[PATCH] D106745: [DAG] DAGCombiner::useDivRem - recognise sub(X,mul(div(X,Y),Y)) as a rem(X,Y)

[Simon Pilgrim via Phabricator via llvm-commits]

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

Attempt to match a sub(X,mul(div(X,Y),Y)) pattern as srem/urem as a last chance to merge into a divrem instruction.

For reference, the DivRemPairs pass explicitly won't merge cases when the sub/mul and div are in the same block:

  // If the target supports div+rem and the instructions are in the same block
  // already, there's nothing to do. The backend should handle this. If the
  // target does not support div+rem, then we will decompose the rem.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D106745

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/div-rem-pair-recomposition-signed.ll
  llvm/test/CodeGen/X86/div-rem-pair-recomposition-unsigned.ll

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