Use `iter::repeat_n` to implement `Vec::extend_with` #133662

paolobarbolini · 2024-11-30T06:22:29Z

This replaces the Vec::extend_with manual implementation with iter::repeat_n, simplifying the code and also possibly fixing the issue identified in #120050.

rustbot · 2024-11-30T06:22:37Z

r? @Noratrieb

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joboet · 2024-11-30T12:47:40Z

Let's see what effect this has in the compiler!
@bors try @rust-timer queue

bors · 2024-11-30T12:48:51Z

⌛ Trying commit 4bf7072 with merge 243c5cc...

…epeatn, r=<try> Use `iter::repeat_n` to implement `Vec::extend_with` This replaces the `Vec::extend_with` manual implementation, which is used by `Vec::resize` and `Vec` `SpecFromElem`, with `iter::repeat_n`. I've compared the codegen output between: 1. the current `Vec::resize` impl 2. this branch 3. this branch + rust-lang#130887 3 gives the closest codegen output to 1, with some output improvements. 2 doesn't look good: https://rust.godbolt.org/z/Yrc83EhjY. May also help rust-lang#120050?

Noratrieb · 2024-11-30T13:48:12Z

given that this branch doesn't look good without #130887, let's block it on that.
@rustbot blocked

bors · 2024-11-30T14:37:20Z

☀️ Try build successful - checks-actions
Build commit: 243c5cc (243c5cc6905efbdf778394d96f4b83701962964f)

rust-timer · 2024-11-30T17:09:58Z

Finished benchmarking commit (243c5cc): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.1%, 0.7%]	16
Regressions ❌ (secondary)	0.4%	[0.1%, 0.6%]	9
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	1
Improvements ✅ (secondary)	-1.3%	[-1.8%, -0.5%]	8
All ❌✅ (primary)	0.3%	[-0.9%, 0.7%]	17

Max RSS (memory usage)

Results (primary 0.1%)

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)	5.6%	[0.9%, 11.4%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-8.1%	[-11.1%, -5.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-11.1%, 11.4%]	5

Cycles

Results (secondary -2.1%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.4%)

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)	0.5%	[0.0%, 1.3%]	43
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	7
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-0.2%, 1.3%]	50

Bootstrap: 773.805s -> 774.205s (0.05%)
Artifact size: 332.32 MiB -> 331.64 MiB (-0.20%)

paolobarbolini · 2024-12-01T09:37:08Z

Could we do another perf run? I've cherry-picked the commit from #130887 since, at least via Compiler Explorer, the codegen looked better

joboet · 2024-12-01T11:04:19Z

Sure!
@bors try @rust-timer queue

bors · 2024-12-01T11:05:32Z

⌛ Trying commit b080e18 with merge 78d5ed4...

…epeatn, r=<try> Use `iter::repeat_n` to implement `Vec::extend_with` This replaces the `Vec::extend_with` manual implementation, which is used by `Vec::resize` and `Vec` `SpecFromElem`, with `iter::repeat_n`. I've compared the codegen output between: 1. the current `Vec::resize` impl 2. this branch 3. this branch + rust-lang#130887 3 gives the closest codegen output to 1, with some output improvements. 2 doesn't look good: https://rust.godbolt.org/z/Yrc83EhjY. May also help rust-lang#120050? --- WARNING: DO NOT MERGE - in order to run the perf run in rust-lang#133662 (comment) this PR currently also contains commits from rust-lang#130887

bors · 2024-12-01T12:50:21Z

☀️ Try build successful - checks-actions
Build commit: 78d5ed4 (78d5ed40d7c459a7e5ea4cb6bea9918a493a800f)

rust-timer · 2024-12-01T14:18:32Z

Finished benchmarking commit (78d5ed4): comparison URL.

Overall result: ❌ regressions - please read the text below

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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.1%, 0.7%]	17
Regressions ❌ (secondary)	1.3%	[0.1%, 3.2%]	16
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.1%, 0.7%]	17

Max RSS (memory usage)

Results (primary -5.6%, secondary 0.3%)

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)	5.3%	[5.3%, 5.3%]	1
Regressions ❌ (secondary)	1.5%	[1.0%, 1.8%]	3
Improvements ✅ (primary)	-11.1%	[-15.5%, -6.8%]	2
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-5.6%	[-15.5%, 5.3%]	3

Cycles

Results (primary -1.5%, secondary 35.1%)

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)	0.9%	[0.9%, 0.9%]	1
Regressions ❌ (secondary)	35.1%	[33.0%, 39.1%]	6
Improvements ✅ (primary)	-4.0%	[-4.0%, -4.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.5%	[-4.0%, 0.9%]	2

Binary size

Results (primary 0.6%)

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%	[0.1%, 1.7%]	33
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	9
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[-0.2%, 1.7%]	42

Bootstrap: 767.632s -> 769.266s (0.21%)
Artifact size: 332.19 MiB -> 332.16 MiB (-0.01%)

paolobarbolini · 2024-12-02T09:12:17Z

Looking at performance data borrow checking time in the Cycles benchmark for wg-grammar is the main culprit. I'm confused why that is.

