New solver opts for `diesel` by nnethercote · Pull Request #163981 · rust-lang/rust

nnethercote · 2026-10-08T10:27:23Z

A collection of small optimizations. Details in individual commits.

Local measurements:

solver         icounts (B)
------         -----------
old            37.9
new (orig)     56.4 (1.49x)
new (this PR)  49.5 (1.31x)

Also some small improvements on a range of other benchmarks.

r? @jdonszelmann

nnethercote · 2026-10-08T10:27:39Z

@bors try @rust-timer queue

New solver opts for `diesel`

rust-bors · 2026-10-08T11:27:00Z

☀️ Try build successful (CI)
Build commit: 72d027b (72d027b9aaffb1bdcbbb7a99d0fa20cbfe294b2c)
Base parent: fc2324d (fc2324d0546aa6782c45b76247266a0c37db0b8a)

rust-timer · 2026-10-08T12:12:50Z

Finished benchmarking commit (72d027b): 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 rustc-perf
@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%, 0.6%]	6
Regressions ❌ (secondary)	0.3%	[0.1%, 0.4%]	3
Improvements ✅ (primary)	-0.2%	[-0.5%, -0.1%]	9
Improvements ✅ (secondary)	-1.1%	[-11.1%, -0.1%]	55
All ❌✅ (primary)	0.0%	[-0.5%, 0.6%]	15

Max RSS (memory usage)

Results (primary -2.7%, 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)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	5.1%	[2.3%, 7.0%]	3
Improvements ✅ (primary)	-6.1%	[-6.1%, -6.1%]	1
Improvements ✅ (secondary)	-4.9%	[-4.9%, -4.9%]	1
All ❌✅ (primary)	-2.7%	[-6.1%, 0.7%]	2

Cycles

Results (primary 2.4%, 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)	2.4%	[2.1%, 2.6%]	2
Regressions ❌ (secondary)	3.9%	[2.5%, 7.5%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.2%	[-7.1%, -5.7%]	4
All ❌✅ (primary)	2.4%	[2.1%, 2.6%]	2

Binary size

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

Bootstrap: 484.956s -> 485.101s (0.03%)
Artifact size: 406.45 MiB -> 406.59 MiB (0.03%)

nnethercote · 2026-10-08T20:13:40Z

LLM disclosure: some of these changes were based on ideas from LLM analysis of profiles. I wrote the code and text myself.

rustbot · 2026-10-08T20:14:12Z

jdonszelmann is currently at their maximum review capacity.
They may take a while to respond.

nnethercote · 2026-10-08T20:17:20Z

The perf results show big wins for diesel and smaller wins for some other benchmarks, including some new solver ones. There are very small regressions on helloworld and a couple of other very short-running benchmarks due to preinterning more values at startup. I already tweaked the amount of interning to get a good balance here; I think a tiny bit of red is worth it for the additional green on the new solver benchmarks.

The rust-analyzer impls of these methods will need to be removed on the next sync.

It's faster than `extend` to initialize these structures.

A lot of work can be skipped if the two values being related are equal. (There are various early-return equality checks like this further down the call chain, this just adds one earlier.)

The former has an early return check and a single call site, so the check can be moved before the call site. Also, in the `Err(NoSolution)` case we can skip the `CandidateHeadUsages::default()` stuff because that's just an empty list and `merge_usages` is a no-op.

Instead of getting it within `fast_reject_assumption`. `fast_reject_assumption` has three call sites. For two of them this change doesn't help perf, but the third call occurs in a loop, and this lets us get the goal lang item once per loop instead of once per loop element.

- Increase the number of preinterned type vars and anon bound types. - Preintern some root-universe placeholder types with anon bounds. - Adjust some comments. - Also rename a lot of the preinterning names for more consistency.

rustbot · 2026-10-11T21:14:16Z

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.

nnethercote · 2026-10-11T21:14:43Z

I rebased. @jdonszelmann, this should be good to go.

jdonszelmann

Looking good! Sorry, took the week off. @bors r+ rollup

View changes since this review

rust-bors · 2026-10-12T06:12:24Z

📌 Commit d1998c0 has been approved by jdonszelmann

It is now in the queue for this repository.

@jdonszelmann

…zelmann New solver opts for `diesel` A collection of small optimizations. Details in individual commits. Local measurements: ``` solver icounts (B) ------ ----------- old 37.9 new (orig) 56.4 (1.49x) new (this PR) 49.5 (1.31x) ``` Also some small improvements on a range of other benchmarks. r? @jdonszelmann

rust-bors · 2026-10-12T07:19:11Z

⌛ Testing commit d1998c0 with merge 592e3a1...

