Simplify size/align_of_val<T: Sized> to size/align_of<T> instead

[scottmcm]

This is relevant to things like Box<[u8; 1024]> where the drop looks at the size_of_val (since obviously it might be DST in general) but where we don't actually need to do that since it's always that same value for the Sized type.

(Equivalent to #152681, but flipped in the rebase so it can land before #152641 instead of depending on it.)

[scottmcm]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 85c1367 (85c13679ed60d98f876a8f50c0b7505fb1ea3260, parent: 139651428df86cf88443295542c12ea617cbb587)

[rust-timer]

Finished benchmarking commit (85c1367): 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)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-0.5%	[-0.5%, -0.5%]	2
All ❌✅ (primary)	-0.4%	[-0.4%, -0.4%]	1

Max RSS (memory usage)

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

Cycles

Results (primary -2.4%, secondary 2.7%)

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)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-2.4%	[-2.8%, -2.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.4%	[-2.8%, -2.0%]	2

Binary size

Results (primary -0.3%)

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)	-0.3%	[-0.6%, -0.0%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-0.6%, -0.0%]	2

Bootstrap: 482.657s -> 485.908s (0.67%)
Artifact size: 397.96 MiB -> 397.86 MiB (-0.03%)

[scottmcm]

r? @cjgillot

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[cjgillot]

@bors r+

[rust-bors]

📌 Commit 649e027 has been approved by cjgillot

It is now in the queue for this repository.

[rust-bors]

☀️ Test successful - CI
Approved by: cjgillot
Duration: 3h 35m
Pushing ef70767 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 7f99507 (parent) -> ef70767 (this PR)

Test differences

Show 6 test diffs

Stage 1

• [mir-opt] tests/mir-opt/instsimplify/align_or_size_of_sized_val.rs: [missing] -> pass (J1)
• [mir-opt] tests/mir-opt/pre-codegen/drop_box_of_sized.rs: [missing] -> pass (J1)

Stage 2

• [mir-opt] tests/mir-opt/instsimplify/align_or_size_of_sized_val.rs: [missing] -> pass (J0)
• [mir-opt] tests/mir-opt/pre-codegen/drop_box_of_sized.rs: [missing] -> pass (J0)

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

Job group index

• J0: aarch64-apple, aarch64-gnu, aarch64-gnu-llvm-20-1, aarch64-msvc-1, arm-android, armhf-gnu, dist-i586-gnu-i586-i686-musl, i686-gnu-1, i686-gnu-nopt-1, i686-msvc-1, test-various, x86_64-gnu, x86_64-gnu-gcc, x86_64-gnu-llvm-20, x86_64-gnu-llvm-20-2, x86_64-gnu-llvm-21-2, x86_64-gnu-nopt, x86_64-gnu-stable, x86_64-mingw-1, x86_64-msvc-1
• J1: x86_64-gnu-llvm-20-3, x86_64-gnu-llvm-21-3

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard ef70767064ab87b0a41400f69e1dc0b55c8d5284 --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: 1h 44m -> 3h 13m (+84.5%)
2. dist-x86_64-apple: 2h 28m -> 3h 12m (+29.6%)
3. x86_64-gnu-llvm-21-3: 1h 36m -> 1h 53m (+16.7%)
4. dist-x86_64-mingw: 2h 18m -> 2h 40m (+15.7%)
5. dist-apple-various: 1h 43m -> 1h 28m (-14.8%)
6. i686-gnu-nopt-1: 1h 56m -> 2h 10m (+12.0%)
7. x86_64-gnu-llvm-20: 1h 15m -> 1h 6m (-11.0%)
8. dist-ohos-armv7: 1h 20m -> 1h 12m (-9.8%)
9. aarch64-gnu-llvm-20-2: 49m 54s -> 45m 9s (-9.5%)
10. dist-powerpc64le-linux-gnu: 1h 41m -> 1h 31m (-9.5%)

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 (ef70767): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary -1.2%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.8%, 2.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.3%	[-3.4%, -3.2%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.2%	[-3.4%, 2.8%]	3

Cycles

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

Binary size

Results (primary -0.0%, secondary -0.0%)

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)	-0.0%	[-0.0%, -0.0%]	7
Improvements ✅ (secondary)	-0.0%	[-0.1%, -0.0%]	4
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	7

Bootstrap: 481.508s -> 496.246s (3.06%)
Artifact size: 397.92 MiB -> 397.86 MiB (-0.01%)