- Compute `new_bor` from `new_tag` and the type of the reference being created.
- `reactivate(bor)`.
- If this is a function argument coming in: `loc.borrows.push(FnBarrier(stack_height))`.
- - `initiate(new_bor)`. Note that this is a NOP if `new_bor` is already active -- in particular, if the location is frozen and this is a shared reference with interior mutability, we do *not* push anything on top of the barrier. This is important, because we do not want to push that might unfreeze the location when being reactivated.
+ - `initiate(new_bor)`. Note that this is a NOP if `new_bor` is already active -- in particular, if the location is frozen and this is a shared reference with interior mutability, we do *not* push anything on top of the barrier. This is important, because any reactivation that unfreezes this location must lead to UB while the barrier is still present.
- Change reference tag to `new_tag`.
* Any time a raw pointer is created from a reference, we might have to do a raw reborrow.
- `reactivate(bor)`.