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GH-106485: "Un-materialize" __dict__s in LOAD_ATTR_WITH_HINT #106496

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2 changes: 2 additions & 0 deletions Include/internal/pycore_dict.h
Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,8 @@ extern uint32_t _PyDictKeys_GetVersionForCurrentState(

extern size_t _PyDict_KeysSize(PyDictKeysObject *keys);

extern void _PyDictKeys_DecRef(PyDictKeysObject *keys);

/* _Py_dict_lookup() returns index of entry which can be used like DK_ENTRIES(dk)[index].
* -1 when no entry found, -3 when compare raises error.
*/
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1 change: 1 addition & 0 deletions Include/pystats.h
Original file line number Diff line number Diff line change
Expand Up @@ -65,6 +65,7 @@ typedef struct _object_stats {
uint64_t dict_materialized_new_key;
uint64_t dict_materialized_too_big;
uint64_t dict_materialized_str_subclass;
uint64_t dict_unmaterialized;
uint64_t type_cache_hits;
uint64_t type_cache_misses;
uint64_t type_cache_dunder_hits;
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11 changes: 6 additions & 5 deletions Lib/test/test_opcache.py
Original file line number Diff line number Diff line change
Expand Up @@ -864,19 +864,20 @@ class C:

items = []
for _ in range(self.ITEMS):
item = C()
item.__dict__
item.a = None
o = C()
o.a = None
# Need to keep a __dict__ reference so it isn't un-materialized:
item = o, o.__dict__
items.append(item)
return items

def read(items):
for item in items:
item.a
item[0].a

def write(items):
for item in items:
item.__dict__[None] = None
item[1][None] = None

opname = "LOAD_ATTR_WITH_HINT"
self.assert_races_do_not_crash(opname, get_items, read, write)
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3 changes: 0 additions & 3 deletions Objects/typeobject.c
Original file line number Diff line number Diff line change
Expand Up @@ -4973,9 +4973,6 @@ type_setattro(PyTypeObject *type, PyObject *name, PyObject *value)
return res;
}

extern void
_PyDictKeys_DecRef(PyDictKeysObject *keys);


static void
type_dealloc_common(PyTypeObject *type)
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28 changes: 24 additions & 4 deletions Python/bytecodes.c
Original file line number Diff line number Diff line change
Expand Up @@ -1902,9 +1902,9 @@ dummy_func(
assert(type_version != 0);
DEOPT_IF(tp->tp_version_tag != type_version, LOAD_ATTR);
assert(tp->tp_flags & Py_TPFLAGS_MANAGED_DICT);
PyDictOrValues dorv = *_PyObject_DictOrValuesPointer(owner);
DEOPT_IF(_PyDictOrValues_IsValues(dorv), LOAD_ATTR);
PyDictObject *dict = (PyDictObject *)_PyDictOrValues_GetDict(dorv);
PyDictOrValues *dorv = _PyObject_DictOrValuesPointer(owner);
DEOPT_IF(_PyDictOrValues_IsValues(*dorv), LOAD_ATTR);
PyDictObject *dict = (PyDictObject *)_PyDictOrValues_GetDict(*dorv);
DEOPT_IF(dict == NULL, LOAD_ATTR);
assert(PyDict_CheckExact((PyObject *)dict));
PyObject *name = GETITEM(FRAME_CO_NAMES, oparg>>1);
Expand All @@ -1920,7 +1920,27 @@ dummy_func(
DEOPT_IF(ep->me_key != name, LOAD_ATTR);
res = ep->me_value;
}
DEOPT_IF(res == NULL, LOAD_ATTR);
if (res == NULL) {
// This is almost never an AttributeError. It's way more likely
// that this __dict__ still shares its keys (for example, if it
// was materialized on request and not heavily modified):
assert(_PyType_HasFeature(tp, Py_TPFLAGS_HEAPTYPE));
PyHeapTypeObject *ht = (PyHeapTypeObject *)tp;
DEOPT_IF(dict->ma_keys != ht->ht_cached_keys, LOAD_ATTR);
assert(dict->ma_values);
DEOPT_IF(Py_REFCNT(dict) != 1, LOAD_ATTR);
// We have an opportunity to do something *really* cool:
// un-materialize it!
_PyDictKeys_DecRef(dict->ma_keys);
_PyDictOrValues_SetValues(dorv, dict->ma_values);
OBJECT_STAT_INC(dict_unmaterialized);
// Don't try this at home, kids:
dict->ma_keys = NULL;
dict->ma_values = NULL;
Py_DECREF(dict);
// Guess what... our caches are still valid!
GO_TO_INSTRUCTION(LOAD_ATTR_INSTANCE_VALUE);
}
STAT_INC(LOAD_ATTR, hit);
Py_INCREF(res);
res2 = NULL;
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