Match RelOptInfos by relids not pointer equality.

Commit 1c2cb2744 added some code that tried to detect whether two
RelOptInfos were the "same" rel by pointer comparison; but it turns
out that inheritance_planner breaks that, through its shenanigans
with copying some relations forward into new subproblems.  Compare
relid sets instead.  Add a regression test case to exercise this
area.

Problem reported by Rushabh Lathia; diagnosis and fix by Amit Langote,
modified a bit by me.

Discussion: https://postgr.es/m/CAGPqQf3anJGj65bqAQ9edDr8gF7qig6_avRgwMT9MsZ19COUPw@mail.gmail.com

src/backend/partitioning/partprune.c

@@ -384,7 +384,7 @@ make_partitionedrel_pruneinfo(PlannerInfo *root, RelOptInfo *parentrel,
 			 * because in later iterations of the loop for child partitions,
 			 * we want to translate from parent to child variables.
 			 */
-			if (parentrel != subpart)
+			if (!bms_equal(parentrel->relids, subpart->relids))
 			{
 				int			nappinfos;
 				AppendRelInfo **appinfos = find_appinfos_by_relids(root,

src/test/regress/expected/partition_prune.out

@@ -2477,6 +2477,85 @@ deallocate ab_q2;
 deallocate ab_q3;
 deallocate ab_q4;
 deallocate ab_q5;
+-- UPDATE on a partition subtree has been seen to have problems.
+insert into ab values (1,2);
+explain (analyze, costs off, summary off, timing off)
+update ab_a1 set b = 3 from ab where ab.a = 1 and ab.a = ab_a1.a;
+                                     QUERY PLAN                                      
+-------------------------------------------------------------------------------------
+ Update on ab_a1 (actual rows=0 loops=1)
+   Update on ab_a1_b1
+   Update on ab_a1_b2
+   Update on ab_a1_b3
+   ->  Nested Loop (actual rows=0 loops=1)
+         ->  Append (actual rows=1 loops=1)
+               ->  Bitmap Heap Scan on ab_a1_b1 ab_a1_b1_1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b1_a_idx (actual rows=0 loops=1)
+                           Index Cond: (a = 1)
+               ->  Bitmap Heap Scan on ab_a1_b2 ab_a1_b2_1 (actual rows=1 loops=1)
+                     Recheck Cond: (a = 1)
+                     Heap Blocks: exact=1
+                     ->  Bitmap Index Scan on ab_a1_b2_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+               ->  Bitmap Heap Scan on ab_a1_b3 ab_a1_b3_1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=0 loops=1)
+                           Index Cond: (a = 1)
+         ->  Materialize (actual rows=0 loops=1)
+               ->  Bitmap Heap Scan on ab_a1_b1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b1_a_idx (actual rows=0 loops=1)
+                           Index Cond: (a = 1)
+   ->  Nested Loop (actual rows=1 loops=1)
+         ->  Append (actual rows=1 loops=1)
+               ->  Bitmap Heap Scan on ab_a1_b1 ab_a1_b1_1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b1_a_idx (actual rows=0 loops=1)
+                           Index Cond: (a = 1)
+               ->  Bitmap Heap Scan on ab_a1_b2 ab_a1_b2_1 (actual rows=1 loops=1)
+                     Recheck Cond: (a = 1)
+                     Heap Blocks: exact=1
+                     ->  Bitmap Index Scan on ab_a1_b2_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+               ->  Bitmap Heap Scan on ab_a1_b3 ab_a1_b3_1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+         ->  Materialize (actual rows=1 loops=1)
+               ->  Bitmap Heap Scan on ab_a1_b2 (actual rows=1 loops=1)
+                     Recheck Cond: (a = 1)
+                     Heap Blocks: exact=1
+                     ->  Bitmap Index Scan on ab_a1_b2_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+   ->  Nested Loop (actual rows=0 loops=1)
+         ->  Append (actual rows=1 loops=1)
+               ->  Bitmap Heap Scan on ab_a1_b1 ab_a1_b1_1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b1_a_idx (actual rows=0 loops=1)
+                           Index Cond: (a = 1)
+               ->  Bitmap Heap Scan on ab_a1_b2 ab_a1_b2_1 (actual rows=1 loops=1)
+                     Recheck Cond: (a = 1)
+                     Heap Blocks: exact=1
+                     ->  Bitmap Index Scan on ab_a1_b2_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+               ->  Bitmap Heap Scan on ab_a1_b3 ab_a1_b3_1 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+         ->  Materialize (actual rows=0 loops=1)
+               ->  Bitmap Heap Scan on ab_a1_b3 (actual rows=0 loops=1)
+                     Recheck Cond: (a = 1)
+                     ->  Bitmap Index Scan on ab_a1_b3_a_idx (actual rows=1 loops=1)
+                           Index Cond: (a = 1)
+(65 rows)
+
+table ab;
+ a | b 
+---+---
+ 1 | 3
+(1 row)
+
 drop table ab, lprt_a;
 -- Join
 create table tbl1(col1 int);

src/test/regress/sql/partition_prune.sql

@@ -554,6 +554,12 @@ deallocate ab_q3;
 deallocate ab_q4;
 deallocate ab_q5;
 
+-- UPDATE on a partition subtree has been seen to have problems.
+insert into ab values (1,2);
+explain (analyze, costs off, summary off, timing off)
+update ab_a1 set b = 3 from ab where ab.a = 1 and ab.a = ab_a1.a;
+table ab;
+
 drop table ab, lprt_a;
 
 -- Join