public ImmutableBitSet getFieldsRefByJoinFilter(RexNode joinFilter) {
    return requireNonNull(
            fieldsRefByJoinFilter.get(joinFilter),
            () -> "joinFilter is not found in fieldsRefByJoinFilter: " + joinFilter);
  }
Returns a bitmap corresponding to the fields referenced by a join filter.

@param joinFilter the filter for which information will be returned
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveLoptMultiJoin.java