[llvm] [DAGCombiner] Fix scalarizeExtractedBinOp for some SETCC cases (PR #123071)

[David Green via llvm-commits]

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@@ -22808,9 +22808,26 @@ static SDValue scalarizeExtractedBinOp(SDNode *ExtElt, SelectionDAG &DAG,
     return SDValue();
 
   EVT ResVT = ExtElt->getValueType(0);
-  if (Opc == ISD::SETCC &&
-      (ResVT != Vec.getValueType().getVectorElementType() || LegalTypes))
-    return SDValue();
+  bool SetCCNeedsSignExt = false;
+  if (Opc == ISD::SETCC) {
+    EVT VecVT = Vec.getValueType();
+    if (ResVT != VecVT.getVectorElementType() || LegalTypes)
+      return SDValue();
+
+    if (ResVT != MVT::i1) {
+      bool VecRequiresSignExt = TLI.getBooleanContents(VecVT) ==
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davemgreen wrote:

I think it is worth making sure all cases work, in case a target with other BooleanContent runs into this in the future. I think the rule boils down to:
 - If you are converting to ZeroOrNegativeOneBooleanContent and from UndefinedBooleanContent or ZeroOrOneBooleanContent, it needs a sext_in_reg.
 - If you are converting to ZeroOrOneBooleanContent and from UndefinedBooleanContent or ZeroOrNegativeOneBooleanContent, it needs a zext_in_reg (an and).
 - Converting to UndefinedBooleanContent is always fine.

If you wanted to rule out the others (return SDValue) that sounds OK, considering the target needs to opt in. I think it would just be a case of tightening up what happens with the other cases.

https://github.com/llvm/llvm-project/pull/123071