set builder's insert point to the last of a couple of instructions

I have a couple of instructions (say 4) in a SetVector<Value*> which belong to a single basic block (they are in no particular order with respect to the BB). I'd like to tell the IRBuilder that the insert point is right after the last of these 4 instructions ('last' with respect to the order in the BB). How would I do that?
I can set the insert point with an BB::iterator, but then it boils down to get that. Can this be done without iterating over all instructions in the BB until the last one is found? (That would take too long)

Thanks,
Frank