def unroll_loops(self, max_loop_unrolling_times):
        if not isinstance(max_loop_unrolling_times, (int, long)) or \
                        max_loop_unrolling_times < 0:
            raise AngrCFGError('Max loop unrolling times must be set to an integer greater than or equal to 0 if ' +
                               'loop unrolling is enabled.')

        # Traverse the CFG and try to find the beginning of loops
        loop_backedges = []

        start = self._starts[0]
        if isinstance(start, tuple):
            start, _ = start  # pylint: disable=unpacking-non-sequence
        start_node = self.get_any_node(start)
        if start_node is None:
            raise AngrCFGError('Cannot find start node when trying to unroll loops. The CFG might be empty.')

        graph_copy = networkx.DiGraph(self.graph)

        while True:
            cycles_iter = networkx.simple_cycles(graph_copy)
            try:
                cycle = cycles_iter.next()
            except StopIteration:
                break

            loop_backedge = (None, None)

            for n in networkx.dfs_preorder_nodes(graph_copy, source=start_node):
                if n in cycle:
                    idx = cycle.index(n)
                    if idx == 0:
                        loop_backedge = (cycle[-1], cycle[idx])
                    else:
                        loop_backedge = (cycle[idx - 1], cycle[idx])
                    break

            if loop_backedge not in loop_backedges:
                loop_backedges.append(loop_backedge)

            # Create a common end node for all nodes whose out_degree is 0
            end_nodes = [n for n in graph_copy.nodes_iter() if graph_copy.out_degree(n) == 0]
            new_end_node = "end_node"

            if len(end_nodes) == 0:
                # We gotta randomly break a loop
                cycles = sorted(networkx.simple_cycles(graph_copy), key=len)
                first_cycle = cycles[0]
                if len(first_cycle) == 1:
                    graph_copy.remove_edge(first_cycle[0], first_cycle[0])
                else:
                    graph_copy.remove_edge(first_cycle[0], first_cycle[1])
                end_nodes = [n for n in graph_copy.nodes_iter() if graph_copy.out_degree(n) == 0]

            for en in end_nodes:
                graph_copy.add_edge(en, new_end_node)

            # postdoms = self.immediate_postdominators(new_end_node, target_graph=graph_copy)
            # reverse_postdoms = defaultdict(list)
            # for k, v in postdoms.iteritems():
            #    reverse_postdoms[v].append(k)

            # Find all loop bodies
            # for src, dst in loop_backedges:
            #    nodes_in_loop = { src, dst }

            #    while True:
            #        new_nodes = set()

            #        for n in nodes_in_loop:
            #            if n in reverse_postdoms:
            #                for node in reverse_postdoms[n]:
            #                    if node not in nodes_in_loop:
            #                        new_nodes.add(node)

            #        if not new_nodes:
            #            break

            #        nodes_in_loop |= new_nodes

            # Unroll the loop body
            # TODO: Finish the implementation

            graph_copy.remove_node(new_end_node)
            src, dst = loop_backedge
            if graph_copy.has_edge(src, dst):  # It might have been removed before
                # Duplicate the dst node
                new_dst = dst.copy()
                new_dst.looping_times = dst.looping_times + 1
                if (
                        graph_copy not in new_dst and
                        # If the new_dst is already in the graph, we don't want to keep unrolling
                        # the this loop anymore since it may *create* a new loop. Of course we
                        # will lose some edges in this way, but in general it is acceptable.
                        new_dst.looping_times <= max_loop_unrolling_times):
                    # Log all successors of the dst node
                    dst_successors = graph_copy.successors(dst)
                    # Add new_dst to the graph
                    edge_data = graph_copy.get_edge_data(src, dst)
                    graph_copy.add_edge(src, new_dst, **edge_data)
                    for ds in dst_successors:
                        if ds.looping_times == 0 and ds not in cycle:
                            edge_data = graph_copy.get_edge_data(dst, ds)
                            graph_copy.add_edge(new_dst, ds, **edge_data)
                # Remove the original edge
                graph_copy.remove_edge(src, dst)

        # Update loop backedges
        self._loop_back_edges = loop_backedges

        self._graph = graph_copy
dataset/ETHPy150Open angr/angr/angr/analyses/cfg_accurate.py/CFGAccurate.unroll_loops/swapped operands of `not in`