python · markshannon · Jun 11, 2025 · Jun 11, 2025 · Jun 11, 2025 · Jun 11, 2025
@@ -264,6 +264,32 @@ PyStackRef_IsNullOrInt(_PyStackRef ref);
 
 static const _PyStackRef PyStackRef_ERROR = { .bits = Py_TAG_INVALID };
 
+/* Wrap a pointer in a stack ref.
+ * The resulting stack reference is not safe and should only be used
+ * in the interpreter to pass values from one uop to another.
+ * The GC should never see one of these stack refs. */
+static inline _PyStackRef
+PyStackRef_Wrap(void *ptr)
+{
+    assert(ptr != NULL);
+#ifdef Py_DEBUG
+    return (_PyStackRef){ .bits = ((uintptr_t)ptr) | Py_TAG_INVALID };
+#else
+    return (_PyStackRef){ .bits = (uintptr_t)ptr };
+#endif
+}
+
+static inline void *
+PyStackRef_Unwrap(_PyStackRef ref)
+{
+#ifdef Py_DEBUG
+    assert ((ref.bits & Py_TAG_BITS) == Py_TAG_INVALID);
+    return (void *)(ref.bits & ~Py_TAG_BITS);
+#else
+    return (void *)(ref.bits);
+#endif
+}
+
 static inline bool
 PyStackRef_IsError(_PyStackRef ref)
 {

diff --git a/Lib/test/test_generated_cases.py b/Lib/test/test_generated_cases.py
@@ -56,14 +56,14 @@ class TestEffects(unittest.TestCase):
     def test_effect_sizes(self):
         stack = Stack()
         inputs = [
-            x := StackItem("x", None, "1"),
-            y := StackItem("y", None, "oparg"),
-            z := StackItem("z", None, "oparg*2"),
+            x := StackItem("x", "1"),
+            y := StackItem("y", "oparg"),
+            z := StackItem("z", "oparg*2"),
         ]
         outputs = [
-            StackItem("x", None, "1"),
-            StackItem("b", None, "oparg*4"),
-            StackItem("c", None, "1"),
+            StackItem("x", "1"),
+            StackItem("b", "oparg*4"),
+            StackItem("c", "1"),
         ]
         null = CWriter.null()
         stack.pop(z, null)
@@ -1103,32 +1103,6 @@ def test_array_of_one(self):
         """
         self.run_cases_test(input, output)
 
-    def test_pointer_to_stackref(self):
-        input = """
-        inst(OP, (arg: _PyStackRef * -- out)) {
-            out = *arg;
-            DEAD(arg);
-        }
-        """
-        output = """
-        TARGET(OP) {
-            #if Py_TAIL_CALL_INTERP
-            int opcode = OP;
-            (void)(opcode);
-            #endif
-            frame->instr_ptr = next_instr;
-            next_instr += 1;
-            INSTRUCTION_STATS(OP);
-            _PyStackRef *arg;
-            _PyStackRef out;
-            arg = (_PyStackRef *)stack_pointer[-1].bits;
-            out = *arg;
-            stack_pointer[-1] = out;
-            DISPATCH();
-        }
-        """
-        self.run_cases_test(input, output)
-
     def test_unused_cached_value(self):
         input = """
         op(FIRST, (arg1 -- out)) {

diff --git a/Misc/NEWS.d/next/Tools-Demos/2025-06-11-12-14-06.gh-issue-135379.25ttXq.rst b/Misc/NEWS.d/next/Tools-Demos/2025-06-11-12-14-06.gh-issue-135379.25ttXq.rst
@@ -0,0 +1,4 @@
+The cases generator no longer accepts type annotations on stack items.
+Conversions to non-default types are now done explictly in bytecodes.c and
+optimizer_bytecodes.c. This will simplify code generation for top-of-stack
+caching and other future features.
@@ -985,12 +985,13 @@ dummy_func(
             STAT_INC(BINARY_OP, hit);
         }
 
-        op(_BINARY_OP_SUBSCR_INIT_CALL, (container, sub, getitem -- new_frame: _PyInterpreterFrame* )) {
-            new_frame = _PyFrame_PushUnchecked(tstate, getitem, 2, frame);
-            new_frame->localsplus[0] = container;
-            new_frame->localsplus[1] = sub;
+        op(_BINARY_OP_SUBSCR_INIT_CALL, (container, sub, getitem -- new_frame)) {
+            _PyInterpreterFrame* pushed_frame = _PyFrame_PushUnchecked(tstate, getitem, 2, frame);
+            pushed_frame->localsplus[0] = container;
+            pushed_frame->localsplus[1] = sub;
             INPUTS_DEAD();
             frame->return_offset = INSTRUCTION_SIZE;
+            new_frame = PyStackRef_Wrap(pushed_frame);
         }
 
         macro(BINARY_OP_SUBSCR_GETITEM) =
@@ -1296,20 +1297,21 @@ dummy_func(
 
         macro(SEND) = _SPECIALIZE_SEND + _SEND;
 
