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[DAGCombiner] Add vector demanded elements support to computeKnownBitsForTargetNode
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Authored by RKSimon on Mar 22 2017, 11:50 AM.

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Summary

Follow up to D25691, this sets up the plumbing necessary to support vector demanded elements support in known bits calculations in target nodes.

Diff Detail

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rL LLVM

Event Timeline

RKSimon created this revision.Mar 22 2017, 11:50 AM
bjope added inline comments.Mar 29 2017, 12:57 AM
include/llvm/Target/TargetLowering.h
2427

Do we need to describe the DemandedElts parameter here?

One thing is that the SelectionDAG::computeKnownBits method currently does the check if DemandedElts is empty. So the method is not supposed to be called with an empty DemandedElts. Is this something that all the target implementations should rely on? Otherwise I guess you need to add the same kind of early-out for each target implementation? (Or is it correct to answer with a set of known bits even if the request was for no element?)
Not really sure if it helps to add a comment about that here, but I guess we have no way to really encode that DemandedElts should be non-empty. Another approach might be to add asserts in every target implementation that DemandedElts isn't empty.

lib/Target/AMDGPU/AMDGPUISelLowering.cpp
3559

It would have been a smaller diff to review if only adding the line with DemandedElts. Now I needed to understand if something else changed as well here due to mixing cleanup and adding functionality in the same patch.
(But maybe this is something that clang-format did for you?)

Anyway, the change looks OK so this is just a minor remark.

RKSimon updated this revision to Diff 93356.Mar 29 2017, 5:28 AM

Updated after clang-format'ing AMDGPUISelLowering.cpp and adding DemandedElts to doxygen comment.

I can add an assertion to the start of each computeKnownBitsForTargetNode if you think its worth it?

bjope edited edge metadata.Mar 30 2017, 10:54 PM

Updated after clang-format'ing AMDGPUISelLowering.cpp and adding DemandedElts to doxygen comment.

I can add an assertion to the start of each computeKnownBitsForTargetNode if you think its worth it?

No, I think we can skip the asserts. I might actually have been thinking wrong about it, since it should be allowed to ignore DemandedElts (and return som known bits) even if DemandedElts is empty.

bjope accepted this revision.Mar 30 2017, 10:55 PM

LGTM

This revision is now accepted and ready to land.Mar 30 2017, 10:55 PM
This revision was automatically updated to reflect the committed changes.