Consider captured regions for opaque type region liveness. by jackh726 · Pull Request #156027 · rust-lang/rust

jackh726 · 2026-05-01T03:45:47Z

For opaques, when we're calculating liveness for opaques, we want to consider any captured lifetimes that can outlive the opaque type, which is more than just the outlives bounds.

r? lqd

lqd · 2026-05-01T12:25:07Z

Until I can look at this next week, @bors try @rust-timer queue

Consider captured regions for opaque type region liveness.

rust-bors · 2026-05-01T14:33:24Z

☀️ Try build successful (CI)
Build commit: 97f0332 (97f0332b563f5fd8ae70b57a13a7b23b27db3012, parent: 0469a92a76c327df972cb6c1356934b7a0c6b86d)

rust-timer · 2026-05-01T15:16:31Z

Finished benchmarking commit (97f0332): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary -2.3%)

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)	-	-	0
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Cycles

Results (secondary 2.0%)

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)	4.1%	[3.3%, 4.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.2%, secondary 0.2%)

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

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.1%, 0.4%]	33
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	24
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.1%, 0.4%]	33

Bootstrap: 481.713s -> 483.106s (0.29%)
Artifact size: 390.96 MiB -> 390.99 MiB (0.01%)

lqd

I also started down this direction so some of this makes sense to me. We stopped because it felt fragile and test coverage was, and still is, weak. So with that caveat this generally feels fine to me, but again, I don't know enough about this area to say what problems there could be.

This direction felt less nice than what lcnr described in the t-types meeting where we described the issue, so I'll defer to them.

View changes since this review

lqd · 2026-05-04T09:23:57Z

+    // Thinking about it, I was originally a bit concerned about something like `'a: 'static`, and
+    // whether or not we need to mark `'a` as live. I don't think *today* we do, since I think regions
+    // that outlive `'static` are special enough, but I *could* imagine some world where we need to be
+    // more careful about this. Given I can't find a test that goes wrong, I'm going to leave in this
+    // optimization.


I was also a bit worried, and we should expand test coverage here. I'm not confident enough in any of this to trust the two tests we have.

lqd · 2026-05-04T10:00:10Z

+    // Unfortunately, we have to use a new `InferCtxt` each call, because
+    // region constraints get added and solved there and we need to test each
+    // call individually.


This is also unfortunate, combined with the fact that it's being called a quadratic number of times (thankfully the N should be small in most cases).

jackh726 · 2026-06-03T11:28:36Z

@bors try

Consider captured regions for opaque type region liveness.

rust-bors · 2026-06-03T13:40:17Z

☀️ Try build successful (CI)
Build commit: 8e819ff (8e819ff5434466e9a823e03871a1775ac7d84ddf, parent: 53509ca37e3b507887607c2f4a7f23bd4838f099)

jackh726 · 2026-06-03T15:05:15Z

@craterbot check

craterbot · 2026-06-03T15:05:39Z

👌 Experiment pr-156027 created and queued.
🤖 Automatically detected try build 8e819ff
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

jackh726 · 2026-06-04T14:21:35Z

@craterbot p=2

We want to get this in so that we can do a nightly preview of Polonius

craterbot · 2026-06-04T14:21:37Z

📝 Configuration of the pr-156027 experiment changed.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-06-05T06:57:03Z

🚧 Experiment pr-156027 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

craterbot · 2026-06-07T15:33:26Z

🎉 Experiment pr-156027 is completed!
📊 65 regressed and 1 fixed (964870 total)
📊 5391 spurious results on the retry-regressed-list.txt, consider a retry¹ if this is a significant amount.
📰 Open the summary report.

⚠️ If you notice any spurious failure please add them to the denylist!
ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

re-run the experiment with crates=https://crater-reports.s3.amazonaws.com/pr-156027/retry-regressed-list.txt ↩

lcnr

I still feel unresolved wrt the why of this change, which makes reviewing the concrete behavior kind of unpleasant. gonna spend some time looking at the non-polonius thing this allows us to fix?

