[all-commits] [llvm/llvm-project] 72eaa0: [AArch64][SelectionDAG] Mask for SUBS with multipl...

[Weihang Fan via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 72eaa0ed9934bfaa2449091bbc6e45648d1396d6
      https://github.com/llvm/llvm-project/commit/72eaa0ed9934bfaa2449091bbc6e45648d1396d6
  Author: Weihang Fan <134108011+weihangf-apple at users.noreply.github.com>
  Date:   2024-05-05 (Sun, 05 May 2024)

  Changed paths:
    M llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
    M llvm/test/CodeGen/AArch64/and-mask-removal.ll

  Log Message:
  -----------
  [AArch64][SelectionDAG] Mask for SUBS with multiple users cannot be elided (#90911)

In DAGCombiner, the `performCONDCombine` function attempts to remove AND
instructions in front of SUBS (cmp) instructions for which the AND is
transparent. The rules for that are correct, but it fails to take into
account the case where the SUBS instruction has multiple users with
different condition codes for comparison and simply removes the AND for
all of them. This causes a miscompilation in the attached test case.



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