GH-95245: Store object values and dict pointers in single tagged pointer. (GH-95278)

3 files changed, 195 insertions, 165 deletions

diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 25e191f..d820348 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -5368,7 +5368,7 @@ init_inline_values(PyObject *obj, PyTypeObject *tp)
     for (int i = 0; i < size; i++) {
         values->values[i] = NULL;
     }
-    *_PyObject_ValuesPointer(obj) = values;
+    _PyDictOrValues_SetValues(_PyObject_DictOrValuesPointer(obj), values);
     return 0;
 }
 
@@ -5394,7 +5394,7 @@ _PyObject_InitializeDict(PyObject *obj)
     if (dict == NULL) {
         return -1;
     }
-    PyObject **dictptr = _PyObject_DictPointer(obj);
+    PyObject **dictptr = _PyObject_ComputedDictPointer(obj);
     *dictptr = dict;
     return 0;
 }
@@ -5422,7 +5422,6 @@ make_dict_from_instance_attributes(PyDictKeysObject *keys, PyDictValues *values)
 PyObject *
 _PyObject_MakeDictFromInstanceAttributes(PyObject *obj, PyDictValues *values)
 {
-    assert(Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT);
     PyDictKeysObject *keys = CACHED_KEYS(Py_TYPE(obj));
     OBJECT_STAT_INC(dict_materialized_on_request);
     return make_dict_from_instance_attributes(keys, values);
@@ -5458,8 +5457,7 @@ _PyObject_StoreInstanceAttribute(PyObject *obj, PyDictValues *values,
         if (dict == NULL) {
             return -1;
         }
-        *_PyObject_ValuesPointer(obj) = NULL;
-        *_PyObject_ManagedDictPointer(obj) = dict;
+        _PyObject_DictOrValuesPointer(obj)->dict = dict;
         if (value == NULL) {
             return PyDict_DelItem(dict, name);
         }
@@ -5488,6 +5486,37 @@ _PyObject_StoreInstanceAttribute(PyObject *obj, PyDictValues *values,
     return 0;
 }
 
+/* Sanity check for managed dicts */
+#if 0
+#define CHECK(val) assert(val); if (!(val)) { return 0; }
+
+int
+_PyObject_ManagedDictValidityCheck(PyObject *obj)
+{
+    PyTypeObject *tp = Py_TYPE(obj);
+    CHECK(tp->tp_flags & Py_TPFLAGS_MANAGED_DICT);
+    PyDictOrValues *dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+    if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+        PyDictValues *values = _PyDictOrValues_GetValues(*dorv_ptr);
+        int size = ((uint8_t *)values)[-2];
+        int count = 0;
+        PyDictKeysObject *keys = CACHED_KEYS(tp);
+        for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
+            if (values->values[i] != NULL) {
+                count++;
+            }
+        }
+        CHECK(size == count);
+    }
+    else {
+        if (dorv_ptr->dict != NULL) {
+            CHECK(PyDict_Check(dorv_ptr->dict));
+        }
+    }
+    return 1;
+}
+#endif
+
 PyObject *
 _PyObject_GetInstanceAttribute(PyObject *obj, PyDictValues *values,
                               PyObject *name)
@@ -5511,105 +5540,94 @@ _PyObject_IsInstanceDictEmpty(PyObject *obj)
     if (tp->tp_dictoffset == 0) {
         return 1;
     }
-    PyObject **dictptr;
+    PyObject *dict;
     if (tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
-        PyDictValues *values = *_PyObject_ValuesPointer(obj);
-        if (values) {
+        PyDictOrValues dorv = *_PyObject_DictOrValuesPointer(obj);
+        if (_PyDictOrValues_IsValues(dorv)) {
             PyDictKeysObject *keys = CACHED_KEYS(tp);
             for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
-                if (values->values[i] != NULL) {
+                if (_PyDictOrValues_GetValues(dorv)->values[i] != NULL) {
                     return 0;
                 }
             }
             return 1;
         }
-        dictptr = _PyObject_ManagedDictPointer(obj);
+        dict = _PyDictOrValues_GetDict(dorv);
     }
     else {
-       dictptr = _PyObject_DictPointer(obj);
+        PyObject **dictptr = _PyObject_ComputedDictPointer(obj);
+        dict = *dictptr;
     }
-    PyObject *dict = *dictptr;
     if (dict == NULL) {
         return 1;
     }
     return ((PyDictObject *)dict)->ma_used == 0;
 }
 
