code: def _low_precision_hook(
      prec: torch.dtype,
      state: LowPrecisionState,
      grad: torch.Tensor,
      output: torch.Tensor,
  ):
      if grad.dtype != prec:
          grad.data = grad.data.to(prec)
      if output is not None:
          if output.dtype != prec:
              output.data = output.data.to(prec)
          reduce_scatter_hook(state, grad, output)
          _decompress(state, output)
      else:
          allreduce_hook(state, grad)
          _decompress(state, grad)
  
file_path: pytorch/torch/distributed/algorithms/_comm_hooks/default_hooks.py
imports: import functools
  import torch
  import torch.distributed
  from typing import Optional
label_desc: Use image node_id 4 for calling a global function with example usage: _low_precision_hook(prec, state, grad, output) without return types