[PATCH] D77300: [X86] Improve combineVectorShiftImm

[Jay Foad via Phabricator via llvm-commits]

foad marked an inline comment as done.
foad added inline comments.


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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:40883
+      (!LogicalShift && ISD::isBuildVectorAllOnes(N0.getNode())))
     return N0;
 
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RKSimon wrote:
> ISD::isBuildVectorAll* leaves UNDEFs in there - we must generate the constant
I don't quite understand why. If there are undefs in there then we will effectively be folding (VSRAI undef, C) -> undef (for some lanes). Isn't that allowed?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D77300/new/

https://reviews.llvm.org/D77300