[llvm] [LV] Emit better debug and opt-report messages when vectorization is disallowed in the LoopVectorizer (PR #158513)

[Tibor Győri via llvm-commits]

TiborGY wrote:

> > > Is this patch NFC? If this is NFC, please mark NFC in the commit title; If not, could you add a test case to show the improvement?
> > 
> > 
> > Thanks for the comment, I will be adding test cases soon (probably next few days)
> 
> Yep, thanks it would be good to add test cases! There are some interesting cases, such as vectorising an outer loop but it requires a pragma.

I have added tests covering all three codepaths. 

https://github.com/llvm/llvm-project/pull/158513