Introduce `TypingMode::Codegen` to avoid layout cycles on coroutines by cjgillot · Pull Request #145477 · rust-lang/rust

cjgillot · 2025-08-16T00:04:12Z

Computing layout of coroutines depends on their optimized_mir. At the same time, MIR opts can require using layouts to work. For instance to evaluate constants. This leads to cycles and clumsy workarounds.

This PR creates a new typing mode for layout computations:

when a coroutine's layout is requested with TypingMode::PostAnalysis or earlier, return LayourError::TooGeneric;
when a coroutine's layout is requested with TypingMode::Codegen, actually compute it.

TypingMode::Codegen is meant be be used by codegen code, and analyses that require coroutine layout, like transmute check and coroutine recursion check.

With this PR, we can remove all is_coroutine checks from rustc_mir_transform and unlock simplifying coroutine MIR.

Perf is not terrific. This PR causes recomputation of a few queries, and I had to insert workarounds.

cjgillot · 2025-08-16T00:05:55Z

@bors try @rust-timer queue

[EXPERIMENT] Introduce `TypingMode::Codegen` to avoid layout cycles

rust-bors · 2025-08-16T02:19:21Z

☀️ Try build successful (CI)
Build commit: 34dd67f (34dd67f42f0f2050c773b332e2dd333618c22743, parent: cd7cbe818e4a66d46fe2df993d1b8518eba8a5cd)

rust-timer · 2025-08-16T07:24:00Z

Finished benchmarking commit (34dd67f): comparison URL.

Overall result: ❌ regressions - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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%	[0.2%, 3.3%]	58
Regressions ❌ (secondary)	1.8%	[0.0%, 19.4%]	58
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.0%]	4
All ❌✅ (primary)	0.5%	[0.2%, 3.3%]	58

Max RSS (memory usage)

Results (primary 1.4%, secondary 4.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.7%	[0.5%, 7.3%]	17
Regressions ❌ (secondary)	5.4%	[1.2%, 12.3%]	6
Improvements ✅ (primary)	-1.3%	[-1.4%, -1.3%]	2
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	1.4%	[-1.4%, 7.3%]	19

Cycles

Results (primary 2.9%, secondary 4.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	5.3%	[2.1%, 12.0%]	12
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.0%	[-4.0%, -4.0%]	1
All ❌✅ (primary)	2.9%	[2.9%, 2.9%]	1

Binary size

Results (primary 0.1%, 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)	0.4%	[0.1%, 0.6%]	2
Regressions ❌ (secondary)	0.3%	[0.1%, 0.4%]	3
Improvements ✅ (primary)	-0.0%	[-0.0%, -0.0%]	3
Improvements ✅ (secondary)	-1.8%	[-7.1%, -0.1%]	5
All ❌✅ (primary)	0.1%	[-0.0%, 0.6%]	5

Bootstrap: 469.562s -> 472.464s (0.62%)
Artifact size: 377.55 MiB -> 377.67 MiB (0.03%)

cjgillot · 2025-08-16T14:48:02Z

@bors try @rust-timer queue

[EXPERIMENT] Introduce `TypingMode::Codegen` to avoid layout cycles

rust-bors · 2025-08-16T17:07:25Z

☀️ Try build successful (CI)
Build commit: 4e9488c (4e9488c147d4057600076145eccb670b130147d5, parent: 2e2642e641a941f0a1400c7827fd89aa86fef8f4)

rust-timer · 2025-08-16T18:40:34Z

Finished benchmarking commit (4e9488c): comparison URL.

Overall result: ❌ regressions - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.4%	[0.2%, 0.9%]	23
Regressions ❌ (secondary)	1.5%	[0.1%, 9.7%]	59
Improvements ✅ (primary)	-1.6%	[-1.6%, -1.6%]	1
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	2
All ❌✅ (primary)	0.4%	[-1.6%, 0.9%]	24

Max RSS (memory usage)

Results (primary 1.7%, secondary 5.0%)

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

	mean	range	count
Regressions ❌ (primary)	1.9%	[0.5%, 7.5%]	19
Regressions ❌ (secondary)	6.6%	[0.4%, 12.9%]	5
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-2.8%	[-2.8%, -2.8%]	1
All ❌✅ (primary)	1.7%	[-1.3%, 7.5%]	20

Cycles

Results (secondary 2.7%)

