[llvm] [LoopInterchange] Remove 'I' dependency (PR #140709)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

It is out-of-scope of this PR, however, I personally think we should fix DependenceAnalysis side.

https://github.com/llvm/llvm-project/blob/48a2836b4de7998018ee4f2b8c8171f7151aebf5/llvm/include/llvm/Analysis/DependenceAnalysis.h#L151-L153

I think the description "Returns the number of common loops surrounding the source and destination of the dependence" is inconsistent with the current implementation, which always returns 0. We should return the proper value, or change the return type to something like `std::optional<unsigned>` to distinguish between cases where the number of common loops is 0 and cases where it is unknown. 

The current implementation is confusing, e.g., AliasAnalysis returns `MayAlias` for a given pair of instructions.
https://github.com/llvm/llvm-project/blob/48a2836b4de7998018ee4f2b8c8171f7151aebf5/llvm/lib/Analysis/DependenceAnalysis.cpp#L3619-L3625

https://github.com/llvm/llvm-project/pull/140709