The InstructionDeleter can remove instructions including their destroys and then insert compensating destroys at a new place.
This is effectively destroy-hoisting which doesn't respect deinit-barriers. Therefore it's not done for lexical lifetimes.
However, since https://github.com/swiftlang/swift/pull/85334, the optimizer should treat _all_ lifetimes as fixed and not only lexical lifetimes.
This change adds a `assumeFixedLifetimes` flag to InstructionDeleter which is on by default.
Only mandatory passes (like OSLogOptimization) should turn this off.
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