Create dummy_{source,sink} lazily.

[nnethercote]

Because they're rarely needed. This gives a very small but very easy perf win.

r? @lqd

[nnethercote]

@bors try @rust-timer queue

[bors]

⌛ Trying commit b8895e9 with merge d82713eb111ca3622504573d2d910ff6a7a2cd35...

[bors]

☀️ Try build successful - checks-actions
Build commit: d82713eb111ca3622504573d2d910ff6a7a2cd35 (d82713eb111ca3622504573d2d910ff6a7a2cd35)

[nnethercote]

I will let the perf run finish for completeness, but I found a different improvement that subsumes this one in #110527.

r? @ghost

[rustbot]

Failed to set assignee to ghost: invalid assignee

Note: Only org members, users with write permissions, or people who have commented on the PR may be assigned.

[lqd]

I can just review the other PR.

[rust-timer]

Finished benchmarking commit (d82713eb111ca3622504573d2d910ff6a7a2cd35): 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
Improvements ✅ (secondary)	-0.5%	[-0.6%, -0.4%]	3
All ❌✅ (primary)	-	-	0

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)	2.8%	[1.8%, 3.7%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[-3.1%, 3.7%]	3

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)	-2.7%	[-4.5%, -1.1%]	9
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.7%	[-4.5%, -1.1%]	9

[nnethercote]

Lots of green that is below the significant threshold but is still meaningful. But #110527 should be better.

[nnethercote]

Closing this in favour of #110527.