Fix non-deterministic encoding of syntax contexts by aerooneqq · Pull Request #161450 · rust-lang/rust

aerooneqq · 2026-08-21T10:20:19Z

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Reiteration of #157409. Explanation can be found in comment for encoding_indices and in the issue.

Fixes #129094. Blocked by #161353.

r? @petrochenkov

No llms used.

petrochenkov · 2026-09-03T12:23:21Z

@bors try @rust-timer queue

…ing, r=<try> Fix non-deterministic encoding of syntax contexts

rust-bors · 2026-09-03T13:23:29Z

☀️ Try build successful (CI)
Build commit: 7e01adf (7e01adfdd3209974b2d32d2eb35d4173deaa540b)
Base parent: 4fcf397 (4fcf39725a9c99bd495d8c73af83628a256ff9a9)

rust-timer · 2026-09-03T14:14:37Z

Finished benchmarking commit (7e01adf): comparison URL.

Overall result: ❌ regressions - please read:

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.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.6%	[0.1%, 1.9%]	72
Regressions ❌ (secondary)	0.6%	[0.1%, 1.7%]	50
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[0.1%, 1.9%]	72

Max RSS (memory usage)

Results (primary 1.0%, 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)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	3.7%	[2.6%, 4.9%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.7%	[-4.6%, -1.4%]	5
All ❌✅ (primary)	1.0%	[1.0%, 1.0%]	1

Cycles

Results (primary -0.2%, secondary 4.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	4.5%	[4.5%, 4.5%]	1
Improvements ✅ (primary)	-2.7%	[-2.7%, -2.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-2.7%, 2.3%]	2

Binary size

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

Bootstrap: 476.065s -> 474.462s (-0.34%)
Artifact size: 401.18 MiB -> 401.32 MiB (0.03%)

rust-timer · 2026-09-14T11:48:55Z

Finished benchmarking commit (75e938b): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

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.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.1%	[0.1%, 0.1%]	1
Regressions ❌ (secondary)	0.4%	[0.3%, 0.5%]	4
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.2%]	4
All ❌✅ (primary)	-0.0%	[-0.2%, 0.1%]	2

Max RSS (memory usage)

Results (primary -1.2%, 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)	3.9%	[3.0%, 4.9%]	3
Improvements ✅ (primary)	-1.2%	[-1.8%, -0.6%]	2
Improvements ✅ (secondary)	-3.9%	[-8.1%, -1.6%]	5
All ❌✅ (primary)	-1.2%	[-1.8%, -0.6%]	2

Cycles

Results (primary -1.2%)

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

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.2%	[-3.1%, 0.6%]	2

Binary size

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

Bootstrap: 498.957s -> 493.438s (-1.11%)
Artifact size: 406.94 MiB -> 406.96 MiB (0.00%)

aerooneqq · 2026-09-15T11:47:22Z

@rustbot ready

petrochenkov · 2026-09-15T13:11:52Z

r=me with the nits addressed.
@bors delegate+
@rustbot author

rust-bors · 2026-09-15T13:11:55Z

✌️ @aerooneqq, you can now approve this pull request!

If @petrochenkov told you to "r=me" after making some further change, then please make that change and post @bors r=petrochenkov.

View changes since this delegation.

rustbot · 2026-09-15T13:11:56Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

aerooneqq · 2026-09-15T16:07:20Z

@bors r=petrochenkov

rust-bors · 2026-09-15T16:07:22Z

📌 Commit 2e35677 has been approved by petrochenkov

It is now in the queue for this repository.

JonathanBrouwer · 2026-09-15T21:27:07Z

@bors p=6 scheduling

rust-bors · 2026-09-16T01:22:01Z

☀️ Test successful - CI
Approved by: petrochenkov
Duration: 3h 9m 26s
Pushing 2b9a7be to main...

github-actions · 2026-09-16T01:25:32Z

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 215a8af (parent) -> 2b9a7be (this PR)

