[Python-checkins] bpo-45107: Make LOAD_METHOD_CLASS safer and faster, clean up comments (GH-28177)
webhook-mailer at python.org
Fri Sep 17 06:47:41 EDT 2021
author: Ken Jin <28750310+Fidget-Spinner at users.noreply.github.com>
committer: Fidget-Spinner <28750310+Fidget-Spinner at users.noreply.github.com>
bpo-45107: Make LOAD_METHOD_CLASS safer and faster, clean up comments (GH-28177)
* Improve comments
* Check cls is a type, remove dict calculation
diff --git a/Python/ceval.c b/Python/ceval.c
index bf95d50b62958..ab692fd8ded15 100644
@@ -4496,6 +4496,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
+ /* LOAD_METHOD, for module methods */
assert(cframe.use_tracing == 0);
PyObject *owner = TOP();
@@ -4515,15 +4516,9 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, InterpreterFrame *frame, int thr
_PyObjectCache *cache2 = &caches[-2].obj;
PyObject *cls = TOP();
- PyTypeObject *cls_type = Py_TYPE(cls);
- assert(cls_type->tp_dictoffset > 0);
- PyObject *dict = *(PyObject **) ((char *)cls + cls_type->tp_dictoffset);
- // Don't care if no dict -- tp_version_tag should catch anything wrong.
- DEOPT_IF(dict != NULL && ((PyDictObject *)dict)->ma_keys->dk_version !=
- cache1->dk_version_or_hint, LOAD_METHOD);
+ DEOPT_IF(!PyType_Check(cls), LOAD_METHOD);
DEOPT_IF(((PyTypeObject *)cls)->tp_version_tag != cache1->tp_version,
- assert(cache1->dk_version_or_hint != 0);
assert(cache1->tp_version != 0);
diff --git a/Python/specialize.c b/Python/specialize.c
index 8e04c8372d76c..398524cdb5ba1 100644
@@ -974,20 +974,19 @@ _Py_Specialize_LoadMethod(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name,
// Fall through.
} // Else owner is maybe a builtin with no dict, or __slots__. Doesn't matter.
- /* `descr` is borrowed. Just check tp_version_tag before accessing in case
- * it's deleted. This is safe for methods (even inherited ones from super
- * classes!) as long as tp_version_tag is validated for two main reasons:
+ /* `descr` is borrowed. This is safe for methods (even inherited ones from
+ * super classes!) as long as tp_version_tag is validated for two main reasons:
* 1. The class will always hold a reference to the method so it will
* usually not be GC-ed. Should it be deleted in Python, e.g.
* `del obj.meth`, tp_version_tag will be invalidated, because of reason 2.
* 2. The pre-existing type method cache (MCACHE) uses the same principles
- * of caching a borrowed descriptor. It does all the heavy lifting for us.
- * E.g. it invalidates on any MRO modification, on any type object
- * change along said MRO, etc. (see PyType_Modified usages in typeobject.c).
- * The type method cache has been working since Python 2.6 and it's
- * battle-tested.
+ * of caching a borrowed descriptor. The MCACHE infrastructure does all the
+ * heavy lifting for us. E.g. it invalidates tp_version_tag on any MRO
+ * modification, on any type object change along said MRO, etc. (see
+ * PyType_Modified usages in typeobject.c). The MCACHE has been
+ * working since Python 2.6 and it's battle-tested.
cache2->obj = descr;
cache1->dk_version_or_hint = keys_version;
More information about the Python-checkins