import tensorflow as tf

    ckpt: Path to existing checkpoint.  If present, returns only the subset of
        variables that exist in given checkpoint.

  Returns:
    List of all variables that need to be saved/restored.
  """
  model_vars = tf.trainable_variables()
  # Add batchnorm variables.
  bn_vars = [v for v in tf.global_variables()
             if 'moving_mean' in v.op.name or 'moving_variance' in v.op.name or
             'mu' in v.op.name or 'sigma' in v.op.name or
             'global_scale_var' in v.op.name]