Test differences

Show 22 test diffs

22 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 2b9a7be8551a6497a952d87d7dbf38484e5bfa5a --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

test-x86_64-gnu-gcc-core-tests: 9m 19s -> 17m 48s (+91.1%)
test-x86_64-gnu-llvm-21-3: 1h 26m -> 2h 3m (+42.8%)
test-x86_64-gnu-llvm-21-1: 44m 26s -> 1h 2m (+40.9%)
dist-powerpc64le-linux-musl: 1h 9m -> 1h 36m (+38.3%)
test-x86_64-gnu-nopt: 1h 48m -> 2h 30m (+38.1%)
test-x86_64-gnu-stdlib-semver-check: 11m 18s -> 15m 26s (+36.6%)
test-x86_64-gnu-llvm-21-2: 1h 16m -> 1h 43m (+35.8%)
test-various: 1h 36m -> 2h 10m (+35.8%)
test-pr-check-1: 30m 33s -> 40m 46s (+33.4%)
dist-riscv64-linux-gnu: 1h 32m -> 1h 2m (-32.5%)

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 · 2026-09-16T02:13:25Z

Finished benchmarking commit (2b9a7be): comparison URL.

Overall result: ❌ regressions - please read:

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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	0.5%	[0.3%, 0.6%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Max RSS (memory usage)

Results (primary -1.5%, secondary -2.1%)

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)	3.5%	[2.1%, 5.5%]	3
Improvements ✅ (primary)	-1.5%	[-2.7%, -0.7%]	6
Improvements ✅ (secondary)	-5.5%	[-8.3%, -2.1%]	5
All ❌✅ (primary)	-1.5%	[-2.7%, -0.7%]	6

Cycles

Results (primary -3.0%, secondary 5.9%)

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)	5.9%	[5.9%, 5.9%]	1
Improvements ✅ (primary)	-3.0%	[-3.0%, -3.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.0%	[-3.0%, -3.0%]	1

Binary size

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

Bootstrap: 498.703s -> 496.542s (-0.43%)
Artifact size: 406.94 MiB -> 406.87 MiB (-0.02%)

HygieneEncodeContext::encode walks a hash set while it writes the syntax context and expansion records into the rmeta, so the byte order of the records follows the iteration order of the set and differs between builds on the arm workers. The added patch sorts both sets before they are written. Upstream tracks this as rust-lang/rust issue 129094 [1] and has fixed it differently in pull request 161450 [2], merged after 1.99 branched. That change is too big to backport to 1.98 safely, so carry this small sort until a rust upgrade contains it. [1] rust-lang/rust#129094 [2] rust-lang/rust#161450 [YOCTO #16376] Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org> Signed-off-by: Sunil Dora <sunilkumar.dora@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 21, 2026

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aerooneqq force-pushed the syntax-ctxt-non-deterministic-encoding branch from b07d315 to 3f750ec Compare August 21, 2026 10:33

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aerooneqq force-pushed the syntax-ctxt-non-deterministic-encoding branch 3 times, most recently from 494d4da to 5fa08c7 Compare August 21, 2026 14:13

aerooneqq mentioned this pull request Aug 25, 2026

Output deterministic AllocIds when emitting MIR #161768

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petrochenkov mentioned this pull request Sep 1, 2026

rustc: Support --reproducible option for requesting reproducible output #160448

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aerooneqq force-pushed the syntax-ctxt-non-deterministic-encoding branch from a34d24f to 3868148 Compare September 2, 2026 08:27

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petrochenkov mentioned this pull request Sep 2, 2026

Promoting Parallel Front End rust-lang/goals#121

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Comment thread compiler/rustc_span/src/hygiene.rs Outdated

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rust-bors Bot pushed a commit that referenced this pull request Sep 3, 2026

Auto merge of #161450 - aerooneqq:syntax-ctxt-non-deterministic-encod…

7e01adf

…ing, r=<try> Fix non-deterministic encoding of syntax contexts

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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 Sep 3, 2026

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aerooneqq force-pushed the syntax-ctxt-non-deterministic-encoding branch from 3868148 to 4846400 Compare September 7, 2026 09:48

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Comment thread compiler/rustc_span/src/hygiene.rs Outdated

Comment thread compiler/rustc_span/src/hygiene.rs Outdated

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Fix non-deterministic encoding of syntax contexts

2e35677

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rust-bors Bot added merged-by-bors This PR was explicitly merged by bors. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 16, 2026

rust-bors Bot merged commit 2b9a7be into rust-lang:main Sep 16, 2026
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rust-timer commented Sep 3, 2026

Overall result: ❌ regressions - please read:

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rust-timer commented Sep 14, 2026

Overall result: ❌✅ regressions and improvements - please read:

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Test differences

Job duration changes

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rust-timer commented Sep 16, 2026

Overall result: ❌ regressions - please read:

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