Remove `HybridBitSet` #133431

nnethercote · 2024-11-25T03:13:00Z

HybridBitSet was introduced under the name HybridIdxSetBuf way back in #53383 where it was a big win for NLL borrow checker performance. In #93984 the more flexible ChunkedBitSet was added. Uses of HybridBitSet have gradually disappeared (e.g. #116152) and there are now few enough that they can be replaced with BitSet or ChunkedBitSet, and HybridBitSet can be removed, cutting more than 700 lines of code.

r? @Mark-Simulacrum

nnethercote · 2024-11-25T05:39:57Z

@bors try @rust-timer queue

Remove `HybridBitSet` r? `@ghost`

bors · 2024-11-25T05:41:07Z

⌛ Trying commit 0a1e447 with merge c734427...

bors · 2024-11-25T07:26:15Z

☀️ Try build successful - checks-actions
Build commit: c734427 (c7344275c2d6ab252d7183a60e2c85fd28ae706c)

rust-timer · 2024-11-25T08:44:55Z

Finished benchmarking commit (c734427): comparison URL.

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

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.2%, 0.2%]	3
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-1.3%, -0.2%]	3
All ❌✅ (primary)	0.2%	[0.2%, 0.2%]	3

Max RSS (memory usage)

Results (primary -3.3%, secondary 3.0%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.0%	[1.8%, 4.2%]	2
Improvements ✅ (primary)	-3.3%	[-4.8%, -1.8%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.3%	[-4.8%, -1.8%]	2

Cycles

Results (primary -2.4%, secondary -3.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-3.1%	[-3.2%, -3.1%]	2
All ❌✅ (primary)	-2.4%	[-2.4%, -2.4%]	1

Binary size

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

Bootstrap: 796.657s -> 796.908s (0.03%)
Artifact size: 336.31 MiB -> 336.25 MiB (-0.02%)

rustbot · 2024-11-25T12:33:44Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

nnethercote · 2024-11-25T12:37:11Z

The perf regressions are tiny and few, and at least partly balanced by the improvements.

@rustbot label: +perf-regression-triaged

Mark-Simulacrum

r=me modulo tests/comments, in case those are unintentional. But happy landing this without the extra tests.

compiler/rustc_index/src/bit_set.rs

`ChunkedBitSet::is_empty` currently does an unnecessary check. This commit removes that check and adds clarifying comments and an assertion that demonstrate why it's unnecessary.

- Fix a typo in a comment. - Remove unnecessary `Chunk::` qualifiers. - Rename `ChunkedBitIter::bitset` as `ChunkedBitIter::bit_set`, because `bit_set` is the form used everywhere else. - Avoid some unnecessary local variables.

The current implementation is slow because it does an operation for every bit in the set, even zero bits. So if you have a large bitset with many zero bits (which is common) it's very slow. This commit improves the iterator to skip over `Zeros` chunks in a single step, and uses the fast `BitIter` for `Mixed` chunks. It also removes the existing `fold` implementation, which was only there because the old iterator was slow.

As part of the larger goal of reducing `HybridBitSet` use in general. This code is for debugging only and isn't performance sensitive, so `ChunkedBitSet` should be fine.

The compiler uses `BitSet<Local>`, because the number of locals doesn't get that high, so clippy should do likewise.

Use `ChunkedBitSet` instead.

It's no longer used.

This is in a test where the arrangement of backticks matters, but the exact words do not.

nnethercote · 2024-11-29T06:25:06Z

@bors r=Mark-Simulacrum

bors · 2024-11-29T06:25:08Z

📌 Commit d626f6a has been approved by Mark-Simulacrum

It is now in the queue for this repository.

bors · 2024-11-29T09:03:53Z

⌛ Testing commit d626f6a with merge 5bbbc09...

bors · 2024-11-29T12:04:32Z

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 5bbbc09 to master...

rust-timer · 2024-11-29T14:11:53Z

Finished benchmarking commit (5bbbc09): comparison URL.

