private RelNode visitJoin(BiRel join) {
      final int x = offset.get();
      visitChild(join, 0, join.getLeft());
      offset.set(x + join.getLeft().getRowType().getFieldCount());
      visitChild(join, 1, join.getRight());
      offset.set(x);
      return join;
    }
Creates a CorelMap by iterating over a {@link RelNode} tree.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java