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

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,58 @@
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17
+
+// integral-type operator&=(integral-type) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_bitwise_and_assign = requires { std::declval<T const>() &= std::declval<T>(); };
+
+template <typename T>
+struct TestDoesNotHaveBitwiseAndAssign {
+  void operator()() const { static_assert(!has_bitwise_and_assign<std::atomic_ref<T>>); }
+};
+
+template <typename T>
+struct TestBitwiseAndAssign {
+  void operator()() const {
+    static_assert(std::is_integral_v<T>);
+
+    T x(T(1));
+    std::atomic_ref<T> const a(x);
+
+    std::same_as<T> auto y = (a &= T(2));
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ldionne wrote:

This test would pass if you implemented `operator&=` as `store(0)`. You should also test a value such that `a &= T(something)` is not `T(0)`.

In fact you could do something like `a &= T(1)` and then check that this is still equal to `T(1)`. Basically bit-and whatever value is already in there, which provides an easy and portable way of making this check.

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