[llvm] [CVP] Keep `ReachableCaseCount` in sync with range of condition (PR #142302)

[Nikita Popov via llvm-commits]

nikic wrote:

> #79993 assumes that a reachable case must be contained by `CR`. However, it doesn't hold for some edge cases.

Why doesn't it hold?

https://github.com/llvm/llvm-project/pull/142302