Add bms_next_member(), and use it where appropriate.

This patch adds a way of iterating through the members of a bitmapset
nondestructively, unlike the old way with bms_first_member().  While
bms_next_member() is very slightly slower than bms_first_member()
(at least for typical-size bitmapsets), eliminating the need to palloc
and pfree a temporary copy of the target bitmapset is a significant win.
So this method should be preferred in all cases where a temporary copy
would be necessary.

Tom Lane, with suggestions from Dean Rasheed and David Rowley

src/backend/optimizer/path/allpaths.c

@@ -2272,19 +2272,17 @@ remove_unused_subquery_outputs(Query *subquery, RelOptInfo *rel)
 static void
 print_relids(Relids relids)
 {
-	Relids		tmprelids;
 	int			x;
 	bool		first = true;
 
-	tmprelids = bms_copy(relids);
-	while ((x = bms_first_member(tmprelids)) >= 0)
+	x = -1;
+	while ((x = bms_next_member(relids, x)) >= 0)
 	{
 		if (!first)
 			printf(" ");
 		printf("%d", x);
 		first = false;
 	}
-	bms_free(tmprelids);
 }
 
 static void

src/backend/optimizer/path/indxpath.c

@@ -1875,9 +1875,8 @@ get_loop_count(PlannerInfo *root, Relids outer_relids)
 	{
 		int			relid;
 
-		/* Need a working copy since bms_first_member is destructive */
-		outer_relids = bms_copy(outer_relids);
-		while ((relid = bms_first_member(outer_relids)) >= 0)
+		relid = -1;
+		while ((relid = bms_next_member(outer_relids, relid)) >= 0)
 		{
 			RelOptInfo *outer_rel;
 
@@ -1900,7 +1899,6 @@ get_loop_count(PlannerInfo *root, Relids outer_relids)
 			if (result == 1.0 || result > outer_rel->rows)
 				result = outer_rel->rows;
 		}
-		bms_free(outer_relids);
 	}
 	return result;
 }

src/backend/optimizer/util/joininfo.c

@@ -96,17 +96,15 @@ add_join_clause_to_rels(PlannerInfo *root,
 						RestrictInfo *restrictinfo,
 						Relids join_relids)
 {
-	Relids		tmprelids;
 	int			cur_relid;
 
-	tmprelids = bms_copy(join_relids);
-	while ((cur_relid = bms_first_member(tmprelids)) >= 0)
+	cur_relid = -1;
+	while ((cur_relid = bms_next_member(join_relids, cur_relid)) >= 0)
 	{
 		RelOptInfo *rel = find_base_rel(root, cur_relid);
 
 		rel->joininfo = lappend(rel->joininfo, restrictinfo);
 	}
-	bms_free(tmprelids);
 }
 
 /*
@@ -125,11 +123,10 @@ remove_join_clause_from_rels(PlannerInfo *root,
 							 RestrictInfo *restrictinfo,
 							 Relids join_relids)
 {
-	Relids		tmprelids;
 	int			cur_relid;
 
-	tmprelids = bms_copy(join_relids);
-	while ((cur_relid = bms_first_member(tmprelids)) >= 0)
+	cur_relid = -1;
+	while ((cur_relid = bms_next_member(join_relids, cur_relid)) >= 0)
 	{
 		RelOptInfo *rel = find_base_rel(root, cur_relid);
 
@@ -140,5 +137,4 @@ remove_join_clause_from_rels(PlannerInfo *root,
 		Assert(list_member_ptr(rel->joininfo, restrictinfo));
 		rel->joininfo = list_delete_ptr(rel->joininfo, restrictinfo);
 	}
-	bms_free(tmprelids);
 }

src/backend/optimizer/util/var.c

@@ -773,11 +773,10 @@ static Relids
 alias_relid_set(PlannerInfo *root, Relids relids)
 {
 	Relids		result = NULL;
-	Relids		tmprelids;
 	int			rtindex;
 
-	tmprelids = bms_copy(relids);
-	while ((rtindex = bms_first_member(tmprelids)) >= 0)
+	rtindex = -1;
+	while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
 	{
 		RangeTblEntry *rte = rt_fetch(rtindex, root->parse->rtable);
 
@@ -786,6 +785,5 @@ alias_relid_set(PlannerInfo *root, Relids relids)
 		else
 			result = bms_add_member(result, rtindex);
 	}
-	bms_free(tmprelids);
 	return result;
 }