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[libc++] Implement C++20 atomic_ref (llvm#76647)
Implement the std::atomic_ref class template by reusing atomic_base_impl. Based on the work from https://reviews.llvm.org/D72240
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‎libcxx/docs/ReleaseNotes/19.rst‎

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@@ -53,6 +53,7 @@ Implemented Papers
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- P2387R3 - Pipe support for user-defined range adaptors
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- P2713R1 - Escaping improvements in ``std::format``
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- P2231R1 - Missing ``constexpr`` in ``std::optional`` and ``std::variant``
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- P0019R8 - ``std::atomic_ref``
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Improvements and New Features
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-----------------------------

‎libcxx/docs/Status/Cxx20Papers.csv‎

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"`P0905R1 <https://wg21.link/P0905R1>`__","CWG","Symmetry for spaceship","Jacksonville","|Complete|","7.0","|spaceship|"
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"`P0966R1 <https://wg21.link/P0966R1>`__","LWG","``string::reserve``\ Should Not Shrink","Jacksonville","|Complete| [#note-P0966]_","12.0"
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"","","","","","",""
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"`P0019R8 <https://wg21.link/P0019R8>`__","LWG","Atomic Ref","Rapperswil","",""
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"`P0019R8 <https://wg21.link/P0019R8>`__","LWG","Atomic Ref","Rapperswil","|Complete|","19.0"
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"`P0458R2 <https://wg21.link/P0458R2>`__","LWG","Checking for Existence of an Element in Associative Containers","Rapperswil","|Complete|","13.0"
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"`P0475R1 <https://wg21.link/P0475R1>`__","LWG","LWG 2511: guaranteed copy elision for piecewise construction","Rapperswil","|Complete|",""
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"`P0476R2 <https://wg21.link/P0476R2>`__","LWG","Bit-casting object representations","Rapperswil","|Complete|","14.0"
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"`P1612R1 <https://wg21.link/P1612R1>`__","LWG","Relocate Endian's Specification","Cologne","|Complete|","10.0"
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"`P1614R2 <https://wg21.link/P1614R2>`__","LWG","The Mothership has Landed","Cologne","|In Progress|",""
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"`P1638R1 <https://wg21.link/P1638R1>`__","LWG","basic_istream_view::iterator should not be copyable","Cologne","|Complete|","16.0","|ranges|"
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"`P1643R1 <https://wg21.link/P1643R1>`__","LWG","Add wait/notify to atomic_ref","Cologne","",""
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"`P1643R1 <https://wg21.link/P1643R1>`__","LWG","Add wait/notify to atomic_ref","Cologne","|Complete|","19.0"
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"`P1644R0 <https://wg21.link/P1644R0>`__","LWG","Add wait/notify to atomic<shared_ptr>","Cologne","",""
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"`P1650R0 <https://wg21.link/P1650R0>`__","LWG","Output std::chrono::days with 'd' suffix","Cologne","|Complete|","16.0"
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"`P1651R0 <https://wg21.link/P1651R0>`__","LWG","bind_front should not unwrap reference_wrapper","Cologne","|Complete|","13.0"

‎libcxx/include/CMakeLists.txt‎

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__atomic/atomic_flag.h
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__atomic/atomic_init.h
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__atomic/atomic_lock_free.h
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__atomic/atomic_ref.h
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__atomic/atomic_sync.h
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__atomic/check_memory_order.h
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__atomic/contention_t.h
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__atomic/is_always_lock_free.h
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__atomic/kill_dependency.h
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__atomic/memory_order.h
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__atomic/to_gcc_order.h
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__availability
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__bit/bit_cast.h
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__bit/bit_ceil.h

‎libcxx/include/__atomic/atomic_ref.h‎

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‎libcxx/include/__atomic/atomic_sync.h‎

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#include <__atomic/contention_t.h>
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#include <__atomic/cxx_atomic_impl.h>
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#include <__atomic/memory_order.h>
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#include <__atomic/to_gcc_order.h>
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#include <__availability>
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#include <__chrono/duration.h>
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#include <__config>

