Drop AST on a separate thread and prefetch hir_crate

[Zoxc]

This drop AST on a separate thread and prefetches hir_crate.

A spawn function is added to the parallel module which spawn some work on the Rayon thread pool.

[rustbot]

r? @cjgillot

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They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[cjgillot]

Did you measure a perf difference?

[Zoxc]

Did you measure a perf difference?

I expect it would below my noise threshold. I did verify the behavior with self profiling though.

[oskgo]

@Zoxc Any updates on this? Thanks!

[JohnCSimon]

@Zoxc
Ping from triage: I'm closing this due to inactivity, Please reopen when you are ready to continue with this.
Note: if you are going to continue please open the PR BEFORE you push to it, else you won't be able to reopen - this is a quirk of github.
Thanks for your contribution.

@rustbot label: +S-inactive

[Zoxc]

r? compiler

[Kobzol]

@bors try @rust-timer queue

[bors]

⌛ Trying commit e727382 with merge 247ff35...

[bors]

☀️ Try build successful - checks-actions
Build commit: 247ff35 (247ff35e9d6791d72ca2b1bd38483cd93fbcf19d)

[rust-timer]

Finished benchmarking commit (247ff35): comparison URL.

Overall result: ❌ regressions - please read the text below

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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.2%, 0.2%]	2
Regressions ❌ (secondary)	0.3%	[0.1%, 0.6%]	25
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[0.2%, 0.2%]	2

Max RSS (memory usage)

Results (primary 0.8%, secondary -2.0%)

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)	3.1%	[3.1%, 3.1%]	1
Regressions ❌ (secondary)	2.3%	[2.2%, 2.5%]	2
Improvements ✅ (primary)	-1.6%	[-1.6%, -1.6%]	1
Improvements ✅ (secondary)	-3.0%	[-4.4%, -0.9%]	9
All ❌✅ (primary)	0.8%	[-1.6%, 3.1%]	2

Cycles

Results (secondary -2.9%)

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)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-3.2%, -2.7%]	2
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 776.507s -> 777.766s (0.16%)
Artifact size: 366.05 MiB -> 365.95 MiB (-0.03%)

[petrochenkov]

@Zoxc What is the status of this PR? Is it ready for review, or something still needs to be done?

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[Zoxc]

Why merging this if the perf diff is below the threshold?

Because I expect it to improve performance. I can see that AST dropping is offloaded to another thread and threads are no longer blocked on hir_crate with self-profiling. Running the parallel compiler is just too noisy to measure any improvements.

[petrochenkov]

Ok, this is simple enough, and looks reasonable, let's merge.
r=me with the comment explaining the weirdness in hir_crate prefetching.

[Zoxc]

@rustbot ready

[petrochenkov]

@bors r+

[bors]

📌 Commit ef94033 has been approved by petrochenkov

It is now in the queue for this repository.

[bors]

⌛ Testing commit ef94033 with merge 0c33fe2...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 0c33fe2 to master...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing b45dd71 (parent) -> 0c33fe2 (this PR)

Test differences

No test diffs found

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 0c33fe2c3d3eecadd17a84b110bb067288a64f1c --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. dist-aarch64-apple: 5535.0s -> 4671.7s (-15.6%)
2. dist-apple-various: 7325.4s -> 6251.0s (-14.7%)
3. x86_64-gnu-llvm-20-1: 5362.5s -> 6091.3s (13.6%)
4. x86_64-gnu-tools: 6417.5s -> 5582.3s (-13.0%)
5. dist-riscv64-linux: 5825.3s -> 5115.1s (-12.2%)
6. x86_64-apple-2: 5647.7s -> 5112.9s (-9.5%)
7. x86_64-msvc-ext1: 7770.1s -> 7146.0s (-8.0%)
8. dist-arm-linux: 4770.1s -> 5128.4s (7.5%)
9. aarch64-apple: 4272.4s -> 4029.3s (-5.7%)
10. dist-x86_64-apple: 8622.8s -> 8269.4s (-4.1%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (0c33fe2): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.9%	[-2.9%, -2.9%]	1

Max RSS (memory usage)

Results (primary 0.1%, secondary -1.6%)

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)	2.6%	[0.8%, 4.7%]	4
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	2
Improvements ✅ (primary)	-0.8%	[-2.8%, -0.4%]	11
Improvements ✅ (secondary)	-4.1%	[-4.5%, -3.9%]	3
All ❌✅ (primary)	0.1%	[-2.8%, 4.7%]	15

Cycles

Results (primary 0.1%, secondary -2.7%)

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)	0.7%	[0.4%, 1.1%]	9
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.0%	[-2.8%, -0.4%]	5
Improvements ✅ (secondary)	-2.7%	[-3.1%, -2.4%]	5
All ❌✅ (primary)	0.1%	[-2.8%, 1.1%]	14

Binary size

Results (primary -1.1%)

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)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Bootstrap: 767.216s -> 768.387s (0.15%)
Artifact size: 365.58 MiB -> 365.56 MiB (-0.01%)