Remove chunk size from each chunk in `ChunkedBitSet`. by cjgillot · Pull Request #145480 · rust-lang/rust

cjgillot · 2025-08-16T01:52:44Z

Almost all chunks in a ChunkedBitSet have the same constant CHUNK_SIZE, except the last in a bitset which takes the remainder domain_size % CHUNK_SIZE.

r? @ghost for perf

cjgillot · 2025-08-16T01:52:58Z

@bors try @rust-timer queue

Remove chunk size from each chunk in `ChunkedBitSet`.

rust-bors · 2025-08-16T04:05:58Z

☀️ Try build successful (CI)
Build commit: acb05a6 (acb05a6e3a3ea9007fbe164aa0c5e056e7463ba6, parent: cd7cbe818e4a66d46fe2df993d1b8518eba8a5cd)

lqd · 2025-08-16T07:39:19Z

We have an open PR on dense bitsets that removes the domain size as well (and one passes it in in the few cases where it’s needed; it’s usually easy to know where the bitsets are constructed and used) with good effects IIRC, it’s also something we could try on chunked bitsets.

rust-timer · 2025-08-16T08:33:00Z

Finished benchmarking commit (acb05a6): 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)	1.8%	[0.3%, 3.3%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-0.5%	[-1.1%, -0.2%]	4
All ❌✅ (primary)	1.1%	[-0.4%, 3.3%]	3

Max RSS (memory usage)

Results (primary -0.8%, 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)	-0.8%	[-0.8%, -0.8%]	1
Improvements ✅ (secondary)	-3.5%	[-3.5%, -3.5%]	1
All ❌✅ (primary)	-0.8%	[-0.8%, -0.8%]	1

Cycles

Results (primary 2.8%, secondary 4.2%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.8%, 2.8%]	1
Regressions ❌ (secondary)	4.2%	[4.2%, 4.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.8%	[2.8%, 2.8%]	1

Binary size

Results (primary 0.7%, secondary -1.7%)

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

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	0.7%	[0.7%, 0.7%]	1

Bootstrap: 469.562s -> 468.956s (-0.13%)
Artifact size: 377.55 MiB -> 377.45 MiB (-0.02%)

cjgillot · 2025-08-16T14:08:46Z

@lqd do you have a link to the PR for dense bitsets?

lqd · 2025-08-16T14:33:28Z

Yes, it’s #141325 — it reduces the bitset size in general, but AFAICT is not yet in an easily reviewable state per se. The author @tage64 has told me they want to wrap that work up though.

cjgillot · 2025-08-24T18:38:40Z

r? compiler

Mark-Simulacrum

r=me with nits fixed (mostly the documentation, open either way on the last_chunk_size comment)

r? @Mark-Simulacrum

View changes since this review

compiler/rustc_index/src/bit_set.rs

Mark-Simulacrum · 2025-08-24T21:04:35Z

compiler/rustc_index/src/bit_set.rs

+        for (chunk_index, (mut self_chunk, other_chunk)) in
+            self.chunks.iter_mut().zip(other.chunks.iter()).enumerate()
+        {
+            let chunk_domain_size = if chunk_index + 1 == num_chunks {


Should this use self.chunk_domain_size(chunk_index)? I guess that maybe doesn't cache the more complex computation (modulus, etc.) but that should only happen once per iteration, so maybe that's better (less register pressure etc)?

We are mutably borrowing self.chunks, so borrowck won't let us. And re-implementing is simple enough.

rustbot · 2025-08-24T22:15:30Z

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

cjgillot · 2025-08-25T00:25:20Z

@bors r=Mark-Simulacrum

bors · 2025-08-25T00:25:23Z

📌 Commit 9c9a89a has been approved by Mark-Simulacrum

It is now in the queue for this repository.

bors · 2025-08-25T04:07:26Z

⌛ Testing commit 9c9a89a with merge ee361e8...

bors · 2025-08-25T07:22:25Z

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing ee361e8 to master...

github-actions · 2025-08-25T07:25:55Z

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 a1dbb44 (parent) -> ee361e8 (this PR)

