Procedure calls may be approached in two ways. The first is to assume the worst case for the call, and the second is to actually perform the data flow analyses throughout the procedure.
For the first approach, default assumptions include assuming no definitions are killed, expressions are nolonger available, etc.
Approach two requires careful following of aliases. An alias is another name for a location. REference parameters are aliases for the actual arguments. Once aliases are identified, the analysis is similar to intraprocedural analysis.