Separating the back folder between backend-agnostic and LLVM-specific code

23 files changed, 2724 insertions, 2467 deletions

diff --git a/src/Cargo.lock b/src/Cargo.lock
index 031dac88df1..8b7f3591a25 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -2129,6 +2129,12 @@ dependencies = [
 [[package]]
 name = "rustc_codegen_ssa"
 version = "0.0.0"
+dependencies = [
+ "cc 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)",
+ "memmap 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "num_cpus 1.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustc-demangle 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
+]
 
 [[package]]
 name = "rustc_codegen_utils"
@@ -2137,13 +2143,11 @@ dependencies = [
  "flate2 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc 0.0.0",
- "rustc_allocator 0.0.0",
  "rustc_data_structures 0.0.0",
  "rustc_incremental 0.0.0",
  "rustc_metadata 0.0.0",
  "rustc_mir 0.0.0",
  "rustc_target 0.0.0",
- "serialize 0.0.0",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",
 ]
diff --git a/src/librustc_codegen_llvm/back/archive.rs b/src/librustc_codegen_llvm/back/archive.rs
index 54245a36017..76c50711639 100644
--- a/src/librustc_codegen_llvm/back/archive.rs
+++ b/src/librustc_codegen_llvm/back/archive.rs
@@ -18,6 +18,7 @@ use std::ptr;
 use std::str;
 
 use back::bytecode::RLIB_BYTECODE_EXTENSION;
+use rustc_codegen_ssa::back::archive::find_library;
 use libc;
 use llvm::archive_ro::{ArchiveRO, Child};
 use llvm::{self, ArchiveKind};
@@ -52,7 +53,6 @@ enum Addition {
     },
 }
 
-
 fn is_relevant_child(c: &Child) -> bool {
     match c.name() {
         Some(name) => !name.contains("SYMDEF"),
@@ -107,7 +107,7 @@ impl<'a> ArchiveBuilder<'a> {
     /// Adds all of the contents of a native library to this archive. This will
     /// search in the relevant locations for a library named `name`.
     pub fn add_native_library(&mut self, name: &str) {
-        let location = ::rustc_codegen_utils::find_library(name, &self.config.lib_search_paths,
+        let location = find_library(name, &self.config.lib_search_paths,
                                     self.config.sess);
         self.add_archive(&location, |_| false).unwrap_or_else(|e| {
             self.config.sess.fatal(&format!("failed to add native library {}: {}",
diff --git a/src/librustc_codegen_llvm/back/link.rs b/src/librustc_codegen_llvm/back/link.rs
index e3143e89f79..20f05d11087 100644
--- a/src/librustc_codegen_llvm/back/link.rs
+++ b/src/librustc_codegen_llvm/back/link.rs
@@ -9,9 +9,12 @@
 // except according to those terms.
 
 use back::wasm;
-use cc::windows_registry;
 use super::archive::{ArchiveBuilder, ArchiveConfig};
 use super::bytecode::RLIB_BYTECODE_EXTENSION;
+use rustc_codegen_ssa::back::linker::Linker;
+use rustc_codegen_ssa::back::link::{remove, ignored_for_lto, each_linked_rlib, linker_and_flavor,
+    get_linker};
+use rustc_codegen_ssa::back::command::Command;
 use super::rpath::RPathConfig;
 use super::rpath;
 use metadata::METADATA_FILENAME;
@@ -20,18 +23,15 @@ use rustc::session::config::{RUST_CGU_EXT, Lto};
 use rustc::session::filesearch;
 use rustc::session::search_paths::PathKind;
 use rustc::session::Session;
-use rustc::middle::cstore::{NativeLibrary, LibSource, NativeLibraryKind};
+use rustc::middle::cstore::{NativeLibrary, NativeLibraryKind};
 use rustc::middle::dependency_format::Linkage;
-use rustc_codegen_ssa::CrateInfo;
-use CodegenResults;
+use rustc_codegen_ssa::CodegenResults;
 use rustc::util::common::time;
 use rustc_fs_util::fix_windows_verbatim_for_gcc;
 use rustc::hir::def_id::CrateNum;
 use tempfile::{Builder as TempFileBuilder, TempDir};
 use rustc_target::spec::{PanicStrategy, RelroLevel, LinkerFlavor};
 use rustc_data_structures::fx::FxHashSet;
-use rustc_codegen_utils::linker::Linker;
-use rustc_codegen_utils::command::Command;
 use context::get_reloc_model;
 use llvm;
 
@@ -51,69 +51,6 @@ pub use rustc_codegen_utils::link::{find_crate_name, filename_for_input, default
                                     invalid_output_for_target, filename_for_metadata,
                                     out_filename, check_file_is_writeable};
 
-// The third parameter is for env vars, used on windows to set up the
-// path for MSVC to find its DLLs, and gcc to find its bundled
-// toolchain
-pub fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> (PathBuf, Command) {
-    let msvc_tool = windows_registry::find_tool(&sess.opts.target_triple.triple(), "link.exe");
-
-    // If our linker looks like a batch script on Windows then to execute this
-    // we'll need to spawn `cmd` explicitly. This is primarily done to handle
-    // emscripten where the linker is `emcc.bat` and needs to be spawned as
-    // `cmd /c emcc.bat ...`.
-    //
-    // This worked historically but is needed manually since #42436 (regression
-    // was tagged as #42791) and some more info can be found on #44443 for
-    // emscripten itself.
-    let mut cmd = match linker.to_str() {
-        Some(linker) if cfg!(windows) && linker.ends_with(".bat") => Command::bat_script(linker),
-        _ => match flavor {
-            LinkerFlavor::Lld(f) => Command::lld(linker, f),
-            LinkerFlavor::Msvc
-                if sess.opts.cg.linker.is_none() && sess.target.target.options.linker.is_none() =>
-            {
-                Command::new(msvc_tool.as_ref().map(|t| t.path()).unwrap_or(linker))
-            },
-            _ => Command::new(linker),
-        }
-    };
-
-    // The compiler's sysroot often has some bundled tools, so add it to the
-    // PATH for the child.
-    let mut new_path = sess.host_filesearch(PathKind::All)
-                           .get_tools_search_paths();
-    let mut msvc_changed_path = false;
-    if sess.target.target.options.is_like_msvc {
-        if let Some(ref tool) = msvc_tool {
-            cmd.args(tool.args());
-            for &(ref k, ref v) in tool.env() {
-                if k == "PATH" {
-                    new_path.extend(env::split_paths(v));
-                    msvc_changed_path = true;
-                } else {
-                    cmd.env(k, v);
-                }
-            }
-        }
-    }
-
-    if !msvc_changed_path {
-        if let Some(path) = env::var_os("PATH") {
-            new_path.extend(env::split_paths(&path));
-        }
-    }
-    cmd.env("PATH", env::join_paths(new_path).unwrap());
-
-    (linker.to_path_buf(), cmd)
-}
-
-pub fn remove(sess: &Session, path: &Path) {
-    if let Err(e) = fs::remove_file(path) {
-        sess.err(&format!("failed to remove {}: {}",
-                          path.display(),
-                          e));
-    }
-}
 
