Use a faster implementation

Author: JukkaL

mypyc/lib-rt/list_ops.c

@@ -235,17 +235,35 @@ void CPyList_SetItemUnsafe(PyObject *list, Py_ssize_t index, PyObject *value) {
     PyList_SET_ITEM(list, index, value);
 }
 
-PyObject *CPyList_PopLast(PyObject *obj)
+#ifdef Py_GIL_DISABLED
+// The original optimized list.pop implementation doesn't work on free-threaded
+// builds, so provide an alternative that is a bit slower but works.
+//
+// Note that this implementation isn't intended to be atomic.
+static inline PyObject *list_pop_index(PyObject *list, Py_ssize_t index) {
+    PyObject *item = PyList_GetItemRef(list, index);
+    if (item == NULL) {
+        return NULL;
+    }
+    if (PySequence_DelItem(list, index) < 0) {
+        Py_DECREF(item);
+        return NULL;
+    }
+    return item;
+}
+#endif
+
+PyObject *CPyList_PopLast(PyObject *list)
 {
 #ifdef Py_GIL_DISABLED
-    // The optimized version causes segfaults on a free-threaded Python 3.14b4 build,
-    // at least on macOS, so fall back to a generic implementation.
-    return PyObject_CallMethod(obj, "pop", NULL);
+    // The other implementation causes segfaults on a free-threaded Python 3.14b4 build.
+    Py_ssize_t index = PyList_GET_SIZE(list) - 1;
+    return list_pop_index(list, index);
 #else
     // I tried a specalized version of pop_impl for just removing the
     // last element and it wasn't any faster in microbenchmarks than
     // the generic one so I ditched it.
-    return list_pop_impl((PyListObject *)obj, -1);
+    return list_pop_impl((PyListObject *)list, -1);
 #endif
 }
 
@@ -254,18 +272,11 @@ PyObject *CPyList_Pop(PyObject *obj, CPyTagged index)
     if (CPyTagged_CheckShort(index)) {
         Py_ssize_t n = CPyTagged_ShortAsSsize_t(index);
 #ifdef Py_GIL_DISABLED
-        static PyObject *interned_pop_str = NULL;
-        if (!interned_pop_str) {
-            interned_pop_str = PyUnicode_InternFromString("pop");
-            if (!interned_pop_str)
-                return NULL;
+        // We must use a slower implementation on free-threaded builds.
+        if (n < 0) {
+            n += PyList_GET_SIZE(obj);
         }
-        PyObject *index_obj = PyLong_FromLong(n);  // New reference
-        if (index_obj == NULL)
-            return NULL;
-        PyObject *result = PyObject_CallMethodOneArg(obj, interned_pop_str, index_obj);
-        Py_DECREF(index_obj);
-        return result;
+        return list_pop_index(obj, n);
 #else
         return list_pop_impl((PyListObject *)obj, n);
 #endif