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Rollup merge of #126472 - onur-ozkan:improve-libcxx-build, r=Kobzol

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build `libcxx-version` only when it doesn't exist

In https://github.com/rust-lang/rust/issues/126423, it seems like c++ parsing takes quite amount of time on bootstrap startups. This PR makes libcxx-version to be compiled only when it doesn't exist.

A simple demonstration on the overhead of buiding `libcxx-version`:

```sh
$ rm -rf build/host/libcxx-version

$ x build
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.07s

 ----- LIBCXX VERSION CHECK TOOK: 509ms
Building tool rustdoc (stage1 -> stage2, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized] target(s) in 0.25s
Build completed successfully in 0:00:02

$ x build
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.07s

 ----- LIBCXX VERSION CHECK TOOK: 2ms
Creating a sysroot for stage2 compiler (use `rustup toolchain link 'name' build/host/stage2`)
Building tool rustdoc (stage1 -> stage2, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized] target(s) in 0.14s
Build completed successfully in 0:00:01
```
This commit is contained in:
Matthias Krüger 2024-06-15 10:56:43 +02:00 committed by GitHub
commit b5dd3d4ada
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2 changed files with 23 additions and 10 deletions
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30
src/bootstrap/src/core/build_steps/tool.rs
View File

@ -823,19 +823,29 @@ impl Step for LibcxxVersionTool {
fn run(self, builder: &Builder<'_>) -> LibcxxVersion {
let out_dir = builder.out.join(self.target.to_string()).join("libcxx-version");
let _ = fs::remove_dir_all(&out_dir);
t!(fs::create_dir_all(&out_dir));
let compiler = builder.cxx(self.target).unwrap();
let mut cmd = Command::new(compiler);
let executable = out_dir.join(exe("libcxx-version", self.target));
cmd.arg("-o").arg(&executable).arg(builder.src.join("src/tools/libcxx-version/main.cpp"));
builder.run_cmd(&mut cmd);
// This is a sanity-check specific step, which means it is frequently called (when using
// CI LLVM), and compiling `src/tools/libcxx-version/main.cpp` at the beginning of the bootstrap
// invocation adds a fair amount of overhead to the process (see https://github.com/rust-lang/rust/issues/126423).
// Therefore, we want to avoid recompiling this file unnecessarily.
if !executable.exists() {
panic!("Something went wrong. {} is not present", executable.display());
if !out_dir.exists() {
t!(fs::create_dir_all(&out_dir));
}
let compiler = builder.cxx(self.target).unwrap();
let mut cmd = Command::new(compiler);
cmd.arg("-o")
.arg(&executable)
.arg(builder.src.join("src/tools/libcxx-version/main.cpp"));
builder.run_cmd(&mut cmd);
if !executable.exists() {
panic!("Something went wrong. {} is not present", executable.display());
}
}
let version_output = output(&mut Command::new(executable));

3
src/bootstrap/src/core/sanity.rs
View File

@ -128,6 +128,9 @@ pub fn check(build: &mut Build) {
eprintln!(
"Consider upgrading libstdc++ or disabling the `llvm.download-ci-llvm` option."
);
eprintln!(
"If you choose to upgrade libstdc++, run `x clean` or delete `build/host/libcxx-version` manually after the upgrade."
);
}
}
tool::LibcxxVersion::Llvm(_) => {