 /// Perform the linkage portion of the compilation phase. This will generate all
 /// of the requested outputs for this compilation session.
@@ -215,60 +152,6 @@ fn preserve_objects_for_their_debuginfo(sess: &Session) -> bool {
     false
 }
 
-pub(crate) fn each_linked_rlib(sess: &Session,
-                               info: &CrateInfo,
-                               f: &mut dyn FnMut(CrateNum, &Path)) -> Result<(), String> {
-    let crates = info.used_crates_static.iter();
-    let fmts = sess.dependency_formats.borrow();
-    let fmts = fmts.get(&config::CrateType::Executable)
-                   .or_else(|| fmts.get(&config::CrateType::Staticlib))
-                   .or_else(|| fmts.get(&config::CrateType::Cdylib))
-                   .or_else(|| fmts.get(&config::CrateType::ProcMacro));
-    let fmts = match fmts {
-        Some(f) => f,
-        None => return Err("could not find formats for rlibs".to_string())
-    };
-    for &(cnum, ref path) in crates {
-        match fmts.get(cnum.as_usize() - 1) {
-            Some(&Linkage::NotLinked) |
-            Some(&Linkage::IncludedFromDylib) => continue,
-            Some(_) => {}
-            None => return Err("could not find formats for rlibs".to_string())
-        }
-        let name = &info.crate_name[&cnum];
-        let path = match *path {
-            LibSource::Some(ref p) => p,
-            LibSource::MetadataOnly => {
-                return Err(format!("could not find rlib for: `{}`, found rmeta (metadata) file",
-                                   name))
-            }
-            LibSource::None => {
-                return Err(format!("could not find rlib for: `{}`", name))
-            }
-        };
-        f(cnum, &path);
-    }
-    Ok(())
-}
-
-/// Returns a boolean indicating whether the specified crate should be ignored
-/// during LTO.
-///
-/// Crates ignored during LTO are not lumped together in the "massive object
-/// file" that we create and are linked in their normal rlib states. See
-/// comments below for what crates do not participate in LTO.
-///
-/// It's unusual for a crate to not participate in LTO. Typically only
-/// compiler-specific and unstable crates have a reason to not participate in
-/// LTO.
-pub(crate) fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
-    // If our target enables builtin function lowering in LLVM then the
-    // crates providing these functions don't participate in LTO (e.g.
-    // no_builtins or compiler builtins crates).
-    !sess.target.target.options.no_builtins &&
-        (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
-}
-
 fn link_binary_output(sess: &Session,
                       codegen_results: &CodegenResults,
                       crate_type: config::CrateType,
@@ -353,8 +236,11 @@ fn archive_config<'a>(sess: &'a Session,
 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
 /// directory being searched for `extern crate` (observing an incomplete file).
 /// The returned path is the temporary file containing the complete metadata.
-fn emit_metadata<'a>(sess: &'a Session, codegen_results: &CodegenResults, tmpdir: &TempDir)
-                     -> PathBuf {
+fn emit_metadata<'a>(
+    sess: &'a Session,
+    codegen_results: &CodegenResults,
+    tmpdir: &TempDir
+) -> PathBuf {
     let out_filename = tmpdir.path().join(METADATA_FILENAME);
     let result = fs::write(&out_filename, &codegen_results.metadata.raw_data);
 
@@ -576,69 +462,6 @@ fn print_native_static_libs(sess: &Session, all_native_libs: &[NativeLibrary]) {
     }
 }
 
-pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
-    fn infer_from(
-        sess: &Session,
-        linker: Option<PathBuf>,
-        flavor: Option<LinkerFlavor>,
-    ) -> Option<(PathBuf, LinkerFlavor)> {
-        match (linker, flavor) {
-            (Some(linker), Some(flavor)) => Some((linker, flavor)),
-            // only the linker flavor is known; use the default linker for the selected flavor
-            (None, Some(flavor)) => Some((PathBuf::from(match flavor {
-                LinkerFlavor::Em  => if cfg!(windows) { "emcc.bat" } else { "emcc" },
-                LinkerFlavor::Gcc => "cc",
-                LinkerFlavor::Ld => "ld",
-                LinkerFlavor::Msvc => "link.exe",
-                LinkerFlavor::Lld(_) => "lld",
-            }), flavor)),
-            (Some(linker), None) => {
-                let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
-                    sess.fatal("couldn't extract file stem from specified linker");
-                }).to_owned();
-
-                let flavor = if stem == "emcc" {
-                    LinkerFlavor::Em
-                } else if stem == "gcc" || stem.ends_with("-gcc") {
-                    LinkerFlavor::Gcc
-                } else if stem == "ld" || stem == "ld.lld" || stem.ends_with("-ld") {
-                    LinkerFlavor::Ld
-                } else if stem == "link" || stem == "lld-link" {
-                    LinkerFlavor::Msvc
-                } else if stem == "lld" || stem == "rust-lld" {
-                    LinkerFlavor::Lld(sess.target.target.options.lld_flavor)
-                } else {
-                    // fall back to the value in the target spec
-                    sess.target.target.linker_flavor
-                };
-
-                Some((linker, flavor))
-            },
-            (None, None) => None,
-        }
-    }
-
-    // linker and linker flavor specified via command line have precedence over what the target
-    // specification specifies
-    if let Some(ret) = infer_from(
-        sess,
-        sess.opts.cg.linker.clone(),
-        sess.opts.debugging_opts.linker_flavor,
-    ) {
-        return ret;
-    }
-
-    if let Some(ret) = infer_from(
-        sess,
-        sess.target.target.options.linker.clone().map(PathBuf::from),
-        Some(sess.target.target.linker_flavor),
-    ) {
-        return ret;
-    }
-
-    bug!("Not enough information provided to determine how to invoke the linker");
-}
-
 // Create a dynamic library or executable
 //
 // This will invoke the system linker/cc to create the resulting file. This
diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs
index 0f62ea6d357..a5f07e46e11 100644
--- a/src/librustc_codegen_llvm/back/lto.rs
+++ b/src/librustc_codegen_llvm/back/lto.rs
@@ -9,12 +9,14 @@
 // except according to those terms.
 
