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[TargetLowering][AMDGPU][X86] Improve SimplifyDemandedBits bitcast handling
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Authored by RKSimon on Apr 9 2019, 6:39 AM.

Details

Summary

This patch adds support for BigBitWidth -> SmallBitWidth bitcasts, splitting the DemandedBits/Elts accordingly.

Re: the AMDGPU regression - @arsenm it looks there isn't much that generates BFE U32/S32 nodes in the DAG its mostly done in ISEL - in this case we need to match srl(and(shl(x,c1),c2),c1) - is this something that needs fixing first or are you OK with this change for now?

The X86 changes are all definite wins.

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rL LLVM

Event Timeline

RKSimon created this revision.Apr 9 2019, 6:39 AM
Herald added a project: Restricted Project. · View Herald TranscriptApr 9 2019, 6:39 AM
RKSimon marked an inline comment as done.Apr 12 2019, 7:50 AM
RKSimon added inline comments.
test/CodeGen/AMDGPU/store-weird-sizes.ll
49

@arsenm Any suggestions on what to do here - is it better to add another isel pattern or start creating bfe_user dag nodes?

nhaehnle added inline comments.Apr 15 2019, 12:53 AM
test/CodeGen/AMDGPU/store-weird-sizes.ll
49

Why doesn't the DAGCombiner simplify this to a single AND node?

RKSimon added inline comments.
test/CodeGen/AMDGPU/store-weird-sizes.ll
49

The AND appears too late (from a bitcasted i64 -> v2i32) for visitShiftByConstant to be called from the SRL node - I'm working on a generic fix at the moment.

RKSimon updated this revision to Diff 196065.Apr 22 2019, 6:47 AM

Add AMDGPU srl(and(x,m),c) -> and(srl(x,c),srl(m,c)) canonicalization to improve BFE recognition

RKSimon marked an inline comment as done.Apr 22 2019, 6:49 AM
RKSimon added inline comments.
lib/Target/AMDGPU/AMDGPUISelLowering.cpp
3170

@nhaehnle @arsenm I think this handles the BFE issue - I investigated putting this in DAGCombine but it caused a lot of noise on other targets - some improvements, some regressions.

arsenm accepted this revision.Apr 22 2019, 6:50 AM

LGTM

lib/Target/AMDGPU/AMDGPUISelLowering.cpp
3162

Braecs around this

This revision is now accepted and ready to land.Apr 22 2019, 6:50 AM
This revision was automatically updated to reflect the committed changes.