Skip codegen_crate call in check mode #148035

bjorn3 · 2025-10-23T15:36:05Z

This way we don't have to spawn the coordinator thread. Some errors will no longer be emitted with this in check mode. For example the check that -Ctarget-cpu is passed on targets that need this.

Suggested by @saethlin

rustbot · 2025-10-23T15:36:08Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

rustbot · 2025-10-23T15:36:11Z

r? @madsmtm

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bjorn3 · 2025-10-23T15:36:15Z

@bors try @rust-timer queue

Skip codegen_crate call in check mode

rust-bors · 2025-10-23T17:49:29Z

☀️ Try build successful (CI)
Build commit: 3eae4c9 (3eae4c9d8d83d9f1eda6239b5443ae80fa3d06bd, parent: 11d2046fe9962720558cb15f72541f7fd170dec9)

scottmcm · 2025-10-23T18:30:22Z

Some errors will no longer be emitted with this in check mode.

Sounds allowed by https://rust-lang.github.io/rfcs/3477-cargo-check-lang-policy.html, so no issue so long as it's not skipping anything that would be needed particularly often.

(Not reporting things that'll be reported for any full build, like missing flags for a target, seems totally fine to me. That wouldn't be part of the core inner dev loop where check is most important.)

rust-timer · 2025-10-23T18:58:27Z

Finished benchmarking commit (3eae4c9): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-1.4%, -0.7%]	5
Improvements ✅ (secondary)	-0.4%	[-1.3%, -0.2%]	21
All ❌✅ (primary)	-0.9%	[-1.4%, -0.7%]	5

Max RSS (memory usage)

Results (primary -1.7%, secondary -3.5%)

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)	-	-	0
Improvements ✅ (primary)	-1.7%	[-2.1%, -1.3%]	3
Improvements ✅ (secondary)	-3.5%	[-4.4%, -2.7%]	2
All ❌✅ (primary)	-1.7%	[-2.1%, -1.3%]	3

Cycles

Results (secondary -2.2%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.4%, -2.1%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary -0.0%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-	-	0

Bootstrap: 474.995s -> 475.128s (0.03%)
Artifact size: 390.51 MiB -> 390.45 MiB (-0.02%)

bjorn3 · 2025-10-24T10:27:19Z

@bors try @rust-timer queue

To check how perf.rust-lang.org handles the change in timers.

Skip codegen_crate call in check mode

rust-bors · 2025-10-24T12:41:25Z

☀️ Try build successful (CI)
Build commit: 1d990a0 (1d990a02a84d5e04783da0e318563db26401bc48, parent: 75948c8bb3bd37f1e8ee20273a04edea4c1f84f8)

rust-timer · 2025-10-24T14:05:08Z

Finished benchmarking commit (1d990a0): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-1.0%, -0.9%]	4
Improvements ✅ (secondary)	-0.4%	[-0.8%, -0.1%]	29
All ❌✅ (primary)	-0.9%	[-1.0%, -0.9%]	4

Max RSS (memory usage)

Results (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
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-2.2%, -0.5%]	2
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 0.7%)

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary 0.0%)

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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 474.959s -> 474.684s (-0.06%)
Artifact size: 390.49 MiB -> 390.51 MiB (0.01%)

madsmtm

+1 on the idea, and the perf improvements look real.

View changes since this review

compiler/rustc_interface/src/passes.rs

compiler/rustc_codegen_ssa/src/back/write.rs

madsmtm

@bors r+

View changes since this review

madsmtm · 2025-10-27T17:06:34Z

@bors ping

bors · 2025-10-27T17:06:37Z

😪 I'm awake I'm awake

madsmtm · 2025-10-27T17:06:43Z

@bors r+

bors · 2025-10-27T17:06:46Z

📌 Commit 5a8ffa4 has been approved by madsmtm

It is now in the queue for this repository.

bors · 2025-10-27T17:24:11Z

⌛ Testing commit 5a8ffa4 with merge adaa838...

matthiaskrgr · 2025-10-27T18:19:04Z

does this mean that check-mode crater runs will be less effective in the future?

madsmtm · 2025-10-27T19:27:55Z

does this mean that check-mode crater runs will be less effective in the future?

