[adwinwhite]

Fix the perf regression in #165335 by moving the fast path back to its previous place.

r? ghost

[adwinwhite]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 970c744 (970c744f1c28668c10069e0a887fce999438f689)
Base parent: ba58c66 (ba58c66e24c2770ae5c820f67549eadd346e9d9e)

[rust-timer]

Finished benchmarking commit (970c744): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

@bors rollup=never rustc-perf
@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)	-1.0%	[-3.4%, -0.2%]	120
Improvements ✅ (secondary)	-1.3%	[-4.0%, -0.2%]	132
All ❌✅ (primary)	-1.0%	[-3.4%, -0.2%]	120

Max RSS (memory usage)

This perf run didn't have relevant results for this metric.

Cycles

Results (primary -3.0%, secondary -2.5%)

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)	3.3%	[2.4%, 4.8%]	5
Improvements ✅ (primary)	-3.0%	[-4.2%, -2.1%]	12
Improvements ✅ (secondary)	-3.8%	[-5.4%, -2.6%]	23
All ❌✅ (primary)	-3.0%	[-4.2%, -2.1%]	12

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 484.686s -> 489.293s (0.95%)
Artifact size: 406.15 MiB -> 406.24 MiB (0.02%)

[jdonszelmann]

That seems to do it. Sorry for the regression! r? me

[jdonszelmann]

@bors r+ rollup=iffy perf

[rust-bors]

📌 Commit 2ea7e03 has been approved by jdonszelmann

It is now in the queue for this repository.

[JonathanBrouwer]

@bors rollup=never

[rustbot]

beta backport approved as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle. Backport labels are handled by them.

[rust-bors]

☀️ Test successful - CI
Approved by: jdonszelmann
Duration: 3h 5m 10s
Pushing fefe61b to main...

[github-actions]

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 495625e (parent) -> fefe61b (this PR)

Test differences

Show 3 test diffs

3 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 fefe61bee03e8d6ff1f3f16bcedc8cb05e3f7bf3 --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

1. test-x86_64-mingw-2: 1h 39m -> 2h 48m (+69.6%)
2. test-i686-msvc: 1h 51m -> 3h 1m (+62.1%)
3. dist-aarch64-apple: 1h 34m -> 2h 31m (+59.7%)
4. dist-x86_64-freebsd: 58m 19s -> 1h 33m (+59.6%)
5. test-x86_64-gnu-llvm-22-2: 1h 16m -> 1h 52m (+47.6%)
6. test-i686-gnu-nopt-1: 1h 39m -> 2h 25m (+45.8%)
7. test-i686-gnu-nopt-2: 2h 31m -> 1h 23m (-44.9%)
8. dist-powerpc-linux: 1h 7m -> 1h 36m (+42.8%)
9. test-x86_64-gnu-llvm-22: 41m 3s -> 58m 4s (+41.5%)
10. test-x86_64-gnu-stdlib-semver-check: 17m 12s -> 10m 13s (-40.6%)

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]

Finished benchmarking commit (fefe61b): 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)	-1.1%	[-3.4%, -0.2%]	115
Improvements ✅ (secondary)	-1.4%	[-3.9%, -0.2%]	128
All ❌✅ (primary)	-1.1%	[-3.4%, -0.2%]	115

Max RSS (memory usage)

This perf run didn't have relevant results for this metric.

Cycles

Results (primary -2.9%, secondary -3.5%)

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)	-2.9%	[-4.1%, -1.6%]	9
Improvements ✅ (secondary)	-3.5%	[-4.5%, -2.1%]	22
All ❌✅ (primary)	-2.9%	[-4.1%, -1.6%]	9

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 482.583s -> 483.426s (0.17%)
Artifact size: 406.20 MiB -> 406.20 MiB (-0.00%)

[cuviper]

It didn't actually reach beta: #165335 (comment)

@rustbot label -beta-nominated -beta-accepted