-        op(_SEND_GEN_FRAME, (receiver, v -- receiver, gen_frame: _PyInterpreterFrame *)) {
+        op(_SEND_GEN_FRAME, (receiver, v -- receiver, gen_frame)) {
             PyGenObject *gen = (PyGenObject *)PyStackRef_AsPyObjectBorrow(receiver);
             DEOPT_IF(Py_TYPE(gen) != &PyGen_Type && Py_TYPE(gen) != &PyCoro_Type);
             DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING);
             STAT_INC(SEND, hit);
-            gen_frame = &gen->gi_iframe;
-            _PyFrame_StackPush(gen_frame, PyStackRef_MakeHeapSafe(v));
+            _PyInterpreterFrame *pushed_frame = &gen->gi_iframe;
+            _PyFrame_StackPush(pushed_frame, PyStackRef_MakeHeapSafe(v));
             DEAD(v);
             gen->gi_frame_state = FRAME_EXECUTING;
             gen->gi_exc_state.previous_item = tstate->exc_info;
             tstate->exc_info = &gen->gi_exc_state;
             assert(INSTRUCTION_SIZE + oparg <= UINT16_MAX);
             frame->return_offset = (uint16_t)(INSTRUCTION_SIZE + oparg);
-            gen_frame->previous = frame;
+            pushed_frame->previous = frame;
+            gen_frame = PyStackRef_Wrap(pushed_frame);
         }
 
         macro(SEND_GEN) =
@@ -2463,7 +2465,7 @@ dummy_func(
             _LOAD_ATTR_CLASS +
             _PUSH_NULL_CONDITIONAL;
 
-        op(_LOAD_ATTR_PROPERTY_FRAME, (fget/4, owner -- new_frame: _PyInterpreterFrame *)) {
+        op(_LOAD_ATTR_PROPERTY_FRAME, (fget/4, owner -- new_frame)) {
             assert((oparg & 1) == 0);
             assert(Py_IS_TYPE(fget, &PyFunction_Type));
             PyFunctionObject *f = (PyFunctionObject *)fget;
@@ -2473,9 +2475,10 @@ dummy_func(
             DEOPT_IF(code->co_argcount != 1);
             DEOPT_IF(!_PyThreadState_HasStackSpace(tstate, code->co_framesize));
             STAT_INC(LOAD_ATTR, hit);
-            new_frame = _PyFrame_PushUnchecked(tstate, PyStackRef_FromPyObjectNew(fget), 1, frame);
-            new_frame->localsplus[0] = owner;
+            _PyInterpreterFrame *pushed_frame = _PyFrame_PushUnchecked(tstate, PyStackRef_FromPyObjectNew(fget), 1, frame);
+            pushed_frame->localsplus[0] = owner;
             DEAD(owner);
+            new_frame = PyStackRef_Wrap(pushed_frame);
         }
 
         macro(LOAD_ATTR_PROPERTY) =
@@ -3344,7 +3347,7 @@ dummy_func(
             _ITER_JUMP_RANGE +
             _ITER_NEXT_RANGE;
 
-        op(_FOR_ITER_GEN_FRAME, (iter, null -- iter, null, gen_frame: _PyInterpreterFrame*)) {
+        op(_FOR_ITER_GEN_FRAME, (iter, null -- iter, null, gen_frame)) {
             PyGenObject *gen = (PyGenObject *)PyStackRef_AsPyObjectBorrow(iter);
             DEOPT_IF(Py_TYPE(gen) != &PyGen_Type);
 #ifdef Py_GIL_DISABLED
@@ -3356,14 +3359,15 @@ dummy_func(
 #endif
             DEOPT_IF(gen->gi_frame_state >= FRAME_EXECUTING);
             STAT_INC(FOR_ITER, hit);
-            gen_frame = &gen->gi_iframe;
-            _PyFrame_StackPush(gen_frame, PyStackRef_None);
+            _PyInterpreterFrame *pushed_frame = &gen->gi_iframe;
+            _PyFrame_StackPush(pushed_frame, PyStackRef_None);
             gen->gi_frame_state = FRAME_EXECUTING;
             gen->gi_exc_state.previous_item = tstate->exc_info;
             tstate->exc_info = &gen->gi_exc_state;
-            gen_frame->previous = frame;
+            pushed_frame->previous = frame;
             // oparg is the return offset from the next instruction.
             frame->return_offset = (uint16_t)(INSTRUCTION_SIZE + oparg);
+            gen_frame = PyStackRef_Wrap(pushed_frame);
         }
 
         macro(FOR_ITER_GEN) =
@@ -3715,7 +3719,7 @@ dummy_func(
         macro(CALL) = _SPECIALIZE_CALL + unused/2 + _MAYBE_EXPAND_METHOD + _DO_CALL + _CHECK_PERIODIC;
         macro(INSTRUMENTED_CALL) = unused/3 + _MAYBE_EXPAND_METHOD + _MONITOR_CALL + _DO_CALL + _CHECK_PERIODIC;
 
