Introduce new bootstrap config section for PGO configuration

bootstrap.example.toml

@@ -973,6 +973,24 @@
 #dist.vendor = if "is a tarball source" || "is a git repository" { true } else { false }
 
 
+# =============================================================================
+# Profile-guided optimization options
+#
+# Configure the PGO profile to be used for compilation, or a path where the
+# profile will be written by an instrumented binary, for individual components
+# =============================================================================
+
+# Use the following profile to PGO optimize the Rust compiler.
+#pgo.rustc.use = "/tmp/profiles/foo.profraw"
+# Instrument the Rust compiler, so that when executed, it will gather profiles
+# to this path.
+#pgo.rustc.generate = "/tmp/profiles/foo.profraw"
+# Use the following profile to PGO optimize LLVM.
+#pgo.llvm.use = "/tmp/profiles/foo.profraw"
+# Instrument LLVM, so that when executed, it will gather profiles
+# Note: for LLVM specifically, this should be a directory, not a file path.
+#pgo.llvm.generate = "/tmp/profiles"
+
 # =============================================================================
 # Options for specific targets
 #

src/bootstrap/src/core/build_steps/compile.rs

@@ -1293,22 +1293,20 @@ pub fn rustc_cargo(
         cargo.rustflag("-Clink-args=-Wl,--icf=all");
     }
 
-    if builder.config.rust_profile_use.is_some() && builder.config.rust_profile_generate.is_some() {
-        panic!("Cannot use and generate PGO profiles at the same time");
-    }
-    let is_collecting = if let Some(path) = &builder.config.rust_profile_generate {
+    let is_collecting = if let Some(path) = &builder.config.rust_pgo.generate_profile {
         if build_compiler.stage == 1 {
-            cargo.rustflag(&format!("-Cprofile-generate={path}"));
+            cargo
+                .rustflag(&format!("-Cprofile-generate={}", path.to_str().expect("non-UTF8 path")));
             // Apparently necessary to avoid overflowing the counters during
             // a Cargo build profile
             cargo.rustflag("-Cllvm-args=-vp-counters-per-site=4");
             true
         } else {
             false
         }
-    } else if let Some(path) = &builder.config.rust_profile_use {
+    } else if let Some(path) = &builder.config.rust_pgo.use_profile {
         if build_compiler.stage == 1 {
-            cargo.rustflag(&format!("-Cprofile-use={path}"));
+            cargo.rustflag(&format!("-Cprofile-use={}", path.to_str().expect("non-UTF8 path")));
             if builder.is_verbose() {
                 cargo.rustflag("-Cllvm-args=-pgo-warn-missing-function");
             }
@@ -1464,7 +1462,7 @@ fn rustc_llvm_env(builder: &Builder<'_>, cargo: &mut Cargo, target: TargetSelect
     // found. This is to avoid the linker errors about undefined references to
     // `__llvm_profile_instrument_memop` when linking `rustc_driver`.
     let mut llvm_linker_flags = String::new();
-    if builder.config.llvm_profile_generate
+    if builder.config.llvm_pgo.generate_profile.is_some()
         && target.is_msvc()
         && let Some(ref clang_cl_path) = builder.config.llvm_clang_cl
     {

src/bootstrap/src/core/build_steps/dist.rs

@@ -3035,11 +3035,11 @@ impl Step for ReproducibleArtifacts {
     fn run(self, builder: &Builder<'_>) -> Self::Output {
         let mut added_anything = false;
         let tarball = Tarball::new(builder, "reproducible-artifacts", &self.target.triple);
-        if let Some(path) = builder.config.rust_profile_use.as_ref() {
+        if let Some(path) = builder.config.rust_pgo.use_profile.as_ref() {
             tarball.add_file(path, ".", FileType::Regular);
             added_anything = true;
         }
-        if let Some(path) = builder.config.llvm_profile_use.as_ref() {
+        if let Some(path) = builder.config.llvm_pgo.use_profile.as_ref() {
             tarball.add_file(path, ".", FileType::Regular);
             added_anything = true;
         }

src/bootstrap/src/core/build_steps/llvm.rs

@@ -19,7 +19,7 @@ use build_helper::git::PathFreshness;
 
 use crate::core::build_steps::llvm;
 use crate::core::builder::{Builder, RunConfig, ShouldRun, Step, StepMetadata};
-use crate::core::config::{Config, TargetSelection};
+use crate::core::config::{Config, LlvmPgoGenerationMode, TargetSelection};
 use crate::utils::build_stamp::{BuildStamp, generate_smart_stamp_hash};
 use crate::utils::exec::command;
 use crate::utils::helpers::{
@@ -369,14 +369,17 @@ impl Step for Llvm {
         // This flag makes sure `FileCheck` is copied in the final binaries directory.
         cfg.define("LLVM_INSTALL_UTILS", "ON");
 
