code: def fast_backward_ops(within_ops, seed_ops, stop_at_ts):
      bwd_ops = set(
          ge.get_backward_walk_ops(seed_ops, stop_at_ts=stop_at_ts)
      )
      ops = bwd_ops.intersection(within_ops).difference(
          [t.op for t in stop_at_ts]
      )
      return list(ops)
  
file_path: gpt-2-simple/gpt_2_simple/src/memory_saving_gradients.py
imports: from toposort import toposort
  import contextlib
  import numpy
  import tensorflow
  import time
  import sys
  from tensorflow.python.ops import gradients
label_desc: Use image node_id 6 for calling a global function with example usage: fast_backward_ops(within_ops, seed_ops, stop_at_ts) and returns: list