Disable transforms that replaced AT TIME ZONE with RelabelType.

These resulted in wrong answers if the relabeled argument could be matched
to an index column, as shown in bug #14504 from Evgeniy Kozlov.  We might
be able to resurrect these optimizations by adjusting the planner's
treatment of RelabelType, or by adjusting btree's rules for selecting
comparison functions, but either solution will take careful analysis
and does not sound like a fit candidate for backpatching.

I left the catalog infrastructure in place and just reduced the transform
functions to always-return-NULL.  This would be necessary anyway in the
back branches, and it doesn't seem important to be more invasive in HEAD.

Bug introduced by commit b8a18ad4.  Back-patch to 9.5 where that came in.

Report: https://postgr.es/m/20170118144828.1432.52823@wrigleys.postgresql.org
Discussion: https://postgr.es/m/18771.1484759439@sss.pgh.pa.us

src/backend/utils/adt/timestamp.c

@@ -5202,84 +5202,15 @@ interval_part(PG_FUNCTION_ARGS)
 
 
 /* timestamp_zone_transform()
- * If the zone argument of a timestamp_zone() or timestamptz_zone() call is a
- * plan-time constant denoting a zone equivalent to UTC, the call will always
- * return its second argument unchanged.  Simplify the expression tree
- * accordingly.  Civil time zones almost never qualify, because jurisdictions
- * that follow UTC today have not done so continuously.
+ * The original optimization here caused problems by relabeling Vars that
+ * could be matched to index entries.  It might be possible to resurrect it
+ * at some point by teaching the planner to be less cavalier with RelabelType
+ * nodes, but that will take careful analysis.
  */
 Datum
 timestamp_zone_transform(PG_FUNCTION_ARGS)
 {
-	Node	   *func_node = (Node *) PG_GETARG_POINTER(0);
-	FuncExpr   *expr = (FuncExpr *) func_node;
-	Node	   *ret = NULL;
-	Node	   *zone_node;
-
-	Assert(IsA(expr, FuncExpr));
-	Assert(list_length(expr->args) == 2);
-
-	zone_node = (Node *) linitial(expr->args);
-
-	if (IsA(zone_node, Const) &&!((Const *) zone_node)->constisnull)
-	{
-		text	   *zone = DatumGetTextPP(((Const *) zone_node)->constvalue);
-		char		tzname[TZ_STRLEN_MAX + 1];
-		char	   *lowzone;
-		int			type,
-					abbrev_offset;
-		pg_tz	   *tzp;
-		bool		noop = false;
-
-		/*
-		 * If the timezone is forever UTC+0, the FuncExpr function call is a
-		 * no-op for all possible timestamps.  This passage mirrors code in
-		 * timestamp_zone().
-		 */
-		text_to_cstring_buffer(zone, tzname, sizeof(tzname));
-		lowzone = downcase_truncate_identifier(tzname,
-											   strlen(tzname),
-											   false);
-		type = DecodeTimezoneAbbrev(0, lowzone, &abbrev_offset, &tzp);
-		if (type == TZ || type == DTZ)
-			noop = (abbrev_offset == 0);
-		else if (type == DYNTZ)
-		{
-			/*
-			 * An abbreviation of a single-offset timezone ought not to be
-			 * configured as a DYNTZ, so don't bother checking.
-			 */
-		}
-		else
-		{
-			long		tzname_offset;
-
-			tzp = pg_tzset(tzname);
-			if (tzp && pg_get_timezone_offset(tzp, &tzname_offset))
-				noop = (tzname_offset == 0);
-		}
-
-		if (noop)
-		{
-			Node	   *timestamp = (Node *) lsecond(expr->args);
-
-			/* Strip any existing RelabelType node(s) */
-			while (timestamp && IsA(timestamp, RelabelType))
-				timestamp = (Node *) ((RelabelType *) timestamp)->arg;
-
-			/*
-			 * Replace the FuncExpr with its timestamp argument, relabeled as
-			 * though the function call had computed it.
-			 */
-			ret = (Node *) makeRelabelType((Expr *) timestamp,
-										   exprType(func_node),
-										   exprTypmod(func_node),
-										   exprCollation(func_node),
-										   COERCE_EXPLICIT_CAST);
-		}
-	}
-
-	PG_RETURN_POINTER(ret);
+	PG_RETURN_POINTER(NULL);
 }
 
