Nate Chandler ad9e090243 [SIL] Only visit final on-stack pai lifetime ends. ...

In OSSA, the `partial_apply [on_stack]` instruction produces a value
with odd characteristics that correspond to the fact that it is lowered
to a stack-allocating instruction.  Among these characteristics is the
fact that copies of such values aren't load bearing.

When visiting the lifetime-ending uses of a `partial_apply [on_stack]`
the lifetime ending uses of (transitive) copies of the partial_apply
must be considered as well.  Otherwise, the borrow scope it defins may be
incorrectly short:

```
%closure = partial_apply %fn(%value) // borrows %value
%closure2 = copy_value %closure
destroy_value %closure // does _not_ end borrow of %value!
...
destroy_value %closure2 // ends borrow of %value
...
destroy_value %value
```

Furthermore, _only_ the final such destroys actually count as the real
lifetime ends.  At least one client (OME) relies on
`visitOnStackLifetimeEnds` visiting at most a single lifetime end on any
path.

Rewrite the utility to use PrunedLiveness, tracking only destroys of
copies and forwards.  The final destroys are the destroys on the
boundary.

rdar://142636711

2025-01-28 10:44:30 -08:00

..

partial_apply_on_stack_lifetime_ends.sil

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