code: def comm_fusion_with_concat(
      gm: IterGraphModule,
      bucket_size_mb: int,
  ) -> None:
      """Run fuse communication with concat.
  
      This implementation uses concat to concat the bucketed gradients.
      """
      comm_blocks = get_all_comm_blocks(
          gm, (CommType.ALLREDUCE, "all_reduce")
      )
      # First ensure the allreduce are scheduled immediately right after the gradients.
      _expedite_comm_ops(gm, comm_blocks)
      # Get the comm_blocks based on the new order.
      comm_blocks = get_all_comm_blocks(
          gm, (CommType.ALLREDUCE, "all_reduce")
      )
      node_indices = {node: i for i, node in enumerate(gm.graph.nodes)}
  
      bucket_size = 1 * 1024**2
      bucket_cap_size = bucket_size_mb * 1024**2
      begin = end = curr_size = 0
      while end < len(comm_blocks):
          # TODO: determine the dtype
          curr_size += (
              cast(torch.Size, comm_blocks[end].shape).numel() * 4
          )
          end += 1
          if curr_size < bucket_size:
              continue
          _fuse_with_cat(gm, comm_blocks[begin:end], node_indices)
          bucket_size = bucket_cap_size
          begin = end
          curr_size = 0
      else:
          if begin < len(comm_blocks):
              _fuse_with_cat(gm, comm_blocks[begin:end], node_indices)
  
imports: import collections
  import itertools
  import logging
  import operator
  import tempfile
  import time
  from dataclasses import dataclass, field
  from functools import wraps
  from typing import Any, Callable, cast, DefaultDict, Dict, Iterable, List, Optional, Set, Tuple, Union
  import torch
  import torch.fx
  from torch._subclasses.fake_tensor import FakeTensor, FakeTensorMode
  from torch.distributed._spmd.graph_utils import CommType, dump_graphs_to_files, find_node, get_output, OP
  from torch.distributed._spmd.iter_graph_module import IterGraphModule
  from torch.fx.passes.shape_prop import TensorMetadata
  from torch.utils import _pytree
  from torch.utils._pytree import tree_flatten, tree_unflatten
label_desc: Use image node_id 11 for calling a global function with example usage: comm_fusion_with_concat(gm, bucket_size_mb) without return types