-
-int
-_PyObject_VisitInstanceAttributes(PyObject *self, visitproc visit, void *arg)
-{
-    PyTypeObject *tp = Py_TYPE(self);
-    assert(Py_TYPE(self)->tp_flags & Py_TPFLAGS_MANAGED_DICT);
-    PyDictValues **values_ptr = _PyObject_ValuesPointer(self);
-    if (*values_ptr == NULL) {
-        return 0;
-    }
-    PyDictKeysObject *keys = CACHED_KEYS(tp);
-    for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
-        Py_VISIT((*values_ptr)->values[i]);
-    }
-    return 0;
-}
-
-void
-_PyObject_ClearInstanceAttributes(PyObject *self)
-{
-    PyTypeObject *tp = Py_TYPE(self);
-    assert(Py_TYPE(self)->tp_flags & Py_TPFLAGS_MANAGED_DICT);
-    PyDictValues **values_ptr = _PyObject_ValuesPointer(self);
-    if (*values_ptr == NULL) {
-        return;
-    }
-    PyDictKeysObject *keys = CACHED_KEYS(tp);
-    for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
-        Py_CLEAR((*values_ptr)->values[i]);
-    }
-}
-
 void
 _PyObject_FreeInstanceAttributes(PyObject *self)
 {
     PyTypeObject *tp = Py_TYPE(self);
     assert(Py_TYPE(self)->tp_flags & Py_TPFLAGS_MANAGED_DICT);
-    PyDictValues **values_ptr = _PyObject_ValuesPointer(self);
-    if (*values_ptr == NULL) {
+    PyDictOrValues dorv = *_PyObject_DictOrValuesPointer(self);
+    if (!_PyDictOrValues_IsValues(dorv)) {
         return;
     }
+    PyDictValues *values = _PyDictOrValues_GetValues(dorv);
     PyDictKeysObject *keys = CACHED_KEYS(tp);
     for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
-        Py_XDECREF((*values_ptr)->values[i]);
+        Py_XDECREF(values->values[i]);
     }
-    free_values(*values_ptr);
+    free_values(values);
 }
 
 int
-_PyObject_VisitManagedDict(PyObject *self, visitproc visit, void *arg)
+_PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg)
 {
-    PyTypeObject *tp = Py_TYPE(self);
+    PyTypeObject *tp = Py_TYPE(obj);
     if((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
         return 0;
     }
     assert(tp->tp_dictoffset);
-    int err = _PyObject_VisitInstanceAttributes(self, visit, arg);
-    if (err) {
-        return err;
+    PyDictOrValues dorv = *_PyObject_DictOrValuesPointer(obj);
+    if (_PyDictOrValues_IsValues(dorv)) {
+        PyDictValues *values = _PyDictOrValues_GetValues(dorv);
+        PyDictKeysObject *keys = CACHED_KEYS(tp);
+        for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
+            Py_VISIT(values->values[i]);
+        }
+    }
+    else {
+        PyObject *dict = _PyDictOrValues_GetDict(dorv);
+        Py_VISIT(dict);
     }
-    Py_VISIT(*_PyObject_ManagedDictPointer(self));
     return 0;
 }
 
-
 void
-_PyObject_ClearManagedDict(PyObject *self)
+_PyObject_ClearManagedDict(PyObject *obj)
 {
-    PyTypeObject *tp = Py_TYPE(self);
+    PyTypeObject *tp = Py_TYPE(obj);
     if((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
         return;
     }
-    _PyObject_FreeInstanceAttributes(self);
-    *_PyObject_ValuesPointer(self) = NULL;
-    Py_CLEAR(*_PyObject_ManagedDictPointer(self));
+    PyDictOrValues *dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+    if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+        PyDictValues *values = _PyDictOrValues_GetValues(*dorv_ptr);
+        PyDictKeysObject *keys = CACHED_KEYS(tp);
+        for (Py_ssize_t i = 0; i < keys->dk_nentries; i++) {
+            Py_CLEAR(values->values[i]);
+        }
+        dorv_ptr->dict = NULL;
+        free_values(values);
+    }
+    else {
+        PyObject *dict = dorv_ptr->dict;
+        if (dict) {
+            dorv_ptr->dict = NULL;
+            Py_DECREF(dict);
+        }
+    }
 }
 
