On head:
                                                                                         QUERY PLAN                                        
                                                 
-------------------------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------
 Limit  (cost=532028.06..532028.06 rows=1 width=44) (actual time=49213.313..49213.314 rows=1 loops=1)
   ->  Sort  (cost=532028.06..532480.72 rows=181066 width=44) (actual time=49213.311..49213.311 rows=1 loops=1)
         Sort Key: (count(DISTINCT partsupp.ps_suppkey)) DESC, part.p_brand, part.p_type, part.p_size
         Sort Method: top-N heapsort  Memory: 25kB
         ->  GroupAggregate  (cost=514691.25..531122.73 rows=181066 width=44) (actual time=45469.589..49191.025 rows=27840 loops=1)
               Group Key: part.p_brand, part.p_type, part.p_size
               ->  Sort  (cost=514691.25..517615.42 rows=1169665 width=44) (actual time=45469.337..46220.575 rows=2375516 loops=1)
                     Sort Key: part.p_brand, part.p_type, part.p_size
                     Sort Method: quicksort  Memory: 285943kB
                     ->  Hash Join  (cost=118466.06..396802.68 rows=1169665 width=44) (actual time=6431.135..26289.132 rows=2375516 loops=1
)
                           Hash Cond: (partsupp.ps_partkey = part.p_partkey)
                           ->  Seq Scan on partsupp  (cost=2959.85..239600.71 rows=7999762 width=16) (actual time=247.486..13048.239 rows=1
5991520 loops=1)
                                 Filter: (NOT (hashed SubPlan 1))
                                 Rows Removed by Filter: 8480
                                 SubPlan 1
                                   ->  Seq Scan on supplier  (cost=0.00..2959.80 rows=20 width=4) (actual time=0.479..247.334 rows=106 loop
s=1)
                                         Filter: ((s_comment)::text ~~ '%Customer%Complaints%'::text)
                                         Rows Removed by Filter: 199894
                           ->  Hash  (cost=108195.63..108195.63 rows=584847 width=40) (actual time=6182.670..6182.670 rows=594194 loops=1)
                                 Buckets: 1048576  Batches: 1  Memory Usage: 51237kB
                                 ->  Seq Scan on part  (cost=0.00..108195.63 rows=584847 width=40) (actual time=0.058..5649.112 rows=594194
 loops=1)
                                       Filter: ((p_brand <> 'Brand#31'::bpchar) AND ((p_type)::text !~~ 'PROMO BRUSHED%'::text) AND (p_size
 = ANY ('{41,4,15,12,42,46,32,30}'::integer[])))
                                       Rows Removed by Filter: 3405806
 Planning time: 1.165 ms
 Execution time: 49221.879 ms
(25 rows)

With patches: 
                                                                                            QUERY PLAN                                     
                                                       
-------------------------------------------------------------------------------------------------------------------------------------------
-------------------------------------------------------
 Limit  (cost=509008.82..509008.82 rows=1 width=44) (actual time=37272.962..37272.963 rows=1 loops=1)
   ->  Sort  (cost=509008.82..509461.49 rows=181066 width=44) (actual time=37272.960..37272.960 rows=1 loops=1)
         Sort Key: (count(DISTINCT partsupp.ps_suppkey)) DESC, part.p_brand, part.p_type, part.p_size
         Sort Method: top-N heapsort  Memory: 25kB
         ->  GroupAggregate  (cost=491672.02..508103.49 rows=181066 width=44) (actual time=33548.001..37250.009 rows=27840 loops=1)
               Group Key: part.p_brand, part.p_type, part.p_size
               ->  Sort  (cost=491672.02..494596.18 rows=1169665 width=44) (actual time=33547.593..34301.735 rows=2375516 loops=1)
                     Sort Key: part.p_brand, part.p_type, part.p_size
                     Sort Method: quicksort  Memory: 285943kB
                     ->  Gather  (cost=119466.06..373783.45 rows=1169665 width=44) (actual time=6563.283..14142.004 rows=2375516 loops=1)
                           Workers Planned: 2
                           Workers Launched: 2
                           ->  Hash Join  (cost=118466.06..255816.95 rows=1169665 width=44) (actual time=6846.209..13804.511 rows=791839 lo
ops=3)
                                 Hash Cond: (partsupp.ps_partkey = part.p_partkey)
                                 ->  Parallel Seq Scan on partsupp  (cost=2959.85..122937.51 rows=3333234 width=16) (actual time=245.699..4
741.889 rows=5330507 loops=3)
                                       Filter: (NOT (hashed SubPlan 1))
                                       Rows Removed by Filter: 2827
                                       SubPlan 1
                                         ->  Seq Scan on supplier  (cost=0.00..2959.80 rows=20 width=4) (actual time=0.474..245.544 rows=10
6 loops=3)
                                               Filter: ((s_comment)::text ~~ '%Customer%Complaints%'::text)
                                               Rows Removed by Filter: 199894
                                 ->  Hash  (cost=108195.63..108195.63 rows=584847 width=40) (actual time=6599.562..6599.562 rows=594194 loo
ps=3)
                                       Buckets: 1048576  Batches: 1  Memory Usage: 51237kB
                                       ->  Seq Scan on part  (cost=0.00..108195.63 rows=584847 width=40) (actual time=0.062..6067.231 rows=
594194 loops=3)
                                             Filter: ((p_brand <> 'Brand#31'::bpchar) AND ((p_type)::text !~~ 'PROMO BRUSHED%'::text) AND (
p_size = ANY ('{41,4,15,12,42,46,32,30}'::integer[])))
                                             Rows Removed by Filter: 3405806
 Planning time: 1.100 ms
 Execution time: 37281.209 ms
(28 rows)