presto-main/src/main/java/io/prestosql/sql/planner/optimizations/PredicatePushDown.java/PredicatePushDown/visitPlan
class PredicatePushDown:        @Override
        public PlanNode visitPlan(PlanNode node, RewriteContext<Expression> context)
        {
            PlanNode rewrittenNode = context.defaultRewrite(node, TRUE_LITERAL);
            if (!context.get().equals(TRUE_LITERAL)) {
                // Drop in a FilterNode b/c we cannot push our predicate down any further
                rewrittenNode = new FilterNode(idAllocator.getNextId(), rewrittenNode, context.get());
            }
            return rewrittenNode;
        }