Author brandtbucher
Recipients brandtbucher
Date 2019-09-30.16:57:25
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Message-id <1569862645.36.0.924344090693.issue38328@roundup.psfhosted.org>
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The attached 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 (elements vs speedup):

 5:  ~5%
10: ~20%
15: ~25%
20: ~30%
25: ~35%
30: ~45%
35: ~50%

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.
History
Date User Action Args
2019-09-30 16:57:25brandtbuchersetrecipients: + brandtbucher
2019-09-30 16:57:25brandtbuchersetmessageid: <1569862645.36.0.924344090693.issue38328@roundup.psfhosted.org>
2019-09-30 16:57:25brandtbucherlinkissue38328 messages
2019-09-30 16:57:25brandtbuchercreate