[llvm] [IR][FunctionAttrs] Clarify memory effects of atomics (PR #193768)

[via llvm-commits]

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@@ -31,3 +32,63 @@ entry:
   %r = load atomic i32, ptr %x seq_cst, align 4
   ret i32 %r
 }
+
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gonzalobg wrote:

Should this file include tests for store release and load acquire as well?

https://github.com/llvm/llvm-project/pull/193768