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Fast path nitpicks #143307

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Miscellaneous commits that I didn't really want to fold into anything else.

Fixes one theoretical bug with the fast path not considering polarity for T: !Sized bounds.
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rustbot commented Jul 2, 2025

r? @SparrowLii

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@rustbot 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 2, 2025
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compiler-errors commented Jul 2, 2025
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compiler/rustc_traits/src/codegen.rs
@@ -34,13 +34,6 @@ pub(crate) fn codegen_select_candidate<'tcx>(
let (infcx, param_env) = tcx.infer_ctxt().ignoring_regions().build_with_typing_env(typing_env);
let mut selcx = SelectionContext::new(&infcx);

if sizedness_fast_path(tcx, trait_ref.upcast(tcx)) {
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@compiler-errors compiler-errors Jul 2, 2025 •
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This function shouldn't ever be reached -- we never do Instance::resolve on Sized.
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@bors2 try @rust-timer queue

r? lcnr perhaps
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rust-bors bot commented Jul 2, 2025

⌛ Trying commit 91c53c9 with merge 227ec3b…

To cancel the try build, run the command @bors2 try cancel.
rust-bors bot added a commit that referenced this pull request Jul 2, 2025
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Auto merge of #143307 - compiler-errors:fast-path-nitpicks, r=<try>
227ec3b 
Fast path nitpicks

Miscellaneous commits that I didn't really want to fold into anything else.

Fixes one theoretical bug with the fast path not considering polarity for `T: !Sized` bounds.
@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 2, 2025
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rust-bors bot commented Jul 2, 2025

☀️ Try build successful (CI)
Build commit: 227ec3b (227ec3b415808af85fe11410d8e1b4d8349c32bc, parent: 71e4c005caa812a16fcb08d0bf1e6f1eda7c8381)
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lcnr
lcnr reviewed Jul 3, 2025
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compiler/rustc_trait_selection/src/traits/util.rs
predicate.kind().skip_binder()
&& trait_pred.polarity == ty::PredicatePolarity::Positive
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this has happened multiple times by now 🤔 forgetting the polarity is too damn easy right now 🤔

I can't really think of a good alternative apart from actually splitting ClauseKind::Trait and ClauseKind::NegTrait 🤔

removing the def_id etc functions on TraitPredicate to require trait_pred.trait_ref.def_id() instead feels really cumbersome and not that helpful 🤔 changing ClauseKind::Trait to have TraitRef and Polarity as separate fields so that we always have to use (_, _) could work but feels really ugly

anyways, not part of this PR
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lcnr commented Jul 3, 2025

@rust-timer build 227ec3b
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lcnr commented Jul 3, 2025

r=me after getting perf to work ☠️
@lcnr 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 3, 2025
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Finished benchmarking commit (227ec3b): comparison URL.

Overall result: ✅ 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
Improvements ✅
(primary)		 -0.2% [-0.2%, -0.2%] 2
Improvements ✅
(secondary)		 - - 0
All ❌✅ (primary) -0.2% [-0.2%, -0.2%] 2

Max RSS (memory usage)

Results (primary -2.1%, secondary -2.0%)

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)		 -2.1% [-2.6%, -1.7%] 2
Improvements ✅
(secondary)		 -2.0% [-2.6%, -1.3%] 2
All ❌✅ (primary) -2.1% [-2.6%, -1.7%] 2

Cycles

Results (primary 0.3%, secondary 0.3%)

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

mean range count
Regressions ❌
(primary)		 1.7% [1.5%, 1.9%] 2
Regressions ❌
(secondary)		 1.6% [0.6%, 2.5%] 2
Improvements ✅
(primary)		 -1.0% [-1.1%, -1.0%] 2
Improvements ✅
(secondary)		 -2.1% [-2.1%, -2.1%] 1
All ❌✅ (primary) 0.3% [-1.1%, 1.9%] 4

Binary size

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

Bootstrap: 463.343s -> 462.134s (-0.26%)
Artifact size: 372.24 MiB -> 372.24 MiB (-0.00%)
@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 3, 2025
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lcnr commented Jul 3, 2025

@bors r+
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bors commented Jul 3, 2025

📌 Commit 91c53c9 has been approved by lcnr

It is now in the queue for this repository.
@bors 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 3, 2025
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@bors rollup
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