[PATCH] D79682: [X86] Add support for forming vXi16 PMULH instructions from shifts.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: RKSimon, spatel.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D79682

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/pmulh.ll

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