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Implement advance_by via try_fold for Sized iterators#141086

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a1phyr:spec_advance_by
May 25, 2025
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Implement advance_by via try_fold for Sized iterators#141086
bors merged 1 commit intorust-lang:masterfrom
a1phyr:spec_advance_by

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@a1phyr a1phyr commented May 16, 2025

When try_fold is overriden, it is usually easier for compilers to optimize.

Example difference: https://iter.godbolt.org/z/z8cEfnKro

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Implement advance_by via try_fold for Sized iterators
5240cd3 
When `try_fold` is overriden, it is usually easier for compilers to
optimize.
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rustbot commented May 16, 2025

r? @jhpratt

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@rustbot 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 May 16, 2025
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jhpratt commented May 24, 2025

@bors r+ rollup=never

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bors commented May 24, 2025

📌 Commit 5240cd3 has been approved by jhpratt

It is now in the queue for this repository.

@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 May 24, 2025
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bors commented May 25, 2025

⌛ Testing commit 5240cd3 with merge 88b3b52...

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bors commented May 25, 2025

☀️ Test successful - checks-actions
Approved by: jhpratt
Pushing 88b3b52 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label May 25, 2025
@bors bors merged commit 88b3b52 into rust-lang:master May 25, 2025
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@rustbot rustbot added this to the 1.89.0 milestone May 25, 2025
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github-actions bot commented May 25, 2025

What is this? This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing aa57e46 (parent) -> 88b3b52 (this PR)

Test differences

Show 548 test diffs

548 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 88b3b520e852e01970c3f519339ba64ed3e7db6d --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

  1. x86_64-apple-2: 5623.9s -> 4338.5s (-22.9%)
  2. aarch64-gnu: 7784.1s -> 6727.4s (-13.6%)
  3. aarch64-gnu-debug: 4592.8s -> 4022.7s (-12.4%)
  4. x86_64-apple-1: 7811.3s -> 6870.0s (-12.1%)
  5. dist-aarch64-apple: 4678.9s -> 5226.2s (11.7%)
  6. dist-powerpc64le-linux-gnu: 5302.2s -> 5625.4s (6.1%)
  7. dist-x86_64-linux-alt: 7107.4s -> 7530.9s (6.0%)
  8. dist-ohos-aarch64: 4473.1s -> 4711.5s (5.3%)
  9. dist-powerpc64le-linux-musl: 5674.5s -> 5388.1s (-5.0%)
  10. dist-apple-various: 6433.6s -> 6694.8s (4.1%)
How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

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rust-timer commented May 25, 2025

Finished benchmarking commit (88b3b52): comparison URL.

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

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

  • If the regression was expected or you think it can be justified,
    please write a comment with sufficient written justification, and add
    @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
  • If you think that you know of a way to resolve the regression, try to create
    a new PR with a fix for the regression.
  • If you do not understand the regression or you think that it is just noise,
    you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
    were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)		 1.4% [0.6%, 3.0%] 4
Regressions ❌
(secondary)		 3.6% [0.3%, 6.8%] 2
Improvements ✅
(primary)		 -0.3% [-0.3%, -0.3%] 1
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 1.0% [-0.3%, 3.0%] 5

Max RSS (memory usage)

Results (primary 1.4%, secondary -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)		 3.9% [2.6%, 5.0%] 5
Regressions ❌
(secondary)		 2.3% [2.1%, 2.4%] 2
Improvements ✅
(primary)		 -5.0% [-6.0%, -4.0%] 2
Improvements ✅
(secondary)		 -6.4% [-6.4%, -6.4%] 1
All ❌✅ (primary) 1.4% [-6.0%, 5.0%] 7

Cycles

Results (primary 1.7%, secondary 2.3%)

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)		 1.7% [1.0%, 3.1%] 3
Regressions ❌
(secondary)		 4.7% [2.8%, 6.5%] 2
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -2.4% [-2.4%, -2.4%] 1
All ❌✅ (primary) 1.7% [1.0%, 3.1%] 3

Binary size

Results (primary 0.2%, secondary 0.5%)

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)		 0.2% [0.0%, 1.2%] 24
Regressions ❌
(secondary)		 0.5% [0.1%, 1.1%] 6
Improvements ✅
(primary)		 -0.4% [-0.4%, -0.4%] 1
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 0.2% [-0.4%, 1.2%] 25

Bootstrap: 776.084s -> 775.765s (-0.04%)
Artifact size: 366.32 MiB -> 366.27 MiB (-0.01%)

@rustbot rustbot added the perf-regression Performance regression. label May 25, 2025
github-actions bot pushed a commit to model-checking/verify-rust-std that referenced this pull request May 26, 2025
@bors
Auto merge of rust-lang#141086 - a1phyr:spec_advance_by, r=jhpratt
725b0db 
Implement `advance_by` via `try_fold` for `Sized` iterators

When `try_fold` is overriden, it is usually easier for compilers to optimize.

Example difference: https://iter.godbolt.org/z/z8cEfnKro
@a1phyr a1phyr deleted the spec_advance_by branch May 26, 2025 21:44
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rylev commented May 27, 2025

@a1phyr @jhpratt - the regression in clap is noise, but the regressions in ripgrep seem to be legit. This might just be more time spent in LLM crunching through things. Thoughts on whether to explore deeper?

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jhpratt commented May 27, 2025

On the assumption you meant LLVM, that seems like a reasonable explanation. The difference is in the backend and linker, which makes sense as there is a small amount more code to work with. This happening to ripgrep isn't super surprising — it's probably the crate that would use this the most.

Personally I'm satisfied with that explanation, but I also wouldn't know where to start if I were to explore further.

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