[llvm] [Xtensa] Implement Xtensa S32C1I Option and atomics lowering. (PR #137134)

[Matt Arsenault via llvm-commits]

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@@ -1241,6 +1275,13 @@ bool XtensaTargetLowering::decomposeMulByConstant(LLVMContext &Context, EVT VT,
   return false;
 }
 
+SDValue XtensaTargetLowering::LowerATOMIC_FENCE(SDValue Op,
+  SelectionDAG &DAG) const {
+SDLoc DL(Op);
+SDValue Chain = Op.getOperand(0);
+return DAG.getNode(XtensaISD::MEMW, DL, MVT::Other, Chain);
+}
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arsenm wrote:

Formatting. Can you make this directly legal and select to memw, or do you really need to do something in the combiner with memw? 

https://github.com/llvm/llvm-project/pull/137134