Also hash spans inside the same file as relative (V2) #150540

JonathanBrouwer · 2025-12-31T13:10:13Z

Hashes spans relatively to their parent, even if they are not contained inside their parent.

Closes #143882, as this is a successor PR
This PR is very closely based on that PR with a few minor changes, so to give proper credit I made @cjgillot coauthor of the commit.

JonathanBrouwer · 2025-12-31T13:14:47Z

@bors try @rust-timer queue

Improve relative hashing of spans

JonathanBrouwer · 2025-12-31T13:56:38Z

@bors try cancel

rust-bors · 2025-12-31T13:56:42Z

Try build cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/20619740301

Improve relative hashing of spans

JonathanBrouwer · 2026-01-01T15:13:22Z

@bors try @rust-timer queue

Improve relative hashing of spans

rust-bors · 2026-01-01T17:35:46Z

☀️ Try build successful (CI)
Build commit: 5702844 (570284477cc4354ae13d7effa889ba163bdab31f, parent: cc08b553b899821331ddbfb970e243a7dd0957a3)

rust-timer · 2026-01-01T18:16:36Z

Finished benchmarking commit (5702844): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	0.2%	[0.1%, 0.4%]	9
Regressions ❌ (secondary)	0.4%	[0.0%, 0.7%]	19
Improvements ✅ (primary)	-1.6%	[-6.5%, -0.1%]	13
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.1%]	6
All ❌✅ (primary)	-0.8%	[-6.5%, 0.4%]	22

Max RSS (memory usage)

Results (primary -0.1%)

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

	mean	range	count
Regressions ❌ (primary)	1.4%	[1.4%, 1.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-0.9%, 1.4%]	3

Cycles

Results (primary 4.7%, secondary 18.3%)

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

	mean	range	count
Regressions ❌ (primary)	8.9%	[3.4%, 13.1%]	9
Regressions ❌ (secondary)	20.6%	[11.9%, 32.3%]	10
Improvements ✅ (primary)	-4.8%	[-6.4%, -1.7%]	4
Improvements ✅ (secondary)	-3.8%	[-3.8%, -3.8%]	1
All ❌✅ (primary)	4.7%	[-6.4%, 13.1%]	13

Binary size

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

Bootstrap: 475.256s -> 475.638s (0.08%)
Artifact size: 390.83 MiB -> 390.83 MiB (0.00%)

JonathanBrouwer · 2026-01-01T18:25:53Z

That's a funny race condition in rustbot, fixed it manually :)

Kobzol · 2026-01-02T16:44:45Z

@bors try @rust-timer queue

The cycle results looked quite weird, rerunning to see if it was noise or not.

Also hash spans inside the same file as relative (V2)

rust-bors · 2026-01-02T19:07:25Z

☀️ Try build successful (CI)
Build commit: 5b25251 (5b25251e673dbd33683e6317e1a307bbc1b74e30, parent: 8a24a202aa02f677fc2a3e0e1a69af7545803952)

rust-timer · 2026-01-02T19:52:45Z

Finished benchmarking commit (5b25251): comparison URL.

Overall result: ❌✅ regressions and improvements - 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)	0.2%	[0.1%, 0.4%]	14
Regressions ❌ (secondary)	0.4%	[0.1%, 0.7%]	16
Improvements ✅ (primary)	-1.6%	[-6.5%, -0.2%]	13
Improvements ✅ (secondary)	-0.2%	[-0.4%, -0.1%]	12
All ❌✅ (primary)	-0.7%	[-6.5%, 0.4%]	27

Max RSS (memory usage)

Results (secondary -3.9%)

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
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.9%	[-6.3%, -2.1%]	5
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -4.9%, secondary 5.2%)

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)	5.2%	[5.2%, 5.2%]	1
Improvements ✅ (primary)	-4.9%	[-5.2%, -4.5%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-4.9%	[-5.2%, -4.5%]	3

Binary size

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

Bootstrap: 473.485s -> 472.607s (-0.19%)
Artifact size: 390.77 MiB -> 390.79 MiB (0.01%)

JonathanBrouwer · 2026-01-02T20:24:57Z

The cycles look better this time I think, so was spurious :)

cjgillot · 2026-01-07T22:58:21Z

This PR is very closely based on that PR with a few minor changes, so to give proper credit I made @cjgillot coauthor of the commit.

Do you mind explaining what are those minor changes?
Thank you for the co-author courtesy :)

compiler/rustc_span/src/lib.rs

Co-authored-by: Camille Gillot <gillot.camille@gmail.com>

JonathanBrouwer

@cjgillot Yes ofc, should've explained the changes, sorry :)
Explained the changes in some comments on the code

View changes since this review

JonathanBrouwer · 2026-01-08T20:28:10Z

compiler/rustc_middle/src/query/on_disk_cache.rs

+        if let Some(parent) = parent
+            && file_lo.contains(parent.lo)
+        {
+            TAG_RELATIVE_SPAN.encode(self);


Your PR introduces a new TAG_RELATIVE_OUTER_SPAN tag here for encoding spans which are outside their parent span, this PR instead reuses the TAG_RELATIVE_SPAN tag. This can be done by encoding the positions in the span (which are u32s) subtracted from their parent, wrapping if necessary. This change seems to be most of the performance gained relative to your PR.

