Properly stall coroutine witnesses in new solver #138845

compiler-errors · 2025-03-22T23:57:55Z

TODO: write description

r? lcnr

rustbot · 2025-03-22T23:58:00Z

Some changes occurred to the core trait solver

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

changes to inspect_obligations.rs

cc @compiler-errors, @lcnr

compiler/rustc_type_ir/src/infer_ctxt.rs

compiler/rustc_trait_selection/src/traits/fulfill.rs

compiler/rustc_trait_selection/src/solve/normalize.rs

compiler-errors · 2025-03-23T00:03:22Z

compiler/rustc_trait_selection/src/solve/normalize.rs

+/// entered before passing `value` to the function. This is currently needed for
+/// `normalize_erasing_regions`, which skips binders as it walks through a type.
+///
+/// TODO: doc


I need to explain that this doesn't return all ambiguous preds, just the ones that are stalled on coroutines.

compiler/rustc_trait_selection/src/solve/fulfill.rs

compiler/rustc_next_trait_solver/src/solve/trait_goals.rs

compiler/rustc_middle/src/query/plumbing.rs

compiler/rustc_hir_typeck/src/writeback.rs

Tweaks to writeback and `Obligation -> Goal` conversion Each of these commits are self-contained, but are prerequisites that I'd like to land before rust-lang#138845, which still needs some cleaning. The ""most controversial"" one is probably [Explicitly don't fold coroutine obligations in writeback](rust-lang@e7d27ba), which I prefer because I think using `fold_predicate` to control against not normalizing predicates seems... easy to mess up 🤔, and we could have *other things* that we don't want to normalize. Explicitly noting whether we want `resolve` to normalize is a lot clearer (and currently in writeback is limited to resolving stalled coroutine obligations), since we can attach it to a comment that explains *why*.

Rollup merge of rust-lang#138846 - compiler-errors:stall-prereqs, r=lcnr Tweaks to writeback and `Obligation -> Goal` conversion Each of these commits are self-contained, but are prerequisites that I'd like to land before rust-lang#138845, which still needs some cleaning. The ""most controversial"" one is probably [Explicitly don't fold coroutine obligations in writeback](rust-lang@e7d27ba), which I prefer because I think using `fold_predicate` to control against not normalizing predicates seems... easy to mess up 🤔, and we could have *other things* that we don't want to normalize. Explicitly noting whether we want `resolve` to normalize is a lot clearer (and currently in writeback is limited to resolving stalled coroutine obligations), since we can attach it to a comment that explains *why*.

bors · 2025-03-24T05:08:29Z

☔ The latest upstream changes (presumably #138873) made this pull request unmergeable. Please resolve the merge conflicts.

compiler/rustc_trait_selection/src/solve/fulfill.rs

lcnr · 2025-03-24T10:14:16Z

compiler/rustc_trait_selection/src/solve/fulfill.rs

+    fn visit_goal(&mut self, inspect_goal: &super::inspect::InspectGoal<'_, 'tcx>) -> Self::Result {
+        inspect_goal.goal().predicate.visit_with(self)?;
+
+        if let Some(candidate) = inspect_goal.unique_applicable_candidate() {


this type visitor feels somewhat fragile and I expect unique_applicable_candidate and the limited recursion depth to cause us to fail to stall obligations in very rare cases. otoh I don't think this is a problem though

so my understanding here is:

for correctness it doesn't matter how many obligations we stall

for diagnostics (and perf) we want to stall as few obligations as possible

failing to stall causes unexpected ambiguity errors

Please add this as a comment somewhere, prolly the stalled_coroutine_obligations field of the typeck results

Yep, that's my understanding. We could perhaps stall obligations if we find coroutines in the predicate or if we hit the recursion limit, but idk if we have a facility to detect when we hit the recursion limit here. Shouldn't be too hard to fix, but I'd rather leave that to when we need it.

compiler-errors · 2025-03-25T16:49:27Z

Let's see how bad the perf is from making items larger.

