[llvm] [IR][AtomicExpand][NVPTX] Add elementwise modifier to atomicrmw; implement ISEL for NVPTX (PR #188393)

[Yonah Goldberg via llvm-commits]

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@@ -1460,6 +1460,9 @@ class MemSDNode : public SDNode {
   bool isNonTemporal() const { return MemSDNodeBits.IsNonTemporal; }
   bool isDereferenceable() const { return MemSDNodeBits.IsDereferenceable; }
   bool isInvariant() const { return MemSDNodeBits.IsInvariant; }
+  bool isElementwiseAtomic() const {
+    return getMemOperand()->isElementwiseAtomic();
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YonahGoldberg wrote:

I think it's actually better to put it as a member of `AtomicSDNode`

https://github.com/llvm/llvm-project/pull/188393