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

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

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@Hayden602 Hayden602 commented Sep 12, 2025 •
edited by fmease
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rustbot commented Sep 12, 2025

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 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
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r? @clubby789

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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.

@rustbot rustbot assigned SparrowLii and unassigned clubby789 Sep 12, 2025
Kobzol
Kobzol reviewed Sep 12, 2025
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Thanks, looks good! Could you please add an Info level entry to the change_tracker.rs file?

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bootstrap.example.toml
@@ -859,6 +859,13 @@
# 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
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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`).

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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

// Add parallel frontend threads configuration
if let Some(threads) = self.config.rust_parallel_frontend_threads {
rustflags.arg(&format!("-Zthreads={}", threads));
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Suggested change
rustflags.arg(&format!("-Zthreads={}", threads));
rustflags.arg(&format!("-Zthreads={threads}"));

bootstrap.example.toml
@@ -859,6 +859,13 @@
# 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
# The valid options are:
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Suggested change
# The valid options are:
# The valid options are:
# 0 - Set the number of threads according to the detected number of threads of the host system

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maybe something like "according to the available parallelism" in the way we document https://doc.rust-lang.org/std/thread/fn.available_parallelism.html?

lqd
lqd reviewed Sep 12, 2025
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bootstrap.example.toml
@@ -859,6 +859,13 @@
# 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
# The valid options are:
# 1 - Use non-parallel compilation
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that's only in the frontend, so it's not "non-parallel compilation"

@fmease 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
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@Hayden602 @rustbot @rust-log-analyzer @lqd @Kobzol @clubby789 @SparrowLii