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

[David Sherwood via llvm-commits]

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@@ -22769,13 +22765,46 @@ static SDValue scalarizeExtractedBinop(SDNode *ExtElt, SelectionDAG &DAG,
       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);
+    // extractelt (setcc X, C, op), IndexC -> setcc (extractelt X, IndexC)), C
+    // extractelt (setcc C, X, op), IndexC -> setcc (extractelt IndexC, X)), C
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david-arm wrote:

Removed extra comments and changed wording

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