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[X86] Add support for forming vXi16 PMULH instructions from shifts.

Authored by craig.topper on Thu, May 14, 10:35 AM.

Description

[X86] Add support for forming vXi16 PMULH instructions from shifts.

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.

Differential Revision: https://reviews.llvm.org/D79682

Details

Committed
craig.topperThu, May 14, 10:58 AM
Differential Revision
D79682: [X86] Add support for forming vXi16 PMULH instructions from shifts.
Parents
rG42a556050346: [AMDGPU] New SIInsertHardClauses pass
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