Clean up and speed up inference variable resolving code by jdonszelmann · Pull Request #160913 · rust-lang/rust

jdonszelmann · 2026-08-11T14:24:56Z

As part of #162126, I found some small performance wins resulting from the fact that shallow_resolve now returns root vids.

The last commit also makes it so calls to shallow_resolve need to explicitly handle the possibility of reusing the existing interned value.

Note

I've not used an LLM for any part of this PR, or any other PR I make. This includes any related work like research.

rustbot · 2026-08-11T14:25:00Z

changes to inspect_obligations.rs

cc @lcnr

changes to the core type system

cc @lcnr

Some changes occurred in need_type_info.rs

cc @lcnr

Some changes occurred to the core trait solver

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

changes to the core type system

cc @lcnr

jdonszelmann · 2026-08-11T14:25:09Z

@bors try @rust-timer queue

Clean up and speed up resolving code

jdonszelmann · 2026-08-11T14:53:08Z

-        match self.inner.borrow_mut().type_variables().probe(vid) {
-            TypeVariableValue::Known { value } => Ok(value),
+        match value {
+            TypeVariableValue::Known { value } => Ok(self.shallow_resolve_non_recursive(value)),


this method (and the one below) now also does the recursive resolving shallow_resolve already did. No tests change here.

View changes since the review

jdonszelmann · 2026-08-11T14:53:33Z

+    // Cold because the case in which a tyvar resolves to an intvar which resolves to a type is
+    // quite rare. It's way more common for `shallow_resolve_non_recursive` to return ty.
+    #[cold]
+    fn shallow_resolve_infer_non_recursive(&self, infer: InferTy, ty: Ty<'tcx>) -> Ty<'tcx> {


the non-recursive caase helps ~0.5% on local benchmarks. Not much, but still a bit.

View changes since the review

jdonszelmann · 2026-08-11T14:59:06Z

+    /// In cases where we do, this can aid performance.
    #[inline(always)]
-    fn shallow_resolve_ty_var(&self, v: TyVid, ty: Ty<'tcx>) -> Ty<'tcx> {
+    fn shallow_resolve_ty_var_with_ty(&self, v: TyVid, ty: Option<Ty<'tcx>>) -> Ty<'tcx> {


By taking an Option here, we can merge more methods' implementations. Doing this has 0 performance overhead, #[inline(always)] makes sure the callsites that always call with Some get optimized properly.

View changes since the review

could we instead change this function to not take a ty and return and Option instead?

rust-bors · 2026-08-11T15:25:32Z

💔 Test for 7e8d4ec failed: CI. Failed job:

try - dist-x86_64-linux-quick (web logs, enhanced plaintext logs)

jdonszelmann · 2026-08-11T15:47:37Z

@bors try (failed due to missing rustdoc changes now applied)

rust-bors · 2026-08-11T15:47:41Z

Unknown argument "(failed". Did you mean to use @bors jobs=<jobs>|parent=<parent>? Run @bors help or go to https://bors.rust-lang.org/help to see available commands.

panstromek · 2026-08-11T16:49:37Z

@bors try

Clean up and speed up resolving code

rust-bors · 2026-08-11T17:49:20Z

☀️ Try build successful (CI)
Build commit: d881e22 (d881e228b79422918a125ef8385170091369309b)
Base parent: a04c7a0 (a04c7a037d59b6dedc9f921e84e391f13a257aa4)

lcnr

reviewed most of the files.

can you split this PR into multiple separate ones. Reviewing that many changes in this PR feels kind of iffy

View changes since this review

rustbot · 2026-09-14T09:30:53Z

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.

… tyvar.

