Optimized vec::IntoIter::next_chunk impl

[the8472]

x86_64v1, default
test vec::bench_next_chunk                               ... bench:         696 ns/iter (+/- 22)
x86_64v1, pr
test vec::bench_next_chunk                               ... bench:         309 ns/iter (+/- 4)

znver2, default
test vec::bench_next_chunk                               ... bench:      17,272 ns/iter (+/- 117)
znver2, pr
test vec::bench_next_chunk                               ... bench:         211 ns/iter (+/- 3)

On znver2 the default impl seems to be slow due to different inlining decisions. It goes through core::array::iter_next_chunk
which has a deep call tree.

[rust-highfive]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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[rust-highfive]

r? @kennytm

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[bors]

☔ The latest upstream changes (presumably #98680) made this pull request unmergeable. Please resolve the merge conflicts.

[Mark-Simulacrum]

r=me

@bors rollup=never in case has unexpected perf effects

[the8472]

@bors r=Mark-Simulacrum

[bors]

📌 Commit 4ba7cac has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[bors]

⌛ Testing commit 4ba7cac with merge b573e10...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing b573e10 to master...

[rust-timer]

Finished benchmarking commit (b573e10): comparison url.

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	2.1%	2.1%	1
Regressions 😿 (secondary)	3.1%	3.9%	2
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.6%	-3.1%	2
All 😿🎉 (primary)	2.1%	2.1%	1

Cycles

Results

• Primary benchmarks: 🎉 relevant improvement found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	N/A	N/A	0
Regressions 😿 (secondary)	3.7%	4.6%	2
Improvements 🎉 (primary)	-7.2%	-7.2%	1
Improvements 🎉 (secondary)	-2.3%	-2.3%	1
All 😿🎉 (primary)	-7.2%	-7.2%	1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

@rustbot label: -perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩²

2. number of relevant changes ↩ ↩²