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

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:


> 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.

If other debug messages need cleaning up, that's unrelated to this change. 

I think it is super useful to understand why delinearization fails and so these debug messages seem useful. I will let @sebpop  answer your question, but I am happy to LGTM this.  

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