diff options
Diffstat (limited to 'third_party/abseil-cpp/absl/base/optimization.h')
| -rw-r--r-- | third_party/abseil-cpp/absl/base/optimization.h | 75 |
1 files changed, 69 insertions, 6 deletions
diff --git a/third_party/abseil-cpp/absl/base/optimization.h b/third_party/abseil-cpp/absl/base/optimization.h index 646523b346..d090be1286 100644 --- a/third_party/abseil-cpp/absl/base/optimization.h +++ b/third_party/abseil-cpp/absl/base/optimization.h @@ -22,13 +22,15 @@ #ifndef ABSL_BASE_OPTIMIZATION_H_ #define ABSL_BASE_OPTIMIZATION_H_ +#include <assert.h> + #include "absl/base/config.h" // ABSL_BLOCK_TAIL_CALL_OPTIMIZATION // -// Instructs the compiler to avoid optimizing tail-call recursion. Use of this -// macro is useful when you wish to preserve the existing function order within -// a stack trace for logging, debugging, or profiling purposes. +// Instructs the compiler to avoid optimizing tail-call recursion. This macro is +// useful when you wish to preserve the existing function order within a stack +// trace for logging, debugging, or profiling purposes. // // Example: // @@ -104,9 +106,10 @@ // Cacheline aligning objects properly allows constructive memory sharing and // prevents destructive (or "false") memory sharing. // -// NOTE: this macro should be replaced with usage of `alignas()` using +// NOTE: callers should replace uses of this macro with `alignas()` using // `std::hardware_constructive_interference_size` and/or -// `std::hardware_destructive_interference_size` when available within C++17. +// `std::hardware_destructive_interference_size` when C++17 becomes available to +// them. // // See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0154r1.html // for more information. @@ -171,11 +174,71 @@ // to yield performance improvements. #if ABSL_HAVE_BUILTIN(__builtin_expect) || \ (defined(__GNUC__) && !defined(__clang__)) -#define ABSL_PREDICT_FALSE(x) (__builtin_expect(x, 0)) +#define ABSL_PREDICT_FALSE(x) (__builtin_expect(false || (x), false)) #define ABSL_PREDICT_TRUE(x) (__builtin_expect(false || (x), true)) #else #define ABSL_PREDICT_FALSE(x) (x) #define ABSL_PREDICT_TRUE(x) (x) #endif +// ABSL_INTERNAL_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. +// 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 + +// ABSL_INTERNAL_UNIQUE_SMALL_NAME(cond) +// This macro forces small unique name on a static file level symbols like +// static local variables or static functions. This is intended to be used in +// macro definitions to optimize the cost of generated code. Do NOT use it on +// symbols exported from translation unit since it may cause a link time +// conflict. +// +// Example: +// +// #define MY_MACRO(txt) +// namespace { +// char VeryVeryLongVarName[] ABSL_INTERNAL_UNIQUE_SMALL_NAME() = txt; +// const char* VeryVeryLongFuncName() ABSL_INTERNAL_UNIQUE_SMALL_NAME(); +// const char* VeryVeryLongFuncName() { return txt; } +// } +// + +#if defined(__GNUC__) +#define ABSL_INTERNAL_UNIQUE_SMALL_NAME2(x) #x +#define ABSL_INTERNAL_UNIQUE_SMALL_NAME1(x) ABSL_INTERNAL_UNIQUE_SMALL_NAME2(x) +#define ABSL_INTERNAL_UNIQUE_SMALL_NAME() \ + asm(ABSL_INTERNAL_UNIQUE_SMALL_NAME1(.absl.__COUNTER__)) +#else +#define ABSL_INTERNAL_UNIQUE_SMALL_NAME() +#endif + #endif // ABSL_BASE_OPTIMIZATION_H_ |