[llvm] [LoopInterchange] Relax the legality check to accept more patterns (PR #118267)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj commented:

Hi @sjoerdmeijer @madhur13490 .

This patch addresses issues with the current legality check being too conservative. I think correctness is more important than this to enable interchange by default, so I won't merge this before it is achieved. However, it would be appreciated if you would remember that this patch improves some of the `S` dependency, which were eliminated in #119345. (I'm not treating the `S` as special in this patch, but rather changing the handling of `*`). I would also like to know if you have any comments at this time.

Thanks.

https://github.com/llvm/llvm-project/pull/118267