[llvm] [VectorCombine] Fold permute of intrinsics into intrinsic of permutes: shuffle(intrinsic, poison/undef) -> intrinsic(shuffle) (PR #170052)

[Jerry Dang via llvm-commits]

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@@ -2960,6 +2961,93 @@ bool VectorCombine::foldShuffleOfIntrinsics(Instruction &I) {
   return true;
 }
 
+/// Try to convert
+/// "shuffle (intrinsic), (poison/undef)" into "intrinsic (shuffle)".
+bool VectorCombine::foldPermuteOfIntrinsic(Instruction &I) {
+  Value *V0, *V1;
+  ArrayRef<int> Mask;
+  if (!match(&I, m_Shuffle(m_OneUse(m_Value(V0)), m_Value(V1), m_Mask(Mask))))
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kuroyukiasuna wrote:

I also considered merging them, but kept them separated for reasons mainly due to cleaness and readability. The permute code path and blend code path differs at both cost analysis and transform, I was trying to avoid having large  blocks of `if (IsPermute) {}` branches in the code. While on the other hand merging and resuse also makes sense - if we feel strongly about merging the two functions I can do that too.

https://github.com/llvm/llvm-project/pull/170052