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lib: specialize Clone of array IntoIter#156634

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Paladynee:lib/array-intoiter-spec-clone
May 29, 2026
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lib: specialize Clone of array IntoIter#156634
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Paladynee:lib/array-intoiter-spec-clone

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@Paladynee Paladynee commented May 16, 2026 •
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This PR adds the TrivialClone specialization to the PolymorphicIter type, which array::IntoIter uses. I also added another coretest for the default case (already existing test catches the specialized one).

There are no unwinding concerns since TrivialClone means cloning = copying and we never call Clone::clone.

array:IntoIter is being used on a lot of places in both core and in user code, and array::IntoIter (nor does its users) override Clone often and just delegate to the inner type PolymorphicIter which does not yet do the TrivialClone specialization and is burdened by the iterator and unwind safety shenanigans for all types, so this PR should address some of that. This should in turn slightly reduce both stack usage and remove unwinding prologue/epilogue etc. from such functions and improve our -Cno-prepopulate-passes codegen too.

perf: https://godbolt.org/z/eTPjj3hP3

@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, 2026
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r? @Mark-Simulacrum

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  • Owners of files modified in this PR: @scottmcm, libs
  • @scottmcm, libs expanded to 8 candidates

@Paladynee Paladynee force-pushed the lib/array-intoiter-spec-clone branch from 1ef1a4b to 5cec957 Compare May 16, 2026 08:31
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joboet commented May 28, 2026 •
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@bors r+
r? joboet

Great, thanks!

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📌 Commit 5cec957 has been approved by joboet

It is now in the queue for this repository.

@rust-bors rust-bors Bot 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 28, 2026
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 28, 2026
@JonathanBrouwer
Rollup merge of rust-lang#156634 - Paladynee:lib/array-intoiter-spec-…
0492291 
…clone, r=joboet

lib: specialize Clone of array IntoIter

This PR adds the `TrivialClone` specialization to the `PolymorphicIter` type, which `array::IntoIter` uses. I also added another coretest for the default case (already existing test catches the specialized one).

There are no unwinding concerns since `TrivialClone` means cloning = copying and we never call `Clone::clone`.

`array:IntoIter` is being used on a lot of places in both `core` and in user code, and `array::IntoIter` (nor does its users) override `Clone` often and just delegate to the inner type `PolymorphicIter` which does not yet do the `TrivialClone` specialization and is burdened by the iterator and unwind safety shenanigans for all types, so this PR should address some of that. This should in turn slightly reduce both stack usage and remove unwinding prologue/epilogue etc. from such functions and improve our `-Cno-prepopulate-passes` codegen too.

perf: https://godbolt.org/z/eTPjj3hP3
@JonathanBrouwer JonathanBrouwer mentioned this pull request May 28, 2026
Closed
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 28, 2026
@JonathanBrouwer
Rollup merge of rust-lang#156634 - Paladynee:lib/array-intoiter-spec-…
4c66d2a 
…clone, r=joboet

lib: specialize Clone of array IntoIter

This PR adds the `TrivialClone` specialization to the `PolymorphicIter` type, which `array::IntoIter` uses. I also added another coretest for the default case (already existing test catches the specialized one).

There are no unwinding concerns since `TrivialClone` means cloning = copying and we never call `Clone::clone`.

`array:IntoIter` is being used on a lot of places in both `core` and in user code, and `array::IntoIter` (nor does its users) override `Clone` often and just delegate to the inner type `PolymorphicIter` which does not yet do the `TrivialClone` specialization and is burdened by the iterator and unwind safety shenanigans for all types, so this PR should address some of that. This should in turn slightly reduce both stack usage and remove unwinding prologue/epilogue etc. from such functions and improve our `-Cno-prepopulate-passes` codegen too.

perf: https://godbolt.org/z/eTPjj3hP3
@JonathanBrouwer JonathanBrouwer mentioned this pull request May 28, 2026
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rust-bors Bot pushed a commit that referenced this pull request May 28, 2026
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Auto merge of #157077 - JonathanBrouwer:rollup-pWvdmJO, r=JonathanBro…
cbfd997 
…uwer

Rollup of 5 pull requests

Successful merges:

 - #153957 (Add bootstrap step for stdarch-verify)
 - #156634 (lib: specialize Clone of array IntoIter)
 - #157050 (Couple of changes to help with moving LTO to the link phase)
 - #156931 (Add splitting caveats to `{read,write}_volatile`)
 - #157071 (Fix `cfg` typo in rustdoc book)
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@rust-bors rust-bors Bot added merged-by-bors This PR was explicitly merged by bors. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels May 29, 2026
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☀️ Test successful - CI
Approved by: joboet
Duration: 3h 10m 13s
Pushing dc375db to main...

@rust-bors rust-bors Bot merged commit dc375db into rust-lang:main May 29, 2026
12 checks passed
@rustbot rustbot added this to the 1.98.0 milestone May 29, 2026
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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 cced03b (parent) -> dc375db (this PR)

Test differences

Show 4 test diffs

Stage 1

  • array::iterator_clone_spec: [missing] -> pass (J0)

Stage 2

  • array::iterator_clone_spec: [missing] -> pass (J1)

Additionally, 2 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard dc375db7d8df0aa450e622c529147c95eee756f5 --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-mingw-1: 2h 18m -> 2h 56m (+27.8%)
  2. x86_64-gnu-gcc-core-tests: 6m 13s -> 7m 47s (+24.9%)
  3. dist-arm-linux-musl: 1h 20m -> 1h 40m (+24.2%)
  4. dist-android: 30m 1s -> 22m 52s (-23.8%)
  5. x86_64-msvc-ext2: 1h 56m -> 1h 29m (-23.2%)
  6. x86_64-gnu-miri: 1h 6m -> 1h 22m (+23.0%)
  7. x86_64-mingw-2: 2h 35m -> 2h 6m (-18.8%)
  8. dist-x86_64-apple: 2h 17m -> 1h 52m (-18.6%)
  9. dist-aarch64-apple: 1h 52m -> 2h 11m (+16.0%)
  10. aarch64-apple: 2h 38m -> 3h 2m (+14.7%)
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.

@rust-timer

rust-timer commented May 29, 2026

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Finished benchmarking commit (dc375db): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -0.1% [-0.1%, -0.1%] 1
All ❌✅ (primary) - - 0

Max RSS (memory usage)

Results (primary 5.3%)

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

mean range count
Regressions ❌
(primary)		 5.3% [5.3%, 5.3%] 1
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) 5.3% [5.3%, 5.3%] 1

Cycles

This perf run didn't have relevant results for this metric.

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 511.528s -> 510.27s (-0.25%)
Artifact size: 400.68 MiB -> 400.65 MiB (-0.01%)

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