Improve jumble squashing through CoerceViaIO and RelabelType

There's no principled reason for query jumbling to only remove the first
layer of RelabelType and CoerceViaIO.  Change it to see through as many
layers as there are.

1 files changed, 16 insertions, 11 deletions

diff --git a/src/backend/nodes/queryjumblefuncs.c b/src/backend/nodes/queryjumblefuncs.c
index fb33e6931ad..62e3a677cd1 100644
--- a/src/backend/nodes/queryjumblefuncs.c
+++ b/src/backend/nodes/queryjumblefuncs.c
@@ -414,7 +414,7 @@ RecordConstLocation(JumbleState *jstate, int location, int len)
  * Subroutine for _jumbleElements: Verify a few simple cases where we can
  * deduce that the expression is a constant:
  *
- * - Ignore a possible wrapping RelabelType and CoerceViaIO.
+ * - See through any wrapping RelabelType and CoerceViaIO layers.
  * - If it's a FuncExpr, check that the function is a builtin
  *   cast and its arguments are Const.
  * - Otherwise test if the expression is a simple Const.
@@ -422,14 +422,22 @@ RecordConstLocation(JumbleState *jstate, int location, int len)
 static bool
 IsSquashableConstant(Node *element)
 {
-	if (IsA(element, RelabelType))
-		element = (Node *) ((RelabelType *) element)->arg;
-
-	if (IsA(element, CoerceViaIO))
-		element = (Node *) ((CoerceViaIO *) element)->arg;
-
+restart:
 	switch (nodeTag(element))
 	{
+		case T_RelabelType:
+			/* Unwrap RelabelType */
+			element = (Node *) ((RelabelType *) element)->arg;
+			goto restart;
+
+		case T_CoerceViaIO:
+			/* Unwrap CoerceViaIO */
+			element = (Node *) ((CoerceViaIO *) element)->arg;
+			goto restart;
+
+		case T_Const:
+			return true;
+
 		case T_FuncExpr:
 			{
 				FuncExpr   *func = (FuncExpr *) element;
@@ -468,11 +476,8 @@ IsSquashableConstant(Node *element)
 			}
 
 		default:
-			if (!IsA(element, Const))
-				return false;
+			return false;
 	}
-
-	return true;
 }
 
 /*