-        op(_PY_FRAME_GENERAL, (callable, self_or_null, args[oparg] -- new_frame: _PyInterpreterFrame*)) {
+        op(_PY_FRAME_GENERAL, (callable, self_or_null, args[oparg] -- new_frame)) {
             PyObject *callable_o = PyStackRef_AsPyObjectBorrow(callable);
 
             // oparg counts all of the args, but *not* self:
@@ -3737,7 +3741,7 @@ dummy_func(
             if (temp == NULL) {
                 ERROR_NO_POP();
             }
-            new_frame = temp;
+            new_frame = PyStackRef_Wrap(temp);
         }
 
         op(_CHECK_FUNCTION_VERSION, (func_version/2, callable, unused, unused[oparg] -- callable, unused, unused[oparg])) {
@@ -3874,27 +3878,26 @@ dummy_func(
             DEOPT_IF(tstate->py_recursion_remaining <= 1);
         }
 
-        replicate(5) pure op(_INIT_CALL_PY_EXACT_ARGS, (callable, self_or_null, args[oparg] -- new_frame: _PyInterpreterFrame*)) {
+        replicate(5) pure op(_INIT_CALL_PY_EXACT_ARGS, (callable, self_or_null, args[oparg] -- new_frame)) {
             int has_self = !PyStackRef_IsNull(self_or_null);
             STAT_INC(CALL, hit);
-            new_frame = _PyFrame_PushUnchecked(tstate, callable, oparg + has_self, frame);
-            _PyStackRef *first_non_self_local = new_frame->localsplus + has_self;
-            new_frame->localsplus[0] = self_or_null;
+            _PyInterpreterFrame *pushed_frame = _PyFrame_PushUnchecked(tstate, callable, oparg + has_self, frame);
+            _PyStackRef *first_non_self_local = pushed_frame->localsplus + has_self;
+            pushed_frame->localsplus[0] = self_or_null;
             for (int i = 0; i < oparg; i++) {
                 first_non_self_local[i] = args[i];
             }
             INPUTS_DEAD();
+            new_frame = PyStackRef_Wrap(pushed_frame);
         }
 
-        op(_PUSH_FRAME, (new_frame: _PyInterpreterFrame* -- )) {
-            // Write it out explicitly because it's subtly different.
-            // Eventually this should be the only occurrence of this code.
+        op(_PUSH_FRAME, (new_frame -- )) {
             assert(tstate->interp->eval_frame == NULL);
-            _PyInterpreterFrame *temp = new_frame;
+            _PyInterpreterFrame *temp = PyStackRef_Unwrap(new_frame);
             DEAD(new_frame);
             SYNC_SP();
             _PyFrame_SetStackPointer(frame, stack_pointer);
-            assert(new_frame->previous == frame || new_frame->previous->previous == frame);
+            assert(temp->previous == frame || temp->previous->previous == frame);
             CALL_STAT_INC(inlined_py_calls);
             frame = tstate->current_frame = temp;
             tstate->py_recursion_remaining--;
@@ -4046,7 +4049,7 @@ dummy_func(
             PyStackRef_CLOSE(temp);
         }
 
-        op(_CREATE_INIT_FRAME, (init, self, args[oparg] -- init_frame: _PyInterpreterFrame *)) {
+        op(_CREATE_INIT_FRAME, (init, self, args[oparg] -- init_frame)) {
             _PyInterpreterFrame *shim = _PyFrame_PushTrampolineUnchecked(
                 tstate, (PyCodeObject *)&_Py_InitCleanup, 1, frame);
             assert(_PyFrame_GetBytecode(shim)[0].op.code == EXIT_INIT_CHECK);
@@ -4063,12 +4066,12 @@ dummy_func(
                 _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,
              * as it will be checked after start_frame */
             tstate->py_recursion_remaining--;
+            init_frame = PyStackRef_Wrap(temp);
         }
 
         macro(CALL_ALLOC_AND_ENTER_INIT) =
@@ -4594,7 +4597,7 @@ dummy_func(
             res = PyStackRef_FromPyObjectSteal(res_o);
         }
 
-        op(_PY_FRAME_KW, (callable, self_or_null, args[oparg], kwnames -- new_frame: _PyInterpreterFrame*)) {
+        op(_PY_FRAME_KW, (callable, self_or_null, args[oparg], kwnames -- new_frame)) {
             PyObject *callable_o = PyStackRef_AsPyObjectBorrow(callable);
 
             // oparg counts all of the args, but *not* self:
@@ -4621,7 +4624,7 @@ dummy_func(
             DEAD(callable);
             SYNC_SP();
             ERROR_IF(temp == NULL);
-            new_frame = temp;
+            new_frame = PyStackRef_Wrap(temp);
         }
 
         op(_CHECK_FUNCTION_VERSION_KW, (func_version/2, callable, unused, unused[oparg], unused -- callable, unused, unused[oparg], unused)) {