 use back::bytecode::{DecodedBytecode, RLIB_BYTECODE_EXTENSION};
-use back::write::{ModuleConfig, with_llvm_pmb, CodegenContext};
-use back::write::{self, DiagnosticHandlers, pre_lto_bitcode_filename};
+use rustc_codegen_ssa::back::symbol_export;
+use rustc_codegen_ssa::back::write::{ModuleConfig, CodegenContext, pre_lto_bitcode_filename};
+use rustc_codegen_ssa::back::lto::{SerializedModule, LtoModuleCodegen, ThinShared, ThinModule};
+use rustc_codegen_ssa::interfaces::*;
+use back::write::{self, DiagnosticHandlers, with_llvm_pmb, save_temp_bitcode, get_llvm_opt_level};
 use errors::{FatalError, Handler};
 use llvm::archive_ro::ArchiveRO;
 use llvm::{self, True, False};
-use memmap;
 use rustc::dep_graph::WorkProduct;
 use rustc::dep_graph::cgu_reuse_tracker::CguReuse;
 use rustc::hir::def_id::LOCAL_CRATE;
@@ -22,9 +24,8 @@ use rustc::middle::exported_symbols::SymbolExportLevel;
 use rustc::session::config::{self, Lto};
 use rustc::util::common::time_ext;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_codegen_utils::symbol_export;
 use time_graph::Timeline;
-use ModuleLlvm;
+use {ModuleLlvm, LlvmCodegenBackend};
 use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
 
 use libc;
@@ -47,71 +48,16 @@ pub fn crate_type_allows_lto(crate_type: config::CrateType) -> bool {
     }
 }
 
-pub(crate) enum LtoModuleCodegen {
-    Fat {
-        module: Option<ModuleCodegen<ModuleLlvm>>,
-        _serialized_bitcode: Vec<SerializedModule>,
-    },
-
-    Thin(ThinModule),
-}
-
-impl LtoModuleCodegen {
-    pub fn name(&self) -> &str {
-        match *self {
-            LtoModuleCodegen::Fat { .. } => "everything",
-            LtoModuleCodegen::Thin(ref m) => m.name(),
-        }
-    }
-
-    /// Optimize this module within the given codegen context.
-    ///
-    /// This function is unsafe as it'll return a `ModuleCodegen` still
-    /// points to LLVM data structures owned by this `LtoModuleCodegen`.
-    /// It's intended that the module returned is immediately code generated and
-    /// dropped, and then this LTO module is dropped.
-    pub(crate) unsafe fn optimize(&mut self,
-                                  cgcx: &CodegenContext,
-                                  timeline: &mut Timeline)
-        -> Result<ModuleCodegen<ModuleLlvm>, FatalError>
-    {
-        match *self {
-            LtoModuleCodegen::Fat { ref mut module, .. } => {
-                let module = module.take().unwrap();
-                {
-                    let config = cgcx.config(module.kind);
-                    let llmod = module.module_llvm.llmod();
-                    let tm = &*module.module_llvm.tm;
-                    run_pass_manager(cgcx, tm, llmod, config, false);
-                    timeline.record("fat-done");
-                }
-                Ok(module)
-            }
-            LtoModuleCodegen::Thin(ref mut thin) => thin.optimize(cgcx, timeline),
-        }
-    }
-
-    /// A "gauge" of how costly it is to optimize this module, used to sort
-    /// biggest modules first.
-    pub fn cost(&self) -> u64 {
-        match *self {
-            // Only one module with fat LTO, so the cost doesn't matter.
-            LtoModuleCodegen::Fat { .. } => 0,
-            LtoModuleCodegen::Thin(ref m) => m.cost(),
-        }
-    }
-}
-
 /// Performs LTO, which in the case of full LTO means merging all modules into
 /// a single one and returning it for further optimizing. For ThinLTO, it will
 /// do the global analysis necessary and return two lists, one of the modules
 /// the need optimization and another for modules that can simply be copied over
 /// from the incr. comp. cache.
-pub(crate) fn run(cgcx: &CodegenContext,
+pub(crate) fn run(cgcx: &CodegenContext<LlvmCodegenBackend>,
                   modules: Vec<ModuleCodegen<ModuleLlvm>>,
-                  cached_modules: Vec<(SerializedModule, WorkProduct)>,
+                  cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
                   timeline: &mut Timeline)
-    -> Result<(Vec<LtoModuleCodegen>, Vec<WorkProduct>), FatalError>
+    -> Result<(Vec<LtoModuleCodegen<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError>
 {
     let diag_handler = cgcx.create_diag_handler();
     let export_threshold = match cgcx.lto {
@@ -230,13 +176,13 @@ pub(crate) fn run(cgcx: &CodegenContext,
     }
 }
 
-fn fat_lto(cgcx: &CodegenContext,
+fn fat_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
            diag_handler: &Handler,
            mut modules: Vec<ModuleCodegen<ModuleLlvm>>,
-           mut serialized_modules: Vec<(SerializedModule, CString)>,
+           mut serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
            symbol_white_list: &[*const libc::c_char],
            timeline: &mut Timeline)
-    -> Result<Vec<LtoModuleCodegen>, FatalError>
+    -> Result<Vec<LtoModuleCodegen<LlvmCodegenBackend>>, FatalError>
 {
     info!("going for a fat lto");
 
