Fix oversight in 8.0 modification of RestrictInfo data structures.

A RestrictInfo representing an OR clause now contains two versions of
the contained expression, one with sub-RestrictInfos and one without.
clause_selectivity() should descend to the version with sub-RestrictInfos
so that it has a chance of caching its results for the OR's sub-clauses.
Failing to do so resulted in redundant planner effort.

src/backend/optimizer/path/clausesel.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.73 2005/06/05 22:32:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/path/clausesel.c,v 1.74 2005/10/11 16:44:40 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -461,8 +461,15 @@ clause_selectivity(PlannerInfo *root,
 			}
 		}
 
-		/* Proceed with examination of contained clause */
-		clause = (Node *) rinfo->clause;
+		/*
+		 * Proceed with examination of contained clause.  If the clause is an
+		 * OR-clause, we want to look at the variant with sub-RestrictInfos,
+		 * so that per-subclause selectivities can be cached.
+		 */
+		if (rinfo->orclause)
+			clause = (Node *) rinfo->orclause;
+		else
+			clause = (Node *) rinfo->clause;
 	}
 
 	if (IsA(clause, Var))