Use LocalDefId for more tcx method calls by zetanumbers · Pull Request #154371 · rust-lang/rust

zetanumbers · 2026-03-25T14:55:23Z

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r? @petrochenkov

Might bring perf improvements

rustbot · 2026-03-25T14:55:28Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in need_type_info.rs

cc @lcnr

Some changes occurred in coverage instrumentation.

cc @Zalathar

petrochenkov · 2026-03-25T15:16:56Z

@bors try @rust-timer queue

Use LocalDefId for more tcx method calls

rust-bors · 2026-03-25T17:28:02Z

☀️ Try build successful (CI)
Build commit: 3c6dc09 (3c6dc097fe81b4e758db660110dd84dc136cf8a5, parent: 8a703520e80d87d4423c01f9d4fbc9e5f6533a02)

rust-timer · 2026-03-25T18:12:52Z

Finished benchmarking commit (3c6dc09): 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 -2.3%, secondary 2.5%)

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Cycles

Results (secondary 4.4%)

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)	6.4%	[4.9%, 10.1%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.7%	[-3.7%, -3.7%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 482.838s -> 489.051s (1.29%)
Artifact size: 394.91 MiB -> 394.93 MiB (0.01%)

petrochenkov · 2026-03-26T12:08:43Z

As the benchmark shows, in general, duplicating methods into foo and foo_local doesn't make sense from performance point of view.
I suggest keeping the subset of DefId -> LocalDefId changes that improves the code (better readability, more clear invariants, etc), I'll mark the changes that I think are worth keeping.

petrochenkov · 2026-03-26T12:15:01Z

compiler/rustc_middle/src/ty/util.rs

+    /// For example, a closure has its own `LocalDefId`, but it is type-checked
+    /// with the containing item. Therefore, when we fetch the `typeck` of the closure,
+    /// for example, we really wind up fetching the `typeck` of the enclosing fn item.
+    pub fn typeck_root_def_id_local(self, def_id: LocalDefId) -> LocalDefId {


The body can be changed to typeck_root_def_id(def_id.to_def_id()).expect_local().
(Because the copy-pasted version doesn't show perf benefits while being more complex.)

compiler/rustc_middle/src/ty/context.rs

compiler/rustc_middle/src/ty/mod.rs

compiler/rustc_span/src/def_id.rs

petrochenkov · 2026-03-26T12:27:29Z

Most of the changes are worth keeping, actually.
@rustbot author

rustbot · 2026-03-26T12:27:34Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

rustbot · 2026-03-27T12:40:30Z

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.

zetanumbers · 2026-03-27T12:42:39Z

@rustbot ready

petrochenkov · 2026-03-27T13:01:45Z

r=me after addressing #154371 (comment).
@rustbot author

petrochenkov · 2026-03-27T13:05:26Z

Okay, #154371 (comment) is not too important.
@bors r+ rollup=maybe

rust-bors · 2026-03-27T13:05:31Z

📌 Commit 62ec331 has been approved by petrochenkov

It is now in the queue for this repository.

Rollup of 10 pull requests Successful merges: - #154070 (Unstable book options parser) - #154371 (Use LocalDefId for more tcx method calls) - #154405 (Improve doc comment unicode guidance) - #154431 (Avoid ICE in explicit reference cast suggestion for unrelated leaf pr…) - #153528 (Fix LegacyKeyValueFormat report from docker build: mips) - #154246 (Add test for issue #101532: dead code warnings in const _) - #154421 (Rustdoc rejects html emits with json output) - #154428 (bootstrap: `-Zjson-target-spec` for synthetic targets) - #154437 (bootstrap.example.toml: Hint how to allow `build.warnings`) - #154454 (fix: [rustfmt] prevent panic when rewritng associated item delegations) Failed merges: - #154450 (Use the normal arg-parsing machinery for `-Zassert-incr-state`)

@petrochenkov

Rollup merge of #154371 - zetanumbers:typeck_root_def_id_local, r=petrochenkov Use LocalDefId for more tcx method calls r? @petrochenkov Might bring perf improvements

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-clippy Relevant to the Clippy team. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 25, 2026

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rust-bors bot pushed a commit that referenced this pull request Mar 25, 2026

Auto merge of #154371 - zetanumbers:typeck_root_def_id_local, r=<try>

3c6dc09

Use LocalDefId for more tcx method calls

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 25, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 25, 2026

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

petrochenkov reviewed Mar 26, 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 Mar 26, 2026

This was referenced Mar 26, 2026

Make typeck a tcx method which calls typeck_root query #154304

Merged

Use tcx.stable_crate_id() more often #154464

Closed

zetanumbers added 4 commits March 27, 2026 15:36

Use tcx.is_typeck_child() more often

08bb61b

Add typeck_root_def_id_local

1b68d92

Use stable_crate_id more often

2bb9d70

Use tcx.local_parent() more often

62ec331

zetanumbers force-pushed the typeck_root_def_id_local branch from ec7d272 to 62ec331 Compare March 27, 2026 12:40

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 Mar 27, 2026

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 Mar 27, 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 27, 2026

fmease mentioned this pull request Mar 27, 2026

Rollup of 10 pull requests #154466

Merged

rust-bors bot merged commit 9ba9194 into rust-lang:main Mar 28, 2026
11 checks passed

rustbot added this to the 1.96.0 milestone Mar 28, 2026

rust-timer added a commit that referenced this pull request Mar 28, 2026

Unrolled build for #154371

12570d7

Rollup merge of #154371 - zetanumbers:typeck_root_def_id_local, r=petrochenkov Use LocalDefId for more tcx method calls r? @petrochenkov Might bring perf improvements

zetanumbers deleted the typeck_root_def_id_local branch March 28, 2026 05:39

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rust-timer commented Mar 25, 2026

Overall result: no relevant changes - no action needed

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zetanumbers commented Mar 25, 2026 •

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