1//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the C++20 <bit> header.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_ADT_BIT_H
14#define LLVM_ADT_BIT_H
15
16#include "llvm/Support/Compiler.h"
17#include <cstring>
18#include <type_traits>
19
20namespace llvm {
21
22// This implementation of bit_cast is different from the C++17 one in two ways:
23// - It isn't constexpr because that requires compiler support.
24// - It requires trivially-constructible To, to avoid UB in the implementation.
25template <
26 typename To, typename From,
27 typename = std::enable_if_t<sizeof(To) == sizeof(From)>
28#if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
29 (defined(__GNUC__) && __GNUC__ >= 5)
30 ,
31 typename = std::enable_if_t<std::is_trivially_constructible<To>::value>
32#elif __has_feature(is_trivially_constructible)
33 ,
34 typename = std::enable_if_t<__is_trivially_constructible(To)>
35#else
36 // See comment below.
37#endif
38#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
39 (defined(__GNUC__) && __GNUC__ >= 5)
40 ,
41 typename = std::enable_if_t<std::is_trivially_copyable<To>::value>,
42 typename = std::enable_if_t<std::is_trivially_copyable<From>::value>
43#elif __has_feature(is_trivially_copyable)
44 ,
45 typename = std::enable_if_t<__is_trivially_copyable(To)>,
46 typename = std::enable_if_t<__is_trivially_copyable(From)>
47#else
48// This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
49// llvm/Support/type_traits.h's is_trivially_copyable we don't want to
50// provide a good-enough answer here: developers in that configuration will hit
51// compilation failures on the bots instead of locally. That's acceptable
52// because it's very few developers, and only until we move past C++11.
53#endif
54 >
55inline To bit_cast(const From &from) noexcept {
56 To to;
57 std::memcpy(&to, &from, sizeof(To));
58 return to;
59}
60
61} // namespace llvm
62
63#endif
64