Fix iterable return type optimization

Author: nikic

ext/opcache/Optimizer/dfa_pass.c

@@ -302,7 +302,8 @@ static inline zend_bool can_elide_return_type_check(
 		return 0;
 	}
 
-	if (ZEND_TYPE_CODE(info->type) == IS_CALLABLE) {
+	/* These types are not represented exactly */
+	if (ZEND_TYPE_CODE(info->type) == IS_CALLABLE || ZEND_TYPE_CODE(info->type) == IS_ITERABLE) {
 		return 0;
 	}
 

ext/opcache/tests/iterable_type_optimization.phpt

@@ -0,0 +1,17 @@
+--TEST--
+Don't optimize object -> iterable
+--FILE--
+<?php
+
+function test(object $arg): iterable {
+    return $arg;
+}
+test(new stdClass);
+
+?>
+--EXPECTF--
+Fatal error: Uncaught TypeError: Return value of test() must be iterable, object returned in %s:%d
+Stack trace:
+#0 %s(%d): test(Object(stdClass))
+#1 {main}
+  thrown in %s on line %d