27c83382d8
This significantly simplifies the code, improves compile times and improves the object layout of types using `__compressed_pair` in the unstable ABI. The only downside is that this is extremely ABI sensitive and pedantically breaks the ABI for empty final types, since the address of the subobject may change. The ABI of the whole object should not be affected. Fixes #91266 Fixes #93069
91 lines
4.6 KiB
C++
91 lines
4.6 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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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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#ifndef _LIBCPP___MEMORY_COMPRESSED_PAIR_H
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#define _LIBCPP___MEMORY_COMPRESSED_PAIR_H
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#include <__config>
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#include <__type_traits/datasizeof.h>
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#include <__type_traits/is_empty.h>
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#include <__type_traits/is_final.h>
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#include <__type_traits/is_reference.h>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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// ================================================================================================================== //
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// The utilites here are for staying ABI compatible with the legacy `__compressed_pair`. They should not be used //
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// for new data structures. Use `_LIBCPP_NO_UNIQUE_ADDRESS` for new data structures instead (but make sure you //
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// understand how it works). //
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// ================================================================================================================== //
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// The first member is aligned to the alignment of the second member to force padding in front of the compressed pair
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// in case there are members before it.
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//
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// For example:
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// (assuming x86-64 linux)
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// class SomeClass {
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// uint32_t member1;
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// _LIBCPP_COMPRESSED_PAIR(uint32_t, member2, uint64_t, member3);
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// }
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//
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// The layout with __compressed_pair is:
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// member1 - offset: 0, size: 4
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// padding - offset: 4, size: 4
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// member2 - offset: 8, size: 4
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// padding - offset: 12, size: 4
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// member3 - offset: 16, size: 8
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//
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// If the [[gnu::aligned]] wasn't there, the layout would instead be:
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// member1 - offset: 0, size: 4
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// member2 - offset: 4, size: 4
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// member3 - offset: 8, size: 8
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#ifndef _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
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template <class _ToPad>
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class __compressed_pair_padding {
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char __padding_[((is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value) || is_reference<_ToPad>::value)
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? 0
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: sizeof(_ToPad) - __datasizeof_v<_ToPad>];
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};
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# define _LIBCPP_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2) \
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_LIBCPP_NO_UNIQUE_ADDRESS __attribute__((__aligned__(_LIBCPP_ALIGNOF(T2)))) T1 Initializer1; \
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_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \
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_LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \
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_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _)
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# define _LIBCPP_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3, Initializer3) \
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_LIBCPP_NO_UNIQUE_ADDRESS \
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__attribute__((__aligned__(_LIBCPP_ALIGNOF(T2)), __aligned__(_LIBCPP_ALIGNOF(T3)))) T1 Initializer1; \
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_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T1> _LIBCPP_CONCAT3(__padding1_, __LINE__, _); \
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_LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \
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_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T2> _LIBCPP_CONCAT3(__padding2_, __LINE__, _); \
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_LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3; \
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_LIBCPP_NO_UNIQUE_ADDRESS ::std::__compressed_pair_padding<T3> _LIBCPP_CONCAT3(__padding3_, __LINE__, _)
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#else
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# define _LIBCPP_COMPRESSED_PAIR(T1, Name1, T2, Name2) \
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_LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \
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_LIBCPP_NO_UNIQUE_ADDRESS T2 Name2
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# define _LIBCPP_COMPRESSED_TRIPLE(T1, Name1, T2, Name2, T3, Name3) \
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_LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \
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_LIBCPP_NO_UNIQUE_ADDRESS T2 Name2; \
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_LIBCPP_NO_UNIQUE_ADDRESS T3 Name3
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#endif // _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___MEMORY_COMPRESSED_PAIR_H
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