Take more advantage of the `isize::MAX` limit in `Layout` #129845

scottmcm · 2024-09-01T08:31:56Z

Things like padding_needed_for are current implemented being super careful to handle things like Layout::size potentially being usize::MAX.

But now that #95295 has happened, that's no longer a concern. It's possible to add two Layout::sizes together without risking overflow now.

So take advantage of that to remove a bunch of checked math that's not actually needed. For example, the round-up-and-add-next-size in extend doesn't need any overflow checks at all, just the final check for compatibility with the alignment.

(And while I was doing that I made it all unstably const, because there's nothing in Layout that's fundamentally runtime-only.)

rustbot · 2024-09-01T08:32:05Z

r? @Noratrieb

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scottmcm · 2024-09-01T08:32:18Z

@bors try @rust-timer queue

Take more advantage of the `isize::MAX` limit in `Layout` Things like `padding_needed_for` are current implemented being super careful to handle things like `Layout::size` potentially being `usize::MAX`. But now that rust-lang#95295 has happened, that's no longer a concern. It's possible to add two `Layout::size`s together without risking overflow now. So this PR adds a wrapper type to allow doing that kind of thing in safe code while still telling LLVM it can't overflow.

bors · 2024-09-01T08:33:29Z

⌛ Trying commit 3fcde40 with merge 3e6e03e...

bors · 2024-09-01T10:29:05Z

☀️ Try build successful - checks-actions
Build commit: 3e6e03e (3e6e03ebf4b270a06fb94686ff63919ccffd2157)

rust-timer · 2024-09-01T12:57:05Z

Finished benchmarking commit (3e6e03e): 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)	0.8%	[0.2%, 2.5%]	65
Regressions ❌ (secondary)	1.1%	[0.3%, 6.0%]	47
Improvements ✅ (primary)	-1.0%	[-1.4%, -0.5%]	2
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.3%]	2
All ❌✅ (primary)	0.8%	[-1.4%, 2.5%]	67

Max RSS (memory usage)

Results (primary 0.3%, secondary 0.1%)

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)	1.3%	[0.4%, 12.0%]	46
Regressions ❌ (secondary)	1.0%	[0.4%, 3.3%]	51
Improvements ✅ (primary)	-1.2%	[-9.5%, -0.4%]	34
Improvements ✅ (secondary)	-0.9%	[-2.3%, -0.4%]	48
All ❌✅ (primary)	0.3%	[-9.5%, 12.0%]	80

Cycles

Results (primary 0.8%, secondary 0.6%)

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%	[0.4%, 3.8%]	105
Regressions ❌ (secondary)	1.0%	[0.4%, 7.3%]	124
Improvements ✅ (primary)	-1.8%	[-4.6%, -0.4%]	7
Improvements ✅ (secondary)	-1.2%	[-5.6%, -0.4%]	33
All ❌✅ (primary)	0.8%	[-4.6%, 3.8%]	112

Binary size

Results (primary 0.6%, secondary 1.6%)

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)	0.7%	[0.0%, 5.4%]	49
Regressions ❌ (secondary)	2.4%	[1.5%, 3.4%]	11
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	9
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	5
All ❌✅ (primary)	0.6%	[-0.1%, 5.4%]	58

Bootstrap: 789.43s -> 800.421s (1.39%)
Artifact size: 338.46 MiB -> 338.68 MiB (0.06%)

scottmcm · 2024-09-01T20:21:00Z

@bors try @rust-timer queue

bors · 2024-09-01T20:22:10Z

⌛ Trying commit 972ff01 with merge 9c711ef...

