Merge commit '11a0cceab966e5ff1058ddbcab5977e8a1d6d290' into subtree-update_cg_gcc_2023-10-09

3 files changed, 435 insertions, 9 deletions

diff --git a/compiler/rustc_codegen_gcc/src/back/lto.rs b/compiler/rustc_codegen_gcc/src/back/lto.rs
new file mode 100644
index 00000000000..529454b119e
--- /dev/null
+++ b/compiler/rustc_codegen_gcc/src/back/lto.rs
@@ -0,0 +1,341 @@
+/// GCC requires to use the same toolchain for the whole compilation when doing LTO.
+/// So, we need the same version/commit of the linker (gcc) and lto front-end binaries (lto1,
+/// lto-wrapper, liblto_plugin.so).
+
+// FIXME(antoyo): the executables compiled with LTO are bigger than those compiled without LTO.
+// Since it is the opposite for cg_llvm, check if this is normal.
+//
+// Maybe we embed the bitcode in the final binary?
+// It doesn't look like we try to generate fat objects for the final binary.
+// Check if the way we combine the object files make it keep the LTO sections on the final link.
+// Maybe that's because the combined object files contain the IR (true) and the final link
+// does not remove it?
+//
+// TODO(antoyo): for performance, check which optimizations the C++ frontend enables.
+//
+// Fix these warnings:
+// /usr/bin/ld: warning: type of symbol `_RNvNvNvNtCs5JWOrf9uCus_5rayon11thread_pool19WORKER_THREAD_STATE7___getit5___KEY' changed from 1 to 6 in /tmp/ccKeUSiR.ltrans0.ltrans.o
+// /usr/bin/ld: warning: type of symbol `_RNvNvNvNvNtNtNtCsAj5i4SGTR7_3std4sync4mpmc5waker17current_thread_id5DUMMY7___getit5___KEY' changed from 1 to 6 in /tmp/ccKeUSiR.ltrans0.ltrans.o
+// /usr/bin/ld: warning: incremental linking of LTO and non-LTO objects; using -flinker-output=nolto-rel which will bypass whole program optimization
+
+use std::ffi::CString;
+use std::fs::{self, File};
+use std::path::{Path, PathBuf};
+
+use gccjit::OutputKind;
+use object::read::archive::ArchiveFile;
+use rustc_codegen_ssa::back::lto::{LtoModuleCodegen, SerializedModule};
+use rustc_codegen_ssa::back::symbol_export;
+use rustc_codegen_ssa::back::write::{CodegenContext, FatLtoInput};
+use rustc_codegen_ssa::traits::*;
+use rustc_codegen_ssa::{looks_like_rust_object_file, ModuleCodegen, ModuleKind};
+use rustc_data_structures::memmap::Mmap;
+use rustc_errors::{FatalError, Handler};
+use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_middle::dep_graph::WorkProduct;
+use rustc_middle::middle::exported_symbols::{SymbolExportInfo, SymbolExportLevel};
+use rustc_session::config::{CrateType, Lto};
+use tempfile::{TempDir, tempdir};
+
+use crate::back::write::save_temp_bitcode;
+use crate::errors::{
+    DynamicLinkingWithLTO, LtoBitcodeFromRlib, LtoDisallowed, LtoDylib,
+};
+use crate::{GccCodegenBackend, GccContext, to_gcc_opt_level};
+
+/// We keep track of the computed LTO cache keys from the previous
+/// session to determine which CGUs we can reuse.
+//pub const THIN_LTO_KEYS_INCR_COMP_FILE_NAME: &str = "thin-lto-past-keys.bin";
+
+pub fn crate_type_allows_lto(crate_type: CrateType) -> bool {
+    match crate_type {
+        CrateType::Executable | CrateType::Dylib | CrateType::Staticlib | CrateType::Cdylib => true,
+        CrateType::Rlib | CrateType::ProcMacro => false,
+    }
+}
+
+struct LtoData {
+    // TODO(antoyo): use symbols_below_threshold.
+    //symbols_below_threshold: Vec<CString>,
+    upstream_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
+    tmp_path: TempDir,
+}
+
+fn prepare_lto(cgcx: &CodegenContext<GccCodegenBackend>, diag_handler: &Handler) -> Result<LtoData, FatalError> {
+    let export_threshold = match cgcx.lto {
+        // We're just doing LTO for our one crate
+        Lto::ThinLocal => SymbolExportLevel::Rust,
+
+        // We're doing LTO for the entire crate graph
+        Lto::Fat | Lto::Thin => symbol_export::crates_export_threshold(&cgcx.crate_types),
+
+        Lto::No => panic!("didn't request LTO but we're doing LTO"),
+    };
+
+    let tmp_path =
+        match tempdir() {
+            Ok(tmp_path) => tmp_path,
+            Err(error) => {
+                eprintln!("Cannot create temporary directory: {}", error);
+                return Err(FatalError);
+            },
