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.

2 files changed, 7 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_ssa/src/back/linker.rs b/compiler/rustc_codegen_ssa/src/back/linker.rs
index e3b0eea0d89..429dc45d6a4 100644
--- a/compiler/rustc_codegen_ssa/src/back/linker.rs
+++ b/compiler/rustc_codegen_ssa/src/back/linker.rs
@@ -286,6 +286,9 @@ impl<'a> GccLinker<'a> {
             config::OptLevel::Aggressive => "O3",
         };
 
+        if let Some(path) = &self.sess.opts.debugging_opts.profile_sample_use {
+            self.linker_arg(&format!("-plugin-opt=sample-profile={}", path.display()));
+        };
         self.linker_arg(&format!("-plugin-opt={}", opt_level));
         self.linker_arg(&format!("-plugin-opt=mcpu={}", self.target_cpu));
     }
diff --git a/compiler/rustc_codegen_ssa/src/back/write.rs b/compiler/rustc_codegen_ssa/src/back/write.rs
index 31722d07414..da34612ce76 100644
--- a/compiler/rustc_codegen_ssa/src/back/write.rs
+++ b/compiler/rustc_codegen_ssa/src/back/write.rs
@@ -83,6 +83,8 @@ pub struct ModuleConfig {
 
     pub pgo_gen: SwitchWithOptPath,
     pub pgo_use: Option<PathBuf>,
+    pub pgo_sample_use: Option<PathBuf>,
+    pub debug_info_for_profiling: bool,
     pub instrument_coverage: bool,
     pub instrument_gcov: bool,
 
@@ -176,6 +178,8 @@ impl ModuleConfig {
                 SwitchWithOptPath::Disabled
             ),
             pgo_use: if_regular!(sess.opts.cg.profile_use.clone(), None),
+            pgo_sample_use: if_regular!(sess.opts.debugging_opts.profile_sample_use.clone(), None),
+            debug_info_for_profiling: sess.opts.debugging_opts.debug_info_for_profiling,
             instrument_coverage: if_regular!(sess.instrument_coverage(), false),
             instrument_gcov: if_regular!(
                 // compiler_builtins overrides the codegen-units settings,