[EXPERIMENT] RawBitSet experiments by Zalathar · Pull Request #153589 · rust-lang/rust

Zalathar · 2026-03-09T03:59:01Z

(Doing some perf runs to see if I'm on the right track with this RawBitSet stuff.)

Zalathar · 2026-03-09T03:59:11Z

[EXPERIMENT] RawBitSet experiments

rust-bors · 2026-03-09T06:09:51Z

☀️ Try build successful (CI)
Build commit: 524f8f3 (524f8f327bef00d806aadab2c3f1cf6d424c6f5a, parent: b41f22de2a13a0babd28771e96feef4c309f54aa)

lqd · 2026-03-09T06:40:30Z

If you’re working on bitsets, it could be cool to take a look at #141325 and bring that to completion. It was a nice win and the author doesn’t have the time to rebase, and finish it.

rust-timer · 2026-03-09T06:50:09Z

Finished benchmarking commit (524f8f3): 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)	0.1%	[0.1%, 0.1%]	2
Regressions ❌ (secondary)	0.6%	[0.0%, 1.1%]	11
Improvements ✅ (primary)	-0.3%	[-0.3%, -0.3%]	2
Improvements ✅ (secondary)	-0.2%	[-0.4%, -0.1%]	18
All ❌✅ (primary)	-0.1%	[-0.3%, 0.1%]	4

Max RSS (memory usage)

Results (primary -5.7%, secondary -1.1%)

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)	-	-	0
Improvements ✅ (primary)	-5.7%	[-10.3%, -1.1%]	2
Improvements ✅ (secondary)	-1.1%	[-1.1%, -1.1%]	1
All ❌✅ (primary)	-5.7%	[-10.3%, -1.1%]	2

Cycles

Results (secondary 3.2%)

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)	3.2%	[3.2%, 3.2%]	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: 478.517s -> 499.35s (4.35%)
Artifact size: 395.02 MiB -> 395.00 MiB (-0.00%)

Zalathar · 2026-03-09T06:56:05Z

If you’re working on bitsets, it could be cool to take a look at #141325 and bring that to completion. It was a nice win and the author doesn’t have the time to rebase, and finish it.

One of my ambitions is to eventually allow a large subset of bitsets to allocate their word storage in a dropless arena (either a local arena or the one in TyCtxt), which could potentially cut down on a lot of allocation bookkeeping.

Zalathar · 2026-03-09T07:31:29Z

Let's make sure a simpler RawBitSet is perf-neutral, before trying to make ambitious changes.

@bors try @rust-timer queue

[EXPERIMENT] RawBitSet experiments

rust-bors · 2026-03-09T09:45:25Z

☀️ Try build successful (CI)
Build commit: 1eba61e (1eba61e69a9a8e83369894aef1ff64dd0b8e66b2, parent: 98e7077b903559d7a4fafb775cd5292cc9427b67)

rust-timer · 2026-03-09T10:25:39Z

Finished benchmarking commit (1eba61e): 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)	0.2%	[0.1%, 0.3%]	3
Regressions ❌ (secondary)	0.2%	[0.0%, 0.3%]	8
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.1%, 0.3%]	3

Max RSS (memory usage)

Results (primary 2.4%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Cycles

Results (primary 2.0%, secondary -2.6%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.0%, -2.1%]	2
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	1

Binary size

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

Bootstrap: 479.865s -> 479.014s (-0.18%)
Artifact size: 395.05 MiB -> 394.98 MiB (-0.02%)

Zalathar · 2026-03-09T10:53:57Z

Hmm, it's frustrating that the monomorphic RawBitSet isn't perf-neutral, even with #[inline] sprinkled everywhere.

Will #[inline(always)] do the trick?