The fact that this also fixes #120050 makes these changes still worth it to me.

paolobarbolini · 2024-12-25T19:10:00Z

@joboet @scottmcm Do you think the combination of #130887 + this PR, plus the fact it could also fix #120050, could have a chance of working out? I'm not too sure how to interpret the benchmarks and if there's a way of fixing the wg-grammar Cycles regression.

Soveu · 2025-06-18T20:29:46Z

@paolobarbolini #130887 has been merged
@rustbot label -S-blocked +S-waiting-on-author

paolobarbolini · 2025-06-18T21:04:29Z

I've rebased on top of master. Should we do another perf run?

scottmcm · 2025-06-19T04:46:59Z

Sure, with the rebase we might as well give it a shot

@bors try @rust-timer queue

…=<try> Use `iter::repeat_n` to implement `Vec::extend_with` This replaces the `Vec::extend_with` manual implementation with `iter::repeat_n`, simplifying the code and also possibly fixing the issue identified in #120050.

bors · 2025-06-19T04:48:11Z

⌛ Trying commit 29565d7 with merge c79c24a...

bors · 2025-06-19T07:18:51Z

☀️ Try build successful - checks-actions
Build commit: c79c24a (c79c24ad439e510f1baa231dcaf131000f552308)

rust-timer · 2025-06-19T12:05:29Z

Finished benchmarking commit (c79c24a): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.2%, 3.0%]	12
Regressions ❌ (secondary)	3.0%	[0.2%, 7.5%]	16
Improvements ✅ (primary)	-0.9%	[-1.3%, -0.5%]	2
Improvements ✅ (secondary)	-0.5%	[-1.2%, -0.2%]	3
All ❌✅ (primary)	0.5%	[-1.3%, 3.0%]	14

Max RSS (memory usage)

Results (primary 2.2%, secondary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	4.9%	[1.1%, 7.3%]	4
Regressions ❌ (secondary)	4.7%	[3.3%, 6.5%]	3
Improvements ✅ (primary)	-3.3%	[-4.2%, -2.4%]	2
Improvements ✅ (secondary)	-7.2%	[-8.5%, -5.9%]	2
All ❌✅ (primary)	2.2%	[-4.2%, 7.3%]	6

Cycles

Results (primary 1.7%, secondary 3.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.7%	[0.7%, 3.6%]	3
Regressions ❌ (secondary)	3.6%	[2.2%, 10.5%]	7
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.7%	[0.7%, 3.6%]	3

Binary size

Results (primary 0.6%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.1%, 1.7%]	38
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[-0.1%, 1.7%]	39

Bootstrap: 692.944s -> 693.357s (0.06%)
Artifact size: 372.01 MiB -> 371.96 MiB (-0.01%)

rustbot assigned Noratrieb Nov 30, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Nov 30, 2024

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rustbot added S-blocked Status: Blocked on something else such as an RFC or other implementation work. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 30, 2024

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Nov 30, 2024

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Dec 1, 2024

paolobarbolini mentioned this pull request Dec 1, 2024

Safer implementation of RepeatN #130887

Merged

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paolobarbolini mentioned this pull request Dec 2, 2024

Vec::resize for bytes should be a single memset #120050

Draft

paolobarbolini force-pushed the vec-extend-with-via-repeatn branch from b080e18 to c45fdfc Compare February 19, 2025 09:43

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-blocked Status: Blocked on something else such as an RFC or other implementation work. labels Jun 18, 2025

Use iter::repeat_n to implement Vec::extend_with

29565d7

paolobarbolini force-pushed the vec-extend-with-via-repeatn branch from c45fdfc to 29565d7 Compare June 18, 2025 21:01

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 19, 2025

Use iter::repeat_n to implement Vec::extend_with #133662

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Use iter::repeat_n to implement Vec::extend_with #133662

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Overall result: ❌✅ regressions and improvements - please read the text below

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Overall result: ❌ regressions - please read the text below

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Overall result: ❌✅ regressions and improvements - please read the text below

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Use `iter::repeat_n` to implement `Vec::extend_with` #133662

Use `iter::repeat_n` to implement `Vec::extend_with` #133662

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