gh-131798: JIT: Optimize _CALL_LEN when the length is known #135260
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tomasr8
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Jun 8, 2025
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| int tuple_length = sym_tuple_length(arg); | ||
| if (tuple_length >= 0) { | ||
| PyObject *temp = PyLong_FromLong(tuple_length); | ||
| if (temp == NULL) { | ||
| goto error; | ||
| } | ||
| if (_Py_IsImmortal(temp)) { | ||
| REPLACE_OP(this_instr, _POP_CALL_ONE_LOAD_CONST_INLINE_BORROW, | ||
| 0, (uintptr_t)temp); | ||
| } | ||
| res = sym_new_const(ctx, temp); | ||
| Py_DECREF(temp); | ||
| } |
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This is basically copied from the recent _GET_LEN optimization
Lib/test/test_capi/test_opt.py
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| def testfunc(n): | ||
| x = 0 | ||
| for _ in range(n): | ||
| a = (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, |
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I don't know how else to create a tuple with more than _PY_NSMALLPOSINTS elements in a way that the optimizer will know the length 😆 (_CALL_TUPLE_1 doesn't have any optimization for instance)
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Class attributes are cached as constants, so maybe something like this would work?
class C:
t = tuple(range(300))
x = 0
for _ in range(n):
if len(C.t) == 300:
x += 1There was a problem hiding this comment.
It does, thanks for the tip!
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This uses the same principle as #135194 to completely remove
_CALL_LENwhen the length is known.I don't know how common it is to actually know the length exactly so please let me know if this is not worth it, but given that
_CALL_LENis the most common builtin call, it felt worth to optimize this case.