[llvm] [SCEV][LV] Invalidate LCSSA exit phis more thoroughly (PR #69909)

[Florian Hahn via llvm-commits]

fhahn wrote:

Yep, addrecs where the main thing I was thinking about. 

In theory, I think there may also be issues with constants (e.g. a lcssa phi with a constant value) where we would need to invalidate those uses once we add an incoming value. This may be mostly theoretical as those would be simplified elsewhere. Mostly curious how expensive invalidating addrecs and/or all roots would be

https://github.com/llvm/llvm-project/pull/69909