@@ -303,7 +249,7 @@ fn fat_lto(cgcx: &CodegenContext,
             serialized_bitcode.push(bc_decoded);
         }
         drop(linker);
-        cgcx.save_temp_bitcode(&module, "lto.input");
+        save_temp_bitcode(&cgcx, &module, "lto.input");
 
         // Internalize everything that *isn't* in our whitelist to help strip out
         // more modules and such
@@ -312,14 +258,14 @@ fn fat_lto(cgcx: &CodegenContext,
             llvm::LLVMRustRunRestrictionPass(llmod,
                                              ptr as *const *const libc::c_char,
                                              symbol_white_list.len() as libc::size_t);
-            cgcx.save_temp_bitcode(&module, "lto.after-restriction");
+            save_temp_bitcode(&cgcx, &module, "lto.after-restriction");
         }
 
         if cgcx.no_landing_pads {
             unsafe {
                 llvm::LLVMRustMarkAllFunctionsNounwind(llmod);
             }
-            cgcx.save_temp_bitcode(&module, "lto.after-nounwind");
+            save_temp_bitcode(&cgcx, &module, "lto.after-nounwind");
         }
         timeline.record("passes");
     }
@@ -386,14 +332,14 @@ impl Drop for Linker<'a> {
 /// calculating the *index* for ThinLTO. This index will then be shared amongst
 /// all of the `LtoModuleCodegen` units returned below and destroyed once
 /// they all go out of scope.
-fn thin_lto(cgcx: &CodegenContext,
+fn thin_lto(cgcx: &CodegenContext<LlvmCodegenBackend>,
             diag_handler: &Handler,
             modules: Vec<ModuleCodegen<ModuleLlvm>>,
-            serialized_modules: Vec<(SerializedModule, CString)>,
-            cached_modules: Vec<(SerializedModule, WorkProduct)>,
+            serialized_modules: Vec<(SerializedModule<ModuleBuffer>, CString)>,
+            cached_modules: Vec<(SerializedModule<ModuleBuffer>, WorkProduct)>,
             symbol_white_list: &[*const libc::c_char],
             timeline: &mut Timeline)
-    -> Result<(Vec<LtoModuleCodegen>, Vec<WorkProduct>), FatalError>
+    -> Result<(Vec<LtoModuleCodegen<LlvmCodegenBackend>>, Vec<WorkProduct>), FatalError>
 {
     unsafe {
         info!("going for that thin, thin LTO");
@@ -556,9 +502,8 @@ fn thin_lto(cgcx: &CodegenContext,
     }
 }
 
-fn run_pass_manager(cgcx: &CodegenContext,
-                    tm: &llvm::TargetMachine,
-                    llmod: &llvm::Module,
+pub(crate) fn run_pass_manager(cgcx: &CodegenContext<LlvmCodegenBackend>,
+                    module: &ModuleCodegen<ModuleLlvm>,
                     config: &ModuleConfig,
                     thin: bool) {
     // Now we have one massive module inside of llmod. Time to run the
@@ -569,7 +514,7 @@ fn run_pass_manager(cgcx: &CodegenContext,
     debug!("running the pass manager");
     unsafe {
         let pm = llvm::LLVMCreatePassManager();
-        llvm::LLVMRustAddAnalysisPasses(tm, pm, llmod);
+        llvm::LLVMRustAddAnalysisPasses(module.module_llvm.tm, pm, module.module_llvm.llmod());
 
         if config.verify_llvm_ir {
             let pass = llvm::LLVMRustFindAndCreatePass("verify\0".as_ptr() as *const _);
@@ -588,12 +533,13 @@ fn run_pass_manager(cgcx: &CodegenContext,
         // Note that in general this shouldn't matter too much as you typically
         // only turn on ThinLTO when you're compiling with optimizations
         // otherwise.
-        let opt_level = config.opt_level.unwrap_or(llvm::CodeGenOptLevel::None);
+        let opt_level = config.opt_level.map(get_llvm_opt_level)
+            .unwrap_or(llvm::CodeGenOptLevel::None);
         let opt_level = match opt_level {
             llvm::CodeGenOptLevel::None => llvm::CodeGenOptLevel::Less,
             level => level,
         };
-        with_llvm_pmb(llmod, config, opt_level, false, &mut |b| {
+        with_llvm_pmb(module.module_llvm.llmod(), config, opt_level, false, &mut |b| {
             if thin {
                 llvm::LLVMRustPassManagerBuilderPopulateThinLTOPassManager(b, pm);
             } else {
@@ -615,29 +561,14 @@ fn run_pass_manager(cgcx: &CodegenContext,
             llvm::LLVMRustAddPass(pm, pass.unwrap());
         }
 
-        time_ext(cgcx.time_passes, None, "LTO passes", || llvm::LLVMRunPassManager(pm, llmod));
+        time_ext(cgcx.time_passes, None, "LTO passes", ||
+             llvm::LLVMRunPassManager(pm, module.module_llvm.llmod()));
 
         llvm::LLVMDisposePassManager(pm);
     }
     debug!("lto done");
 }
 
-pub enum SerializedModule {
-    Local(ModuleBuffer),
-    FromRlib(Vec<u8>),
-    FromUncompressedFile(memmap::Mmap),
-}
-
-impl SerializedModule {
-    fn data(&self) -> &[u8] {
-        match *self {
-            SerializedModule::Local(ref m) => m.data(),
-            SerializedModule::FromRlib(ref m) => m,
-            SerializedModule::FromUncompressedFile(ref m) => m,
-        }
-    }
-}
-
 pub struct ModuleBuffer(&'static mut llvm::ModuleBuffer);
 
 unsafe impl Send for ModuleBuffer {}
@@ -649,8 +580,10 @@ impl ModuleBuffer {
             llvm::LLVMRustModuleBufferCreate(m)
         })
     }
+}
 
-    pub fn data(&self) -> &[u8] {
+impl ModuleBufferMethods for ModuleBuffer {
+    fn data(&self) -> &[u8] {
         unsafe {
             let ptr = llvm::LLVMRustModuleBufferPtr(self.0);
             let len = llvm::LLVMRustModuleBufferLen(self.0);
@@ -665,19 +598,7 @@ impl Drop for ModuleBuffer {
     }
 }
 
