[llvm] [VectorCombine] support mismatching extract/insert indices for foldInsExtFNeg (PR #126408)

[Simon Pilgrim via llvm-commits]

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@@ -664,79 +664,89 @@ bool VectorCombine::foldExtractExtract(Instruction &I) {
 /// shuffle.
 bool VectorCombine::foldInsExtFNeg(Instruction &I) {
   // Match an insert (op (extract)) pattern.
-  Value *DestVec;
-  uint64_t Index;
+  Value *DstVec;
+  uint64_t ExtIdx, InsIdx;
   Instruction *FNeg;
-  if (!match(&I, m_InsertElt(m_Value(DestVec), m_OneUse(m_Instruction(FNeg)),
-                             m_ConstantInt(Index))))
+  if (!match(&I, m_InsertElt(m_Value(DstVec), m_OneUse(m_Instruction(FNeg)),
+                             m_ConstantInt(InsIdx))))
     return false;
 
   // Note: This handles the canonical fneg instruction and "fsub -0.0, X".
   Value *SrcVec;
   Instruction *Extract;
   if (!match(FNeg, m_FNeg(m_CombineAnd(
                        m_Instruction(Extract),
-                       m_ExtractElt(m_Value(SrcVec), m_SpecificInt(Index))))))
+                       m_ExtractElt(m_Value(SrcVec), m_ConstantInt(ExtIdx))))))
     return false;
 
-  auto *VecTy = cast<FixedVectorType>(I.getType());
-  auto *ScalarTy = VecTy->getScalarType();
+  auto *DstVecTy = cast<FixedVectorType>(DstVec->getType());
+  auto *DstVecScalarTy = DstVecTy->getScalarType();
   auto *SrcVecTy = dyn_cast<FixedVectorType>(SrcVec->getType());
-  if (!SrcVecTy || ScalarTy != SrcVecTy->getScalarType())
+  if (!SrcVecTy || DstVecScalarTy != SrcVecTy->getScalarType())
     return false;
 
   // Ignore bogus insert/extract index.
-  unsigned NumElts = VecTy->getNumElements();
-  if (Index >= NumElts)
+  unsigned NumDstElts = DstVecTy->getNumElements();
+  unsigned NumSrcElts = SrcVecTy->getNumElements();
+  if (InsIdx >= NumDstElts || ExtIdx >= NumSrcElts || NumDstElts == 1)
     return false;
 
   // We are inserting the negated element into the same lane that we extracted
   // from. This is equivalent to a select-shuffle that chooses all but the
   // negated element from the destination vector.
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RKSimon wrote:

Update the comment

https://github.com/llvm/llvm-project/pull/126408