View changes since this review

lcnr · 2026-07-03T14:59:33Z

+    ///     (and so is `T`, since `T: 'static` implies `T: 'a`)
+    ///   - `bar` outlives `'static`, so we know that no args are potentially live and we can return an empty set
+    ///   - `baz` has no outlives bound, so return `None` and let the caller decide what to do
+    query live_args_for_alias_from_outlives_bounds(kind: ty::AliasTyKind<'tcx>) -> &'tcx Option<ty::EarlyBinder<'tcx, Vec<ty::GenericArg<'tcx>>>> {


There should no difference between AliasTyKind and DefId wrt what information they give you. Both are just a DefId, where AliasTyKind also has some information about DefKind in there.

Reconstructing an AliasTy from a DefId is intentionally vaguely annoying 🤔 even though I'd expect that the query system is significantly better at dealing with raw DefIds I guess it's whatever whether to use AliasTy or DefId here

lcnr · 2026-07-03T15:12:15Z

+    let parent_param_env = tcx.param_env(parent_def_id);
+    tracing::debug!(?parent_param_env);
+
+    // Map the outlives regions to the parent regions


I mean concretely for this loop 🤔 this is a lot of nothing which feels unrelated to the actual semantics of this function?

Like, we take self_identity_args and give back a parent_outlives_regions. I do not understand why this is necessary or what exactly it even does. What does parent_outlives_regions represent, why do we need to do this etc?

…arams, use tcx.assumed_wf_types, and test polonius_alpha in gat-outlives-implied test

lqd · 2026-07-09T15:54:19Z

I am still left feeling unclear why polonius cares about liveness the way it does

NLLs introduced liveness to allow invalidations on dead loans, and its regions are sets of CFG points. The points where the regions are live, the regions they outlive (in a flow-insensitive manner) and vice-versa, and so on are used to compute the CFG points that represent regions. A loan is considered live at a point if the region where it was introduced contains this point (modulo kills, unimportant here).

To support flow-sensitivity, polonius regions are sets of loans, and loan liveness needs to track the outlives relationships between regions more precisely: a loan is considered live if it is contained in a live region. Polonius thus needs the accurate liveness of regions to check if an invalidation is indeed an error. As an NLL superset, if a loan is contained in a dead region and is invalidated, polonius will accept that as well. If the region is unexpectedly dead like in the #153215 examples, this is of course a soundness issue, and this PR fixes the current inaccuracy in liveness for some regions related to aliases.

The approach makes sense to me, and we've talked about it with jack and niko, and despite the complexity I think this is an improvement we need. There may be ways to simplify in the near future, a part of it is caused by the mapping and our current encoding of opaque types, etc. lcnr has told jack that we can land this if I'm also happy with it, and I am. It does get us closer to enabling polonius alpha on nightly.

If there are more improvements to do after this handful of review rounds, I think it's fine to do them in follow-ups.

Let's do this 🚀, @bors r+

rust-bors · 2026-07-09T15:54:22Z

📌 Commit 055af58 has been approved by lqd

It is now in the queue for this repository.

Consider captured regions for opaque type region liveness. Fixes rust-lang#153215 For opaques, when we're calculating liveness for opaques, we want to consider any captured lifetimes that can outlive the opaque type, which is more than just the outlives bounds. r? lqd

…uwer Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158510 (Enable `static_position_independent_executables` on all gnu and musl targets) - #158541 (Move `std::io::Write` to `core::io`) - #158899 (Fix `unaligned_volatile_store` by removing `MemFlags::UNALIGNED`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes)

Consider captured regions for opaque type region liveness. Fixes rust-lang#153215 For opaques, when we're calculating liveness for opaques, we want to consider any captured lifetimes that can outlive the opaque type, which is more than just the outlives bounds. r? lqd

