Function calc_nestloop_required_outer

src/backend/optimizer/util/pathnode.c:3804–3829

* calc_nestloop_required_outer * Compute the required_outer set for a nestloop join path * * Note: result must not share storage with either input */

 * Note: result must not share storage with either input
 */
Relids
calc_nestloop_required_outer(Relids outerrelids,
							 Relids outer_paramrels,
							 Relids innerrelids,
							 Relids inner_paramrels)
{
	Relids		required_outer;

	/* inner_path can require rels from outer path, but not vice versa */
	Assert(!bms_overlap(outer_paramrels, innerrelids));
	/* easy case if inner path is not parameterized */
	if (!inner_paramrels)
		return bms_copy(outer_paramrels);
	/* else, form the union ... */
	required_outer = bms_union(outer_paramrels, inner_paramrels);
	/* ... and remove any mention of now-satisfied outer rels */
	required_outer = bms_del_members(required_outer,
									 outerrelids);
	/* maintain invariant that required_outer is exactly NULL if empty */
	if (bms_is_empty(required_outer))
	{
		bms_free(required_outer);
		required_outer = NULL;
	}
	return required_outer;
}

/*
 * calc_non_nestloop_required_outer