protected Object handlePredicates(Node nd, ExprWalkerInfo prunePreds, OpWalkerInfo owi)
        throws SemanticException {
      if (HiveConf.getBoolVar(owi.getParseContext().getConf(),
          HiveConf.ConfVars.HIVE_PPD_REMOVE_DUPLICATE_FILTERS)) {
        return createFilter((Operator)nd, prunePreds.getResidualPredicates(true), owi);
      }
      return null;
    }
Determines predicates for which alias can be pushed to it's parents. See
the comments for getQualifiedAliases function.
ql/src/java/org/apache/hadoop/hive/ql/ppd/OpProcFactory.java