-        if builder.config.llvm_profile_generate {
+        if let Some(mode) = builder.config.llvm_pgo.generate_profile.as_ref() {
             cfg.define("LLVM_BUILD_INSTRUMENTED", "IR");
-            if let Ok(llvm_profile_dir) = std::env::var("LLVM_PROFILE_DIR") {
-                cfg.define("LLVM_PROFILE_DATA_DIR", llvm_profile_dir);
+            match mode {
+                LlvmPgoGenerationMode::Implicit => {}
+                LlvmPgoGenerationMode::Directory(llvm_profile_dir) => {
+                    cfg.define("LLVM_PROFILE_DATA_DIR", llvm_profile_dir);
+                }
             }
             cfg.define("LLVM_BUILD_RUNTIME", "No");
         }
-        if let Some(path) = builder.config.llvm_profile_use.as_ref() {
+        if let Some(path) = builder.config.llvm_pgo.use_profile.as_ref() {
             cfg.define("LLVM_PROFDATA_FILE", path);
         }
 
@@ -1326,7 +1329,7 @@ impl Step for Lld {
         // when doing PGO on CI, cmake or clang-cl don't automatically link clang's
         // profiler runtime in. In that case, we need to manually ask cmake to do it, to avoid
         // linking errors, much like LLVM's cmake setup does in that situation.
-        if builder.config.llvm_profile_generate
+        if builder.config.llvm_pgo.generate_profile.is_some()
             && target.is_msvc()
             && let Some(clang_cl_path) = builder.config.llvm_clang_cl.as_ref()
         {

src/bootstrap/src/core/config/config.rs

@@ -41,6 +41,7 @@ use crate::core::config::toml::dist::Dist;
 use crate::core::config::toml::gcc::Gcc;
 use crate::core::config::toml::install::Install;
 use crate::core::config::toml::llvm::Llvm;
+use crate::core::config::toml::pgo::{Pgo, PgoConfig};
 use crate::core::config::toml::rust::{
     BootstrapOverrideLld, Rust, RustOptimize, check_incompatible_options_for_ci_rustc,
     parse_codegen_backends,
@@ -190,6 +191,7 @@ pub struct Config {
     pub llvm_cxxflags: Option<String>,
     pub llvm_ldflags: Option<String>,
     pub llvm_use_libcxx: bool,
+    pub llvm_pgo: LlvmPgoConfig,
 
     // gcc codegen options
     pub gcc_ci_mode: GccCiMode,
@@ -225,17 +227,14 @@ pub struct Config {
     pub rust_remap_debuginfo: bool,
     pub rust_new_symbol_mangling: Option<bool>,
     pub rust_annotate_moves_size_limit: Option<u64>,
-    pub rust_profile_use: Option<String>,
-    pub rust_profile_generate: Option<String>,
     pub rust_lto: RustcLto,
     pub rust_validate_mir_opts: Option<u32>,
     pub rust_std_features: BTreeSet<String>,
     pub rust_break_on_ice: bool,
     pub rust_parallel_frontend_threads: Option<u32>,
     pub rust_rustflags: Vec<String>,
+    pub rust_pgo: PgoConfig,
 
-    pub llvm_profile_use: Option<String>,
-    pub llvm_profile_generate: bool,
     pub llvm_libunwind_default: Option<LlvmLibunwind>,
     pub enable_bolt_settings: bool,
 
@@ -456,8 +455,20 @@ impl Config {
 
         // Now load the TOML config, as soon as possible
         let (mut toml, toml_path) = load_toml_config(&src, flags_config, &get_toml);
-
         postprocess_toml(&mut toml, &src, toml_path.clone(), &exec_ctx, &flags_set, &get_toml);
+        let TomlConfig {
+            change_id: toml_change_id,
+            build: toml_build,
+            install: toml_install,
+            llvm: toml_llvm,
+            gcc: toml_gcc,
+            rust: toml_rust,
+            target: toml_target,
+            dist: toml_dist,
+            pgo: toml_pgo,
+            profile: _,
+            include: _,
+        } = toml;
 
