docstr: Performs entire backward pass in depth-first order.
docstr_tok: ["Performs","entire","backward","pass","in","depth-first","order","."]
code: def __call__(self):
      """
      Performs entire backward pass in depth-first order.
      """
      message = None
      stack = [(self, message)]
      while stack:
          bwd, message = stack.pop()
          stack.extend(bwd.process(message))
  
imports: import weakref
  from abc import ABCMeta, abstractmethod
  import torch
  from pyro.ops import packed
  from pyro.util import jit_iter
label_desc: Use image node_id 1 for calling the Backward obj's underlying member method code with example usage: obj.__call__() without return types