[PATCH] D103274: [X86] AMD Zen 3 has fast per-lane variable shuffles

Thu May 27 14:59:52 PDT 2021

lebedev.ri marked an inline comment as not done.
lebedev.ri added inline comments.

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Comment at: llvm/lib/Target/X86/X86ISelLowering.cpp:36097
   // which is much simpler than any shuffle.
-  if (UnaryShuffle && MaskContainsZeros && AllowVariableMask &&
       isSequentialOrUndefOrZeroInRange(Mask, 0, NumMaskElts, 0) &&
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craig.topper wrote:
> lebedev.ri wrote:
> > This one is weird. I'm not sure why fast-ness of variable shuffles matters here.
> You mean because it's just AND/FAND not a shuffle? Fastness was added to AllowVariableMask later. Initially it was just the depth check. Probably guarding the constant pool?
> You mean because it's just AND/FAND not a shuffle?

Yes.

> Fastness was added to AllowVariableMask later. Initially it was just the depth check. Probably guarding the constant pool?

Yes, i think so.

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https://reviews.llvm.org/D103274