markshannon · Sep 15, 2022 · May 3, 2022 · May 3, 2022 · May 3, 2022 · May 3, 2022
diff --git a/Include/cpython/funcobject.h b/Include/cpython/funcobject.h
@@ -69,6 +69,7 @@ PyAPI_FUNC(PyObject *) PyFunction_GetGlobals(PyObject *);
 PyAPI_FUNC(PyObject *) PyFunction_GetModule(PyObject *);
 PyAPI_FUNC(PyObject *) PyFunction_GetDefaults(PyObject *);
 PyAPI_FUNC(int) PyFunction_SetDefaults(PyObject *, PyObject *);
+PyAPI_FUNC(int) PyFunction_SetVectorcall(PyFunctionObject *, vectorcallfunc);
 PyAPI_FUNC(PyObject *) PyFunction_GetKwDefaults(PyObject *);
 PyAPI_FUNC(int) PyFunction_SetKwDefaults(PyObject *, PyObject *);
 PyAPI_FUNC(PyObject *) PyFunction_GetClosure(PyObject *);

diff --git a/Lib/test/test_call.py b/Lib/test/test_call.py
@@ -665,6 +665,15 @@ def __call__(self, *args):
                 self.assertEqual(expected, meth(*args1, **kwargs))
                 self.assertEqual(expected, wrapped(*args, **kwargs))
 
+    def test_setvectorcall(self):
+        from _testcapi import pyobject_setvectorcall
+        def f(num): return num + 1
+        num = 10
+        assert f(num) is 11
+        pyobject_setvectorcall(f)
+        # make sure specializer is triggered by running > 50 times
+        for _ in range(51):
+            assert f(num) is None
 
 class A:
     def method_two_args(self, x, y):

diff --git a/Misc/NEWS.d/next/C API/2022-05-03-19-35-37.gh-issue-92193.61VoFL.rst b/Misc/NEWS.d/next/C API/2022-05-03-19-35-37.gh-issue-92193.61VoFL.rst
@@ -0,0 +1,6 @@
+CPython extensions providing optimized execution of Python bytecode (like Cinder JIT and Pyjion)
+can benefit from being able to modify the vectorcall field on instances of PyFunctionObject to allow calling the optimized path (e.g. JIT-compiled) directly.
+
+This PR introduces an API call where vectorcall field can be modified like so:
+
+`void PyFunction_SetVectorcall(PyFunctionObject *func, vectorcallfunc vectorcall);`
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
@@ -5285,6 +5285,26 @@ test_pyobject_vectorcall(PyObject *self, PyObject *args)
 }
 
 
+static PyObject *
+override_vectorcall(
+    PyObject *callable, PyObject *const *args, size_t nargsf, PyObject *kwnames) {
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+test_pyobject_setvectorcall(PyObject *self, PyObject *args)
+{
+    PyFunctionObject *func = NULL;
+    if (!PyArg_ParseTuple(args, "O", &func)) {
+        return NULL;
+    }
+    if(PyFunction_SetVectorcall(func, (vectorcallfunc)override_vectorcall) != 0) {
+        PyErr_SetString(PyExc_TypeError, "Something went wrong setting vectorcall field");
+        return NULL;
+    }
+    Py_RETURN_NONE;
+}
+
 static PyObject *
 test_pyvectorcall_call(PyObject *self, PyObject *args)
 {
@@ -6186,6 +6206,7 @@ static PyMethodDef TestMethods[] = {
     {"pyobject_fastcall", test_pyobject_fastcall, METH_VARARGS},
     {"pyobject_fastcalldict", test_pyobject_fastcalldict, METH_VARARGS},
     {"pyobject_vectorcall", test_pyobject_vectorcall, METH_VARARGS},
+    {"pyobject_setvectorcall", test_pyobject_setvectorcall, METH_VARARGS},
     {"pyvectorcall_call", test_pyvectorcall_call, METH_VARARGS},
     {"stack_pointer", stack_pointer, METH_NOARGS},
 #ifdef W_STOPCODE

diff --git a/Objects/funcobject.c b/Objects/funcobject.c
@@ -133,6 +133,9 @@ uint32_t _PyFunction_GetVersionForCurrentState(PyFunctionObject *func)
     if (func->func_version != 0) {
         return func->func_version;
     }
+    if (func->vectorcall != _PyFunction_Vectorcall) {
+        return 0;
+    }
     if (next_func_version == 0) {
         return 0;
     }
@@ -208,6 +211,14 @@ PyFunction_SetDefaults(PyObject *op, PyObject *defaults)
     return 0;
 }
 
+int
+PyFunction_SetVectorcall(PyFunctionObject *func, vectorcallfunc vectorcall)
+{
+    func->func_version = 0;
+    func->vectorcall = vectorcall;
+    return 0;
+}
+
 PyObject *
 PyFunction_GetKwDefaults(PyObject *op)
 {

@@ -4792,7 +4792,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
             PyObject *function = PEEK(total_args + 1);
             int positional_args = total_args - KWNAMES_LEN();
             // Check if the call can be inlined or not
-            if (Py_TYPE(function) == &PyFunction_Type && tstate->interp->eval_frame == NULL) {
+            if (Py_TYPE(function) == &PyFunction_Type && tstate->interp->eval_frame == NULL && ((PyFunctionObject *)function)->vectorcall == _PyFunction_Vectorcall) {
                 int code_flags = ((PyCodeObject*)PyFunction_GET_CODE(function))->co_flags;
                 PyObject *locals = code_flags & CO_OPTIMIZED ? NULL : PyFunction_GET_GLOBALS(function);
                 STACK_SHRINK(total_args);