[PATCH] D83073: [x86] improve codegen for bit-masked vector compare and select (PR46531)

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: RKSimon, craig.topper, lebedev.ri.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.

We canonicalize patterns like:

  %s = lshr i32 %a0, 1
  %t = trunc i32 %s to i1

to:

  %a = and i32 %a0, 2
  %c = icmp ne i32 %a, 0

...in IR, but the bit-shifting original sequence may be better for x86 vector codegen.

I tried several variants of the transform, and it's tricky to not induce regressions. In particular, I did not find a way to cleanly handle non-splat constants, so I've left that as a TODO item here (negative tests for those are included here). AVX512 resulted in some diffs, but didn't look meaningful, so I left that out too. Some of the 256-bit AVX1 diffs are questionable, but close enough that it's probably not meaningful.


https://reviews.llvm.org/D83073

Files:
  llvm/lib/Target/X86/X86ISelLowering.cpp
  llvm/test/CodeGen/X86/vselect-pcmp.ll

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