def _elaborate_declare_vars(s):
    """ Convention: the top level component on which we call elaborate
    declare variables in _declare_vars; it shouldn't have them before
    elaboration.

    Convention: the variables that hold all metadata of descendants
    should have _all prefix."""
    s._dsl.all_upblks = set()
    s._dsl.all_upblk_hostobj = {}
    s._dsl.all_U_U_constraints = set()
    s._dsl.all_components = set()
