[PATCH] D101375: [InstCombine] Add a few more patterns for folding select of select

[Juneyoung Lee via Phabricator via llvm-commits]

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This is a patch that folds select of select to salvage some optimizations after select -> and/or folding is disabled.

  select (select a, true, b), c, false -> select a, c, false
  select c, (select a, true, b), false -> select c, a, false
    if c implies that b is false (isImpliedCondition).

https://alive2.llvm.org/ce/z/ANatjt, https://alive2.llvm.org/ce/z/rv8zTB

  sel (sel c, a, false), true, (sel !c, b, false) -> sel c, a, b
  sel (sel !c, a, false), true, (sel c, b, false) -> sel c, b, a

https://alive2.llvm.org/ce/z/U2kp-t, https://alive2.llvm.org/ce/z/bc88EE

See D101191 <https://reviews.llvm.org/D101191>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101375

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/select-safe-transforms.ll

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