Propagate `#[allow(dead_code)]` on adts to their inherent impls by mu001999 · Pull Request #157885 · rust-lang/rust

mu001999 · 2026-06-14T10:44:36Z

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This PR does:

propagate #[allow(dead_code)] on adts to their inherent impls and impl items
refactor the previous implementation for impl items of traits, and improve the performance (extracted to Refactor the #[allow(dead_code)] propagation for impl items of traits #161571 and Only check #[allow(dead_code)] on the trait #161932)

After the above, there is still some slight perf regressions because we indeed do more things (for inherent impls).

Fixes #149142

mu001999 · 2026-06-15T00:41:31Z

@bors try @rust-timer queue

Propagate `#[allow(dead_code)]` on adts to their inherent impls

rust-bors · 2026-06-15T02:53:19Z

☀️ Try build successful (CI)
Build commit: 25aedf1 (25aedf1c569cd8fb010ed559082eacf12d56aaa2, parent: 3daae5e42ec9ba435212987331af1b7b8634fa90)

rust-timer · 2026-06-15T03:34:20Z

Finished benchmarking commit (25aedf1): comparison URL.

Overall result: ❌ regressions - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.5%	[0.1%, 0.9%]	52
Regressions ❌ (secondary)	0.4%	[0.2%, 0.7%]	16
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-0.2%, 0.9%]	53

Max RSS (memory usage)

Results (primary -2.3%, secondary -1.0%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.9%	[-6.9%, -0.9%]	3
Improvements ✅ (secondary)	-1.0%	[-1.0%, -1.0%]	1
All ❌✅ (primary)	-2.3%	[-6.9%, 2.3%]	4

Cycles

Results (secondary 21.3%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	21.3%	[20.3%, 22.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 519.503s -> 518.599s (-0.17%)
Artifact size: 401.51 MiB -> 401.51 MiB (-0.00%)

mu001999 · 2026-06-16T16:18:49Z

@bors try @rust-timer queue

Propagate `#[allow(dead_code)]` on adts to their inherent impls

rust-bors · 2026-06-16T18:30:21Z

☀️ Try build successful (CI)
Build commit: 848b0fa (848b0fabbf422f36bd3435a5abda617bf5da7395, parent: 89a99936d9e76a50e8df622e7242190841fd871b)

rust-timer · 2026-06-16T19:11:13Z

Finished benchmarking commit (848b0fa): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.2%	[0.2%, 0.2%]	3
Regressions ❌ (secondary)	0.3%	[0.2%, 0.4%]	12
Improvements ✅ (primary)	-0.3%	[-0.7%, -0.2%]	14
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	2
All ❌✅ (primary)	-0.2%	[-0.7%, 0.2%]	17

Max RSS (memory usage)

Results (primary -5.4%, secondary 1.7%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.3%	[1.6%, 5.8%]	3
Improvements ✅ (primary)	-5.4%	[-5.4%, -5.4%]	1
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-5.4%	[-5.4%, -5.4%]	1

Cycles

Results (secondary 1.4%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.4%	[4.4%, 4.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 522.035s -> 522.314s (0.05%)
Artifact size: 401.81 MiB -> 401.26 MiB (-0.14%)

mu001999 · 2026-06-17T01:16:45Z

@bors try @rust-timer queue

rust-bors · 2026-06-18T09:24:04Z

☀️ Try build successful (CI)
Build commit: ac3f172 (ac3f1720b43fdf1c580ee653c1a9db9b9e07b739)
Base parent: 3768ec0 (3768ec06c826ef667b65a7d084610a11baf10776)

rust-timer · 2026-06-18T10:28:14Z

Finished benchmarking commit (ac3f172): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.2%	[0.2%, 0.3%]	3
Regressions ❌ (secondary)	0.4%	[0.4%, 0.4%]	6
Improvements ✅ (primary)	-0.6%	[-1.4%, -0.2%]	29
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.3%]	2
All ❌✅ (primary)	-0.5%	[-1.4%, 0.3%]	32

Max RSS (memory usage)

Results (primary -1.0%)

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

	mean	range	count
Regressions ❌ (primary)	1.3%	[1.3%, 1.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.2%	[-2.8%, -1.5%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.0%	[-2.8%, 1.3%]	3

Cycles

Results (primary 2.9%, 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)	2.9%	[2.2%, 4.0%]	5
Regressions ❌ (secondary)	2.8%	[2.8%, 2.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.1%	[-3.1%, -3.1%]	1
All ❌✅ (primary)	2.9%	[2.2%, 4.0%]	5

Binary size

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

Bootstrap: 522.822s -> 523.673s (0.16%)
Artifact size: 401.33 MiB -> 401.44 MiB (0.03%)

rustbot · 2026-06-18T14:44:05Z

r? @dingxiangfei2009

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mu001999 · 2026-07-14T05:57:21Z

@dingxiangfei2009 friendly ping

mu001999 · 2026-07-15T09:58:59Z

Seems @dingxiangfei2009 has no time to review this, so @rustbot reroll

fee1-dead · 2026-07-15T17:32:57Z

#[allow(dead_code)]
struct Foo;

impl Foo {
    fn foo(&self) {}
}

Do we think this should actually make dead_code not fire on impl Foo? I think this is a bit subtle and I can see both ways. Nominating for T-lang.

@rustbot nominate lang

rustbot · 2026-07-15T17:33:28Z

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rustbot · 2026-08-23T03:53:31Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

…kang Refactor the `#[allow(dead_code)]` propagation for impl items of traits Extracted from #157885. This PR does the refactor and corrects the previous implementation. The following will fail currently ([play](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=3279902b2d2e6b0fe75c5af565b1cddd)): ```rust #![deny(dead_code)] #![deny(unfulfilled_lint_expectations)] #[allow(dead_code)] pub trait Tr { fn foo(&self); } struct Foo; impl Tr for Foo { fn foo(&self) { bar(); } } #[expect(dead_code)] fn bar() {} fn main() {} ``` After this PR, we could handle the `#[allow(dead_code)]` propagation correctly, and should get perf improvement.

rust-bors · 2026-08-28T11:27:25Z

☔ The latest upstream changes (presumably #161571) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 14, 2026

qaijuang reviewed Jun 14, 2026

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Comment thread compiler/rustc_passes/src/dead.rs Outdated

qaijuang reviewed Jun 14, 2026

View reviewed changes

Comment thread compiler/rustc_passes/src/dead.rs Outdated

mu001999 force-pushed the dead-code/improve branch from 0ff50d6 to 93cdd71 Compare June 14, 2026 14:43