gh-115999: Enable specialization of `CALL` instructions in free-threaded builds (#127123)

The CALL family of instructions were mostly thread-safe already and only required a small number of changes, which are documented below.

A few changes were needed to make CALL_ALLOC_AND_ENTER_INIT thread-safe:

Added _PyType_LookupRefAndVersion, which returns the type version corresponding to the returned ref.

Added _PyType_CacheInitForSpecialization, which takes an init method and the corresponding type version and only populates the specialization cache if the current type version matches the supplied version. This prevents potentially caching a stale value in free-threaded builds if we race with an update to __init__.

Only cache __init__ functions that are deferred in free-threaded builds. This ensures that the reference to __init__ that is stored in the specialization cache is valid if the type version guard in _CHECK_AND_ALLOCATE_OBJECT passes.
Fix a bug in _CREATE_INIT_FRAME where the frame is pushed to the stack on failure.

A few other miscellaneous changes were also needed:

Use {LOCK,UNLOCK}_OBJECT in LIST_APPEND. This ensures that the list's per-object lock is held while we are appending to it.

Add missing co_tlbc for _Py_InitCleanup.

Stop/start the world around setting the eval frame hook. This allows us to read interp->eval_frame non-atomically and preserves the behavior of _CHECK_PEP_523 documented below.

1 files changed, 14 insertions, 0 deletions

diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index c52ed8f..ce876b0 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -835,6 +835,20 @@ extern int _PyObject_StoreInstanceAttribute(PyObject *obj,
                                             PyObject *name, PyObject *value);
 extern bool _PyObject_TryGetInstanceAttribute(PyObject *obj, PyObject *name,
                                               PyObject **attr);
+extern PyObject *_PyType_LookupRefAndVersion(PyTypeObject *, PyObject *,
+                                             unsigned int *);
+
+// Cache the provided init method in the specialization cache of type if the
+// provided type version matches the current version of the type.
+//
+// The cached value is borrowed and is only valid if guarded by a type
+// version check. In free-threaded builds the init method must also use
+// deferred reference counting.
+//
+// Returns 1 if the value was cached or 0 otherwise.
+extern int _PyType_CacheInitForSpecialization(PyHeapTypeObject *type,
+                                              PyObject *init,
+                                              unsigned int tp_version);
 
 #ifdef Py_GIL_DISABLED
 #  define MANAGED_DICT_OFFSET    (((Py_ssize_t)sizeof(PyObject *))*-1)