Original query:

david=# set enable_sort=false;
SET
Time: 0.182 ms
david=# explain SELECT DISTINCT v                                                           FROM (VALUES ('1.2.1'::SEMVER), ('1.2.1-RC1'), ('2.0.0-ALPH')) AS v(v);
                             QUERY PLAN                             
--------------------------------------------------------------------
 HashAggregate  (cost=0.05..0.08 rows=3 width=32)
   Group Key: "*VALUES*".column1
   ->  Values Scan on "*VALUES*"  (cost=0.00..0.04 rows=3 width=32)
(3 rows)