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[X86] Add support for forming vXi16 PMULH instructions from shifts.
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Authored by craig.topper on Sat, May 9, 6:13 PM.

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Summary

We already form PMULH when the shift is truncated. But we can
also do it from just a shift by extending the result.

Unfortunately, I get regressions if I try to replace the truncate
combine with this as we turn the truncate into a more complicated
sequence first. Then we are unable to combine that sequence with
the extend produced at the end of this combine.

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Event Timeline

craig.topper created this revision.Sat, May 9, 6:13 PM
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RKSimon accepted this revision.Thu, May 14, 5:02 AM

LGTM

This revision is now accepted and ready to land.Thu, May 14, 5:02 AM
This revision was automatically updated to reflect the committed changes.