Take more advantage of the `isize::MAX` limit in `Layout` Things like `padding_needed_for` are current implemented being super careful to handle things like `Layout::size` potentially being `usize::MAX`. But now that rust-lang#95295 has happened, that's no longer a concern. It's possible to add two `Layout::size`s together without risking overflow now. So this PR adds a wrapper type to allow doing that kind of thing in safe code while still telling LLVM it can't overflow.

bors · 2024-09-01T22:13:37Z

☀️ Try build successful - checks-actions
Build commit: 9c711ef (9c711ef9097c622d73290d954556a9597f541f93)

rust-timer · 2024-09-02T00:52:32Z

Finished benchmarking commit (9c711ef): 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)	1.0%	[0.2%, 3.0%]	57
Regressions ❌ (secondary)	1.5%	[0.3%, 6.2%]	28
Improvements ✅ (primary)	-1.4%	[-1.4%, -1.4%]	1
Improvements ✅ (secondary)	-0.5%	[-0.8%, -0.3%]	15
All ❌✅ (primary)	1.0%	[-1.4%, 3.0%]	58

Max RSS (memory usage)

Results (primary -0.2%, secondary -0.6%)

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)	1.4%	[0.4%, 11.2%]	29
Regressions ❌ (secondary)	0.7%	[0.4%, 1.3%]	18
Improvements ✅ (primary)	-1.1%	[-9.6%, -0.4%]	51
Improvements ✅ (secondary)	-0.9%	[-3.5%, -0.4%]	77
All ❌✅ (primary)	-0.2%	[-9.6%, 11.2%]	80

Cycles

Results (primary 0.6%, secondary 0.4%)

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)	1.1%	[0.4%, 3.3%]	67
Regressions ❌ (secondary)	1.4%	[0.4%, 6.8%]	71
Improvements ✅ (primary)	-1.3%	[-6.5%, -0.4%]	16
Improvements ✅ (secondary)	-0.9%	[-5.6%, -0.4%]	52
All ❌✅ (primary)	0.6%	[-6.5%, 3.3%]	83

Binary size

Results (primary 0.6%, secondary 1.6%)

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)	0.7%	[0.0%, 5.5%]	50
Regressions ❌ (secondary)	2.4%	[1.5%, 3.4%]	11
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	9
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	5
All ❌✅ (primary)	0.6%	[-0.1%, 5.5%]	59

Bootstrap: 787.22s -> 796.262s (1.15%)
Artifact size: 338.38 MiB -> 338.74 MiB (0.11%)

scottmcm · 2024-09-02T04:47:35Z

@bors try @rust-timer queue

bors · 2024-09-02T06:43:08Z

☀️ Try build successful - checks-actions
Build commit: c8e94c4 (c8e94c4117a6137fc79bbc3baa14733caf2fda8c)

rust-timer · 2024-09-02T11:42:16Z

Finished benchmarking commit (c8e94c4): 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
Regressions ❌ (secondary)	3.4%	[0.4%, 8.4%]	3
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.3%]	5
Improvements ✅ (secondary)	-0.7%	[-1.3%, -0.3%]	4
All ❌✅ (primary)	-0.3%	[-0.4%, -0.3%]	5

Max RSS (memory usage)

Results (primary -0.1%, secondary -0.9%)

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)	1.5%	[0.4%, 8.1%]	22
Regressions ❌ (secondary)	0.8%	[0.4%, 1.6%]	12
Improvements ✅ (primary)	-0.8%	[-3.0%, -0.4%]	53
Improvements ✅ (secondary)	-1.0%	[-3.0%, -0.4%]	117
All ❌✅ (primary)	-0.1%	[-3.0%, 8.1%]	75

Cycles

Results (primary -0.5%, secondary -0.4%)

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)	1.1%	[0.4%, 2.5%]	8
Regressions ❌ (secondary)	1.1%	[0.4%, 4.3%]	33
Improvements ✅ (primary)	-0.8%	[-1.9%, -0.4%]	52
Improvements ✅ (secondary)	-0.9%	[-3.4%, -0.4%]	105
All ❌✅ (primary)	-0.5%	[-1.9%, 2.5%]	60

Binary size

Results (primary -0.0%)

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)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.0%	[-0.9%, 0.8%]	2

Bootstrap: 751.284s -> 755.684s (0.59%)
Artifact size: 338.27 MiB -> 338.31 MiB (0.01%)

scottmcm · 2024-09-02T19:59:58Z

Ah, there we go. #129845 (comment) looks great.

@rustbot ready

Noratrieb

two comments, which you may optionally address

Noratrieb · 2024-09-15T10:06:03Z

library/core/src/alloc/layout.rs

-        // The safe constructor is called here to enforce the isize size limit.
-        Layout::from_size_alignment(new_size, self.align)
+    pub const fn extend_packed(&self, next: Self) -> Result<Self, LayoutError> {
+        if let Some(new_size) = self.size.checked_add(next.size) {


This can't overflow, right?

