Add parallel-frontend-threads to bootstrap.toml and enable multi-threaded parallel compilation #146458

Hayden602 · 2025-09-12T01:45:55Z

Add the option to use the parallel compiler when building Rust code in bootstrap.

rustbot · 2025-09-12T01:45:57Z

This PR modifies bootstrap.example.toml.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

rustbot · 2025-09-12T01:45:59Z

r? @clubby789

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Hayden602 · 2025-09-12T09:16:10Z

r? @SparrowLii @Kobzol
Hi，I’ve finished handling the issue regarding enabling parallel front end in bootstrap. Please help review if it looks appropriate. Thank you.

Kobzol

Thanks, looks good! Could you please add an Info level entry to the change_tracker.rs file?

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Kobzol · 2025-09-12T13:30:49Z

bootstrap.example.toml

 # Trigger a `DebugBreak` after an internal compiler error during bootstrap on Windows
 #rust.break-on-ice = true

+# Set the number of threads used during rustc compilation


Suggested change

# Set the number of threads used during rustc compilation

# Set the number of threads for the compiler frontend used during rustc compilation (passed to `-Zthreads`).

This change also isn't limited to what is "used during rustc compilation", right? Tools, std, etc will get -Zthreads as well it seems?

src/bootstrap/src/core/builder/cargo.rs

bootstrap.example.toml

lqd · 2025-09-12T15:42:42Z

bootstrap.example.toml


+# Set the number of threads used during rustc compilation
+# The valid options are:
+# 1 - Use non-parallel compilation


that's only in the frontend, so it's not "non-parallel compilation"

rustbot · 2025-09-15T06:23:23Z

This PR was rebased onto a different master 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.

src/bootstrap/src/utils/change_tracker.rs

Kobzol

As lqd said, it's not only the compilation of rustc (the compiler), but pretty much all Rust code built by bootstrap. Left three suggestions, if you accept them, and then squash the commits, I think we can go ahead and merge this :) Thanks!

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bootstrap.example.toml

…aded parallel compilation

klensy · 2025-09-16T10:03:20Z

bootstrap.example.toml

+# 0 - Set the number of threads according to the detected number of threads of the host system
+# 0 - Set the number of threads according to the detected number of threads of the host system


Equal lines.

Kobzol · 2025-09-17T05:31:33Z

Thank you!

@bors r+ rollup

bors · 2025-09-17T05:31:36Z

📌 Commit 929c933 has been approved by Kobzol

It is now in the queue for this repository.

Rollup of 7 pull requests Successful merges: - #146458 (Add parallel-frontend-threads to bootstrap.toml and enable multi-threaded parallel compilation) - #146485 (Remove unsized arg handling in `ArgAbiBuilderMethods::store_fn_arg` implementations) - #146536 (clean up several trait related UI tests) - #146598 (Make llvm_enzyme a regular cargo feature) - #146647 (Move `#[rustc_coherence_is_core]` to the `crate_level` file) - #146654 (Do not use `git -C dir`) - #146681 (Add space after brace in `Box<[T]>::new_uninit_slice` example) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #146458 - Hayden602:bootstrap, r=Kobzol Add parallel-frontend-threads to bootstrap.toml and enable multi-threaded parallel compilation Add the option to use the parallel compiler when building Rust code in bootstrap.

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-bootstrap Relevant to the bootstrap subteam: Rust's build system (x.py and src/bootstrap) labels Sep 12, 2025

rustbot assigned clubby789 Sep 12, 2025

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Hayden602 force-pushed the bootstrap branch from 009b6b1 to feed02f Compare September 12, 2025 05:38

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Hayden602 force-pushed the bootstrap branch from feed02f to d4ce225 Compare September 12, 2025 06:36

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Hayden602 force-pushed the bootstrap branch 2 times, most recently from ebc3e15 to 7c0230f Compare September 12, 2025 07:13

rustbot assigned SparrowLii and unassigned clubby789 Sep 12, 2025

Kobzol reviewed Sep 12, 2025

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lqd reviewed Sep 12, 2025

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fmease changed the title ~~Add parallel-frontend-threads to bootstrap.toml and enable multi-thre…~~ Add parallel-frontend-threads to bootstrap.toml and enable multi-threaded parallel compilation Sep 12, 2025

Hayden602 force-pushed the bootstrap branch 2 times, most recently from 264a516 to b5ebe58 Compare September 15, 2025 06:23

Kobzol reviewed Sep 15, 2025

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Add parallel-frontend-threads to bootstrap.toml and enable multi-thre…

929c933

…aded parallel compilation

klensy reviewed Sep 16, 2025

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Hayden602 force-pushed the bootstrap branch from f09635a to 929c933 Compare September 17, 2025 02:31

bors 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 Sep 17, 2025

jdonszelmann mentioned this pull request Sep 17, 2025

Rollup of 7 pull requests #146685

Merged

bors merged commit 0a2be63 into rust-lang:master Sep 18, 2025
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rustbot added this to the 1.92.0 milestone Sep 18, 2025

	# Set the number of threads used during rustc compilation
	# Set the number of threads for the compiler frontend used during rustc compilation (passed to `-Zthreads`).

		# 0 - Set the number of threads according to the detected number of threads of the host system
		# 0 - Set the number of threads according to the detected number of threads of the host system

Add parallel-frontend-threads to bootstrap.toml and enable multi-threaded parallel compilation #146458

Add parallel-frontend-threads to bootstrap.toml and enable multi-threaded parallel compilation #146458

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