Pass alignments through the shim as Alignment (not usize)

[scottmcm]

We're using Layout on both sides, so might as well skip the transmutes back and forth to usize.

The mir-opt test shows that doing so allows simplifying the boxed-slice drop slightly, for example.

[rustbot]

r? @Mark-Simulacrum

rustbot has assigned @Mark-Simulacrum.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @ChrisDenton, libs
• @ChrisDenton, libs expanded to 8 candidates
• Random selection from Mark-Simulacrum, joboet

[scottmcm]

I don't think this'll make a big difference, but to make sure it doesn't do something terrible,
@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: cbb8a9d (cbb8a9dfbcf43b0848077acc814b5f9f74f33862, parent: f403dee04e6a801fe0f49a9c351fcd2ae8edd37c)

[rust-timer]

Finished benchmarking commit (cbb8a9d): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.6%	[-0.6%, -0.6%]	1

Max RSS (memory usage)

Results (primary 4.3%, secondary 3.0%)

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

	mean	range	count
Regressions ❌ (primary)	4.3%	[3.3%, 5.3%]	2
Regressions ❌ (secondary)	5.1%	[5.0%, 5.2%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	4.3%	[3.3%, 5.3%]	2

Cycles

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

Binary size

Results (primary -0.2%, secondary -0.1%)

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)	-0.2%	[-0.4%, -0.1%]	2
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	2
All ❌✅ (primary)	-0.2%	[-0.4%, -0.1%]	2

Bootstrap: 481.836s -> 481.056s (-0.16%)
Artifact size: 398.12 MiB -> 398.12 MiB (0.00%)

[bjorn3]

This should be fine given that Alignment is repr(transparent).

[Mark-Simulacrum]

@bors r+

[rust-bors]

📌 Commit 774268a has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: Mark-Simulacrum
Duration: 3h 13m 22s
Pushing 2219766 to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 4c37f6d (parent) -> 2219766 (this PR)

Test differences

Show 2 test diffs

2 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 2219766af622ad1f051ca96ae40650106b1bd9bd --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. dist-aarch64-apple: 2h 26m -> 3h 4m (+25.9%)
2. dist-x86_64-apple: 2h 49m -> 2h 17m (-19.1%)
3. aarch64-apple: 3h 35m -> 2h 54m (-18.9%)
4. x86_64-gnu-llvm-21-2: 1h 32m -> 1h 43m (+12.2%)
5. x86_64-gnu-tools: 1h 3m -> 56m 12s (-11.0%)
6. dist-aarch64-msvc: 1h 39m -> 1h 29m (-9.8%)
7. dist-aarch64-llvm-mingw: 1h 44m -> 1h 34m (-9.0%)
8. dist-riscv64-linux: 1h 20m -> 1h 27m (+8.9%)
9. dist-android: 28m 3s -> 25m 46s (-8.1%)
10. dist-aarch64-linux: 1h 44m -> 1h 52m (+7.5%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (2219766): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -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)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	0.5%	[0.5%, 0.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	1

Max RSS (memory usage)

Results (primary 1.6%, secondary -1.2%)

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

	mean	range	count
Regressions ❌ (primary)	5.3%	[2.3%, 8.0%]	4
Regressions ❌ (secondary)	4.4%	[4.4%, 4.4%]	1
Improvements ✅ (primary)	-3.3%	[-3.9%, -3.0%]	3
Improvements ✅ (secondary)	-6.7%	[-6.7%, -6.7%]	1
All ❌✅ (primary)	1.6%	[-3.9%, 8.0%]	7

Cycles

Results (secondary -3.7%)

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)	-3.7%	[-4.2%, -3.2%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.7%, secondary -0.1%)

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)	0.1%	[0.1%, 0.1%]	14
Improvements ✅ (primary)	-0.7%	[-0.7%, -0.7%]	2
Improvements ✅ (secondary)	-2.6%	[-2.6%, -2.6%]	1
All ❌✅ (primary)	-0.7%	[-0.7%, -0.7%]	2

Bootstrap: 480.702s -> 485.129s (0.92%)
Artifact size: 397.88 MiB -> 398.01 MiB (0.03%)