Replace has_multiple_baserels() with a bitmap test on all_baserels.

Since we added the PlannerInfo.all_baserels set, it's not really
necessary to grovel over the rangetable to count baserels in the
current query.  So let's drop has_multiple_baserels() in favor
of a bms_membership() test.  This might be microscopically
faster, but the main point is to remove some unnecessary code.

Richard Guo

Discussion: https://postgr.es/m/CAMbWs4_8RcSbbfs1ASZLrMuL0c0EQgXWcoLTQD8swBRY_pQQiA@mail.gmail.com

Author: tglsfdc

src/backend/optimizer/path/allpaths.c

@@ -2190,28 +2190,6 @@ set_dummy_rel_pathlist(RelOptInfo *rel)
 	set_cheapest(rel);
 }
 
-/* quick-and-dirty test to see if any joining is needed */
-static bool
-has_multiple_baserels(PlannerInfo *root)
-{
-	int			num_base_rels = 0;
-	Index		rti;
-
-	for (rti = 1; rti < root->simple_rel_array_size; rti++)
-	{
-		RelOptInfo *brel = root->simple_rel_array[rti];
-
-		if (brel == NULL)
-			continue;
-
-		/* ignore RTEs that are "other rels" */
-		if (brel->reloptkind == RELOPT_BASEREL)
-			if (++num_base_rels > 1)
-				return true;
-	}
-	return false;
-}
-
 /*
  * find_window_run_conditions
  *		Determine if 'wfunc' is really a WindowFunc and call its prosupport
@@ -2661,7 +2639,7 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
 		root->hasHavingQual ||
 		parse->distinctClause ||
 		parse->sortClause ||
-		has_multiple_baserels(root))
+		bms_membership(root->all_baserels) == BMS_MULTIPLE)
 		tuple_fraction = 0.0;	/* default case */
 	else
 		tuple_fraction = root->tuple_fraction;