[llvm] [VPlan] Convert to concrete recipes before dissolving loop regions. NFCI (PR #141999)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

That should be fine,. but currently there is a ordering constraint between convertToConcreteRecipes and dissolveLoopRegions, as replacing the CanIV before removing the region makes the region invalid (althoug just temporarily). 

We should probably remove the canonical IV together with removing its region: https://github.com/llvm/llvm-project/pull/142372

That resolves the ordering issue

https://github.com/llvm/llvm-project/pull/141999