The embedded bitcode should always be prepared for LTO/ThinLTO

compiler/rustc_codegen_llvm/src/back/lto.rs

@@ -604,7 +604,17 @@ pub(crate) fn run_pass_manager(
     debug!("running the pass manager");
     let opt_stage = if thin { llvm::OptStage::ThinLTO } else { llvm::OptStage::FatLTO };
     let opt_level = config.opt_level.unwrap_or(config::OptLevel::No);
-    unsafe { write::llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage) }?;
+    unsafe {
+        write::llvm_optimize(
+            cgcx,
+            dcx,
+            module.module_llvm.llmod(),
+            &*module.module_llvm.tm,
+            config,
+            opt_level,
+            opt_stage,
+        )
+    }?;
     debug!("lto done");
     Ok(())
 }

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -513,7 +513,8 @@ fn get_instr_profile_output_path(config: &ModuleConfig) -> Option<CString> {
 pub(crate) unsafe fn llvm_optimize(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     dcx: DiagCtxtHandle<'_>,
-    module: &ModuleCodegen<ModuleLlvm>,
+    llmod: &llvm::Module,
+    tm: &llvm::TargetMachine,
     config: &ModuleConfig,
     opt_level: config::OptLevel,
     opt_stage: llvm::OptStage,
@@ -572,8 +573,8 @@ pub(crate) unsafe fn llvm_optimize(
 
     let result = unsafe {
         llvm::LLVMRustOptimize(
-            module.module_llvm.llmod(),
-            &*module.module_llvm.tm,
+            llmod,
+            tm,
             to_pass_builder_opt_level(opt_level),
             opt_stage,
             cgcx.opts.cg.linker_plugin_lto.enabled(),
@@ -635,8 +636,51 @@ pub(crate) unsafe fn optimize(
             _ if cgcx.opts.cg.linker_plugin_lto.enabled() => llvm::OptStage::PreLinkThinLTO,
             _ => llvm::OptStage::PreLinkNoLTO,
         };
-        return unsafe { llvm_optimize(cgcx, dcx, module, config, opt_level, opt_stage) };
+        if opt_stage == llvm::OptStage::PreLinkNoLTO
+            && config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full)
+        {
+            let _timer = cgcx.prof.generic_activity_with_arg(
+                "LLVM_module_codegen_prepare_embed_bitcode",
+                &*module.name,
+            );
+            // The embedded bitcode is used to run LTO/ThinLTO.
+            // `OptStage::PreLinkNoLTO` is not suitable as input for LTO,
+            // as it may run certain passes that cannot be executed multiple times,
+            // such as LLVM's Call Graph Profile pass. So, we create a copy to
+            // run `OptStage::PreLinkThinLTO` for the subsequent LTO process.
+            let llmod = unsafe { llvm::LLVMCloneModule(module.module_llvm.llmod()) };
+            unsafe {
+                llvm_optimize(
+                    cgcx,
+                    dcx,
+                    llmod,
+                    &*module.module_llvm.tm,
+                    config,
+                    opt_level,
+                    llvm::OptStage::PreLinkThinLTO,
+                )
+            }?;
+            let embed_thin =
+                ThinBuffer::new(llmod, config.emit_thin_lto, config.emit_thin_lto_summary);
+            let thin_bc_out = cgcx.output_filenames.temp_path(OutputType::ThinBitcode, module_name);
+            if let Err(err) = fs::write(&thin_bc_out, embed_thin.data()) {
+                dcx.emit_err(WriteBytecode { path: &thin_bc_out, err });
+            }
+            unsafe { llvm::LLVMDisposeModule(llmod) };
+        }
+        unsafe {
+            llvm_optimize(
+                cgcx,
+                dcx,
+                module.module_llvm.llmod(),
+                &*module.module_llvm.tm,
+                config,
+                opt_level,
+                opt_stage,
+            )
+        }?;
     }
+
     Ok(())
 }
 
@@ -716,11 +760,54 @@ pub(crate) unsafe fn codegen(
         //   asm from LLVM and use `gcc` to create the object file.
 
         let bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
-        let bc_summary_out =
-            cgcx.output_filenames.temp_path(OutputType::ThinLinkBitcode, module_name);
         let obj_out = cgcx.output_filenames.temp_path(OutputType::Object, module_name);
 
