 6f72da5 | 2009-02-13 20:00:20 +0000 | [diff] [blame] | 623 | permutation/shuffle/swizzle operations. This builtin is also very important for |
| 624 | the implementation of various target-specific header files like |
| 625 | <tt><xmmintrin.h></tt>. |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 626 | </p> |
| 627 | |
| 628 | <p><b>Syntax:</b></p> |
| 629 | |
| 630 | <pre> |
Chris Lattner | 6f72da5 | 2009-02-13 20:00:20 +0000 | [diff] [blame] | 631 | __builtin_shufflevector(vec1, vec2, index1, index2, ...) |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 632 | </pre> |
| 633 | |
| 634 | <p><b>Examples:</b></p> |
| 635 | |
| 636 | <pre> |
Chris Lattner | 6f72da5 | 2009-02-13 20:00:20 +0000 | [diff] [blame] | 637 | // Identity operation - return 4-element vector V1. |
| 638 | __builtin_shufflevector(V1, V1, 0, 1, 2, 3) |
| 639 | |
| 640 | // "Splat" element 0 of V1 into a 4-element result. |
| 641 | __builtin_shufflevector(V1, V1, 0, 0, 0, 0) |
| 642 | |
| 643 | // Reverse 4-element vector V1. |
| 644 | __builtin_shufflevector(V1, V1, 3, 2, 1, 0) |
| 645 | |
| 646 | // Concatenate every other element of 4-element vectors V1 and V2. |
| 647 | __builtin_shufflevector(V1, V2, 0, 2, 4, 6) |
| 648 | |
| 649 | // Concatenate every other element of 8-element vectors V1 and V2. |
| 650 | __builtin_shufflevector(V1, V2, 0, 2, 4, 6, 8, 10, 12, 14) |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 651 | </pre> |
| 652 | |
| 653 | <p><b>Description:</b></p> |
| 654 | |
Chris Lattner | 6f72da5 | 2009-02-13 20:00:20 +0000 | [diff] [blame] | 655 | <p>The first two arguments to __builtin_shufflevector are vectors that have the |
| 656 | same element type. The remaining arguments are a list of integers that specify |
| 657 | the elements indices of the first two vectors that should be extracted and |
| 658 | returned in a new vector. These element indices are numbered sequentially |
| 659 | starting with the first vector, continuing into the second vector. Thus, if |
| 660 | vec1 is a 4-element vector, index 5 would refer to the second element of vec2. |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 661 | </p> |
| 662 | |
Chris Lattner | 6f72da5 | 2009-02-13 20:00:20 +0000 | [diff] [blame] | 663 | <p>The result of __builtin_shufflevector is a vector |
| 664 | with the same element type as vec1/vec2 but that has an element count equal to |
| 665 | the number of indices specified. |
| 666 | </p> |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 667 | |
Chris Lattner | 21190d5 | 2009-09-21 03:09:59 +0000 | [diff] [blame] | 668 | <p>Query for this feature with __has_builtin(__builtin_shufflevector).</p> |
| 669 | |
| 670 | <!-- ======================================================================= --> |
| 671 | <h3 id="__builtin_unreachable">__builtin_unreachable</h3> |
| 672 | <!-- ======================================================================= --> |
| 673 | |
| 674 | <p><tt>__builtin_unreachable</tt> is used to indicate that a specific point in |
| 675 | the program cannot be reached, even if the compiler might otherwise think it |
| 676 | can. This is useful to improve optimization and eliminates certain warnings. |
| 677 | For example, without the <tt>__builtin_unreachable</tt> in the example below, |
| 678 | the compiler assumes that the inline asm can fall through and prints a "function |
| 679 | declared 'noreturn' should not return" warning. |
| 680 | </p> |
| 681 | |
| 682 | <p><b>Syntax:</b></p> |
| 683 | |
| 684 | <pre> |
| 685 | __builtin_unreachable() |
| 686 | </pre> |
| 687 | |
| 688 | <p><b>Example of Use:</b></p> |
| 689 | |
