common/opthelpers.h

   1 #ifndef OPTHELPERS_H
   2 #define OPTHELPERS_H
   3
   4 #include <cstdint>
   5 #include <utility>
   6 #include <memory>
   7
   8 #ifdef __has_builtin
   9 #define HAS_BUILTIN __has_builtin
  10 #else
  11 #define HAS_BUILTIN(x) (0)
  12 #endif
  13
  14 #ifdef __GNUC__
  15 #define force_inline [[gnu::always_inline]] inline
  16 #elif defined(_MSC_VER)
  17 #define force_inline __forceinline
  18 #else
  19 #define force_inline inline
  20 #endif
  21
  22 /* Unlike the likely attribute, ASSUME requires the condition to be true or
  23  * else it invokes undefined behavior. It's essentially an assert without
  24  * actually checking the condition at run-time, allowing for stronger
  25  * optimizations than the likely attribute.
  26  */
  27 #if HAS_BUILTIN(__builtin_assume)
  28 #define ASSUME __builtin_assume
  29 #elif defined(_MSC_VER)
  30 #define ASSUME __assume
  31 #elif __has_attribute(assume)
  32 #define ASSUME(x) [[assume(x)]]
  33 #elif HAS_BUILTIN(__builtin_unreachable)
  34 #define ASSUME(x) do { if(x) break; __builtin_unreachable(); } while(0)
  35 #else
  36 #define ASSUME(x) ((void)0)
  37 #endif
  38
  39 namespace al {
  40
  41 template<typename T>
  42 constexpr std::underlying_type_t<T> to_underlying(T e) noexcept
  43 { return static_cast<std::underlying_type_t<T>>(e); }
  44
  45 [[noreturn]] inline void unreachable()
  46 {
  47 #if HAS_BUILTIN(__builtin_unreachable)
  48     __builtin_unreachable();
  49 #else
  50     ASSUME(false);
  51 #endif
  52 }
  53
  54 template<std::size_t alignment, typename T>
  55 force_inline constexpr auto assume_aligned(T *ptr) noexcept
  56 {
  57 #ifdef __cpp_lib_assume_aligned
  58     return std::assume_aligned<alignment,T>(ptr);
  59 #elif HAS_BUILTIN(__builtin_assume_aligned)
  60     return static_cast<T*>(__builtin_assume_aligned(ptr, alignment));
  61 #elif defined(_MSC_VER)
  62     constexpr std::size_t alignment_mask{(1<<alignment) - 1};
  63     if((reinterpret_cast<std::uintptr_t>(ptr)&alignment_mask) == 0)
  64         return ptr;
  65     __assume(0);
  66 #elif defined(__ICC)
  67     __assume_aligned(ptr, alignment);
  68     return ptr;
  69 #else
  70     return ptr;
  71 #endif
  72 }
  73
  74 } // namespace al
  75
  76 #endif /* OPTHELPERS_H */