Resolve: more preperation work for parallelizing the import resolution loop by LorrensP-2158466 · Pull Request #159440 · rust-lang/rust

LorrensP-2158466 · 2026-07-17T12:42:34Z

This is basically #158845 but we do not:

actually use par_slice because:
we do not migrate CmRefCell to use RwLocks (yet) because of perf reasons.

The resolution loop is now in place instead of recollecting indeterminate imports.

Also implemented the unsafe traits DynSend/DynSync for RefOrMut and CmCell and tried to write correct SAFETY comments.

r? @petrochenkov

LorrensP-2158466 · 2026-07-17T15:09:46Z

I double-checked with git diff f3d5c561f4c compiler/rustc_resolve and I only see comments or the unsafe impls as + diff.

@rustbot ready

…par_slice`. Currently it is all still single threaded, but almost everything needed to make the loop use multithreaded code is done in this commit. For performance reasons we do the resolution now in place instead of recollecting the indeterminate imports ([see benchmark pr](rust-lang#159387) and pr of this commit). With the accompanying changes to make datastructures concurrent: - populating external resolution tables now use `Once` to ensure only 1 thread builds the table and all others wait if they need it - implement `DynSync`/`DynSend` for `RefOrMut` and `CmCell` so it is allowed to use the `par_slice` function. `Cache(Ref)Cells` are not tackled yet because they are not needed here (and require extra work).

petrochenkov · 2026-07-17T20:09:51Z

+        &self,
+        def_id: DefId,
+        map_lock: &mut RefMut<'_, FxIndexMap<DefId, ExternModule<'ra>>>,
+    ) -> Option<Module<'ra>> {


Suggested change

) -> Option<Module<'ra>> {

) -> Option<ExternModule<'ra>> {

View changes since the review

petrochenkov · 2026-07-17T20:11:32Z

+                    while let MacroRulesScope::Invocation(invoc_id) = scope {
+                        if let Some(next) = self.output_macro_rules_scopes.get(&invoc_id) {
+                            scope = next.get();
+                            macro_rules_scope.set(scope);


Suggested change

macro_rules_scope.set(scope);

macro_rules_scope.set(next.get());

Does the RwLock version really not work in the nicer way, like before?

View changes since the review

petrochenkov · 2026-07-17T20:12:24Z

            indeterminate_count = 0;
-            let mut resolutions = Vec::new();
+
+            let mut to_resolve_imports = mem::take(&mut self.indeterminate_imports);


Suggested change

let mut to_resolve_imports = mem::take(&mut self.indeterminate_imports);

let mut imports_to_resolve = mem::take(&mut self.indeterminate_imports);

View changes since the review

petrochenkov · 2026-07-17T20:14:09Z

+                    let (new_resolution, import_indeterminate_count) =
+                        cm_resolver.reborrow_ref().resolve_import(*import);
+                    *resolution = new_resolution;
+                    *indeterminate_count = import_indeterminate_count


Suggested change

*indeterminate_count = import_indeterminate_count

(*resolution, *indeterminate_count) = cm_resolver.reborrow_ref().resolve_import(*import);

This should actually work (it's a destructuring assignment).

View changes since the review

petrochenkov · 2026-07-17T20:16:01Z

+            self.write_import_resolutions(&to_resolve_imports);
+
+            self.indeterminate_imports = to_resolve_imports
+                .extract_if(.., |(_, _, count)| {


It would be nicer to extract_if into determined_imports instead and then do self.indeterminate_imports = imports_to_resolve;.
But it may be slower due to majority of the elements in the vector being determinate.
I'll benchmark it separately later after this PR lands.

View changes since the review

petrochenkov · 2026-07-17T20:17:11Z


-        for (import, resolution) in import_resolutions {
-            let ImportResolution { imported_module, kind: resolution_kind } = resolution;
+        for (import, resolution, _) in import_resolutions {


Suggested change

for (import, resolution, _) in import_resolutions {

for &(import, resolution, _) in import_resolutions {

Could you do something like this here to avoid *s below?

View changes since the review

petrochenkov · 2026-07-17T20:19:24Z

 type CmResolver<'r, 'ra, 'tcx> = ref_mut::RefOrMut<'r, Resolver<'ra, 'tcx>>;

+// FIXME: this should be removed in the process of migration to parallel name resolution.
+unsafe impl<'ra, 'tcx> DynSync for Resolver<'ra, 'tcx> {}


Could you remove the Dyn(Sync,Send) impls from this PR?
I don't think they are justified yet, before the migration to RwLock (and probably not yet used too).

Or maybe they are? At least for RefOrMut.
I'm not actually sure.

View changes since the review

rustbot assigned petrochenkov Jul 17, 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 Jul 17, 2026

LorrensP-2158466 mentioned this pull request Jul 17, 2026

Resolver: Parallelize the import resolution loop #158845

Open

This comment has been minimized.

Sign in to view

petrochenkov reviewed Jul 17, 2026

View reviewed changes

Comment thread compiler/rustc_resolve/src/lib.rs Outdated

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 Jul 17, 2026

LorrensP-2158466 force-pushed the inplace-import-res branch from 0d9f4a2 to aa051d9 Compare July 17, 2026 15:09

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 Jul 17, 2026

This comment has been minimized.

Sign in to view

LorrensP-2158466 force-pushed the inplace-import-res branch from aa051d9 to 2e9c9d2 Compare July 17, 2026 15:23

petrochenkov reviewed Jul 17, 2026

View reviewed changes

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 Jul 17, 2026

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Uh oh!

Resolve: more preperation work for parallelizing the import resolution loop#159440

Resolve: more preperation work for parallelizing the import resolution loop#159440
LorrensP-2158466 wants to merge 1 commit into
rust-lang:mainfrom
LorrensP-2158466:inplace-import-res

LorrensP-2158466 commented Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

This comment has been minimized.

Uh oh!

LorrensP-2158466 commented Jul 17, 2026

Uh oh!

This comment has been minimized.

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

	macro_rules_scope.set(scope);
	macro_rules_scope.set(next.get());

	let mut to_resolve_imports = mem::take(&mut self.indeterminate_imports);
	let mut imports_to_resolve = mem::take(&mut self.indeterminate_imports);

	*indeterminate_count = import_indeterminate_count
	(resolution, indeterminate_count) = cm_resolver.reborrow_ref().resolve_import(*import);

	for (import, resolution, _) in import_resolutions {
	for &(import, resolution, _) in import_resolutions {

Uh oh!

Uh oh!

Conversation

LorrensP-2158466 commented Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

This comment has been minimized.

Uh oh!

LorrensP-2158466 commented Jul 17, 2026

Uh oh!

This comment has been minimized.

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

petrochenkov Jul 17, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

LorrensP-2158466 commented Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading

petrochenkov Jul 17, 2026 •

edited by rustbot

Loading