[llvm] [RISCV] Fold vmnot.m of an integer compare into the compare (PR #222553)

[Luke Lau via llvm-commits]

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@@ -19253,6 +19253,28 @@ static SDValue performORCombine(SDNode *N, TargetLowering::DAGCombinerInfo &DCI,
   return combineSelectAndUseCommutative(N, DAG, /*AllOnes*/ false, Subtarget);
 }
 
+// Fold (vmxor_vl (setcc_vl a, b, cc), vmset_vl) -> (setcc_vl a, b, !cc) for
+// integer compares.
+static SDValue combineVMNOTOfSetCC(SDNode *N, SelectionDAG &DAG) {
+  SDValue Cmp = N->getOperand(0);
+  if (Cmp.getOpcode() == RISCVISD::VMSET_VL)
+    Cmp = N->getOperand(1);
+  else if (N->getOperand(1).getOpcode() != RISCVISD::VMSET_VL)
+    return SDValue();
+
+  if (Cmp.getOpcode() != RISCVISD::SETCC_VL || !Cmp.hasOneUse() ||
+      !Cmp.getOperand(0).getValueType().isInteger() ||
+      !Cmp.getOperand(3).isUndef() ||
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lukel97 wrote:

Is there a reason why we restrict the mask to not undef?

https://github.com/llvm/llvm-project/pull/222553