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Revert "[ADT] restrict bit_cast to trivially-constructible To" 

Of course some bots don't have std::is_trivially_constructible...

llvm-svn: 342711
This commit is contained in:
JF Bastien 2018-09-21 05:34:12 +00:00
parent 86f732a6a8
commit b6eb21c29f
1 changed files with 11 additions and 7 deletions
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18
llvm/include/llvm/ADT/bit.h
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@ -20,12 +20,8 @@
namespace llvm { 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 template <typename To, typename From
, typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
, typename = typename std::is_trivially_constructible<To>::type
#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \ #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
(defined(__GNUC__) && __GNUC__ >= 5) (defined(__GNUC__) && __GNUC__ >= 5)
, typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
@ -42,9 +38,17 @@ template <typename To, typename From
#endif #endif
> >
inline To bit_cast(const From &from) noexcept { inline To bit_cast(const From &from) noexcept {
To to; alignas(To) unsigned char storage[sizeof(To)];
std::memcpy(&to, &from, sizeof(To)); std::memcpy(&storage, &from, sizeof(To));
return 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
} }
} // namespace llvm } // namespace llvm