Make bridge::Buffer generic again.

[nnethercote]

It was made non-generic in #97004, but that (surprisingly) caused a mild
performance regression.

r? @eddyb

[nnethercote]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit b41ece9 with merge 2032e7bcf336d8021dd5ab28f20766209c37ea49...

[alex]

I'd have guessed the being non-generic was a performance regression because of the impact on cross-crate inlining, but all the changes here are in a single create 🤷

[bors]

☀️ Try build successful - checks-actions
Build commit: 2032e7bcf336d8021dd5ab28f20766209c37ea49 (2032e7bcf336d8021dd5ab28f20766209c37ea49)

[rust-timer]

Queued 2032e7bcf336d8021dd5ab28f20766209c37ea49 with parent 28b8919, future comparison URL.

[mystor]

I'd have guessed the being non-generic was a performance regression because of the impact on cross-crate inlining, but all the changes here are in a single create 🤷

The type is used in generic code by the proc_macro server when specializing it for use by proc_macro_server.rs when configuring the server types, which is probably where the regression came from. Marking the methods as #[inline] probably will have a similar impact to making it generic again.

[rust-timer]

Finished benchmarking commit (2032e7bcf336d8021dd5ab28f20766209c37ea49): comparison url.

Instruction count

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: 🎉 relevant improvements found

	mean1	max	count2
Regressions 😿 (primary)	2.2%	2.2%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-0.8%	-1.4%	7
All 😿🎉 (primary)	2.2%	2.2%	1

Max RSS (memory usage)

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: 😿 relevant regressions found

	mean1	max	count2
Regressions 😿 (primary)	2.4%	2.4%	1
Regressions 😿 (secondary)	3.1%	4.1%	2
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	2.4%	2.4%	1

Cycles

Results

• Primary benchmarks: 😿 relevant regression found
• Secondary benchmarks: no relevant changes found

	mean1	max	count2
Regressions 😿 (primary)	3.3%	3.3%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	3.3%	3.3%	1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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-review -S-waiting-on-perf +perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³

[eddyb]

r=me if this is acceptable, but @mystor's #[inline] suggestion is what I came here to also suggest, it might be simpler?

[nnethercote]

Which methods would need inlining?

[eddyb]

Actually, every fn in this module might need #[inline] (all 17 of them), so can you just edit the comment to say that without generics, #[inline] would be needed everywhere to avoid performance regressions and r=me?

[nnethercote]

I tried the inlining approach and it gave slightly better performance, so I have opened #97604.