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These instructions model a conversion in between ownership kinds without the result actually being owned by anything. As a result:
1. From an operand perspective, the instruction is treated like a pointer escape.
2. From a value perspective, the instruction returns a value with
OwnershipKind::Unowned (to force the value to be copied before it can be used
in an owned or guaranteed way) and
Example:
```
sil @example : $@convention(thin) (@owned Klass) -> @owned @sil_unowned Klass {
bb0(%0 : @owned $Klass):
// Note that the ref_to_unowned does not consume %0 but instead converts %0
// from a "strong" value to a "safe unowned" value. A "safe unowned" value is
// a value that corresponds to an 'unowned' value at the Swift level that use
// unowned reference counting. At the SIL level these values can be recognized
// by their types having the type attribute @sil_unowned. We have not
// incremented the unowned ref count of %1 so we must treat %1 as unowned.
%1 = ref_to_unowned %0 : $Klass
// Then before we can use %2 in any way as a "safe unowned" value we need to
// bump its unowned ref count by making a copy of the value. %2 will be a
// "safe unowned" value with OwnershipKind::Owned ensuring that we decrement
// the unowned ref count and do not leak said ref count.
%2 = copy_value %1 : $@sil_unowned $Klass
// Then since the original ref_to_unowned did not consume %0, we need to
// destroy it here.
destroy_value %0 : $Klass
// And then return out OwnershipKind::Owned @sil_unowned Klass.
return %2 : $@sil_unowned $Klass
}
```