Auto merge of #129295 - Zalathar:profiler-builtins, r=Kobzol

Build `library/profiler_builtins` from `ci-llvm` if appropriate

Running all of `tests/coverage` requires the LLVM profiler runtime, which requires setting `build.profiler = true`.

Historically, doing that has required checking out the entire `src/llvm-project` submodule. For compiler contributors who otherwise don't need that submodule (thanks to `download-ci-vm`), that's quite inconvenient.

However, thanks to #129116, the downloaded CI LLVM tarball now contains a copy of LLVM's `compiler-rt` directory, which includes all the files needed to build the profiler runtime. So with a little bit of extra logic in bootstrap, we can have `library/profiler_builtins` look for the `compiler-rt` files in `ci-llvm` instead of the `src/llvm-project` submodule.

library/profiler_builtins/build.rs

@@ -3,7 +3,7 @@
 //! See the build.rs for libcompiler_builtins crate for details.
 
 use std::env;
-use std::path::Path;
+use std::path::PathBuf;
 
 fn main() {
  println!("cargo:rerun-if-env-changed=LLVM_PROFILER_RT_LIB");
@@ -79,17 +79,25 @@ fn main() {
  cfg.define("COMPILER_RT_HAS_ATOMICS", Some("1"));
  }
 
- // Note that this should exist if we're going to run (otherwise we just
- // don't build profiler builtins at all).
- let root = Path::new("../../src/llvm-project/compiler-rt");
+ // Get the LLVM `compiler-rt` directory from bootstrap.
+ println!("cargo:rerun-if-env-changed=RUST_COMPILER_RT_FOR_PROFILER");
+ let root = PathBuf::from(env::var("RUST_COMPILER_RT_FOR_PROFILER").unwrap_or_else(|_| {
+ let path = "../../src/llvm-project/compiler-rt";
+ println!("RUST_COMPILER_RT_FOR_PROFILER was not set; falling back to {path:?}");
+ path.to_owned()
+ }));
 
  let src_root = root.join("lib").join("profile");
+ assert!(src_root.exists(), "profiler runtime source directory not found: {src_root:?}");
+ let mut n_sources_found = 0u32;
  for src in profile_sources {
  let path = src_root.join(src);
  if path.exists() {
  cfg.file(path);
+ n_sources_found += 1;
  }
  }
+ assert!(n_sources_found > 0, "couldn't find any profiler runtime source files in {src_root:?}");
 
  cfg.include(root.join("include"));
  cfg.warnings(false);

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

@@ -199,16 +199,6 @@ impl Step for Std {
 
  builder.require_submodule("library/stdarch", None);
 
- // Profiler information requires LLVM's compiler-rt
- if builder.config.profiler {
- builder.require_submodule(
- "src/llvm-project",
- Some(
- "The `build.profiler` config option requires `compiler-rt` sources from LLVM.",
- ),
- );
- }
-
  let mut target_deps = builder.ensure(StartupObjects { compiler, target });
 
  let compiler_to_use = builder.compiler_for(compiler.stage, compiler.host, target);
@@ -466,15 +456,45 @@ pub fn std_crates_for_run_make(run: &RunConfig<'_>) -> Vec<String> {
  }
 }
 
+/// Tries to find LLVM's `compiler-rt` source directory, for building `library/profiler_builtins`.
+///
+/// Normally it lives in the `src/llvm-project` submodule, but if we will be using a
+/// downloaded copy of CI LLVM, then we try to use the `compiler-rt` sources from
+/// there instead, which lets us avoid checking out the LLVM submodule.
+fn compiler_rt_for_profiler(builder: &Builder<'_>) -> PathBuf {
+ // Try to use `compiler-rt` sources from downloaded CI LLVM, if possible.
+ if builder.config.llvm_from_ci {
+ // CI LLVM might not have been downloaded yet, so try to download it now.
+ builder.config.maybe_download_ci_llvm();
+ let ci_llvm_compiler_rt = builder.config.ci_llvm_root().join("compiler-rt");
+ if ci_llvm_compiler_rt.exists() {
+ return ci_llvm_compiler_rt;
+ }
+ }
+
+ // Otherwise, fall back to requiring the LLVM submodule.
+ builder.require_submodule("src/llvm-project", {
+ Some("The `build.profiler` config option requires `compiler-rt` sources from LLVM.")
+ });
+ builder.src.join("src/llvm-project/compiler-rt")
+}
+
 /// Configure cargo to compile the standard library, adding appropriate env vars
 /// and such.
 pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, cargo: &mut Cargo) {
  if let Some(target) = env::var_os("MACOSX_STD_DEPLOYMENT_TARGET") {
  cargo.env("MACOSX_DEPLOYMENT_TARGET", target);
  }
 
+ // Paths needed by `library/profiler_builtins/build.rs`.
  if let Some(path) = builder.config.profiler_path(target) {
  cargo.env("LLVM_PROFILER_RT_LIB", path);
+ } else if builder.config.profiler_enabled(target) {
+ let compiler_rt = compiler_rt_for_profiler(builder);
+ // Currently this is separate from the env var used by `compiler_builtins`
+ // (below) so that adding support for CI LLVM here doesn't risk breaking
+ // the compiler builtins. But they could be unified if desired.
+ cargo.env("RUST_COMPILER_RT_FOR_PROFILER", compiler_rt);
  }
 
  // Determine if we're going to compile in optimized C intrinsics to
@@ -507,8 +527,8 @@ pub fn std_cargo(builder: &Builder<'_>, target: TargetSelection, stage: u32, car
  );
  let compiler_builtins_root = builder.src.join("src/llvm-project/compiler-rt");
  assert!(compiler_builtins_root.exists());
- // Note that `libprofiler_builtins/build.rs` also computes this so if
- // you're changing something here please also change that.
+ // The path to `compiler-rt` is also used by `profiler_builtins` (above),
+ // so if you're changing something here please also change that as appropriate.
  cargo.env("RUST_COMPILER_RT_ROOT", &compiler_builtins_root);
  " compiler-builtins-c"
  } else {

src/bootstrap/src/utils/change_tracker.rs

@@ -230,4 +230,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
  severity: ChangeSeverity::Warning,
  summary: "./x test --rustc-args was renamed to --compiletest-rustc-args as it only applies there. ./x miri --rustc-args was also removed.",
  },
+ ChangeInfo {
+ change_id: 129295,
+ severity: ChangeSeverity::Info,
+ summary: "The `build.profiler` option now tries to use source code from `download-ci-llvm` if possible, instead of checking out the `src/llvm-project` submodule.",
+ },
 ];