[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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