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

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* 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.
This commit is contained in:
Mark Shannon 2021-12-07 16:02:53 +00:00 • committed by GitHub
parent c7e7a4b969
commit 8319114fee
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GPG key ID: 4AEE18F83AFDEB23
19 changed files with 260 additions and 285 deletions
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71
Objects/object.c
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@ -1073,6 +1073,9 @@ _PyObject_DictPointer(PyObject *obj)
Py_ssize_t dictoffset;
PyTypeObject *tp = Py_TYPE(obj);
if (tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
return _PyObject_ManagedDictPointer(obj);
}
dictoffset = tp->tp_dictoffset;
if (dictoffset == 0)
return NULL;
@ -1096,24 +1099,20 @@ _PyObject_DictPointer(PyObject *obj)
PyObject **
_PyObject_GetDictPtr(PyObject *obj)
{
PyObject **dict_ptr = _PyObject_DictPointer(obj);
if (dict_ptr == NULL) {
return NULL;
}
if (*dict_ptr != NULL) {
return dict_ptr;
if ((Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
return _PyObject_DictPointer(obj);
}
PyObject **dict_ptr = _PyObject_ManagedDictPointer(obj);
PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
if (values_ptr == NULL || *values_ptr == NULL) {
if (*values_ptr == NULL) {
return dict_ptr;
}
assert(*dict_ptr == NULL);
PyObject *dict = _PyObject_MakeDictFromInstanceAttributes(obj, *values_ptr);
if (dict == NULL) {
PyErr_Clear();
return NULL;
}
assert(*dict_ptr == NULL);
assert(*values_ptr != NULL);
*values_ptr = NULL;
*dict_ptr = dict;
return dict_ptr;
@ -1185,10 +1184,12 @@ _PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
}
}
}
PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
if (values_ptr && *values_ptr) {
PyDictValues *values;
if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) &&
(values = *_PyObject_ValuesPointer(obj)))
{
assert(*_PyObject_DictPointer(obj) == NULL);
PyObject *attr = _PyObject_GetInstanceAttribute(obj, *values_ptr, name);
PyObject *attr = _PyObject_GetInstanceAttribute(obj, values, name);
if (attr != NULL) {
*method = attr;
Py_XDECREF(descr);
@ -1240,17 +1241,6 @@ _PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **method)
return 0;
}
PyDictValues **
_PyObject_ValuesPointer(PyObject *obj)
{
PyTypeObject *tp = Py_TYPE(obj);
Py_ssize_t offset = tp->tp_inline_values_offset;
if (offset == 0) {
return NULL;
}
return (PyDictValues **) ((char *)obj + offset);
}
/* Generic GetAttr functions - put these in your tp_[gs]etattro slot. */
PyObject *
@ -1267,7 +1257,6 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
PyObject *descr = NULL;
PyObject *res = NULL;
descrgetfunc f;
Py_ssize_t dictoffset;
PyObject **dictptr;
if (!PyUnicode_Check(name)){
@ -1299,8 +1288,10 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
}
}
if (dict == NULL) {
PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
if (values_ptr && *values_ptr) {
if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) &&
*_PyObject_ValuesPointer(obj))
{
PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
if (PyUnicode_CheckExact(name)) {
assert(*_PyObject_DictPointer(obj) == NULL);
res = _PyObject_GetInstanceAttribute(obj, *values_ptr, name);
@ -1320,22 +1311,8 @@ _PyObject_GenericGetAttrWithDict(PyObject *obj, PyObject *name,
}
}
else {
/* Inline _PyObject_DictPointer */
dictoffset = tp->tp_dictoffset;
if (dictoffset != 0) {
if (dictoffset < 0) {
Py_ssize_t tsize = Py_SIZE(obj);
if (tsize < 0) {
tsize = -tsize;
}
size_t size = _PyObject_VAR_SIZE(tp, tsize);
_PyObject_ASSERT(obj, size <= PY_SSIZE_T_MAX);
dictoffset += (Py_ssize_t)size;
_PyObject_ASSERT(obj, dictoffset > 0);
_PyObject_ASSERT(obj, dictoffset % SIZEOF_VOID_P == 0);
}
dictptr = (PyObject **) ((char *)obj + dictoffset);
dictptr = _PyObject_DictPointer(obj);
if (dictptr) {
dict = *dictptr;
}
}
@ -1426,9 +1403,8 @@ _PyObject_GenericSetAttrWithDict(PyObject *obj, PyObject *name,
}
if (dict == NULL) {
PyDictValues **values_ptr = _PyObject_ValuesPointer(obj);
if (values_ptr && *values_ptr) {
res = _PyObject_StoreInstanceAttribute(obj, *values_ptr, name, value);
if ((tp->tp_flags & Py_TPFLAGS_MANAGED_DICT) && *_PyObject_ValuesPointer(obj)) {
res = _PyObject_StoreInstanceAttribute(obj, *_PyObject_ValuesPointer(obj), name, value);
}
else {
PyObject **dictptr = _PyObject_DictPointer(obj);
@ -1478,8 +1454,9 @@ PyObject_GenericSetDict(PyObject *obj, PyObject *value, void *context)
{
PyObject **dictptr = _PyObject_GetDictPtr(obj);
if (dictptr == NULL) {
PyDictValues** values_ptr = _PyObject_ValuesPointer(obj);
if (values_ptr != NULL && *values_ptr != NULL) {
if (_PyType_HasFeature(Py_TYPE(obj), Py_TPFLAGS_MANAGED_DICT) &&
*_PyObject_ValuesPointer(obj) != NULL)
{
/* Was unable to convert to dict */
PyErr_NoMemory();
}