The following analysis is based on version 15.14, but also applies to later versions.
Function join_clause_is_movable_to() is called from multiple callers, like match_join_clauses_to_index(), extract_restriction_or_clauses(), etc. When called from match_join_clauses_to_index(), it's necessary to perform the 4th check, i.e. if (bms_overlap(baserel->lateral_referencers, rinfo->clause_relids)), because the referencers can't be put on the outer side of a nestloop with the target relation. However, when called from extract_restriction_or_clauses(), the 4th check is unnecessary because what we are going to do is not putting referencers on the outer side of a nestloop with the target relation, but extracting restriction for the target rel from the or-clause and push the extracted restriction to the target rel, which does no harm even if the target rel has lateral referencers. For example, consider this query:
select * from a, lateral(select sum(b1),sum(b2),b3,b4 from b where b3+b4<a1+a2 group by b3,b4 )I where (b3=a3 and a4=74) or (b3=a3-99 and a4=12);
removing the 4th check from join_clause_is_movable_to() when it is called from extract_restriction_or_clauses() can produce a plan which push (a4 = 74 OR a4 = 12) to relation A in the first place, significantly accelerating execution. So I suggest add an additional parameter to join_clause_is_movable_to() to indicate its caller, if it's called from extract_restriction_or_clauses(), simply skip the 4th check for lateral referencers.
Best Regards
