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 __has_cpp_attribute
  15 #define HAS_ATTRIBUTE __has_cpp_attribute
  16 #else
  17 #define HAS_ATTRIBUTE(x) (0)
  18 #endif
  19
  20 #ifdef __GNUC__
  21 #define force_inline [[gnu::always_inline]] inline
  22 #define NOINLINE [[gnu::noinline]]
  23 #elif defined(_MSC_VER)
  24 #define force_inline __forceinline
  25 #define NOINLINE __declspec(noinline)
  26 #else
  27 #define force_inline inline
  28 #define NOINLINE
  29 #endif
  30
  31 /* Unlike the likely attribute, ASSUME requires the condition to be true or
  32  * else it invokes undefined behavior. It's essentially an assert without
  33  * actually checking the condition at run-time, allowing for stronger
  34  * optimizations than the likely attribute.
  35  */
  36 #if HAS_BUILTIN(__builtin_assume)
  37 #define ASSUME __builtin_assume
  38 #elif defined(_MSC_VER)
  39 #define ASSUME __assume
  40 #elif __has_attribute(assume)
  41 #define ASSUME(x) [[assume(x)]]
  42 #elif HAS_BUILTIN(__builtin_unreachable)
  43 #define ASSUME(x) do { if(x) break; __builtin_unreachable(); } while(0)
  44 #else
  45 #define ASSUME(x) (static_cast<void>(0))
  46 #endif
  47
  48 /* This shouldn't be needed since unknown attributes are ignored, but older
  49  * versions of GCC choke on the attribute syntax in certain situations.
  50  */
  51 #if HAS_ATTRIBUTE(likely)
  52 #define LIKELY [[likely]]
  53 #define UNLIKELY [[unlikely]]
  54 #else
  55 #define LIKELY
  56 #define UNLIKELY
  57 #endif
  58
  59 namespace al {
  60
  61 template<typename T>
  62 constexpr std::underlying_type_t<T> to_underlying(T e) noexcept
  63 { return static_cast<std::underlying_type_t<T>>(e); }
  64
  65 [[noreturn]] inline void unreachable()
  66 {
  67 #if HAS_BUILTIN(__builtin_unreachable)
  68     __builtin_unreachable();
  69 #else
  70     ASSUME(false);
  71 #endif
  72 }
  73
  74 template<std::size_t alignment, typename T>
  75 force_inline constexpr auto assume_aligned(T *ptr) noexcept
  76 {
  77 #ifdef __cpp_lib_assume_aligned
  78     return std::assume_aligned<alignment,T>(ptr);
  79 #elif HAS_BUILTIN(__builtin_assume_aligned)
  80     return static_cast<T*>(__builtin_assume_aligned(ptr, alignment));
  81 #elif defined(_MSC_VER)
  82     constexpr std::size_t alignment_mask{(1<<alignment) - 1};
  83     if((reinterpret_cast<std::uintptr_t>(ptr)&alignment_mask) == 0)
  84         return ptr;
  85     __assume(0);
  86 #elif defined(__ICC)
  87     __assume_aligned(ptr, alignment);
  88     return ptr;
  89 #else
  90     return ptr;
  91 #endif
  92 }
  93
  94 } // namespace al
  95
  96 #endif /* OPTHELPERS_H */