| 690 | <pre> |
| 691 | void myabort(void) __attribute__((noreturn)); |
| 692 | void myabort(void) { |
| 693 | asm("int3"); |
| 694 | __builtin_unreachable(); |
| 695 | } |
| 696 | </pre> |
| 697 | |
| 698 | <p><b>Description:</b></p> |
| 699 | |
| 700 | <p>The __builtin_unreachable() builtin has completely undefined behavior. Since |
| 701 | it has undefined behavior, it is a statement that it is never reached and the |
| 702 | optimizer can take advantage of this to produce better code. This builtin takes |
| 703 | no arguments and produces a void result. |
| 704 | </p> |
| 705 | |
| 706 | <p>Query for this feature with __has_builtin(__builtin_unreachable).</p> |
| 707 | |
| 708 | |
Chris Lattner | 1177f91 | 2009-04-09 19:58:15 +0000 | [diff] [blame] | 709 | <!-- ======================================================================= --> |
| 710 | <h2 id="targetspecific">Target-Specific Extensions</h2> |
| 711 | <!-- ======================================================================= --> |
| 712 | |
| 713 | <p>Clang supports some language features conditionally on some targets.</p> |
| 714 | |
| 715 | <!-- ======================================================================= --> |
| 716 | <h3 id="x86-specific">X86/X86-64 Language Extensions</h3> |
| 717 | <!-- ======================================================================= --> |
| 718 | |
| 719 | <p>The X86 backend has these language extensions:</p> |
| 720 | |
| 721 | <!-- ======================================================================= --> |
| 722 | <h4 id="x86-gs-segment">Memory references off the GS segment</h4> |
| 723 | <!-- ======================================================================= --> |
| 724 | |
| 725 | <p>Annotating a pointer with address space #256 causes it to be code generated |
Chris Lattner | a021e7c | 2009-05-05 18:54:47 +0000 | [diff] [blame] | 726 | relative to the X86 GS segment register, and address space #257 causes it to be |
| 727 | relative to the X86 FS segment. Note that this is a very very low-level |
| 728 | feature that should only be used if you know what you're doing (for example in |
| 729 | an OS kernel).</p> |
Chris Lattner | 1177f91 | 2009-04-09 19:58:15 +0000 | [diff] [blame] | 730 | |
| 731 | <p>Here is an example:</p> |
| 732 | |
| 733 | <pre> |
| 734 | #define GS_RELATIVE __attribute__((address_space(256))) |
| 735 | int foo(int GS_RELATIVE *P) { |
| 736 | return *P; |
| 737 | } |
| 738 | </pre> |
| 739 | |
| 740 | <p>Which compiles to (on X86-32):</p> |
| 741 | |
| 742 | <pre> |
| 743 | _foo: |
| 744 | movl 4(%esp), %eax |
| 745 | movl %gs:(%eax), %eax |
| 746 | ret |
| 747 | </pre> |
| 748 | |
Ted Kremenek | ed86931 | 2009-04-10 05:03:33 +0000 | [diff] [blame] | 749 | <!-- ======================================================================= --> |
| 750 | <h2 id="analyzerspecific">Static Analysis-Specific Extensions</h2> |
| 751 | <!-- ======================================================================= --> |
| 752 | |
| 753 | <p>Clang supports additional attributes that are useful for documenting program |
| 754 | invariants and rules for static analysis tools. The extensions documented here |
| 755 | are used by the <a |
| 756 | href="http://clang.llvm.org/StaticAnalysis.html">path-sensitive static analyzer |
| 757 | engine</a> that is part of Clang's Analysis library.</p> |
| 758 | |
John McCall | 8749401 | 2011-03-18 03:51:49 +0000 | [diff] [blame] | 759 | <h3 id="attr_analyzer_noreturn">The <tt>analyzer_noreturn</tt> attribute</h3> |
Ted Kremenek | ed86931 | 2009-04-10 05:03:33 +0000 | [diff] [blame] | 760 | |
