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bpo-42927: Inline cache for attributes defined with '__slots__' (#24216)
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@gvanrossum
gvanrossum authored Jan 30, 2021
1 parent ba7a99d commit 5c5a938
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-01-15-20-05-56.bpo-42927.GI-l-7.rst
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@@ -0,0 +1,2 @@
The inline cache for ``LOAD_ATTR`` now also optimizes access to attributes defined by ``__slots__``.
This makes reading such attribute up to 30% faster.
180 changes: 116 additions & 64 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@
#include "opcode.h"
#include "pydtrace.h"
#include "setobject.h"
#include "structmember.h" // struct PyMemberDef, T_OFFSET_EX

#include <ctype.h>

Expand Down Expand Up @@ -3169,114 +3170,165 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
if (co_opcache != NULL && PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG))
{
if (co_opcache->optimized > 0) {
/* Fast path -- cache hit makes LOAD_ATTR ~30% faster */
// Fast path -- cache hit makes LOAD_ATTR ~30% faster.
la = &co_opcache->u.la;
if (la->type == type && la->tp_version_tag == type->tp_version_tag)
{
assert(type->tp_dict != NULL);
assert(type->tp_dictoffset > 0);

dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
dict = *dictptr;
if (dict != NULL && PyDict_CheckExact(dict)) {
Py_ssize_t hint = la->hint;
Py_INCREF(dict);
res = NULL;
la->hint = _PyDict_GetItemHint((PyDictObject*)dict, name, hint, &res);

// Hint >= 0 is a dict index; hint == -1 is a dict miss.
// Hint < -1 is an inverted slot offset: offset is strictly > 0,
// so ~offset is strictly < -1 (assuming 2's complement).
if (la->hint < -1) {
// Even faster path -- slot hint.
Py_ssize_t offset = ~la->hint;
// fprintf(stderr, "Using hint for offset %zd\n", offset);
char *addr = (char *)owner + offset;
res = *(PyObject **)addr;
if (res != NULL) {
if (la->hint == hint && hint >= 0) {
/* Our hint has helped -- cache hit. */
OPCACHE_STAT_ATTR_HIT();
} else {
/* The hint we provided didn't work.
Maybe next time? */
OPCACHE_MAYBE_DEOPT_LOAD_ATTR();
}

Py_INCREF(res);
SET_TOP(res);
Py_DECREF(owner);
Py_DECREF(dict);
DISPATCH();
}
// Else slot is NULL. Fall through to slow path to raise AttributeError(name).
// Don't DEOPT, since the slot is still there.
} else {
// Fast path for dict.
assert(type->tp_dict != NULL);
assert(type->tp_dictoffset > 0);

dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
dict = *dictptr;
if (dict != NULL && PyDict_CheckExact(dict)) {
Py_ssize_t hint = la->hint;
Py_INCREF(dict);
res = NULL;
la->hint = _PyDict_GetItemHint((PyDictObject*)dict, name, hint, &res);

if (res != NULL) {
if (la->hint == hint && hint >= 0) {
// Our hint has helped -- cache hit.
OPCACHE_STAT_ATTR_HIT();
} else {
// The hint we provided didn't work.
// Maybe next time?
OPCACHE_MAYBE_DEOPT_LOAD_ATTR();
}

Py_INCREF(res);
SET_TOP(res);
Py_DECREF(owner);
Py_DECREF(dict);
DISPATCH();
} else {
// This attribute can be missing sometimes;
// we don't want to optimize this lookup.
OPCACHE_DEOPT_LOAD_ATTR();
Py_DECREF(dict);
}
} else {
// This attribute can be missing sometimes -- we
// don't want to optimize this lookup.
// There is no dict, or __dict__ doesn't satisfy PyDict_CheckExact.
OPCACHE_DEOPT_LOAD_ATTR();
Py_DECREF(dict);
}
} else {
// There is no dict, or __dict__ doesn't satisfy PyDict_CheckExact
OPCACHE_DEOPT_LOAD_ATTR();
}
} else {
// The type of the object has either been updated,
// or is different. Maybe it will stabilize?
OPCACHE_MAYBE_DEOPT_LOAD_ATTR();
}

