@Override
    public RelNode visit(final HiveFilter filter) {
      try {
        Stacks.push(stack, filter);
        filter.getCondition().accept(rexVisitor(filter));
      } finally {
        Stacks.pop(stack, filter);
      }
      return super.visit(filter);
    }
Creates a CorelMap by iterating over a {@link RelNode} tree.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java