Fix issue with _CREATE_INIT_FRAME

Fix a bug in `_CREATE_INIT_FRAME` where the frame is pushed to the stack on failure.
`_CREATE_INIT_FRAME` 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 and will be exposed to the generic
error handling code in the interpreter loop. This worked in default builds because
`PyStackRef_NULL` is `NULL` in default builds, which is not the case in free-threaded
builds.

Author: mpage

Lib/test/test_opcache.py

@@ -500,6 +500,11 @@ def __init__(self):
         pass
 
 
+class InitTakesArg:
+    def __init__(self, arg):
+        self.arg = arg
+
+
 class TestCallCache(TestBase):
     def test_too_many_defaults_0(self):
         def f():
@@ -547,6 +552,20 @@ def count_args(self, *args):
         MyClass.__init__.__code__ = count_args.__code__
         instantiate()
 
+    @disabling_optimizer
+    @requires_specialization_ft
+    def test_push_init_frame_fails(self):
+        def instantiate():
+            return InitTakesArg()
+
+        for _ in range(2):
+            with self.assertRaises(TypeError):
+                instantiate()
+        self.assert_specialized(instantiate, "CALL_ALLOC_AND_ENTER_INIT")
+
+        with self.assertRaises(TypeError):
+            instantiate()
+
 
 @threading_helper.requires_working_threading()
 class TestRacesDoNotCrash(TestBase):

Python/bytecodes.c

@@ -3744,13 +3744,14 @@ dummy_func(
             shim->localsplus[0] = PyStackRef_DUP(self[0]);
             DEAD(init);
             DEAD(self);
-            init_frame = _PyEvalFramePushAndInit(
+            _PyInterpreterFrame *temp = _PyEvalFramePushAndInit(
                 tstate, init[0], NULL, args-1, oparg+1, NULL, shim);
             SYNC_SP();
-            if (init_frame == NULL) {
+            if (temp == NULL) {
                 _PyEval_FrameClearAndPop(tstate, shim);
                 ERROR_NO_POP();
             }
+            init_frame = temp;
             frame->return_offset = 1 + INLINE_CACHE_ENTRIES_CALL;
             /* Account for pushing the extra frame.
              * We don't check recursion depth here,