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gh-131525: Cache the result of tuple_hash (#131529)

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* gh-131525: Cache the result of tuple_hash

* Fix debug builds

* Add blurb

* Fix formatting

* Pre-compute empty tuple singleton

* Mostly set the cache within tuple_alloc

* Fixes for TSAN

* Pre-compute empty tuple singleton

* Fix for 32-bit platforms

* Assert that op != NULL in _PyTuple_RESET_HASH_CACHE

* Use FT_ATOMIC_STORE_SSIZE_RELAXED macro

* Update Include/internal/pycore_tuple.h

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

* Fix alignment

* atomic load

* Update Objects/tupleobject.c

Co-authored-by: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>

---------

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
This commit is contained in:
Michael Droettboom 2025-03-27 09:57:06 -04:00 • committed by GitHub
parent cf5e438c02
commit 8614f86b71
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GPG key ID: B5690EEEBB952194
102 changed files with 1218 additions and 183 deletions
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50
Objects/tupleobject.c
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@ -45,6 +45,7 @@ tuple_alloc(Py_ssize_t size)
if (index < PyTuple_MAXSAVESIZE) {
PyTupleObject *op = _Py_FREELIST_POP(PyTupleObject, tuples[index]);
if (op != NULL) {
_PyTuple_RESET_HASH_CACHE(op);
return op;
}
}
@ -53,7 +54,11 @@ tuple_alloc(Py_ssize_t size)
sizeof(PyObject *))) / sizeof(PyObject *)) {
return (PyTupleObject *)PyErr_NoMemory();
}
return PyObject_GC_NewVar(PyTupleObject, &PyTuple_Type, size);
PyTupleObject *result = PyObject_GC_NewVar(PyTupleObject, &PyTuple_Type, size);
if (result != NULL) {
_PyTuple_RESET_HASH_CACHE(result);
}
return result;
}
// The empty tuple singleton is not tracked by the GC.
@ -296,50 +301,41 @@ error:
For the xxHash specification, see
https://github.com/Cyan4973/xxHash/blob/master/doc/xxhash_spec.md
Below are the official constants from the xxHash specification. Optimizing
compilers should emit a single "rotate" instruction for the
_PyHASH_XXROTATE() expansion. If that doesn't happen for some important
platform, the macro could be changed to expand to a platform-specific rotate
spelling instead.
The constants for the hash function are defined in pycore_tuple.h.
*/
#if SIZEOF_PY_UHASH_T > 4
#define _PyHASH_XXPRIME_1 ((Py_uhash_t)11400714785074694791ULL)
#define _PyHASH_XXPRIME_2 ((Py_uhash_t)14029467366897019727ULL)
#define _PyHASH_XXPRIME_5 ((Py_uhash_t)2870177450012600261ULL)
#define _PyHASH_XXROTATE(x) ((x << 31) | (x >> 33)) /* Rotate left 31 bits */
#else
#define _PyHASH_XXPRIME_1 ((Py_uhash_t)2654435761UL)
#define _PyHASH_XXPRIME_2 ((Py_uhash_t)2246822519UL)
#define _PyHASH_XXPRIME_5 ((Py_uhash_t)374761393UL)
#define _PyHASH_XXROTATE(x) ((x << 13) | (x >> 19)) /* Rotate left 13 bits */
#endif
/* Tests have shown that it's not worth to cache the hash value, see
https://bugs.python.org/issue9685 */
static Py_hash_t
tuple_hash(PyObject *op)
{
PyTupleObject *v = _PyTuple_CAST(op);
Py_uhash_t acc = FT_ATOMIC_LOAD_SSIZE_RELAXED(v->ob_hash);
if (acc != (Py_uhash_t)-1) {
return acc;
}
Py_ssize_t len = Py_SIZE(v);
PyObject **item = v->ob_item;
Py_uhash_t acc = _PyHASH_XXPRIME_5;
acc = _PyTuple_HASH_XXPRIME_5;
for (Py_ssize_t i = 0; i < len; i++) {
Py_uhash_t lane = PyObject_Hash(item[i]);
if (lane == (Py_uhash_t)-1) {
return -1;
}
acc += lane * _PyHASH_XXPRIME_2;
acc = _PyHASH_XXROTATE(acc);
acc *= _PyHASH_XXPRIME_1;
acc += lane * _PyTuple_HASH_XXPRIME_2;
acc = _PyTuple_HASH_XXROTATE(acc);
acc *= _PyTuple_HASH_XXPRIME_1;
}
/* Add input length, mangled to keep the historical value of hash(()). */
acc += len ^ (_PyHASH_XXPRIME_5 ^ 3527539UL);
acc += len ^ (_PyTuple_HASH_XXPRIME_5 ^ 3527539UL);
if (acc == (Py_uhash_t)-1) {
return 1546275796;
acc = 1546275796;
}
FT_ATOMIC_STORE_SSIZE_RELAXED(v->ob_hash, acc);
return acc;
}
@ -764,6 +760,8 @@ tuple_subtype_new(PyTypeObject *type, PyObject *iterable)
}
Py_DECREF(tmp);
_PyTuple_RESET_HASH_CACHE(newobj);
// Don't track if a subclass tp_alloc is PyType_GenericAlloc()
if (!_PyObject_GC_IS_TRACKED(newobj)) {
_PyObject_GC_TRACK(newobj);