+        };
+
+    let symbol_filter = &|&(ref name, info): &(String, SymbolExportInfo)| {
+        if info.level.is_below_threshold(export_threshold) || info.used {
+            Some(CString::new(name.as_str()).unwrap())
+        } else {
+            None
+        }
+    };
+    let exported_symbols = cgcx.exported_symbols.as_ref().expect("needs exported symbols for LTO");
+    let mut symbols_below_threshold = {
+        let _timer = cgcx.prof.generic_activity("GCC_lto_generate_symbols_below_threshold");
+        exported_symbols[&LOCAL_CRATE].iter().filter_map(symbol_filter).collect::<Vec<CString>>()
+    };
+    info!("{} symbols to preserve in this crate", symbols_below_threshold.len());
+
+    // If we're performing LTO for the entire crate graph, then for each of our
+    // upstream dependencies, find the corresponding rlib and load the bitcode
+    // from the archive.
+    //
+    // We save off all the bytecode and GCC module file path for later processing
+    // with either fat or thin LTO
+    let mut upstream_modules = Vec::new();
+    if cgcx.lto != Lto::ThinLocal {
+        // Make sure we actually can run LTO
+        for crate_type in cgcx.crate_types.iter() {
+            if !crate_type_allows_lto(*crate_type) {
+                diag_handler.emit_err(LtoDisallowed);
+                return Err(FatalError);
+            } else if *crate_type == CrateType::Dylib {
+                if !cgcx.opts.unstable_opts.dylib_lto {
+                    diag_handler.emit_err(LtoDylib);
+                    return Err(FatalError);
+                }
+            }
+        }
+
+        if cgcx.opts.cg.prefer_dynamic && !cgcx.opts.unstable_opts.dylib_lto {
+            diag_handler.emit_err(DynamicLinkingWithLTO);
+            return Err(FatalError);
+        }
+
+        for &(cnum, ref path) in cgcx.each_linked_rlib_for_lto.iter() {
+            let exported_symbols =
+                cgcx.exported_symbols.as_ref().expect("needs exported symbols for LTO");
+            {
+                let _timer =
+                    cgcx.prof.generic_activity("GCC_lto_generate_symbols_below_threshold");
+                symbols_below_threshold
+                    .extend(exported_symbols[&cnum].iter().filter_map(symbol_filter));
+            }
+
+            let archive_data = unsafe {
+                Mmap::map(File::open(&path).expect("couldn't open rlib"))
+                    .expect("couldn't map rlib")
+            };
+            let archive = ArchiveFile::parse(&*archive_data).expect("wanted an rlib");
+            let obj_files = archive
+                .members()
+                .filter_map(|child| {
+                    child.ok().and_then(|c| {
+                        std::str::from_utf8(c.name()).ok().map(|name| (name.trim(), c))
+                    })
+                })
+                .filter(|&(name, _)| looks_like_rust_object_file(name));
+            for (name, child) in obj_files {
+                info!("adding bitcode from {}", name);
+                let path = tmp_path.path().join(name);
+                match save_as_file(child.data(&*archive_data).expect("corrupt rlib"), &path) {
+                    Ok(()) => {
+                        let buffer = ModuleBuffer::new(path);
+                        let module = SerializedModule::Local(buffer);
+                        upstream_modules.push((module, CString::new(name).unwrap()));
+                    }
+                    Err(e) => {
+                        diag_handler.emit_err(e);
+                        return Err(FatalError);
+                    }
+                }
+            }
+        }
+    }
+
+    Ok(LtoData {
+        //symbols_below_threshold,
+        upstream_modules,
+        tmp_path,
+    })
+}
+
+fn save_as_file(obj: &[u8], path: &Path) -> Result<(), LtoBitcodeFromRlib> {
+    fs::write(path, obj)
+        .map_err(|error| LtoBitcodeFromRlib {
+            gcc_err: format!("write object file to temp dir: {}", error)
+        })
+}
+
+/// Performs fat LTO by merging all modules into a single one and returning it
+/// for further optimization.
+pub(crate) fn run_fat(
+    cgcx: &CodegenContext<GccCodegenBackend>,
