Make lowering incremental, take 3/N by cjgillot · Pull Request #142830 · rust-lang/rust

cjgillot · 2025-06-21T15:26:00Z

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Rebase of #88186 that was rebased by #127262

No real change in design, so I'm not expecting a perf miracle.

r? @ghost

cjgillot · 2025-06-21T16:12:09Z

@bors try @rust-timer queue

bors · 2025-06-21T16:13:19Z

⌛ Trying commit 0e2f90b with merge a6b131d...

Make lowering incremental, take 3/N Rebase of #88186 that was rebased by #127262 No real change in design, so I'm not expecting a perf miracle. r? `@ghost`

bors · 2025-06-21T18:43:11Z

☀️ Try build successful - checks-actions
Build commit: a6b131d (a6b131d42573c085b032a153779366b448148b9d)

rust-timer · 2025-06-21T20:41:55Z

Finished benchmarking commit (a6b131d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@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)	0.8%	[0.2%, 1.8%]	157
Regressions ❌ (secondary)	1.1%	[0.2%, 4.3%]	69
Improvements ✅ (primary)	-0.4%	[-0.5%, -0.3%]	5
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	7
All ❌✅ (primary)	0.7%	[-0.5%, 1.8%]	162

Max RSS (memory usage)

Results (primary 10.5%, secondary 10.1%)

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

	mean	range	count
Regressions ❌ (primary)	10.5%	[3.1%, 28.6%]	249
Regressions ❌ (secondary)	10.1%	[2.2%, 31.4%]	142
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	10.5%	[3.1%, 28.6%]	249

Cycles

Results (primary 2.5%, secondary 4.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.5%	[1.4%, 5.5%]	35
Regressions ❌ (secondary)	4.1%	[1.8%, 7.5%]	22
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.5%	[1.4%, 5.5%]	35

Binary size

Results (primary -0.1%, secondary -0.2%)

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)	-0.1%	[-0.2%, -0.0%]	82
Improvements ✅ (secondary)	-0.2%	[-0.9%, -0.0%]	43
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	82

Bootstrap: 690.042s -> 689.298s (-0.11%)
Artifact size: 371.86 MiB -> 371.81 MiB (-0.01%)

cjgillot · 2025-06-22T16:12:05Z

@bors try @rust-timer queue

bors · 2025-06-22T16:13:39Z

⌛ Trying commit 8ab4e63 with merge 31325ff...

Make lowering incremental, take 3/N Rebase of #88186 that was rebased by #127262 No real change in design, so I'm not expecting a perf miracle. r? `@ghost`

bors · 2025-06-22T18:48:06Z

☀️ Try build successful - checks-actions
Build commit: 31325ff (31325ff312ad91d8a2dd156c832cacc0435f9ea1)

rust-timer · 2025-06-22T21:45:31Z

Finished benchmarking commit (31325ff): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@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)	0.5%	[0.2%, 1.3%]	120
Regressions ❌ (secondary)	0.8%	[0.2%, 3.2%]	77
Improvements ✅ (primary)	-0.7%	[-1.3%, -0.2%]	12
Improvements ✅ (secondary)	-0.6%	[-1.3%, -0.2%]	37
All ❌✅ (primary)	0.4%	[-1.3%, 1.3%]	132

Max RSS (memory usage)

Results (primary 10.8%, secondary 10.4%)

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

	mean	range	count
Regressions ❌ (primary)	10.8%	[2.3%, 29.1%]	248
Regressions ❌ (secondary)	10.4%	[1.9%, 31.7%]	143
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	10.8%	[2.3%, 29.1%]	248

Cycles

Results (primary 2.1%, secondary 4.1%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[1.2%, 3.8%]	20
Regressions ❌ (secondary)	4.1%	[1.7%, 6.6%]	16
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.1%	[1.2%, 3.8%]	20

Binary size

Results (primary -0.1%, secondary -0.2%)

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)	-0.1%	[-0.2%, -0.0%]	83
Improvements ✅ (secondary)	-0.2%	[-0.9%, -0.0%]	43
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	83

Bootstrap: 689.082s -> 688.79s (-0.04%)
Artifact size: 371.89 MiB -> 371.87 MiB (-0.00%)

rustbot · 2026-06-05T08:24:28Z

Some changes occurred in coverage instrumentation.

cc @Zalathar

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

cjgillot · 2026-06-05T08:26:16Z

I don't think I will be able to do much better in terms of perf. Meanwhile, it unblocks making progress on more incremental name resolution.

r? @petrochenkov
cc @oli-obk

petrochenkov · 2026-06-05T14:52:36Z

+#[derive(Debug)]
+pub enum AstOwner {
+    NonOwner,
+    Synthetic(rustc_span::def_id::LocalDefId),


Suggested change

Synthetic(rustc_span::def_id::LocalDefId),

Synthetic(LocalDefId),

View changes since the review

petrochenkov · 2026-06-05T14:55:30Z

+#[derive(Debug)]
+pub enum AstOwner {
+    NonOwner,
+    Synthetic(rustc_span::def_id::LocalDefId),


This is used specifically for nested imports, maybe use a more specific name and add an explanation comment?

View changes since the review

petrochenkov · 2026-06-05T15:00:04Z

-    query resolver_for_lowering_raw(_: ()) -> (&'tcx Steal<(ty::ResolverAstLowering<'tcx>, Arc<ast::Crate>)>, &'tcx ty::ResolverGlobalCtxt) {
+    query resolver_for_lowering_raw(_: ()) -> (
+        &'tcx Steal<ty::ResolverAstLowering<'tcx>>,
+        &'tcx Steal<ast::Crate>,


It would be useful to add a comment telling why the Steals are used here.

