[PATCH] D142786: [InstCombine] Improve transforms for (icmp uPred X * Z, Y * Z) -> (icmp uPred X, Y)

[Noah Goldstein via Phabricator via llvm-commits]

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Several cases where missing.

1. `(icmp eq/ne X*Z, Y*Z) [if Z % 2 != 0] -> (icmp eq/ne X, Y)` EQ: https://alive2.llvm.org/ce/z/6_HPZ5 NE: https://alive2.llvm.org/ce/z/c34qSU

  There was previously an implementation of this that work of `Y` was non-constant, but it was missing if `Y*Z` evaluated to a constant and/or `nsw`/`nuw` where both false. As well it only worked if `Z` was a constant but we can check 1s bit of `KnownBits` to cover more cases.

2. `(icmp eq/ne X*Z, Y*Z) [if Z != 0 and nsw(X*Y) and nsw(Y*Z)] -> (icmp eq/ne X, Y)` EQ: https://alive2.llvm.org/ce/z/6SdAG6 NE: https://alive2.llvm.org/ce/z/fjsq_b

  This was previously implemented only to work if `Z` was constant, but we can use `isKnownNonZero` to cover more cases.

3. `(icmp uPred X*Y, Y*Z) [if Z != 0 and nuw(X*Y) and nuw(X*Y)] -> (icmp uPred X, Y)` EQ:  https://alive2.llvm.org/ce/z/FqWQLX NE:  https://alive2.llvm.org/ce/z/2gHrd2 ULT: https://alive2.llvm.org/ce/z/MUAWgZ ULE: https://alive2.llvm.org/ce/z/szQQ2L UGT: https://alive2.llvm.org/ce/z/McVUdu UGE: https://alive2.llvm.org/ce/z/95uyC8

  This was previously implemented only for `eq/ne` cases. As well only if `Z` was constant, but again we can use `isKnownNonZero` to cover more cases.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D142786

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
  llvm/test/Transforms/InstCombine/icmp-mul.ll
  llvm/test/Transforms/InstCombine/pr38677.ll

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