[llvm] [LV] Ignore some costs when loop gets fully unrolled (PR #106699)

[David Sherwood via llvm-commits]

https://github.com/david-arm commented:

I think the idea is good, i.e. teach the vectoriser about exit costs when the branch and compare will be removed. However, I think you've assumed that the induction variables have no other uses and so have almost certainly underestimated the costs in some loops. Also, I noticed that this patch doesn't remove the branch cost either. It's possible that removing the branch and comparison costs are enough to get what you want? It might be easier than analysing the users of all the incremented induction variables.

https://github.com/llvm/llvm-project/pull/106699