// backedges of the graph, orders the nodes and infers the shapes.
  // PrepareConvert needs to ensure that the original `graph` is cloned prior
  // execution. The cloning procedure relies on the roundtrip through the
  // GraphDef. Graph to GraphDef def conversion is heavy, in case, `graph_def`
  // was obtained previously provide it to the PrepareConvert to reuse.
  Status PrepareConvert(const Graph& graph,