| 761 | <p>Clang's static analysis engine understands the standard <tt>noreturn</tt> |
Ted Kremenek | 4df2114 | 2009-04-10 05:04:22 +0000 | [diff] [blame] | 762 | attribute. This attribute, which is typically affixed to a function prototype, |
| 763 | indicates that a call to a given function never returns. Function prototypes for |
| 764 | common functions like <tt>exit</tt> are typically annotated with this attribute, |
| 765 | as well as a variety of common assertion handlers. Users can educate the static |
| 766 | analyzer about their own custom assertion handles (thus cutting down on false |
| 767 | positives due to false paths) by marking their own "panic" functions |
| 768 | with this attribute.</p> |
Ted Kremenek | ed86931 | 2009-04-10 05:03:33 +0000 | [diff] [blame] | 769 | |
| 770 | <p>While useful, <tt>noreturn</tt> is not applicable in all cases. Sometimes |
Nick Lewycky | 625b586 | 2009-06-14 04:08:08 +0000 | [diff] [blame] | 771 | there are special functions that for all intents and purposes should be |
| 772 | considered panic functions (i.e., they are only called when an internal program |
| 773 | error occurs) but may actually return so that the program can fail gracefully. |
| 774 | The <tt>analyzer_noreturn</tt> attribute allows one to annotate such functions |
| 775 | as being interpreted as "no return" functions by the analyzer (thus |
Chris Lattner | 2893589 | 2009-04-10 05:54:56 +0000 | [diff] [blame] | 776 | pruning bogus paths) but will not affect compilation (as in the case of |
Ted Kremenek | ed86931 | 2009-04-10 05:03:33 +0000 | [diff] [blame] | 777 | <tt>noreturn</tt>).</p> |
| 778 | |
| 779 | <p><b>Usage</b>: The <tt>analyzer_noreturn</tt> attribute can be placed in the |
Chris Lattner | 2893589 | 2009-04-10 05:54:56 +0000 | [diff] [blame] | 780 | same places where the <tt>noreturn</tt> attribute can be placed. It is commonly |
Ted Kremenek | ed86931 | 2009-04-10 05:03:33 +0000 | [diff] [blame] | 781 | placed at the end of function prototypes:</p> |
| 782 | |
| 783 | <pre> |
| 784 | void foo() <b>__attribute__((analyzer_noreturn))</b>; |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 785 | </pre> |
| 786 | |
John McCall | 8749401 | 2011-03-18 03:51:49 +0000 | [diff] [blame] | 787 | <p>Query for this feature with |
| 788 | <tt>__has_attribute(analyzer_noreturn)</tt>.</p> |
Chris Lattner | 148772a | 2009-06-13 07:13:28 +0000 | [diff] [blame] | 789 | |
John McCall | 8749401 | 2011-03-18 03:51:49 +0000 | [diff] [blame] | 790 | <h3 id="attr_method_family">The <tt>objc_method_family</tt> attribute</h3> |
| 791 | |
| 792 | <p>Many methods in Objective-C have conventional meanings determined |
| 793 | by their selectors. For the purposes of static analysis, it is |
| 794 | sometimes useful to be able to mark a method as having a particular |
| 795 | conventional meaning despite not having the right selector, or as not |
| 796 | having the conventional meaning that its selector would suggest. |
| 797 | For these use cases, we provide an attribute to specifically describe |
| 798 | the <q>method family</q> that a method belongs to.</p> |
| 799 | |
| 800 | <p><b>Usage</b>: <tt>__attribute__((objc_method_family(X)))</tt>, |
| 801 | where <tt>X</tt> is one of <tt>none</tt>, <tt>alloc</tt>, <tt>copy</tt>, |
| 802 | <tt>init</tt>, <tt>mutableCopy</tt>, or <tt>new</tt>. This attribute |
| 803 | can only be placed at the end of a method declaration:</p> |
| 804 | |
| 805 | <pre> |
| 806 | - (NSString*) initMyStringValue <b>__attribute__((objc_method_family(none)))</b>; |
| 807 | </pre> |
| 808 | |
| 809 | <p>Users who do not wish to change the conventional meaning of a |
