Constructs a CFG

    :param androguard.core.analysis.analysis.DVMBasicBlock start_block: The startpoint
    :param vmap: variable mapping
    :param exceptions: list of androguard.core.analysis.analysis.ExceptionAnalysis

    :rtype: Graph

def construct(start_block, vmap, exceptions):
    """
    Constructs a CFG

    :param androguard.core.analysis.analysis.DVMBasicBlock start_block: The startpoint
    :param vmap: variable mapping
    :param exceptions: list of androguard.core.analysis.analysis.ExceptionAnalysis

    :rtype: Graph
    """
    bfs_blocks = bfs(start_block)

    graph = Graph()
    gen_ret = GenInvokeRetName()

    # Construction of a mapping of basic blocks into Nodes
    block_to_node = {}

    exceptions_start_block = []
    for exception in exceptions:
        for _, _, block in exception.exceptions:
            exceptions_start_block.append(block)

    for block in bfs_blocks:
        node = make_node(graph, block, block_to_node, vmap, gen_ret)
        graph.add_node(node)

    graph.entry = block_to_node[start_block]
    del block_to_node, bfs_blocks

    graph.compute_rpo()
    graph.number_ins()

    for node in graph.rpo:
        preds = [pred for pred in graph.all_preds(node) if pred.num < node.num]
        if preds and all(pred.in_catch for pred in preds):
            node.in_catch = True

    # Create a list of Node which are 'return' node
    # There should be one and only one node of this type
    # If this is not the case, try to continue anyway by setting the exit node
    # to the one which has the greatest RPO number (not necessarily the case)
    lexit_nodes = [node for node in graph if node.type.is_return]

    if len(lexit_nodes) > 1:
        # Not sure that this case is possible...
        logger.error('Multiple exit nodes found !')
        graph.exit = graph.rpo[-1]
    elif len(lexit_nodes) < 1:
        # A method can have no return if it has throw statement(s) or if its
        # body is a while(1) whitout break/return.
        logger.debug('No exit node found !')
    else:
        graph.exit = lexit_nodes[0]

    return graph