Experiment: spaceship in MIR

[scottmcm]

As mentioned in #108788 (comment), Ord::cmp on primitives generates a large amount of MIR, preventing (or at least discouraging) it from mir-inlining.

Let's see whether making it a MIR primitive helps stuff -- derived (Partial)Ord in particular, if we're lucky.

r? @ghost

[scottmcm]

@bors try @rust-timer queue

[bors]

⌛ Trying commit d6fa338 with merge afab298db3408356c94adab4dfc262c869673b6d...

[bors]

☀️ Try build successful - checks-actions
Build commit: afab298db3408356c94adab4dfc262c869673b6d (afab298db3408356c94adab4dfc262c869673b6d)

[fbstj]

a question for my own understanding: is there a reason why it's better (or has to be) for this to be in a single instance of the fn cmp rather than either #[cfg(bootstrap)] fn cmp(...) or on the impl?

[scottmcm]

I just put it here because it's the least copy-pasting. Doing it at other levels would work too, but would mean duplicating the #[inline] or stability attributes, which leaves more opportunities for me to get it wrong.

[Noratrieb]

You don't have the duplicate the signature and the #[inline] attribute. But it doesn't make that much of a difference (also hopefully we'll get rid of these cfg(bootstrap) inside the standard library soon anyways🤞)

[rust-timer]

Finished benchmarking commit (afab298db3408356c94adab4dfc262c869673b6d): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.3%, 0.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.0%	[-1.1%, -0.9%]	2
Improvements ✅ (secondary)	-2.2%	[-2.6%, -2.0%]	7
All ❌✅ (primary)	-0.3%	[-1.1%, 0.5%]	4

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.2%	[2.1%, 4.3%]	2
Regressions ❌ (secondary)	3.7%	[3.7%, 3.7%]	1
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.1%	[-0.1%, 4.3%]	3

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.5%	[-2.5%, -2.5%]	1
All ❌✅ (primary)	-	-	0

[Dylan-DPC]

Closing this as it was an experiment