message: Use ObjectIdentitySet instead of set()
diff: @@ -27,6 +27,7 @@ from tensorflow.python.ops import control_flow_ops
  from tensorflow.python.ops import control_flow_util
  from tensorflow.python.ops import tensor_array_ops
  from tensorflow.python.util import nest
  +from tensorflow.python.util import object_identity
  from tensorflow.python.util import tf_decorator
  # Op types that should not run in program order, e.g. because they need to run
  @@ -110,7 +111,7 @@ class AutomaticControlDependencies(object):
  """
  def __init__(self):
  - self._returned_tensors = set()
  + self._returned_tensors = object_identity.ObjectIdentitySet()
  self.ops_which_must_run = set()
  def mark_as_return(self, tensor):
  