private static ImmutableBitSet fieldBitmap(RexNode joinFilter) {
    final RelOptUtil.InputFinder inputFinder = new RelOptUtil.InputFinder();
    joinFilter.accept(inputFinder);
    return inputFinder.build();
  }
Returns a bitmap representing the factors referenced in a join filter.

@param joinFilter the join filter
@param setFields if true, add the fields referenced by the join filter
into a map

@return the bitmap containing the factor references
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveLoptMultiJoin.java