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