[all-commits] [llvm/llvm-project] 3099b7: [Passes] Move LoopInterchange into optimization pi...

[Ryotaro Kasuga via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 3099b7eb5da7605995ab89695353866189e06ac3
      https://github.com/llvm/llvm-project/commit/3099b7eb5da7605995ab89695353866189e06ac3
  Author: Ryotaro Kasuga <kasuga.ryotaro at fujitsu.com>
  Date:   2025-07-04 (Fri, 04 Jul 2025)

  Changed paths:
    M llvm/lib/Passes/PassBuilderPipelines.cpp
    A llvm/test/Transforms/LoopInterchange/position-in-pipeline.ll

  Log Message:
  -----------
  [Passes] Move LoopInterchange into optimization pipeline (#145503)

As mentioned in https://github.com/llvm/llvm-project/pull/145071,
LoopInterchange should be part of the optimization pipeline rather than
the simplification pipeline. This patch moves LoopInterchange into the
optimization pipeline.

More contexts:

- By default, LoopInterchange attempts to improve data locality,
however, it also takes increasing vectorization opportunities into
account. Given that, it is reasonable to run it as close to
vectorization as possible.
- I looked into previous changes related to the placement of
LoopInterchange, but couldn’t find any strong motivation suggesting that
it benefits other simplifications.
- As far as I tried some tests (including llvm-test-suite), removing
LoopInterchange from the simplification pipeline does not affect other
simplifications. Therefore, there doesn't seem to be much value in
keeping it there.
- The new position reduces compile-time for ThinLTO, probably because it
only runs once per function in post-link optimization, rather than both
in pre-link and post-link optimization.

I haven't encountered any cases where the positional difference affects
optimization results, so please feel free to revert if you run into any issues.



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