Does it matter?
In phase 1 we never go to landing pads, so we never restore registers.

Assuming the model is:
- in _Unwind_RaiseException, unw_getcontext originally skips VFP (or other) registers
- we use a different copy of the VRS (the cursor) in phase 1 and phase 2
- in phase 1, we never copy the VRS to the real set (unw_resume)
- we lazily copy the VFP set (or individual registers?) from the real registers the first time they're accessed during unwind, keeping that state in the VRS
- when installing the context (unw_resume) we copy the registers to the real set if and only if they have been loaded from the real set.

Then worst case we copy the registers from the real set into the VRS twice, but we save a bunch of logic.