…er a shallow_resolve

jdonszelmann · 2026-09-14T12:41:21Z

@rustbot review

jdonszelmann · 2026-09-14T12:56:31Z

@bors try @rust-timer queue

Clean up and speed up inference variable resolving code

rust-bors · 2026-09-14T13:56:34Z

☀️ Try build successful (CI)
Build commit: d1e451b (d1e451b7a55281baa0835ac114e0c403139ce187)
Base parent: ed77b7b (ed77b7b8699e342c2dc842c83cb5fe4025252ee8)

rust-timer · 2026-09-14T14:40:54Z

Finished benchmarking commit (d1e451b): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.2%]	43
Improvements ✅ (secondary)	-0.5%	[-1.0%, -0.2%]	79
All ❌✅ (primary)	-0.3%	[-0.5%, -0.2%]	43

Max RSS (memory usage)

Results (primary 6.5%)

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

	mean	range	count
Regressions ❌ (primary)	6.5%	[6.5%, 6.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	6.5%	[6.5%, 6.5%]	1

Cycles

Results (primary 1.9%, secondary -8.7%)

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

	mean	range	count
Regressions ❌ (primary)	1.9%	[1.9%, 1.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-8.7%	[-8.7%, -8.6%]	2
All ❌✅ (primary)	1.9%	[1.9%, 1.9%]	1

Binary size

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

Bootstrap: 495.332s -> 496.666s (0.27%)
Artifact size: 406.96 MiB -> 406.96 MiB (0.00%)

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 11, 2026

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rust-bors Bot pushed a commit that referenced this pull request Aug 11, 2026

Auto merge of #160913 - jdonszelmann:cleanup-resolving, r=<try>

7e8d4ec

Clean up and speed up resolving code

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jdonszelmann force-pushed the cleanup-resolving branch from 3dde145 to b5fe24d Compare August 11, 2026 14:45

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jdonszelmann commented Aug 11, 2026

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Comment thread compiler/rustc_infer/src/infer/canonical/canonicalizer.rs Outdated

jdonszelmann commented Aug 11, 2026

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rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 11, 2026

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jdonszelmann force-pushed the cleanup-resolving branch from b5fe24d to 6b88c26 Compare August 11, 2026 15:47

rustbot added the T-rustdoc-frontend Relevant to the rustdoc-frontend team, which will review and decide on the web UI/UX output. label Aug 11, 2026

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rust-bors Bot pushed a commit that referenced this pull request Aug 11, 2026

Auto merge of #160913 - jdonszelmann:cleanup-resolving, r=<try>

d881e22

Clean up and speed up resolving code

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jdonszelmann force-pushed the cleanup-resolving branch from 9ddd601 to 68fded2 Compare August 21, 2026 09:17

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jdonszelmann force-pushed the cleanup-resolving branch from 68fded2 to aad9f36 Compare August 24, 2026 08:11

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lcnr reviewed Aug 24, 2026

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jdonszelmann force-pushed the cleanup-resolving branch from aad9f36 to 25e4653 Compare September 1, 2026 13:18

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jdonszelmann force-pushed the cleanup-resolving branch from 25e4653 to 5ca7e19 Compare September 14, 2026 09:30

jdonszelmann added 4 commits September 14, 2026 12:44

optimize resolve, and properly document the related methods

12c02e8

use probe_key_value for shallow_resolve_region

3e841b1

Make const methods consistent and expose methods to shallow resolve a…

92f5fb0

… tyvar.

fixup various sites that use root_{ty,const}_var that can skip it aft…

54c6525

…er a shallow_resolve

jdonszelmann force-pushed the cleanup-resolving branch from 5ca7e19 to 7cf7138 Compare September 14, 2026 12:37

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rust-bors Bot pushed a commit that referenced this pull request Sep 14, 2026

Auto merge of #160913 - jdonszelmann:cleanup-resolving, r=<try>

d1e451b

Clean up and speed up inference variable resolving code

make reusing after resolving more explicit

3cbad4a

jdonszelmann force-pushed the cleanup-resolving branch from 7cf7138 to 3cbad4a Compare September 14, 2026 12:58

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 14, 2026

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rust-timer commented Sep 14, 2026

Overall result: ✅ improvements - no action needed

Instruction count

Max RSS (memory usage)

Cycles

Binary size

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