+        if config.emit_ir {
+            let _timer =
+                cgcx.prof.generic_activity_with_arg("LLVM_module_codegen_emit_ir", &*module.name);
+            let out = cgcx.output_filenames.temp_path(OutputType::LlvmAssembly, module_name);
+            let out_c = path_to_c_string(&out);
+
+            extern "C" fn demangle_callback(
+                input_ptr: *const c_char,
+                input_len: size_t,
+                output_ptr: *mut c_char,
+                output_len: size_t,
+            ) -> size_t {
+                let input =
+                    unsafe { slice::from_raw_parts(input_ptr as *const u8, input_len as usize) };
+
+                let Ok(input) = str::from_utf8(input) else { return 0 };
+
+                let output = unsafe {
+                    slice::from_raw_parts_mut(output_ptr as *mut u8, output_len as usize)
+                };
+                let mut cursor = io::Cursor::new(output);
+
+                let Ok(demangled) = rustc_demangle::try_demangle(input) else { return 0 };
+
+                if write!(cursor, "{demangled:#}").is_err() {
+                    // Possible only if provided buffer is not big enough
+                    return 0;
+                }
+
+                cursor.position() as size_t
+            }
+
+            let result =
+                unsafe { llvm::LLVMRustPrintModule(llmod, out_c.as_ptr(), demangle_callback) };
+
+            if result == llvm::LLVMRustResult::Success {
+                record_artifact_size(&cgcx.prof, "llvm_ir", &out);
+            }
+
+            result.into_result().map_err(|()| llvm_err(dcx, LlvmError::WriteIr { path: &out }))?;
+        }
+
         if config.bitcode_needed() {
+            let bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
+            let bc_summary_out =
+                cgcx.output_filenames.temp_path(OutputType::ThinLinkBitcode, module_name);
             let _timer = cgcx
                 .prof
                 .generic_activity_with_arg("LLVM_module_codegen_make_bitcode", &*module.name);
@@ -767,54 +854,22 @@ pub(crate) unsafe fn codegen(
                 let _timer = cgcx
                     .prof
                     .generic_activity_with_arg("LLVM_module_codegen_embed_bitcode", &*module.name);
+                let thin_bc_out =
+                    cgcx.output_filenames.temp_path(OutputType::ThinBitcode, module_name);
+                let thin_data;
+                let mut data = data;
+                if thin_bc_out.exists() {
+                    thin_data = fs::read(&thin_bc_out).unwrap();
+                    debug!("removing embed bitcode file {:?}", thin_bc_out);
+                    ensure_removed(dcx, &thin_bc_out);
+                    data = thin_data.as_slice();
+                }
                 unsafe {
                     embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, data);
                 }
             }
         }
 
-        if config.emit_ir {
-            let _timer =
-                cgcx.prof.generic_activity_with_arg("LLVM_module_codegen_emit_ir", &*module.name);
-            let out = cgcx.output_filenames.temp_path(OutputType::LlvmAssembly, module_name);
-            let out_c = path_to_c_string(&out);
-
-            extern "C" fn demangle_callback(
-                input_ptr: *const c_char,
-                input_len: size_t,
-                output_ptr: *mut c_char,
-                output_len: size_t,
-            ) -> size_t {
-                let input =
-                    unsafe { slice::from_raw_parts(input_ptr as *const u8, input_len as usize) };
-
-                let Ok(input) = str::from_utf8(input) else { return 0 };
-
-                let output = unsafe {
-                    slice::from_raw_parts_mut(output_ptr as *mut u8, output_len as usize)
-                };
-                let mut cursor = io::Cursor::new(output);
-
-                let Ok(demangled) = rustc_demangle::try_demangle(input) else { return 0 };
-
-                if write!(cursor, "{demangled:#}").is_err() {
-                    // Possible only if provided buffer is not big enough
-                    return 0;
-                }
-
-                cursor.position() as size_t
-            }
-
-            let result =
-                unsafe { llvm::LLVMRustPrintModule(llmod, out_c.as_ptr(), demangle_callback) };
-
-            if result == llvm::LLVMRustResult::Success {
-                record_artifact_size(&cgcx.prof, "llvm_ir", &out);
-            }
-
-            result.into_result().map_err(|()| llvm_err(dcx, LlvmError::WriteIr { path: &out }))?;
-        }
-
         if config.emit_asm {
             let _timer =
                 cgcx.prof.generic_activity_with_arg("LLVM_module_codegen_emit_asm", &*module.name);

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -870,6 +870,7 @@ unsafe extern "C" {
     pub fn LLVMModuleCreateWithNameInContext(ModuleID: *const c_char, C: &Context) -> &Module;
     pub fn LLVMGetModuleContext(M: &Module) -> &Context;
     pub fn LLVMCloneModule(M: &Module) -> &Module;
+    pub fn LLVMDisposeModule(M: &Module);
 
     /// Data layout. See Module::getDataLayout.
     pub fn LLVMGetDataLayoutStr(M: &Module) -> *const c_char;

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -618,6 +618,9 @@ fn produce_final_output_artifacts(
                 // them for making an rlib.
                 copy_if_one_unit(OutputType::Bitcode, true);
             }
+            OutputType::ThinBitcode => {
+                copy_if_one_unit(OutputType::ThinBitcode, true);
+            }
             OutputType::ThinLinkBitcode => {
                 copy_if_one_unit(OutputType::ThinLinkBitcode, false);
             }

