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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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100
Python/specialize.c
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@ -451,6 +451,7 @@ initial_counter_value(void) {
#define SPEC_FAIL_NON_OBJECT_SLOT 14
#define SPEC_FAIL_READ_ONLY 15
#define SPEC_FAIL_AUDITED_SLOT 16
#define SPEC_FAIL_NOT_MANAGED_DICT 17
/* Methods */
@ -506,7 +507,7 @@ specialize_module_load_attr(
PyObject *value = NULL;
PyObject *getattr;
_Py_IDENTIFIER(__getattr__);
assert(owner->ob_type->tp_inline_values_offset == 0);
assert((owner->ob_type->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0);
PyDictObject *dict = (PyDictObject *)m->md_dict;
if (dict == NULL) {
SPECIALIZATION_FAIL(opcode, SPEC_FAIL_NO_DICT);
@ -634,66 +635,44 @@ specialize_dict_access(
assert(kind == NON_OVERRIDING || kind == NON_DESCRIPTOR || kind == ABSENT ||
kind == BUILTIN_CLASSMETHOD || kind == PYTHON_CLASSMETHOD);
// No descriptor, or non overriding.
if (type->tp_dictoffset < 0) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
if ((type->tp_flags & Py_TPFLAGS_MANAGED_DICT) == 0) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NOT_MANAGED_DICT);
return 0;
}
if (type->tp_dictoffset > 0) {
PyObject **dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
PyDictObject *dict = (PyDictObject *)*dictptr;
if (type->tp_inline_values_offset && dict == NULL) {
// Virtual dictionary
PyDictKeysObject *keys = ((PyHeapTypeObject *)type)->ht_cached_keys;
assert(type->tp_inline_values_offset > 0);
assert(PyUnicode_CheckExact(name));
Py_ssize_t index = _PyDictKeys_StringLookup(keys, name);
assert (index != DKIX_ERROR);
if (index != (uint16_t)index) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
return 0;
}
cache1->tp_version = type->tp_version_tag;
cache0->index = (uint16_t)index;
*instr = _Py_MAKECODEUNIT(values_op, _Py_OPARG(*instr));
PyObject **dictptr = _PyObject_ManagedDictPointer(owner);
PyDictObject *dict = (PyDictObject *)*dictptr;
if (dict == NULL) {
// Virtual dictionary
PyDictKeysObject *keys = ((PyHeapTypeObject *)type)->ht_cached_keys;
assert(PyUnicode_CheckExact(name));
Py_ssize_t index = _PyDictKeys_StringLookup(keys, name);
assert (index != DKIX_ERROR);
if (index != (uint16_t)index) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
return 0;
}
else {
if (dict == NULL || !PyDict_CheckExact(dict)) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NO_DICT);
return 0;
}
// We found an instance with a __dict__.
PyObject *value = NULL;
Py_ssize_t hint =
_PyDict_GetItemHint(dict, name, -1, &value);
if (hint != (uint32_t)hint) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
return 0;
}
cache1->dk_version_or_hint = (uint32_t)hint;
cache1->tp_version = type->tp_version_tag;
*instr = _Py_MAKECODEUNIT(hint_op, _Py_OPARG(*instr));
return 1;
cache1->tp_version = type->tp_version_tag;
cache0->index = (uint16_t)index;
*instr = _Py_MAKECODEUNIT(values_op, _Py_OPARG(*instr));
}
else {
if (!PyDict_CheckExact(dict)) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NO_DICT);
return 0;
}
// We found an instance with a __dict__.
PyObject *value = NULL;
Py_ssize_t hint =
_PyDict_GetItemHint(dict, name, -1, &value);
if (hint != (uint32_t)hint) {
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_OUT_OF_RANGE);
return 0;
}
cache1->dk_version_or_hint = (uint32_t)hint;
cache1->tp_version = type->tp_version_tag;
*instr = _Py_MAKECODEUNIT(hint_op, _Py_OPARG(*instr));
}
assert(type->tp_dictoffset == 0);
/* No attribute in instance dictionary */
switch(kind) {
case NON_OVERRIDING:
case BUILTIN_CLASSMETHOD:
case PYTHON_CLASSMETHOD:
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NON_OVERRIDING_DESCRIPTOR);
return 0;
case NON_DESCRIPTOR:
/* To do -- Optimize this case */
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_NOT_DESCRIPTOR);
return 0;
case ABSENT:
SPECIALIZATION_FAIL(base_op, SPEC_FAIL_EXPECTED_ERROR);
return 0;
default:
Py_UNREACHABLE();
}
return 1;
}
int
@ -965,12 +944,6 @@ _Py_Specialize_LoadMethod(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name,
}
goto success;
}
// Technically this is fine for bound method calls, but it's uncommon and
// slightly slower at runtime to get dict.
if (owner_cls->tp_dictoffset < 0) {
SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_OUT_OF_RANGE);
goto fail;
}
PyObject *descr = NULL;
DesciptorClassification kind = 0;
@ -980,9 +953,8 @@ _Py_Specialize_LoadMethod(PyObject *owner, _Py_CODEUNIT *instr, PyObject *name,
SPECIALIZATION_FAIL(LOAD_METHOD, load_method_fail_kind(kind));
goto fail;
}
if (owner_cls->tp_inline_values_offset) {
PyObject **owner_dictptr = _PyObject_DictPointer(owner);
assert(owner_dictptr);
if (owner_cls->tp_flags & Py_TPFLAGS_MANAGED_DICT) {
PyObject **owner_dictptr = _PyObject_ManagedDictPointer(owner);
if (*owner_dictptr) {
SPECIALIZATION_FAIL(LOAD_METHOD, SPEC_FAIL_IS_ATTR);
goto fail;