 PyObject *
@@ -5618,25 +5636,26 @@ PyObject_GenericGetDict(PyObject *obj, void *context)
     PyObject *dict;
     PyTypeObject *tp = Py_TYPE(obj);
     if (_PyType_HasFeature(tp, Py_TPFLAGS_MANAGED_DICT)) {
-        PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
-        PyObject **dictptr = _PyObject_ManagedDictPointer(obj);
-        if (*values_ptr) {
-            assert(*dictptr == NULL);
+        PyDictOrValues *dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+        if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+            PyDictValues *values = _PyDictOrValues_GetValues(*dorv_ptr);
             OBJECT_STAT_INC(dict_materialized_on_request);
-            *dictptr = dict = make_dict_from_instance_attributes(CACHED_KEYS(tp), *values_ptr);
+            dict = make_dict_from_instance_attributes(CACHED_KEYS(tp), values);
             if (dict != NULL) {
-                *values_ptr = NULL;
+                dorv_ptr->dict = dict;
             }
         }
-        else if (*dictptr == NULL) {
-            *dictptr = dict = PyDict_New();
-        }
         else {
-            dict = *dictptr;
+            dict = _PyDictOrValues_GetDict(*dorv_ptr);
+            if (dict == NULL) {
+                dictkeys_incref(CACHED_KEYS(tp));
+                dict = new_dict_with_shared_keys(CACHED_KEYS(tp));
+                dorv_ptr->dict = dict;
+            }
         }
     }
     else {
-        PyObject **dictptr = _PyObject_DictPointer(obj);
+        PyObject **dictptr = _PyObject_ComputedDictPointer(obj);
         if (dictptr == NULL) {
             PyErr_SetString(PyExc_AttributeError,
                             "This object has no __dict__");
diff --git a/Objects/object.c b/Objects/object.c
index 758b79e..f0c0434 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -1054,14 +1054,12 @@ PyObject_SetAttr(PyObject *v, PyObject *name, PyObject *value)
 }
 
 PyObject **
-_PyObject_DictPointer(PyObject *obj)
+_PyObject_ComputedDictPointer(PyObject *obj)
 {
     Py_ssize_t dictoffset;
     PyTypeObject *tp = Py_TYPE(obj);
 
-    if (tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
-        return _PyObject_ManagedDictPointer(obj);
-    }
+    assert((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0);
     dictoffset = tp->tp_dictoffset;
     if (dictoffset == 0)
         return NULL;
@@ -1086,22 +1084,18 @@ PyObject **
 _PyObject_GetDictPtr(PyObject *obj)
 {
     if ((Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
-        return _PyObject_DictPointer(obj);
-    }
-    PyObject **dict_ptr = _PyObject_ManagedDictPointer(obj);
-    PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
-    if (*values_ptr == NULL) {
-        return dict_ptr;
+        return _PyObject_ComputedDictPointer(obj);
     }
-    assert(*dict_ptr == NULL);
-    PyObject *dict = _PyObject_MakeDictFromInstanceAttributes(obj, *values_ptr);
-    if (dict == NULL) {
-        PyErr_Clear();
-        return NULL;
+    PyDictOrValues *dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+    if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+        PyObject *dict = _PyObject_MakeDictFromInstanceAttributes(obj, _PyDictOrValues_GetValues(*dorv_ptr));
+        if (dict == NULL) {
+            PyErr_Clear();
+            return NULL;
+        }
+        dorv_ptr->dict = dict;
     }
-    *values_ptr = NULL;
-    *dict_ptr = dict;
-    return dict_ptr;
+    return &dorv_ptr->dict;
 }
 
 PyObject *
@@ -1170,36 +1164,46 @@ _PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
             }
         }
     }
-    PyDictValues *values;
-    if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) &&
-        (values = *_PyObject_ValuesPointer(obj)))
-    {
-        assert(*_PyObject_DictPointer(obj) == NULL);
-        PyObject *attr = _PyObject_GetInstanceAttribute(obj, values, name);
-        if (attr != NULL) {
-            *method = attr;
-            Py_XDECREF(descr);
-            return 0;
-        }
-    }
-    else {
-        PyObject **dictptr = _PyObject_DictPointer(obj);
-        PyObject *dict;
-        if (dictptr != NULL && (dict = *dictptr) != NULL) {
-            Py_INCREF(dict);
-            PyObject *attr = PyDict_GetItemWithError(dict, name);
+    PyObject *dict;
+    if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT)) {
+        PyDictOrValues* dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+        if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+            PyDictValues *values = _PyDictOrValues_GetValues(*dorv_ptr);
+            PyObject *attr = _PyObject_GetInstanceAttribute(obj, values, name);
             if (attr != NULL) {
-                *method = Py_NewRef(attr);
-                Py_DECREF(dict);
+                *method = attr;
                 Py_XDECREF(descr);
                 return 0;
             }
+            dict = NULL;
+        }
+        else {
+            dict = dorv_ptr->dict;
+        }
+    }
+    else {
+        PyObject **dictptr = _PyObject_ComputedDictPointer(obj);
+        if (dictptr != NULL) {
+            dict = *dictptr;
+        }
+        else {
+            dict = NULL;
+        }
+    }
+    if (dict != NULL) {
+        Py_INCREF(dict);
+        PyObject *attr = PyDict_GetItemWithError(dict, name);
+        if (attr != NULL) {
+            *method = Py_NewRef(attr);
             Py_DECREF(dict);
+            Py_XDECREF(descr);
+            return 0;
+        }
+        Py_DECREF(dict);
 
