rustdoc: use strategic ThinVec/Box to shrink clean::ItemKind

[notriddle]

No description provided.

[rustbot]

r? @GuillaumeGomez

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[notriddle]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 3abf0ba with merge 66af8f1...

[bors]

☀️ Try build successful - checks-actions
Build commit: 66af8f1 (66af8f13b6aea4ee11989c1cff435246f4b1e45f)

[rust-timer]

Finished benchmarking commit (66af8f1): comparison URL.

Overall result: ✅ improvements - no 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.

@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.3%, -0.2%]	2
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	3
All ❌✅ (primary)	-0.2%	[-0.3%, -0.2%]	2

Max RSS (memory usage)

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

Cycles

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

Binary size

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

Bootstrap: 771.748s -> 770.461s (-0.17%)
Artifact size: 329.08 MiB -> 329.01 MiB (-0.02%)

[notriddle]

Odd that instructions are improved instead of memory, while I'd have expected it the other way around.

Improvement's an improvement, I guess.

[rustbot]

Some changes occurred in src/librustdoc/clean/types.rs

cc @camelid

[workingjubilee]

Hmm. I am guessing dropping a few eightbytes, mostly off the stack, doesn't even register in "allocated stack space at peak"?

Whereas frequent copies to move data are common in Rust programs. Like, really common. ThinVec and ThinBox are the "right move" if you don't even look at them except to access them, basically.

[GuillaumeGomez]

Thanks for the extra information @workingjubilee !

Thanks @notriddle for the improvement!

@bors r+ rollup=iffy

[bors]

📌 Commit 3abf0ba has been approved by GuillaumeGomez

It is now in the queue for this repository.