[mypyc] Speed up and improve multiple assignment #9800
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| # Assign sequence items to the target lvalues. | ||
| for lvalue, value in zip(target.items, values): | ||
| self.assign(lvalue, value, line) |
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The iterator code below assigns as it goes. Do we know which Python does? It's all pretty marginal, and if we wanted to say we aren't aiming to exactly replicate execution order in some marginal cases, that's probably fine, but we should do it with eyes open. (In general I've tried to match things but I know we mismatch in at least one case with method calls.)
I guess in this case we wouldn't be able to do unsafe get items if we were assigning as we went (because it could get modified.)
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CPython reads all the values before performing the assignments, so this brings the semantics a bit closer to Python. I'll create an issue about updating the generic iterable case to also match Python semantics.
Speed up multiple assignment from variable-length lists and tuples.
This speeds up the
multiple_assignmentbenchmark by around 80%.Fix multiple lvalues in fixed-length sequence assignments.
Optimize some cases of list expressions in assignments.
Fixes mypyc/mypyc#729.