Improve RowMark handling during Self-Join Elimination

The Self-Join Elimination SJE feature messes up keeping and removing RowMark's
in remove_self_joins_one_group().  That didn't lead to user-level error,
because the planned RowMark is only used to reference a rtable entry in later
execution stages.  An RTE entry for keeping and removing relations is
identical and refers to the same relation OID.

To reduce confusion and prevent future issues, this commit cleans up the code
and fixes the incorrect behaviour.  Furthermore, it includes sanity checks in
setrefs.c on existing non-null RTE and RelOptInfo entries for each RowMark.

Discussion: https://postgr.es/m/18c6bd6c-6d2a-419a-b0da-dfedef34b585%40gmail.com
Author: Andrei Lepikhov <lepihov@gmail.com>
Reviewed-by: Greg Sabino Mullane <htamfids@gmail.com>
Backpatch-through: 18

src/backend/optimizer/plan/analyzejoins.c

@@ -631,6 +631,7 @@ remove_leftjoinrel_from_query(PlannerInfo *root, int relid,
 	 * remove_join_clause_from_rels will touch it.)
 	 */
 	root->simple_rel_array[relid] = NULL;
+	root->simple_rte_array[relid] = NULL;
 
 	/* And nuke the RelOptInfo, just in case there's another access path */
 	pfree(rel);
@@ -1979,10 +1980,12 @@ remove_self_join_rel(PlannerInfo *root, PlanRowMark *kmark, PlanRowMark *rmark,
 	 * remove_join_clause_from_rels will touch it.)
 	 */
 	root->simple_rel_array[toRemove->relid] = NULL;
+	root->simple_rte_array[toRemove->relid] = NULL;
 
 	/* And nuke the RelOptInfo, just in case there's another access path. */
 	pfree(toRemove);
 
+
 	/*
 	 * Now repeat construction of attr_needed bits coming from all other
 	 * sources.
@@ -2194,12 +2197,12 @@ remove_self_joins_one_group(PlannerInfo *root, Relids relids)
 			{
 				PlanRowMark *rowMark = (PlanRowMark *) lfirst(lc);
 
-				if (rowMark->rti == k)
+				if (rowMark->rti == r)
 				{
 					Assert(rmark == NULL);
 					rmark = rowMark;
 				}
-				else if (rowMark->rti == r)
+				else if (rowMark->rti == k)
 				{
 					Assert(kmark == NULL);
 					kmark = rowMark;
@@ -2254,7 +2257,7 @@ remove_self_joins_one_group(PlannerInfo *root, Relids relids)
 			selfjoinquals = list_concat(selfjoinquals, krel->baserestrictinfo);
 
 			/*
-			 * Determine if the rrel can duplicate outer rows.  We must bypass
+			 * Determine if the rrel can duplicate outer rows. We must bypass
 			 * the unique rel cache here since we're possibly using a subset
 			 * of join quals. We can use 'force_cache' == true when all join
 			 * quals are self-join quals.  Otherwise, we could end up putting

src/backend/optimizer/plan/setrefs.c

@@ -307,6 +307,10 @@ set_plan_references(PlannerInfo *root, Plan *plan)
 		PlanRowMark *rc = lfirst_node(PlanRowMark, lc);
 		PlanRowMark *newrc;
 
+		/* sanity check on existing row marks */
+		Assert(root->simple_rel_array[rc->rti] != NULL &&
+			   root->simple_rte_array[rc->rti] != NULL);
+
 		/* flat copy is enough since all fields are scalars */
 		newrc = (PlanRowMark *) palloc(sizeof(PlanRowMark));
 		memcpy(newrc, rc, sizeof(PlanRowMark));