@bors try @rust-timer queue

[EXPERIMENT] RawBitSet experiments

rust-bors · 2026-03-09T13:04:10Z

☀️ Try build successful (CI)
Build commit: 861e8d4 (861e8d4337f9d836ac906e4daf4a6de867cb24a9, parent: 98e7077b903559d7a4fafb775cd5292cc9427b67)

rust-timer · 2026-03-09T13:59:10Z

Finished benchmarking commit (861e8d4): 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)	0.2%	[0.1%, 0.3%]	5
Regressions ❌ (secondary)	0.2%	[0.0%, 0.3%]	10
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.1%, 0.3%]	5

Max RSS (memory usage)

Results (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)	-	-	0
Regressions ❌ (secondary)	1.9%	[1.9%, 1.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.3%	[-1.3%, -1.3%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.4%, secondary 1.8%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.3%, 2.6%]	3
Regressions ❌ (secondary)	3.6%	[2.9%, 4.5%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.3%, -1.9%]	2
All ❌✅ (primary)	2.4%	[2.3%, 2.6%]	3

Binary size

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

Bootstrap: 479.865s -> 482.574s (0.56%)
Artifact size: 395.05 MiB -> 394.89 MiB (-0.04%)

Zalathar · 2026-03-10T00:01:19Z

Try marking a few more things inline, in case that matters.

@bors try @rust-timer queue

[EXPERIMENT] RawBitSet experiments

rust-bors · 2026-03-10T02:10:35Z

☀️ Try build successful (CI)
Build commit: b23642a (b23642a594620ff09011307479d2d9db23b1bccb, parent: 2d76d9bc76f27b03b4899e72ce561c7ac2c5cf6b)

rust-timer · 2026-03-10T02:51:09Z

Finished benchmarking commit (b23642a): 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)	0.2%	[0.1%, 0.3%]	4
Regressions ❌ (secondary)	0.2%	[0.0%, 0.3%]	13
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.1%, 0.3%]	4

Max RSS (memory usage)

Results (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)	1.7%	[0.8%, 2.5%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-0.9%, -0.9%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -0.2%, secondary -0.4%)

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)	2.3%	[2.3%, 2.3%]	1
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-0.2%	[-2.4%, 2.1%]	2

Binary size

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

Bootstrap: 479.112s -> 479.675s (0.12%)
Artifact size: 395.06 MiB -> 394.91 MiB (-0.04%)

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 Mar 9, 2026

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rust-bors bot pushed a commit that referenced this pull request Mar 9, 2026

Auto merge of #153589 - Zalathar:bit-set, r=<try>

524f8f3

[EXPERIMENT] RawBitSet experiments

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 9, 2026

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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 Mar 9, 2026

Zalathar force-pushed the bit-set branch from c730ac2 to c65afd6 Compare March 9, 2026 07:30

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rust-bors bot pushed a commit that referenced this pull request Mar 9, 2026

Auto merge of #153589 - Zalathar:bit-set, r=<try>

1eba61e

[EXPERIMENT] RawBitSet experiments

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 9, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 9, 2026

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rust-bors bot pushed a commit that referenced this pull request Mar 9, 2026

Auto merge of #153589 - Zalathar:bit-set, r=<try>

861e8d4

[EXPERIMENT] RawBitSet experiments

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 9, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 9, 2026

Zalathar added 4 commits March 10, 2026 11:00

Remove the unused impl ToString for DenseBitSet

b90c854

Rename the cryptic bitwise and bitwise_changes functions

e35b0e6

Extract a RawBitSet from DenseBitSet

b7b34f0

!! (WIP) make sure absolutely every new function is inline

5de9d12

Zalathar force-pushed the bit-set branch from 64aba27 to 5de9d12 Compare March 10, 2026 00:00

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rust-bors bot pushed a commit that referenced this pull request Mar 10, 2026

Auto merge of #153589 - Zalathar:bit-set, r=<try>

b23642a

[EXPERIMENT] RawBitSet experiments

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 10, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 10, 2026

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

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Overall result: ❌ regressions - please read the text below

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Overall result: ❌ regressions - please read the text below

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Overall result: ❌ regressions - please read the text below

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