typedef std::map<PBQP::Graph::ConstNodeItr, unsigned,
PBQP::NodeItrComparator> Node2VReg;
typedef DenseMap<unsigned, PBQP::Graph::NodeItr> VReg2Node;
typedef std::map<PBQP::Graph::ConstNodeItr, unsigned,
PBQP::NodeItrComparator> Node2VReg;
typedef DenseMap<unsigned, PBQP::Graph::NodeItr> VReg2Node;