[PATCH] D104065: [AArch64][GlobalISel] Legalize scalar G_CTTZ + G_CTTZ_ZERO_UNDEF

[Jessica Paquette via Phabricator via llvm-commits]

paquette created this revision.
paquette added reviewers: aemerson, jroelofs.
Herald added subscribers: danielkiss, hiraditya, kristof.beyls, rovka.
paquette requested review of this revision.
Herald added a project: LLVM.

This adds legalization for scalar G_CTTZ and G_CTTZ_ZERO_UNDEF. Vector support requires handling vector G_BITREVERSE, which I haven't gotten around to yet.

For G_CTTZ_ZERO_UNDEF, we just lower it to G_CTTZ.

For G_CTTZ, we match SelectionDAG's lowering to a G_BITREVERSE + G_CTLZ.

e.g. https://godbolt.org/z/nPEseYh1s

(With this patch, we have slightly worse codegen than SDAG for types smaller than s32; it seems like we're missing a combine.)

Also, this adds in a function to build G_BITREVERSE to MachineIRBuilder.


https://reviews.llvm.org/D104065

Files:
  llvm/include/llvm/CodeGen/GlobalISel/MachineIRBuilder.h
  llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp
  llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.h
  llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz-zero-undef.mir
  llvm/test/CodeGen/AArch64/GlobalISel/legalize-cttz.mir
  llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir

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