private Double costPerTuple(RexNode e) {
      return e.accept(new RexFunctionCost());
    }
Nodes in an OR clause are sorted by a rank value calculated as:
rank = (-selectivity) / cost per tuple
The intuition is that less selective/cheaper conditions should be evaluated
first in the OR clause, since TRUE will end the evaluation.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveFilterSortPredicates.java