gh-115999: Specialize `CALL_KW` in free-threaded builds (#127713)

* Enable specialization of CALL_KW

* Fix bug pushing frame in _PY_FRAME_KW

`_PY_FRAME_KW` pushes a pointer to the new frame onto the stack for
consumption by the next uop. When pushing the frame fails, we do not
want to push the result, `NULL`, to the stack because it is not
a valid stackref. This works in the default build because `PyStackRef_NULL`
 and `NULL` are the same value, so the `PyStackRef_XCLOSE()` in the error
handler ignores it. In the free-threaded build the values are not the same;
`PyStackRef_XCLOSE()` will attempt to decref a null pointer.

1 files changed, 7 insertions, 4 deletions

diff --git a/Python/executor_cases.c.h b/Python/executor_cases.c.h
index 987ff2e..18f1977 100644
--- a/Python/executor_cases.c.h
+++ b/Python/executor_cases.c.h
@@ -5235,7 +5235,7 @@
             int code_flags = ((PyCodeObject*)PyFunction_GET_CODE(callable_o))->co_flags;
             PyObject *locals = code_flags & CO_OPTIMIZED ? NULL : Py_NewRef(PyFunction_GET_GLOBALS(callable_o));
             _PyFrame_SetStackPointer(frame, stack_pointer);
-            new_frame = _PyEvalFramePushAndInit(
+            _PyInterpreterFrame *temp = _PyEvalFramePushAndInit(
                 tstate, callable[0], locals,
                 args, positional_args, kwnames_o, frame
             );
@@ -5243,12 +5243,15 @@
             PyStackRef_CLOSE(kwnames);
             // The frame has stolen all the arguments from the stack,
             // so there is no need to clean them up.
-            stack_pointer[-3 - oparg].bits = (uintptr_t)new_frame;
-            stack_pointer += -2 - oparg;
+            stack_pointer += -3 - oparg;
             assert(WITHIN_STACK_BOUNDS());
-            if (new_frame == NULL) {
+            if (temp == NULL) {
                 JUMP_TO_ERROR();
             }
+            new_frame = temp;
+            stack_pointer[0].bits = (uintptr_t)new_frame;
+            stack_pointer += 1;
+            assert(WITHIN_STACK_BOUNDS());
             break;
         }