[llvm] [LoopUnroll] Allow expensive trip count emitting which is estimated to be infinite (PR #79869)

[Aleksandr Popov via llvm-commits]

aleks-tmb wrote:

> Makes sense conceptually. I wonder whether it would make sense to integrate this in getLoopEstimatedTripCount(), by returning UINT_MAX in this case?

Thanks, I had the idea to return UINT_MAX from the `getLoopEstimatedTripCount()`, but decided to be more conservative and make changes only for that exact spot in the LoopUnroll. 
So, after your comment I went back to the approach, but got some failures with it. I'll investigate them and get back with the results.  
 

https://github.com/llvm/llvm-project/pull/79869