[New-bugs-announce] [issue38328] Speed up the creation time of constant list literals.

[Brandt Bucher]

New submission from Brandt Bucher <brandtbucher at gmail.com>:

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.

----------
components: Interpreter Core
messages: 353599
nosy: brandtbucher
priority: normal
severity: normal
status: open
title: Speed up the creation time of constant list literals.
type: performance
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38328>
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