[PATCH] D92095: [DAG] Legalize abs(x) -> smax(x,sub(0,x)) iff smax/sub are legal

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: spatel, lebedev.ri, nemanjai, craig.topper.
Herald added subscribers: steven.zhang, pengfei, kbarton, hiraditya.
Herald added a project: LLVM.
RKSimon requested review of this revision.

If smax() is legal, this is likely to result in smaller codegen expansion for abs(x) than the xor(add,ashr) method.

This is also what powerpc has been doing for its abs implementation, so it lets us get rid of a load of custom lowering code there (and which was never updated when they added smax lowering).

Alive2 check : https://alive2.llvm.org/ce/z/xRk3cD


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D92095

Files:
  llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.cpp
  llvm/lib/Target/PowerPC/PPCISelLowering.h
  llvm/test/CodeGen/X86/abs.ll
  llvm/test/CodeGen/X86/combine-abs.ll
  llvm/test/CodeGen/X86/viabs.ll

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