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b20ef5f960
As noted in https://bugs.llvm.org/show_bug.cgi?id=36651, the specialization for isPodLike<std::pair<...>> did not match the expectation of std::is_trivially_copyable which makes the memcpy optimization invalid. This patch renames the llvm::isPodLike trait into llvm::is_trivially_copyable. Unfortunately std::is_trivially_copyable is not portable across compiler / STL versions. So a portable version is provided too. Note that the following specialization were invalid: std::pair<T0, T1> llvm::Optional<T> Tests have been added to assert that former specialization are respected by the standard usage of llvm::is_trivially_copyable, and that when a decent version of std::is_trivially_copyable is available, llvm::is_trivially_copyable is compared to std::is_trivially_copyable. As of this patch, llvm::Optional is no longer considered trivially copyable, even if T is. This is to be fixed in a later patch, as it has impact on a long-running bug (see r347004) Note that GCC warns about this UB, but this got silented by https://reviews.llvm.org/D50296. Differential Revision: https://reviews.llvm.org/D54472 llvm-svn: 351701
59 lines
2.3 KiB
C++
59 lines
2.3 KiB
C++
//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the C++20 <bit> header.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ADT_BIT_H
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#define LLVM_ADT_BIT_H
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#include "llvm/Support/Compiler.h"
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#include <cstring>
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#include <type_traits>
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namespace llvm {
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// This implementation of bit_cast is different from the C++17 one in two ways:
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// - It isn't constexpr because that requires compiler support.
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// - It requires trivially-constructible To, to avoid UB in the implementation.
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template <typename To, typename From
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, typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
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#if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
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(defined(__GNUC__) && __GNUC__ >= 5)
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, typename = typename std::is_trivially_constructible<To>::type
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#elif __has_feature(is_trivially_constructible)
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, typename = typename std::enable_if<__is_trivially_constructible(To)>::type
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#else
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// See comment below.
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#endif
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#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
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(defined(__GNUC__) && __GNUC__ >= 5)
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, typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
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, typename = typename std::enable_if<std::is_trivially_copyable<From>::value>::type
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#elif __has_feature(is_trivially_copyable)
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, typename = typename std::enable_if<__is_trivially_copyable(To)>::type
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, typename = typename std::enable_if<__is_trivially_copyable(From)>::type
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#else
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// This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
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// llvm/Support/type_traits.h's is_trivially_copyable we don't want to
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// provide a good-enough answer here: developers in that configuration will hit
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// compilation failures on the bots instead of locally. That's acceptable
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// because it's very few developers, and only until we move past C++11.
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#endif
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>
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inline To bit_cast(const From &from) noexcept {
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To to;
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std::memcpy(&to, &from, sizeof(To));
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return to;
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}
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} // namespace llvm
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#endif
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