[mypyc] feat: cache len for iterating over immutable types and expressions with length known at compile time #19503
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BobTheBuidler
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@ilevkivskyi this one is also ready for review if and when you get a chance, though its definitely a bit more involved than #19497 |
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BobTheBuidler
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| @@ -1147,3 +1187,33 @@ def gen_step(self) -> None: | |||
| def gen_cleanup(self) -> None: | |||
| for gen in self.gens: | |||
| gen.gen_cleanup() | |||
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| def get_expr_length(expr: Expression) -> int | None: | |||
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These 2 helper functions can be extended to cover more cases and used for other length-based optimizations I have in mind
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Currently, if a user uses an immutable type as the sequence input for a for loop, the length is checked once at each iteration which, while necessary for some container types such as list and dictionaries, is not necessary for iterating over immutable types tuple, str, and bytes.
This PR modifies the codebase such that the length is only checked at the first iteration, and reused from there.
Also, in cases where a simple genexp is the input argument for a tuple, the length is currently checked one additional time before entering the iteration (this is done to determine how to size the new tuple). In those cases, we don't even need a length check at the first iteration step, and can reuse the result of that first
lencall (or compile-time determined constant) instead.Lastly, in cases where a tuple is created from a genexp and the length of the genexp is knowable at compile time, this PR replaces PyList_AsTuple with the tuple constructor fast-path.