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

[Stephen Tozer via llvm-commits]

SLTozer wrote:

> Sorry for only raising this now. Is there a good reason for not putting isFakeUse() into MachineInstr::isPosition() instead of sprinkling it over the codebase? Putting into isPosition would make it a scheduling boundary, ignored by CSE, unsafe to move and therefore ignored by DCE and MachineSink.

It's not something I've thought about, but I'm happy to take a look at it and see if a refactoring patch would be worthwhile.


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