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):
        """
        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).
        """
        # Is that edge already in the graph ?
        # If at least one is new, then we are not redoing the same path again
        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)