Stop using `LinkedGraph` in `lexical_region_resolve` by Zalathar · Pull Request #153012 · rust-lang/rust

Zalathar · 2026-02-23T09:42:08Z

There are only two users of the older LinkedGraph data structure, and this is one.

It turns out that this diagnostic-related code doesn't need any non-trivial graph operations (since it does its own graph traversal); it just needs the ability to get a list of in-edges or out-edges (constraints) for any particular node. That's easy enough to do with a simple custom data structure.

Inspired by #152621, which wants to make changes to LinkedGraph that wouldn't make sense for this use-site.

rustbot · 2026-02-23T09:42:13Z

r? @fmease

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Zalathar · 2026-02-23T09:42:29Z

I don't expect this to be on a hot path for perf, but let's check.

@bors try @rust-timer queue

Stop using `LinkedGraph` in `lexical_region_resolve`

rust-bors · 2026-02-23T11:54:02Z

☀️ Try build successful (CI)
Build commit: 71438fe (71438fe7132483fe73da8fa49bc361feb85ab6dd, parent: d3e8bd94cc042c65e30a6c60146a8a00531d1292)

rust-timer · 2026-02-23T12:34:10Z

Finished benchmarking commit (71438fe): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

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

Instruction count

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

Max RSS (memory usage)

Results (primary 1.8%, secondary 2.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.8%	[1.5%, 2.1%]	2
Regressions ❌ (secondary)	2.4%	[1.7%, 2.7%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.8%	[1.5%, 2.1%]	2

Cycles

Results (secondary -1.9%)

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)	-1.9%	[-1.9%, -1.9%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 480.206s -> 480.109s (-0.02%)
Artifact size: 397.91 MiB -> 397.93 MiB (0.00%)

Zalathar · 2026-02-23T12:51:04Z

@bors rollup=maybe

compiler/rustc_infer/src/infer/lexical_region_resolve/indexed_edges.rs

petrochenkov · 2026-02-25T14:01:55Z

This makes sense if the goal is to eliminate LinkedGraph entirely.
And maybe even makes sense by itself, the amount of duplication with LinkedGraph here is very tiny.
@rustbot author

rustbot · 2026-02-26T01:38:09Z

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.

Zalathar · 2026-02-26T02:16:14Z

compiler/rustc_infer/src/infer/lexical_region_resolve/indexed_edges.rs

+            // Only push a var out-edge for `VarSub...` constraints.
+            match c.kind {
+                ConstraintKind::VarSubVar | ConstraintKind::VarSubReg => {
+                    out_edges[c.sub.as_var()].push(pair)
+                }
+                ConstraintKind::RegSubVar | ConstraintKind::RegSubReg => {}
+            }


I applied the suggestions, but to me this new version seems more confusing, because the visual pattern from before is now obscured.

Zalathar · 2026-02-26T02:17:11Z

I applied the suggested changes: (diff)

@rustbot ready

petrochenkov · 2026-02-26T13:36:22Z

Thanks!
@bors r+

rust-bors · 2026-02-26T13:36:25Z

📌 Commit 4b7a05e has been approved by petrochenkov

It is now in the queue for this repository.

Stop using `LinkedGraph` in `lexical_region_resolve` There are only two users of the older `LinkedGraph` data structure, and this is one. It turns out that this diagnostic-related code doesn't need any non-trivial graph operations (since it does its own graph traversal); it just needs the ability to get a list of in-edges or out-edges (constraints) for any particular node. That's easy enough to do with a simple custom data structure. Inspired by rust-lang#152621, which wants to make changes to `LinkedGraph` that wouldn't make sense for this use-site.

Rollup of 7 pull requests Successful merges: - #151143 (explicit tail calls: support indirect arguments) - #153012 (Stop using `LinkedGraph` in `lexical_region_resolve`) - #150828 (Improved security section in rustdoc for `current_exe`) - #153117 (Remove mutation from macro path URL construction) - #153128 (Recover feature lang_items for emscripten) - #153138 (Print path root when printing path) - #153159 (Work around a false `err.emit();` type error in rust-analyzer)

Stop using `LinkedGraph` in `lexical_region_resolve` There are only two users of the older `LinkedGraph` data structure, and this is one. It turns out that this diagnostic-related code doesn't need any non-trivial graph operations (since it does its own graph traversal); it just needs the ability to get a list of in-edges or out-edges (constraints) for any particular node. That's easy enough to do with a simple custom data structure. Inspired by rust-lang#152621, which wants to make changes to `LinkedGraph` that wouldn't make sense for this use-site.

