code: def forward(self, logits, labels):
      shift_logits = logits[..., :-1, :].contiguous()
      shift_labels = labels[..., 1:].contiguous()
      # Flatten the tokens
      return self.loss_fn(
          shift_logits.view(-1, shift_logits.size(-1)),
          shift_labels.view(-1),
      )
  
imports: import argparse
  import time
  from functools import partial
  import torch
  from model_zoo import model_builder
  from torch import nn
  from colossalai.fx import ColoTracer
  from colossalai.fx.passes.adding_split_node_pass import gpipe_dp_split_pass, split_with_split_nodes_pass
  from colossalai.fx.passes.meta_info_prop import MetaInfoProp
  from colossalai.legacy.pipeline.middleware.adaptor import get_fx_topology
  from colossalai.legacy.pipeline.rpc._pipeline_schedule import FillDrainPipelineEngine
  from colossalai.legacy.pipeline.rpc.utils import rpc_run
  from colossalai.logging import disable_existing_loggers, get_dist_logger
label_desc: Use image node_id 2 for calling the GPTLMLoss obj's underlying member method code with example usage: obj.forward(logits, labels) and returns: self