[PERF] non behavior changing coercion changes #148415

BoxyUwU · 2025-11-02T21:35:16Z

This has three main effects: 1. we now leak check for closure->fnptr and fnptr->closure coercions 2. we now leak check normal subtyping in HIR typeck when going through coercions 3. we now leak check normal lubbing when there is no coercion

BoxyUwU · 2025-11-02T21:36:53Z

@bors try @rust-timer queue

[PERF] non behavior changing coercion changes

rust-bors · 2025-11-02T23:49:39Z

☀️ Try build successful (CI)
Build commit: 7a58efb (7a58efbaffa8988bd6eb238f5098444b74216db1, parent: 8483293b3b4eb209e8e8bd0d069e61de790018a8)

rust-timer · 2025-11-03T01:30:33Z

Finished benchmarking commit (7a58efb): 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)

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

Cycles

Results (secondary -3.2%)

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
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 473.503s -> 473.376s (-0.03%)
Artifact size: 390.87 MiB -> 390.84 MiB (-0.01%)

BoxyUwU · 2025-11-03T12:02:36Z

@bors try @rust-timer queue

[PERF] non behavior changing coercion changes

rust-bors · 2025-11-03T14:13:42Z

☀️ Try build successful (CI)
Build commit: a803a24 (a803a241710ac8e33643fc524092d4fd8de7610f, parent: f2bae990e89bf696e86706b524ac32ab72945438)

rust-timer · 2025-11-03T16:01:40Z

Finished benchmarking commit (a803a24): comparison URL.

Overall result: ❌ regressions - 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)	0.6%	[0.1%, 1.7%]	17
Regressions ❌ (secondary)	1.4%	[0.1%, 5.0%]	33
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.1%, 1.7%]	17

Max RSS (memory usage)

Results (primary 0.2%, secondary 1.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.6%	[1.8%, 3.7%]	3
Regressions ❌ (secondary)	1.5%	[1.5%, 1.5%]	1
Improvements ✅ (primary)	-1.6%	[-2.8%, -0.8%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-2.8%, 3.7%]	7

Cycles

Results (primary -2.0%, secondary 3.6%)

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)	3.6%	[2.5%, 4.7%]	9
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Binary size

Results (primary 0.0%)

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

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.1%, 0.2%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.0%	[-0.0%, -0.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[-0.0%, 0.2%]	4

Bootstrap: 475.169s -> 474.06s (-0.23%)
Artifact size: 390.81 MiB -> 390.81 MiB (-0.00%)

BoxyUwU · 2025-11-03T17:57:09Z

@bors try @rust-timer queue

[PERF] non behavior changing coercion changes

rust-log-analyzer · 2025-11-03T18:01:34Z

The job tidy failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[TIMING:end] tool::ToolBuild { build_compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu, tool: "tidy", path: "src/tools/tidy", mode: ToolBootstrap, source_type: InTree, extra_features: [], allow_features: "", cargo_args: [], artifact_kind: Binary } -- 10.507
[TIMING:end] tool::Tidy { compiler: Compiler { stage: 0, host: x86_64-unknown-linux-gnu, forced_compiler: false }, target: x86_64-unknown-linux-gnu } -- 0.000
fmt check
Diff in /checkout/compiler/rustc_hir_typeck/src/coercion.rs:1168:
             if is_capturing_closure(prev_ty) || is_capturing_closure(new_ty) {
                 (None, None)
             } else {
-                let lubbed_tys = || self.commit_if_ok(|snapshot| {
-                    let outer_universe = self.infcx.universe();
+                let lubbed_tys = || {
+                    self.commit_if_ok(|snapshot| {
+                        let outer_universe = self.infcx.universe();
 
-                    // We need to eagerly handle nested obligations due to lazy norm.
-                    let result = if self.next_trait_solver() {
-                        let ocx = ObligationCtxt::new(self);
-                        let value = ocx.lub(cause, self.param_env, prev_ty, new_ty)?;
-                        if ocx.try_evaluate_obligations().is_empty() {
-                            Ok(InferOk { value, obligations: ocx.into_pending_obligations() })
+                        // We need to eagerly handle nested obligations due to lazy norm.
+                        let result = if self.next_trait_solver() {
+                            let ocx = ObligationCtxt::new(self);
+                            let value = ocx.lub(cause, self.param_env, prev_ty, new_ty)?;
+                            if ocx.try_evaluate_obligations().is_empty() {
+                                Ok(InferOk { value, obligations: ocx.into_pending_obligations() })
+                            } else {
+                                Err(TypeError::Mismatch)
+                            }
                         } else {
-                            Err(TypeError::Mismatch)
-                        }
-                    } else {
-                        self.at(cause, self.param_env).lub(prev_ty, new_ty)
-                    };
+                            self.at(cause, self.param_env).lub(prev_ty, new_ty)
+                        };
 
-                    self.leak_check(outer_universe, Some(snapshot))?;
-                    result
-                });
+                        self.leak_check(outer_universe, Some(snapshot))?;
+                        result
+                    })
+                };
 
                 match (prev_ty.kind(), new_ty.kind()) {
                     // Don't coerce pairs of fndefs or pairs of closures to fn ptrs
fmt: checked 6519 files
Bootstrap failed while executing `test src/tools/tidy tidyselftest --extra-checks=py,cpp,js,spellcheck`
Build completed unsuccessfully in 0:00:47
  local time: Mon Nov  3 18:01:21 UTC 2025
  network time: Mon, 03 Nov 2025 18:01:21 GMT

rust-bors · 2025-11-03T20:08:21Z

☀️ Try build successful (CI)
Build commit: 89acb14 (89acb145aa646f0ff9d994a9b762f383b266450d, parent: f5711a55f5d5e2f942057d0f6d648dd2d8b2c37b)

rust-timer · 2025-11-04T11:02:00Z

Finished benchmarking commit (89acb14): comparison URL.

Overall result: ❌ regressions - 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
Regressions ❌ (secondary)	0.2%	[0.2%, 0.3%]	22
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

Results (secondary -3.2%)

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
Improvements ✅ (secondary)	-3.2%	[-4.0%, -2.4%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 474.205s -> 499.227s (5.28%)
Artifact size: 390.90 MiB -> 390.85 MiB (-0.01%)

BoxyUwU added 6 commits October 30, 2025 15:05

non-behaviour changing cleanups

36972bb

remove normalize call

e207940

leak check in Coerce::unify_raw

4706583

This has three main effects: 1. we now leak check for closure->fnptr and fnptr->closure coercions 2. we now leak check normal subtyping in HIR typeck when going through coercions 3. we now leak check normal lubbing when there is no coercion

leak check lub in fndef<->fndef coerce-lubs

58090da

leak check and lub for closure<->closure coerce-lubs

24f1c6a

leak check closure<->fndef and fndef<->closure coerce-lubs

5afeb5e

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 Nov 2, 2025