compiler/rustc_session/src/config.rs

@@ -508,6 +508,7 @@ impl FromStr for SplitDwarfKind {
 pub enum OutputType {
     Bitcode,
     ThinLinkBitcode,
+    ThinBitcode,
     Assembly,
     LlvmAssembly,
     Mir,
@@ -538,6 +539,7 @@ impl OutputType {
             OutputType::Exe | OutputType::DepInfo | OutputType::Metadata => true,
             OutputType::Bitcode
             | OutputType::ThinLinkBitcode
+            | OutputType::ThinBitcode
             | OutputType::Assembly
             | OutputType::LlvmAssembly
             | OutputType::Mir
@@ -549,6 +551,7 @@ impl OutputType {
         match *self {
             OutputType::Bitcode => "llvm-bc",
             OutputType::ThinLinkBitcode => "thin-link-bitcode",
+            OutputType::ThinBitcode => "thin-llvm-bc",
             OutputType::Assembly => "asm",
             OutputType::LlvmAssembly => "llvm-ir",
             OutputType::Mir => "mir",
@@ -566,6 +569,7 @@ impl OutputType {
             "mir" => OutputType::Mir,
             "llvm-bc" => OutputType::Bitcode,
             "thin-link-bitcode" => OutputType::ThinLinkBitcode,
+            "thin-llvm-bc" => OutputType::ThinBitcode,
             "obj" => OutputType::Object,
             "metadata" => OutputType::Metadata,
             "link" => OutputType::Exe,
@@ -576,9 +580,10 @@ impl OutputType {
 
     fn shorthands_display() -> String {
         format!(
-            "`{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}`",
+            "`{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}`, `{}",
             OutputType::Bitcode.shorthand(),
             OutputType::ThinLinkBitcode.shorthand(),
+            OutputType::ThinBitcode.shorthand(),
             OutputType::Assembly.shorthand(),
             OutputType::LlvmAssembly.shorthand(),
             OutputType::Mir.shorthand(),
@@ -593,6 +598,7 @@ impl OutputType {
         match *self {
             OutputType::Bitcode => "bc",
             OutputType::ThinLinkBitcode => "indexing.o",
+            OutputType::ThinBitcode => "thin.bc",
             OutputType::Assembly => "s",
             OutputType::LlvmAssembly => "ll",
             OutputType::Mir => "mir",
@@ -611,6 +617,7 @@ impl OutputType {
             | OutputType::DepInfo => true,
             OutputType::Bitcode
             | OutputType::ThinLinkBitcode
+            | OutputType::ThinBitcode
             | OutputType::Object
             | OutputType::Metadata
             | OutputType::Exe => false,
@@ -698,6 +705,7 @@ impl OutputTypes {
         self.0.keys().any(|k| match *k {
             OutputType::Bitcode
             | OutputType::ThinLinkBitcode
+            | OutputType::ThinBitcode
             | OutputType::Assembly
             | OutputType::LlvmAssembly
             | OutputType::Mir
@@ -712,6 +720,7 @@ impl OutputTypes {
         self.0.keys().any(|k| match *k {
             OutputType::Bitcode
             | OutputType::ThinLinkBitcode
+            | OutputType::ThinBitcode
             | OutputType::Assembly
             | OutputType::LlvmAssembly
             | OutputType::Mir

tests/run-make/pgo-embed-bc-lto/interesting.rs

@@ -0,0 +1,10 @@
+#![crate_name = "interesting"]
+#![crate_type = "rlib"]
+
+extern crate opaque;
+
+#[no_mangle]
+#[inline(never)]
+pub fn function_called_once() {
+    opaque::foo();
+}

tests/run-make/pgo-embed-bc-lto/main.rs

@@ -0,0 +1,5 @@
+extern crate interesting;
+
+fn main() {
+    interesting::function_called_once();
+}

tests/run-make/pgo-embed-bc-lto/opaque.rs

@@ -0,0 +1,5 @@
+#![crate_name = "opaque"]
+#![crate_type = "rlib"]
+
+#[inline(never)]
+pub fn foo() {}

tests/run-make/pgo-embed-bc-lto/rmake.rs

@@ -0,0 +1,42 @@
+// This test case verifies that we successfully complete an LTO build with PGO
+// using the embedded bitcode.
+// It also ensures that the generated IR correctly includes the call results.
+
+//@ needs-profiler-runtime
+//@ ignore-cross-compile
+
+use std::path::Path;
+
+use run_make_support::{llvm_filecheck, llvm_profdata, rfs, run, rustc};
+
+fn main() {
+    let path_prof_data_dir = Path::new("prof_data_dir");
+    let path_merged_profdata = path_prof_data_dir.join("merged.profdata");
+    rustc().input("opaque.rs").codegen_units(1).run();
+    rfs::create_dir_all(&path_prof_data_dir);
+    rustc()
+        .input("interesting.rs")
+        .profile_generate(&path_prof_data_dir)
+        .opt()
+        .codegen_units(1)
+        .run();
+    rustc()
+        .input("main.rs")
+        .arg("-Clto=thin")
+        .opt()
+        .codegen_units(1)
+        .profile_generate(&path_prof_data_dir)
+        .opt()
+        .run();
+    run("main");
+    llvm_profdata().merge().output(&path_merged_profdata).input(path_prof_data_dir).run();
+    rustc().input("interesting.rs").profile_use(&path_merged_profdata).opt().codegen_units(1).run();
+    rustc()
+        .input("main.rs")
+        .arg("-Clto=thin")
+        .opt()
+        .codegen_units(1)
+        .profile_use(&path_merged_profdata)
+        .opt()
+        .run();
+}