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

[Adrian Prantl via llvm-commits]

adrian-prantl wrote:

> So, depending on how/when these intrinsics are generated, this patch could affect a few different targets.

And it would introduce a situation we usually try to avoid: the presence of debug info could significantly change code generation.


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