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[InstCombine] Don't transform (select c, ext(TI), ext(FI)) if ext is free
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Authored by Carrot on Jan 15 2021, 6:04 PM.

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lebedev.ri
Summary

Function InstCombinerImpl::foldSelectOpOp can do following transformation

(select c, ext(TI), ext(FI))  ==> (ext(select c, TI, FI))

If TI and FI are load, then ext is free on x86, in this situation we should not move ext out of select.

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Event Timeline

Carrot created this revision.Jan 15 2021, 6:04 PM
Carrot requested review of this revision.Jan 15 2021, 6:04 PM
Herald added a project: Restricted Project. · View Herald TranscriptJan 15 2021, 6:04 PM
lebedev.ri requested changes to this revision.Jan 16 2021, 1:58 AM
lebedev.ri added a subscriber: lebedev.ri.

InstCombine is a canonicalization pass, and by design it must not make use of TTI.
This should be fixed by a reverse transformation in backend.

This revision now requires changes to proceed.Jan 16 2021, 1:58 AM

Thanks for the info.

I will discard this patch and reverse the pattern at function CodeGenPrepare::optimizeExt.

Carrot abandoned this revision.Jan 19 2021, 1:04 PM

Thanks for the info.

I will discard this patch and reverse the pattern at function CodeGenPrepare::optimizeExt.

Not really sure why that would go into CodeGenPrepare, which is a temporary hack,
DAGCombine is the usual counterpart.

Thanks for the info.

I will discard this patch and reverse the pattern at function CodeGenPrepare::optimizeExt.

Not really sure why that would go into CodeGenPrepare, which is a temporary hack,
DAGCombine is the usual counterpart.

Because I found CodeGenPrepare::optimizeExt does some ext(load( )) optimization.
Will look into DAGCombine.
Thanks.