Simplify parallel! macro #152329

Zoxc · 2026-02-08T10:24:34Z

This replaces the parallel! macro with a par_fns function.

Zoxc · 2026-02-08T10:27:00Z

Simplify parallel! macro

rust-bors · 2026-02-08T12:38:36Z

☀️ Try build successful (CI)
Build commit: 00e0ea3 (00e0ea3c8c5e6aab513ed4e366a2cea0708cc658, parent: 13c38730d981289cc7ae4cc109fd7756bf83ee67)

rust-timer · 2026-02-08T13:19:32Z

Finished benchmarking commit (00e0ea3): comparison URL.

Overall result: no relevant changes - 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.

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@rustbot label: -S-waiting-on-perf -perf-regression

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Results (secondary -5.9%)

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	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.9%	[-5.9%, -5.9%]	1
All ❌✅ (primary)	-	-	0

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	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-3.3%, -3.3%]	1
All ❌✅ (primary)	-	-	0

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Bootstrap: 471.737s -> 472.587s (0.18%)
Artifact size: 397.92 MiB -> 397.90 MiB (-0.00%)

rustbot · 2026-02-09T02:12:07Z

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nnethercote

Nice change, the function form is much nicer to read than the macro. A few nits below.

View changes since this review

nnethercote · 2026-02-10T09:18:46Z

compiler/rustc_data_structures/src/sync/parallel.rs

+                    return;
+                };
+
+                // Reverse the order of the later closures since Rayon executes them in reverse order


"later" can be removed? The order here is just simple reversed, right?

I'm referring to rest and specifically excluding first, as first always runs first as we directly execute it.

nnethercote · 2026-02-10T09:19:20Z

compiler/rustc_data_structures/src/sync/parallel.rs

+                    });
+                }
+
+                guard.run(|| first[0]());


Probably worth a brief comment about how/why the first function is run on the current thread, to avoid an unnecessary spawn.

compiler/rustc_data_structures/src/sync/parallel.rs

nnethercote · 2026-02-10T09:20:32Z

compiler/rustc_data_structures/src/sync/parallel.rs

+///
+/// The first block is executed immediately on the current thread.
+/// Use that for the longest running block.
+pub fn par_fns(funcs: &mut [&mut (dyn FnMut() + DynSend)]) {


Is it better to just keep the name parallel?

I like the par prefix for fork-join functions. I changed it to par_blocks, that seems to match the current use better. I also renamed join to match.

nnethercote

Getting closer. Can you also squash the two commits together? Thanks.

View changes since this review

nnethercote · 2026-02-12T02:03:29Z

compiler/rustc_data_structures/src/sync/parallel.rs

-/// Use that for the longest running block.
-pub fn par_fns(funcs: &mut [&mut (dyn FnMut() + DynSend)]) {
+/// Use that for the longest running block for better scheduling.
+pub fn par_blocks(funcs: &mut [&mut (dyn FnMut() + DynSend)]) {


par_blocks would have made sense with the macro implementation, because blocks are a macro concept. But it doesn't make sense here. par_fns is better. And the comments that refer to blocks should be changed to say "functions".

…`par_join`

nnethercote · 2026-02-12T22:26:08Z

Good change, thanks.

nnethercote · 2026-02-12T22:26:16Z

@bors r+ rollup

rust-bors · 2026-02-12T22:26:19Z

📌 Commit 8c5ce26 has been approved by nnethercote

It is now in the queue for this repository.

…hercote Simplify parallel! macro This replaces the `parallel!` macro with a `par_fns` function.

Rollup of 18 pull requests Successful merges: - #150551 (Compute localized outlives constraints lazily) - #150752 (Update libc to v0.2.181) - #150988 (Improve code suggestion for incorrect macro_rules! usage) - #152422 (Change query proc macro to be more rust-analyzer friendly) - #152496 (Fix multi-cgu+debug builds using autodiff by delaying autodiff till lto) - #152514 (Collect active query jobs into struct `QueryJobMap`) - #152520 (Don't use `DepContext` in `rustc_middle::traits::cache`) - #152528 (Support serializing CodegenContext) - #152082 (Move tests) - #152232 (Add must_use for FileTimes) - #152329 (Simplify parallel! macro) - #152444 (`-Znext-solver` Prevent committing unfulfilled unsized coercion) - #152486 (remove redundant backchain attribute in codegen) - #152519 (Fix feature gating for new `try bikeshed` expressions) - #152529 (sparc64: enable abi compatibility test) - #152548 (reject inline const patterns pre-expansion) - #152550 (Port #[prelude_import] to the attribute parser) - #152552 (Add 2048-bit HvxVectorPair support to Hexagon SIMD ABI checks)

…hercote Simplify parallel! macro This replaces the `parallel!` macro with a `par_fns` function.

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Feb 8, 2026

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rust-bors bot pushed a commit that referenced this pull request Feb 8, 2026

Auto merge of #152329 - Zoxc:simple-parallel-macro, r=<try>

00e0ea3

Simplify parallel! macro

rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 8, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 8, 2026

Zoxc force-pushed the simple-parallel-macro branch from 4926482 to 95495be Compare February 9, 2026 01:54

Zoxc marked this pull request as ready for review February 9, 2026 02:12

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 9, 2026

rustbot assigned jackh726 Feb 9, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Feb 9, 2026

nnethercote reviewed Feb 10, 2026

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nnethercote assigned nnethercote and unassigned jackh726 Feb 10, 2026

nnethercote reviewed Feb 12, 2026

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Replace parallel! macro with par_fns function and rename join to …

8c5ce26

…`par_join`

Zoxc force-pushed the simple-parallel-macro branch from a6727dd to 8c5ce26 Compare February 12, 2026 11:35

nnethercote approved these changes Feb 12, 2026

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rust-bors bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 12, 2026

Zalathar added a commit to Zalathar/rust that referenced this pull request Feb 13, 2026

Rollup merge of rust-lang#152329 - Zoxc:simple-parallel-macro, r=nnet…

a7385a9

…hercote Simplify parallel! macro This replaces the `parallel!` macro with a `par_fns` function.

Zalathar mentioned this pull request Feb 13, 2026

Rollup of 18 pull requests #152560

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Zalathar added a commit to Zalathar/rust that referenced this pull request Feb 13, 2026

Rollup merge of rust-lang#152329 - Zoxc:simple-parallel-macro, r=nnet…

09720ec

…hercote Simplify parallel! macro This replaces the `parallel!` macro with a `par_fns` function.

Zalathar mentioned this pull request Feb 13, 2026

Rollup of 17 pull requests #152562

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rust-timer commented Feb 8, 2026

Overall result: no relevant changes - no action needed

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