JonathanBrouwer · 2026-01-08T20:29:03Z

compiler/rustc_span/src/lib.rs

+            // This span is relative to another span in the same file,
+            // only hash the relative position.
+            Hash::hash(&TAG_RELATIVE_SPAN, hasher);
+            Hash::hash(&(span.lo.0.wrapping_sub(parent.lo.0)), hasher);


When hashing, your PR hashes an isize here, this PR instead hashes a u32 by using a wrapping_sub. Haven't explored if this makes any perf difference

JonathanBrouwer · 2026-01-08T20:30:21Z

compiler/rustc_span/src/lib.rs

+
        Hash::hash(&TAG_VALID_SPAN, hasher);
-        Hash::hash(&file, hasher);
+        Hash::hash(&file.stable_id, hasher);


Your PR hashed the TAG_VALID_SPAN and stable_id if file.contains(parent.lo), this PR doesn't. Again, Haven't explored if this makes any perf difference

cjgillot · 2026-01-10T14:19:17Z

Great! I agree, we did not need to make much more of a difference in hashing and encoding between the "contained in parent span" and the "in same file" cases.

@bors r+ rollup=never

rust-bors · 2026-01-10T14:19:21Z

📌 Commit dc505a5 has been approved by cjgillot

It is now in the queue for this repository.

Zalathar · 2026-01-11T08:30:59Z

Scheduling: Encourage a mixture of rollup and non-rollup PRs.

@bors p=5

rust-bors · 2026-01-11T12:16:02Z

☀️ Test successful - CI
Approved by: cjgillot
Pushing 08f833a to main...

github-actions · 2026-01-11T12:18:44Z

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 9bc8b40 (parent) -> 08f833a (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 08f833aa179952037d5d0c5d949d4c3ec18ec212 --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

aarch64-apple: 10551.8s -> 8759.5s (-17.0%)
x86_64-gnu-llvm-20-2: 5055.0s -> 5900.1s (+16.7%)
x86_64-gnu-tools: 3274.3s -> 3777.4s (+15.4%)
pr-check-1: 1687.3s -> 1937.2s (+14.8%)
x86_64-gnu-gcc: 3291.1s -> 3775.8s (+14.7%)
x86_64-rust-for-linux: 2770.2s -> 3176.5s (+14.7%)
aarch64-gnu-llvm-20-2: 2769.2s -> 3151.9s (+13.8%)
arm-android: 5733.4s -> 6513.6s (+13.6%)
pr-check-2: 2356.1s -> 2637.1s (+11.9%)
aarch64-gnu-debug: 3868.3s -> 4309.3s (+11.4%)

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 · 2026-01-11T12:58:03Z

Finished benchmarking commit (08f833a): 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)	0.3%	[0.1%, 0.4%]	6
Regressions ❌ (secondary)	0.3%	[0.1%, 0.7%]	27
Improvements ✅ (primary)	-1.2%	[-6.5%, -0.2%]	20
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	8
All ❌✅ (primary)	-0.9%	[-6.5%, 0.4%]	26

Max RSS (memory usage)

Results (secondary -2.4%)

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)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -3.2%, 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)	2.6%	[2.6%, 2.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-5.1%	[-5.8%, -3.9%]	3
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-3.2%	[-5.8%, 2.6%]	4

Binary size

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

Bootstrap: 473.122s -> 474.227s (0.23%)
Artifact size: 391.33 MiB -> 391.32 MiB (-0.00%)

JonathanBrouwer · 2026-01-11T13:00:38Z

@rustbot label: +perf-regression-triaged
Matches the expected performance, net positive

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rust-bors bot added a commit that referenced this pull request Dec 31, 2025

Auto merge of #150540 - JonathanBrouwer:incremental_test, r=<try>

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Improve relative hashing of spans

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Auto merge of #150540 - JonathanBrouwer:incremental_test, r=<try>

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Improve relative hashing of spans

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JonathanBrouwer force-pushed the incremental_test branch from 5a3b9bc to 3730e30 Compare January 1, 2026 15:13

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Auto merge of #150540 - JonathanBrouwer:incremental_test, r=<try>

5702844

Improve relative hashing of spans

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Auto merge of #150540 - JonathanBrouwer:incremental_test, r=<try>

5b25251

Also hash spans inside the same file as relative (V2)

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cjgillot reviewed Jan 7, 2026

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compiler/rustc_span/src/lib.rs Outdated Show resolved Hide resolved

Hash all spans relatively to their parent

dc505a5

Co-authored-by: Camille Gillot <gillot.camille@gmail.com>

JonathanBrouwer force-pushed the incremental_test branch from 4ce96aa to dc505a5 Compare January 8, 2026 20:20

JonathanBrouwer commented Jan 8, 2026

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rust-bors bot added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Jan 10, 2026

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rust-bors bot added the merged-by-bors This PR was explicitly merged by bors. label Jan 11, 2026

rust-bors bot merged commit 08f833a into rust-lang:main Jan 11, 2026
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rustbot added this to the 1.94.0 milestone Jan 11, 2026

rustbot added the perf-regression-triaged The performance regression has been triaged. label Jan 11, 2026

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Also hash spans inside the same file as relative (V2) #150540

Also hash spans inside the same file as relative (V2) #150540

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

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

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Test differences

Job duration changes

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rust-timer commented Jan 11, 2026

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

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