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bootstrap: Don't trigger an unnecessary LLVM build from check builds #144011

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76780d0
Don't trigger an LLVM build from check builds using the stage 0 compiler
Zalathar Jul 16, 2025
bf75472
Clean up an unused compiler-stage parameter
Zalathar Jul 16, 2025
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2 changes: 1 addition & 1 deletion src/bootstrap/src/core/build_steps/check.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -350,7 +350,7 @@ impl Step for CodegenBackend {
cargo
.arg("--manifest-path")
.arg(builder.src.join(format!("compiler/rustc_codegen_{backend}/Cargo.toml")));
rustc_cargo_env(builder, &mut cargo, target, build_compiler.stage);
rustc_cargo_env(builder, &mut cargo, target);

let _guard = builder.msg_check(format!("rustc_codegen_{backend}"), target, None);

Expand Down
20 changes: 7 additions & 13 deletions src/bootstrap/src/core/build_steps/compile.rs
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Expand Up @@ -1316,15 +1316,10 @@ pub fn rustc_cargo(
cargo.env("RUSTC_WRAPPER", ccache);
}

rustc_cargo_env(builder, cargo, target, build_compiler.stage);
rustc_cargo_env(builder, cargo, target);
}

pub fn rustc_cargo_env(
builder: &Builder<'_>,
cargo: &mut Cargo,
target: TargetSelection,
build_stage: u32,
) {
pub fn rustc_cargo_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelection) {
// Set some configuration variables picked up by build scripts and
// the compiler alike
cargo
Expand Down Expand Up @@ -1384,13 +1379,12 @@ pub fn rustc_cargo_env(
// detected that LLVM is already built and good to go which helps prevent
// busting caches (e.g. like #71152).
if builder.config.llvm_enabled(target) {
let building_is_expensive =
let building_llvm_is_expensive =
crate::core::build_steps::llvm::prebuilt_llvm_config(builder, target, false)
.should_build();
// `top_stage == stage` might be false for `check --stage 1`, if we are building the stage 1 compiler
let can_skip_build = builder.kind == Kind::Check && builder.top_stage == build_stage;
let should_skip_build = building_is_expensive && can_skip_build;
if !should_skip_build {

let skip_llvm = (builder.kind == Kind::Check) && building_llvm_is_expensive;
if !skip_llvm {
rustc_llvm_env(builder, cargo, target)
}
}
Expand Down Expand Up @@ -1665,7 +1659,7 @@ impl Step for CodegenBackend {
cargo
.arg("--manifest-path")
.arg(builder.src.join(format!("compiler/rustc_codegen_{backend}/Cargo.toml")));
rustc_cargo_env(builder, &mut cargo, target, compiler.stage);
rustc_cargo_env(builder, &mut cargo, target);

// Ideally, we'd have a separate step for the individual codegen backends,
// like we have in tests (test::CodegenGCC) but that would require a lot of restructuring.
Expand Down
4 changes: 2 additions & 2 deletions src/bootstrap/src/core/build_steps/test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3386,7 +3386,7 @@ impl Step for CodegenCranelift {
cargo
.arg("--manifest-path")
.arg(builder.src.join("compiler/rustc_codegen_cranelift/build_system/Cargo.toml"));
compile::rustc_cargo_env(builder, &mut cargo, target, compiler.stage);
compile::rustc_cargo_env(builder, &mut cargo, target);

// Avoid incremental cache issues when changing rustc
cargo.env("CARGO_BUILD_INCREMENTAL", "false");
Expand Down Expand Up @@ -3518,7 +3518,7 @@ impl Step for CodegenGCC {
cargo
.arg("--manifest-path")
.arg(builder.src.join("compiler/rustc_codegen_gcc/build_system/Cargo.toml"));
compile::rustc_cargo_env(builder, &mut cargo, target, compiler.stage);
compile::rustc_cargo_env(builder, &mut cargo, target);
add_cg_gcc_cargo_flags(&mut cargo, &gcc);

// Avoid incremental cache issues when changing rustc
Expand Down
48 changes: 40 additions & 8 deletions src/bootstrap/src/core/builder/tests.rs
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Expand Up @@ -630,6 +630,46 @@ fn any_debug() {
assert_eq!(x.downcast_ref::<MyStruct>(), Some(&MyStruct { x: 7 }));
}

#[test]
fn test_check_compiler_doesnt_build_llvm() {
// Checking the stage 1 compiler uses the bootstrap compiler, and therefore
// should not need to build LLVM.
{
let config = configure_with_args(
&["check", "compiler", "--stage=1"],
&[TEST_TRIPLE_1],
&[TEST_TRIPLE_1],
);
let mut cache = run_build(&config.paths.clone(), config);

assert!(!cache.contains::<llvm::Llvm>());
}

// Checking the stage 1 library uses the stage 1 compiler, so it will need LLVM.
{
let config = configure_with_args(
&["check", "library", "--stage=1"],
&[TEST_TRIPLE_1],
&[TEST_TRIPLE_1],
);
let mut cache = run_build(&config.paths.clone(), config);

assert!(cache.contains::<llvm::Llvm>());
}

// Checking the stage 2 compiler uses the stage 1 compiler, so it will need LLVM.
{
let config = configure_with_args(
&["check", "compiler", "--stage=2"],
&[TEST_TRIPLE_1],
&[TEST_TRIPLE_1],
);
let mut cache = run_build(&config.paths.clone(), config);

assert!(cache.contains::<llvm::Llvm>());
}
}

/// These tests use insta for snapshot testing.
/// See bootstrap's README on how to bless the snapshots.
mod snapshot {
Expand Down Expand Up @@ -1294,7 +1334,6 @@ mod snapshot {
ctx.config("check")
.path("compiler")
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> cranelift 1 <host>
[check] rustc 0 <host> -> gcc 1 <host>
Expand All @@ -1304,7 +1343,6 @@ mod snapshot {
ctx.config("check")
.path("rustc")
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
");
}
Expand All @@ -1324,7 +1362,6 @@ mod snapshot {
.path("compiler")
.stage(1)
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> cranelift 1 <host>
[check] rustc 0 <host> -> gcc 1 <host>
Expand Down Expand Up @@ -1456,7 +1493,6 @@ mod snapshot {
.paths(&["library", "compiler"])
.args(&args)
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> cranelift 1 <host>
[check] rustc 0 <host> -> gcc 1 <host>
Expand All @@ -1470,7 +1506,6 @@ mod snapshot {
ctx.config("check")
.path("miri")
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> Miri 1 <host>
");
Expand All @@ -1491,7 +1526,6 @@ mod snapshot {
.path("miri")
.stage(1)
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> Miri 1 <host>
");
Expand Down Expand Up @@ -1544,7 +1578,6 @@ mod snapshot {
ctx.config("check")
.path("rustc_codegen_cranelift")
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> cranelift 1 <host>
[check] rustc 0 <host> -> gcc 1 <host>
Expand All @@ -1558,7 +1591,6 @@ mod snapshot {
ctx.config("check")
.path("rust-analyzer")
.render_steps(), @r"
[build] llvm <host>
[check] rustc 0 <host> -> rustc 1 <host>
[check] rustc 0 <host> -> rust-analyzer 1 <host>
");
Expand Down
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