[clang] [Sema] atomic_compare_exchange: check failure memory order (PR #74959)

[James Y Knight via cfe-commits]

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@@ -8728,7 +8728,13 @@ def err_atomic_op_needs_atomic_int : Error<
   "%select{|atomic }0integer (%1 invalid)">;
 def warn_atomic_op_has_invalid_memory_order : Warning<
   "memory order argument to atomic operation is invalid">,
-  InGroup<DiagGroup<"atomic-memory-ordering">>;
+  InGroup<AtomicMemoryOrdering>;
+def warn_atomic_op_has_invalid_failure_memory_order : Warning<
+  "failure memory order argument to atomic operation is invalid">,
+  InGroup<AtomicMemoryOrdering>;
+def warn_atomic_op_failure_memory_order_stronger_than_success : Warning<
+  "failure memory order cannot be stronger than success memory order">,
+  InGroup<AtomicMemoryOrdering>;
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jyknight wrote:

This isn't a requirement any more, since C++17, and we applied that to all language modes. So remove this diagnostic.
https://eel.is/c++draft/atomics#ref.ops-18

https://github.com/llvm/llvm-project/pull/74959