[llvm] [ValueTracking] Handle not cond to assume. (PR #127140)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

I don't really like special-casing the not here.

What would happen if we treat any instruction that feeds into the assume as ephemeral, even if it has other users?

https://github.com/llvm/llvm-project/pull/127140