…uwer Rollup of 11 pull requests Successful merges: - #151431 (Add new unstable attribute: `#[export_visibility = ...]`.) - #153012 (Stop using `LinkedGraph` in `lexical_region_resolve`) - #153179 (Force a CI LLVM stamp bump) - #150828 (Improved security section in rustdoc for `current_exe`) - #152673 (rustc_public: rewrite `bridge_impl` to reduce boilerplate) - #152674 (rustc_public: remove the `CrateDefItems` trait) - #153073 (Fix mem::conjure_zst panic message to use any::type_name instead) - #153117 (Remove mutation from macro path URL construction) - #153128 (Recover feature lang_items for emscripten) - #153138 (Print path root when printing path) - #153159 (Work around a false `err.emit();` type error in rust-analyzer)

Stop using `LinkedGraph` in `lexical_region_resolve` There are only two users of the older `LinkedGraph` data structure, and this is one. It turns out that this diagnostic-related code doesn't need any non-trivial graph operations (since it does its own graph traversal); it just needs the ability to get a list of in-edges or out-edges (constraints) for any particular node. That's easy enough to do with a simple custom data structure. Inspired by rust-lang#152621, which wants to make changes to `LinkedGraph` that wouldn't make sense for this use-site.

…uwer Rollup of 12 pull requests Successful merges: - #151143 (explicit tail calls: support indirect arguments) - #153012 (Stop using `LinkedGraph` in `lexical_region_resolve`) - #153175 (Clarify a confusing green-path function) - #153179 (Force a CI LLVM stamp bump) - #150828 (Improved security section in rustdoc for `current_exe`) - #152673 (rustc_public: rewrite `bridge_impl` to reduce boilerplate) - #152674 (rustc_public: remove the `CrateDefItems` trait) - #153073 (Fix mem::conjure_zst panic message to use any::type_name instead) - #153117 (Remove mutation from macro path URL construction) - #153128 (Recover feature lang_items for emscripten) - #153138 (Print path root when printing path) - #153159 (Work around a false `err.emit();` type error in rust-analyzer)

Rollup merge of #153012 - Zalathar:lexical, r=petrochenkov Stop using `LinkedGraph` in `lexical_region_resolve` There are only two users of the older `LinkedGraph` data structure, and this is one. It turns out that this diagnostic-related code doesn't need any non-trivial graph operations (since it does its own graph traversal); it just needs the ability to get a list of in-edges or out-edges (constraints) for any particular node. That's easy enough to do with a simple custom data structure. Inspired by #152621, which wants to make changes to `LinkedGraph` that wouldn't make sense for this use-site.

rustbot assigned fmease Feb 23, 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. labels Feb 23, 2026

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rust-bors bot pushed a commit that referenced this pull request Feb 23, 2026

Auto merge of #153012 - Zalathar:lexical, r=<try>

71438fe

Stop using `LinkedGraph` in `lexical_region_resolve`

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 23, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 23, 2026

petrochenkov mentioned this pull request Feb 24, 2026

LinkedGraph: support adding nodes and edges in arbitrary order #152621

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petrochenkov self-assigned this Feb 24, 2026

petrochenkov reviewed Feb 25, 2026

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rustbot 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 Feb 25, 2026

fmease assigned petrochenkov and unassigned petrochenkov and fmease Feb 25, 2026

Zalathar force-pushed the lexical branch from 3e6b94e to 0be16e6 Compare February 26, 2026 01:38

Stop using LinkedGraph in lexical_region_resolve

4b7a05e

Zalathar force-pushed the lexical branch from 0be16e6 to 4b7a05e Compare February 26, 2026 02:01

Zalathar commented Feb 26, 2026

View reviewed changes

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Feb 26, 2026

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 26, 2026

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 Feb 26, 2026

JonathanBrouwer mentioned this pull request Feb 26, 2026

Rollup of 5 pull requests #153137

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matthiaskrgr mentioned this pull request Feb 27, 2026

Rollup of 7 pull requests #153167

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JonathanBrouwer mentioned this pull request Feb 27, 2026

Rollup of 10 pull requests #153171

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JonathanBrouwer mentioned this pull request Feb 27, 2026

Rollup of 11 pull requests #153180

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This was referenced Feb 27, 2026

Rollup of 12 pull requests #153182

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Rollup of 12 pull requests #153183

Merged

rust-bors bot merged commit 383ef53 into rust-lang:main Feb 28, 2026
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rustbot added this to the 1.95.0 milestone Feb 28, 2026

Zalathar deleted the lexical branch February 28, 2026 01:38

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rust-timer commented Feb 23, 2026

Overall result: no relevant changes - no action needed

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