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gh-131798: constant fold special method lookup in JIT #148432

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gh-131798: constant fold special method lookup in JIT #148432

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d18afa0
JIT constant fold special method lookup
kumaraditya303 Apr 12, 2026
9da1b9d
refactor it a bit
kumaraditya303 Apr 13, 2026
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4 changes: 2 additions & 2 deletions Include/internal/pycore_opcode_metadata.h
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19 changes: 19 additions & 0 deletions Lib/test/test_capi/test_opt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3316,6 +3316,25 @@ def f(n):
self.assertNotIn("_LOAD_ATTR_METHOD_NO_DICT", uops)
self.assertIn("_LOAD_CONST_INLINE_BORROW", uops)

def test_cached_load_special(self):
class CM:
def __enter__(self):
return self
def __exit__(self, *args):
pass
def f(n):
cm = CM()
x = 0
for _ in range(n):
with cm:
x += 1
return x
res, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
self.assertIsNotNone(ex)
self.assertEqual(res, TIER2_THRESHOLD)
uops = get_opnames(ex)
self.assertNotIn("_LOAD_SPECIAL", uops)

def test_store_fast_refcount_elimination(self):
def foo(x):
# Since x is known to be
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1 change: 1 addition & 0 deletions Python/bytecodes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3887,6 +3887,7 @@ dummy_func(
}

macro(LOAD_SPECIAL) =
_RECORD_TOS_TYPE +
_INSERT_NULL +
_LOAD_SPECIAL;

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27 changes: 25 additions & 2 deletions Python/optimizer_bytecodes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1682,8 +1682,31 @@ dummy_func(void) {
}

op(_LOAD_SPECIAL, (method_and_self[2] -- method_and_self[2])) {
method_and_self[0] = sym_new_not_null(ctx);
method_and_self[1] = sym_new_unknown(ctx);
Comment on lines -1685 to -1686
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@Fidget-Spinner Fidget-Spinner Apr 13, 2026

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You might want to leave these behind.
Some branches don't set method_and_self[1] and method_and_self[0], if you leave this. You can avoid all the complicated setting and else branches.

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@kumaraditya303 kumaraditya303 Apr 13, 2026

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if I leave this then wouldn't the value of these change and then I can't use the recorded values?

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@Fidget-Spinner Fidget-Spinner Apr 13, 2026

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oh yeah woops

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@kumaraditya303 kumaraditya303 Apr 13, 2026

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is it necessary to set these on all paths? I think we only care about the optimized path

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@Fidget-Spinner Fidget-Spinner Apr 13, 2026

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You need to check LOAD_SPECIAL in bytecodes.c, if it creates a new value, it must be a new symbol

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@kumaraditya303 kumaraditya303 Apr 13, 2026

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I refactored it a bit to set in all cases when it is not optimized.

bool optimized = false;
PyTypeObject *type = sym_get_probable_type(method_and_self[1]);
if (type != NULL) {
PyObject *name = _Py_SpecialMethods[oparg].name;
PyObject *descr = _PyType_Lookup(type, name);
if (descr != NULL && _PyType_HasFeature(Py_TYPE(descr), Py_TPFLAGS_METHOD_DESCRIPTOR))
{
ADD_OP(_GUARD_TYPE_VERSION, 0, type->tp_version_tag);
bool immortal = _Py_IsImmortal(descr) || (type->tp_flags & Py_TPFLAGS_IMMUTABLETYPE);
ADD_OP(immortal ? _LOAD_CONST_INLINE_BORROW : _LOAD_CONST_INLINE,
0, (uintptr_t)descr);
ADD_OP(_SWAP, 3, 0);
ADD_OP(_POP_TOP, 0, 0);
if ((type->tp_flags & Py_TPFLAGS_IMMUTABLETYPE) == 0) {
PyType_Watch(TYPE_WATCHER_ID, (PyObject *)type);
_Py_BloomFilter_Add(dependencies, type);
}
method_and_self[0] = sym_new_const(ctx, descr);
optimized = true;
}
}
if (!optimized) {
method_and_self[0] = sym_new_not_null(ctx);
method_and_self[1] = sym_new_unknown(ctx);
}
}

op(_JUMP_TO_TOP, (--)) {
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27 changes: 25 additions & 2 deletions Python/optimizer_cases.c.h
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1 change: 1 addition & 0 deletions Python/record_functions.c.h
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