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AMDGPU: Fix high 16-bit optimization on gfx9

Authored by arsenm on Jun 18 2021, 3:07 PM.



We can do this optimization in the majority of cases, but we currently
don't have a way to do it. We do not track/model which instructions
have which behavior, the control bit to change the high bit behavior,
or making use of preserved bits at all. This is a bit fuzzy since we
don't know precisely how the source instruction will be lowered, but
that only really matters in one case (for fma_mixlo).

We do need to fixup some of these cases after selection, but the
pattern helps eliminate many of these zexts.

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arsenm created this revision.Jun 18 2021, 3:07 PM
arsenm requested review of this revision.Jun 18 2021, 3:07 PM
Herald added a project: Restricted Project. · View Herald TranscriptJun 18 2021, 3:07 PM
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foad accepted this revision.Jun 21 2021, 5:55 AM
This revision is now accepted and ready to land.Jun 21 2021, 5:55 AM
arsenm updated this revision to Diff 353372.Jun 21 2021, 7:49 AM

Fix tests on intermediate commit