================
@@ -0,0 +1,65 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// https://github.com/llvm/llvm-project/issues/30023
+// compare exchange does not work with types of which the size is not a power
of 2
+
+#include <atomic>
+#include <cstring>
+#include <cassert>
+
+template <int Size>
+struct S {
+ char data[Size];
+
+ explicit S(char v = 0) noexcept { memset(&data[0], v, sizeof(data)); }
+
+ // only used in the test to check the results. Not used in atomic operations.
+ friend bool operator==(const S& lhs, const S& rhs) noexcept {
+ return memcmp(&lhs.data[0], &rhs.data[0], sizeof(lhs.data)) == 0;
+ }
+ friend bool operator!=(const S& lhs, const S& rhs) noexcept { return !(lhs
== rhs); }
+};
+
+template <int Size>
+struct Expected {
+ S<Size> s;
+ bool b = true; // used to validate that s's operation won't overwrite the
memory next to it
+};
+
+template <int Size>
+void test() {
+ using T = S<Size>;
+ std::atomic<T> a(T(0));
+ Expected<Size> expected{T(17)};
+
+ assert(a.load() != expected.s);
+ assert(expected.b);
+
+ auto r1 = a.compare_exchange_strong(expected.s, T(18),
std::memory_order_relaxed);
+
+ assert(!r1);
+ assert(expected.s == T(0)); // expected.s is modified by
compare_exchange_strong
+ assert(expected.b);
+ assert(a.load() == T(0));
+
+ auto r2 = a.compare_exchange_strong(expected.s, T(18),
std::memory_order_relaxed);
+ assert(r2);
+ assert(a.load() == T(18));
+ assert(expected.s == T(0));
+ assert(expected.b);
+}
+
+int main() {
----------------
ldionne wrote:
```suggestion
int main(int, char**) {
```
https://github.com/llvm/llvm-project/pull/78707
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