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bpo-38328: Speed up the creation time of constant list literals.#16498
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brandtbucher wants to merge 7 commits into
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bpo-38328: Speed up the creation time of constant list literals.#16498brandtbucher wants to merge 7 commits into
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September 30, 2019 17:02
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@serhiy-storchaka Since you proposed something similar a while back, do you mind taking a look at this when you have the chance? |
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Thanks for the feedback @serhiy-storchaka. Tests are passing, ready for another review. |
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October 14, 2019 19:04
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Nothing particular. I just want to fix the issue with list overallocation first. Your PR is good, thank you. |
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This PR contains a small change to the peephole optimizer that converts sequences of:
LOAD_CONST(a),LOAD_CONST(b), ...,BUILD_LIST(n)to
LOAD_CONST((a, b, ...)),BUILD_LIST_UNPACK(1)The improvement quickly becomes significant for lists larger than a few items:
This can be tested on any version of Python by comparing the performance of
[0, 1, 2, ...]vs[*(0, 1, 2, ...)]. The common cases of empty and single-element lists are not affected by this change.This is related to bpo-33325, but that was an invasive change for all collection literals that had an unknown affect on performance. I've limited this one to lists and kept it to a few lines in the peephole optimizer.
https://bugs.python.org/issue38328