[llvm] [VPlan] Delay adding canonical IV increment and exit branches. (PR #82270)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

> Worth starting with delaying the introduction of canonicalIVIncrement alone, while keeping a terminating branch (existing branch-on-count or introducing some other branch, temporarily)? This seems to provide substantial incremental improvement while incurring smaller changes, i.e., w/o affecting VPlanVerifier or introducing IsAbstract.
> 
> Delaying the introduction of the loop-region-closing branch may deserve separate attention.


Done in the updated version, thanks!

https://github.com/llvm/llvm-project/pull/82270