-pub struct ThinModule {
-    shared: Arc<ThinShared>,
-    idx: usize,
-}
-
-struct ThinShared {
-    data: ThinData,
-    thin_buffers: Vec<ThinBuffer>,
-    serialized_modules: Vec<SerializedModule>,
-    module_names: Vec<CString>,
-}
-
-struct ThinData(&'static mut llvm::ThinLTOData);
+pub struct ThinData(&'static mut llvm::ThinLTOData);
 
 unsafe impl Send for ThinData {}
 unsafe impl Sync for ThinData {}
@@ -702,8 +623,10 @@ impl ThinBuffer {
             ThinBuffer(buffer)
         }
     }
+}
 
-    pub fn data(&self) -> &[u8] {
+impl ThinBufferMethods for ThinBuffer {
+    fn data(&self) -> &[u8] {
         unsafe {
             let ptr = llvm::LLVMRustThinLTOBufferPtr(self.0) as *const _;
             let len = llvm::LLVMRustThinLTOBufferLen(self.0);
@@ -720,161 +643,142 @@ impl Drop for ThinBuffer {
     }
 }
 
-impl ThinModule {
-    fn name(&self) -> &str {
-        self.shared.module_names[self.idx].to_str().unwrap()
-    }
-
-    fn cost(&self) -> u64 {
-        // Yes, that's correct, we're using the size of the bytecode as an
-        // indicator for how costly this codegen unit is.
-        self.data().len() as u64
-    }
-
-    fn data(&self) -> &[u8] {
-        let a = self.shared.thin_buffers.get(self.idx).map(|b| b.data());
-        a.unwrap_or_else(|| {
-            let len = self.shared.thin_buffers.len();
-            self.shared.serialized_modules[self.idx - len].data()
-        })
-    }
-
-    unsafe fn optimize(&mut self, cgcx: &CodegenContext, timeline: &mut Timeline)
-        -> Result<ModuleCodegen<ModuleLlvm>, FatalError>
-    {
-        let diag_handler = cgcx.create_diag_handler();
-        let tm = (cgcx.tm_factory)().map_err(|e| {
-            write::llvm_err(&diag_handler, &e)
-        })?;
-
-        // Right now the implementation we've got only works over serialized
-        // modules, so we create a fresh new LLVM context and parse the module
-        // into that context. One day, however, we may do this for upstream
-        // crates but for locally codegened modules we may be able to reuse
-        // that LLVM Context and Module.
-        let llcx = llvm::LLVMRustContextCreate(cgcx.fewer_names);
-        let llmod_raw = llvm::LLVMRustParseBitcodeForThinLTO(
+pub unsafe fn optimize_thin_module(
+    thin_module: &mut ThinModule<LlvmCodegenBackend>,
+    cgcx: &CodegenContext<LlvmCodegenBackend>,
+    timeline: &mut Timeline
+) -> Result<ModuleCodegen<ModuleLlvm>, FatalError> {
+    let diag_handler = cgcx.create_diag_handler();
+    let tm = (cgcx.tm_factory)().map_err(|e| {
+        write::llvm_err(&diag_handler, &e)
+    })?;
+
+    // Right now the implementation we've got only works over serialized
+    // modules, so we create a fresh new LLVM context and parse the module
+    // into that context. One day, however, we may do this for upstream
+    // crates but for locally codegened modules we may be able to reuse
+    // that LLVM Context and Module.
+    let llcx = llvm::LLVMRustContextCreate(cgcx.fewer_names);
+    let llmod_raw = llvm::LLVMRustParseBitcodeForThinLTO(
+        llcx,
+        thin_module.data().as_ptr(),
+        thin_module.data().len(),
+        thin_module.shared.module_names[thin_module.idx].as_ptr(),
+    ).ok_or_else(|| {
+        let msg = "failed to parse bitcode for thin LTO module";
+        write::llvm_err(&diag_handler, msg)
+    })? as *const _;
+    let module = ModuleCodegen {
+        module_llvm: ModuleLlvm {
+            llmod_raw,
             llcx,
-            self.data().as_ptr(),
-            self.data().len(),
-            self.shared.module_names[self.idx].as_ptr(),
-        ).ok_or_else(|| {
-            let msg = "failed to parse bitcode for thin LTO module";
-            write::llvm_err(&diag_handler, msg)
-        })? as *const _;
-        let module = ModuleCodegen {
-            module_llvm: ModuleLlvm {
-                llmod_raw,
-                llcx,
-                tm,
-            },
-            name: self.name().to_string(),
-            kind: ModuleKind::Regular,
-        };
-        {
-            let llmod = module.module_llvm.llmod();
-            cgcx.save_temp_bitcode(&module, "thin-lto-input");
-
-            // Before we do much else find the "main" `DICompileUnit` that we'll be
-            // using below. If we find more than one though then rustc has changed
-            // in a way we're not ready for, so generate an ICE by returning
-            // an error.
-            let mut cu1 = ptr::null_mut();
-            let mut cu2 = ptr::null_mut();
-            llvm::LLVMRustThinLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2);
-            if !cu2.is_null() {
-                let msg = "multiple source DICompileUnits found";
-                return Err(write::llvm_err(&diag_handler, msg))
-            }
+            tm,
+        },
+        name: thin_module.name().to_string(),
+        kind: ModuleKind::Regular,
+    };
+    {
+        let llmod = module.module_llvm.llmod();
+        save_temp_bitcode(&cgcx, &module, "thin-lto-input");
+
+        // Before we do much else find the "main" `DICompileUnit` that we'll be
+        // using below. If we find more than one though then rustc has changed
+        // in a way we're not ready for, so generate an ICE by returning
+        // an error.
+        let mut cu1 = ptr::null_mut();
+        let mut cu2 = ptr::null_mut();
+        llvm::LLVMRustThinLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2);
+        if !cu2.is_null() {
+            let msg = "multiple source DICompileUnits found";
+            return Err(write::llvm_err(&diag_handler, msg))
+        }
 
