Unbind methods at _LOAD_ATTR time eagerly for better specialization

Author: Fidget-Spinner

Lib/test/test_opcache.py

@@ -2008,6 +2008,27 @@ class MyList(list): pass
         self.assert_no_opcode(my_list_append, "CALL_LIST_APPEND")
         self.assert_no_opcode(my_list_append, "CALL")
 
+    @cpython_only
+    @requires_specialization
+    def test_load_and_call_classmethod(self):
+
+        r = range(_testinternalcapi.SPECIALIZATION_THRESHOLD)
+
+        class C:
+            @classmethod
+            def val(self):
+                return 1
+
+        def class_method_call():
+            for _ in r:
+                C.val()
+
+        class_method_call()
+        # gh-148608: To improve specialization, the classmethod should've become unbound.
+        self.assert_specialized(class_method_call, "CALL_PY_EXACT_ARGS")
+        self.assert_no_opcode(class_method_call, "CALL_BOUND_METHOD_EXACT_ARGS")
+        self.assert_no_opcode(class_method_call, "CALL")
+
     @cpython_only
     @requires_specialization
     def test_load_attr_module_with_getattr(self):

Objects/object.c

@@ -1773,6 +1773,15 @@ _PyObject_GetMethodStackRef(PyThreadState *ts, _PyStackRef *self,
         PyObject *res = PyObject_GetAttr(obj, name);
         PyStackRef_CLEAR(*self);
         if (res != NULL) {
+            // gh-148608: If it's a method, unbind it right now to improve
+            // specialization later on.
+            if (Py_IS_TYPE(res, &PyMethod_Type)) {
+                PyMethodObject *as_meth = ((PyMethodObject *)res);
+                *method = PyStackRef_FromPyObjectNew(as_meth->im_func);
+                *self = PyStackRef_FromPyObjectNew(as_meth->im_self);
+                Py_DECREF(res);
+                return 1;
+            }
             *method = PyStackRef_FromPyObjectSteal(res);
             return 0;
         }