[all-commits] [llvm/llvm-project] 313a33: [InstCombine] Reduce nested logical operator if po...

[XChy via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 313a33b9dff44dc2b0048484e54f9328d9a0d9db
      https://github.com/llvm/llvm-project/commit/313a33b9dff44dc2b0048484e54f9328d9a0d9db
  Author: XChy <xxs_chy at outlook.com>
  Date:   2024-04-10 (Wed, 10 Apr 2024)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    M llvm/test/Transforms/InstCombine/and-or-icmps.ll
    M llvm/test/Transforms/InstCombine/logical-select.ll

  Log Message:
  -----------
  [InstCombine] Reduce nested logical operator if poison is implied (#86823)

Fixes #76623
Alive2 proof: https://alive2.llvm.org/ce/z/gX6znJ (I'm not sure how to
write a proof for such transform, maybe there are mistakes)

In most cases, `icmp(a, C1) && (other_cond && icmp(a, C2))` will be
reduced to `icmp(a, C1) & (other_cond && icmp(a, C2))`, since latter
icmp always implies the poison of the former. After reduction, it's
easier to simplify the icmp chain.
Similarly, this patch does the same thing for `(A && B) && C --> A && (B
& C)`. Maybe we could constraint such reduction only on icmps if there
is regression in benchmarks.



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