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Optimize unnecessary check in VecDeque::retain #88075

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Merged
merged 2 commits into from
Aug 22, 2021
Merged

Optimize unnecessary check in VecDeque::retain #88075

merged 2 commits into from
Aug 22, 2021

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Xuanwo
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@Xuanwo Xuanwo commented Aug 16, 2021

This pr is highly inspired by #88060 which shared the same idea: we can split the for loop into stages so that we can remove unnecessary checks like del > 0.

Benchmarks

Before

test collections::vec_deque::tests::bench_retain_half_10000  ... bench:     290,125 ns/iter (+/- 8,717)
test collections::vec_deque::tests::bench_retain_odd_10000   ... bench:     291,588 ns/iter (+/- 9,621)
test collections::vec_deque::tests::bench_retain_whole_10000 ... bench:     287,426 ns/iter (+/- 9,009)

After

test collections::vec_deque::tests::bench_retain_half_10000  ... bench:     243,940 ns/iter (+/- 8,563)
test collections::vec_deque::tests::bench_retain_odd_10000   ... bench:     242,768 ns/iter (+/- 3,903)
test collections::vec_deque::tests::bench_retain_whole_10000 ... bench:     202,926 ns/iter (+/- 6,332)

Based on the current benchmark, this PR will improve the perf of VecDeque::retain by around 16%. For special cases, the improvement will be up to 30%.

Signed-off-by: Xuanwo [email protected]

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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @dtolnay (or someone else) soon.

Please see the contribution instructions for more information.

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Aug 16, 2021
@TennyZhuang
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I ran the benchmark on my Mac

sysctl -n machdep.cpu.brand_string
Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz

Before optimization:

test collections::vec_deque::tests::bench_retain_half_10000  ... bench:     397,713 ns/iter (+/- 19,098)
test collections::vec_deque::tests::bench_retain_odd_10000   ... bench:     382,615 ns/iter (+/- 17,406)
test collections::vec_deque::tests::bench_retain_whole_10000 ... bench:     386,554 ns/iter (+/- 11,450)

After optimization:

test collections::vec_deque::tests::bench_retain_half_10000  ... bench:     318,491 ns/iter (+/- 34,193)
test collections::vec_deque::tests::bench_retain_odd_10000   ... bench:     354,253 ns/iter (+/- 21,848)
test collections::vec_deque::tests::bench_retain_whole_10000 ... bench:     288,971 ns/iter (+/- 16,016)

dtolnay
dtolnay approved these changes Aug 21, 2021
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Nice!

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dtolnay commented Aug 21, 2021

@bors r+ rollup=never

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bors commented Aug 21, 2021

📌 Commit e32f4c0 has been approved by dtolnay

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 21, 2021
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bors commented Aug 21, 2021

⌛ Testing commit e32f4c0 with merge 9faa714...

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bors commented Aug 22, 2021

☀️ Test successful - checks-actions
Approved by: dtolnay
Pushing 9faa714 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Aug 22, 2021
@bors bors merged commit 9faa714 into rust-lang:master Aug 22, 2021
@rustbot rustbot added this to the 1.56.0 milestone Aug 22, 2021
@Xuanwo Xuanwo deleted the vec_deque_retain branch August 22, 2021 04:28
@TennyZhuang TennyZhuang mentioned this pull request Aug 24, 2021
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@dtolnay dtolnay dtolnay approved these changes

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@Xuanwo @rust-highfive @TennyZhuang @dtolnay @bors @rustbot