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| <h1>Clang Language Extensions</h1> |
| |
| <ul> |
| <li><a href="#intro">Introduction</a></li> |
| <li><a href="#vectors">Vectors and Extended Vectors</a></li> |
| <li><a href="#blocks">Blocks</a></li> |
| <li><a href="#builtins">Builtin Functions</a> |
| <ul> |
| <li><a href="#__builtin_overload">__builtin_overload</a></li> |
| <li><a href="#__builtin_shufflevector">__builtin_shufflevector</a></li> |
| </ul> |
| </li> |
| </ul> |
| |
| |
| <!-- ======================================================================= --> |
| <h2 id="intro">Introduction</h2> |
| <!-- ======================================================================= --> |
| |
| <p>This document describes the language extensions provided by Clang. In |
| addition to the langauge extensions listed here, Clang aims to support a broad |
| range of GCC extensions. Please see the <a |
| href="http://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html">GCC manual</a> for |
| more information on these extensions.</p> |
| |
| <!-- ======================================================================= --> |
| <h2 id="vectors">Vectors and Extended Vectors</h2> |
| <!-- ======================================================================= --> |
| |
| <p>Supports the GCC vector extensions, plus some stuff like V[1]. ext_vector |
| with V.xyzw syntax and other tidbits. See also <a |
| href="#__builtin_shufflevector">__builtin_shufflevector</a>.</p> |
| |
| <!-- ======================================================================= --> |
| <h2 id="blocks">Blocks</h2> |
| <!-- ======================================================================= --> |
| |
| <p>The idea, syntax, and semantics.</p> |
| |
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| <h2 id="builtins">Builtin Functions</h2> |
| <!-- ======================================================================= --> |
| |
| <p>Clang supports a number of builtin library functions with the same syntax as |
| GCC, including things like <tt>__builtin_nan</tt>, |
| <tt>__builtin_constant_p</tt>, <tt>__builtin_choose_expr</tt>, |
| <tt>__builtin_types_compatible_p</tt>, <tt>__sync_fetch_and_add</tt>, etc. In |
| addition to the GCC builtins, Clang supports a number of builtins that GCC does |
| not, which are listed here.</p> |
| |
| <p>Please note that Clang does not and will not support all of the GCC builtins |
| for vector operations. Instead of using builtins, you should use the functions |
| defined in target-specific header files like <tt><xmmintrin.h></tt>, which |
| define portable wrappers for these. Many of the Clang versions of these |
| functions are implemented directly in terms of <a href="#vectors">extended |
| vector support</a> instead of builtins, in order to reduce the number of |
| builtins that we need to implement.</p> |
| |
| |
| <!-- ======================================================================= --> |
| <h3 id="__builtin_overload">__builtin_overload</h3> |
| <!-- ======================================================================= --> |
| |
| <p><tt>__builtin_overload</tt> is used to implement type-generic "overloaded" |
| functions in C. This builtin is used to implement the <tt><tgmath.h></tt> |
| header file, but is intended to be usable for a broad variety of other similar |
| situations, like the <tt><altivec.h></tt> header. |
| </p> |
| |
| <p><b>Syntax:</b></p> |
| |
| <pre> |
| __builtin_overload(FnNameStr, PromotionRuleStr, NumArgs, arg1, arg2, ... |
| overloadcandidate1, overloadcandidate2, ...) |
| </pre> |
| |
| <p><b>Examples:</b></p> |
| |
| <pre> |
| #define sin(x) \ |
| (__builtin_overload("sin", "tgmath", 1, x, sinf, sin, sinl, |
| csinf, csin, csinl)(x)) |
| #define fma(x,y,z) \ |
| (__builtin_overload("fma", "tgmath", 3, x, y, z, fmaf, fma, fmal)(x,y,z)) |
| #define ldexp(x, y) \ |
| (__builtin_overload("ldexp", "tgmath1", 2, x, 0, ldexpf, ldexp, ldexpl)(x,y)) |
| </pre> |
| |
| <p><b>Description:</b></p> |
| |
| <p>The first argument to __builtin_overload is a string that is the name of the |
| "function" being implemented. This is used to produce diagnostics that make |
| sense to the user. For example, if you accidentally pass a pointer argument to |
| "sin" in GCC, it emits 6 errors about incompatible types. This name allows |
| Clang to diagnose the error in a way the user can understand. |
| </p> |
| |
| <p>The second argument is a string that indicates a set of promotion rules to |
| apply to the arguments before prototype matching occurs. The currently |
| supported rules are:</p> |
| |
| <dl> |
| <dt>tgmath</dt> |
| <dd>Follow the rules of C99 7.22 to determine a single common type, and use it |
| for every argument.</dd> |
| <dt>tgmath1</dt> |
| <dd>Follow the rules of C99 7.22 to determine a single common type of just the |
| first argument (e.g. treat ints as doubles).</dd> |
| </dl> |
| |
| <p>The third argument is an integer that specifies the arity of the function |
| being overloaded. After this are N expression arguments which are promoted |
| according to the rules specified by the promotion rule string.</p> |
| |
| <p>The final arguments are functions or function pointers with different |
| signatures. __builtin_overload will match and evaluate to the first function |
| pointer whose signature is compatible and does not cause value truncation of |
| any arguments to the function.</p> |
| |
| |
| <!-- ======================================================================= --> |
| <h3 id="__builtin_shufflevector">__builtin_shufflevector</h3> |
| <!-- ======================================================================= --> |
| |
| <p>todo describe me.</p> |
| |
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