def get_concat_input_op_slices(concat_ops, op_reg_manager):
  """Returns OpSlice for concat input ops to concatenate.

  For concat, all input OpSlice should be stacked to align with the concat
  OpSlice.  Also, the last input is the axis which should be omitted.

  Args:
    concat_ops: List of tf.Operation which provide inputs to the concat op.
    op_reg_manager: OpRegularizerManager that tracks the slicing.

  Returns:
    List of list of OpSlice, where the outer list only has 1 element, and the
    inner list is the concatenation of input OpSlice.
  """
  concat_input_op_slices = []
  for concat_op in concat_ops:
    concat_input_op_slices.extend(op_reg_manager.get_op_slices(concat_op))

  return [concat_input_op_slices]