Speed up freshening type variables #14323
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svalentin
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Dec 20, 2022
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| if self.seen_aliases is None: | ||
| self.seen_aliases = set() |
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Can we just start with an empty set rather than a None? That should simplify this.
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We start with None since it saves the creation (and deletion) of an empty set in the common code path where we don't use the set at all. It's a micro-optimization for sure, but allocating objects is kind of expensive in CPython and this is a hot code path, so it should make things a little bit faster.
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Only perform type variable freshening if it's needed, i.e. there is a nested generic callable, since it's fairly expensive. Make the check for generic callables fast by creating a specialized type query visitor base class for queries with bool results. The visitor tries hard to avoid memory allocation in typical cases, since allocation is slow.
This addresses at least some of the performance regression in #14095. This improved self-check performance by about 3% when compiled with mypyc (-O2).
The new visitor class can potentially help with other type queries as well. I'll explore it in follow-up PRs.