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)	4.2%	[2.1%, 10.2%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-3.8%, -2.2%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, secondary -1.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.1%, 0.1%]	1
Regressions ❌ (secondary)	0.2%	[0.1%, 0.4%]	4
Improvements ✅ (primary)	-0.0%	[-0.0%, -0.0%]	3
Improvements ✅ (secondary)	-2.9%	[-6.8%, -0.0%]	3
All ❌✅ (primary)	0.0%	[-0.0%, 0.1%]	4

Bootstrap: 470.222s -> 472.094s (0.40%)
Artifact size: 377.51 MiB -> 377.42 MiB (-0.02%)

bors · 2025-08-23T06:22:24Z

☔ The latest upstream changes (presumably #145469) made this pull request unmergeable. Please resolve the merge conflicts.

rustbot · 2026-06-03T14:16:59Z

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.

cjgillot · 2026-06-03T16:16:21Z

@bors r=oli-obk

rust-bors · 2026-06-03T16:16:25Z

📌 Commit ac71b54 has been approved by oli-obk

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 5. This pull request will be tested once the tree is reopened.

rust-bors · 2026-06-04T02:28:39Z

☀️ Test successful - CI
Approved by: oli-obk
Duration: 3h 13m 59s
Pushing 76dfce2 to main...

github-actions · 2026-06-04T02:31:27Z

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 b354133 (parent) -> 76dfce2 (this PR)

Test differences

Show 12 test diffs

12 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 76dfce2cb2d3f7b7f34d62e6ffe044f7e7d76948 --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-apple-various: 1h 25m -> 2h 16m (+59.5%)
dist-x86_64-msvc-alt: 2h 50m -> 1h 40m (-41.1%)
x86_64-gnu-miri: 1h 11m -> 1h 38m (+37.3%)
x86_64-mingw-1: 2h 54m -> 1h 50m (-36.4%)
dist-armv7-linux: 1h 31m -> 59m 29s (-35.3%)
dist-aarch64-apple: 2h 12m -> 1h 26m (-34.3%)
x86_64-gnu-distcheck: 1h 51m -> 2h 26m (+30.8%)
x86_64-msvc-2: 2h 42m -> 1h 55m (-29.0%)
dist-loongarch64-musl: 1h 27m -> 1h 50m (+26.7%)
x86_64-msvc-1: 2h 1m -> 2h 30m (+24.6%)

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 · 2026-06-04T03:10:37Z

Finished benchmarking commit (76dfce2): comparison URL.

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

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)	0.5%	[0.1%, 1.1%]	51
Regressions ❌ (secondary)	1.5%	[0.1%, 9.9%]	43
Improvements ✅ (primary)	-0.5%	[-0.5%, -0.5%]	1
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.4%]	1
All ❌✅ (primary)	0.4%	[-0.5%, 1.1%]	52

Max RSS (memory usage)

Results (primary 1.2%, secondary -1.8%)

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

	mean	range	count
Regressions ❌ (primary)	1.6%	[0.7%, 2.8%]	13
Regressions ❌ (secondary)	2.8%	[2.8%, 2.8%]	1
Improvements ✅ (primary)	-1.0%	[-1.4%, -0.6%]	2
Improvements ✅ (secondary)	-2.9%	[-8.2%, -1.0%]	4
All ❌✅ (primary)	1.2%	[-1.4%, 2.8%]	15

Cycles

Results (secondary 1.9%)

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%	[2.1%, 6.6%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.6%, -2.2%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 511.076s -> 511.359s (0.06%)
Artifact size: 400.68 MiB -> 400.66 MiB (-0.01%)

lcnr · 2026-06-04T09:37:43Z

two thoughts, this feels related to the addition of TypingMode::ErasedNonCoherence, i.e. the trait solver mostly doesn't care which typingmode we're in between these two post-analysis modes, so we can probably extend this Erased behavior to also handle different codegen modes if perf requires it

the other one is that I am vaguely unhappy about adding new TypingMode. They have a fairly high complexity cost and I want to really stay on top of the ones we add.

I don't think this PR is necessarily wrong, I would like this to have gone through a types MCP or at least nomination.

nbdd0121 · 2026-06-05T15:25:43Z

+        // We are in codegen. It's very likely this constant has been evaluated in PostAnalysis
+        // before. Try to reuse this evaluation, and only re-run if we hit a `TooGeneric` error.
+        ty::TypingMode::Codegen => {
+            let with_postanalysis =
+                ty::TypingEnv::new(typing_env.param_env, ty::TypingMode::PostAnalysis);
+            let with_postanalysis = f(with_postanalysis.as_query_input(value));
+            match with_postanalysis {
+                Ok(_) | Err(ErrorHandled::Reported(..)) => return Some(with_postanalysis),
+                Err(ErrorHandled::TooGeneric(_)) => {}
+            }


I think the fact that this exists make me feel that this is not the right approach.

