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// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP___MEMORY_COMPRESSED_PAIR_H
#define _LIBCPP___MEMORY_COMPRESSED_PAIR_H
#include <__config>
#include <__cstddef/size_t.h>
#include <__type_traits/datasizeof.h>
#include <__type_traits/is_empty.h>
#include <__type_traits/is_final.h>
#include <__type_traits/is_reference.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
// ================================================================================================================== //
// The utilites here are for staying ABI compatible with the legacy `__compressed_pair`. They should not be used //
// for new data structures. Use `_LIBCPP_NO_UNIQUE_ADDRESS` for new data structures instead (but make sure you //
// understand how it works). //
// ================================================================================================================== //
// The first member is aligned to the alignment of the second member to force padding in front of the compressed pair
// in case there are members before it.
//
// For example:
// (assuming x86-64 linux)
// class SomeClass {
// uint32_t member1;
// _LIBCPP_COMPRESSED_PAIR(uint32_t, member2, uint64_t, member3);
// }
//
// The layout with __compressed_pair is:
// member1 - offset: 0, size: 4
// padding - offset: 4, size: 4
// member2 - offset: 8, size: 4
// padding - offset: 12, size: 4
// member3 - offset: 16, size: 8
//
// If the [[gnu::aligned]] wasn't there, the layout would instead be:
// member1 - offset: 0, size: 4
// member2 - offset: 4, size: 4
// member3 - offset: 8, size: 8
//
// Furthermore, that alignment must be the same as what was used in the old __compressed_pair layout, so we must
// handle reference types specially since alignof(T&) == alignof(T).
// See https://github.com/llvm/llvm-project/issues/118559.
#ifndef _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
template <class _Tp>
inline const size_t __compressed_pair_alignment = _LIBCPP_ALIGNOF(_Tp);
template <class _Tp>
inline const size_t __compressed_pair_alignment<_Tp&> = _LIBCPP_ALIGNOF(void*);
template <class _ToPad,
bool _Empty = ((is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value) ||
is_reference<_ToPad>::value || sizeof(_ToPad) == __datasizeof_v<_ToPad>)>
class __compressed_pair_padding {
char __padding_[sizeof(_ToPad) - __datasizeof_v<_ToPad>] = {};
};
template <class _ToPad>
class __compressed_pair_padding<_ToPad, true> {};
# define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2) \
_LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>))) T1 Initializer1; \
_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \
_LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \
_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _)
# define _LIBCPP_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3, Initializer3) \
_LIBCPP_NO_UNIQUE_ADDRESS \
__attribute__((__aligned__(::std::__compressed_pair_alignment<T2>), \
__aligned__(::std::__compressed_pair_alignment<T3>))) T1 Initializer1; \
_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \
_LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \
_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _); \
_LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3; \
_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T3> _LIBCPP_CONCAT3(__padding3_, __LINE__, _)
#else
# define _LIBCPP_COMPRESSED_PAIR(T1, Name1, T2, Name2) \
_LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \
_LIBCPP_NO_UNIQUE_ADDRESS T2 Name2
# define _LIBCPP_COMPRESSED_TRIPLE(T1, Name1, T2, Name2, T3, Name3) \
_LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \
_LIBCPP_NO_UNIQUE_ADDRESS T2 Name2; \
_LIBCPP_NO_UNIQUE_ADDRESS T3 Name3
#endif // _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___MEMORY_COMPRESSED_PAIR_H
|
