mirror of https://github.com/python/cpython
gh-94155: Reduce hash collisions for code objects (#100183)
* Uses a better hashing algorithm to get better dispersion and remove commutativity. * Incorporates `co_firstlineno`, `Py_SIZE(co)`, and bytecode instructions. * This is now the entire set of criteria used in `code_richcompare`, except for `_PyCode_ConstantKey` (which would incorporate the types of `co_consts` rather than just their values).
This commit is contained in:
parent
36d358348d
commit
a98d9ea56e
|
@ -465,6 +465,32 @@ class CodeTest(unittest.TestCase):
|
|||
self.assertNotEqual(code_b, code_d)
|
||||
self.assertNotEqual(code_c, code_d)
|
||||
|
||||
def test_code_hash_uses_firstlineno(self):
|
||||
c1 = (lambda: 1).__code__
|
||||
c2 = (lambda: 1).__code__
|
||||
self.assertNotEqual(c1, c2)
|
||||
self.assertNotEqual(hash(c1), hash(c2))
|
||||
c3 = c1.replace(co_firstlineno=17)
|
||||
self.assertNotEqual(c1, c3)
|
||||
self.assertNotEqual(hash(c1), hash(c3))
|
||||
|
||||
def test_code_hash_uses_order(self):
|
||||
# Swapping posonlyargcount and kwonlyargcount should change the hash.
|
||||
c = (lambda x, y, *, z=1, w=1: 1).__code__
|
||||
self.assertEqual(c.co_argcount, 2)
|
||||
self.assertEqual(c.co_posonlyargcount, 0)
|
||||
self.assertEqual(c.co_kwonlyargcount, 2)
|
||||
swapped = c.replace(co_posonlyargcount=2, co_kwonlyargcount=0)
|
||||
self.assertNotEqual(c, swapped)
|
||||
self.assertNotEqual(hash(c), hash(swapped))
|
||||
|
||||
def test_code_hash_uses_bytecode(self):
|
||||
c = (lambda x, y: x + y).__code__
|
||||
d = (lambda x, y: x * y).__code__
|
||||
c1 = c.replace(co_code=d.co_code)
|
||||
self.assertNotEqual(c, c1)
|
||||
self.assertNotEqual(hash(c), hash(c1))
|
||||
|
||||
|
||||
def isinterned(s):
|
||||
return s is sys.intern(('_' + s + '_')[1:-1])
|
||||
|
|
|
@ -0,0 +1 @@
|
|||
Improved the hashing algorithm for code objects, mitigating some hash collisions.
|
|
@ -1842,28 +1842,41 @@ code_richcompare(PyObject *self, PyObject *other, int op)
|
|||
static Py_hash_t
|
||||
code_hash(PyCodeObject *co)
|
||||
{
|
||||
Py_hash_t h, h0, h1, h2, h3;
|
||||
h0 = PyObject_Hash(co->co_name);
|
||||
if (h0 == -1) return -1;
|
||||
h1 = PyObject_Hash(co->co_consts);
|
||||
if (h1 == -1) return -1;
|
||||
h2 = PyObject_Hash(co->co_names);
|
||||
if (h2 == -1) return -1;
|
||||
h3 = PyObject_Hash(co->co_localsplusnames);
|
||||
if (h3 == -1) return -1;
|
||||
Py_hash_t h4 = PyObject_Hash(co->co_linetable);
|
||||
if (h4 == -1) {
|
||||
return -1;
|
||||
Py_uhash_t uhash = 20221211;
|
||||
#define SCRAMBLE_IN(H) do { \
|
||||
uhash ^= (Py_uhash_t)(H); \
|
||||
uhash *= _PyHASH_MULTIPLIER; \
|
||||
} while (0)
|
||||
#define SCRAMBLE_IN_HASH(EXPR) do { \
|
||||
Py_hash_t h = PyObject_Hash(EXPR); \
|
||||
if (h == -1) { \
|
||||
return -1; \
|
||||
} \
|
||||
SCRAMBLE_IN(h); \
|
||||
} while (0)
|
||||
|
||||
SCRAMBLE_IN_HASH(co->co_name);
|
||||
SCRAMBLE_IN_HASH(co->co_consts);
|
||||
SCRAMBLE_IN_HASH(co->co_names);
|
||||
SCRAMBLE_IN_HASH(co->co_localsplusnames);
|
||||
SCRAMBLE_IN_HASH(co->co_linetable);
|
||||
SCRAMBLE_IN_HASH(co->co_exceptiontable);
|
||||
SCRAMBLE_IN(co->co_argcount);
|
||||
SCRAMBLE_IN(co->co_posonlyargcount);
|
||||
SCRAMBLE_IN(co->co_kwonlyargcount);
|
||||
SCRAMBLE_IN(co->co_flags);
|
||||
SCRAMBLE_IN(co->co_firstlineno);
|
||||
SCRAMBLE_IN(Py_SIZE(co));
|
||||
for (int i = 0; i < Py_SIZE(co); i++) {
|
||||
int deop = _PyOpcode_Deopt[_Py_OPCODE(_PyCode_CODE(co)[i])];
|
||||
SCRAMBLE_IN(deop);
|
||||
SCRAMBLE_IN(_Py_OPARG(_PyCode_CODE(co)[i]));
|
||||
i += _PyOpcode_Caches[deop];
|
||||
}
|
||||
Py_hash_t h5 = PyObject_Hash(co->co_exceptiontable);
|
||||
if (h5 == -1) {
|
||||
return -1;
|
||||
if ((Py_hash_t)uhash == -1) {
|
||||
return -2;
|
||||
}
|
||||
h = h0 ^ h1 ^ h2 ^ h3 ^ h4 ^ h5 ^
|
||||
co->co_argcount ^ co->co_posonlyargcount ^ co->co_kwonlyargcount ^
|
||||
co->co_flags;
|
||||
if (h == -1) h = -2;
|
||||
return h;
|
||||
return (Py_hash_t)uhash;
|
||||
}
|
||||
|
||||
|
||||
|
|
Loading…
Reference in New Issue