remove more trivial regions in evaluate_added_goals_and_make_canonical_response by sjwang05 · Pull Request #162032 · rust-lang/rust

sjwang05 · 2026-08-30T23:06:33Z

cc #161575. I don't think it fixes the issue per se, since the most principled fix would be to just deny unconstrained lifetime args like we do for types and consts already. At the very least, though, it Makes Things Go Faster.

In the example from #161575 (comment), each 'unconstrained appears only once in the entire response: in the rhs of the 'a: 'unconstrained#N bound. Since they are mentioned nowhere else and are created only when proving our own nested goals, these outlives constraints are all satisfiable by setting 'unconstrained := 'empty, which tells us nothing about 'a. Therefore, (I think) that makes it safe to treat all of these constraints as trivial and drop them entirely, drop all of these requirements entirely, similar to what we already do with reflexive or duplicate region constraints. In other words, if a ReVar appears only once in the entire response, and that place is the rhs of an outlives constraint, then it is safe to drop that constraint.

I'm a little worried about the perf impact of the visitor on "normal" code, but fwiw even a 100-deep nested version of the reproducer compiles in about 0.05s on my machine.

r? lcnr

sjwang05 · 2026-08-30T23:13:02Z

Fun fact: the number of outlives constraints grows exactly as fib(2 * depth) :D

ShoyuVanilla · 2026-08-31T06:03:31Z

@bors try @rust-timer queue

remove more trivial regions in evaluate_added_goals_and_make_canonical_response

rust-bors · 2026-08-31T07:03:23Z

☀️ Try build successful (CI)
Build commit: 0be4976 (0be497690edf5f58dfd2a6cfff82660c9c75ffa6)
Base parent: 5321a4f (5321a4f40c957cf3587c055e77461febc2ebc865)

rust-timer · 2026-08-31T09:16:13Z

Finished benchmarking commit (0be4976): 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)

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

Cycles

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

Binary size

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

Bootstrap: missing data
Artifact size: 402.71 MiB -> 402.86 MiB (0.04%)

Kobzol · 2026-08-31T09:33:56Z

(Sorry, a rustc-perf failure, looking into it)

ShoyuVanilla · 2026-08-31T09:46:20Z

Would rerunning with the same artifact make sense?

Kobzol · 2026-08-31T09:47:14Z

Yup, I deleted the result from the DB, and will rerun the artifact for you (once the underlying bug is fixed and deployed, which should happen in ~20 minutes).

ShoyuVanilla · 2026-08-31T09:49:37Z

Yup, I deleted the result from the DB, and will rerun the artifact for you (once the underlying bug is fixed and deployed, which should happen in ~20 minutes).

Huge thanks! 😄

Kobzol · 2026-08-31T10:10:18Z

@rust-timer build 0be4976

rust-timer · 2026-08-31T10:54:10Z

Finished benchmarking commit (0be4976): 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 -1.8%, 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)	-	-	0
Improvements ✅ (primary)	-1.8%	[-2.2%, -1.1%]	3
Improvements ✅ (secondary)	-2.6%	[-3.6%, -1.2%]	4
All ❌✅ (primary)	-1.8%	[-2.2%, -1.1%]	3

Cycles

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

Binary size

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

Bootstrap: 477.635s -> 477.178s (-0.10%)
Artifact size: 402.71 MiB -> 402.86 MiB (0.04%)

…ke_canonical_response

ShoyuVanilla · 2026-09-06T05:15:46Z

@bors try @rust-timer queue

remove more trivial regions in evaluate_added_goals_and_make_canonical_response

rust-bors · 2026-09-06T06:15:07Z

☀️ Try build successful (CI)
Build commit: 1ca580b (1ca580bb8c7d10c1e90e3221f9f7ab80d8fdd70c)
Base parent: f248f40 (f248f4038796913873f11ca65b1b901e311c8dae)

rust-timer · 2026-09-06T07:03:08Z

Finished benchmarking commit (1ca580b): 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 -4.0%, secondary 7.0%)

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)	7.0%	[7.0%, 7.0%]	1
Improvements ✅ (primary)	-4.0%	[-4.0%, -4.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-4.0%	[-4.0%, -4.0%]	1

Cycles

Results (primary 3.4%)

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

	mean	range	count
Regressions ❌ (primary)	3.4%	[3.4%, 3.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.4%	[3.4%, 3.4%]	1

Binary size

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

Bootstrap: 476.686s -> 484.632s (1.67%)
Artifact size: 403.40 MiB -> 403.41 MiB (0.00%)

ShoyuVanilla

Though there's no noticable change in perf, I think having less trivial bounds in the query output is generally good and the other points stated in the PR description make sense.

