[PATCH] D63233: [CodeGenPrepare] shift both sides of a vector select when profitable

[Sanjay Patel via Phabricator via llvm-commits]

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

This is based on the example/discussion in PR37428:
https://bugs.llvm.org/show_bug.cgi?id=37428

Proper vector shift instructions don't appear until AVX2, so we may generate several extra instructions within a loop trying to compensate for that. It's difficult to recover from that expansion later than this, so use the existing TLI hook and splat analysis to enable better codegen.


https://reviews.llvm.org/D63233

Files:
  llvm/lib/CodeGen/CodeGenPrepare.cpp
  llvm/test/CodeGen/X86/vector-shift-lshr-128.ll
  llvm/test/CodeGen/X86/vector-shift-shl-128.ll
  llvm/test/Transforms/CodeGenPrepare/X86/vec-shift.ll

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