Vec::resize for bytes should be a single memset

[scottmcm]

Really I just started by trying to see if specializing iter::repeat_n would help the perf issue that kept me from removing Vec::extend_with last time I tried, but I noticed in the process that a resize for bytes doesn't set all the new space with a single memset: https://play.rust-lang.org/?version=nightly&mode=release&edition=2021&gist=35175ec844b46fcd95e2d0aad526859e

So using repeat_n to implement it -- like VecDeque uses, with the specialization for next to avoid a branch -- means that the optimizer notices the resize can set all the values with a single memset.

[rustbot]

r? @m-ou-se

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[scottmcm]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 8652062 with merge 0db48a7...

[bors]

☀️ Try build successful - checks-actions
Build commit: 0db48a7 (0db48a7c3c2ca5e498da14eae53a7474e16886df)

[rust-timer]

Finished benchmarking commit (0db48a7): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.2%, 0.5%]	15
Regressions ❌ (secondary)	3.3%	[3.1%, 3.7%]	6
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-1.5%, 0.5%]	16

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.9%	[0.3%, 5.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-8.3%	[-12.7%, -4.7%]	4
Improvements ✅ (secondary)	-4.9%	[-4.9%, -4.9%]	1
All ❌✅ (primary)	-4.6%	[-12.7%, 5.5%]	6

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	20.2%	[18.6%, 22.7%]	6
Improvements ✅ (primary)	-1.5%	[-1.5%, -1.5%]	1
Improvements ✅ (secondary)	-2.9%	[-4.3%, -2.3%]	5
All ❌✅ (primary)	-1.5%	[-1.5%, -1.5%]	1

Binary size

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

Bootstrap: 665.423s -> 664.993s (-0.06%)
Artifact size: 308.34 MiB -> 308.35 MiB (0.01%)

[Kobzol]

Looks like something bad has happened in borrow checking of wg-grammar (https://perf.rust-lang.org/detailed-query.html?commit=0db48a7c3c2ca5e498da14eae53a7474e16886df&benchmark=wg-grammar-check&scenario=full&base_commit=f45fe573a587f5d82e9e78cbece64bad4b3709f8.

[scottmcm]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 6c32590 with merge 27371af...

[bors]

☀️ Try build successful - checks-actions
Build commit: 27371af (27371af9b8c50c2f3b165000d3bcd9684c4a0807)

[rust-timer]

Finished benchmarking commit (27371af): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.3%, 0.7%]	13
Regressions ❌ (secondary)	2.1%	[1.9%, 2.3%]	6
Improvements ✅ (primary)	-0.5%	[-0.9%, -0.3%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-0.9%, 0.7%]	17

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	4.3%	[0.2%, 8.4%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-3.7%, -1.4%]	2
Improvements ✅ (secondary)	-1.2%	[-1.5%, -0.7%]	3
All ❌✅ (primary)	0.9%	[-3.7%, 8.4%]	4

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-1.1%, 1.1%]	2

Binary size

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.4%, 0.9%]	29
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[0.4%, 0.9%]	29

Bootstrap: 663.454s -> 664.862s (0.21%)
Artifact size: 308.30 MiB -> 308.31 MiB (0.01%)

[scottmcm]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf