[llvm] [RISCV] DAGCombine canonicalizes the true operand of vselect to have one use (PR #206449)

[Luke Lau via llvm-commits]

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@@ -20406,6 +20355,40 @@ static SDValue useInversedSetcc(SDNode *N, SelectionDAG &DAG,
   return SDValue();
 }
 
+static SDValue
+canonicalizeVSelectTrueToOneUse(SDNode *N, SelectionDAG &DAG,
+                                const RISCVSubtarget &Subtarget) {
+  SDValue CC = N->getOperand(0);
+  SDValue TrueVal = N->getOperand(1);
+  SDValue FalseVal = N->getOperand(2);
+
+  if (CC.getOpcode() != ISD::SETCC || !CC.hasOneUse() || TrueVal.hasOneUse() ||
+      !FalseVal.hasOneUse())
+    return SDValue();
+
+  ISD::CondCode CCVal = cast<CondCodeSDNode>(CC.getOperand(2))->get();
+  if (CCVal != ISD::SETEQ && CCVal != ISD::SETNE)
+    return SDValue();
+
+  EVT VT = TrueVal.getValueType();
+  if (!VT.isSimple())
+    return SDValue();
+
+  if (VT.getVectorElementType().getSizeInBits() > Subtarget.getXLen())
+    return SDValue();
+
+  if (DAG.isSplatValue(TrueVal) || DAG.isSplatValue(FalseVal))
+    return SDValue();
+
+  SDLoc DL(N);
+  // Only handles ISD::SETEQ and ISD::SETNE; no extra RVV introduced.
+  ISD::CondCode InvCC = CCVal == ISD::SETEQ ? ISD::SETNE : ISD::SETEQ;
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lukel97 wrote:

nit, you can use `getSetCCInverse`

https://github.com/llvm/llvm-project/pull/206449