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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _fix(node):
 """Fix the naive construction of the adjont. See `fixes.py` for details. This function also returns the result of reaching definitions analysis so that `split` mode can use this to carry over the state from primal to adjoint. Args: node: A module with the primal and adjoint function definitions as returned by `reverse_ad`. Returns: node: A module with the primal and adjoint function with additional variable definitions and such added so that pushes onto the stack and gradient accumulations are all valid. defined: The variables defined at the end of the primal. reaching: The variable definitions that reach the end of the primal. """

  # Do reaching definitions analysis on primal and adjoint
  pri_cfg = cfg.CFG.build_cfg(node.body[0])
  defined = cfg.Defined()
  defined.visit(pri_cfg.entry)
  reaching = cfg.ReachingDefinitions()
  reaching.visit(pri_cfg.entry)

  cfg.forward(node.body[1], cfg.Defined())
  cfg.forward(node.body[1], cfg.ReachingDefinitions())

  # Remove pushes of variables that were never defined
  fixes.CleanStack().visit(node)
  fixes.FixStack().visit(node.body[0])

  # Change accumulation into definition if possible
  fixes.CleanGrad().visit(node.body[1])
  # Define gradients that might or might not be defined
  fixes.FixGrad().visit(node.body[1])
  return node, defined.exit, reaching.exit