gh-143361: Pass PY_VECTORCALL_ARGUMENTS_OFFSET in _Py_CallBuiltinClass_StackRefSteal (GH-143367)

a12k · Aaron Wieczorek · web-flow · commit b538c2832d58 · 2026-01-02T20:43:00.000Z
Co-authored-by: Aaron Wieczorek &lt;woz@Aarons-MacBook-Pro.local&gt;
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-01-02-17-11-16.gh-issue-143361.YDnvdC.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-01-02-17-11-16.gh-issue-143361.YDnvdC.rst
@@ -0,0 +1,2 @@
+Add ``PY_VECTORCALL_ARGUMENTS_OFFSET`` to ``_Py_CallBuiltinClass_StackRefSteal`` to
+avoid redundant allocations
diff --git a/Python/ceval.c b/Python/ceval.c
@@ -1273,7 +1273,7 @@ _Py_CallBuiltinClass_StackRefSteal(
         goto cleanup;
     }
     PyTypeObject *tp = (PyTypeObject *)PyStackRef_AsPyObjectBorrow(callable);
-    res = tp->tp_vectorcall((PyObject *)tp, args_o, total_args, NULL);
+    res = tp->tp_vectorcall((PyObject *)tp, args_o, total_args | PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);
     STACKREFS_TO_PYOBJECTS_CLEANUP(args_o);
     assert((res != NULL) ^ (PyErr_Occurred() != NULL));
 cleanup:

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Add ``PY_VECTORCALL_ARGUMENTS_OFFSET`` to ``_Py_CallBuiltinClass_StackRefSteal`` to
	`2`	`+avoid redundant allocations`
Original file line number	Diff line number	Diff line change
`@@ -1273,7 +1273,7 @@ _Py_CallBuiltinClass_StackRefSteal(`
`1273`	`1273`	`goto cleanup;`
`1274`	`1274`	`}`
`1275`	`1275`	`PyTypeObject tp = (PyTypeObject )PyStackRef_AsPyObjectBorrow(callable);`
`1276`		`- res = tp->tp_vectorcall((PyObject *)tp, args_o, total_args, NULL);`
	`1276`	`+ res = tp->tp_vectorcall((PyObject *)tp, args_o, total_args \| PY_VECTORCALL_ARGUMENTS_OFFSET, NULL);`
`1277`	`1277`	`STACKREFS_TO_PYOBJECTS_CLEANUP(args_o);`
`1278`	`1278`	`assert((res != NULL) ^ (PyErr_Occurred() != NULL));`
`1279`	`1279`	`cleanup:`