[llvm] [LV] Add assertion for loop predecessor (and terminator of) existing when checking out of loop inst for poison (PR #154603)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

I'm not sure if we need those assertions; each valid basic block must have a terminator I think and I think we must check that there's a loop predecessor somewhere previously.

Is there any particular issue you are trying to fix/guard against? I think there are quite a number of places where we have a similar pattern

https://github.com/llvm/llvm-project/pull/154603