         // Now override TOML values with flags, to make sure that we won't later override flags with
         // TOML values by accident instead, because flags have higher priority.
@@ -523,7 +534,7 @@ impl Config {
             ccache: build_ccache,
             exclude: build_exclude,
             compiletest_allow_stage0: build_compiletest_allow_stage0,
-        } = toml.build.unwrap_or_default();
+        } = toml_build.unwrap_or_default();
 
         let Install {
             prefix: install_prefix,
@@ -533,7 +544,7 @@ impl Config {
             libdir: install_libdir,
             mandir: install_mandir,
             datadir: install_datadir,
-        } = toml.install.unwrap_or_default();
+        } = toml_install.unwrap_or_default();
 
         let Rust {
             optimize: rust_optimize,
@@ -595,7 +606,7 @@ impl Config {
             std_features: rust_std_features,
             break_on_ice: rust_break_on_ice,
             rustflags: rust_rustflags,
-        } = toml.rust.unwrap_or_default();
+        } = toml_rust.unwrap_or_default();
 
         let Llvm {
             optimize: llvm_optimize,
@@ -627,7 +638,7 @@ impl Config {
             enable_warnings: llvm_enable_warnings,
             download_ci_llvm: llvm_download_ci_llvm,
             build_config: llvm_build_config,
-        } = toml.llvm.unwrap_or_default();
+        } = toml_llvm.unwrap_or_default();
 
         let Dist {
             sign_folder: dist_sign_folder,
@@ -637,12 +648,57 @@ impl Config {
             compression_profile: dist_compression_profile,
             include_mingw_linker: dist_include_mingw_linker,
             vendor: dist_vendor,
-        } = toml.dist.unwrap_or_default();
+        } = toml_dist.unwrap_or_default();
 
         let Gcc {
             download_ci_gcc: gcc_download_ci_gcc,
             libgccjit_libs_dir: gcc_libgccjit_libs_dir,
-        } = toml.gcc.unwrap_or_default();
+        } = toml_gcc.unwrap_or_default();
+
+        let Pgo { rustc: pgo_rustc, llvm: pgo_llvm } = toml_pgo.unwrap_or_default();
+
+        // Backcompat: flags have priority over config
+        if flags_rust_profile_use.is_some() || flags_rust_profile_generate.is_some() {
+            eprintln!(
+                "WARNING: the `--rust-profile-generate` and `--rust-profile-use` flags have been deprecated. Configure PGO through the config file instead, in the [pgo.rustc] section."
+            );
+        }
+        if rust_profile_use.is_some() || rust_profile_generate.is_some() {
+            eprintln!(
+                "WARNING: the `rust.profile-generate` and `rust.profile-use` config options have been deprecated. Configure PGO through the config file instead, in the [pgo.rustc] section."
+            );
+        }
+        if flags_llvm_profile_use.is_some() || flags_llvm_profile_generate {
+            eprintln!(
+                "WARNING: the `--llvm-profile-generate` and `--llvm-profile-use` flags have been deprecated. Configure PGO through the config file instead, in the [pgo.llvm] section."
+            );
+        }
+
+        let mut pgo_rustc = pgo_rustc.unwrap_or_default();
+        pgo_rustc.use_profile =
+            flags_rust_profile_use.or(pgo_rustc.use_profile).or(rust_profile_use);
+        pgo_rustc.generate_profile =
+            flags_rust_profile_generate.or(pgo_rustc.generate_profile).or(rust_profile_generate);
+        if pgo_rustc.use_profile.is_some() && pgo_rustc.generate_profile.is_some() {
+            panic!("Cannot use and generate rust PGO profiles at the same time");
+        }
+
+        let pgo_llvm = pgo_llvm.unwrap_or_default();
+        let pgo_llvm = LlvmPgoConfig {
+            use_profile: flags_llvm_profile_use.or(pgo_llvm.use_profile),
+            generate_profile: if flags_llvm_profile_generate {
+                Some(if let Ok(llvm_profile_dir) = std::env::var("LLVM_PROFILE_DIR") {
+                    LlvmPgoGenerationMode::Directory(PathBuf::from(llvm_profile_dir))
+                } else {
+                    LlvmPgoGenerationMode::Implicit
+                })
+            } else {
+                pgo_llvm.generate_profile.map(LlvmPgoGenerationMode::Directory)
+            },
+        };
+        if pgo_llvm.use_profile.is_some() && pgo_llvm.generate_profile.is_some() {
+            panic!("Cannot use and generate LLVM PGO profiles at the same time");
+        }
 
         if rust_bootstrap_override_lld.is_some() && rust_bootstrap_override_lld_legacy.is_some() {
             panic!(
@@ -877,7 +933,7 @@ impl Config {
         // Linux targets for which the user explicitly overrode the used linker
         let mut targets_with_user_linker_override = HashSet::new();
 
