bpo-37337: Add _PyObject_VectorcallMethod() (GH-14228)

2 files changed, 46 insertions, 7 deletions

diff --git a/Objects/call.c b/Objects/call.c
index bde5513..2b52bdf 100644
--- a/Objects/call.c
+++ b/Objects/call.c
@@ -1078,6 +1078,38 @@ object_vacall(PyObject *base, PyObject *callable, va_list vargs)
 
 
 PyObject *
+_PyObject_VectorcallMethod(PyObject *name, PyObject *const *args,
+                           size_t nargsf, PyObject *kwnames)
+{
+    assert(name != NULL);
+    assert(args != NULL);
+    assert(PyVectorcall_NARGS(nargsf) >= 1);
+
+    PyObject *callable = NULL;
+    /* Use args[0] as "self" argument */
+    int unbound = _PyObject_GetMethod(args[0], name, &callable);
+    if (callable == NULL) {
+        return NULL;
+    }
+
+    if (unbound) {
+        /* We must remove PY_VECTORCALL_ARGUMENTS_OFFSET since
+         * that would be interpreted as allowing to change args[-1] */
+        nargsf &= ~PY_VECTORCALL_ARGUMENTS_OFFSET;
+    }
+    else {
+        /* Skip "self". We can keep PY_VECTORCALL_ARGUMENTS_OFFSET since
+         * args[-1] in the onward call is args[0] here. */
+        args++;
+        nargsf--;
+    }
+    PyObject *result = _PyObject_Vectorcall(callable, args, nargsf, kwnames);
+    Py_DECREF(callable);
+    return result;
+}
+
+
+PyObject *
 PyObject_CallMethodObjArgs(PyObject *obj, PyObject *name, ...)
 {
     if (obj == NULL || name == NULL) {
diff --git a/Objects/descrobject.c b/Objects/descrobject.c
index 806c0af..a0eb505 100644
--- a/Objects/descrobject.c
+++ b/Objects/descrobject.c
@@ -851,15 +851,22 @@ static PySequenceMethods mappingproxy_as_sequence = {
 };
 
 static PyObject *
-mappingproxy_get(mappingproxyobject *pp, PyObject *args)
+mappingproxy_get(mappingproxyobject *pp, PyObject *const *args, Py_ssize_t nargs)
 {
-    PyObject *key, *def = Py_None;
-    _Py_IDENTIFIER(get);
+    /* newargs: mapping, key, default=None */
+    PyObject *newargs[3];
+    newargs[0] = pp->mapping;
+    newargs[2] = Py_None;
 
-    if (!PyArg_UnpackTuple(args, "get", 1, 2, &key, &def))
+    if (!_PyArg_UnpackStack(args, nargs, "get", 1, 2,
+                            &newargs[1], &newargs[2]))
+    {
         return NULL;
-    return _PyObject_CallMethodIdObjArgs(pp->mapping, &PyId_get,
-                                         key, def, NULL);
+    }
+    _Py_IDENTIFIER(get);
+    return _PyObject_VectorcallMethodId(&PyId_get, newargs,
+                                        3 | PY_VECTORCALL_ARGUMENTS_OFFSET,
+                                        NULL);
 }
 
 static PyObject *
@@ -894,7 +901,7 @@ mappingproxy_copy(mappingproxyobject *pp, PyObject *Py_UNUSED(ignored))
             to the underlying mapping */
 
 static PyMethodDef mappingproxy_methods[] = {
-    {"get",       (PyCFunction)mappingproxy_get,        METH_VARARGS,
+    {"get",       (PyCFunction)mappingproxy_get,        METH_FASTCALL,
      PyDoc_STR("D.get(k[,d]) -> D[k] if k in D, else d."
                "  d defaults to None.")},
     {"keys",      (PyCFunction)mappingproxy_keys,       METH_NOARGS,