[llvm] [DA] Check monotonicity for subscripts (PR #154527)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

@Meinersbur  I'd like to get your thoughts on whether this approach seems reasonable. What do you think about this?

Also, I believe similar checks are needed in other parts of the DA as well, for example [this function](https://github.com/llvm/llvm-project/blob/a0d05ec13ce11b3e895a502adfe50fc94aa54bbb/llvm/lib/Analysis/DependenceAnalysis.cpp#L3097-L3117).

https://github.com/llvm/llvm-project/pull/154527