OPCACHE_STAT_ATTR_MISS();
}

if (co_opcache != NULL && /* co_opcache can be NULL after a DEOPT() call. */
if (co_opcache != NULL && // co_opcache can be NULL after a DEOPT() call.
type->tp_getattro == PyObject_GenericGetAttr)
{
Py_ssize_t ret;

if (type->tp_dictoffset > 0) {
if (type->tp_dict == NULL) {
if (PyType_Ready(type) < 0) {
Py_DECREF(owner);
SET_TOP(NULL);
goto error;
}
if (type->tp_dict == NULL) {
if (PyType_Ready(type) < 0) {
Py_DECREF(owner);
SET_TOP(NULL);
goto error;
}
if (_PyType_Lookup(type, name) == NULL) {
dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
dict = *dictptr;
}
PyObject *descr = _PyType_Lookup(type, name);
if (descr != NULL) {
// We found an attribute with a data-like descriptor.
PyTypeObject *dtype = Py_TYPE(descr);
if (dtype == &PyMemberDescr_Type) { // It's a slot
PyMemberDescrObject *member = (PyMemberDescrObject *)descr;
struct PyMemberDef *dmem = member->d_member;
if (dmem->type == T_OBJECT_EX) {
Py_ssize_t offset = dmem->offset;
assert(offset > 0); // 0 would be confused with dict hint == -1 (miss).

if (co_opcache->optimized == 0) {
// First time we optimize this opcode.
OPCACHE_STAT_ATTR_OPT();
co_opcache->optimized = OPCODE_CACHE_MAX_TRIES;
// fprintf(stderr, "Setting hint for %s, offset %zd\n", dmem->name, offset);
}

if (dict != NULL && PyDict_CheckExact(dict)) {
Py_INCREF(dict);
res = NULL;
ret = _PyDict_GetItemHint((PyDictObject*)dict, name, -1, &res);
la = &co_opcache->u.la;
la->type = type;
la->tp_version_tag = type->tp_version_tag;
la->hint = ~offset;

char *addr = (char *)owner + offset;
res = *(PyObject **)addr;
if (res != NULL) {
Py_INCREF(res);
Py_DECREF(dict);
Py_DECREF(owner);
SET_TOP(res);

if (co_opcache->optimized == 0) {
// First time we optimize this opcode. */
OPCACHE_STAT_ATTR_OPT();
co_opcache->optimized = OPCODE_CACHE_MAX_TRIES;
}

la = &co_opcache->u.la;
la->type = type;
la->tp_version_tag = type->tp_version_tag;
la->hint = ret;

DISPATCH();
}
// Else slot is NULL. Fall through to slow path to raise AttributeError(name).
}
// Else it's a slot of a different type. We don't handle those.
}
// Else it's some other kind of descriptor that we don't handle.
OPCACHE_DEOPT_LOAD_ATTR();
} else if (type->tp_dictoffset > 0) {
// We found an instance with a __dict__.
dictptr = (PyObject **) ((char *)owner + type->tp_dictoffset);
dict = *dictptr;

if (dict != NULL && PyDict_CheckExact(dict)) {
Py_INCREF(dict);
res = NULL;
Py_ssize_t hint = _PyDict_GetItemHint((PyDictObject*)dict, name, -1, &res);
if (res != NULL) {
Py_INCREF(res);
Py_DECREF(dict);
} else {
// There is no dict, or __dict__ doesn't satisfy PyDict_CheckExact
OPCACHE_DEOPT_LOAD_ATTR();
Py_DECREF(owner);
SET_TOP(res);

if (co_opcache->optimized == 0) {
// First time we optimize this opcode.
OPCACHE_STAT_ATTR_OPT();
co_opcache->optimized = OPCODE_CACHE_MAX_TRIES;
}

la = &co_opcache->u.la;
la->type = type;
la->tp_version_tag = type->tp_version_tag;
la->hint = hint;

DISPATCH();
}
Py_DECREF(dict);
} else {
// We failed to find an attribute without a data-like descriptor
// There is no dict, or __dict__ doesn't satisfy PyDict_CheckExact.
OPCACHE_DEOPT_LOAD_ATTR();
}
} else {
// The object's class does not have a tp_dictoffset we can use
// The object's class does not have a tp_dictoffset we can use.
OPCACHE_DEOPT_LOAD_ATTR();
}
} else if (type->tp_getattro != PyObject_GenericGetAttr) {
OPCACHE_DEOPT_LOAD_ATTR();
}
}

/* slow path */
// Slow path.
res = PyObject_GetAttr(owner, name);
Py_DECREF(owner);
SET_TOP(res);
Expand Down

1 comment on commit 5c5a938

@UltiRequiem
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Nice!

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