// corresponds to a constant value.
  ValuePortResultMap results_;

  // Map from a function to the callers of that function.
  SymbolTableCollection symbol_table_;
  SymbolUserMap symbol_users_;

  // Queue of functions being processed.
  llvm::DenseSet<func::FuncOp> queue_set_;
  std::queue<func::FuncOp> queue_;

  int64_t graph_version_;