LLVM  9.0.0svn
bit.h
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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 
20 namespace 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.
25 template <typename To, typename From
26  , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
27 #if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
28  (defined(__GNUC__) && __GNUC__ >= 5)
29  , typename = typename std::is_trivially_constructible<To>::type
30 #elif __has_feature(is_trivially_constructible)
31  , typename = typename std::enable_if<__is_trivially_constructible(To)>::type
32 #else
33  // See comment below.
34 #endif
35 #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
36  (defined(__GNUC__) && __GNUC__ >= 5)
37  , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
38  , typename = typename std::enable_if<std::is_trivially_copyable<From>::value>::type
39 #elif __has_feature(is_trivially_copyable)
40  , typename = typename std::enable_if<__is_trivially_copyable(To)>::type
41  , typename = typename std::enable_if<__is_trivially_copyable(From)>::type
42 #else
43 // This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
44 // llvm/Support/type_traits.h's is_trivially_copyable we don't want to
45 // provide a good-enough answer here: developers in that configuration will hit
46 // compilation failures on the bots instead of locally. That's acceptable
47 // because it's very few developers, and only until we move past C++11.
48 #endif
49 >
50 inline To bit_cast(const From &from) noexcept {
51  To to;
52  std::memcpy(&to, &from, sizeof(To));
53  return to;
54 }
55 
56 } // namespace llvm
57 
58 #endif
This class represents lattice values for constants.
Definition: AllocatorList.h:23
BlockVerifier::State From
To bit_cast(const From &from) noexcept
Definition: bit.h:50