diff options
Diffstat (limited to 'absl/base/optimization.h')
| -rw-r--r-- | absl/base/optimization.h | 51 |
1 files changed, 28 insertions, 23 deletions
diff --git a/absl/base/optimization.h b/absl/base/optimization.h index 6fe03c43..db5cc097 100644 --- a/absl/base/optimization.h +++ b/absl/base/optimization.h @@ -181,32 +181,21 @@ #define ABSL_PREDICT_TRUE(x) (x) #endif -// Platform and compilation mode dependent implementation of ABSL_ASSUME. -#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 - // ABSL_ASSUME(cond) +// // Informs the compiler that 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. +// it to be true for optimization purposes. +// +// WARNING: If the condition is false, the program can produce undefined and +// potentially dangerous behavior. +// // In !NDEBUG mode, the condition is checked with an assert(). +// // NOTE: The expression must not have side effects, as it may only be evaluated -// in some compilation modes and not others. +// in some compilation modes and not others. Some compilers may issue a warning +// if the compiler cannot prove the expression has no side effects. For example, +// the expression should not use a function call since the compiler cannot prove +// that a function call does not have side effects. // // Example: // @@ -216,7 +205,23 @@ // // assumption specified above. // int y = x / 16; // -#define ABSL_ASSUME(cond) ABSL_INTERNAL_ASSUME(cond) +#if !defined(NDEBUG) +#define ABSL_ASSUME(cond) assert(cond) +#elif ABSL_HAVE_BUILTIN(__builtin_assume) +#define ABSL_ASSUME(cond) __builtin_assume(cond) +#elif defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable) +#define ABSL_ASSUME(cond) \ + do { \ + if (!(cond)) __builtin_unreachable(); \ + } while (0) +#elif defined(_MSC_VER) +#define ABSL_ASSUME(cond) __assume(cond) +#else +#define ABSL_ASSUME(cond) \ + do { \ + static_cast<void>(false && (cond)); \ + } while (0) +#endif // ABSL_INTERNAL_UNIQUE_SMALL_NAME(cond) // This macro forces small unique name on a static file level symbols like |