Store dep_kind_vtables in an array inside QuerySystem

[Zalathar]

This should hopefully avoid a bounds-check and indirection on every DepKindVTable lookup, and also makes query system init a little nicer.

[Zalathar]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: e73bdda (e73bddaca21d935693863670e21052a90fd15a1e, parent: fe7294f8793d001bc3f9d197e7cdef6cdb46c15a)

[rust-timer]

Finished benchmarking commit (e73bdda): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.2%	[-0.3%, -0.0%]	59
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.1%]	29
All ❌✅ (primary)	-0.2%	[-0.3%, -0.0%]	59

Max RSS (memory usage)

Results (primary -0.6%, secondary -2.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	0.7%	[0.7%, 0.7%]	1
Improvements ✅ (primary)	-1.8%	[-1.8%, -1.8%]	1
Improvements ✅ (secondary)	-3.6%	[-6.9%, -1.0%]	5
All ❌✅ (primary)	-0.6%	[-1.8%, 0.6%]	2

Cycles

Results (primary -3.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.0%	[-3.0%, -3.0%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.0%	[-3.0%, -3.0%]	1

Binary size

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

Bootstrap: 482.3s -> 482.558s (0.05%)
Artifact size: 394.83 MiB -> 396.83 MiB (0.51%)

[Zalathar]

Looks like a very modest across-the-board perf win.

I would be reluctant to accept that for a PR that added complexity in the name of performance, but since this PR is aiming to reduce complexity, getting a slim perf boost is a nice bonus.

[Zalathar]

It would be nice to make the DepKindVTable array fully static, but that might require #![feature(external_item_impls)] since we want to define it downstream in rustc_query_impl.

[rust-bors]

☔ The latest upstream changes (presumably #154289) made this pull request unmergeable. Please resolve the merge conflicts.