Add some targeted `assume(bytes <= isize::MAX)` around slices #123575

scottmcm · 2024-04-06T22:38:56Z

Putting it on every single slice length was pretty expensive, but let's see if doing it just in slice::from_raw_parts(_mut) ~~and slice::Iter(Mut)::len~~ works better.

rustbot · 2024-04-06T22:39:04Z

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scottmcm · 2024-04-06T22:40:28Z

library/core/src/slice/raw.rs

        );
+        intrinsics::assume(len <= T::MAX_SLICE_LEN);


Given this was already assert_unsafe_preconditioned, might as well assume it too.

(Not using assert_unchecked because it doesn't need a second UbCheck.)

scottmcm · 2024-04-06T22:53:07Z

@bors try @rust-timer queue

bors · 2024-04-06T22:54:18Z

⌛ Trying commit 2be8c36 with merge a4009ef...

Add some targeted `assume(bytes <= isize::MAX)` around slices Putting it on every single slice length was pretty expensive, but let's see if doing it just in `slice::from_raw_parts(_mut)` and `slice::Iter(Mut)::len` works better.

bors · 2024-04-07T00:34:12Z

☀️ Try build successful - checks-actions
Build commit: a4009ef (a4009ef679b4340bef4d86f8c96d4135102cca59)

rust-timer · 2024-04-07T03:12:32Z

Finished benchmarking commit (a4009ef): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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 a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.1%, 3.4%]	130
Regressions ❌ (secondary)	0.4%	[0.2%, 1.2%]	53
Improvements ✅ (primary)	-1.5%	[-4.1%, -0.2%]	3
Improvements ✅ (secondary)	-0.8%	[-1.7%, -0.2%]	11
All ❌✅ (primary)	0.6%	[-4.1%, 3.4%]	133

Max RSS (memory usage)

Results

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)	3.7%	[2.1%, 5.3%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-3.2%, -1.6%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.3%	[-3.2%, 5.3%]	5

Cycles

Results

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)	1.9%	[0.8%, 2.9%]	21
Regressions ❌ (secondary)	1.0%	[1.0%, 1.0%]	1
Improvements ✅ (primary)	-4.3%	[-4.3%, -4.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.6%	[-4.3%, 2.9%]	22

Binary size

Results

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)	0.2%	[0.0%, 0.8%]	11
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.0%]	46
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.0%]	5
All ❌✅ (primary)	-0.0%	[-0.3%, 0.8%]	57

Bootstrap: 670.181s -> 676.772s (0.98%)
Artifact size: 318.20 MiB -> 318.14 MiB (-0.02%)

…ed, r=<try> Have `offset_from_unsigned` assume the `isize::MAX` restriction Split off from rust-lang#123575; hopefully this won't be as perf-painful. (Notably it doesn't change MIR, so hopefully can't affect check/debug.)

Putting it on every single slice length was pretty expensive, but let's see if doing it just in `slice::from_raw_parts(_mut)` and `slice::Iter(Mut)::len` works better.

scottmcm · 2024-04-07T16:04:40Z

Split off half of it over to #123598; let's see just this bit.

@bors try @rust-timer queue

bors · 2024-04-07T16:05:50Z

⌛ Trying commit 5c95280 with merge ada8fc8...

Add some targeted `assume(bytes <= isize::MAX)` around slices Putting it on every single slice length was pretty expensive, but let's see if doing it just in `slice::from_raw_parts(_mut)` ~~and `slice::Iter(Mut)::len`~~ works better.

bors · 2024-04-07T17:45:01Z

☀️ Try build successful - checks-actions
Build commit: ada8fc8 (ada8fc8c65b4d8b6834976d9cff03e93d277a713)

rust-timer · 2024-04-07T19:24:14Z

Finished benchmarking commit (ada8fc8): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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 a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.2%, 3.3%]	141
Regressions ❌ (secondary)	0.4%	[0.2%, 1.1%]	45
Improvements ✅ (primary)	-4.2%	[-4.2%, -4.2%]	1
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.2%]	2
All ❌✅ (primary)	0.6%	[-4.2%, 3.3%]	142

Max RSS (memory usage)

Results

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)	2.7%	[2.2%, 3.0%]	4
Regressions ❌ (secondary)	2.6%	[2.1%, 3.2%]	10
Improvements ✅ (primary)	-6.9%	[-6.9%, -6.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[-6.9%, 3.0%]	5

Cycles

Results

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)	2.1%	[1.1%, 3.1%]	16
Regressions ❌ (secondary)	5.9%	[1.1%, 10.7%]	2
Improvements ✅ (primary)	-4.1%	[-4.1%, -4.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.7%	[-4.1%, 3.1%]	17

Binary size

Results

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)	0.1%	[0.0%, 0.3%]	15
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.0%]	41
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.0%]	5
All ❌✅ (primary)	-0.0%	[-0.3%, 0.3%]	56

Bootstrap: 667.449s -> 673.747s (0.94%)
Artifact size: 318.47 MiB -> 318.41 MiB (-0.02%)

scottmcm · 2024-04-07T20:11:37Z

Wow, even worse. Clearly we can't do this.

rustbot assigned joboet Apr 6, 2024

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-libs Relevant to the library team, which will review and decide on the PR/issue. labels Apr 6, 2024

scottmcm commented Apr 6, 2024

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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 Apr 7, 2024

scottmcm mentioned this pull request Apr 7, 2024

Have offset_from_unsigned assume the isize::MAX restriction #123598

Closed

Add some targeted assume(bytes <= isize::MAX) around slices

5c95280

Putting it on every single slice length was pretty expensive, but let's see if doing it just in `slice::from_raw_parts(_mut)` and `slice::Iter(Mut)::len` works better.

scottmcm force-pushed the assume-raw-parts branch from 2be8c36 to 5c95280 Compare April 7, 2024 16:03

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 7, 2024

scottmcm closed this Apr 7, 2024

scottmcm deleted the assume-raw-parts branch April 7, 2024 20:11

EFanZh mentioned this pull request Oct 4, 2024

Asserts the maximum value that can be returned from Vec::len #131193

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Add some targeted `assume(bytes <= isize::MAX)` around slices #123575

Add some targeted `assume(bytes <= isize::MAX)` around slices #123575

scottmcm commented Apr 6, 2024 •

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Add some targeted assume(bytes <= isize::MAX) around slices #123575

Add some targeted assume(bytes <= isize::MAX) around slices #123575

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

scottmcm commented Apr 7, 2024

Add some targeted `assume(bytes <= isize::MAX)` around slices #123575

Add some targeted `assume(bytes <= isize::MAX)` around slices #123575

scottmcm commented Apr 6, 2024 •

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