Add LLVM range attributes to slice length parameters

[scottmcm]

It'll take a bunch more work to do this in layout -- because of cycles in struct Foo<'a>(&'a Foo<'a>); -- so until we figure out how to do that well, just look for slices specifically and add the proper range for the length.

[rustbot]

r? @JonathanBrouwer

rustbot has assigned @JonathanBrouwer.
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

[scottmcm]

This file is the simplest demonstration of LLVM taking advantage of it. See https://rust.godbolt.org/z/7jxqsaaTx showing that it didn't know nuw/nsw for these things previously.

[scottmcm]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 398e28a (398e28a631e9d9248dbf3cef0409d1b7a684b917, parent: 82ae0ee6487e93bd6c05167ccb2ef3485fdbc890)

[rust-timer]

Finished benchmarking commit (398e28a): 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)	0.2%	[0.2%, 0.2%]	1
Regressions ❌ (secondary)	1.0%	[0.1%, 2.0%]	20
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-0.4%	[-0.7%, -0.1%]	15
All ❌✅ (primary)	-0.1%	[-0.4%, 0.2%]	2

Max RSS (memory usage)

Results (secondary -1.1%)

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)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.1%	[-4.1%, -4.1%]	1
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary 0.6%)

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%	[2.1%, 3.8%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-2.9%, -2.1%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.1%, 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%]	1
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	14
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	37
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	14

Bootstrap: 475.716s -> 474.193s (-0.32%)
Artifact size: 390.89 MiB -> 390.71 MiB (-0.04%)