diff options
Diffstat (limited to 'absl/base/optimization.h')
| -rw-r--r-- | absl/base/optimization.h | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/absl/base/optimization.h b/absl/base/optimization.h index 646523b3..1541d7a8 100644 --- a/absl/base/optimization.h +++ b/absl/base/optimization.h @@ -178,4 +178,38 @@ #define ABSL_PREDICT_TRUE(x) (x) #endif +// ABSL_INTERNAL_ASSUME(cond) +// Informs the compiler than a condition is always true and that it can assume +// it to be true for optimization purposes. The call has undefined behavior if +// the condition is false. +// In !NDEBUG mode, the condition is checked with an assert(). +// NOTE: The expression must not have side effects, as it will only be evaluated +// in some compilation modes and not others. +// +// Example: +// +// int x = ...; +// ABSL_INTERNAL_ASSUME(x >= 0); +// // The compiler can optimize the division to a simple right shift using the +// // assumption specified above. +// int y = x / 16; +// +#if !defined(NDEBUG) +#define ABSL_INTERNAL_ASSUME(cond) assert(cond) +#elif ABSL_HAVE_BUILTIN(__builtin_assume) +#define ABSL_INTERNAL_ASSUME(cond) __builtin_assume(cond) +#elif defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable) +#define ABSL_INTERNAL_ASSUME(cond) \ + do { \ + if (!(cond)) __builtin_unreachable(); \ + } while (0) +#elif defined(_MSC_VER) +#define ABSL_INTERNAL_ASSUME(cond) __assume(cond) +#else +#define ABSL_INTERNAL_ASSUME(cond) \ + do { \ + static_cast<void>(false && (cond)); \ + } while (0) +#endif + #endif // ABSL_BASE_OPTIMIZATION_H_ |