v0 mangling for std on nightly #149148

davidtwco · 2025-11-20T14:55:57Z

Following #89917 and rust-lang/compiler-team#938, it doesn't make sense that std for these channels would have legacy mangling while the user's code would use v0.

r? @Kobzol

rustbot · 2025-11-20T14:56:02Z

Kobzol is not on the review rotation at the moment.
They may take a while to respond.

Kobzol · 2025-11-20T15:50:25Z

Makes sense, thanks! Prioritizing slightly since it still might get into today's nightly (although I worry some tests might fail..).

@bors r+ p=1

bors · 2025-11-20T15:50:28Z

📌 Commit 5e4a05f has been approved by Kobzol

It is now in the queue for this repository.

v0 mangling for std on nightly Following #89917 and rust-lang/compiler-team#938, it doesn't make sense that `std` for these channels would have legacy mangling while the user's code would use `v0`. r? `@Kobzol`

bors · 2025-11-20T16:41:10Z

⌛ Testing commit 5e4a05f with merge 06596c0...

bors · 2025-11-20T17:36:27Z

💔 Test failed - checks-actions

Kobzol · 2025-11-21T11:44:14Z

Let's perf this in the meantime.

@bors try @rust-timer queue

v0 mangling for std on nightly

rust-bors · 2025-11-21T14:00:47Z

☀️ Try build successful (CI)
Build commit: 70ed8a5 (70ed8a5c71bbc001f48c2ff53905d9ba4b418d22, parent: e22dab387f6b4f6a87dfc54ac2f6013dddb41e68)

rust-timer · 2025-11-21T15:54:16Z

Finished benchmarking commit (70ed8a5): 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)	0.8%	[0.7%, 0.8%]	4
Regressions ❌ (secondary)	0.5%	[0.3%, 0.8%]	15
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[0.7%, 0.8%]	4

Max RSS (memory usage)

Results (secondary 0.9%)

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)	0.9%	[0.9%, 0.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -2.3%, secondary -6.0%)

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)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-6.0%	[-6.0%, -6.0%]	1
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Binary size

Results (primary 1.2%, secondary 5.1%)

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

	mean	range	count
Regressions ❌ (primary)	3.0%	[0.5%, 10.5%]	35
Regressions ❌ (secondary)	6.2%	[0.0%, 10.5%]	90
Improvements ✅ (primary)	-0.0%	[-0.1%, -0.0%]	47
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	20
All ❌✅ (primary)	1.2%	[-0.1%, 10.5%]	82

Bootstrap: 473.456s -> 472.364s (-0.23%)
Artifact size: 388.90 MiB -> 389.49 MiB (0.15%)

Kobzol · 2025-11-21T16:03:33Z

3% larger stdlib. Slightly annoying, but not a big deal, I think. #145343 might reduce that size considerably, once I can finally get back to it someday.. :D

…td, r=Kobzol v0 mangling for std on nightly Following rust-lang#89917 and rust-lang/compiler-team#938, it doesn't make sense that `std` for these channels would have legacy mangling while the user's code would use `v0`. r? `@Kobzol`

rustbot · 2025-11-24T16:06:55Z

Some changes occurred in tests/ui/sanitizer

cc @rcvalle

davidtwco · 2025-11-24T17:01:50Z

I've checked on an x86 machine with sanitizers that the change to the dataflow-abilist.txt fixes the test.

davidtwco · 2025-11-25T09:27:27Z

@bors r=Kobzol

bors · 2025-11-25T09:27:30Z

📌 Commit 62c5ea6 has been approved by Kobzol

It is now in the queue for this repository.

bors · 2025-11-25T10:25:50Z

⌛ Testing commit 62c5ea6 with merge 7934bbd...

bors · 2025-11-25T13:39:09Z

☀️ Test successful - checks-actions
Approved by: Kobzol
Pushing 7934bbd to main...