Perhaps we should just not use optimized_mir for coroutine layout computation? Coud we just run a fixed list of passes that does not require knowing layouts for coroutine layout computation?

View changes since the review

Upstream rustc changes [1] `fully_monomophized` to `TypingMode::Codegen` instead of `TypingMode::post_analysis`. This causes many queries to run multiple times and cause issues because these modes do not compare equal. Switch everything to use `TypingEnv::codegen` to still have a single typing env shared by all analysis. Link: rust-lang/rust#145477 [1] Signed-off-by: Gary Guo <gary@garyguo.net>

Introduce `TypingMode::Codegen` to avoid layout cycles on coroutines Computing layout of coroutines depends on their `optimized_mir`. At the same time, MIR opts can require using layouts to work. For instance to evaluate constants. This leads to cycles and clumsy workarounds. This PR creates a new typing mode for layout computations: - when a coroutine's layout is requested with `TypingMode::PostAnalysis` or earlier, return `LayourError::TooGeneric`; - when a coroutine's layout is requested with `TypingMode::Codegen`, actually compute it. `TypingMode::Codegen` is meant be be used by codegen code, and analyses that require coroutine layout, like transmute check and coroutine recursion check. With this PR, we can remove all `is_coroutine` checks from `rustc_mir_transform` and unlock simplifying coroutine MIR. Perf is not terrific. This PR causes recomputation of a few queries, and I had to insert workarounds.

frewsxcv · 2026-06-23T21:13:08Z

This fixed an ICE. See: #158328

danderson · 2026-06-23T21:32:02Z

Just to be a pessimist: it's possible my reproducer on that bug is just fragile, and this change incidentally makes that specific repro avoid the panic codepath. I defer to rustc experts though, I don't have anywhere near the knowledge of rustc internals to evaluate that.

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rust-bors Bot added a commit that referenced this pull request Aug 16, 2025

Auto merge of #145477 - cjgillot:codegen-mode, r=<try>

34dd67f

[EXPERIMENT] Introduce `TypingMode::Codegen` to avoid layout cycles

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Aug 16, 2025

cjgillot force-pushed the codegen-mode branch from a35a84a to 3f6e4db Compare August 16, 2025 14:30

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rust-bors Bot added a commit that referenced this pull request Aug 16, 2025

Auto merge of #145477 - cjgillot:codegen-mode, r=<try>

4e9488c

[EXPERIMENT] Introduce `TypingMode::Codegen` to avoid layout cycles

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 16, 2025

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cjgillot force-pushed the codegen-mode branch from 7bde1fe to bdb8bf2 Compare August 23, 2025 18:31

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rustbot added the perf-regression-triaged The performance regression has been triaged. label Jun 3, 2026

cjgillot added 5 commits June 3, 2026 14:11

Introduce TypingMode::Codegen.

ebaf329

Reuse result from eval_to_const_value_raw.

090d210

Reuse cached layout from PostAnalysis when possible.

dabbc7f

Do not compute coroutine layout in non-Codegen typing mode.

4b6f78d

Reduce TypingMode duplication.

ac71b54

cjgillot force-pushed the codegen-mode branch from 57ce693 to ac71b54 Compare June 3, 2026 14:16

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 3, 2026

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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 Jun 4, 2026

rust-bors Bot merged commit 76dfce2 into rust-lang:main Jun 4, 2026
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rustbot added this to the 1.98.0 milestone Jun 4, 2026

This was referenced Jun 4, 2026

Remove 'static requirement on try_as_dyn #150161

Open

Reduce verbosity of cycle errors when possible #157342

Merged

cjgillot deleted the codegen-mode branch June 4, 2026 08:07

nbdd0121 reviewed Jun 5, 2026

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danderson mentioned this pull request Jun 23, 2026

[ICE]: Found unstable fingerprints for evaluate_obligation(...): Ok(EvaluatedToOk) #158328

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Overall result: ❌ regressions - please read the text below

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Overall result: ❌ regressions - please read the text below

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Test differences

Job duration changes

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rust-timer commented Jun 4, 2026

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

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