 /*	timestamp_zone()
@@ -5376,49 +5307,15 @@ timestamp_zone(PG_FUNCTION_ARGS)
 }
 
 /* timestamp_izone_transform()
- * If we deduce at plan time that a particular timestamp_izone() or
- * timestamptz_izone() call can only compute tz=0, the call will always return
- * its second argument unchanged.  Simplify the expression tree accordingly.
+ * The original optimization here caused problems by relabeling Vars that
+ * could be matched to index entries.  It might be possible to resurrect it
+ * at some point by teaching the planner to be less cavalier with RelabelType
+ * nodes, but that will take careful analysis.
  */
 Datum
 timestamp_izone_transform(PG_FUNCTION_ARGS)
 {
-	Node	   *func_node = (Node *) PG_GETARG_POINTER(0);
-	FuncExpr   *expr = (FuncExpr *) func_node;
-	Node	   *ret = NULL;
-	Node	   *zone_node;
-
-	Assert(IsA(expr, FuncExpr));
-	Assert(list_length(expr->args) == 2);
-
-	zone_node = (Node *) linitial(expr->args);
-
-	if (IsA(zone_node, Const) &&!((Const *) zone_node)->constisnull)
-	{
-		Interval   *zone;
-
-		zone = DatumGetIntervalP(((Const *) zone_node)->constvalue);
-		if (zone->month == 0 && zone->day == 0 && zone->time == 0)
-		{
-			Node	   *timestamp = (Node *) lsecond(expr->args);
-
-			/* Strip any existing RelabelType node(s) */
-			while (timestamp && IsA(timestamp, RelabelType))
-				timestamp = (Node *) ((RelabelType *) timestamp)->arg;
-
-			/*
-			 * Replace the FuncExpr with its timestamp argument, relabeled as
-			 * though the function call had computed it.
-			 */
-			ret = (Node *) makeRelabelType((Expr *) timestamp,
-										   exprType(func_node),
-										   exprTypmod(func_node),
-										   exprCollation(func_node),
-										   COERCE_EXPLICIT_CAST);
-		}
-	}
-
-	PG_RETURN_POINTER(ret);
+	PG_RETURN_POINTER(NULL);
 }
 
 /* timestamp_izone()

src/test/regress/expected/timestamptz.out

@@ -2638,3 +2638,22 @@ select count(distinct utc_offset) >= 24 as ok from pg_timezone_abbrevs;
  t
 (1 row)
 
+--
+-- Test that AT TIME ZONE isn't misoptimized when using an index (bug #14504)
+--
+create temp table tmptz (f1 timestamptz primary key);
+insert into tmptz values ('2017-01-18 00:00+00');
+explain (costs off)
+select * from tmptz where f1 at time zone 'utc' = '2017-01-18 00:00';
+                                           QUERY PLAN                                            
+-------------------------------------------------------------------------------------------------
+ Seq Scan on tmptz
+   Filter: (timezone('utc'::text, f1) = 'Wed Jan 18 00:00:00 2017'::timestamp without time zone)
+(2 rows)
+
+select * from tmptz where f1 at time zone 'utc' = '2017-01-18 00:00';
+              f1              
+------------------------------
+ Tue Jan 17 16:00:00 2017 PST
+(1 row)
+

src/test/regress/sql/timestamptz.sql

@@ -484,3 +484,12 @@ set timezone_abbreviations = 'Australia';
 select count(distinct utc_offset) >= 24 as ok from pg_timezone_abbrevs;
 set timezone_abbreviations = 'India';
 select count(distinct utc_offset) >= 24 as ok from pg_timezone_abbrevs;
+
+--
+-- Test that AT TIME ZONE isn't misoptimized when using an index (bug #14504)
+--
+create temp table tmptz (f1 timestamptz primary key);
+insert into tmptz values ('2017-01-18 00:00+00');
+explain (costs off)
+select * from tmptz where f1 at time zone 'utc' = '2017-01-18 00:00';
+select * from tmptz where f1 at time zone 'utc' = '2017-01-18 00:00';