| 810 | method, and who merely want to document its non-standard retain and |
| 811 | release semantics, should use the |
| 812 | <a href="#attr_retain_release">retaining behavior attributes</a> |
| 813 | described below.</p> |
| 814 | |
| 815 | <p>Query for this feature with |
| 816 | <tt>__has_attribute(objc_method_family)</tt>.</p> |
| 817 | |
| 818 | <h3 id="attr_retain_release">Objective-C retaining behavior attributes</h3> |
John McCall | 630b7ae | 2011-01-25 04:26:21 +0000 | [diff] [blame] | 819 | |
| 820 | <p>In Objective-C, functions and methods are generally assumed to take |
| 821 | and return objects with +0 retain counts, with some exceptions for |
| 822 | special methods like <tt>+alloc</tt> and <tt>init</tt>. However, |
| 823 | there are exceptions, and so Clang provides attributes to allow these |
| 824 | exceptions to be documented, which helps the analyzer find leaks (and |
John McCall | 8749401 | 2011-03-18 03:51:49 +0000 | [diff] [blame] | 825 | ignore non-leaks). Some exceptions may be better described using |
| 826 | the <a href="#attr_method_family"><tt>objc_method_family</tt></a> |
| 827 | attribute instead.</p> |
John McCall | 630b7ae | 2011-01-25 04:26:21 +0000 | [diff] [blame] | 828 | |
| 829 | <p><b>Usage</b>: The <tt>ns_returns_retained</tt>, <tt>ns_returns_not_retained</tt>, |
| 830 | <tt>ns_returns_autoreleased</tt>, <tt>cf_returns_retained</tt>, |
| 831 | and <tt>cf_returns_not_retained</tt> attributes can be placed on |
| 832 | methods and functions that return Objective-C or CoreFoundation |
| 833 | objects. They are commonly placed at the end of a function prototype |
| 834 | or method declaration:</p> |
| 835 | |
| 836 | <pre> |
| 837 | id foo() <b>__attribute__((ns_returns_retained))</b>; |
| 838 | |
| 839 | - (NSString*) bar: (int) x <b>__attribute__((ns_returns_retained))</b>; |
| 840 | </pre> |
| 841 | |
| 842 | <p>The <tt>*_returns_retained</tt> attributes specify that the |
| 843 | returned object has a +1 retain count. |
| 844 | The <tt>*_returns_not_retained</tt> attributes specify that the return |
| 845 | object has a +0 retain count, even if the normal convention for its |
| 846 | selector would be +1. <tt>ns_returns_autoreleased</tt> specifies that the |
| 847 | returned object is +0, but is guaranteed to live at least as long as the |
| 848 | next flush of an autorelease pool.</p> |
| 849 | |
| 850 | <p><b>Usage</b>: The <tt>ns_consumed</tt> and <tt>cf_consumed</tt> |
| 851 | attributes can be placed on an parameter declaration; they specify |
| 852 | that the argument is expected to have a +1 retain count, which will be |
| 853 | balanced in some way by the function or method. |
| 854 | The <tt>ns_consumes_self</tt> attribute can only be placed on an |
| 855 | Objective-C method; it specifies that the method expects |
| 856 | its <tt>self</tt> parameter to have a +1 retain count, which it will |
| 857 | balance in some way.</p> |
| 858 | |
| 859 | <pre> |
| 860 | void <b>foo(__attribute__((ns_consumed))</b> NSString *string); |
| 861 | |
| 862 | - (void) bar <b>__attribute__((ns_consumes_self))</b>; |
| 863 | - (void) baz: (id) <b>__attribute__((ns_consumed))</b> x; |
| 864 | </pre> |
Ted Kremenek | ed86931 | 2009-04-10 05:03:33 +0000 | [diff] [blame] | 865 | |
John McCall | 8749401 | 2011-03-18 03:51:49 +0000 | [diff] [blame] | 866 | <p>Query for these features with <tt>__has_attribute(ns_consumed)</tt>, |
| 867 | <tt>__has_attribute(ns_returns_retained)</tt>, etc.</p> |
| 868 | |
Chris Lattner | 5ce933f | 2009-02-09 08:46:11 +0000 | [diff] [blame] | 869 | </div> |
| 870 | </body> |
| 871 | </html> |