[llvm] [VectorCombine] Allow shuffling between vectors the same type but different element sizes (PR #121216)

[Simon Pilgrim via llvm-commits]

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@@ -3059,6 +3087,13 @@ bool VectorCombine::foldInsExtVectorToShuffle(Instruction &I) {
   if (OldCost < NewCost)
     return false;
 
+  if (NeedExpOrNarrow) {
+    if (!NeedDstSrcSwap)
+      SrcVec = Builder.CreateShuffleVector(SrcVec, ExtToVecMask);
+    else
+      DstVec = Builder.CreateShuffleVector(DstVec, ExtToVecMask);
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RKSimon wrote:

Haven't you already swapped the SrcVec/DstVec?

https://github.com/llvm/llvm-project/pull/121216