Marginal performance hack: use a dedicated routine instead of copyObject

to copy nodes that are known to be Vars during plan reference adjustment.
Saves useless memzero operation as well as the big switch in copyObject.

src/backend/optimizer/plan/setrefs.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/setrefs.c,v 1.134 2007/04/06 22:57:20 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/plan/setrefs.c,v 1.135 2007/04/30 00:16:43 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -565,6 +565,22 @@ trivial_subqueryscan(SubqueryScan *plan)
 	return true;
 }
 
+/*
+ * copyVar
+ *		Copy a Var node.
+ *
+ * fix_scan_expr and friends do this enough times that it's worth having
+ * a bespoke routine instead of using the generic copyObject() function.
+ */
+static inline Var *
+copyVar(Var *var)
+{
+	Var		   *newvar = (Var *) palloc(sizeof(Var));
+
+	*newvar = *var;
+	return newvar;
+}
+
 /*
  * fix_scan_expr
  *		Do set_plan_references processing on a scan-level expression
@@ -588,7 +604,7 @@ fix_scan_expr_mutator(Node *node, fix_scan_expr_context *context)
 		return NULL;
 	if (IsA(node, Var))
 	{
-		Var		   *var = (Var *) copyObject(node);
+		Var		   *var = copyVar((Var *) node);
 
 		Assert(var->varlevelsup == 0);
 		/*
@@ -1091,7 +1107,7 @@ search_indexed_tlist_for_var(Var *var, indexed_tlist *itlist,
 		if (vinfo->varno == varno && vinfo->varattno == varattno)
 		{
 			/* Found a match */
-			Var		   *newvar = (Var *) copyObject(var);
+			Var		   *newvar = copyVar(var);
 
 			newvar->varno = newvarno;
 			newvar->varattno = vinfo->resno;
@@ -1213,7 +1229,7 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
 		/* If it's for acceptable_rel, adjust and return it */
 		if (var->varno == context->acceptable_rel)
 		{
-			var = (Var *) copyObject(var);
+			var = copyVar(var);
 			var->varno += context->rtoffset;
 			var->varnoold += context->rtoffset;
 			return (Node *) var;