[llvm] [CostModel][X86] Add initial costs for non-lane-crossing one/two input shuffles (PR #114680)

[Simon Pilgrim via llvm-commits]

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@@ -1559,6 +1559,22 @@ InstructionCost X86TTIImpl::getShuffleCost(
       return TTI::TCC_Free;
   }
 
+  // Attempt to detect a cheaper inlane shuffle, avoiding 128-bit subvector
+  // permutation.
+  bool IsInLaneShuffle = false;
+  if (BaseTp->getPrimitiveSizeInBits() > 0 &&
+      (BaseTp->getPrimitiveSizeInBits() % 128) == 0 &&
+      Mask.size() == BaseTp->getElementCount().getKnownMinValue()) {
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RKSimon wrote:

Sure, I think checking the scalar sizes match should be enough - I'll add that shortly 

https://github.com/llvm/llvm-project/pull/114680