In both cases here, x represents a statement, and without that statement being bound, the body predicate must be called to traverse all Units in the codebase to check whether it matches your criteria. This can be particularly slow if the matching criteria itself is expensive.
Remember DeepWeaver doesn't just analyse the class or package you specified, if you call an unbound assign or call predicate it will dive into the libraries and look for results. This includes looking through classes such as Object and Throwable from which common Java features are derived. Needless to say, it's going to slow you down.
At time of writing there's no artificial predicate to limit the scope based on what is specified in your command line, but there's an easy way to do this manually.
If you want to restrict yourself to a certain class or set of classes, simply specify:
scope(u)=class(c,"org.owasp.webgoat.session.User*"), units(body(sootmethod(c,<-),<-),u);
and then
scope(u), assign(u,y,z), ...
and now the first predicate in assign is bound to be a unit from some class beginning with User in the specified package. This dramatically restricts the scope of possible values for u and thus greatly improves the resulting performance.
Notice the use of wildcards here, you may use wildcards in both the class and package name but you must attempt to specify the class name to some degree. So you could say org.owasp.*.User* to find your classes, or ever org.*.* but that dot is essential to include, or it will assume your package to be a class name and fail to find the result you're looking for.
