presto-main/src/main/java/io/prestosql/sql/planner/optimizations/IndexJoinOptimizer.java/IndexSourceRewriter/visitSort
class IndexSourceRewriter:        @Override
        public PlanNode visitSort(SortNode node, RewriteContext<Context> context)
        {
            // Sort has no bearing when building an index, so just ignore the sort
            return context.rewrite(node.getSource(), context.get());
        }