+    modules: Vec<FatLtoInput<GccCodegenBackend>>,
+    cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
+) -> Result<LtoModuleCodegen<GccCodegenBackend>, FatalError> {
+    let diag_handler = cgcx.create_diag_handler();
+    let lto_data = prepare_lto(cgcx, &diag_handler)?;
+    /*let symbols_below_threshold =
+        lto_data.symbols_below_threshold.iter().map(|c| c.as_ptr()).collect::<Vec<_>>();*/
+    fat_lto(cgcx, &diag_handler, modules, cached_modules, lto_data.upstream_modules, lto_data.tmp_path,
+        //&symbols_below_threshold,
+    )
+}
+
+fn fat_lto(cgcx: &CodegenContext<GccCodegenBackend>, _diag_handler: &Handler, modules: Vec<FatLtoInput<GccCodegenBackend>>, cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>, mut serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>, tmp_path: TempDir,
+    //symbols_below_threshold: &[*const libc::c_char],
+) -> Result<LtoModuleCodegen<GccCodegenBackend>, FatalError> {
+    let _timer = cgcx.prof.generic_activity("GCC_fat_lto_build_monolithic_module");
+    info!("going for a fat lto");
+
+    // Sort out all our lists of incoming modules into two lists.
+    //
+    // * `serialized_modules` (also and argument to this function) contains all
+    //   modules that are serialized in-memory.
+    // * `in_memory` contains modules which are already parsed and in-memory,
+    //   such as from multi-CGU builds.
+    //
+    // All of `cached_modules` (cached from previous incremental builds) can
+    // immediately go onto the `serialized_modules` modules list and then we can
+    // split the `modules` array into these two lists.
+    let mut in_memory = Vec::new();
+    serialized_modules.extend(cached_modules.into_iter().map(|(buffer, wp)| {
+        info!("pushing cached module {:?}", wp.cgu_name);
+        (buffer, CString::new(wp.cgu_name).unwrap())
+    }));
+    for module in modules {
+        match module {
+            FatLtoInput::InMemory(m) => in_memory.push(m),
+            FatLtoInput::Serialized { name, buffer } => {
+                info!("pushing serialized module {:?}", name);
+                let buffer = SerializedModule::Local(buffer);
+                serialized_modules.push((buffer, CString::new(name).unwrap()));
+            }
+        }
+    }
+
+    // Find the "costliest" module and merge everything into that codegen unit.
+    // All the other modules will be serialized and reparsed into the new
+    // context, so this hopefully avoids serializing and parsing the largest
+    // codegen unit.
+    //
+    // Additionally use a regular module as the base here to ensure that various
+    // file copy operations in the backend work correctly. The only other kind
+    // of module here should be an allocator one, and if your crate is smaller
+    // than the allocator module then the size doesn't really matter anyway.
+    let costliest_module = in_memory
+        .iter()
+        .enumerate()
+        .filter(|&(_, module)| module.kind == ModuleKind::Regular)
+        .map(|(i, _module)| {
+            //let cost = unsafe { llvm::LLVMRustModuleCost(module.module_llvm.llmod()) };
+            // TODO(antoyo): compute the cost of a module if GCC allows this.
+            (0, i)
+        })
+        .max();
+
+    // If we found a costliest module, we're good to go. Otherwise all our
+    // inputs were serialized which could happen in the case, for example, that
+    // all our inputs were incrementally reread from the cache and we're just
+    // re-executing the LTO passes. If that's the case deserialize the first
+    // module and create a linker with it.
+    let mut module: ModuleCodegen<GccContext> = match costliest_module {
+        Some((_cost, i)) => in_memory.remove(i),
+        None => {
+            unimplemented!("Incremental");
+            /*assert!(!serialized_modules.is_empty(), "must have at least one serialized module");
+            let (buffer, name) = serialized_modules.remove(0);
+            info!("no in-memory regular modules to choose from, parsing {:?}", name);
+            ModuleCodegen {
+                module_llvm: GccContext::parse(cgcx, &name, buffer.data(), diag_handler)?,
