How are callees resolved?

I have a question concerning the behavior of "loading" moduleless llvm:Function* into the ExecutionEngine using something like getOrInsertFunction(). The question I have is how are Call instructions affected by such a load? Do I have to specify apriori w.r.t. functions already loaded in the modules associated with the EE when building such functions or is it possible to have some sort of link phase where these the callees are reresolved?

Thanks in advance.