-            if (PyErr_Occurred()) {
-                Py_XDECREF(descr);
-                return 0;
-            }
+        if (PyErr_Occurred()) {
+            Py_XDECREF(descr);
+            return 0;
         }
     }
 
@@ -1243,7 +1247,6 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
     PyObject *descr = NULL;
     PyObject *res = NULL;
     descrgetfunc f;
-    PyObject **dictptr;
 
     if (!PyUnicode_Check(name)){
         PyErr_Format(PyExc_TypeError,
@@ -1274,30 +1277,31 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
         }
     }
     if (dict == NULL) {
-        if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) &&
-            *_PyObject_ValuesPointer(obj))
-        {
-            PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
-            if (PyUnicode_CheckExact(name)) {
-                assert(*_PyObject_DictPointer(obj) == NULL);
-                res = _PyObject_GetInstanceAttribute(obj, *values_ptr, name);
-                if (res != NULL) {
-                    goto done;
+        if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT)) {
+            PyDictOrValues* dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+            if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+                PyDictValues *values = _PyDictOrValues_GetValues(*dorv_ptr);
+                if (PyUnicode_CheckExact(name)) {
+                    res = _PyObject_GetInstanceAttribute(obj, values, name);
+                    if (res != NULL) {
+                        goto done;
+                    }
+                }
+                else {
+                    dict = _PyObject_MakeDictFromInstanceAttributes(obj, values);
+                    if (dict == NULL) {
+                        res = NULL;
+                        goto done;
+                    }
+                    dorv_ptr->dict = dict;
                 }
             }
             else {
-                dictptr = _PyObject_DictPointer(obj);
-                assert(dictptr != NULL && *dictptr == NULL);
-                *dictptr = dict = _PyObject_MakeDictFromInstanceAttributes(obj, *values_ptr);
-                if (dict == NULL) {
-                    res = NULL;
-                    goto done;
-                }
-                *values_ptr = NULL;
+                dict = _PyDictOrValues_GetDict(*dorv_ptr);
             }
         }
         else {
-            dictptr = _PyObject_DictPointer(obj);
+            PyObject **dictptr = _PyObject_ComputedDictPointer(obj);
             if (dictptr) {
                 dict = *dictptr;
             }
@@ -1389,27 +1393,34 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
     }
 
     if (dict == NULL) {
-        if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) && *_PyObject_ValuesPointer(obj)) {
-            res = _PyObject_StoreInstanceAttribute(obj, *_PyObject_ValuesPointer(obj), name, value);
+        PyObject **dictptr;
+        if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT)) {
+            PyDictOrValues *dorv_ptr = _PyObject_DictOrValuesPointer(obj);
+            if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+                res = _PyObject_StoreInstanceAttribute(
+                    obj, _PyDictOrValues_GetValues(*dorv_ptr), name, value);
+                goto error_check;
+            }
+            dictptr = &dorv_ptr->dict;
         }
         else {
-            PyObject **dictptr = _PyObject_DictPointer(obj);
-            if (dictptr == NULL) {
-                if (descr == NULL) {
-                    PyErr_Format(PyExc_AttributeError,
-                                "'%.100s' object has no attribute '%U'",
-                                tp->tp_name, name);
-                }
-                else {
-                    PyErr_Format(PyExc_AttributeError,
-                                "'%.50s' object attribute '%U' is read-only",
-                                tp->tp_name, name);
-                }
-                goto done;
+            dictptr = _PyObject_ComputedDictPointer(obj);
+        }
+        if (dictptr == NULL) {
+            if (descr == NULL) {
+                PyErr_Format(PyExc_AttributeError,
+                            "'%.100s' object has no attribute '%U'",
+                            tp->tp_name, name);
             }
             else {
-                res = _PyObjectDict_SetItem(tp, dictptr, name, value);
+                PyErr_Format(PyExc_AttributeError,
+                            "'%.50s' object attribute '%U' is read-only",
+                            tp->tp_name, name);
             }
+            goto done;
+        }
+        else {
+            res = _PyObjectDict_SetItem(tp, dictptr, name, value);
         }
     }
     else {
@@ -1420,6 +1431,7 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
             res = PyDict_SetItem(dict, name, value);
         Py_DECREF(dict);
     }
+  error_check:
     if (res < 0 && PyErr_ExceptionMatches(PyExc_KeyError)) {
         if (PyType_IsSubtype(tp, &PyType_Type)) {
             PyErr_Format(PyExc_AttributeError,
@@ -1451,7 +1463,7 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
     PyObject **dictptr = _PyObject_GetDictPtr(obj);
     if (dictptr == NULL) {
         if (_PyType_HasFeature(Py_TYPE(obj), Py_TPFLAGS_MANAGED_DICT) &&
-            *_PyObject_ValuesPointer(obj) != NULL)
+            _PyDictOrValues_IsValues(*_PyObject_DictOrValuesPointer(obj)))
         {
             /* Was unable to convert to dict */
             PyErr_NoMemory();
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index e4adf1c..d33befc0 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -1310,15 +1310,13 @@ subtype_traverse(PyObject *self, visitproc visit, void *arg)
     }
 