+                name: name.into_string().unwrap(),
+                kind: ModuleKind::Regular,
+            }*/
+        }
+    };
+    let mut serialized_bitcode = Vec::new();
+    {
+        info!("using {:?} as a base module", module.name);
+
+        // We cannot load and merge GCC contexts in memory like cg_llvm is doing.
+        // Instead, we combine the object files into a single object file.
+        for module in in_memory {
+            let path = tmp_path.path().to_path_buf().join(&module.name);
+            let path = path.to_str().expect("path");
+            let context = &module.module_llvm.context;
+            let config = cgcx.config(module.kind);
+            // NOTE: we need to set the optimization level here in order for LTO to do its job.
+            context.set_optimization_level(to_gcc_opt_level(config.opt_level));
+            context.add_command_line_option("-flto=auto");
+            context.add_command_line_option("-flto-partition=one");
+            context.compile_to_file(OutputKind::ObjectFile, path);
+            let buffer = ModuleBuffer::new(PathBuf::from(path));
+            let llmod_id = CString::new(&module.name[..]).unwrap();
+            serialized_modules.push((SerializedModule::Local(buffer), llmod_id));
+        }
+        // Sort the modules to ensure we produce deterministic results.
+        serialized_modules.sort_by(|module1, module2| module1.1.cmp(&module2.1));
+
+        // We add the object files and save in should_combine_object_files that we should combine
+        // them into a single object file when compiling later.
+        for (bc_decoded, name) in serialized_modules {
+            let _timer = cgcx
+                .prof
+                .generic_activity_with_arg_recorder("GCC_fat_lto_link_module", |recorder| {
+                    recorder.record_arg(format!("{:?}", name))
+                });
+            info!("linking {:?}", name);
+            match bc_decoded {
+                SerializedModule::Local(ref module_buffer) => {
+                    module.module_llvm.should_combine_object_files = true;
+                    module.module_llvm.context.add_driver_option(module_buffer.0.to_str().expect("path"));
+                },
+                SerializedModule::FromRlib(_) => unimplemented!("from rlib"),
+                SerializedModule::FromUncompressedFile(_) => unimplemented!("from uncompressed file"),
+            }
+            serialized_bitcode.push(bc_decoded);
+        }
+        save_temp_bitcode(cgcx, &module, "lto.input");
+
+        // Internalize everything below threshold to help strip out more modules and such.
+        /*unsafe {
+            let ptr = symbols_below_threshold.as_ptr();
+            llvm::LLVMRustRunRestrictionPass(
+                llmod,
+                ptr as *const *const libc::c_char,
+                symbols_below_threshold.len() as libc::size_t,
+            );*/
+            save_temp_bitcode(cgcx, &module, "lto.after-restriction");
+        //}
+    }
+
+    // NOTE: save the temporary directory used by LTO so that it gets deleted after linking instead
+    // of now.
+    module.module_llvm.temp_dir = Some(tmp_path);
+
+    Ok(LtoModuleCodegen::Fat { module, _serialized_bitcode: serialized_bitcode })
+}
+
+pub struct ModuleBuffer(PathBuf);
+
+impl ModuleBuffer {
+    pub fn new(path: PathBuf) -> ModuleBuffer {
+        ModuleBuffer(path)
+    }
+}
+
+impl ModuleBufferMethods for ModuleBuffer {
+    fn data(&self) -> &[u8] {
+        unimplemented!("data not needed for GCC codegen");
+    }
+}
diff --git a/compiler/rustc_codegen_gcc/src/back/mod.rs b/compiler/rustc_codegen_gcc/src/back/mod.rs
index d692799d764..10187eab0d7 100644
--- a/compiler/rustc_codegen_gcc/src/back/mod.rs
+++ b/compiler/rustc_codegen_gcc/src/back/mod.rs
@@ -1 +1,2 @@
+pub mod lto;
 pub mod write;
diff --git a/compiler/rustc_codegen_gcc/src/back/write.rs b/compiler/rustc_codegen_gcc/src/back/write.rs
index 5f54ac4ebc6..04772d7707a 100644
--- a/compiler/rustc_codegen_gcc/src/back/write.rs
+++ b/compiler/rustc_codegen_gcc/src/back/write.rs
@@ -2,27 +2,71 @@ use std::{env, fs};
 
