--Benchmark with the following code:

/*
	else if (sjinfo->jointype == JOIN_SEMI)
		{
			List	   *columnlist;
			RelOptInfo *rel;
			bool result;
			int x;

			for (x = 0; x < 1000000; x++)
				result = semiorantijoin_is_removable(root, sjinfo, &columnlist, &rel);

			/* Skip if not removable */
			if (!result)
				continue;

			Assert(columnlist != NIL);
			convert_semijoin_to_isnotnull_quals(root, rel, columnlist);
		}
*/

create table t2 (id int primary key);
create table t1 (value1 int references t2, value2 int, value3 int, value4 int);

-- test 1. Successful removal with single fk
explain select * from t1 where value1 in(select id from t2);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
425.019
413.903
407.200
411.014
411.370

-- as above, but with with bms_get_singleton patch applied
405.971
390.838
401.959
407.593
393.540

-- unpatched master planning time for above query
0.207
0.216
0.203
0.194
0.200

-- test 2. Non var in outer join condition.
explain select * from t1 where value1 in(select 0 from t2);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
40.419
40.374
36.831
42.832
40.248

-- as above, but with with bms_get_singleton patch applied
31.064
32.176
30.028
31.654
34.571

-- unpatched master planning time for above query
0.169
0.171
0.156
0.155
0.157

-- test 3. Fail case. No foreign key defined.
explain select * from t1 where value2 in(select id from t2);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
409.801
414.237
406.165
406.959
401.322

-- as above, but with with bms_get_singleton patch applied
367.536
347.254
349.383
348.291
348.063

-- unpatched master planning time for above query
0.214
0.200
0.199
0.195
0.248

-- test 4. 2 foreign keys defined. (with join removed)
ALTER TABLE t1 ADD CONSTRAINT t1_value2_fkey FOREIGN KEY (value2) REFERENCES t2;

explain select * from t1 where value2 in(select id from t2);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
431.408
421.737
426.109
419.222
418.526

-- as above, but with with bms_get_singleton patch applied
392.525
392.785
393.102
388.653
393.168

-- unpatched master planning time for above query
0.211
0.201
0.235
0.236
0.230

-- test 5. 2 foreign keys defined (without join removed)
explain select * from t1 where value3 in(select id from t2);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
426.327
423.019
431.331
423.405
413.779

-- as above, but with with bms_get_singleton patch applied
411.991
412.971
402.479
405.715
416.528

-- unpatched master planning time for above query
0.237
0.261
0.266
0.214
0.218

-- test 6. wrong operator.
explain select * from t1 where exists(select 1 from t2 where value1 > id);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
122.176
117.536
119.057
125.618
118.249

-- as above, but with with bms_get_singleton patch applied
109.182
108.424
109.526
110.091
107.240

-- unpatched master planning time for above query
0.181
0.220
0.171
0.178
0.170

-- test 7. No foreign keys
alter table t1 drop constraint t1_value1_fkey;
alter table t1 drop constraint t1_value2_fkey;

explain select * from t1 where value1 in(select id from t2);

--times in milliseconds for planning plus 1 million semiorantijoin_is_removable calls
21.320
20.776
20.984
20.564
20.845

-- as above, but with with bms_get_singleton patch applied
15.353
15.450
15.295
15.354
16.239

-- unpatched master planning time for above query
0.191
0.200
0.219
0.193
0.204