Perf regression fix

[Kivooeo]

The only thing changed from the previous PR is that I removed output_is_inhabited from hot path, and hide it behind condition, so now it will compute it less frequent

follow up on #149664

[Kivooeo]

@rust-timer build 9124eca

[Kivooeo]

@Kobzol how do i run this

[Kobzol]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 48c5d38 (48c5d3879672c42316e3b17a082885381ab2cfb9, parent: 95a27adcf907bcc1046602c3746dad8cfdf3bf3f)

[rust-timer]

Finished benchmarking commit (48c5d38): 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%	[-0.3%, -0.2%]	19
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.2%]	12
All ❌✅ (primary)	-0.2%	[-0.3%, -0.2%]	19

Max RSS (memory usage)

Results (primary 2.1%, secondary 2.2%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.1%	[2.1%, 2.1%]	1

Cycles

Results (secondary -2.7%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-2.9%, -2.5%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 479.485s -> 478.535s (-0.20%)
Artifact size: 390.32 MiB -> 390.28 MiB (-0.01%)

[Kivooeo]

hm, wait how do I even understand if perf is fine? is there a way to check perf between two commits? I believe there's been a numerous amount of changes in this period of time that affects a bootstrap time

but on the other hand it's not a 5 second reduce, not sure how to interpret this results

[Kobzol]

Bootstrap time is not super important here, I would say. Based on the icount results, it looks like this change does indeed fix the regression!

[rustbot]

r? @SparrowLii

rustbot has assigned @SparrowLii.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[Kivooeo]

r? @davidtwco

[Kivooeo]

Based on the icount results, it looks like this change does indeed fix the regression!

Ah, thanks for the clarification!

[Kivooeo]

I want to try different approach, should be even better, do I need to rerun bors try before next perf run?

[Kobzol]

Yes, rustc-perf always benchmarks the result of the try build :)

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: da3c48f (da3c48f3bacfa34354f911642899ba5eb24ea620, parent: 31010ca61c3ff019e1480dda0a7ef16bd2bd51c0)

[rust-timer]

Finished benchmarking commit (da3c48f): 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%	[-0.3%, -0.2%]	18
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.2%]	10
All ❌✅ (primary)	-0.2%	[-0.3%, -0.2%]	18

Max RSS (memory usage)

Results (primary 2.0%, 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)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	4.3%	[4.3%, 4.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.0%, -2.3%]	2
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Cycles

Results (secondary 3.1%)

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%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 479.038s -> 478.549s (-0.10%)
Artifact size: 390.32 MiB -> 390.27 MiB (-0.01%)

[Kivooeo]

looks slightly better right?

[Kobzol]

Looks pretty much the same to me.

[Kivooeo]

Nominate this to beta backport as was discussed on todays triage meeting because it's a follow up on a beta accepted PR

@rustbot label +beta-nominated

[davidtwco]

@bors r+

[bors]

📌 Commit fc0d01b has been approved by davidtwco

It is now in the queue for this repository.

[bors]

⌛ Testing commit fc0d01b with merge 806c2a3...

[bors]

☀️ Test successful - checks-actions
Approved by: davidtwco
Pushing 806c2a3 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 b889870 (parent) -> 806c2a3 (this PR)

Test differences

Show 2 test diffs

2 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 806c2a35dcc1db7867864fea0a7a65554a5238b7 --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. aarch64-apple: 11536.2s -> 9361.6s (-18.9%)
2. pr-check-1: 1913.0s -> 1559.0s (-18.5%)
3. x86_64-gnu-miri: 4858.9s -> 4149.4s (-14.6%)
4. x86_64-gnu-tools: 3753.8s -> 3258.4s (-13.2%)
5. test-various: 7619.6s -> 6635.9s (-12.9%)
6. x86_64-gnu-llvm-21-3: 7077.5s -> 6224.2s (-12.1%)
7. i686-gnu-2: 6017.0s -> 5310.1s (-11.7%)
8. i686-gnu-1: 8459.0s -> 7480.3s (-11.6%)
9. dist-powerpc64-linux: 5940.8s -> 5281.5s (-11.1%)
10. dist-x86_64-apple: 7408.8s -> 8153.6s (+10.1%)

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 (806c2a3): 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)	-0.2%	[-0.3%, -0.2%]	18
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.1%]	12
All ❌✅ (primary)	-0.2%	[-0.3%, -0.2%]	18

Max RSS (memory usage)

Results (primary -3.5%, secondary 1.6%)

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)	1.6%	[0.9%, 2.2%]	2
Improvements ✅ (primary)	-3.5%	[-6.5%, -1.5%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.5%	[-6.5%, -1.5%]	3

Cycles

Results (primary 6.7%, secondary 4.7%)

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

	mean	range	count
Regressions ❌ (primary)	6.7%	[2.2%, 18.8%]	7
Regressions ❌ (secondary)	4.7%	[2.1%, 9.7%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	6.7%	[2.2%, 18.8%]	7

Binary size

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

Bootstrap: 479.396s -> 477.964s (-0.30%)
Artifact size: 390.52 MiB -> 390.53 MiB (0.00%)

[apiraino]

Beta backport declined as per compiler team on Zulip. The advantages are thin and don't make the backport a compelling choice.

@rustbot label -beta-nominated