[llvm] [NFC] Add assertions for Src and Dst vec types in VecCombine folding (PR #134432)

[Simon Pilgrim via llvm-commits]

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@@ -2052,6 +2052,9 @@ bool VectorCombine::foldShuffleOfSelects(Instruction &I) {
 
   auto *SrcVecTy = dyn_cast<FixedVectorType>(T1->getType());
   auto *DstVecTy = dyn_cast<FixedVectorType>(I.getType());
+  assert(SrcVecTy && DstVecTy &&
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RKSimon wrote:

yes - replace those 2 dyn_cast with cast - the previous dyn_cast checks for the select condition operands should be ensuring FixedVectorType for everything

https://github.com/llvm/llvm-project/pull/134432