Slightly, though I'd guess that most of the code that we now avoid running is exercised with a single rustc --emit=obj invocation, and the rest wouldn't be caught by crater anyhow (it'd only be hit with weird rustc flag combinations).

saethlin · 2025-10-27T19:42:59Z

I think the only thing that this omits is errors that would be produced by creating the codegen backend. If someone was actually doing crater check runs to find those errors, I have questions.

bors · 2025-10-27T20:34:10Z

☀️ Test successful - checks-actions
Approved by: madsmtm
Pushing adaa838 to master...

github-actions · 2025-10-27T20:37:53Z

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 9ea8d67 (parent) -> adaa838 (this PR)

Test differences

Show 4 test diffs

4 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 adaa838976ff99a4f0661136322f64cb466b58a0 --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

dist-aarch64-apple: 7049.4s -> 8934.0s (26.7%)
dist-apple-various: 4102.4s -> 3018.4s (-26.4%)
x86_64-gnu-llvm-20: 2867.7s -> 2188.9s (-23.7%)
pr-check-1: 1852.4s -> 1458.7s (-21.3%)
dist-various-1: 3730.3s -> 4326.5s (16.0%)
x86_64-gnu-gcc: 3344.7s -> 2836.0s (-15.2%)
aarch64-gnu-llvm-20-2: 2580.1s -> 2238.8s (-13.2%)
i686-gnu-nopt-1: 8544.3s -> 7428.2s (-13.1%)
x86_64-msvc-2: 7237.6s -> 6390.4s (-11.7%)
i686-gnu-2: 6152.2s -> 5502.0s (-10.6%)

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 · 2025-10-27T22:11:08Z

Finished benchmarking commit (adaa838): 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

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

	mean	range	count
Regressions ❌ (primary)	1.2%	[1.2%, 1.2%]	1
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-0.8%	[-0.8%, -0.8%]	3
Improvements ✅ (secondary)	-0.3%	[-0.7%, -0.2%]	11
All ❌✅ (primary)	-0.3%	[-0.8%, 1.2%]	4

Max RSS (memory usage)

Results (secondary 4.4%)

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)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -3.0%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-3.0%, -3.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (secondary -0.0%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-	-	0

Bootstrap: 474.628s -> 473.263s (-0.29%)
Artifact size: 390.61 MiB -> 390.54 MiB (-0.02%)

madsmtm · 2025-10-28T12:14:21Z

Seems like it was only the syn-2.0.101 benchmark that regressed, and an earlier perf run showed only improvements, so it was probably spurious.

@rustbot label: +perf-regression-triaged

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Oct 23, 2025

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rust-bors bot added a commit that referenced this pull request Oct 23, 2025

Auto merge of #148035 - bjorn3:check_skip_codegen_crate, r=<try>

3eae4c9

Skip codegen_crate call in check mode

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 23, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 23, 2025

Kobzol mentioned this pull request Oct 23, 2025

Ensure that compilation sections are always present rust-lang/rustc-perf#2300

Merged

Skip codegen_crate call in check mode

5a8ffa4

bjorn3 force-pushed the check_skip_codegen_crate branch from 3e6df8b to 5a8ffa4 Compare October 24, 2025 10:25

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rust-bors bot added a commit that referenced this pull request Oct 24, 2025

Auto merge of #148035 - bjorn3:check_skip_codegen_crate, r=<try>

1d990a0

Skip codegen_crate call in check mode

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 24, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 24, 2025

madsmtm reviewed Oct 27, 2025

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compiler/rustc_codegen_ssa/src/back/write.rs Show resolved Hide resolved

madsmtm approved these changes Oct 27, 2025

View reviewed changes

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 Oct 27, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Oct 27, 2025

bors merged commit adaa838 into rust-lang:master Oct 27, 2025
13 checks passed

rustbot added this to the 1.93.0 milestone Oct 27, 2025

bjorn3 deleted the check_skip_codegen_crate branch October 27, 2025 21:19

rustbot added the perf-regression Performance regression. label Oct 27, 2025

rustbot added the perf-regression-triaged The performance regression has been triaged. label Oct 28, 2025

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Skip codegen_crate call in check mode #148035

Skip codegen_crate call in check mode #148035

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Overall result: ✅ improvements - no action needed

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Overall result: ✅ improvements - no action needed

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Test differences

Job duration changes

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rust-timer commented Oct 27, 2025

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

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