public static SemanticNodeProcessor getStopProc() {
    return new ConstantPropagateStopProc();
  }
The Node Processor for Constant Propagation for Operators which is designed to stop propagate.
Currently these kinds of Operators include UnionOperator and ScriptOperator.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/ConstantPropagateProcFactory.java