Create a single value cache for the () query key

[Zoxc]

Since queries using () as the key can only store a single value, specialize for that case.

This looks like a minor performance improvement:

Benchmark	Before	After
	Time	Time	%
🟣 clap:check	1.8477s	1.8415s	-0.33%
🟣 hyper:check	0.2666s	0.2655s	-0.40%
🟣 syntex_syntax:check	6.3943s	6.3686s	-0.40%
🟣 syn:check	1.6413s	1.6345s	-0.42%
🟣 regex:check	1.0337s	1.0313s	-0.24%
Total	11.1836s	11.1414s	-0.38%
Summary	1.0000s	0.9964s	-0.36%

[rustbot]

r? @michaelwoerister

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

[Kobzol]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 0b5596289641e0a47ca3d884f307a7e96bdfc151 with merge 9b74d0d9d6c9601238b6a07f19da4ca467e78dcd...

[cjgillot]

@bors try @rust-timer queue

[bors]

⌛ Trying commit ba143bc3067c723344af9cdd305732d909f12597 with merge b3fa81ef1f2c856493537937ac8080386c81739a...

[bors]

☀️ Try build successful - checks-actions
Build commit: b3fa81ef1f2c856493537937ac8080386c81739a (b3fa81ef1f2c856493537937ac8080386c81739a)

[rust-timer]

Finished benchmarking commit (b3fa81ef1f2c856493537937ac8080386c81739a): comparison URL.

Overall result: ❌✅ regressions and improvements - 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.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@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)	0.6%	[0.5%, 0.7%]	3
Improvements ✅ (primary)	-0.3%	[-0.3%, -0.2%]	8
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	3
All ❌✅ (primary)	-0.3%	[-0.3%, -0.2%]	8

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)	3.5%	[2.7%, 4.6%]	4
Regressions ❌ (secondary)	2.8%	[0.6%, 4.7%]	24
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.5%	[2.7%, 4.6%]	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)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	2
Improvements ✅ (secondary)	-1.7%	[-2.1%, -1.5%]	6
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	2

[cjgillot]

My pending review was asking for a version with arena, but considering this discussion https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/.60arena_cache.60.20query.20option

Perf is neutral-green, within <1% range.

@bors r+

[bors]

📌 Commit ba143bc3067c723344af9cdd305732d909f12597 has been approved by cjgillot

It is now in the queue for this repository.

[klensy]

Perf is neutral-green, within <1% range.

While instructions ok, max-rss not so neutral.

[bors]

⌛ Testing commit ba143bc3067c723344af9cdd305732d909f12597 with merge 788404bfb6f4f482a386e1306606a5fe59ed273f...

[bors]

💔 Test failed - checks-actions

[cjgillot]

@bors retry curl: (6) Could not resolve host: ci-mirrors.rust-lang.org

[bors]

⌛ Testing commit ba143bc3067c723344af9cdd305732d909f12597 with merge 9550d95507c1c9af656f32551702ab3e9f1b9d49...

[bors]

💔 Test failed - checks-actions

[cjgillot]

@bors r+

[bors]

📌 Commit 80d2652 has been approved by cjgillot

It is now in the queue for this repository.

[bors]

⌛ Testing commit 80d2652 with merge 5b8f284...

[bors]

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing 5b8f284 to master...

[rust-timer]

Finished benchmarking commit (5b8f284): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -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)	1.2%	[1.2%, 1.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.2%	[-4.2%, -4.2%]	1
All ❌✅ (primary)	1.2%	[1.2%, 1.2%]	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)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.9%	[-3.9%, -3.9%]	1
All ❌✅ (primary)	-	-	0

Cycles

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