13b167770c
Emergency stack slots are a new kind of stack slot added relatively recently. They need to be allocated a stack offset just like explicit and spill slots. Also, make StackSlotData's offset field an Option, to catch problems like this in the future. Previously the value 0 was used when offsets weren't assigned yet, however that made it non-obvious when the field meant "not assigned yet" and when it meant "assigned the value 0".