[PATCH] D95703: [GlobalISel] Propagate extends through G_PHIs into the incoming value blocks.

[Amara Emerson via Phabricator via llvm-commits]

aemerson created this revision.
aemerson added reviewers: paquette, arsenm, foad.
aemerson added a project: LLVM.
Herald added subscribers: hiraditya, kristof.beyls, rovka.
aemerson requested review of this revision.
Herald added a subscriber: wdng.

This combine tries to do inter-block hoisting of extends of G_PHIs, into the originating blocks of the phi's incoming value. The idea is to expose further optimization opportunities that are normally obscured by the PHI.

Some basic heuristics, and a target hook for AArch64 is added, to allow tuning. E.g. if the extend is used by a G_PTR_ADD, it doesn't perform this combine since it may be folded into the addressing mode during selection.

There are very minor code size improvements on AArch64 -Os, but the real benefit is that it unlocks optimizations like AArch64 conditional compares on some benchmarks.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D95703

Files:
  llvm/include/llvm/CodeGen/GlobalISel/CombinerHelper.h
  llvm/include/llvm/CodeGen/TargetInstrInfo.h
  llvm/include/llvm/Target/GlobalISel/Combine.td
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/lib/Target/AArch64/AArch64InstrInfo.cpp
  llvm/lib/Target/AArch64/AArch64InstrInfo.h
  llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-prop-extends-phi.mir

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