 use gccjit::OutputKind;
 use rustc_codegen_ssa::{CompiledModule, ModuleCodegen};
-use rustc_codegen_ssa::back::write::{CodegenContext, EmitObj, ModuleConfig};
+use rustc_codegen_ssa::back::link::ensure_removed;
+use rustc_codegen_ssa::back::write::{BitcodeSection, CodegenContext, EmitObj, ModuleConfig};
 use rustc_errors::Handler;
+use rustc_fs_util::link_or_copy;
 use rustc_session::config::OutputType;
 use rustc_span::fatal_error::FatalError;
 use rustc_target::spec::SplitDebuginfo;
 
 use crate::{GccCodegenBackend, GccContext};
+use crate::errors::CopyBitcode;
 
-pub(crate) unsafe fn codegen(cgcx: &CodegenContext<GccCodegenBackend>, _diag_handler: &Handler, module: ModuleCodegen<GccContext>, config: &ModuleConfig) -> Result<CompiledModule, FatalError> {
-    let _timer = cgcx.prof.generic_activity_with_arg("LLVM_module_codegen", &*module.name);
+pub(crate) unsafe fn codegen(cgcx: &CodegenContext<GccCodegenBackend>, diag_handler: &Handler, module: ModuleCodegen<GccContext>, config: &ModuleConfig) -> Result<CompiledModule, FatalError> {
+    let _timer = cgcx.prof.generic_activity_with_arg("GCC_module_codegen", &*module.name);
     {
         let context = &module.module_llvm.context;
 
         let module_name = module.name.clone();
+
+        let should_combine_object_files = module.module_llvm.should_combine_object_files;
+
         let module_name = Some(&module_name[..]);
 
-        let _bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
+        // NOTE: Only generate object files with GIMPLE when this environment variable is set for
+        // now because this requires a particular setup (same gcc/lto1/lto-wrapper commit as libgccjit).
+        let fat_lto = env::var("EMBED_LTO_BITCODE").as_deref() == Ok("1");
+
+        let bc_out = cgcx.output_filenames.temp_path(OutputType::Bitcode, module_name);
         let obj_out = cgcx.output_filenames.temp_path(OutputType::Object, module_name);
 
-        if config.bitcode_needed() {
+        if config.bitcode_needed() && fat_lto {
+            let _timer = cgcx
+                .prof
+                .generic_activity_with_arg("GCC_module_codegen_make_bitcode", &*module.name);
+
             // TODO(antoyo)
+            /*if let Some(bitcode_filename) = bc_out.file_name() {
+                cgcx.prof.artifact_size(
+                    "llvm_bitcode",
+                    bitcode_filename.to_string_lossy(),
+                    data.len() as u64,
+                );
+            }*/
+
+            if config.emit_bc || config.emit_obj == EmitObj::Bitcode {
+                let _timer = cgcx
+                    .prof
+                    .generic_activity_with_arg("GCC_module_codegen_emit_bitcode", &*module.name);
+                context.add_command_line_option("-flto=auto");
+                context.add_command_line_option("-flto-partition=one");
+                context.compile_to_file(OutputKind::ObjectFile, bc_out.to_str().expect("path to str"));
+            }
+
+            if config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full) {
+                let _timer = cgcx
+                    .prof
+                    .generic_activity_with_arg("GCC_module_codegen_embed_bitcode", &*module.name);
+                // TODO(antoyo): maybe we should call embed_bitcode to have the proper iOS fixes?
+                //embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, data);
+
+                context.add_command_line_option("-flto=auto");
+                context.add_command_line_option("-flto-partition=one");
+                context.add_command_line_option("-ffat-lto-objects");
+                // TODO(antoyo): Send -plugin/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/liblto_plugin.so to linker (this should be done when specifying the appropriate rustc cli argument).
+                context.compile_to_file(OutputKind::ObjectFile, bc_out.to_str().expect("path to str"));
+            }
         }
 
