Issue #26110: Add LOAD_METHOD/CALL_METHOD opcodes.

Special thanks to INADA Naoki for pushing the patch through
the last mile, Serhiy Storchaka for reviewing the code, and to
Victor Stinner for suggesting the idea (originally implemented
in the PyPy project).

Objects/object.c

@@ -1025,11 +1025,99 @@ _PyObject_NextNotImplemented(PyObject *self)
     return NULL;
 }
 
-/* Generic GetAttr functions - put these in your tp_[gs]etattro slot */
+
+/* Specialized version of _PyObject_GenericGetAttrWithDict
+   specifically for the LOAD_METHOD opcode.
+
+   Return 1 if a method is found, 0 if it's a regular attribute
+   from __dict__ or something returned by using a descriptor
+   protocol.
+
+   `method` will point to the resolved attribute or NULL.  In the
+   latter case, an error will be set.
+*/
+int
+_PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
+{
+    PyTypeObject *tp = Py_TYPE(obj);
+    PyObject *descr;
+    descrgetfunc f = NULL;
+    PyObject **dictptr, *dict;
+    PyObject *attr;
+    int meth_found = 0;
+
+    assert(*method == NULL);
+
+    if (Py_TYPE(obj)->tp_getattro != PyObject_GenericGetAttr
+            || !PyUnicode_Check(name)) {
+        *method = PyObject_GetAttr(obj, name);
+        return 0;
+    }
+
+    if (tp->tp_dict == NULL && PyType_Ready(tp) < 0)
+        return 0;
+
+    descr = _PyType_Lookup(tp, name);
+    if (descr != NULL) {
+        Py_INCREF(descr);
+        if (PyFunction_Check(descr)) {
+            /* A python method. */
+            meth_found = 1;
+        } else {
+            f = descr->ob_type->tp_descr_get;
+            if (f != NULL && PyDescr_IsData(descr)) {
+                *method = f(descr, obj, (PyObject *)obj->ob_type);
+                Py_DECREF(descr);
+                return 0;
+            }
+        }
+    }
+
+    dictptr = _PyObject_GetDictPtr(obj);
+    if (dictptr != NULL && (dict = *dictptr) != NULL) {
+        Py_INCREF(dict);
+        attr = PyDict_GetItem(dict, name);
+        if (attr != NULL) {
+            Py_INCREF(attr);
+            *method = attr;
+            Py_DECREF(dict);
+            Py_XDECREF(descr);
+            return 0;
+        }
+        Py_DECREF(dict);
+    }
+
+    if (meth_found) {
+        *method = descr;
+        return 1;
+    }
+
+    if (f != NULL) {
+        *method = f(descr, obj, (PyObject *)Py_TYPE(obj));
+        Py_DECREF(descr);
+        return 0;
+    }
+
+    if (descr != NULL) {
+        *method = descr;
+        return 0;
+    }
+
+    PyErr_Format(PyExc_AttributeError,
+                 "'%.50s' object has no attribute '%U'",
+                 tp->tp_name, name);
+    return 0;
+}
+
+/* Generic GetAttr functions - put these in your tp_[gs]etattro slot. */
 
 PyObject *
 _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name, PyObject *dict)
 {
+    /* Make sure the logic of _PyObject_GetMethod is in sync with
+       this method.
+    */
+
     PyTypeObject *tp = Py_TYPE(obj);
     PyObject *descr = NULL;
     PyObject *res = NULL;