diff options
Diffstat (limited to 'llvm')
| -rw-r--r-- | llvm/include/llvm/ADT/bit.h | 25 |
1 files changed, 14 insertions, 11 deletions
diff --git a/llvm/include/llvm/ADT/bit.h b/llvm/include/llvm/ADT/bit.h index 0e383212712..a4aba7b6a9e 100644 --- a/llvm/include/llvm/ADT/bit.h +++ b/llvm/include/llvm/ADT/bit.h @@ -20,8 +20,19 @@ namespace llvm { +// This implementation of bit_cast is different from the C++17 one in two ways: +// - It isn't constexpr because that requires compiler support. +// - It requires trivially-constructible To, to avoid UB in the implementation. template <typename To, typename From , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type +#if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \ + (defined(__GNUC__) && __GNUC__ >= 5) + , typename = typename std::is_trivially_constructible<To>::type +#elif __has_feature(is_trivially_constructible) + , typename = typename std::enable_if<__is_trivially_constructible(To)>::type +#else + // See comment below. +#endif #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \ (defined(__GNUC__) && __GNUC__ >= 5) , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type @@ -38,17 +49,9 @@ template <typename To, typename From #endif > inline To bit_cast(const From &from) noexcept { - alignas(To) unsigned char storage[sizeof(To)]; - std::memcpy(&storage, &from, sizeof(To)); -#if defined(__GNUC__) - // Before GCC 7.2, GCC thought that this violated strict aliasing. -#pragma GCC diagnostic push -#pragma GCC diagnostic ignored "-Wstrict-aliasing" -#endif - return reinterpret_cast<To &>(storage); -#if defined(__GNUC__) -#pragma GCC diagnostic pop -#endif + To to; + std::memcpy(&to, &from, sizeof(To)); + return to; } } // namespace llvm |
