bpo-45947: Place dict and values pointer at fixed (negative) offset just before GC header. (GH-29879)

* Place __dict__ immediately before GC header for plain Python objects.

* Fix up lazy dict creation logic to use managed dict pointers.

* Manage values pointer, placing them directly before managed dict pointers.

* Convert hint-based load/store attr specialization target managed dict classes.

* Specialize LOAD_METHOD for managed dict objects.

* Remove unsafe _PyObject_GC_Calloc function.

* Remove unsafe _PyObject_GC_Malloc() function.

* Add comment explaning use of Py_TPFLAGS_MANAGED_DICT.

1 files changed, 11 insertions, 13 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index a8bbad3..446772d 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -3599,9 +3599,9 @@ check_eval_breaker:
             _PyAttrCache *cache1 = &caches[-1].attr;
             assert(cache1->tp_version != 0);
             DEOPT_IF(tp->tp_version_tag != cache1->tp_version, LOAD_ATTR);
-            assert(tp->tp_dictoffset > 0);
-            assert(tp->tp_inline_values_offset > 0);
-            PyDictValues *values = *(PyDictValues **)(((char *)owner) + tp->tp_inline_values_offset);
+            assert(tp->tp_dictoffset < 0);
+            assert(tp->tp_flags & Py_TPFLAGS_MANAGED_DICT);
+            PyDictValues *values = *_PyObject_ValuesPointer(owner);
             DEOPT_IF(values == NULL, LOAD_ATTR);
             res = values->values[cache0->index];
             DEOPT_IF(res == NULL, LOAD_ATTR);
@@ -3633,8 +3633,8 @@ check_eval_breaker:
             _PyAttrCache *cache1 = &caches[-1].attr;
             assert(cache1->tp_version != 0);
             DEOPT_IF(tp->tp_version_tag != cache1->tp_version, LOAD_ATTR);
-            assert(tp->tp_dictoffset > 0);
-            PyDictObject *dict = *(PyDictObject **)(((char *)owner) + tp->tp_dictoffset);
+            assert(tp->tp_flags & Py_TPFLAGS_MANAGED_DICT);
+            PyDictObject *dict = *(PyDictObject **)_PyObject_ManagedDictPointer(owner);
             DEOPT_IF(dict == NULL, LOAD_ATTR);
             assert(PyDict_CheckExact((PyObject *)dict));
             PyObject *name = GETITEM(names, cache0->original_oparg);
@@ -3701,9 +3701,8 @@ check_eval_breaker:
             _PyAttrCache *cache1 = &caches[-1].attr;
             assert(cache1->tp_version != 0);
             DEOPT_IF(tp->tp_version_tag != cache1->tp_version, STORE_ATTR);
-            assert(tp->tp_dictoffset > 0);
-            assert(tp->tp_inline_values_offset > 0);
-            PyDictValues *values = *(PyDictValues **)(((char *)owner) + tp->tp_inline_values_offset);
+            assert(tp->tp_flags & Py_TPFLAGS_MANAGED_DICT);
+            PyDictValues *values = *_PyObject_ValuesPointer(owner);
             DEOPT_IF(values == NULL, STORE_ATTR);
             STAT_INC(STORE_ATTR, hit);
             int index = cache0->index;
@@ -3731,8 +3730,8 @@ check_eval_breaker:
             _PyAttrCache *cache1 = &caches[-1].attr;
             assert(cache1->tp_version != 0);
             DEOPT_IF(tp->tp_version_tag != cache1->tp_version, STORE_ATTR);
-            assert(tp->tp_dictoffset > 0);
-            PyDictObject *dict = *(PyDictObject **)(((char *)owner) + tp->tp_dictoffset);
+            assert(tp->tp_flags & Py_TPFLAGS_MANAGED_DICT);
+            PyDictObject *dict = *(PyDictObject **)_PyObject_ManagedDictPointer(owner);
             DEOPT_IF(dict == NULL, STORE_ATTR);
             assert(PyDict_CheckExact((PyObject *)dict));
             PyObject *name = GETITEM(names, cache0->original_oparg);
@@ -4506,9 +4505,8 @@ check_eval_breaker:
             _PyObjectCache *cache2 = &caches[-2].obj;
 
             DEOPT_IF(self_cls->tp_version_tag != cache1->tp_version, LOAD_METHOD);
-            assert(self_cls->tp_dictoffset > 0);
-            assert(self_cls->tp_inline_values_offset > 0);
-            PyDictObject *dict = *(PyDictObject **)(((char *)self) + self_cls->tp_dictoffset);
+            assert(self_cls->tp_flags & Py_TPFLAGS_MANAGED_DICT);
+            PyDictObject *dict = *(PyDictObject**)_PyObject_ManagedDictPointer(self);
             DEOPT_IF(dict != NULL, LOAD_METHOD);
             DEOPT_IF(((PyHeapTypeObject *)self_cls)->ht_cached_keys->dk_version != cache1->dk_version_or_hint, LOAD_METHOD);
             STAT_INC(LOAD_METHOD, hit);