[PATCH] D77152: [SelectionDAG] Better legalization for FSHL and FSHR

Thu Jul 16 01:10:50 PDT 2020

RKSimon added inline comments.

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Comment at: llvm/test/CodeGen/PowerPC/funnel-shift.ll:22-24
+; CHECK-NEXT:    clrlwi 5, 5, 27
+; CHECK-NEXT:    srwi 4, 4, 1
+; CHECK-NEXT:    clrlwi 6, 6, 27
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foad wrote:
> RKSimon wrote:
> > foad wrote:
> > > This is a slight regression. We need one more instruction overall because of the two clrlwi instructions to mask both normal and the inverted shift amounts.
> > Any luck with this?
> No. I think it would need a target-specific lowering to take advantage of the fact that shift by 32 is well defined on PowerPC. Can I leave this for a later patch, and/or could a PowerPC expert volunteer to help with it?
So we're not just missing a micro optimization we can add to the powerpc backend as part of this patch? @hfinkel Any suggestions?

Repository:
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  https://reviews.llvm.org/D77152/new/

https://reviews.llvm.org/D77152