Let's say the two devices are named dev1 & dev2, the links from them to the switch respectively L1 & L2 and the link from the switch to the router L3.
The two devices will have to share the gigabit, meaning that if only dev1 is transmitting, dev1 will have 1 gigabit for itself but if the two of them are transmitting at the same time, they will most probably have 500 Megabit each.
If we speak about capacity of each link, capa(L1)=capa(L2)=capa(L3)=1 Gigabit (if your wires are indeed gigabit compliant). So the maximum throughput you can have on l3 is 1 gigabit.