message: Try to infer pfor loop iterations statically, if possible, for the call made
  from tf.vectorized_map.
diff: @@ -386,5 +386,10 @@ def vectorized_map(fn, elems):
  def loop_fn(i):
  gathered_elems = nest.map_structure(lambda x: array_ops.gather(x, i), elems)
  return fn(gathered_elems)
  - batch_size = array_ops.shape(nest.flatten(elems)[0])[0]
  + batch_size = None
  + first_elem_shape = nest.flatten(elems)[0].shape
  + if first_elem_shape.rank is not None:
  + batch_size = first_elem_shape.as_list()[0]
  + if batch_size is None:
  + batch_size = array_ops.shape()[0]
  return pfor(loop_fn, batch_size)
  