[llvm] [LoopInterchange] Exit early in certain cases in legality check (NFC) (PR #139254)

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur approved this pull request.

Can you make the title more concrete than "certain cases"? It's not an early exit either

Suggestion: Skip legality check if surronding loops already guarantee dependency

https://github.com/llvm/llvm-project/pull/139254