Just pass Layout directly to box_new_uninit

[scottmcm]

We have a constant for it already (used in RawVec for basically the same polymorphization) so let's use it.

This is a simple follow-up to #148190 from one of the comments.

[rustbot]

r? @Mark-Simulacrum

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The reviewer was selected based on:

• Owners of files modified in this PR: libs
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[scottmcm]

Since we saw this code is perf-sensitive, to make sure it doesn't blow up...
@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8dd6c97 (8dd6c970aade6a83f0d68d1c80913bde8aa79b32, parent: 3c9faa0d037b9eecda4a440cc482ff7f960fb8a5)

[rust-timer]

Finished benchmarking commit (8dd6c97): 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)	0.7%	[0.4%, 1.0%]	3
Regressions ❌ (secondary)	0.6%	[0.6%, 0.6%]	2
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.2%]	2
Improvements ✅ (secondary)	-1.0%	[-3.2%, -0.4%]	8
All ❌✅ (primary)	0.3%	[-0.4%, 1.0%]	5

Max RSS (memory usage)

Results (primary -2.3%, secondary 3.4%)

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)	3.4%	[2.4%, 4.2%]	5
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.2%, secondary -2.0%)

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

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.5%, -0.0%]	19
Improvements ✅ (secondary)	-2.0%	[-4.2%, -0.7%]	15
All ❌✅ (primary)	-0.2%	[-0.5%, 0.3%]	20

Bootstrap: 480.798s -> 483.051s (0.47%)
Artifact size: 395.81 MiB -> 395.83 MiB (0.00%)

[scottmcm]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: b517e4f (b517e4fd131ad3e507891d12ba6980349893b354, parent: d1a11b670b617f1370f7b1cdf86e225a4e070f15)

[rust-timer]

Finished benchmarking commit (b517e4f): 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)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	0.8%	[0.6%, 0.9%]	5
Improvements ✅ (primary)	-0.7%	[-1.2%, -0.3%]	13
Improvements ✅ (secondary)	-1.8%	[-4.1%, -0.8%]	11
All ❌✅ (primary)	-0.6%	[-1.2%, 0.8%]	14

Max RSS (memory usage)

Results (primary 1.3%, 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)	4.1%	[2.8%, 8.5%]	5
Regressions ❌ (secondary)	3.4%	[1.3%, 5.7%]	13
Improvements ✅ (primary)	-3.4%	[-3.5%, -3.2%]	3
Improvements ✅ (secondary)	-3.8%	[-4.1%, -3.4%]	3
All ❌✅ (primary)	1.3%	[-3.5%, 8.5%]	8

Cycles

Results (primary 2.3%, 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)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.5%	[-3.6%, -3.2%]	3
All ❌✅ (primary)	2.3%	[2.3%, 2.3%]	1

Binary size

Results (primary -0.6%, 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)	-	-	0
Improvements ✅ (primary)	-0.6%	[-1.2%, -0.0%]	21
Improvements ✅ (secondary)	-2.1%	[-3.6%, -0.1%]	18
All ❌✅ (primary)	-0.6%	[-1.2%, -0.0%]	21

Bootstrap: 483.207s -> 482.56s (-0.13%)
Artifact size: 397.79 MiB -> 397.80 MiB (0.00%)

[RalfJung]

Nice :)

r=me with safety comment fixed, unless you have further plans.

View changes since this review

[RalfJung]

This first point seems outdated now.

[scottmcm]

@bors r=RalfJung

[rust-bors]

📌 Commit 4b03b97 has been approved by RalfJung

It is now in the queue for this repository.