Nate Chandler ebf602803e [OSSACanOwned] Fix liveness passed to completion. ...

To determine where a lifetime ends within dead-end blocks,
OSSACanonicalizeOwned uses OSSACompleteLifetime's
visitAvailabilityBoundary.  This API takes a liveness which it uses to
walk forward to the availability boundary.  Specifically, the liveness
passed from OSSACanonicalizeOwned to OSSACompleteLifetime is a variation
of OSSACanonicalizeOwned's own liveness (it has destroys added).

There is a mismatch in the characteristics of livenesses created by
OSSACanonicalizeOwned and OSSACompleteLifetime:  The former deals with
not only direct uses of a value but also uses of its copies; that
introduces the possibility for consuming uses in the middle of liveness.
The latter on the other hand deals only with uses of a single value
(nestedly, but at each level of nesting only a single value).  Passing a
liveness from the former to the latter without handling this mismatch
is incorrect: OSSACompleteLifetime understands consuming uses to always
end a lifetime, even when they are in the middle of a copy-extended
liveness.  The result is that OSSACompleteLifetime produces non-sensical
results when provided with such a liveness.

To address this, fixup the liveness passed from OSSACanonicalizeOwned to
OSSACompleteLifetime by demoting consuming uses that appear within
(that's to say _not_ on the boundary) of liveness to non-consuming uses.

rdar://142846936

2025-01-15 11:57:13 -08:00

59 KiB

Raw Permalink Blame History

View Raw