[PATCH] D158063: [GISel][AArch64] Combine G_BUILD_VECTOR(G_UNMERGE) with undef elements

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: arsenm, aemerson, paquette, stuij, chuongg3.
Herald added a subscriber: kristof.beyls.
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dmgreen requested review of this revision.
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This extends the existing legalization combine to fold G_BUILD_VECTOR where the sources are all from the same G_UNMERGE, to handle cases where some of the lanes are undef. This comes up in the legalization of `<3 x ..>` vectors in AArch64, where they are padded with undef.

There are two choices for what to create. This patch generates an identity G_SHUFFLE_VECTOR with undef lanes marked as undef. This keeps the information about which lanes are undef, but the alternative would be to just reuse the source directly. I think both have advantages and disadvantages.


https://reviews.llvm.org/D158063

Files:
  llvm/include/llvm/CodeGen/GlobalISel/LegalizationArtifactCombiner.h
  llvm/test/CodeGen/AArch64/fabs.ll
  llvm/test/CodeGen/AArch64/fcvt.ll
  llvm/test/CodeGen/AArch64/fminimummaximum.ll
  llvm/test/CodeGen/AArch64/fminmax.ll
  llvm/test/CodeGen/AArch64/fpext.ll
  llvm/test/CodeGen/AArch64/fptrunc.ll
  llvm/test/CodeGen/AArch64/fsqrt.ll

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