Overall result: ❌ regressions - 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

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.1%, 0.2%]	6
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.1%, 0.2%]	6

Max RSS (memory usage)

Results (primary -0.4%, secondary 0.2%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	1.4%	[1.4%, 1.5%]	2
Improvements ✅ (primary)	-1.2%	[-1.3%, -1.0%]	2
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	-0.4%	[-1.3%, 1.0%]	3

Cycles

Results (secondary 2.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	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: 773.306s -> 772.63s (-0.09%)
Artifact size: 331.98 MiB -> 331.98 MiB (0.00%)

rylev · 2024-12-04T03:07:32Z

Triage: Post merge perf results are a bit different from the pre-merge run, but they look similar enough that this doesn't require more investigation.

nnethercote · 2024-12-05T09:36:02Z

The very slight perf regressions here are more than made up for by #133891.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. labels Nov 25, 2024

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Nov 25, 2024

bors added a commit to rust-lang-ci/rust that referenced this pull request Nov 25, 2024

Auto merge of rust-lang#133431 - nnethercote:rm-HybridBitSet, r=<try>

c734427

Remove `HybridBitSet` r? `@ghost`

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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 25, 2024

rustbot assigned Mark-Simulacrum Nov 25, 2024

nnethercote marked this pull request as ready for review November 25, 2024 12:33

rustbot added the perf-regression-triaged The performance regression has been triaged. label Nov 25, 2024

Mark-Simulacrum reviewed Nov 28, 2024

View reviewed changes

compiler/rustc_index/src/bit_set.rs Outdated Show resolved Hide resolved

nnethercote added 9 commits November 29, 2024 17:01

Clarify ChunkSize invariants.

15b24c4

`ChunkedBitSet::is_empty` currently does an unnecessary check. This commit removes that check and adds clarifying comments and an assertion that demonstrate why it's unnecessary.

Tiny ChunkedBitSet improvements.

ff78002

- Fix a typo in a comment. - Remove unnecessary `Chunk::` qualifiers. - Rename `ChunkedBitIter::bitset` as `ChunkedBitIter::bit_set`, because `bit_set` is the form used everywhere else. - Avoid some unnecessary local variables.

Remove unused HybridBitSet methods from BitSetExt.

346929c

Stop using HybridBitSet in dataflow diffs.

0df6a01

As part of the larger goal of reducing `HybridBitSet` use in general. This code is for debugging only and isn't performance sensitive, so `ChunkedBitSet` should be fine.

Stop using HybridBitSet in clippy.

688f28d

The compiler uses `BitSet<Local>`, because the number of locals doesn't get that high, so clippy should do likewise.

Stop using HybridBitSet in SparseBitMatrix.

b7ff2ae

Use `ChunkedBitSet` instead.

Remove HybridBitSet.

4846c19

It's no longer used.

Remove last vestiges of HybridBitSet.

d626f6a

This is in a test where the arrangement of backticks matters, but the exact words do not.

nnethercote force-pushed the rm-HybridBitSet branch from 0a1e447 to d626f6a Compare November 29, 2024 06:23

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 29, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 29, 2024

bors merged commit 5bbbc09 into rust-lang:master Nov 29, 2024
7 checks passed

rustbot added this to the 1.85.0 milestone Nov 29, 2024

nnethercote deleted the rm-HybridBitSet branch November 30, 2024 20:55

nnethercote mentioned this pull request Dec 5, 2024

Introduce MixedBitSet #133891

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Remove `HybridBitSet` #133431

Remove `HybridBitSet` #133431

nnethercote commented Nov 25, 2024 •

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rylev commented Dec 4, 2024 •

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nnethercote commented Dec 5, 2024

Remove HybridBitSet #133431

Remove HybridBitSet #133431

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rust-timer commented Nov 25, 2024

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

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rust-timer commented Nov 29, 2024

Overall result: ❌ regressions - please read the text below

rylev commented Dec 4, 2024 • edited Loading

nnethercote commented Dec 5, 2024

Remove `HybridBitSet` #133431

Remove `HybridBitSet` #133431

nnethercote commented Nov 25, 2024 •

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rylev commented Dec 4, 2024 •

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