rustdoc: microoptimize render_item, move stuff out of common path

[lolbinarycat]

No description provided.

[lolbinarycat]

@bors2 try @rust-timer queue

[rust-bors]

💥 Test timed out after 21600s

[lolbinarycat]

Well that's weird.

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: 6b58920 (6b589205722c3dd266a9917cb1ea3210eda969db, parent: af5c5b74c8f2c0b1dfd9a201453bf2df538e93e0)

[rust-timer]

Finished benchmarking commit (6b58920): comparison URL.

Overall result: ✅ 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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.7%	[-3.1%, -0.4%]	2
Improvements ✅ (secondary)	-1.5%	[-3.0%, -1.2%]	7
All ❌✅ (primary)	-1.7%	[-3.1%, -0.4%]	2

Max RSS (memory usage)

Results (primary -2.3%)

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)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Cycles

Results (primary 2.4%, secondary 2.0%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	2.0%	[1.7%, 2.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Binary size

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

Bootstrap: 475.694s -> 475.403s (-0.06%)
Artifact size: 388.39 MiB -> 388.40 MiB (0.00%)

[lolbinarycat]

Finally managed to find a simple optimization that actually leads to statistically significant improvements!