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replace vec::Drain drop loops with drop_in_place#85157

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the8472:drain-drop-in-place
Dec 9, 2021
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replace vec::Drain drop loops with drop_in_place#85157
bors merged 3 commits into
rust-lang:masterfrom
the8472:drain-drop-in-place

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@the8472 the8472 commented May 10, 2021 •
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The Drain::drop implementation came up in #82185 (comment) as potentially interfering with other optimization work due its widespread use somewhere in println!

@rustbot label T-libs-impl

@rustbot rustbot added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label May 10, 2021
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rust-highfive commented May 10, 2021

r? @yaahc

(rust-highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 10, 2021
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Mark-Simulacrum commented May 10, 2021

@bors try @rust-timer queue

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rust-timer commented May 10, 2021

Awaiting bors try build completion.

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

@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label May 10, 2021
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bors commented May 10, 2021

⌛ Trying commit 5cd25a3c8de8ac50571849c91869d27b0aedf1b4 with merge f43378a4f09d5d51bfbc4bca4d5abbd28238f176...

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bors commented May 10, 2021

💔 Test failed - checks-actions

@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 10, 2021
SkiFire13
SkiFire13 reviewed May 10, 2021
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Comment thread library/alloc/src/vec/drain.rs Outdated
@the8472 the8472 force-pushed the drain-drop-in-place branch from 5cd25a3 to 032fa35 Compare May 10, 2021 21:24
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Mark-Simulacrum commented May 10, 2021

@bors try

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bors commented May 10, 2021

⌛ Trying commit 032fa35 with merge 29e55f8f91bd74ab69933dd9166d41317e0146b7...

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bors commented May 10, 2021

☀️ Try build successful - checks-actions
Build commit: 29e55f8f91bd74ab69933dd9166d41317e0146b7 (29e55f8f91bd74ab69933dd9166d41317e0146b7)

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rust-timer commented May 10, 2021

Queued 29e55f8f91bd74ab69933dd9166d41317e0146b7 with parent 6fd7a6d, future comparison URL.

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rust-timer commented May 11, 2021

Finished benchmarking try commit (29e55f8f91bd74ab69933dd9166d41317e0146b7): comparison url.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. Please note that if the perf results are neutral, you should likely undo the rollup=never given below by specifying rollup- to bors.

Importantly, though, if the results of this run are non-neutral do not roll this PR up -- it will mask other regressions or improvements in the roll up.

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

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels May 11, 2021
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the8472 commented May 11, 2021

seems kind of mixed. @SkiFire13 do you think it would make sense to test your changes on top of these?

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SkiFire13 commented May 11, 2021

I might give it a try, give me a sec to rebase my pr on top of yours.

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@JohnCSimon JohnCSimon added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 31, 2021
@JohnTitor JohnTitor removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jun 15, 2021
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JohnCSimon commented Nov 8, 2021

triage:
@yaahc This has been sitting in review state since may

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yaahc commented Nov 15, 2021

triage: @yaahc This has been sitting in review state since may

Still on my radar, just haven't had a chance to review it yet.

Mark-Simulacrum
Mark-Simulacrum reviewed Nov 19, 2021
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Comment thread library/alloc/src/vec/drain.rs Outdated
Mark-Simulacrum
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Comment thread library/alloc/src/vec/drain.rs
@the8472 the8472 force-pushed the drain-drop-in-place branch from 032fa35 to 6851b8d Compare November 20, 2021 00:29
@Mark-Simulacrum Mark-Simulacrum added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 20, 2021
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Mark-Simulacrum commented Dec 7, 2021

@the8472 if you want to leave the cleanup of spare capacity to something simpler for the future, that seems OK to me as well I think.

@the8472 the8472 added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Dec 8, 2021
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Mark-Simulacrum commented Dec 9, 2021

@bors r+

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bors commented Dec 9, 2021

📌 Commit 2d8a11b has been approved by Mark-Simulacrum

@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 Dec 9, 2021
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bors commented Dec 9, 2021

⌛ Testing commit 2d8a11b with merge 0b42dea...

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bors commented Dec 9, 2021

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 0b42dea to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Dec 9, 2021
@bors bors merged commit 0b42dea into rust-lang:master Dec 9, 2021
@rustbot rustbot added this to the 1.59.0 milestone Dec 9, 2021
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rust-timer commented Dec 9, 2021

Finished benchmarking commit (0b42dea): comparison url.

Summary: This change led to large relevant improvements 🎉 in compiler performance.

  • Large improvement in instruction counts (up to -1.7% on full builds of match-stress-enum)

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

@rustbot label: -perf-regression

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the8472 commented Dec 9, 2021

Nice, better results than the previous perf run.

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RalfJung commented Dec 11, 2021

Is it possible that this introduced a use-after-free?

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Comment thread library/alloc/src/vec/drain.rs
mem::forget(guard);
let iter = mem::replace(&mut self.iter, (&mut []).iter());
let drop_len = iter.len();
let drop_ptr = iter.as_slice().as_ptr();
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@RalfJung RalfJung Dec 11, 2021

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Specifically, Miri says that in this line as_slice points to dangling memory (in some cases, here triggered by the test_replace_range testcase)

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I'm under the impression that the iter should be valid at all times, but I'll have a closer look at the test-case.

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(Continuing in #91772)

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