Auto merge of #113592 - Kobzol:pgo-script-bolt, r=Mark-Simulacrum

Move BOLT from `bootstrap` to `opt-dist`

Currently, we use BOLT to optimize LLVM for x64 Linux. The BOLT instrumentation and optimization step is implemented in `bootstrap`, but it was always quite hacky, because BOLT works quite differently than PGO. Rather than building an instrumented artifact, it takes an already built artifact and instruments it in-place. This is not a good fit for the bootstrap caching mechanism, and it meant that we had to run BOLT "on-the-fly" when packaging LLVM artifacts into the created sysroot.

The BOLT code was also really only used by the PGO script (now called `opt-dist`) and nothing else, so it was quite hardcoded for this one single usage. And even if someone wanted to use the `--llvm-bolt-profile-[use/generate]` bootstrap flags outside of the PGO script, they would also need to implement profile gathering, as this is not performed by bootstrap anyway.

I think that it could be more practical to move the BOLT logic to the `opt-dist` tool instead. This simplifies bootstrap, removes unneeded implementation of BOLT caching (we will now do it exactly once - no need to check if it has been performed already when bootstrap copies `libLLVM.so` around multiple times) and removes two BOLT-specific bootstrap flags, and also one special case for building LLVM (instead I pass the linker flags with `--set llvm.ldflags` from `opt-dist` now).

There are also a few disadvantages to this new approach:
- We have to guess/find the path to the built `libLLVM.so` file (but currently this is quite easy, it's just in `stage2/lib`).
- We have to provide the BOLT profile externally to bootstrap, so that it is packaged into the reproducible artifacts archive. Doesn't seem like a big deal to me.
- We are depending on some inner behavior of boostrap in `opt-dist` (namely, that `libLLVM.so` is hardlinked). But we do that for many other things in the `opt-dist` tool anyway, it's tied quite closely to bootstrap.

I would like to go back to my attempts to also use BOLT for `librustc_driver.so`, and I think that it might be a bit simpler if I also do it from the `opt-dist` tool, so this is the first step towards that.

Anyway, let me know what you think about this. It's just a refactoring in a way, no big deal.

r? bootstrap

Cargo.lock

@@ -2495,6 +2495,7 @@ dependencies = [
  "serde_json",
  "sysinfo",
  "tar",
+ "tempfile",
  "xz",
  "zip",
 ]

src/bootstrap/config.rs

@@ -232,8 +232,8 @@ pub struct Config {
     pub llvm_profile_use: Option<String>,
     pub llvm_profile_generate: bool,
     pub llvm_libunwind_default: Option<LlvmLibunwind>,
-    pub llvm_bolt_profile_generate: bool,
-    pub llvm_bolt_profile_use: Option<String>,
+
+    pub reproducible_artifacts: Vec<String>,
 
     pub build: TargetSelection,
     pub hosts: Vec<TargetSelection>,
@@ -1127,15 +1127,6 @@ impl Config {
         config.free_args = std::mem::take(&mut flags.free_args);
         config.llvm_profile_use = flags.llvm_profile_use;
         config.llvm_profile_generate = flags.llvm_profile_generate;
-        config.llvm_bolt_profile_generate = flags.llvm_bolt_profile_generate;
-        config.llvm_bolt_profile_use = flags.llvm_bolt_profile_use;
-
-        if config.llvm_bolt_profile_generate && config.llvm_bolt_profile_use.is_some() {
-            eprintln!(
-                "Cannot use both `llvm_bolt_profile_generate` and `llvm_bolt_profile_use` at the same time"
-            );
-            exit!(1);
-        }
 
         // Infer the rest of the configuration.
 
@@ -1471,6 +1462,8 @@ impl Config {
             config.rust_profile_generate = flags.rust_profile_generate;
         }
 
+        config.reproducible_artifacts = flags.reproducible_artifact;
+
         // rust_info must be set before is_ci_llvm_available() is called.
         let default = config.channel == "dev";
         config.omit_git_hash = omit_git_hash.unwrap_or(default);

src/bootstrap/dist.rs

@@ -18,9 +18,7 @@ use std::process::Command;
 
 use object::read::archive::ArchiveFile;
 use object::BinaryFormat;
-use sha2::Digest;
 
-use crate::bolt::{instrument_with_bolt, optimize_with_bolt};
 use crate::builder::{Builder, Kind, RunConfig, ShouldRun, Step};
 use crate::cache::{Interned, INTERNER};
 use crate::channel;
@@ -1941,19 +1939,7 @@ fn install_llvm_file(builder: &Builder<'_>, source: &Path, destination: &Path) {
         return;
     }
 
-    // After LLVM is built, we modify (instrument or optimize) the libLLVM.so library file.
-    // This is not done in-place so that the built LLVM files are not "tainted" with BOLT.
-    // We perform the instrumentation/optimization here, on the fly, just before they are being
-    // packaged into some destination directory.
-    let postprocessed = if builder.config.llvm_bolt_profile_generate {
-        builder.ensure(BoltInstrument::new(source.to_path_buf()))
-    } else if let Some(path) = &builder.config.llvm_bolt_profile_use {
-        builder.ensure(BoltOptimize::new(source.to_path_buf(), path.into()))
-    } else {
-        source.to_path_buf()
-    };
-
-    builder.install(&postprocessed, destination, 0o644);
+    builder.install(&source, destination, 0o644);
 }
 
 /// Maybe add LLVM object files to the given destination lib-dir. Allows either static or dynamic linking.
@@ -2038,117 +2024,6 @@ pub fn maybe_install_llvm_runtime(builder: &Builder<'_>, target: TargetSelection
     }
 }
 
