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