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

[Orlando Cazalet-Hyams via llvm-commits]

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+# Parsing dwarfdump's output to determine whether the location list for the
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OCHyams wrote:

Maybe I'm not fully understanding this use case, but can't we replicate these checks with filecheck instead? IMO that would be cleaner than introducing some special equipment, if we can avoid it. Wdyt?

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