Test differences

No test diffs found

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard ee361e8fca1c30e13e7a31cc82b64c045339d3a8 --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

pr-check-1: 1382.1s -> 1719.0s (24.4%)
dist-x86_64-apple: 7454.1s -> 8879.5s (19.1%)
i686-gnu-2: 5575.9s -> 6374.6s (14.3%)
aarch64-apple: 7247.2s -> 6253.4s (-13.7%)
dist-x86_64-msvc-alt: 9035.1s -> 10246.0s (13.4%)
x86_64-gnu-llvm-19: 2548.2s -> 2862.2s (12.3%)
i686-gnu-1: 7751.1s -> 8629.5s (11.3%)
x86_64-gnu-tools: 3445.2s -> 3827.8s (11.1%)
aarch64-gnu-llvm-19-2: 2290.0s -> 2535.9s (10.7%)
x86_64-gnu-llvm-20-1: 3274.8s -> 3574.8s (9.2%)

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 · 2025-08-25T08:31:53Z

Finished benchmarking commit (ee361e8): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (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)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -3.0%, secondary -3.7%)

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)	-3.0%	[-3.8%, -2.3%]	2
Improvements ✅ (secondary)	-3.7%	[-3.7%, -3.7%]	1
All ❌✅ (primary)	-3.0%	[-3.8%, -2.3%]	2

Binary size

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

Bootstrap: 469.015s -> 467.59s (-0.30%)
Artifact size: 378.43 MiB -> 378.37 MiB (-0.02%)

Clear `ChunkedBitSet` without reallocating There doesn't appear to be any reason to clear a ChunkedBitSet via its constructor (which allocates a new list of chunks), when we could just fill the existing allocation with `Chunk::Zeros` instead. For comparison, the `insert_all` impl added by the same PR (rust-lang#93984) does the simple thing here and just overwrites every chunk with `Chunk::Ones`. (That fill was then made somewhat easier by rust-lang#145480, which removes the chunk size from all-zero/all-one chunks.) r? nnethercote (or compiler)

Rollup merge of #147623 - Zalathar:clear-mixed, r=nnethercote Clear `ChunkedBitSet` without reallocating There doesn't appear to be any reason to clear a ChunkedBitSet via its constructor (which allocates a new list of chunks), when we could just fill the existing allocation with `Chunk::Zeros` instead. For comparison, the `insert_all` impl added by the same PR (#93984) does the simple thing here and just overwrites every chunk with `Chunk::Ones`. (That fill was then made somewhat easier by #145480, which removes the chunk size from all-zero/all-one chunks.) r? nnethercote (or compiler)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 16, 2025

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rust-bors bot added a commit that referenced this pull request Aug 16, 2025

Auto merge of #145480 - cjgillot:sizeless-chunks, r=<try>

acb05a6

Remove chunk size from each chunk in `ChunkedBitSet`.

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 16, 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 Aug 16, 2025

cjgillot force-pushed the sizeless-chunks branch from 8a28a3d to 8fa6c55 Compare August 16, 2025 14:07

cjgillot marked this pull request as ready for review August 16, 2025 14:08

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 16, 2025

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cjgillot force-pushed the sizeless-chunks branch from 8fa6c55 to e2f33ee Compare August 16, 2025 16:15

Remove chunk size from each chunk.

262c8c9

rustbot assigned jieyouxu Aug 24, 2025

Mark-Simulacrum reviewed Aug 24, 2025

View reviewed changes

rustbot assigned Mark-Simulacrum and unassigned jieyouxu Aug 24, 2025

Mark-Simulacrum added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 24, 2025

Update documentation.

9c9a89a

cjgillot force-pushed the sizeless-chunks branch from e2f33ee to 9c9a89a Compare August 24, 2025 22:15

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 25, 2025

bors mentioned this pull request Aug 25, 2025

Fix attribute target checking for macro calls #145788

Merged

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

bors merged commit ee361e8 into rust-lang:master Aug 25, 2025
11 checks passed

rustbot added this to the 1.91.0 milestone Aug 25, 2025

rustbot removed the perf-regression Performance regression. label Aug 25, 2025

cjgillot deleted the sizeless-chunks branch August 25, 2025 10:46

Zalathar mentioned this pull request Oct 13, 2025

Clear ChunkedBitSet without reallocating #147623

Merged

cjgillot mentioned this pull request Oct 17, 2025

Store chunk_domain_size explicitly in Chunk. #147802

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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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Overall result: no relevant changes - no action needed

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