-            // Like with "fat" LTO, get some better optimizations if landing pads
-            // are disabled by removing all landing pads.
-            if cgcx.no_landing_pads {
-                llvm::LLVMRustMarkAllFunctionsNounwind(llmod);
-                cgcx.save_temp_bitcode(&module, "thin-lto-after-nounwind");
-                timeline.record("nounwind");
-            }
+        // Like with "fat" LTO, get some better optimizations if landing pads
+        // are disabled by removing all landing pads.
+        if cgcx.no_landing_pads {
+            llvm::LLVMRustMarkAllFunctionsNounwind(llmod);
+            save_temp_bitcode(&cgcx, &module, "thin-lto-after-nounwind");
+            timeline.record("nounwind");
+        }
 
-            // Up next comes the per-module local analyses that we do for Thin LTO.
-            // Each of these functions is basically copied from the LLVM
-            // implementation and then tailored to suit this implementation. Ideally
-            // each of these would be supported by upstream LLVM but that's perhaps
-            // a patch for another day!
-            //
-            // You can find some more comments about these functions in the LLVM
-            // bindings we've got (currently `PassWrapper.cpp`)
-            if !llvm::LLVMRustPrepareThinLTORename(self.shared.data.0, llmod) {
-                let msg = "failed to prepare thin LTO module";
-                return Err(write::llvm_err(&diag_handler, msg))
-            }
-            cgcx.save_temp_bitcode(&module, "thin-lto-after-rename");
-            timeline.record("rename");
-            if !llvm::LLVMRustPrepareThinLTOResolveWeak(self.shared.data.0, llmod) {
-                let msg = "failed to prepare thin LTO module";
-                return Err(write::llvm_err(&diag_handler, msg))
-            }
-            cgcx.save_temp_bitcode(&module, "thin-lto-after-resolve");
-            timeline.record("resolve");
-            if !llvm::LLVMRustPrepareThinLTOInternalize(self.shared.data.0, llmod) {
-                let msg = "failed to prepare thin LTO module";
-                return Err(write::llvm_err(&diag_handler, msg))
-            }
-            cgcx.save_temp_bitcode(&module, "thin-lto-after-internalize");
-            timeline.record("internalize");
-            if !llvm::LLVMRustPrepareThinLTOImport(self.shared.data.0, llmod) {
-                let msg = "failed to prepare thin LTO module";
-                return Err(write::llvm_err(&diag_handler, msg))
-            }
-            cgcx.save_temp_bitcode(&module, "thin-lto-after-import");
-            timeline.record("import");
-
-            // Ok now this is a bit unfortunate. This is also something you won't
-            // find upstream in LLVM's ThinLTO passes! This is a hack for now to
-            // work around bugs in LLVM.
-            //
-            // First discovered in #45511 it was found that as part of ThinLTO
-            // importing passes LLVM will import `DICompileUnit` metadata
-            // information across modules. This means that we'll be working with one
-            // LLVM module that has multiple `DICompileUnit` instances in it (a
-            // bunch of `llvm.dbg.cu` members). Unfortunately there's a number of
-            // bugs in LLVM's backend which generates invalid DWARF in a situation
-            // like this:
-            //
-            //  https://bugs.llvm.org/show_bug.cgi?id=35212
-            //  https://bugs.llvm.org/show_bug.cgi?id=35562
-            //
-            // While the first bug there is fixed the second ended up causing #46346
-            // which was basically a resurgence of #45511 after LLVM's bug 35212 was
-            // fixed.
-            //
-            // This function below is a huge hack around this problem. The function
-            // below is defined in `PassWrapper.cpp` and will basically "merge"
-            // all `DICompileUnit` instances in a module. Basically it'll take all
-            // the objects, rewrite all pointers of `DISubprogram` to point to the
-            // first `DICompileUnit`, and then delete all the other units.
-            //
-            // This is probably mangling to the debug info slightly (but hopefully
-            // not too much) but for now at least gets LLVM to emit valid DWARF (or
-            // so it appears). Hopefully we can remove this once upstream bugs are
-            // fixed in LLVM.
-            llvm::LLVMRustThinLTOPatchDICompileUnit(llmod, cu1);
-            cgcx.save_temp_bitcode(&module, "thin-lto-after-patch");
-            timeline.record("patch");
-
-            // Alright now that we've done everything related to the ThinLTO
-            // analysis it's time to run some optimizations! Here we use the same
-            // `run_pass_manager` as the "fat" LTO above except that we tell it to
-            // populate a thin-specific pass manager, which presumably LLVM treats a
-            // little differently.
-            info!("running thin lto passes over {}", module.name);
-            let config = cgcx.config(module.kind);
-            run_pass_manager(cgcx, module.module_llvm.tm, llmod, config, true);
-            cgcx.save_temp_bitcode(&module, "thin-lto-after-pm");
-            timeline.record("thin-done");
+        // Up next comes the per-module local analyses that we do for Thin LTO.
+        // Each of these functions is basically copied from the LLVM
+        // implementation and then tailored to suit this implementation. Ideally
+        // each of these would be supported by upstream LLVM but that's perhaps
+        // a patch for another day!
+        //
+        // You can find some more comments about these functions in the LLVM
+        // bindings we've got (currently `PassWrapper.cpp`)
+        if !llvm::LLVMRustPrepareThinLTORename(thin_module.shared.data.0, llmod) {
+            let msg = "failed to prepare thin LTO module";
+            return Err(write::llvm_err(&diag_handler, msg))
         }
+        save_temp_bitcode(cgcx, &module, "thin-lto-after-rename");
+        timeline.record("rename");
+        if !llvm::LLVMRustPrepareThinLTOResolveWeak(thin_module.shared.data.0, llmod) {
+            let msg = "failed to prepare thin LTO module";
+            return Err(write::llvm_err(&diag_handler, msg))
+        }
+        save_temp_bitcode(cgcx, &module, "thin-lto-after-resolve");
+        timeline.record("resolve");
+        if !llvm::LLVMRustPrepareThinLTOInternalize(thin_module.shared.data.0, llmod) {
+            let msg = "failed to prepare thin LTO module";
+            return Err(write::llvm_err(&diag_handler, msg))
+        }
+        save_temp_bitcode(cgcx, &module, "thin-lto-after-internalize");
+        timeline.record("internalize");
+        if !llvm::LLVMRustPrepareThinLTOImport(thin_module.shared.data.0, llmod) {
+            let msg = "failed to prepare thin LTO module";
+            return Err(write::llvm_err(&diag_handler, msg))
+        }
+        save_temp_bitcode(cgcx, &module, "thin-lto-after-import");
+        timeline.record("import");
 