-        if let Some(t) = toml.target {
+        if let Some(t) = toml_target {
             for (triple, cfg) in t {
                 let TomlTarget {
                     cc: target_cc,
@@ -1337,7 +1393,7 @@ NOTE: Please add `--stage 2` to your command line, or if you're sure you want to
             cargo_info,
             cargo_native_static: build_cargo_native_static.unwrap_or(false),
             ccache,
-            change_id: toml.change_id.inner,
+            change_id: toml_change_id.inner,
             channel,
             ci_env,
             clippy_info,
@@ -1428,10 +1484,9 @@ NOTE: Please add `--stage 2` to your command line, or if you're sure you want to
             ),
             llvm_offload: llvm_offload.unwrap_or(false),
             llvm_optimize: llvm_optimize.unwrap_or(true),
+            llvm_pgo: pgo_llvm,
             llvm_plugins: llvm_plugin.unwrap_or(false),
             llvm_polly: llvm_polly.unwrap_or(false),
-            llvm_profile_generate: flags_llvm_profile_generate,
-            llvm_profile_use: flags_llvm_profile_use,
             llvm_release_debuginfo: llvm_release_debuginfo.unwrap_or(false),
             llvm_static_stdcpp: llvm_static_libstdcpp.unwrap_or(false),
             llvm_targets,
@@ -1496,8 +1551,7 @@ NOTE: Please add `--stage 2` to your command line, or if you're sure you want to
                 .or(rust_overflow_checks)
                 .unwrap_or(rust_debug == Some(true)),
             rust_parallel_frontend_threads: rust_parallel_frontend_threads.map(threads_from_config),
-            rust_profile_generate: flags_rust_profile_generate.or(rust_profile_generate),
-            rust_profile_use: flags_rust_profile_use.or(rust_profile_use),
+            rust_pgo: pgo_rustc,
             rust_randomize_layout: rust_randomize_layout.unwrap_or(false),
             rust_remap_debuginfo: rust_remap_debuginfo.unwrap_or(false),
             rust_rpath: rust_rpath.unwrap_or(true),
@@ -2030,6 +2084,20 @@ fn compute_src_directory(src_dir: Option<PathBuf>, exec_ctx: &ExecutionContext)
     None
 }
 
+#[derive(Clone)]
+pub enum LlvmPgoGenerationMode {
+    /// Enable PGO instrumentation that will write profiles into a default path.
+    Implicit,
+    /// Enable PGO instrumentation that will write profiles into the specified directory.
+    Directory(PathBuf),
+}
+
+#[derive(Clone)]
+pub struct LlvmPgoConfig {
+    pub use_profile: Option<PathBuf>,
+    pub generate_profile: Option<LlvmPgoGenerationMode>,
+}
+
 /// Loads bootstrap TOML config and returns the config together with a path from where
 /// it was loaded.
 /// `src` is the source root directory, and `config_path` is an optionally provided path to the

src/bootstrap/src/core/config/flags.rs

@@ -153,18 +153,22 @@ pub struct Flags {
 
     /// generate PGO profile with rustc build
     #[arg(global = true, value_hint = clap::ValueHint::FilePath, long, value_name = "PROFILE")]
-    pub rust_profile_generate: Option<String>,
+    // FIXME: Remove this option at the end of 2026
+    pub rust_profile_generate: Option<PathBuf>,
     /// use PGO profile for rustc build
+    // FIXME: Remove this option at the end of 2026
     #[arg(global = true, value_hint = clap::ValueHint::FilePath, long, value_name = "PROFILE")]
-    pub rust_profile_use: Option<String>,
+    pub rust_profile_use: Option<PathBuf>,
     /// use PGO profile for LLVM build
+    // FIXME: Remove this option at the end of 2026
     #[arg(global = true, value_hint = clap::ValueHint::FilePath, long, value_name = "PROFILE")]
-    pub llvm_profile_use: Option<String>,
+    pub llvm_profile_use: Option<PathBuf>,
     // LLVM doesn't support a custom location for generating profile
     // information.
     //
     // llvm_out/build/profiles/ is the location this writes to.
     /// generate PGO profile with llvm built for rustc
+    // FIXME: Remove this option at the end of 2026
     #[arg(global = true, long)]
     pub llvm_profile_generate: bool,
     /// Enable BOLT link flags