View changes since the review

petrochenkov · 2026-06-05T15:00:33Z

    }

+    query index_ast(_: ()) -> &'tcx IndexVec<LocalDefId, Steal<(
+        Arc<ty::ResolverAstLowering<'tcx>>,


It would be useful to add a comment telling why the Arcs are used here.

View changes since the review

petrochenkov · 2026-06-05T15:02:59Z

+    query lower_to_hir(key: LocalDefId) -> hir::MaybeOwner<'tcx> {
        eval_always
-        desc { "lowering the delayed AST owner `{}`", tcx.def_path_str(def_id) }
+        desc { "lowering HIR for `{}`", tcx.def_path_str(key.to_def_id()) }


Suggested change

desc { "lowering HIR for `{}`", tcx.def_path_str(key.to_def_id()) }

desc { "lowering HIR for `{}`", tcx.def_path_str(def_id) }

View changes since the review

petrochenkov · 2026-06-05T15:06:32Z

    /// Pre-computed hash of the full HIR. Used in the crate hash. Only present
    /// when incr. comp. is enabled.
-    pub opt_hash_including_bodies: Option<Fingerprint>,
+    pub opt_hash: Option<Fingerprint>,


Does the hash still include bodies?
Is it not valuable to mention it? (Perhaps it can be mentioned in the comment above.)

View changes since the review

petrochenkov · 2026-06-05T15:12:06Z

Started reviewing today, starting from the easy parts, will continue on Monday.

petrochenkov · 2026-06-08T13:13:39Z

+                span,
+                vis: Visibility { kind: VisibilityKind::Public, span, tokens: None },
+                // Lacking a better choice, we replace the contents with a macro call.
+                // Unexpanded macros should never reach lowering, so this is not confusing.


Macro expansion uses the same approach (compiler\rustc_expand\src\placeholders.rs), maybe it can even be reused here.

View changes since the review

petrochenkov · 2026-06-08T13:17:31Z

 pub type ForeignItem = Item<ForeignItemKind>;

+#[derive(Debug)]
+pub enum AstOwner {


If it's only used in AST lowering, then maybe it's better to move it there.

View changes since the review

petrochenkov · 2026-06-08T13:35:35Z

+        AstOwner::ImplItem(item) => item_lowerer.lower_impl_item(&item),
+        AstOwner::ForeignItem(item) => item_lowerer.lower_foreign_item(&item),
+        AstOwner::Synthetic(parent_id) => fallback_to_parent(*parent_id),
+        AstOwner::NonOwner => fallback_to_parent(tcx.local_parent(def_id)),


In which cases AstOwner::NonOwners appear at all? Only during error recovery?

View changes since the review

Co-authored-by: Camille Gillot <gillot.camille@gmail.com>

rustbot · 2026-06-10T12:56:59Z

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.

rustbot added PG-exploit-mitigations Project group: Exploit mitigations T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Jun 21, 2025

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 21, 2025

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bors added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jun 21, 2025

cjgillot force-pushed the lower-incr-2 branch from d715668 to 0e2f90b Compare June 21, 2025 16:11

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bors added a commit that referenced this pull request Jun 21, 2025

Auto merge of #142830 - cjgillot:lower-incr-2, r=<try>

a6b131d

Make lowering incremental, take 3/N Rebase of #88186 that was rebased by #127262 No real change in design, so I'm not expecting a perf miracle. r? `@ghost`

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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 Jun 21, 2025

cjgillot force-pushed the lower-incr-2 branch from 0e2f90b to 8ab4e63 Compare June 22, 2025 16:11

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 22, 2025

bors added a commit that referenced this pull request Jun 22, 2025

Auto merge of #142830 - cjgillot:lower-incr-2, r=<try>

31325ff

Make lowering incremental, take 3/N Rebase of #88186 that was rebased by #127262 No real change in design, so I'm not expecting a perf miracle. r? `@ghost`

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bors mentioned this pull request Jun 22, 2025

Document subdirectories of UI tests with README files #141597

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cjgillot marked this pull request as ready for review June 5, 2026 08:24

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 Jun 5, 2026

rustbot assigned petrochenkov Jun 5, 2026

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petrochenkov reviewed Jun 8, 2026

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petrochenkov 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 Jun 8, 2026

oli-obk self-assigned this Jun 9, 2026

cjgillot added 10 commits June 10, 2026 10:58

Stop stealing ResolverAstLowering.

c84bda3

Make lowering incremental.

9b00341

Co-authored-by: Camille Gillot <gillot.camille@gmail.com>

Precompute hash for OwnerInfo too.

809641d

Split-up the AST to index it.

b61ad9a

Steal ResolverAstLowering when indexing AST.

ceb3718

Document AstOwner.

134ec5c

Document HIR queries.

6ebb931

std::mem is already imported.

04c7b09

Do not insert owner in node_id_to_local_id.

ab9c8c6

Explain NodeId generation.

422088e

cjgillot force-pushed the lower-incr-2 branch from dfc150b to bbcd374 Compare June 10, 2026 12:56

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cjgillot added 3 commits June 10, 2026 13:58

Add comments.

8ce4632

Style.

747e159

Remove useless call.

cfa0bc2

cjgillot force-pushed the lower-incr-2 branch from bbcd374 to cfa0bc2 Compare June 10, 2026 13:58

	Synthetic(rustc_span::def_id::LocalDefId),
	Synthetic(LocalDefId),

	desc { "lowering HIR for `{}`", tcx.def_path_str(key.to_def_id()) }
	desc { "lowering HIR for `{}`", tcx.def_path_str(def_id) }

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rust-timer commented Jun 21, 2025

Overall result: ❌✅ regressions and improvements - please read the text below

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rust-timer commented Jun 22, 2025

Overall result: ❌✅ regressions and improvements - please read the text below

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