[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.

0 files changed, 0 insertions, 0 deletions