Misc. cleanups to librustdocs "clean" fns

[yotamofek]

Small cleanups while working on bigger stuff.

Might have very slight performance improvement (408dc50 avoids a few unneeded Clones), but I doubt they'll register on a perf run. So this is mostly just making the code (hopefully) a bit nicer.

[rustbot]

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[GuillaumeGomez]

I'm surprised by this change, but looks good to me. Let's confirm perf results and then let's r+ it. :)

@bors try @rust-timer queue

[bors]

⌛ Trying commit eb8e7d4 with merge 3c1d700...

[bors]

☀️ Try build successful - checks-actions
Build commit: 3c1d700 (3c1d700d9816ba61883b811680a446c4ed7a12e6)

[rust-timer]

Finished benchmarking commit (3c1d700): comparison URL.

Overall result: ❌✅ regressions and 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)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	-0.5%	[-1.3%, 0.3%]	2

Max RSS (memory usage)

Results (secondary -1.5%)

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
Improvements ✅ (secondary)	-1.5%	[-1.6%, -1.3%]	6
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 1.5%)

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

	mean	range	count
Regressions ❌ (primary)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.5%	[1.5%, 1.5%]	1

Binary size

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

Bootstrap: 689.082s -> 690.29s (0.18%)
Artifact size: 371.89 MiB -> 371.92 MiB (0.01%)

[GuillaumeGomez]

Seems like it ends with the small perf reduction in syn2.

[yotamofek]

Ah damn, let me see if I can keep some of the cleanups while resolving the perf hit.