diff options
Diffstat (limited to 'absl/base/optimization.h')
-rw-r--r-- | absl/base/optimization.h | 30 |
1 files changed, 19 insertions, 11 deletions
diff --git a/absl/base/optimization.h b/absl/base/optimization.h index d090be12..db5cc097 100644 --- a/absl/base/optimization.h +++ b/absl/base/optimization.h @@ -181,35 +181,43 @@ #define ABSL_PREDICT_TRUE(x) (x) #endif -// ABSL_INTERNAL_ASSUME(cond) +// 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 will only be evaluated -// in some compilation modes and not others. +// +// NOTE: The expression must not have side effects, as it may only be evaluated +// 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: // // int x = ...; -// ABSL_INTERNAL_ASSUME(x >= 0); +// ABSL_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) +#define ABSL_ASSUME(cond) assert(cond) #elif ABSL_HAVE_BUILTIN(__builtin_assume) -#define ABSL_INTERNAL_ASSUME(cond) __builtin_assume(cond) +#define ABSL_ASSUME(cond) __builtin_assume(cond) #elif defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable) -#define ABSL_INTERNAL_ASSUME(cond) \ +#define ABSL_ASSUME(cond) \ do { \ if (!(cond)) __builtin_unreachable(); \ } while (0) #elif defined(_MSC_VER) -#define ABSL_INTERNAL_ASSUME(cond) __assume(cond) +#define ABSL_ASSUME(cond) __assume(cond) #else -#define ABSL_INTERNAL_ASSUME(cond) \ +#define ABSL_ASSUME(cond) \ do { \ static_cast<void>(false && (cond)); \ } while (0) |