Enable AutoFDO.

This largely involves implementing the options debug-info-for-profiling
and profile-sample-use and forwarding them on to LLVM.

AutoFDO can be used on x86-64 Linux like this:
rustc -O -Cdebug-info-for-profiling main.rs -o main
perf record -b ./main
create_llvm_prof --binary=main --out=code.prof
rustc -O -Cprofile-sample-use=code.prof main.rs -o main2

Now `main2` will have feedback directed optimization applied to it.

The create_llvm_prof tool can be obtained from this github repository:
https://github.com/google/autofdo

Fixes #64892.

3 files changed, 23 insertions, 0 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 32aa035e1cd..ac4bce7350b 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -2009,6 +2009,15 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         );
     }
 
+    if debugging_opts.profile_sample_use.is_some()
+        && (cg.profile_generate.enabled() || cg.profile_use.is_some())
+    {
+        early_error(
+            error_format,
+            "option `-Z profile-sample-use` cannot be used with `-C profile-generate` or `-C profile-use`",
+        );
+    }
+
     if debugging_opts.instrument_coverage.is_some()
         && debugging_opts.instrument_coverage != Some(InstrumentCoverage::Off)
     {
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 8ecb7a031ad..b3d36b396c5 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1040,6 +1040,8 @@ options! {
         "combine CGUs into a single one"),
     crate_attr: Vec<String> = (Vec::new(), parse_string_push, [TRACKED],
         "inject the given attribute in the crate"),
+    debug_info_for_profiling: bool = (false, parse_bool, [TRACKED],
+        "emit discriminators and other data necessary for AutoFDO"),
     debug_macros: bool = (false, parse_bool, [TRACKED],
         "emit line numbers debug info inside macros (default: no)"),
     deduplicate_diagnostics: bool = (true, parse_bool, [UNTRACKED],
@@ -1242,6 +1244,8 @@ options! {
         (default based on relative source path)"),
     profiler_runtime: String = (String::from("profiler_builtins"), parse_string, [TRACKED],
         "name of the profiler runtime crate to automatically inject (default: `profiler_builtins`)"),
+    profile_sample_use: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
+        "use the given `.prof` file for sampled profile-guided optimization (also known as AutoFDO)"),
     query_dep_graph: bool = (false, parse_bool, [UNTRACKED],
         "enable queries of the dependency graph for regression testing (default: no)"),
     query_stats: bool = (false, parse_bool, [UNTRACKED],
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index bf04154a3da..b6ba6cc1dd6 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1353,6 +1353,16 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
         }
     }
 
+    // Do the same for sample profile data.
+    if let Some(ref path) = sess.opts.debugging_opts.profile_sample_use {
+        if !path.exists() {
+            sess.err(&format!(
+                "File `{}` passed to `-C profile-sample-use` does not exist.",
+                path.display()
+            ));
+        }
+    }
+
     // Unwind tables cannot be disabled if the target requires them.
     if let Some(include_uwtables) = sess.opts.cg.force_unwind_tables {
         if sess.target.requires_uwtable && !include_uwtables {