[llvm] [ValueLattice] Reset the count of range extensions when merging an undef with a constant range. (PR #77307)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

So previously when merging in the first other lattice value, it would re-use that lattice value's NumRangeExtension, whereas now it gets set to 0. This should guarantee that we still converge as it's only set when merging with Unknown, but possibly slower.

In particular `consumer-typeset`'s compile-time seems to noticeably increase. Do you have any insight why that is and if we could do better? It looks like there's also a notable size change for `consumer-typeset`, do you know if those are an improvement?

https://github.com/llvm/llvm-project/pull/77307