Workflow: https://github.com/rust-lang/rust/actions/runs/38217070561

@jdonszelmann

New solver opts for `diesel` A collection of small optimizations. Details in individual commits. Local measurements: ``` solver icounts (B) ------ ----------- old 37.9 new (orig) 56.4 (1.49x) new (this PR) 49.5 (1.31x) ``` Also some small improvements on a range of other benchmarks. r? @jdonszelmann

jhpratt · 2026-10-12T07:22:55Z

@bors yield to rollup

rust-bors · 2026-10-12T07:22:58Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/38217070561

The next pull request likely to be tested is #164193.

Rollup of 5 pull requests Successful merges: - #163981 (New solver opts for `diesel`) - #164088 (const-check: clarify when and how we can rely on non-UB assumptions) - #164105 (Remove unnecessary indirection around `hir::ConstArg`) - #164181 (Tweak output on unused/unaccessible local macro) - #164186 (Update actions/upload-artifact action to v7.0.2)

rust-bors · 2026-10-12T07:48:55Z

⌛ Testing commit d1998c0 with merge 23d41dc...

Workflow: https://github.com/rust-lang/rust/actions/runs/38219857701

@jdonszelmann

New solver opts for `diesel` A collection of small optimizations. Details in individual commits. Local measurements: ``` solver icounts (B) ------ ----------- old 37.9 new (orig) 56.4 (1.49x) new (this PR) 49.5 (1.31x) ``` Also some small improvements on a range of other benchmarks. r? @jdonszelmann

jhpratt · 2026-10-12T07:50:42Z

@bors yield (spurious)

rust-bors · 2026-10-12T07:50:46Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/38219857701

The next pull request likely to be tested is #164193.

Rollup of 5 pull requests Successful merges: - #163981 (New solver opts for `diesel`) - #164088 (const-check: clarify when and how we can rely on non-UB assumptions) - #164105 (Remove unnecessary indirection around `hir::ConstArg`) - #164181 (Tweak output on unused/unaccessible local macro) - #164186 (Update actions/upload-artifact action to v7.0.2)

@jdonszelmann

Rollup merge of #163981 - nnethercote:diesel-opts-1, r=jdonszelmann New solver opts for `diesel` A collection of small optimizations. Details in individual commits. Local measurements: ``` solver icounts (B) ------ ----------- old 37.9 new (orig) 56.4 (1.49x) new (this PR) 49.5 (1.31x) ``` Also some small improvements on a range of other benchmarks. r? @jdonszelmann

rust-timer · 2026-10-12T12:21:02Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (bc8e72c): 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)	0.3%	[0.2%, 0.6%]	4
Regressions ❌ (secondary)	0.3%	[0.1%, 0.7%]	7
Improvements ✅ (primary)	-0.2%	[-0.5%, -0.1%]	7
Improvements ✅ (secondary)	-1.5%	[-11.1%, -0.1%]	36
All ❌✅ (primary)	-0.0%	[-0.5%, 0.6%]	11

Max RSS (memory usage)

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

Cycles

Results (secondary -4.0%)

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)	3.7%	[3.7%, 3.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.6%	[-6.8%, -6.4%]	3
All ❌✅ (primary)	-	-	0

Binary size

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

Artifact size: 406.60 MiB -> 407.61 MiB (0.25%)

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Oct 8, 2026

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rust-bors Bot pushed a commit that referenced this pull request Oct 8, 2026

Auto merge of #163981 - nnethercote:diesel-opts-1, r=<try>

72d027b

New solver opts for `diesel`

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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 Oct 8, 2026

rustbot assigned jdonszelmann Oct 8, 2026

nnethercote marked this pull request as ready for review October 8, 2026 20:17

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 8, 2026

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nnethercote added 6 commits October 12, 2026 08:05

Remove some unused Interner trait methods

27e12b6

The rust-analyzer impls of these methods will need to be removed on the next sync.

Use clone_from in canonicalize_param_env

83930ed

It's faster than `extend` to initialize these structures.

Add early return to unify_query_var_values

f1922ca

A lot of work can be skipped if the two values being related are equal. (There are various early-return equality checks like this further down the call chain, this just adds one earlier.)

Preintern more types

d1998c0

- Increase the number of preinterned type vars and anon bound types. - Preintern some root-universe placeholder types with anon bounds. - Adjust some comments. - Also rename a lot of the preinterning names for more consistency.

nnethercote force-pushed the diesel-opts-1 branch from 072a4a4 to d1998c0 Compare October 11, 2026 21:14

jdonszelmann reviewed Oct 12, 2026

View reviewed changes

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 Oct 12, 2026

jhpratt mentioned this pull request Oct 12, 2026

Rollup of 5 pull requests #164192

Closed

jhpratt mentioned this pull request Oct 12, 2026

Rollup of 5 pull requests #164193

Merged

rust-bors Bot merged commit ebe0c47 into rust-lang:main Oct 12, 2026
14 of 15 checks passed

rustbot added this to the 1.101.0 milestone Oct 12, 2026

nnethercote deleted the diesel-opts-1 branch October 12, 2026 20:29

nnethercote mentioned this pull request Oct 13, 2026

New solver opts for diesel (part 2) #164234

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

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