-        Ok(module)
+        // Ok now this is a bit unfortunate. This is also something you won't
+        // find upstream in LLVM's ThinLTO passes! This is a hack for now to
+        // work around bugs in LLVM.
+        //
+        // First discovered in #45511 it was found that as part of ThinLTO
+        // importing passes LLVM will import `DICompileUnit` metadata
+        // information across modules. This means that we'll be working with one
+        // LLVM module that has multiple `DICompileUnit` instances in it (a
+        // bunch of `llvm.dbg.cu` members). Unfortunately there's a number of
+        // bugs in LLVM's backend which generates invalid DWARF in a situation
+        // like this:
+        //
+        //  https://bugs.llvm.org/show_bug.cgi?id=35212
+        //  https://bugs.llvm.org/show_bug.cgi?id=35562
+        //
+        // While the first bug there is fixed the second ended up causing #46346
+        // which was basically a resurgence of #45511 after LLVM's bug 35212 was
+        // fixed.
+        //
+        // This function below is a huge hack around this problem. The function
+        // below is defined in `PassWrapper.cpp` and will basically "merge"
+        // all `DICompileUnit` instances in a module. Basically it'll take all
+        // the objects, rewrite all pointers of `DISubprogram` to point to the
+        // first `DICompileUnit`, and then delete all the other units.
+        //
+        // This is probably mangling to the debug info slightly (but hopefully
+        // not too much) but for now at least gets LLVM to emit valid DWARF (or
+        // so it appears). Hopefully we can remove this once upstream bugs are
+        // fixed in LLVM.
+        llvm::LLVMRustThinLTOPatchDICompileUnit(llmod, cu1);
+        save_temp_bitcode(cgcx, &module, "thin-lto-after-patch");
+        timeline.record("patch");
+
+        // Alright now that we've done everything related to the ThinLTO
+        // analysis it's time to run some optimizations! Here we use the same
+        // `run_pass_manager` as the "fat" LTO above except that we tell it to
+        // populate a thin-specific pass manager, which presumably LLVM treats a
+        // little differently.
+        info!("running thin lto passes over {}", module.name);
+        let config = cgcx.config(module.kind);
+        run_pass_manager(cgcx, &module, config, true);
+        save_temp_bitcode(cgcx, &module, "thin-lto-after-pm");
+        timeline.record("thin-done");
     }
+    Ok(module)
 }
 
 #[derive(Debug, Default)]
diff --git a/src/librustc_codegen_llvm/back/write.rs b/src/librustc_codegen_llvm/back/write.rs
index 1e167046daf..97adfab516f 100644
--- a/src/librustc_codegen_llvm/back/write.rs
+++ b/src/librustc_codegen_llvm/back/write.rs
@@ -10,57 +10,35 @@
 
 use attributes;
 use back::bytecode::{self, RLIB_BYTECODE_EXTENSION};
-use back::lto::{self, ThinBuffer, SerializedModule};
-use back::link::{self, get_linker, remove};
+use back::lto::ThinBuffer;
+use rustc_codegen_ssa::back::write::{CodegenContext, ModuleConfig, run_assembler};
+use rustc_codegen_ssa::interfaces::*;
 use base;
 use consts;
-use memmap;
-use rustc_incremental::{copy_cgu_workproducts_to_incr_comp_cache_dir,
-                        in_incr_comp_dir, in_incr_comp_dir_sess};
-use rustc::dep_graph::{WorkProduct, WorkProductId, WorkProductFileKind};
-use rustc::dep_graph::cgu_reuse_tracker::CguReuseTracker;
-use rustc::middle::cstore::EncodedMetadata;
-use rustc::session::config::{self, OutputFilenames, OutputType, Passes, Sanitizer, Lto};
+use rustc::session::config::{self, OutputType, Passes, Lto};
 use rustc::session::Session;
-use rustc::util::nodemap::FxHashMap;
-use time_graph::{self, TimeGraph, Timeline};
+use time_graph::Timeline;
 use llvm::{self, DiagnosticInfo, PassManager, SMDiagnostic};
 use llvm_util;
-use {CodegenResults, ModuleLlvm};
-use rustc_codegen_ssa::{ModuleCodegen, ModuleKind, CachedModuleCodegen, CompiledModule, CrateInfo};
-use rustc::hir::def_id::{CrateNum, LOCAL_CRATE};
-use rustc::ty::TyCtxt;
-use rustc::util::common::{time_ext, time_depth, set_time_depth, print_time_passes_entry};
+use ModuleLlvm;
+use rustc_codegen_ssa::{ModuleCodegen, CompiledModule};
+use rustc::util::common::time_ext;
 use rustc_fs_util::{path2cstr, link_or_copy};
 use rustc_data_structures::small_c_str::SmallCStr;
-use rustc_data_structures::svh::Svh;
-use rustc_codegen_utils::command::Command;
-use rustc_codegen_utils::linker::LinkerInfo;
-use rustc_codegen_utils::symbol_export::ExportedSymbols;
-use errors::{self, Handler, Level, DiagnosticBuilder, FatalError, DiagnosticId};
-use errors::emitter::{Emitter};
-use syntax::attr;
-use syntax::ext::hygiene::Mark;
-use syntax_pos::MultiSpan;
-use syntax_pos::symbol::Symbol;
+use errors::{self, Handler, FatalError};
 use type_::Type;
 use context::{is_pie_binary, get_reloc_model};
 use common;
-use jobserver::{Client, Acquired};
+use LlvmCodegenBackend;
 use rustc_demangle;
 
