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

[via llvm-commits]

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@@ -3067,42 +3067,69 @@ bool VectorCombine::foldInsExtVectorToShuffle(Instruction &I) {
                          m_ConstantInt(InsIdx))))
     return false;
 
-  auto *VecTy = dyn_cast<FixedVectorType>(I.getType());
-  if (!VecTy || SrcVec->getType() != VecTy)
+  auto *DstVecTy = dyn_cast<FixedVectorType>(I.getType());
+  auto *SrcVecTy = dyn_cast<FixedVectorType>(SrcVec->getType());
+  // We can try combining vectors with different element sizes.
+  if (!DstVecTy || !SrcVecTy ||
+      SrcVecTy->getElementType() != DstVecTy->getElementType())
     return false;
 
-  unsigned NumElts = VecTy->getNumElements();
-  if (ExtIdx >= NumElts || InsIdx >= NumElts)
+  unsigned NumDstElts = DstVecTy->getNumElements();
+  unsigned NumSrcElts = SrcVecTy->getNumElements();
+  if (InsIdx >= NumDstElts || ExtIdx >= NumSrcElts || NumDstElts == 1)
     return false;
 
   // Insertion into poison is a cheaper single operand shuffle.
   TargetTransformInfo::ShuffleKind SK;
-  SmallVector<int> Mask(NumElts, PoisonMaskElem);
-  if (isa<PoisonValue>(DstVec) && !isa<UndefValue>(SrcVec)) {
+  SmallVector<int> Mask(NumDstElts, PoisonMaskElem);
+
+  bool NeedExpOrNarrow = NumSrcElts != NumDstElts;
+  bool NeedDstSrcSwap = isa<PoisonValue>(DstVec) && !isa<UndefValue>(SrcVec);
+  if (NeedDstSrcSwap) {
     SK = TargetTransformInfo::SK_PermuteSingleSrc;
-    Mask[InsIdx] = ExtIdx;
+    if (!NeedExpOrNarrow)
+      Mask[InsIdx] = ExtIdx;
+    else
+      Mask[InsIdx] = 0;
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ParkHanbum wrote:

sorry but I can't understand where can be use a `SK_Select`. when I changed `TargetTransformInfo::SK_PermuteTwoSrc` to `SK = TargetTransformInfo::SK_Select` there is a lot of changed appear include PhaseOrdering/X86/hadd.ll



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