Reshapes first two dimensions in to single dimension.

  Args:
    tensor: Tensor to reshape of shape [A, B, ...]

  Returns:
    Reshaped tensor of shape [A*B, ...]

def _merge_beam_dim(tensor):
  """Reshapes first two dimensions in to single dimension.

  Args:
    tensor: Tensor to reshape of shape [A, B, ...]

  Returns:
    Reshaped tensor of shape [A*B, ...]
  """
  shape = common_layers.shape_list(tensor)
  shape[0] *= shape[1]  # batch -> batch * beam_size
  shape.pop(1)  # Remove beam dim
  return tf.reshape(tensor, shape)