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1// -*- C++ -*-2//===----------------------------------------------------------------------===//3//4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.5// See https://llvm.org/LICENSE.txt for license information.6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception7//8//===----------------------------------------------------------------------===//9 10#ifndef _LIBCPP___MEMORY_COMPRESSED_PAIR_H11#define _LIBCPP___MEMORY_COMPRESSED_PAIR_H12 13#include <__config>14#include <__cstddef/size_t.h>15#include <__type_traits/datasizeof.h>16#include <__type_traits/is_empty.h>17#include <__type_traits/is_final.h>18 19#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)20# pragma GCC system_header21#endif22 23_LIBCPP_BEGIN_NAMESPACE_STD24 25// ================================================================================================================== //26// The utilites here are for staying ABI compatible with the legacy `__compressed_pair`. They should not be used //27// for new data structures. Use `_LIBCPP_NO_UNIQUE_ADDRESS` for new data structures instead (but make sure you //28// understand how it works). //29// ================================================================================================================== //30 31// On GCC, the first member is aligned to the alignment of the second member to force padding in front of the compressed32// pair in case there are members before it.33//34// For example:35// (assuming x86-64 linux)36// class SomeClass {37// uint32_t member1;38// _LIBCPP_COMPRESSED_PAIR(uint32_t, member2, uint64_t, member3);39// }40//41// The layout with __compressed_pair is:42// member1 - offset: 0, size: 443// padding - offset: 4, size: 444// member2 - offset: 8, size: 445// padding - offset: 12, size: 446// member3 - offset: 16, size: 847//48// If the [[gnu::aligned]] wasn't there, the layout would instead be:49// member1 - offset: 0, size: 450// member2 - offset: 4, size: 451// member3 - offset: 8, size: 852//53// Furthermore, that alignment must be the same as what was used in the old __compressed_pair layout, so we must54// handle reference types specially since alignof(T&) == alignof(T).55// See https://llvm.org/PR118559.56//57// On Clang, this is unnecessary, since we use anonymous structs instead, which automatically handle the alignment58// correctly.59 60#ifndef _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING61 62template <class _Tp>63inline const size_t __compressed_pair_alignment = _LIBCPP_ALIGNOF(_Tp);64 65template <class _Tp>66inline const size_t __compressed_pair_alignment<_Tp&> = _LIBCPP_ALIGNOF(void*);67 68template <class _ToPad>69inline const bool __is_reference_or_unpadded_object =70 (is_empty<_ToPad>::value && !__is_final_v<_ToPad>) || sizeof(_ToPad) == __datasizeof_v<_ToPad>;71 72template <class _Tp>73inline const bool __is_reference_or_unpadded_object<_Tp&> = true;74 75template <class _Tp>76inline const bool __is_reference_or_unpadded_object<_Tp&&> = true;77 78template <class _ToPad, bool _Empty = __is_reference_or_unpadded_object<_ToPad> >79class __compressed_pair_padding {80 char __padding_[sizeof(_ToPad) - __datasizeof_v<_ToPad>] = {};81};82 83template <class _ToPad>84class __compressed_pair_padding<_ToPad, true> {};85 86# define _LIBCPP_COMPRESSED_ELEMENT(T1, Initializer1) \87 _LIBCPP_NO_UNIQUE_ADDRESS T1 Initializer1; \88 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding_, __LINE__, _)89 90// TODO: Fix the ABI for GCC as well once https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121637 is fixed91# ifdef _LIBCPP_COMPILER_GCC92# define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2) \93 _LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>))) T1 Initializer1; \94 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \95 _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \96 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _)97 98# define _LIBCPP_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3, Initializer3) \99 _LIBCPP_NO_UNIQUE_ADDRESS \100 __attribute__((__aligned__(::std::__compressed_pair_alignment<T2>), \101 __aligned__(::std::__compressed_pair_alignment<T3>))) T1 Initializer1; \102 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \103 _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \104 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _); \105 _LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3; \106 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T3> _LIBCPP_CONCAT3(__padding3_, __LINE__, _)107# else108# define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2) \109 struct { \110 _LIBCPP_NO_UNIQUE_ADDRESS T1 Initializer1; \111 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \112 _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \113 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _); \114 }115 116# define _LIBCPP_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3, Initializer3) \117 struct { \118 _LIBCPP_NO_UNIQUE_ADDRESS T1 Initializer1; \119 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \120 _LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \121 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _); \122 _LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3; \123 _LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T3> _LIBCPP_CONCAT3(__padding3_, __LINE__, _); \124 }125# endif126 127#else128# define _LIBCPP_COMPRESSED_ELEMENT(T1, Initializer1) _LIBCPP_NO_UNIQUE_ADDRESS T1 Initializer1129 130# define _LIBCPP_COMPRESSED_PAIR(T1, Name1, T2, Name2) \131 _LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \132 _LIBCPP_NO_UNIQUE_ADDRESS T2 Name2133 134# define _LIBCPP_COMPRESSED_TRIPLE(T1, Name1, T2, Name2, T3, Name3) \135 _LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \136 _LIBCPP_NO_UNIQUE_ADDRESS T2 Name2; \137 _LIBCPP_NO_UNIQUE_ADDRESS T3 Name3138#endif // _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING139 140_LIBCPP_END_NAMESPACE_STD141 142#endif // _LIBCPP___MEMORY_COMPRESSED_PAIR_H143