[PERF] [rustdoc] Try to speed up search index building

[yotamofek]

@GuillaumeGomez

[yotamofek]

this is the (hopefully) impactful part: FunctionData is an OTW representation of IndexItemFunctionType, and there's no need to do the writing and parsing part until we leave the boundaries of the current process invocation

[yotamofek]

first commit is just a cleanup (IMHO, probably a matter of taste): 15c5e34

[GuillaumeGomez]

cc @notriddle as well.

Starting perf check. :)

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 53439ce (53439ceb215dbeebc67ba002601a21921d427a98, parent: d2acb427e424fd7d52377698046a06109e9777b4)

[rust-timer]

Finished benchmarking commit (53439ce): 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)	-0.2%	[-0.3%, -0.1%]	5
Improvements ✅ (secondary)	-0.9%	[-1.0%, -0.8%]	6
All ❌✅ (primary)	-0.2%	[-0.3%, -0.1%]	5

Max RSS (memory usage)

Results (primary -0.5%, 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)	1.4%	[1.4%, 1.4%]	1
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	-0.5%	[-2.3%, 1.4%]	2

Cycles

Results (secondary -2.6%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-3.2%, -2.1%]	3
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 470.924s -> 473.064s (0.45%)
Artifact size: 388.38 MiB -> 388.26 MiB (-0.03%)