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Use thread::available_parallelism as the default limit for backend parallelism #160424

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Merged
rust-bors merged 1 commit into from
Aug 4, 2026
+7 −28
Merged

Use thread::available_parallelism as the default limit for backend parallelism #160424

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6 changes: 2 additions & 4 deletions compiler/rustc_interface/src/interface.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@ use rustc_parse::lexer::StripTokens;
use rustc_parse::new_parser_from_source_str;
use rustc_parse::parser::Recovery;
use rustc_query_impl::print_query_stack;
use rustc_session::config::{self, BackendJobs, Cfg, CheckCfg, ExpectedValues, Input, OutFileName};
use rustc_session::config::{self, Cfg, CheckCfg, ExpectedValues, Input, OutFileName};
use rustc_session::parse::ParseSess;
use rustc_session::{CompilerIO, EarlyDiagCtxt, Session, lint};
use rustc_span::source_map::{FileLoader, RealFileLoader, SourceMapInputs};
Expand Down Expand Up @@ -375,9 +375,7 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se

// Initialize jobserver as early as possible.
let early_dcx = EarlyDiagCtxt::new(config.opts.error_format);
if let Some(limit) =
config.opts.jobs.frontend.max(config.opts.jobs.backend.map(BackendJobs::value))
{
if let Some(limit) = config.opts.jobs.frontend.max(config.opts.jobs.backend) {
jobserver::initialize(limit.get(), |err| {
let note = "the build environment is likely misconfigured";
early_dcx.early_struct_warn(err).with_note(note).emit()
Expand Down
29 changes: 5 additions & 24 deletions compiler/rustc_session/src/config.rs
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Expand Up @@ -1649,26 +1649,6 @@ impl PointerAuthOption {
}
}

#[derive(Clone, Copy)]
pub enum BackendJobs {
/// The number of backend jobs has a static limit.
Limited(NonZero<usize>),
/// The number of backend jobs is either unlimited if there's an inherited jobserver,
/// or limited to 32 if there's no inherited jobserver.
/// This variant exists only to preserve the historical behavior.
/// FIXME: Just use `thread::available_parallelism` as the default static limit.
UnlimitedOr32,
}

impl BackendJobs {
pub fn value(self) -> NonZero<usize> {
match self {
BackendJobs::Limited(n) => n,
BackendJobs::UnlimitedOr32 => NonZero::new(32).unwrap(),
}
}
}

#[derive(Clone, Copy)]
pub enum LinkerJobs {
/// Do not pass anything to the linker, use it's default behavior.
Expand All @@ -1682,7 +1662,7 @@ pub enum LinkerJobs {
#[derive(Clone, Copy)]
pub struct Jobs {
pub frontend: Option<NonZero<usize>>,
pub backend: Option<BackendJobs>,
pub backend: Option<NonZero<usize>>,
pub linker: LinkerJobs,
}

Expand Down Expand Up @@ -1735,11 +1715,12 @@ fn parse_jobs_all(
let backend =
parse_jobs_one(early_dcx, opt_name, &jobs_backend, unstable, &mut available);
check_upper_limit(backend, opt_name);
backend.map(BackendJobs::Limited)
backend
}
None => match jobs {
Some(n) => n.map(BackendJobs::Limited),
None => Some(BackendJobs::UnlimitedOr32),
Some(n) => n,
// Use all available parallelism as the default.
None => parse_jobs_one(early_dcx, "", "0", unstable, &mut available),
},
};
let linker = match matches.opt_str("jobs-linker") {
Expand Down
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