diff options
Diffstat (limited to 'src/include/c.h')
| -rw-r--r-- | src/include/c.h | 49 |
1 files changed, 30 insertions, 19 deletions
diff --git a/src/include/c.h b/src/include/c.h index 8cdc16a0f4a..6d4495bdd9f 100644 --- a/src/include/c.h +++ b/src/include/c.h @@ -333,6 +333,36 @@ #endif /* + * pg_assume(expr) states that we assume `expr` to evaluate to true. In assert + * enabled builds pg_assume() is turned into an assertion, in optimized builds + * we try to clue the compiler into the fact that `expr` is true. + * + * This is useful for two purposes: + * + * 1) Avoid compiler warnings by telling the compiler about assumptions the + * code makes. This is particularly useful when building with optimizations + * and w/o assertions. + * + * 2) Help the compiler to generate more efficient code + * + * It is unspecified whether `expr` is evaluated, therefore it better be + * side-effect free. + */ +#if defined(USE_ASSERT_CHECKING) +#define pg_assume(expr) Assert(expr) +#elif defined(HAVE__BUILTIN_UNREACHABLE) +#define pg_assume(expr) \ + do { \ + if (!(expr)) \ + __builtin_unreachable(); \ + } while (0) +#elif defined(_MSC_VER) +#define pg_assume(expr) __assume(expr) +#else +#define pg_assume(expr) ((void) 0) +#endif + +/* * Hints to the compiler about the likelihood of a branch. Both likely() and * unlikely() return the boolean value of the contained expression. * @@ -376,25 +406,7 @@ * pretty trivial: VA_ARGS_NARGS_() returns its 64th argument, and we set up * the call so that that is the appropriate one of the list of constants. * This idea is due to Laurent Deniau. - * - * MSVC has an implementation of __VA_ARGS__ that doesn't conform to the - * standard unless you use the /Zc:preprocessor compiler flag, but that - * isn't available before Visual Studio 2019. For now, use a different - * definition that also works on older compilers. */ -#ifdef _MSC_VER -#define EXPAND(args) args -#define VA_ARGS_NARGS(...) \ - VA_ARGS_NARGS_ EXPAND((__VA_ARGS__, \ - 63,62,61,60, \ - 59,58,57,56,55,54,53,52,51,50, \ - 49,48,47,46,45,44,43,42,41,40, \ - 39,38,37,36,35,34,33,32,31,30, \ - 29,28,27,26,25,24,23,22,21,20, \ - 19,18,17,16,15,14,13,12,11,10, \ - 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)) -#else - #define VA_ARGS_NARGS(...) \ VA_ARGS_NARGS_(__VA_ARGS__, \ 63,62,61,60, \ @@ -404,7 +416,6 @@ 29,28,27,26,25,24,23,22,21,20, \ 19,18,17,16,15,14,13,12,11,10, \ 9, 8, 7, 6, 5, 4, 3, 2, 1, 0) -#endif #define VA_ARGS_NARGS_( \ _01,_02,_03,_04,_05,_06,_07,_08,_09,_10, \ |