[llvm] [VPlan] Optimize more IV increment exit users by using a map (PR #147016)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

What are the cases that we currently miss and catch with that? Could we detect them differently? Having a map seems like it may be    a bit fragile, as the referenced VPValues may be replaced/removed in between.

https://github.com/llvm/llvm-project/pull/147016