@bors r+

View changes since this review

rust-bors · 2026-09-06T07:10:11Z

📌 Commit e9ab50c has been approved by ShoyuVanilla

It is now in the queue for this repository.

rust-bors · 2026-09-06T08:51:32Z

⌛ Testing commit e9ab50c with merge 633abdc...

Workflow: https://github.com/rust-lang/rust/actions/runs/34023044567

remove more trivial regions in evaluate_added_goals_and_make_canonical_response cc #161575. I don't think it *fixes* the issue per se, since the most principled fix would be to just deny unconstrained lifetime args like we do for types and consts already. At the very least, though, it Makes Things Go Faster. In the example from #161575 (comment), each `'unconstrained` appears only once in the entire response: in the rhs of the `'a: 'unconstrained#N` bound. Since they are mentioned nowhere else and are created only when proving our own nested goals, these outlives constraints are all satisfiable by setting `'unconstrained := 'empty`, which tells us nothing about `'a`. Therefore, (I think) that makes it safe to treat all of these constraints as trivial and drop them entirely, drop all of these requirements entirely, similar to what we already do with reflexive or duplicate region constraints. In other words, if a `ReVar` appears only once in the entire response, and that place is the rhs of an outlives constraint, then it is safe to drop that constraint. I'm a little worried about the perf impact of the visitor on "normal" code, but fwiw even a 100-deep nested version of the reproducer compiles in about 0.05s on my machine. r? lcnr

JonathanBrouwer · 2026-09-06T09:20:54Z

@bors yield
Yielding to enclosing rollup

rust-bors · 2026-09-06T09:20:57Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/34023044567

The next pull request likely to be tested is #162362.

…uwer Rollup of 4 pull requests Successful merges: - #162032 (remove more trivial regions in evaluate_added_goals_and_make_canonical_response) - #161607 (Add #[track_caller] to signed integer div/rem methods) - #162339 (Revert "bootstrap: Enable rustdoc mergeable CCI for std and internal docs #161716") - #162158 (Revise documentation of `NumBuffer` and `format_into()`.)

Rollup merge of #162032 - sjwang05:more-region-dedup, r=ShoyuVanilla remove more trivial regions in evaluate_added_goals_and_make_canonical_response cc #161575. I don't think it *fixes* the issue per se, since the most principled fix would be to just deny unconstrained lifetime args like we do for types and consts already. At the very least, though, it Makes Things Go Faster. In the example from #161575 (comment), each `'unconstrained` appears only once in the entire response: in the rhs of the `'a: 'unconstrained#N` bound. Since they are mentioned nowhere else and are created only when proving our own nested goals, these outlives constraints are all satisfiable by setting `'unconstrained := 'empty`, which tells us nothing about `'a`. Therefore, (I think) that makes it safe to treat all of these constraints as trivial and drop them entirely, drop all of these requirements entirely, similar to what we already do with reflexive or duplicate region constraints. In other words, if a `ReVar` appears only once in the entire response, and that place is the rhs of an outlives constraint, then it is safe to drop that constraint. I'm a little worried about the perf impact of the visitor on "normal" code, but fwiw even a 100-deep nested version of the reproducer compiles in about 0.05s on my machine. r? lcnr

rustbot assigned lcnr Aug 30, 2026

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 Aug 30, 2026

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sjwang05 force-pushed the more-region-dedup branch from 0125479 to bc71d10 Compare August 31, 2026 00:16

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Auto merge of #162032 - sjwang05:more-region-dedup, r=<try>

0be4976

remove more trivial regions in evaluate_added_goals_and_make_canonical_response

ShoyuVanilla reviewed Aug 31, 2026

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Comment thread compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs Outdated

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sjwang05 force-pushed the more-region-dedup branch from bc71d10 to 33ac2c4 Compare August 31, 2026 21:27

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sjwang05 force-pushed the more-region-dedup branch from 33ac2c4 to 3278ea3 Compare September 1, 2026 03:29

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Comment thread compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

Comment thread compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs Outdated

treat more kinds of regions as trivial in evaluate_added_goals_and_ma…

e9ab50c

…ke_canonical_response

sjwang05 force-pushed the more-region-dedup branch from 3278ea3 to e9ab50c Compare September 6, 2026 04:49

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rust-bors Bot pushed a commit that referenced this pull request Sep 6, 2026

Auto merge of #162032 - sjwang05:more-region-dedup, r=<try>

1ca580b

remove more trivial regions in evaluate_added_goals_and_make_canonical_response

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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 Sep 6, 2026

JonathanBrouwer mentioned this pull request Sep 6, 2026

Rollup of 4 pull requests #162362

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rust-bors Bot merged commit 45d62b0 into rust-lang:main Sep 6, 2026
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