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.

cjgillot · 2026-05-03T22:23:45Z

@bors try @rust-timer queue

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

rust-bors · 2026-05-04T00:33:51Z

☀️ Try build successful (CI)
Build commit: 7bf3ad1 (7bf3ad14920af19fbbbe356a5ebb7be3d73010d4, parent: ad3a598ca4bc7c68bcbbce3e0d3be9a7618df190)

rust-timer · 2026-05-04T01:57:30Z

Finished benchmarking commit (7bf3ad1): 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%	[0.2%, 1.2%]	75
Regressions ❌ (secondary)	1.2%	[0.2%, 9.8%]	81
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	1
Improvements ✅ (secondary)	-0.4%	[-0.7%, -0.3%]	7
All ❌✅ (primary)	0.5%	[-0.1%, 1.2%]	76

Max RSS (memory usage)

Results (primary 1.6%, secondary 1.5%)

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%, 4.3%]	12
Regressions ❌ (secondary)	2.6%	[0.4%, 6.7%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.4%	[-1.6%, -1.1%]	2
All ❌✅ (primary)	1.6%	[0.7%, 4.3%]	12

Cycles

Results (primary -3.0%, secondary 2.6%)

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)	3.0%	[0.5%, 8.9%]	18
Improvements ✅ (primary)	-3.0%	[-3.5%, -2.5%]	2
Improvements ✅ (secondary)	-0.6%	[-0.7%, -0.5%]	2
All ❌✅ (primary)	-3.0%	[-3.5%, -2.5%]	2

Binary size

Results (primary 0.3%, secondary -0.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	0.4%	[0.3%, 0.5%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.9%	[-7.3%, -0.1%]	4
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	1

Bootstrap: 495.343s -> 498.406s (0.62%)
Artifact size: 394.42 MiB -> 395.17 MiB (0.19%)

rustbot · 2026-05-24T09:46:57Z

The Clippy subtree was changed

cc @rust-lang/clippy

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred in match checking

cc @Nadrieril

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred to the core trait solver

cc @rust-lang/initiative-trait-system-refactor

rustbot · 2026-05-24T09:46:59Z

r? @oli-obk

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RalfJung · 2026-05-24T10:02:45Z

+    match key.typing_env.typing_mode().assert_not_erased() {
+        ty::TypingMode::PostAnalysis => {}
+        // 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.


Is it reasonably practical to not have to repeat this logic twice?

View changes since the review