[PATCH] D97290: [LoopInterchange] Replace tightly-nesting-ness check with the one from `LoopNest`

[Ta-Wei Tu via Phabricator via llvm-commits]

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The check `tightlyNested()` in `LoopInterchange` is similar to the one in `LoopNest`.
In fact, the former misses some cases where loop-interchange is not feasible and results in incorrect behaviour.
Replacing it with the much robust version provided by `LoopNest` reduces code duplications and fixes https://bugs.llvm.org/show_bug.cgi?id=48113.

`LoopInterchange` has a weaker definition of tightly or perfectly nesting-ness than the one implemented in `LoopNest::arePerfectlyNested()`.
Therefore, `tightlyNested()` is instead implemented with `LoopNest::checkLoopsStructure` and additional checks for unsafe instructions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97290

Files:
  llvm/include/llvm/Analysis/LoopNestAnalysis.h
  llvm/lib/Analysis/LoopNestAnalysis.cpp
  llvm/lib/Transforms/Scalar/LoopInterchange.cpp
  llvm/test/Transforms/LoopInterchange/pr48113.ll

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