[llvm] [InstCombine] Fold variable extract of a constant-strided pointer vector (PR #217078)

[Matt Arsenault via llvm-commits]

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@@ -410,6 +410,83 @@ static ConstantInt *getPreferredVectorIndex(ConstantInt *IndexC) {
                           IndexC->getValue().zextOrTrunc(64));
 }
 
+/// Fold a variable extract from a vector of pointers that all point into the
+/// same object at a constant stride
+static Value *
+foldExtractOfStridedPointerVector(ExtractElementInst &EI,
+                                  InstCombiner::BuilderTy &Builder,
+                                  const DataLayout &DL) {
+  auto *VecTy = dyn_cast<FixedVectorType>(EI.getVectorOperandType());
+  if (!VecTy || !VecTy->getElementType()->isPointerTy())
+    return nullptr;
+
+  unsigned NumElts = VecTy->getNumElements();
+  if (NumElts < 2)
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arsenm wrote:

Missing test for degenerate case 

https://github.com/llvm/llvm-project/pull/217078