[llvm] improve debug messages in dependence analysis (PR #156367)

[Ryotaro Kasuga via llvm-commits]

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

Are these new debug messages really necessary? DA already has a large number of debug messages, and I don't think they are well organized. If possible, I'd prefer not to add much more.

https://github.com/llvm/llvm-project/pull/156367