Simplify the `cache_on_disk_if` modifier to just `cache_on_disk` by Zalathar · Pull Request #154576 · rust-lang/rust

Zalathar · 2026-03-30T10:14:40Z

Thanks to #154304, there is now only one remaining query with a non-trivial cache-on-disk condition (check_liveness). But prior experiments at #153441 (comment) indicate that check_liveness can also be made non-disk-caching with little or no measurable effect.

This PR takes advantage of those facts to replace the cache_on_disk_if modifier with a simpler cache_on_disk modifier:

When combined with separate_provide_extern, only values for “local” keys are cached to disk.
For any other query with cache_on_disk, values are cached to disk unconditionally.

r? nnethercote (or compiler)

Zalathar · 2026-03-30T10:15:22Z

cc @Zoxc @zetanumbers

Zalathar · 2026-03-30T10:15:27Z

@bors try @rust-timer queue

Simplify the `cache_on_disk_if` modifier to just `cache_on_disk`

zetanumbers · 2026-03-30T11:24:20Z

Ok, that's good

zetanumbers · 2026-03-30T13:56:20Z

Zulip topic for context: #t-compiler/query-system > Removing key_fingerprint_style and cache_on_disk_if

rust-bors · 2026-03-30T16:24:33Z

💔 Test for 72527f8 failed: CI

lqd · 2026-03-30T16:26:33Z

timeout
@bors try

Simplify the `cache_on_disk_if` modifier to just `cache_on_disk`

rust-bors · 2026-03-30T18:34:09Z

☀️ Try build successful (CI)
Build commit: 5a1a969 (5a1a969187f4afe604cb916bc5740a09c5062f4b, parent: cf7da0b7277cad05b79f91b60c290aa08a17a6f0)

rust-timer · 2026-03-30T19:14:23Z

Finished benchmarking commit (5a1a969): 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
Regressions ❌ (secondary)	0.8%	[0.8%, 0.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.6%, -0.1%]	8
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 1.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.4%	[1.4%, 1.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.4%	[1.4%, 1.4%]	1

Cycles

Results (secondary -1.6%)

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)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.4%	[-5.4%, -5.4%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 483.836s -> 485.128s (0.27%)
Artifact size: 394.90 MiB -> 394.80 MiB (-0.02%)

nnethercote · 2026-03-31T02:29:05Z

compiler/rustc_query_impl/src/query_impl.rs

+                    _tcx: TyCtxt<'tcx>,
+                    _key: rustc_middle::queries::$name::Key<'tcx>,
+                ) -> bool {
+                    if !cfg!($cache_on_disk) {


Can you use #[cfg] instead of cfg!?

Alternatively, cfg_select! might make this function nicer.

The cfg_select! version ends up being a bit visually “messier”, but has the benefit of being very explicit about exhaustively listing all possible cases, which seems like an improvement. 👍

This is the only remaining query with a non-trivial `cache_on_disk_if` condition, but previous perf experiments indicate that it can be removed entirely, with little or no measurable effect.

rustbot · 2026-03-31T03:45:50Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Queries with both `cache_on_disk` and `separate_provide_extern` will only disk-cache values for local keys. Other queries with `cache_on_disk` will disk-cache all values unconditionally.

Zalathar · 2026-03-31T04:05:12Z

@rustbot ready

rustbot assigned nnethercote Mar 30, 2026

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rust-bors bot pushed a commit that referenced this pull request Mar 30, 2026

Auto merge of #154576 - Zalathar:cache-on-disk, r=<try>

72527f8

Simplify the `cache_on_disk_if` modifier to just `cache_on_disk`

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Mar 30, 2026

zetanumbers mentioned this pull request Mar 30, 2026

Remove will_cache_on_disk_for_key_fn #154591

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rust-bors bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 30, 2026

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Auto merge of #154576 - Zalathar:cache-on-disk, r=<try>

5a1a969

Simplify the `cache_on_disk_if` modifier to just `cache_on_disk`

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Mar 30, 2026

nnethercote reviewed Mar 31, 2026

View reviewed changes

Don't cache query check_liveness on disk

2a1340a

This is the only remaining query with a non-trivial `cache_on_disk_if` condition, but previous perf experiments indicate that it can be removed entirely, with little or no measurable effect.

Zalathar force-pushed the cache-on-disk branch from cc70ec0 to 771cc33 Compare March 31, 2026 03:45

Zalathar added 2 commits March 31, 2026 14:53

Simplify the cache_on_disk_if modifier to just cache_on_disk

f77d3dd

Queries with both `cache_on_disk` and `separate_provide_extern` will only disk-cache values for local keys. Other queries with `cache_on_disk` will disk-cache all values unconditionally.

Remove the tcx parameter from will_cache_on_disk_for_key_fn

5b7f8e6

Zalathar force-pushed the cache-on-disk branch from 771cc33 to 5b7f8e6 Compare March 31, 2026 03:55

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 31, 2026

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rust-timer commented Mar 30, 2026

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

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Binary size

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