[all-commits] [llvm/llvm-project] 32ecd3: [LoopInterchange] Bail out when outer loop latch P...

[Ryotaro Kasuga via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 32ecd3e7ff64cab044716e39d14f880cf5a7367d
      https://github.com/llvm/llvm-project/commit/32ecd3e7ff64cab044716e39d14f880cf5a7367d
  Author: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
  Date:   2026-06-11 (Thu, 11 Jun 2026)

  Changed paths:
    M llvm/lib/Transforms/Scalar/LoopInterchange.cpp
    M llvm/test/Transforms/LoopInterchange/non-phi-uses-lcssa-phi.ll

  Log Message:
  -----------
  [LoopInterchange] Bail out when outer loop latch PHI has non-PHI user (#201923)

When there are non-PHI instructions in the outer loop that use values
originating from the LCSSA PHIs of the inner loop, it becomes difficult
to adjust the wiring during the transformation. In fact, multiple issues
(#200819 and #201571) have been raised related to this pattern. #201059
tried to resolve the issue by modifying the transformation phase, but it
was insufficient.
Instead of spending effort in the transformation phase, this patch adds
an additional check in the legality check and rejects such cases. I
think the cases rejected by this additional check are not very
practical, so the impact on realistic cases should be low, and it is
simpler than adjusting the wiring in the transformation phase.
This patch also effectively reverts #201059, as it is no longer
necessary.

Fix #201571.



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