[all-commits] [llvm/llvm-project] 2fdeee: [X86] Add support for forming vXi16 PMULH instruct...

[topperc via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 2fdeee9c8282df6e1fc0af02a503b4d2c908e49e
      https://github.com/llvm/llvm-project/commit/2fdeee9c8282df6e1fc0af02a503b4d2c908e49e
  Author: Craig Topper <craig.topper at intel.com>
  Date:   2020-05-14 (Thu, 14 May 2020)

  Changed paths:
    M llvm/lib/Target/X86/X86ISelLowering.cpp
    M llvm/test/CodeGen/X86/pmulh.ll

  Log Message:
  -----------
  [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