[libcxx-commits] [libcxx] [libc++] Implement C++20 atomic_ref (PR #76647)

[Damien L-G via libcxx-commits]

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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
+//
+//                        Kokkos v. 4.0
+//       Copyright (2022) National Technology & Engineering
+//               Solutions of Sandia, LLC (NTESS).
+//
+// Under the terms of Contract DE-NA0003525 with NTESS,
+// the U.S. Government retains certain rights in this software.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ATOMIC_ATOMIC_REF_H
+#define _LIBCPP___ATOMIC_ATOMIC_REF_H
+
+#include <__assert>
+#include <__atomic/atomic_sync.h>
+#include <__atomic/check_memory_order.h>
+#include <__atomic/to_gcc_order.h>
+#include <__concepts/arithmetic.h>
+#include <__concepts/same_as.h>
+#include <__config>
+#include <__memory/addressof.h>
+#include <__type_traits/has_unique_object_representation.h>
+#include <__type_traits/is_trivially_copyable.h>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _Tp>
+struct __atomic_ref_base {
+  _Tp* __ptr_;
+
+  _LIBCPP_HIDE_FROM_ABI static _Tp* __clear_padding(_Tp& __val) noexcept {
+    _Tp* __ptr = std::addressof(__val);
+#  if __has_builtin(__builtin_clear_padding)
+    __builtin_clear_padding(__ptr);
+#  endif
+    return __ptr;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI __atomic_ref_base(_Tp& __obj) : __ptr_(std::addressof(__obj)) {}
+
+  using value_type = _Tp;
+
+  static constexpr size_t required_alignment = alignof(_Tp);
+
+  static constexpr bool is_always_lock_free =
+      __atomic_always_lock_free(sizeof(_Tp), reinterpret_cast<void*>(-required_alignment));
+
+  _LIBCPP_HIDE_FROM_ABI bool is_lock_free() const noexcept { return __atomic_is_lock_free(sizeof(_Tp), __ptr_); }
+
+  _LIBCPP_HIDE_FROM_ABI void store(_Tp __desired, memory_order __order = memory_order::seq_cst) const noexcept
+      _LIBCPP_CHECK_STORE_MEMORY_ORDER(__order) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __order == memory_order::relaxed || __order == memory_order::release || __order == memory_order::seq_cst,
+        "atomic_ref: memory order argument to atomic store operation is invalid");
+    __atomic_store(__ptr_, __clear_padding(__desired), std::__to_gcc_order(__order));
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp operator=(_Tp __desired) const noexcept {
+    store(__desired);
+    return __desired;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI _Tp load(memory_order __order = memory_order::seq_cst) const noexcept
+      _LIBCPP_CHECK_LOAD_MEMORY_ORDER(__order) {
+    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
+        __order == memory_order::relaxed || __order == memory_order::consume || __order == memory_order::acquire ||
+            __order == memory_order::seq_cst,
+        "atomic_ref: memory order argument to atomic load operation is invalid");
+    alignas(_Tp) unsigned char __mem[sizeof(_Tp)];
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dalg24 wrote:

Sure.  Done.

https://github.com/llvm/llvm-project/pull/76647