Rollup of 24 pull requests Successful merges: - #150946 (intrinsics: Add a fallback for non-const libm float functions) - #158541 (Move `std::io::Write` to `core::io`) - #156027 (Consider captured regions for opaque type region liveness.) - #156370 (Reject linked dylib EII default overrides) - #156508 (Infer all anonymous lifetimes in assoc consts as `'static`) - #157561 (rustdoc: do not include extra stuff in span) - #158617 (allow mGCA const arguments to fall back to anon consts) - #158645 (Fix splat ICEs and ban it in closures) - #158859 (Improve `-Zls` diagnostic message on `.rs` files) - #158988 (Redo `TokenStreamIter`) - #158347 (Improve generic parameters handling for #[diagnostic::on_const]) - #158384 (Allow BackwardIncompatibleDropHint in polonius legacy) - #158722 (delegation: do not always inherit `ConstArgHasType` predicates) - #158739 (view-types: HIR lowering) - #158877 (borrowck: Keep returned `path` from `best_blame_constraint()` consistent) - #158883 (tests: fix enum-match.rs to handle LLVM 23) - #158886 (Add documentation for the `no_std` attribute) - #158940 (Implement feature `char_to_u32`) - #158951 (Merge three `MaxUniverse`s into one) - #158960 (Fix bootstrap submodule path prefix matching) - #158961 (Reapply "LLVM 23: Run AssignGUIDPass in some places") - #158995 (Use REST API in linkchecker script) - #158996 ([compiler] Implement `PartialOrd` via `Ord` for `Span` and newtype_indexes) - #159036 (bootstrap: expand '@argfile' arguments to rustc shim)

Rollup merge of #156027 - jackh726:opaque-liveness, r=lqd Consider captured regions for opaque type region liveness. Fixes #153215 For opaques, when we're calculating liveness for opaques, we want to consider any captured lifetimes that can outlive the opaque type, which is more than just the outlives bounds. r? lqd

JonathanBrouwer · 2026-07-10T12:56:44Z

@rust-timer build 9b082ed

rust-timer · 2026-07-10T13:37:33Z

Finished benchmarking commit (9b082ed): 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)	0.4%	[0.3%, 0.4%]	2
Regressions ❌ (secondary)	0.1%	[0.0%, 0.2%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	3
All ❌✅ (primary)	0.4%	[0.3%, 0.4%]	2

Max RSS (memory usage)

Results (primary -1.3%, 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)	4.0%	[0.7%, 8.8%]	5
Improvements ✅ (primary)	-1.3%	[-3.5%, -0.7%]	6
Improvements ✅ (secondary)	-3.6%	[-7.8%, -1.2%]	6
All ❌✅ (primary)	-1.3%	[-3.5%, -0.7%]	6

Cycles

Results (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
Regressions ❌ (secondary)	4.0%	[2.0%, 9.1%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.8%	[-9.4%, -1.8%]	7
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.2%, secondary 0.2%)

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

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.0%, 0.8%]	75
Regressions ❌ (secondary)	0.2%	[0.0%, 0.8%]	47
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.0%, 0.8%]	75

Bootstrap: 490.768s -> 490.144s (-0.13%)
Artifact size: 389.74 MiB -> 389.16 MiB (-0.15%)

JonathanBrouwer · 2026-07-10T13:40:17Z

@rustbot label: +perf-regression-triaged
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Auto merge of #156027 - jackh726:opaque-liveness, r=<try>

97f0332

Consider captured regions for opaque type region liveness.

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Auto merge of #156027 - jackh726:opaque-liveness, r=<try>

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Consider captured regions for opaque type region liveness.

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Stabilize and model Polonius Alpha rust-lang/rust-project-goals#118

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Rename variable and add comment

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jackh726 added 2 commits July 9, 2026 00:01

A couple minor things: rename args_known_to_outlive_associated_type_p…

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…arams, use tcx.assumed_wf_types, and test polonius_alpha in gat-outlives-implied test

Remove compile-fail

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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-review Status: Awaiting review from the assignee but also interested parties. labels Jul 9, 2026

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Rollup of 24 pull requests #159037

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Rollup of 25 pull requests #159045

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Rollup of 24 pull requests #159046

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