Otherwise, DestroyHoisting attemps to compute interior liveness
and inserts destoys at the ends. CanonicalizeOSSALifetimes is
designed to do this and not DestroyHoisting.
Set the visitInnerUses flag. This is only a quick, partial fix.
InteriorUseWalker does not generate complete liveness for two reasons
1. pointer escapes. The client must always check for escapes before assuming
complete liveness.
2. dead end blocks. Until we have complete OSSA lifetimes, the algorithm for
handling nested borrows is incorrect. The visitInnerUses flag works around this
problem, but it isn't well tested and I'm not sure it's properly records escapes yet.
It hoists `destroy_value` instructions without shrinking an object's lifetime.
This is done if it can be proved that another copy of a value (either in an SSA value or in memory) keeps the referenced object(s) alive until the original position of the `destroy_value`.
```
%1 = copy_value %0
...
last_use_of %0
// other instructions
destroy_value %0 // %1 is still alive here
```
->
```
%1 = copy_value %0
...
last_use_of %0
destroy_value %0
// other instructions
```
The benefit of this optimization is that it can enable copy-propagation by moving destroys above deinit barries and access scopes.
