Decouple SCC annotations from SCCs

[amandasystems]

This rewires SCC annotations to have them be a separate, visitor-type data structure. It was broken out of #130227, which needed them to be able to remove unused annotations after computation without recomputing the SCCs themselves.

As a drive-by it also removes some redundant code from the hot loop in SCC construction for a performance improvement.

r? lcnr

[lcnr]

@bors try @rust-timer queue

[bors]

⌛ Trying commit ae763d6 with merge 207b712...

[bors]

☀️ Try build successful - checks-actions
Build commit: 207b712 (207b712831b7b56fe9f65a990e17ad17f59246e1)

[rust-timer]

Finished benchmarking commit (207b712): 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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.7%, secondary -1.7%)

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)	0.9%	[0.4%, 2.3%]	11
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-0.6%, -0.4%]	2
Improvements ✅ (secondary)	-1.7%	[-1.7%, -1.7%]	1
All ❌✅ (primary)	0.7%	[-0.6%, 2.3%]	13

Cycles

Results (primary 0.5%, secondary 3.5%)

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%]	1
Regressions ❌ (secondary)	3.5%	[3.5%, 3.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Binary size

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

Bootstrap: 775.789s -> 774.37s (-0.18%)
Artifact size: 364.79 MiB -> 364.78 MiB (-0.00%)