github-actions · 2025-11-25T13:42:08Z

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 cdb4236 (parent) -> 7934bbd (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 7934bbdf84a6b9a30297caf4f4f38286dedf876a --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

dist-x86_64-apple: 6997.7s -> 10608.5s (+51.6%)
dist-apple-various: 4070.0s -> 5016.8s (+23.3%)
dist-aarch64-apple: 6285.2s -> 7715.5s (+22.8%)
i686-gnu-nopt-1: 8104.9s -> 6754.9s (-16.7%)
pr-check-1: 1935.7s -> 1654.6s (-14.5%)
x86_64-rust-for-linux: 3034.5s -> 2644.8s (-12.8%)
i686-gnu-2: 6192.7s -> 5428.4s (-12.3%)
tidy: 142.8s -> 160.1s (+12.1%)
x86_64-gnu-llvm-20: 2782.2s -> 2448.1s (-12.0%)
test-various: 6851.7s -> 6098.7s (-11.0%)

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 · 2025-11-25T14:58:53Z

Finished benchmarking commit (7934bbd): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

If the regression was expected or you think it can be justified,
please write a comment with sufficient written justification, and add
@rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
If you think that you know of a way to resolve the regression, try to create
a new PR with a fix for the regression.
If you do not understand the regression or you think that it is just noise,
you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.8%	[0.6%, 0.8%]	5
Regressions ❌ (secondary)	0.5%	[0.0%, 0.9%]	23
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-1.1%, -0.1%]	5
All ❌✅ (primary)	0.8%	[0.6%, 0.8%]	5

Max RSS (memory usage)

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)	1.6%	[0.9%, 2.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.1%	[-6.6%, -2.0%]	9
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 4.1%)

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)	5.7%	[2.2%, 9.5%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.6%	[-5.6%, -5.6%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 2.3%, secondary 5.4%)

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

	mean	range	count
Regressions ❌ (primary)	3.0%	[0.5%, 10.5%]	35
Regressions ❌ (secondary)	6.2%	[0.0%, 10.4%]	90
Improvements ✅ (primary)	-0.0%	[-0.0%, -0.0%]	9
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	13
All ❌✅ (primary)	2.3%	[-0.0%, 10.5%]	44

Bootstrap: 471.494s -> 472.579s (0.23%)
Artifact size: 388.26 MiB -> 386.92 MiB (-0.35%)

Kobzol · 2025-11-25T15:32:39Z

Binary size regressions caused by longer v0 symbols, that is expected. The small regressions on helloworld most likely (as is usual) due to the larger binary size of the programs being loaded.

This makes the release helloworld binary almost 20 KiB larger :(

@rustbot label: +perf-regression-triaged

rustbot assigned Kobzol Nov 20, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Nov 20, 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 Nov 20, 2025

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rust-bors bot added a commit that referenced this pull request Nov 21, 2025

Auto merge of #149148 - davidtwco:v0-mangling-on-nightly-std, r=<try>

70ed8a5

v0 mangling for std on nightly

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 21, 2025

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Nov 21, 2025

v0 mangling for std on nightly

62c5ea6

davidtwco force-pushed the v0-mangling-on-nightly-std branch from 5e4a05f to 62c5ea6 Compare November 24, 2025 16:06

rustbot added the PG-exploit-mitigations Project group: Exploit mitigations label Nov 24, 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 Nov 25, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 25, 2025

bors merged commit 7934bbd into rust-lang:main Nov 25, 2025
12 checks passed

rustbot added this to the 1.93.0 milestone Nov 25, 2025

davidtwco deleted the v0-mangling-on-nightly-std branch November 25, 2025 13:55

rustbot added the perf-regression-triaged The performance regression has been triaged. label Nov 25, 2025

v0 mangling for std on nightly #149148

v0 mangling for std on nightly #149148

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Overall result: ❌ regressions - please read the text below

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Test differences

Job duration changes

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Overall result: ❌✅ regressions and improvements - please read the text below

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