[llvm] [ExtendLifetimes] Implement llvm.fake.use to extend variable lifetimes (PR #86149)

[Felipe de Azevedo Piovezan via llvm-commits]

felipepiovezan wrote:

 > Conceptually, though, extend-lifetimes is purely a codegen change. It could stand on its own, even though it would only be useful to improve debuggability. I think it's important to separate the 2 concepts. Debug info generation by itself does not trigger extend-lifetimes unless we specifically also request extend-lifetimes as well.

Isn't the following statement contradicting the above?

> The extend lifetimes flag is intended to eventually be set on by -Og

https://github.com/llvm/llvm-project/pull/86149