'Add an edge in the graph from `s_a` to statement `s_b`, where `s_a` and `s_b` are tuples of statements of the
form (irsb_addr, stmt_idx).'

def _add_edge(self, s_a, s_b, **edge_labels):

    if ((s_a, s_b) not in self.graph.edges()):
        self.graph.add_edge(s_a, s_b, **edge_labels)
        self._new = True
        l.info('New    edge:    %s    -->    %s', s_a, s_b)
