[PATCH] D143193: [DAG] Add visitABD optimizations

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: RKSimon, spatel, jaykang10.
Herald added subscribers: StephenFan, ecnelises, hiraditya.
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This adds basic a visitABD to optimize ABDS and ABDU nodes, similar to the existing visitAVG method.

The fold I was initially interested in was folding shuffles though the binop. This also:

- Marks ABDS and ABDU as commutative binops (https://alive2.llvm.org/ce/z/oCDogb and https://alive2.llvm.org/ce/z/7zrs86).
- Add constant folding using `max(x,y)-min(x,y)`
- Canonicalizes constants to the RHS
- Folds `abds x, 0 -> abs(x)` (https://alive2.llvm.org/ce/z/4ZEibv)
- Folds `abdu x, 0 -> x` (https://alive2.llvm.org/ce/z/J_rKqx)
- Folds `abd x, undef -> 0` (https://alive2.llvm.org/ce/z/NV6Nsv and https://alive2.llvm.org/ce/z/vs92hu).


https://reviews.llvm.org/D143193

Files:
  llvm/include/llvm/CodeGen/TargetLowering.h
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
  llvm/test/CodeGen/AArch64/abd-combine.ll
  llvm/test/CodeGen/AArch64/arm64-neon-aba-abd.ll
  llvm/test/CodeGen/Thumb2/mve-vabdus.ll

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