[llvm] [NVPTX] Add syncscope support for cmpxchg (PR #140812)

[via llvm-commits]

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@@ -325,13 +327,18 @@ bool AtomicExpandImpl::processAtomicInstr(Instruction *I) {
       // expandAtomicCmpXchg in that case.
       FenceOrdering = CASI->getMergedOrdering();
       auto CASOrdering = TLI->atomicOperationOrderAfterFenceSplit(CASI);
+      SSID = CASI->getSyncScopeID();
 
       CASI->setSuccessOrdering(CASOrdering);
       CASI->setFailureOrdering(CASOrdering);
+      // If CAS ordering is monotonic, then the operation will
+      // take default scope. Otherwise, it will retain its scope
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gonzalobg wrote:

Thank you for calling this out.
The comment explains what the code does, but it does not explain "why" it does it, and from looking around its not obvious to me why it is correct for CAS monotonic to take the default scope.

https://github.com/llvm/llvm-project/pull/140812