Andrew Trick f470b29747 Disable fix_lifetime DCE. ...

Unless the type is a trivial scalar. As a follow-up we could try to
prove that the referenced object is unique, but that seems more
natural for DeadObjectElimination.

This optimization was never correct because references may alias. See
rdar://36038096 ([SR-6608] DeadCodeElimination removes fix_lifetime
instructions.)

Fixes rdar://74759728 (The compiler/optimizer seems to be shortening
the lifetime too early)

2021-02-26 11:06:10 -08:00

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