‎libcxx/include/__atomic/check_memory_order.h‎

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_LIBCPP_DIAGNOSE_WARNING(__f == memory_order_release || __f == memory_order_acq_rel, \
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"memory order argument to atomic operation is invalid")
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#define _LIBCPP_CHECK_WAIT_MEMORY_ORDER(__m) \
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_LIBCPP_DIAGNOSE_WARNING(__m == memory_order_release || __m == memory_order_acq_rel, \
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"memory order argument to atomic operation is invalid")
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#endif // _LIBCPP___ATOMIC_CHECK_MEMORY_ORDER_H

‎libcxx/include/__atomic/cxx_atomic_impl.h‎

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#define _LIBCPP___ATOMIC_CXX_ATOMIC_IMPL_H
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#include <__atomic/memory_order.h>
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#include <__atomic/to_gcc_order.h>
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#include <__config>
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#include <__memory/addressof.h>
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#include <__type_traits/is_assignable.h>
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_Tp __a_value;
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};
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_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_order(memory_order __order) {
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// Avoid switch statement to make this a constexpr.
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return __order == memory_order_relaxed
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? __ATOMIC_RELAXED
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: (__order == memory_order_acquire
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? __ATOMIC_ACQUIRE
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: (__order == memory_order_release
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? __ATOMIC_RELEASE
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: (__order == memory_order_seq_cst
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? __ATOMIC_SEQ_CST
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: (__order == memory_order_acq_rel ? __ATOMIC_ACQ_REL : __ATOMIC_CONSUME))));
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}
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_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_failure_order(memory_order __order) {
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// Avoid switch statement to make this a constexpr.
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return __order == memory_order_relaxed
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? __ATOMIC_RELAXED
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: (__order == memory_order_acquire
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? __ATOMIC_ACQUIRE
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: (__order == memory_order_release
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? __ATOMIC_RELAXED
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: (__order == memory_order_seq_cst
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? __ATOMIC_SEQ_CST
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: (__order == memory_order_acq_rel ? __ATOMIC_ACQUIRE : __ATOMIC_CONSUME))));
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}
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template <typename _Tp>
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_LIBCPP_HIDE_FROM_ABI void __cxx_atomic_init(volatile __cxx_atomic_base_impl<_Tp>* __a, _Tp __val) {
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__cxx_atomic_assign_volatile(__a->__a_value, __val);

‎libcxx/include/__atomic/to_gcc_order.h‎

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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___ATOMIC_TO_GCC_ORDER_H
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#define _LIBCPP___ATOMIC_TO_GCC_ORDER_H
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#include <__atomic/memory_order.h>
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#include <__config>
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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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#if defined(__ATOMIC_RELAXED) && defined(__ATOMIC_CONSUME) && defined(__ATOMIC_ACQUIRE) && \
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defined(__ATOMIC_RELEASE) && defined(__ATOMIC_ACQ_REL) && defined(__ATOMIC_SEQ_CST)
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_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_order(memory_order __order) {
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// Avoid switch statement to make this a constexpr.
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return __order == memory_order_relaxed
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? __ATOMIC_RELAXED
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: (__order == memory_order_acquire
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? __ATOMIC_ACQUIRE
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: (__order == memory_order_release
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? __ATOMIC_RELEASE
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: (__order == memory_order_seq_cst
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? __ATOMIC_SEQ_CST
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: (__order == memory_order_acq_rel ? __ATOMIC_ACQ_REL : __ATOMIC_CONSUME))));
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}
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_LIBCPP_HIDE_FROM_ABI inline _LIBCPP_CONSTEXPR int __to_gcc_failure_order(memory_order __order) {
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// Avoid switch statement to make this a constexpr.
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return __order == memory_order_relaxed
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? __ATOMIC_RELAXED
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: (__order == memory_order_acquire
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? __ATOMIC_ACQUIRE
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: (__order == memory_order_release
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? __ATOMIC_RELAXED
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: (__order == memory_order_seq_cst
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? __ATOMIC_SEQ_CST
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: (__order == memory_order_acq_rel ? __ATOMIC_ACQUIRE : __ATOMIC_CONSUME))));
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}
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#endif
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ATOMIC_TO_GCC_ORDER_H

‎libcxx/include/atomic‎

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#include <__atomic/atomic_flag.h>
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#include <__atomic/atomic_init.h>
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#include <__atomic/atomic_lock_free.h>
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#include <__atomic/atomic_ref.h>
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#include <__atomic/atomic_sync.h>
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#include <__atomic/check_memory_order.h>
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#include <__atomic/contention_t.h>

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