rustdoc: Optimize impl sorting during rendering

[petrochenkov]

This should fix the perf regression on bitmaps-3.1.0 from #107765.

The bitmaps crate has a lot of impls:

impl Bits for BitsImpl<1> { ... }
impl Bits for BitsImpl<2> { ... }
// ...
impl Bits for BitsImpl<1023> { ... }
impl Bits for BitsImpl<1024> { ... }

and the logic in fn print_item sorts them in natural order.

Before #107765 the impls came in source order, which happened to be already sorted in the necessary way.
So the comparison function was called fewer times.

After #107765 the impls came in "stable" order (based on def path hash).
So the comparison function was called more times to sort them.

The comparison function was terribly inefficient, so it caused a large perf regression.
This PR attempts to make it more efficient by using cached keys during sorting.

[rustbot]

r? @jsha

(rustbot has picked a reviewer for you, use r? to override)

[petrochenkov]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 4d55aff with merge 27184c344642b1a44cda998413b1b72972b11c05...

[bors]

☀️ Try build successful - checks-actions
Build commit: 27184c344642b1a44cda998413b1b72972b11c05 (27184c344642b1a44cda998413b1b72972b11c05)

[rust-timer]

Finished benchmarking commit (27184c344642b1a44cda998413b1b72972b11c05): 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)	-3.8%	[-10.1%, -0.4%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.8%	[-10.1%, -0.4%]	3

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-2.9%	[-4.1%, -1.7%]	8
All ❌✅ (primary)	0.2%	[-0.6%, 0.5%]	4

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.6%	[-6.7%, -0.6%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.6%	[-6.7%, -0.6%]	3

[GuillaumeGomez]

Thanks!

@bors r+ rollup=never

[bors]

📌 Commit 4d55aff has been approved by GuillaumeGomez

It is now in the queue for this repository.

[bors]

⌛ Testing commit 4d55aff with merge d13a19801c0a45c55c11f0cdb582b8b7da4f4f9d...

[bors]

💔 Test failed - checks-actions

[lqd]

C:\a\rust\rust\mingw64\bin\ranlib.exe: could not create temporary file whilst writing archive: no more archived files

@bors retry #108227

[bors]

⌛ Testing commit 4d55aff with merge f63fb86b6aeb292fd6a86ae476f1156b7c674b4f...

[bors]

💔 Test failed - checks-actions

[ehuss]

@bors retry

github incident

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[bors]

⌛ Testing commit 4d55aff with merge d012d2f...

[bors]

☀️ Test successful - checks-actions
Approved by: GuillaumeGomez
Pushing d012d2f to master...

[rust-timer]

Finished benchmarking commit (d012d2f): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.7%	[0.7%, 0.7%]	1
Improvements ✅ (primary)	-10.1%	[-10.1%, -10.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-10.1%	[-10.1%, -10.1%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.6%	[0.8%, 2.3%]	2
Regressions ❌ (secondary)	3.1%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.0%	[-1.9%, -0.5%]	5
All ❌✅ (primary)	1.6%	[0.8%, 2.3%]	2

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.7%	[1.4%, 2.0%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-7.8%	[-7.8%, -7.8%]	1
Improvements ✅ (secondary)	-0.5%	[-0.8%, -0.4%]	5
All ❌✅ (primary)	-0.2%	[-7.8%, 2.0%]	5

[rylev]

The one regression is noise.

@rustbot label: +perf-regression-triaged