         if config.emit_ir {
@@ -32,7 +76,7 @@ pub(crate) unsafe fn codegen(cgcx: &CodegenContext<GccCodegenBackend>, _diag_han
         if config.emit_asm {
             let _timer = cgcx
                 .prof
-                .generic_activity_with_arg("LLVM_module_codegen_emit_asm", &*module.name);
+                .generic_activity_with_arg("GCC_module_codegen_emit_asm", &*module.name);
             let path = cgcx.output_filenames.temp_path(OutputType::Assembly, module_name);
             context.compile_to_file(OutputKind::Assembler, path.to_str().expect("path to str"));
         }
@@ -41,7 +85,7 @@ pub(crate) unsafe fn codegen(cgcx: &CodegenContext<GccCodegenBackend>, _diag_han
             EmitObj::ObjectCode(_) => {
                 let _timer = cgcx
                     .prof
-                    .generic_activity_with_arg("LLVM_module_codegen_emit_obj", &*module.name);
+                    .generic_activity_with_arg("GCC_module_codegen_emit_obj", &*module.name);
                 if env::var("CG_GCCJIT_DUMP_MODULE_NAMES").as_deref() == Ok("1") {
                     println!("Module {}", module.name);
                 }
@@ -60,11 +104,36 @@ pub(crate) unsafe fn codegen(cgcx: &CodegenContext<GccCodegenBackend>, _diag_han
                     context.set_debug_info(true);
                     context.dump_to_file(path, true);
                 }
-                context.compile_to_file(OutputKind::ObjectFile, obj_out.to_str().expect("path to str"));
+                if should_combine_object_files && fat_lto {
+                    context.add_command_line_option("-flto=auto");
+                    context.add_command_line_option("-flto-partition=one");
+
+                    context.add_driver_option("-Wl,-r");
+                    // NOTE: we need -nostdlib, otherwise, we get the following error:
+                    // /usr/bin/ld: cannot find -lgcc_s: No such file or directory
+                    context.add_driver_option("-nostdlib");
+                    // NOTE: without -fuse-linker-plugin, we get the following error:
+                    // lto1: internal compiler error: decompressed stream: Destination buffer is too small
+                    context.add_driver_option("-fuse-linker-plugin");
+
+                    // NOTE: this doesn't actually generate an executable. With the above flags, it combines the .o files together in another .o.
+                    context.compile_to_file(OutputKind::Executable, obj_out.to_str().expect("path to str"));
+                }
+                else {
+                    context.compile_to_file(OutputKind::ObjectFile, obj_out.to_str().expect("path to str"));
+                }
             }
 
             EmitObj::Bitcode => {
-                // TODO(antoyo)
+                debug!("copying bitcode {:?} to obj {:?}", bc_out, obj_out);
+                if let Err(err) = link_or_copy(&bc_out, &obj_out) {
+                    diag_handler.emit_err(CopyBitcode { err });
+                }
+
+                if !config.emit_bc {
+                    debug!("removing_bitcode {:?}", bc_out);
+                    ensure_removed(diag_handler, &bc_out);
+                }
             }
 
             EmitObj::None => {}
@@ -82,3 +151,18 @@ pub(crate) unsafe fn codegen(cgcx: &CodegenContext<GccCodegenBackend>, _diag_han
 pub(crate) fn link(_cgcx: &CodegenContext<GccCodegenBackend>, _diag_handler: &Handler, mut _modules: Vec<ModuleCodegen<GccContext>>) -> Result<ModuleCodegen<GccContext>, FatalError> {
     unimplemented!();
 }
+
+pub(crate) fn save_temp_bitcode(cgcx: &CodegenContext<GccCodegenBackend>, _module: &ModuleCodegen<GccContext>, _name: &str) {
+    if !cgcx.save_temps {
+        return;
+    }
+    unimplemented!();
+    /*unsafe {
+        let ext = format!("{}.bc", name);
+        let cgu = Some(&module.name[..]);
+        let path = cgcx.output_filenames.temp_path_ext(&ext, cgu);
+        let cstr = path_to_c_string(&path);
+        let llmod = module.module_llvm.llmod();
+        llvm::LLVMWriteBitcodeToFile(llmod, cstr.as_ptr());
+    }*/
+}