bpo-40222: "Zero cost" exception handling#25729
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…o restore when re-raising.
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…e evaluation stack, not the block stack.
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The failure on |
@markshannon Unfortunately the ASAN failure is legit. Check the BPO issue for more details. |
| PyAPI_FUNC(PyCodeObject *) PyCode_New( | ||
| int, int, int, int, int, PyObject *, PyObject *, | ||
| PyObject *, PyObject *, PyObject *, PyObject *, | ||
| PyObject *, PyObject *, int, PyObject *); | ||
| PyObject *, PyObject *, int, PyObject *, PyObject *); | ||
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| PyAPI_FUNC(PyCodeObject *) PyCode_NewWithPosOnlyArgs( | ||
| int, int, int, int, int, int, PyObject *, PyObject *, | ||
| PyObject *, PyObject *, PyObject *, PyObject *, | ||
| PyObject *, PyObject *, int, PyObject *); | ||
| PyObject *, PyObject *, int, PyObject *, PyObject *); |
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This C-API change seems worth mentioning somewhere.
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Check the discussion in https://bugs.python.org/issue40222
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| def parse_varint(iterator): | ||
| b = next(iterator) | ||
| val = b & 63 |
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Just curious, how does this work? I guess the constant numbers are about 64-bit?
would love to get your explanation, thanks. @markshannon
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For example, this function:
compiles as follows on main:
with this PR it compiles as follows:
This is not quite zero-cost at the moment, as it leaves a
NOPs for eachtry, and possibly a few other.Removing
NOPs that are on a line by themselves will require changes to the line number table, which has nothing to do with exception handling and I don't want to mix the two PRs.Although the code is slightly longer overall, there is less work done on the non-exceptional path, one
NOPversus aSETUP_FINALLYandPOP_BLOCK.Not only is there a reduction in work done in the bytecode, but in the size of frames is reduced a lot:
On master:
with this PR:
https://bugs.python.org/issue40222