-/// Creates an output path to a BOLT-manipulated artifact for the given `file`.
-/// The hash of the file is used to make sure that we don't mix BOLT artifacts amongst different
-/// files with the same name.
-///
-/// We need to keep the file-name the same though, to make sure that copying the manipulated file
-/// to a directory will not change the final file path.
-fn create_bolt_output_path(builder: &Builder<'_>, file: &Path, hash: &str) -> PathBuf {
-    let directory = builder.out.join("bolt").join(hash);
-    t!(fs::create_dir_all(&directory));
-    directory.join(file.file_name().unwrap())
-}
-
-/// Instrument the provided file with BOLT.
-/// Returns a path to the instrumented artifact.
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
-pub struct BoltInstrument {
-    file: PathBuf,
-    hash: String,
-}
-
-impl BoltInstrument {
-    fn new(file: PathBuf) -> Self {
-        let mut hasher = sha2::Sha256::new();
-        hasher.update(t!(fs::read(&file)));
-        let hash = hex::encode(hasher.finalize().as_slice());
-
-        Self { file, hash }
-    }
-}
-
-impl Step for BoltInstrument {
-    type Output = PathBuf;
-
-    const ONLY_HOSTS: bool = false;
-    const DEFAULT: bool = false;
-
-    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
-        run.never()
-    }
-
-    fn run(self, builder: &Builder<'_>) -> PathBuf {
-        if builder.build.config.dry_run() {
-            return self.file.clone();
-        }
-
-        if builder.build.config.llvm_from_ci {
-            println!("warning: trying to use BOLT with LLVM from CI, this will probably not work");
-        }
-
-        println!("Instrumenting {} with BOLT", self.file.display());
-
-        let output_path = create_bolt_output_path(builder, &self.file, &self.hash);
-        if !output_path.is_file() {
-            instrument_with_bolt(&self.file, &output_path);
-        }
-        output_path
-    }
-}
-
-/// Optimize the provided file with BOLT.
-/// Returns a path to the optimized artifact.
-///
-/// The hash is stored in the step to make sure that we don't optimize the same file
-/// twice (even under  different file paths).
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
-pub struct BoltOptimize {
-    file: PathBuf,
-    profile: PathBuf,
-    hash: String,
-}
-
-impl BoltOptimize {
-    fn new(file: PathBuf, profile: PathBuf) -> Self {
-        let mut hasher = sha2::Sha256::new();
-        hasher.update(t!(fs::read(&file)));
-        hasher.update(t!(fs::read(&profile)));
-        let hash = hex::encode(hasher.finalize().as_slice());
-
-        Self { file, profile, hash }
-    }
-}
-
-impl Step for BoltOptimize {
-    type Output = PathBuf;
-
-    const ONLY_HOSTS: bool = false;
-    const DEFAULT: bool = false;
-
-    fn should_run(run: ShouldRun<'_>) -> ShouldRun<'_> {
-        run.never()
-    }
-
-    fn run(self, builder: &Builder<'_>) -> PathBuf {
-        if builder.build.config.dry_run() {
-            return self.file.clone();
-        }
-
-        if builder.build.config.llvm_from_ci {
-            println!("warning: trying to use BOLT with LLVM from CI, this will probably not work");
-        }
-
-        println!("Optimizing {} with BOLT", self.file.display());
-
-        let output_path = create_bolt_output_path(builder, &self.file, &self.hash);
-        if !output_path.is_file() {
-            optimize_with_bolt(&self.file, &self.profile, &output_path);
-        }
-        output_path
-    }
-}
-
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct LlvmTools {
     pub target: TargetSelection,
@@ -2390,8 +2265,8 @@ impl Step for ReproducibleArtifacts {
             tarball.add_file(path, ".", 0o644);
             added_anything = true;
         }
-        if let Some(path) = builder.config.llvm_bolt_profile_use.as_ref() {
-            tarball.add_file(path, ".", 0o644);
+        for profile in &builder.config.reproducible_artifacts {
+            tarball.add_file(profile, ".", 0o644);
             added_anything = true;
         }
         if added_anything { Some(tarball.generate()) } else { None }

src/bootstrap/flags.rs

@@ -149,12 +149,9 @@ pub struct Flags {
     /// generate PGO profile with llvm built for rustc
     #[arg(global(true), long)]
     pub llvm_profile_generate: bool,
-    /// generate BOLT profile for LLVM build
+    /// Additional reproducible artifacts that should be added to the reproducible artifacts archive.
     #[arg(global(true), long)]
-    pub llvm_bolt_profile_generate: bool,
-    /// use BOLT profile for LLVM build
-    #[arg(global(true), value_hint = clap::ValueHint::FilePath, long, value_name = "PROFILE")]
-    pub llvm_bolt_profile_use: Option<String>,
+    pub reproducible_artifact: Vec<String>,
     #[arg(global(true))]
     /// paths for the subcommand
     pub paths: Vec<PathBuf>,

src/bootstrap/lib.rs

@@ -39,7 +39,6 @@ use crate::util::{
     dir_is_empty, exe, libdir, mtime, output, run, run_suppressed, symlink_dir, try_run_suppressed,
 };
 
-mod bolt;
 mod builder;
 mod cache;
 mod cc_detect;

src/bootstrap/llvm.rs

@@ -342,12 +342,6 @@ impl Step for Llvm {
         if let Some(path) = builder.config.llvm_profile_use.as_ref() {
             cfg.define("LLVM_PROFDATA_FILE", &path);
         }
-        if builder.config.llvm_bolt_profile_generate
-            || builder.config.llvm_bolt_profile_use.is_some()
-        {
-            // Relocations are required for BOLT to work.
-            ldflags.push_all("-Wl,-q");
-        }
 
         // Disable zstd to avoid a dependency on libzstd.so.
         cfg.define("LLVM_ENABLE_ZSTD", "OFF");