GH-96793: Change FOR_ITER to not pop the iterator on exhaustion.
#96801
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With the tweaks to skip the |
iritkatriel
reviewed
Oct 26, 2022
Python/specialize.c
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| SPECIALIZATION_FAIL(FOR_ITER, | ||
| _PySpecialization_ClassifyIterator(iter)); | ||
| goto failure; | ||
| if (_Py_OPCODE(instr[INLINE_CACHE_ENTRIES_FOR_ITER + oparg + 1]) == POP_TOP) { |
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Why would it not be POP_TOP?
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The compiler did something clever.
I don't know what that might be, but I don't want to rely on the compiler not transforming the code.
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I'm considering changing the |
iritkatriel
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Oct 26, 2022
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gvanrossum
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Oct 28, 2022
…on. (pythonGH-96801) Change FOR_ITER to have the same stack effect regardless of whether it branches or not. Performance is unchanged as FOR_ITER (and specialized forms jump over the cleanup code).
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Requires an additional
POP_TOPat the end of the loop. By itself, this would be a pointless change, but as part of #96793 it makes sense.Pyperformance shows a 1% slowdown but I suspect that is a bit noisy. The 11% slowdown of
unpack_sequencemakes no sense.Given the dispatching overhead is in the 10-15% and
FOR_ITERrepresents 1-2% of instructions executed we would expect at worst a 0.3% slowdown.I will get performance numbers for the whole of #96793 before merging the parts.
for gen():, and awaiting coroutines,await coro()#96793