gh-119053: Implement the fast path for list.__getitem__

corona10 · corona10 · commit f895ca9b3a48 · 2024-05-17T02:24:29.000-04:00
diff --git a/Objects/listobject.c b/Objects/listobject.c
@@ -656,6 +656,16 @@ list_item(PyObject *aa, Py_ssize_t i)
         return NULL;
     }
     PyObject *item;
+#ifdef Py_GIL_DISABLED
+    PyObject **ob_item = _Py_atomic_load_ptr(&a->ob_item);
+    item = _Py_TryXGetRef(&ob_item[i]);
+    if (item) {
+        if (_Py_atomic_load_ptr(&ob_item[i]) == item) {
+            return item;
+        }
+        Py_DECREF(item);
+    }
+#endif
     Py_BEGIN_CRITICAL_SECTION(a);
 #ifdef Py_GIL_DISABLED
     if (!_Py_IsOwnedByCurrentThread((PyObject *)a) && !_PyObject_GC_IS_SHARED(a)) {
