10000 GH-131798: Narrow the return type of isinstance for some known argume… · python/cpython@8d490b3 · GitHub
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GH-131798: Narrow the return type of isinstance for some known arguments in the JIT (GH-133172)
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‎Lib/test/test_capi/test_opt.py

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@@ -1959,6 +1959,121 @@ def testfunc(n):
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self.assertNotIn("_GUARD_THIRD_NULL", uops)
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self.assertNotIn("_GUARD_CALLABLE_ISINSTANCE", uops)
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def test_call_isinstance_is_true(self):
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def testfunc(n):
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x = 0
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for _ in range(n):
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y = isinstance(42, int)
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if y:
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x += 1
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return x
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res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
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self.assertEqual(res, TIER2_THRESHOLD)
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self.assertIsNotNone(ex)
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uops = get_opnames(ex)
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self.assertIn("_CALL_ISINSTANCE", uops)
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self.assertNotIn("_TO_BOOL_BOOL", uops)
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self.assertNotIn("_GUARD_IS_TRUE_POP", uops)
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def test_call_isinstance_is_false(self):
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def testfunc(n):
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x = 0
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for _ in range(n):
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y = isinstance(42, str)
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if not y:
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x += 1
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return x
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res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
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self.assertEqual(res, TIER2_THRESHOLD)
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self.assertIsNotNone(ex)
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uops = get_opnames(ex)
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self.assertIn("_CALL_ISINSTANCE", uops)
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self.assertNotIn("_TO_BOOL_BOOL", uops)
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self.assertNotIn("_GUARD_IS_FALSE_POP", uops)
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def test_call_isinstance_subclass(self):
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def testfunc(n):
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x = 0
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for _ in range(n):
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y = isinstance(True, int)
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if y:
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x += 1
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return x
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res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
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self.assertEqual(res, TIER2_THRESHOLD)
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self.assertIsNotNone(ex)
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uops = get_opnames(ex)
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self.assertIn("_CALL_ISINSTANCE", uops)
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self.assertNotIn("_TO_BOOL_BOOL", uops)
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self.assertNotIn("_GUARD_IS_TRUE_POP", uops)
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def test_call_isinstance_unknown_object(self):
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def testfunc(n):
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x = 0
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for _ in range(n):
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# The optimizer doesn't know the return type here:
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bar = eval("42")
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# This will only narrow to bool:
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y = isinstance(bar, int)
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if y:
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x += 1
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return x
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res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
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self.assertEqual(res, TIER2_THRESHOLD)
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self.assertIsNotNone(ex)
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uops = get_opnames(ex)
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self.assertIn("_CALL_ISINSTANCE", uops)
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self.assertNotIn("_TO_BOOL_BOOL", uops)
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self.assertIn("_GUARD_IS_TRUE_POP", uops)
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def test_call_isinstance_tuple_of_classes(self):
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def testfunc(n):
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x = 0
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for _ in range(n):
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# A tuple of classes is currently not optimized,
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# so this is only narrowed to bool:
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y = isinstance(42, (int, str))
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if y:
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x += 1
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return x
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res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
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self.assertEqual(res, TIER2_THRESHOLD)
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self.assertIsNotNone(ex)
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uops = get_opnames(ex)
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self.assertIn("_CALL_ISINSTANCE", uops)
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self.assertNotIn("_TO_BOOL_BOOL", uops)
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self.assertIn("_GUARD_IS_TRUE_POP", uops)
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def test_call_isinstance_metaclass(self):
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class EvenNumberMeta(type):
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def __instancecheck__(self, number):
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return number % 2 == 0
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class EvenNumber(metaclass=EvenNumberMeta):
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pass
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2060+
def testfunc(n):
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x = 0
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for _ in range(n):
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# Only narrowed to bool
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y = isinstance(42, EvenNumber)
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if y:
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x += 1
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return x
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res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
2070+
self.assertEqual(res, TIER2_THRESHOLD)
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self.assertIsNotNone(ex)
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uops = get_opnames(ex)
2073+
self.assertIn("_CALL_ISINSTANCE", uops)
2074+
self.assertNotIn("_TO_BOOL_BOOL", uops)
2075+
self.assertIn("_GUARD_IS_TRUE_POP", uops)
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19622077

19632078
def global_identity(x):
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return x

‎Misc/NEWS.d/next/Core_and_Builtins/2025-04-26-17-50-01.gh-issue-131798.XiOgw5.rst

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@@ -0,0 +1,2 @@
1+
Narrow the return type and constant-evaluate ``CALL_ISINSTANCE`` for a
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subset of known values in the JIT. Patch by Tomas Roun

‎Python/optimizer_bytecodes.c

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -890,6 +890,26 @@ dummy_func(void) {
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}
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}
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893+
op(_CALL_ISINSTANCE, (unused, unused, instance, cls -- res)) {
894+
// the result is always a bool, but sometimes we can
895+
// narrow it down to True or False
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res = sym_new_type(ctx, &PyBool_Type);
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PyTypeObject *inst_type = sym_get_type(instance);
898+
PyTypeObject *cls_o = (PyTypeObject *)sym_get_const(ctx, cls);
899+
if (inst_type && cls_o && sym_matches_type(cls, &PyType_Type)) {
900+
// isinstance(inst, cls) where both inst and cls have
901+
// known types, meaning we can deduce either True or False
902+
903+
// The below check is equivalent to PyObject_TypeCheck(inst, cls)
904+
if (inst_type == cls_o || PyType_IsSubtype(inst_type, cls_o)) {
905+
sym_set_const(res, Py_True);
906+
}
907+
else {
908+
sym_set_const(res, Py_False);
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}
910+
}
911+
}
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893913
op(_GUARD_IS_TRUE_POP, (flag -- )) {
894914
if (sym_is_const(ctx, flag)) {
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PyObject *value = sym_get_const(ctx, flag);

‎Python/optimizer_cases.c.h

Lines changed: 15 additions & 1 deletion
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