@bors try @rust-timer queue

compiler-errors · 2025-03-25T16:50:47Z

@bors try @rust-timer queue

…<try> Properly stall coroutine witnesses in new solver TODO: write description r? lcnr

bors · 2025-03-25T16:52:00Z

⌛ Trying commit b6f1961 with merge 5443aaa...

bors · 2025-03-25T18:59:20Z

☀️ Try build successful - checks-actions
Build commit: 5443aaa (5443aaa4127ecdfcad1a50e7d7f2e4650bb52877)

rust-timer · 2025-03-25T20:21:23Z

Finished benchmarking commit (5443aaa): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.1%, 0.5%]	71
Regressions ❌ (secondary)	0.3%	[0.1%, 0.5%]	38
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.1%, 0.5%]	71

Max RSS (memory usage)

Results (primary 1.2%, secondary -1.8%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.5%	[0.5%, 3.9%]	18
Regressions ❌ (secondary)	2.5%	[1.0%, 3.9%]	3
Improvements ✅ (primary)	-1.6%	[-2.5%, -0.7%]	2
Improvements ✅ (secondary)	-3.7%	[-6.8%, -0.9%]	7
All ❌✅ (primary)	1.2%	[-2.5%, 3.9%]	20

Cycles

Results (secondary -1.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-4.5%, -1.0%]	2
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 777.999s -> 780.062s (0.27%)
Artifact size: 365.81 MiB -> 365.88 MiB (0.02%)

compiler-errors · 2025-03-25T22:15:23Z

Let me try putting coroutines into the same list as the opaques 🤔

lcnr · 2025-03-25T22:30:09Z

alternatively, intern TypingEnv itself. We should only very rarely access its value and it's already 2 ptrs wide

bors · 2025-04-22T17:22:11Z

💔 Test failed - checks-actions

compiler-errors · 2025-04-22T17:51:07Z

@bors try @rust-timer queue

…<try> Properly stall coroutine witnesses in new solver TODO: write description r? lcnr

bors · 2025-04-22T17:52:18Z

⌛ Trying commit ec741c3 with merge 637680b...

compiler-errors · 2025-04-22T18:36:34Z

@bors try @rust-timer queue

…<try> Properly stall coroutine witnesses in new solver TODO: write description r? lcnr

bors · 2025-04-22T18:37:45Z

⌛ Trying commit b153a5c with merge c8c6c9843459bf86142c2f876549f36d561823dd...

bors · 2025-04-22T20:44:06Z

☀️ Try build successful - checks-actions
Build commit: c8c6c98 (c8c6c9843459bf86142c2f876549f36d561823dd)

rust-timer · 2025-04-22T22:10:18Z

Finished benchmarking commit (c8c6c98): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.1%, 0.5%]	48
Regressions ❌ (secondary)	0.3%	[0.1%, 0.5%]	32
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.0%	[-1.0%, -1.0%]	1
All ❌✅ (primary)	0.3%	[0.1%, 0.5%]	48

Max RSS (memory usage)

Results (primary 0.8%, secondary -2.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.6%, 1.8%]	10
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	2
Improvements ✅ (secondary)	-2.1%	[-2.2%, -2.0%]	5
All ❌✅ (primary)	0.8%	[-0.9%, 1.8%]	12

Cycles

Results (secondary 2.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 774.196s -> 776.919s (0.35%)
Artifact size: 365.08 MiB -> 365.28 MiB (0.06%)

compiler-errors · 2025-04-22T23:32:18Z

@bors try @rust-timer queue

bors · 2025-04-22T23:33:28Z

⌛ Trying commit 7ad9c9d with merge 7984f3d...

…<try> Properly stall coroutine witnesses in new solver TODO: write description r? lcnr

bors · 2025-04-23T01:38:16Z

☀️ Try build successful - checks-actions
Build commit: 7984f3d (7984f3d67d3a114e7af02ace3d8a24d9fca54df5)

rust-timer · 2025-04-23T04:05:48Z

Finished benchmarking commit (7984f3d): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.1%, 0.1%]	3
Regressions ❌ (secondary)	0.2%	[0.1%, 0.2%]	10
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.1%, 0.1%]	3

Max RSS (memory usage)

Results (primary -0.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-0.9%, -0.4%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.9%, 0.8%]	3

Cycles

Results (secondary 0.8%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.8%	[0.8%, 0.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 774.196s -> 774.363s (0.02%)
Artifact size: 365.08 MiB -> 365.20 MiB (0.03%)

rustbot assigned lcnr Mar 22, 2025

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. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Mar 22, 2025

compiler-errors mentioned this pull request Mar 22, 2025

Tweaks to writeback and Obligation -> Goal conversion #138846

Merged

compiler-errors commented Mar 23, 2025

View reviewed changes

compiler/rustc_type_ir/src/infer_ctxt.rs Outdated Show resolved Hide resolved

compiler-errors commented Mar 23, 2025

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