Noratrieb · 2024-09-15T10:12:31Z

library/core/src/alloc/layout.rs

+    /// because the original size is at most `isize::MAX`.
+    #[inline]
+    const fn size_rounded_up_to_custom_align(&self, align: Alignment) -> usize {
+        let len = self.size;


this variable with a slighty confusing name is used once, can we just remove it and call it "size" instead of "len" everywhere?

Good point. I'd left it because it was in the old code, but apparently I then refactored enough that the diff doesn't notice that, so might as well just remove it as you say.

scottmcm · 2024-09-18T03:00:52Z

@bors r=Noratrieb

bors · 2024-09-18T03:00:55Z

📌 Commit b824dc4 has been approved by Noratrieb

It is now in the queue for this repository.

Things like `padding_needed_for` are current implemented being super careful to handle things like `Layout::size` potentially being `usize::MAX`. But now that 95295 has happened, that's no longer a concern. It's possible to add two `Layout::size`s together without risking overflow now. So take advantage of that to remove a bunch of checked math that's not actually needed. For example, the round-up-and-add-next-size in `extend` doesn't need any overflow checks at all, just the final check for compatibility with the alignment. (And while I was doing that I made it all unstably const, because there's nothing in `Layout` that's fundamentally runtime-only.)

scottmcm · 2024-09-18T03:06:56Z

Diff fixing the PR comments: https://github.com/rust-lang/rust/compare/7ccc088c808f0ba169824dd9f6cdd83000a8b8ac..18ca8bf8ee77deb13967620b1f4829f22c16dae1

(multiple pushes because apparently I'm bad at updating comments)

@bors r=Noratrieb

bors · 2024-09-18T03:06:58Z

📌 Commit 18ca8bf has been approved by Noratrieb

It is now in the queue for this repository.

bors · 2024-09-18T07:05:17Z

⌛ Testing commit 18ca8bf with merge f68c28b...

bors · 2024-09-18T09:23:54Z

☀️ Test successful - checks-actions
Approved by: Noratrieb
Pushing f68c28b to master...

rust-timer · 2024-09-18T10:39:36Z

Finished benchmarking commit (f68c28b): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-0.2%	[-0.2%, -0.2%]	1

Max RSS (memory usage)

Results (primary -0.9%, 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)	-	-	0
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	1
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-0.9%	[-0.9%, -0.9%]	1

Cycles

Results (secondary 2.6%)

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)	2.6%	[2.0%, 3.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.0%)

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)	0.3%	[0.1%, 1.1%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.5%, -0.0%]	17
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.0%	[-0.5%, 1.1%]	22

Bootstrap: 767.306s -> 765.816s (-0.19%)
Artifact size: 341.25 MiB -> 341.29 MiB (0.01%)

rustbot assigned Noratrieb Sep 1, 2024

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scottmcm force-pushed the redo-layout branch from 3fcde40 to 972ff01 Compare September 1, 2024 20:08

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scottmcm marked this pull request as ready for review September 2, 2024 20:00

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Sep 2, 2024

Noratrieb approved these changes Sep 15, 2024

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scottmcm force-pushed the redo-layout branch from 7ccc088 to b824dc4 Compare September 18, 2024 03:00

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 Sep 18, 2024

scottmcm force-pushed the redo-layout branch from b824dc4 to 29262a1 Compare September 18, 2024 03:05

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bors added the merged-by-bors This PR was explicitly merged by bors. label Sep 18, 2024

bors merged commit f68c28b into rust-lang:master Sep 18, 2024
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Take more advantage of the `isize::MAX` limit in `Layout` #129845

Take more advantage of the `isize::MAX` limit in `Layout` #129845

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Take more advantage of the isize::MAX limit in Layout #129845

Take more advantage of the isize::MAX limit in Layout #129845

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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Overall result: ✅ improvements - no action needed

Take more advantage of the `isize::MAX` limit in `Layout` #129845

Take more advantage of the `isize::MAX` limit in `Layout` #129845

scottmcm commented Sep 1, 2024 •

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