Split DepGraph::read_index in two.

[nnethercote]

DepGraph::read_index is a reasonably large function and it is currently inlined into query_get_at which is very hot and instantiated many times.

The compiler becomes smaller and faster if we inline only the outermost check. (This check always fails in non-incremental builds and always succeeds in incremental builds).

Note: this pattern of having a method in DepGraph and another one with the same name in DepGraphData is well established, e.g. try_mark_green, node_color, encode_side_effect.

[nnethercote]

@bors try @rust-timer queue

[nnethercote]

@bors try cancel

[rust-bors]

Try build cancelled. Cancelled workflows:

• https://github.com/rust-lang/rust/actions/runs/23033383212

[nnethercote]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: e9658c4 (e9658c4f4597c5eb9f24368cbaa5db617f76e99a, parent: 4efe3dc40fdd5ed3d001e7736ff384f2d21d7361)

[rust-timer]

Finished benchmarking commit (e9658c4): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@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)	0.3%	[0.1%, 0.5%]	68
Regressions ❌ (secondary)	0.4%	[0.0%, 1.0%]	40
Improvements ✅ (primary)	-0.3%	[-0.4%, -0.1%]	13
Improvements ✅ (secondary)	-0.6%	[-1.7%, -0.1%]	10
All ❌✅ (primary)	0.2%	[-0.4%, 0.5%]	81

Max RSS (memory usage)

Results (primary -2.5%, secondary 0.3%)

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)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-0.9%	[-0.9%, -0.8%]	2
All ❌✅ (primary)	-2.5%	[-2.5%, -2.5%]	1

Cycles

Results (secondary -2.8%)

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)	-	-	0
Improvements ✅ (secondary)	-2.8%	[-2.8%, -2.8%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 482.458s -> 478.131s (-0.90%)
Artifact size: 394.92 MiB -> 394.78 MiB (-0.04%)