     if (type->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
-        assert(type->tp_dictoffset);
-        int err = _PyObject_VisitInstanceAttributes(self, visit, arg);
+        int err = _PyObject_VisitManagedDict(self, visit, arg);
         if (err) {
             return err;
         }
     }
-
-    if (type->tp_dictoffset != base->tp_dictoffset) {
-        PyObject **dictptr = _PyObject_DictPointer(self);
+    else if (type->tp_dictoffset != base->tp_dictoffset) {
+        PyObject **dictptr = _PyObject_ComputedDictPointer(self);
         if (dictptr && *dictptr)
             Py_VISIT(*dictptr);
     }
@@ -1379,10 +1377,10 @@ subtype_clear(PyObject *self)
     /* Clear the instance dict (if any), to break cycles involving only
        __dict__ slots (as in the case 'self.__dict__ is self'). */
     if (type->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
-        _PyObject_ClearInstanceAttributes(self);
+        _PyObject_ClearManagedDict(self);
     }
-    if (type->tp_dictoffset != base->tp_dictoffset) {
-        PyObject **dictptr = _PyObject_DictPointer(self);
+    else if (type->tp_dictoffset != base->tp_dictoffset) {
+        PyObject **dictptr = _PyObject_ComputedDictPointer(self);
         if (dictptr && *dictptr)
             Py_CLEAR(*dictptr);
     }
@@ -1526,18 +1524,17 @@ subtype_dealloc(PyObject *self)
 
     /* If we added a dict, DECREF it, or free inline values. */
     if (type->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
-        PyObject **dictptr = _PyObject_ManagedDictPointer(self);
-        if (*dictptr != NULL) {
-            assert(*_PyObject_ValuesPointer(self) == NULL);
-            Py_DECREF(*dictptr);
-            *dictptr = NULL;
+        PyDictOrValues *dorv_ptr = _PyObject_DictOrValuesPointer(self);
+        if (_PyDictOrValues_IsValues(*dorv_ptr)) {
+            _PyObject_FreeInstanceAttributes(self);
         }
         else {
-            _PyObject_FreeInstanceAttributes(self);
+            Py_XDECREF(_PyDictOrValues_GetDict(*dorv_ptr));
         }
+        dorv_ptr->values = NULL;
     }
     else if (type->tp_dictoffset && !base->tp_dictoffset) {
-        PyObject **dictptr = _PyObject_DictPointer(self);
+        PyObject **dictptr = _PyObject_ComputedDictPointer(self);
         if (dictptr != NULL) {
             PyObject *dict = *dictptr;
             if (dict != NULL) {
@@ -5137,7 +5134,9 @@ object_set_class(PyObject *self, PyObject *value, void *closure)
          * so we must materialize the dictionary first. */
         assert((oldto->tp_flags & Py_TPFLAGS_MANAGED_DICT) == (newto->tp_flags & Py_TPFLAGS_MANAGED_DICT));
         _PyObject_GetDictPtr(self);
-        if (oldto->tp_flags & Py_TPFLAGS_MANAGED_DICT && *_PyObject_ValuesPointer(self)) {
+        if (oldto->tp_flags & Py_TPFLAGS_MANAGED_DICT &&
+            _PyDictOrValues_IsValues(*_PyObject_DictOrValuesPointer(self)))
+        {
             /* Was unable to convert to dict */
             PyErr_NoMemory();
             return -1;