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       1             : //===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : //
      10             : // This file implements the C++20 <bit> header.
      11             : //
      12             : //===----------------------------------------------------------------------===//
      13             : 
      14             : #ifndef LLVM_ADT_BIT_H
      15             : #define LLVM_ADT_BIT_H
      16             : 
      17             : #include "llvm/Support/Compiler.h"
      18             : #include <cstring>
      19             : #include <type_traits>
      20             : 
      21             : namespace llvm {
      22             : 
      23             : // This implementation of bit_cast is different from the C++17 one in two ways:
      24             : //  - It isn't constexpr because that requires compiler support.
      25             : //  - It requires trivially-constructible To, to avoid UB in the implementation.
      26             : template <typename To, typename From
      27             :           , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
      28             : #if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
      29             :     (defined(__GNUC__) && __GNUC__ >= 5)
      30             :           , typename = typename std::is_trivially_constructible<To>::type
      31             : #elif __has_feature(is_trivially_constructible)
      32             :           , typename = typename std::enable_if<__is_trivially_constructible(To)>::type
      33             : #else
      34             :   // See comment below.
      35             : #endif
      36             : #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
      37             :     (defined(__GNUC__) && __GNUC__ >= 5)
      38             :           , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
      39             :           , typename = typename std::enable_if<std::is_trivially_copyable<From>::value>::type
      40             : #elif __has_feature(is_trivially_copyable)
      41             :           , typename = typename std::enable_if<__is_trivially_copyable(To)>::type
      42             :           , typename = typename std::enable_if<__is_trivially_copyable(From)>::type
      43             : #else
      44             :   // This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
      45             :   // llvm/Support/type_traits.h's isPodLike we don't want to provide a
      46             :   // good-enough answer here: developers in that configuration will hit
      47             :   // compilation failures on the bots instead of locally. That's acceptable
      48             :   // because it's very few developers, and only until we move past C++11.
      49             : #endif
      50             : >
      51           0 : inline To bit_cast(const From &from) noexcept {
      52             :   To to;
      53   276014071 :   std::memcpy(&to, &from, sizeof(To));
      54           0 :   return to;
      55             : }
      56             : 
      57             : } // namespace llvm
      58             : 
      59             : #endif