class_docstr: Gather the input from sequence parallel region and concatenate.
code: def backward(ctx, grad_output):
      if ctx.to_model_parallel:
          return _reduce_scatter_along_first_dim(grad_output), None
      else:
          return _split_along_first_dim(grad_output), None
  
imports: import torch
  from apex.transformer.parallel_state import get_tensor_model_parallel_group
  from apex.transformer.parallel_state import get_tensor_model_parallel_world_size
  from apex.transformer.parallel_state import get_tensor_model_parallel_rank
  from apex.transformer.tensor_parallel.utils import split_tensor_along_last_dim
label_desc: Use image node_id 3 for calling the _GatherFromSequenceParallelRegion obj's underlying member method code with example usage: obj.backward(ctx, grad_output) and returns: _reduce_scatter_along_first_dim,  None, _split_along_first_dim,  None