Message416735
For reference, chaining is about 1.18x slower in this microbenchmark on GCC:
./python -m pyperf timeit -s "x = 100" "if 10 < x < 30: print('no')" --duplicate=10
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Mean +- std dev: 21.3 ns +- 0.2 ns
./python -m pyperf timeit -s "x = 100" "if 10 < x and x < 30: print('no')" --duplicate=10
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Mean +- std dev: 18.0 ns +- 0.5 ns
For a related case, in GH-30970, the bytecode generate by "a, b = a0, b0" was changed.
Before: [load_a0, load_b0, swap, store_a, store_b]
After: [load_a0, load_b0, store_b, store_a]
However, this was only changed when the stores were STORE_FASTs. STORE_GLOBAL/STORE_NAME/STORE_DEREF cases still have the SWAP.
In the STORE_GLOBAL cases, you can construct scenarios with custom __del__ methods where storing b and then a has different behavior than storing a and then b. No such cases can be constructed for STORE_FAST without resorting to frame hacking.
I wonder if the same argument applies here: maybe @akuvfx's PR could be altered to use LOAD_FAST twice for each variable *only* if everything in sight is the result of a LOAD_FAST or a LOAD_CONST. My example above uses a LOAD_DEREF, so its behavior could remain unchanged.
The argument that this would within the language spec is maybe a little bit more dubious than the "a, b = a0, b0" case though, since custom `__lt__` methods are a bit more well-specified than custom `__del__` methods.
Thoughts? |
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Date |
User |
Action |
Args |
2022-04-05 03:14:58 | Dennis Sweeney | set | recipients:
+ Dennis Sweeney, tim.peters, steven.daprano, serhiy.storchaka, akuvfx |
2022-04-05 03:14:58 | Dennis Sweeney | set | messageid: <1649128498.38.0.488387437838.issue45542@roundup.psfhosted.org> |
2022-04-05 03:14:58 | Dennis Sweeney | link | issue45542 messages |
2022-04-05 03:14:58 | Dennis Sweeney | create | |
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