some more rustc_borrowck cleanups #151374

BoxyUwU · 2026-01-19T16:30:09Z

r? lcnr

compiler/rustc_borrowck/src/type_check/input_output.rs

BoxyUwU · 2026-01-19T16:33:21Z

compiler/rustc_borrowck/src/type_check/input_output.rs

-        if let Err(_) =
-            self.eq_types(a, b, Locations::All(span), ConstraintCategory::BoringNoLocation)
-        {


i assume removing this "fast path" is perf sensitive so will do a perf run 🤔

like 0.2% in a few secondary benchmarks #151374 (comment)

I don't think a simple cleanup of yeeting this is worth it given those results?

can you instead do

if infcx.next_Trait_solver() { return eq_types(); }

and then keep the old body with updated comments, rn the formatting is kinda ass here

BoxyUwU · 2026-01-19T16:34:36Z

tests/ui/associated-types/normalization-generality-2.rs

@@ -1,4 +1,7 @@
 //@ build-pass
+//@ revisions: current next


all of these are tests that fail in the old solver if you remove the normalization in equate_normalized_input_or_output

BoxyUwU · 2026-01-19T16:44:26Z

@bors try @rust-timer queue

some more rustc_borrowck cleanups

rust-bors · 2026-01-19T19:00:51Z

☀️ Try build successful (CI)
Build commit: 97360bc (97360bc76d9408f19d17edb2abcda5774e0132cf, parent: d940e56841ddcc05671ead99290e35ff2e98369f)

rust-timer · 2026-01-19T20:45:58Z

Finished benchmarking commit (97360bc): comparison URL.

Overall result: ❌ regressions - 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

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)	0.2%	[0.2%, 0.3%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 2.0%, secondary 5.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	5.7%	[4.3%, 7.0%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Cycles

Results (primary 2.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.7%, 2.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.7%	[2.7%, 2.7%]	1

Binary size

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

Bootstrap: 473.058s -> 474.427s (0.29%)
Artifact size: 383.29 MiB -> 383.36 MiB (0.02%)

BoxyUwU · 2026-01-20T11:32:47Z

@bors try @rust-timer queue

some more rustc_borrowck cleanups

rust-bors · 2026-01-20T13:54:01Z

☀️ Try build successful (CI)
Build commit: e28fa5a (e28fa5a4bbbf7c674c73962c058f6c9f02e1ba82, parent: 79818181387879de7a521366d9bea23624728462)

rust-timer · 2026-01-20T14:34:57Z

Finished benchmarking commit (e28fa5a): 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 -2.0%, secondary 1.7%)

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)	3.1%	[2.4%, 4.4%]	3
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-2.8%	[-2.8%, -2.8%]	1
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Cycles

Results (secondary 2.6%)

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)	2.6%	[2.0%, 3.1%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.0%, secondary -0.0%)

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)	-0.0%	[-0.0%, -0.0%]	3
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	3

Bootstrap: 473.092s -> 474.982s (0.40%)
Artifact size: 383.30 MiB -> 383.28 MiB (-0.01%)

BoxyUwU · 2026-01-20T14:39:03Z

compiler/rustc_borrowck/src/type_check/mod.rs

-        "there should be no incoming region assumptions = {pre_assumptions:#?}",
-    );
+    {
+        // Scope these variables so it's clear they're not used later


this seemed kinda scary to me when i was reading it :> but i think this would have made it not seem so scary

BoxyUwU · 2026-01-20T14:40:21Z

compiler/rustc_borrowck/src/type_check/input_output.rs

            );
        }

-        // Return types are a bit more complex. They may contain opaque `impl Trait` types.


Am I missing something here? The actual logic here is no more complex than any of the previous relations we do.

BoxyUwU · 2026-01-20T14:43:11Z

compiler/rustc_borrowck/src/type_check/input_output.rs

-            // Note: if we have to introduce new placeholders during normalization above, then we
-            // won't have added those universes to the universe info, which we would want in
-            // `relate_tys`.


i am missing something here. This comment would seem to imply we do things differently to avoid calling relate_types (note taht there is no such thing as relate_tys) but eq_types is a trivial wrapper around relate_tys.

I guess the point is that there will be universes made during the normalization call which this eq_types is unaware of the origin for? I don't quite get why this is worth calling out, but maybe it's worth keeping this :>

at minimum I think I'd want to move this comment to the actual normalize call as that's where the source of the "weirdness" is? but also we don't have a similar comment in other places we normalize and maybe we should if we do want this?

I also do not get this comment. I don't think it's relevant 🤔

lcnr · 2026-01-20T15:27:25Z

compiler/rustc_borrowck/src/type_check/canonical.rs

+        //
+        // I am not sure of a test case where this actually matters. There is a similar
+        // hack in `equate_inputs_and_outputs` which does have associated test cases.
+        let mir_ty = match self.infcx.tcx.next_trait_solver_globally() {


Suggested change

let mir_ty = match self.infcx.tcx.next_trait_solver_globally() {

let mir_ty = match self.infcx.next_trait_solver() {

lcnr · 2026-01-20T15:34:08Z

compiler/rustc_borrowck/src/type_check/mod.rs

+    {
+        // Scope these variables so it's clear they're not used later
+        let pre_obligations = infcx.take_registered_region_obligations();
+        assert!(


why have these as variables at all, we could just do

assert_eq!( infcx.take_registered_region_obligations(), vec![], "there should be no incoming region obligations" );

🤔 this assert is hard to read/noisy

rustbot assigned lcnr Jan 19, 2026

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jan 19, 2026

BoxyUwU commented Jan 19, 2026

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rust-bors bot pushed a commit that referenced this pull request Jan 19, 2026

Auto merge of #151374 - BoxyUwU:borrowck_cleanup_3, r=<try>

97360bc

some more rustc_borrowck cleanups

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 19, 2026

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 20, 2026

rust-bors bot pushed a commit that referenced this pull request Jan 20, 2026

Auto merge of #151374 - BoxyUwU:borrowck_cleanup_3, r=<try>

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some more rustc_borrowck cleanups

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BoxyUwU force-pushed the borrowck_cleanup_3 branch 2 times, most recently from e322fbf to f330bf8 Compare January 20, 2026 14:28

Misc cleanups to borrowck crate

df106b6

BoxyUwU force-pushed the borrowck_cleanup_3 branch from f330bf8 to df106b6 Compare January 20, 2026 14:33

rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jan 20, 2026

BoxyUwU commented Jan 20, 2026

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BoxyUwU marked this pull request as ready for review January 20, 2026 14:39

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 Jan 20, 2026

BoxyUwU commented Jan 20, 2026

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lcnr reviewed Jan 20, 2026

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	let mir_ty = match self.infcx.tcx.next_trait_solver_globally() {
	let mir_ty = match self.infcx.next_trait_solver() {

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rust-timer commented Jan 19, 2026

Overall result: ❌ regressions - no action needed

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Overall result: no relevant changes - no action needed

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