CorelMap build(RelNode rel) {
      stripHep(rel).accept(this);
      return new CorelMap(mapRefRelToCorRef, mapCorToCorRel,
              mapFieldAccessToCorVar);
    }
Creates a CorelMap by iterating over a {@link RelNode} tree.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveRelDecorrelator.java