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

[Louis Dionne via libcxx-commits]

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+//
+// 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
+
+// bool compare_exchange_strong(T&, T, memory_order, memory_order) const noexcept;
+// bool compare_exchange_strong(T&, T, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_helpers.h"
+#include "test_helper.h"
+#include "test_macros.h"
+
+template <typename T>
+struct TestCompareExchangeStrong {
+  void operator()() const {
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> auto y = a.compare_exchange_strong(t, T(2));
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_strong(t, T(3));
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_strong(t, T(2)));
+    }
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> auto y = a.compare_exchange_strong(t, T(2), std::memory_order_seq_cst);
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_strong(t, T(3), std::memory_order_seq_cst);
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_strong(t, T(2), std::memory_order_seq_cst));
+    }
+    {
+      T x(T(1));
+      std::atomic_ref<T> const a(x);
+
+      T t(T(1));
+      std::same_as<bool> auto y =
+          a.compare_exchange_strong(t, T(2), std::memory_order_release, std::memory_order_relaxed);
+      assert(y == true);
+      assert(a == T(2));
+      assert(t == T(1));
+      y = a.compare_exchange_strong(t, T(3), std::memory_order_release, std::memory_order_relaxed);
+      assert(y == false);
+      assert(a == T(2));
+      assert(t == T(2));
+
+      ASSERT_NOEXCEPT(a.compare_exchange_strong(t, T(2), std::memory_order_release, std::memory_order_relaxed));
+    }
+
+    // success memory_order::release
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::release, std::memory_order::relaxed);
+        assert(r);
+      };
+
+      auto load = [](std::atomic_ref<T> const& x) { return x.load(std::memory_order::acquire); };
+      test_acquire_release<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::release);
+        assert(r);
+      };
+      test_acquire_release<T>(store_one_arg, load);
+    }
+
+    // success memory_order::acquire
+    {
+      auto store = [](std::atomic_ref<T> const& x, T, T new_val) { x.store(new_val, std::memory_order::release); };
+
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acquire, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acquire)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load_one_arg);
+    }
+
+    // success memory_order::acq_rel
+    {
+      auto store = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::acq_rel, std::memory_order::relaxed);
+        assert(r);
+      };
+      auto load = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acq_rel, std::memory_order::relaxed)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store, load);
+
+      auto store_one_arg = [](std::atomic_ref<T> const& x, T old_val, T new_val) {
+        auto r = x.compare_exchange_strong(old_val, new_val, std::memory_order::acq_rel);
+        assert(r);
+      };
+      auto load_one_arg = [](std::atomic_ref<T> const& x) {
+        auto val = x.load(std::memory_order::relaxed);
+        while (!x.compare_exchange_strong(val, val, std::memory_order::acq_rel)) {
+        }
+        return val;
+      };
+      test_acquire_release<T>(store_one_arg, load_one_arg);
+    }
+
+    // success memory_oreder::seq_cst
----------------
ldionne wrote:

```suggestion
    // success memory_order::seq_cst
```

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