Skip walking into param-env component if it has no placeholder/re-var #143500

compiler-errors · 2025-07-05T18:40:27Z

Although it only provides a minor perf improvement, it seems like it could matter in more pathological cases.

…/re-var

compiler-errors · 2025-07-05T18:40:34Z

@bors2 try @rust-timer queue

rust-bors · 2025-07-05T18:40:37Z

⌛ Trying commit e13757e with merge e3ecd5f…

To cancel the try build, run the command @bors2 try cancel.

[perf] Skip walking into param-env component if it has no placeholder/re-var

rust-bors · 2025-07-05T20:56:40Z

☀️ Try build successful (CI)
Build commit: e3ecd5f (e3ecd5f5fd02f50bc278c1f0cd5b4dbd9e07242a, parent: 6dec76f1c2809fded082dd44d3752d3f6220d767)

rust-timer · 2025-07-05T23:21:05Z

Finished benchmarking commit (e3ecd5f): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

Results (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)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 461.008s -> 461.232s (0.05%)
Artifact size: 372.14 MiB -> 372.18 MiB (0.01%)

compiler-errors · 2025-07-06T00:16:33Z

r? lcnr

lcnr · 2025-07-07T08:58:08Z

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

                ControlFlow::Continue(())
            }
-        } else {
+        } else if ty.has_type_flags(TypeFlags::HAS_PLACEHOLDER | TypeFlags::HAS_RE_INFER) {


why only RE_INFER instead of full infer?

bc we only care about infer regions in this folder's logic -- it would not even be necessary if we didn't replace free regions with infer

why would we care about ty/ct infer for this folder anyways? 🤔

we only care as in: there should never be infer types/consts in the param_env 😁 if we end up with a ty var for whatever reason, then this folder would start incorrectly treating (): Trait<?x> as global evne though it shouldn't be. It currently detects ambiguous aliases in the env as global

I don't see how that is the case and how this behavior would change with this fast path, given that visit_ty does not care about infer types at all and because structurally_normalize_ty just returns Ok(_) for infer types.

Can you explain in more detail, because I am obviously missing something here?

if you've got u32: Trait<AmbiguousAlias>, structurally normalizing that alias results in Ok(_).

At this point we return ControlFlow::Continue(()), treating this where-bound as global. The fast path doesn't matter here 🤔 I generally feel like the way we're handling ambiguous aliases/ty infer vars here isn't right.

I can't really think of an example where this matters. HAving a TAIT in the where-clauses makes it possible to encounter this in theory, but I can't think of a program where this is matters.

I guess 🤷

lcnr · 2025-07-25T10:17:19Z

@bors r+

bors · 2025-07-25T10:17:22Z

📌 Commit e13757e has been approved by lcnr

It is now in the queue for this repository.

bors · 2025-07-26T16:57:49Z

⌛ Testing commit e13757e with merge ce5fdd7...

bors · 2025-07-26T19:57:54Z

☀️ Test successful - checks-actions
Approved by: lcnr
Pushing ce5fdd7 to master...

github-actions · 2025-07-26T20:01:16Z

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 133798f (parent) -> ce5fdd7 (this PR)

Test differences

Show 8 test diffs

8 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard ce5fdd7d42aba9a2925692e11af2bd39cf37798a --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

x86_64-apple-1: 6290.1s -> 7734.4s (23.0%)
dist-x86_64-apple: 9145.1s -> 7364.4s (-19.5%)
dist-apple-various: 6846.8s -> 5803.0s (-15.2%)
pr-check-2: 2710.7s -> 2445.1s (-9.8%)
arm-android: 6632.2s -> 6062.0s (-8.6%)
aarch64-gnu-debug: 4480.1s -> 4147.5s (-7.4%)
x86_64-gnu-llvm-19-3: 7184.3s -> 6669.5s (-7.2%)
x86_64-gnu-llvm-19: 2948.1s -> 2737.3s (-7.2%)
x86_64-rust-for-linux: 3051.6s -> 2837.7s (-7.0%)
aarch64-gnu-llvm-19-1: 3759.8s -> 3518.1s (-6.4%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

rust-timer · 2025-07-26T21:08:56Z

Finished benchmarking commit (ce5fdd7): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.6%	[-0.6%, -0.5%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -3.2%, secondary -1.0%)

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)	1.0%	[1.0%, 1.0%]	1
Improvements ✅ (primary)	-3.2%	[-3.2%, -3.2%]	1
Improvements ✅ (secondary)	-3.0%	[-3.0%, -3.0%]	1
All ❌✅ (primary)	-3.2%	[-3.2%, -3.2%]	1

Cycles

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

Binary size

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

Bootstrap: 466.195s -> 466.456s (0.06%)
Artifact size: 376.61 MiB -> 376.58 MiB (-0.01%)

[perf] Skip walking into param-env component if it has no placeholder…

e13757e

…/re-var

rustbot added T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. WG-trait-system-refactor The Rustc Trait System Refactor Initiative (-Znext-solver) labels Jul 5, 2025

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rust-bors bot added a commit that referenced this pull request Jul 5, 2025

Auto merge of #143500 - compiler-errors:characterize-less, r=<try>

e3ecd5f

[perf] Skip walking into param-env component if it has no placeholder/re-var

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 5, 2025

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 5, 2025

compiler-errors changed the title ~~[perf] Skip walking into param-env component if it has no placeholder/re-var~~ Skip walking into param-env component if it has no placeholder/re-var Jul 6, 2025

rustbot assigned lcnr Jul 6, 2025

compiler-errors marked this pull request as ready for review July 6, 2025 17:18

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 6, 2025

lcnr reviewed Jul 7, 2025

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lcnr 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 11, 2025

compiler-errors 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 11, 2025

bors 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-review Status: Awaiting review from the assignee but also interested parties. labels Jul 25, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 26, 2025

bors merged commit ce5fdd7 into rust-lang:master Jul 26, 2025
12 checks passed

rustbot added this to the 1.90.0 milestone Jul 26, 2025

lcnr mentioned this pull request Jul 29, 2025

Next-generation trait solver rust-lang/rust-project-goals#113

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Skip walking into param-env component if it has no placeholder/re-var #143500

Skip walking into param-env component if it has no placeholder/re-var #143500

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Overall result: ❌✅ regressions and improvements - no action needed

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Test differences

Job duration changes

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rust-timer commented Jul 26, 2025

Overall result: ✅ improvements - no action needed

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