[llvm] [DAGCombiner] Add support for scalarising extracts of a vector setcc (PR #116031)

[Paul Walker via llvm-commits]

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@@ -22763,19 +22769,23 @@ static SDValue scalarizeExtractedBinop(SDNode *ExtElt, SelectionDAG &DAG,
   SDValue Op0 = Vec.getOperand(0);
   SDValue Op1 = Vec.getOperand(1);
   APInt SplatVal;
-  if (isAnyConstantBuildVector(Op0, true) ||
-      ISD::isConstantSplatVector(Op0.getNode(), SplatVal) ||
-      isAnyConstantBuildVector(Op1, true) ||
-      ISD::isConstantSplatVector(Op1.getNode(), SplatVal)) {
-    // extractelt (binop X, C), IndexC --> binop (extractelt X, IndexC), C'
-    // extractelt (binop C, X), IndexC --> binop C', (extractelt X, IndexC)
-    EVT VT = ExtElt->getValueType(0);
-    SDValue Ext0 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, VT, Op0, Index);
-    SDValue Ext1 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, VT, Op1, Index);
-    return DAG.getNode(Vec.getOpcode(), DL, VT, Ext0, Ext1);
-  }
+  if (!isAnyConstantBuildVector(Op0, true) &&
+      !ISD::isConstantSplatVector(Op0.getNode(), SplatVal) &&
+      !isAnyConstantBuildVector(Op1, true) &&
+      !ISD::isConstantSplatVector(Op1.getNode(), SplatVal))
+    return SDValue();
 
-  return SDValue();
+  // extractelt (op X, C), IndexC --> op (extractelt X, IndexC), C'
+  // extractelt (op C, X), IndexC --> op C', (extractelt X, IndexC)
+  EVT OpVT = Op0->getValueType(0).getVectorElementType();
+  Op0 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, OpVT, Op0, Index);
+  Op1 = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, OpVT, Op1, Index);
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paulwalker-arm wrote:

Given the `ResVT == Vec.getValueType().getVectorElementType()` restriction, can you use `ResVT` here and remove the need for `OpVT`?

https://github.com/llvm/llvm-project/pull/116031