Fix potential memleak with singleton CTE subplan

src/backend/optimizer/path/allpaths.c

@@ -2140,9 +2140,20 @@ set_cte_pathlist(PlannerInfo *root, RelOptInfo *rel, RangeTblEntry *rte)
 		 * shared plan with another SegmentGeneral node. Thus, we should avoid
 		 * sharing SegmentGeneral subplans.
 		 */
-		subplan = (cteplaninfo->subplan->flow->locustype != CdbLocusType_SegmentGeneral) ?
-		          share_prepared_plan(cteroot, cteplaninfo->subplan) :
-		          (Plan *) copyObject(cteplaninfo->subplan);
+		if (cteplaninfo->subplan->flow->locustype != CdbLocusType_SegmentGeneral)
+		{
+			subplan = share_prepared_plan(cteroot, cteplaninfo->subplan);
+		}
+		else
+		{
+			/*
+			 * If we are not sharing and subplan was created just now, use it.
+			 * Otherwise, make a copy of it to avoid construction of DAG
+			 * instead of a tree.
+			 */
+			if (subplan == NULL)
+				subplan = (Plan *) copyObject(cteplaninfo->subplan);
+		}
 
 		subroot = cteplaninfo->subroot;
 	}

src/test/regress/expected/with.out

@@ -2290,9 +2290,9 @@ DROP TABLE IF EXISTS r;
 NOTICE:  table "r" does not exist, skipping
 --end_ignore
 CREATE TABLE d (a int, b int) DISTRIBUTED BY (a);
-INSERT INTO d VALUES (1,2),(2,3);
+INSERT INTO d VALUES ( 1, 2 ),( 2, 3 );
 CREATE TABLE r (a int, b int) DISTRIBUTED REPLICATED;
-INSERT INTO r VALUES (1,2),(3,4);
+INSERT INTO r VALUES ( 1, 2 ),( 3, 4 );
 EXPLAIN (COSTS off)
 WITH cte AS (
     SELECT count(*) a FROM r

src/test/regress/sql/with.sql

@@ -1093,9 +1093,9 @@ DROP TABLE IF EXISTS r;
 --end_ignore
 
 CREATE TABLE d (a int, b int) DISTRIBUTED BY (a);
-INSERT INTO d VALUES (1,2),(2,3);
+INSERT INTO d VALUES ( 1, 2 ),( 2, 3 );
 CREATE TABLE r (a int, b int) DISTRIBUTED REPLICATED;
-INSERT INTO r VALUES (1,2),(3,4);
+INSERT INTO r VALUES ( 1, 2 ),( 3, 4 );
 
 EXPLAIN (COSTS off)
 WITH cte AS (