public void setRootOperators(Deque<Operator<? extends OperatorDesc>> roots) {
    this.rootOperators = roots;
  }
OptimizeTezProcContext. OptimizeTezProcContext maintains information
about the current operator plan as we walk the operator tree
to do some additional optimizations on it.
ql/src/java/org/apache/hadoop/hive/ql/parse/OptimizeTezProcContext.java