[Python-checkins] bpo-42927: Inline cache for attributes defined with '__slots__' (#24216)
gvanrossum
webhook-mailer at python.org
Fri Jan 29 21:02:33 EST 2021
https://github.com/python/cpython/commit/5c5a938573ce665f00e362c7766912d9b3f3b44e
commit: 5c5a938573ce665f00e362c7766912d9b3f3b44e
branch: master
author: Guido van Rossum <guido at python.org>
committer: gvanrossum <gvanrossum at gmail.com>
date: 2021-01-29T18:02:29-08:00
summary:
bpo-42927: Inline cache for attributes defined with '__slots__' (#24216)
files:
A Misc/NEWS.d/next/Core and Builtins/2021-01-15-20-05-56.bpo-42927.GI-l-7.rst
M Python/ceval.c
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-01-15-20-05-56.bpo-42927.GI-l-7.rst b/Misc/NEWS.d/next/Core and Builtins/2021-01-15-20-05-56.bpo-42927.GI-l-7.rst
new file mode 100644
index 0000000000000..8ee578e816215
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-01-15-20-05-56.bpo-42927.GI-l-7.rst
@@ -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.
\ No newline at end of file
diff --git a/Python/ceval.c b/Python/ceval.c
index be9ea24454768..3aa2aa2c9bc19 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -29,6 +29,7 @@
#include "opcode.h"
#include "pydtrace.h"
#include "setobject.h"
+#include "structmember.h" // struct PyMemberDef, T_OFFSET_EX
#include <ctype.h>
@@ -3169,106 +3170,157 @@ _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) {
@@ -3276,7 +3328,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
}
}
- /* slow path */
+ // Slow path.
res = PyObject_GetAttr(owner, name);
Py_DECREF(owner);
SET_TOP(res);
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