[llvm] [VectorCombine] Remove dead node immediately in VectorCombine (PR #149047)

[Simon Pilgrim via llvm-commits]

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@@ -563,52 +576,41 @@ static ExtractElementInst *translateExtract(ExtractElementInst *ExtElt,
 
   Value *Shuf = createShiftShuffle(X, cast<ConstantInt>(C)->getZExtValue(),
                                    NewIndex, Builder);
-  return dyn_cast<ExtractElementInst>(
-      Builder.CreateExtractElement(Shuf, NewIndex));
+  return Shuf;
 }
 
 /// Try to reduce extract element costs by converting scalar compares to vector
 /// compares followed by extract.
 /// cmp (ext0 V0, C), (ext1 V1, C)
-void VectorCombine::foldExtExtCmp(ExtractElementInst *Ext0,
-                                  ExtractElementInst *Ext1, Instruction &I) {
+Value *VectorCombine::foldExtExtCmp(Value *V0, Value *V1, Value *ExtIndex,
+                                    Instruction &I) {
   assert(isa<CmpInst>(&I) && "Expected a compare");
-  assert(cast<ConstantInt>(Ext0->getIndexOperand())->getZExtValue() ==
-             cast<ConstantInt>(Ext1->getIndexOperand())->getZExtValue() &&
-         "Expected matching constant extract indexes");
 
   // cmp Pred (extelt V0, C), (extelt V1, C) --> extelt (cmp Pred V0, V1), C
   ++NumVecCmp;
   CmpInst::Predicate Pred = cast<CmpInst>(&I)->getPredicate();
-  Value *V0 = Ext0->getVectorOperand(), *V1 = Ext1->getVectorOperand();
   Value *VecCmp = Builder.CreateCmp(Pred, V0, V1);
-  Value *NewExt = Builder.CreateExtractElement(VecCmp, Ext0->getIndexOperand());
-  replaceValue(I, *NewExt);
+  return Builder.CreateExtractElement(VecCmp, ExtIndex, "foldExtExtCmp");
 }
 
 /// Try to reduce extract element costs by converting scalar binops to vector
 /// binops followed by extract.
 /// bo (ext0 V0, C), (ext1 V1, C)
-void VectorCombine::foldExtExtBinop(ExtractElementInst *Ext0,
-                                    ExtractElementInst *Ext1, Instruction &I) {
+Value *VectorCombine::foldExtExtBinop(Value *V0, Value *V1, Value *ExtIndex,
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RKSimon wrote:

(pedantic) update the comment to use ExtIndex (or another common varname)

https://github.com/llvm/llvm-project/pull/149047