Also simplify size/align_of_val<T: Sized> to size/align_of<T> instead

[scottmcm]

Follow-up to #152641

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.

[scottmcm]

Conveniently, these extra blocks just disappear once the intrinsics are placed with constants.

[scottmcm]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: c0dc515 (c0dc515acf5ddad0df0c3ff3ba7f87438f6f9c84, parent: 873b4beb0cc726493b94c8ef21f68795c04fbbc1)

[rust-timer]

Finished benchmarking commit (c0dc515): 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)	4.4%	[0.2%, 16.1%]	4
Regressions ❌ (secondary)	0.4%	[0.1%, 0.8%]	6
Improvements ✅ (primary)	-0.5%	[-1.1%, -0.2%]	4
Improvements ✅ (secondary)	-1.1%	[-3.2%, -0.2%]	17
All ❌✅ (primary)	2.0%	[-1.1%, 16.1%]	8

Max RSS (memory usage)

Results (primary -1.3%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.3%, 2.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.9%, -1.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.3%	[-3.9%, 2.5%]	6

Cycles

Results (primary 12.2%, 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)	12.2%	[12.2%, 12.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.2%	[-3.9%, -2.6%]	3
All ❌✅ (primary)	12.2%	[12.2%, 12.2%]	1

Binary size

Results (primary 0.3%, secondary -0.9%)

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

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.0%, 1.4%]	14
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	8
Improvements ✅ (primary)	-0.4%	[-0.8%, -0.0%]	5
Improvements ✅ (secondary)	-1.4%	[-2.2%, -0.6%]	16
All ❌✅ (primary)	0.3%	[-0.8%, 1.4%]	19

Bootstrap: 481.904s -> 482.488s (0.12%)
Artifact size: 397.95 MiB -> 396.01 MiB (-0.49%)

[scottmcm]

Closing in favour of #152689