-use std::any::Any;
 use std::ffi::{CString, CStr};
 use std::fs;
 use std::io::{self, Write};
-use std::mem;
-use std::path::{Path, PathBuf};
+use std::path::Path;
 use std::str;
 use std::sync::Arc;
-use std::sync::mpsc::{channel, Sender, Receiver};
 use std::slice;
-use std::time::Instant;
-use std::thread;
 use libc::{c_uint, c_void, c_char, size_t};
 
 pub const RELOC_MODEL_ARGS : [(&str, llvm::RelocMode); 7] = [
@@ -87,8 +65,6 @@ pub const TLS_MODEL_ARGS : [(&str, llvm::ThreadLocalMode); 4] = [
     ("local-exec", llvm::ThreadLocalMode::LocalExec),
 ];
 
-const PRE_THIN_LTO_BC_EXT: &str = "pre-thin-lto.bc";
-
 pub fn llvm_err(handler: &errors::Handler, msg: &str) -> FatalError {
     match llvm::last_error() {
         Some(err) => handler.fatal(&format!("{}: {}", msg, err)),
@@ -115,7 +91,7 @@ pub fn write_output_file(
     }
 }
 
-fn get_llvm_opt_level(optimize: config::OptLevel) -> llvm::CodeGenOptLevel {
+pub(crate) fn get_llvm_opt_level(optimize: config::OptLevel) -> llvm::CodeGenOptLevel {
     match optimize {
       config::OptLevel::No => llvm::CodeGenOptLevel::None,
       config::OptLevel::Less => llvm::CodeGenOptLevel::Less,
@@ -125,7 +101,7 @@ fn get_llvm_opt_level(optimize: config::OptLevel) -> llvm::CodeGenOptLevel {
     }
 }
 
-fn get_llvm_opt_size(optimize: config::OptLevel) -> llvm::CodeGenOptSize {
+pub(crate) fn get_llvm_opt_size(optimize: config::OptLevel) -> llvm::CodeGenOptSize {
     match optimize {
       config::OptLevel::Size => llvm::CodeGenOptSizeDefault,
       config::OptLevel::SizeMin => llvm::CodeGenOptSizeAggressive,
@@ -223,212 +199,31 @@ pub fn target_machine_factory(sess: &Session, find_features: bool)
     })
 }
 
-/// Module-specific configuration for `optimize_and_codegen`.
-pub struct ModuleConfig {
-    /// Names of additional optimization passes to run.
-    passes: Vec<String>,
-    /// Some(level) to optimize at a certain level, or None to run
-    /// absolutely no optimizations (used for the metadata module).
-    pub opt_level: Option<llvm::CodeGenOptLevel>,
-
-    /// Some(level) to optimize binary size, or None to not affect program size.
-    opt_size: Option<llvm::CodeGenOptSize>,
-
-    pgo_gen: Option<String>,
-    pgo_use: String,
-
-    // Flags indicating which outputs to produce.
-    pub emit_pre_thin_lto_bc: bool,
-    emit_no_opt_bc: bool,
-    emit_bc: bool,
-    emit_bc_compressed: bool,
-    emit_lto_bc: bool,
-    emit_ir: bool,
-    emit_asm: bool,
-    emit_obj: bool,
-    // Miscellaneous flags.  These are mostly copied from command-line
-    // options.
-    pub verify_llvm_ir: bool,
-    no_prepopulate_passes: bool,
-    no_builtins: bool,
-    time_passes: bool,
-    vectorize_loop: bool,
-    vectorize_slp: bool,
-    merge_functions: bool,
-    inline_threshold: Option<usize>,
-    // Instead of creating an object file by doing LLVM codegen, just
-    // make the object file bitcode. Provides easy compatibility with
-    // emscripten's ecc compiler, when used as the linker.
-    obj_is_bitcode: bool,
-    no_integrated_as: bool,
-    embed_bitcode: bool,
-    embed_bitcode_marker: bool,
-}
-
-impl ModuleConfig {
-    fn new(passes: Vec<String>) -> ModuleConfig {
-        ModuleConfig {
-            passes,
-            opt_level: None,
-            opt_size: None,
-
-            pgo_gen: None,
-            pgo_use: String::new(),
-
-            emit_no_opt_bc: false,
-            emit_pre_thin_lto_bc: false,
-            emit_bc: false,
-            emit_bc_compressed: false,
-            emit_lto_bc: false,
-            emit_ir: false,
-            emit_asm: false,
-            emit_obj: false,
-            obj_is_bitcode: false,
-            embed_bitcode: false,
-            embed_bitcode_marker: false,
-            no_integrated_as: false,
-
-            verify_llvm_ir: false,
-            no_prepopulate_passes: false,
-            no_builtins: false,
-            time_passes: false,
-            vectorize_loop: false,
-            vectorize_slp: false,
-            merge_functions: false,
-            inline_threshold: None
-        }
-    }
-
-    fn set_flags(&mut self, sess: &Session, no_builtins: bool) {
-        self.verify_llvm_ir = sess.verify_llvm_ir();
-        self.no_prepopulate_passes = sess.opts.cg.no_prepopulate_passes;
-        self.no_builtins = no_builtins || sess.target.target.options.no_builtins;
-        self.time_passes = sess.time_passes();
-        self.inline_threshold = sess.opts.cg.inline_threshold;
-        self.obj_is_bitcode = sess.target.target.options.obj_is_bitcode ||
-                              sess.opts.debugging_opts.cross_lang_lto.enabled();
-        let embed_bitcode = sess.target.target.options.embed_bitcode ||
-                            sess.opts.debugging_opts.embed_bitcode;
-        if embed_bitcode {
-            match sess.opts.optimize {
-                config::OptLevel::No |
-                config::OptLevel::Less => {
-                    self.embed_bitcode_marker = embed_bitcode;
-                }
-                _ => self.embed_bitcode = embed_bitcode,
-            }
-        }
-
-        // Copy what clang does by turning on loop vectorization at O2 and
-        // slp vectorization at O3. Otherwise configure other optimization aspects
-        // of this pass manager builder.
-        // Turn off vectorization for emscripten, as it's not very well supported.
-        self.vectorize_loop = !sess.opts.cg.no_vectorize_loops &&
-                             (sess.opts.optimize == config::OptLevel::Default ||
-                              sess.opts.optimize == config::OptLevel::Aggressive) &&
-                             !sess.target.target.options.is_like_emscripten;
-
-        self.vectorize_slp = !sess.opts.cg.no_vectorize_slp &&
-                            sess.opts.optimize == config::OptLevel::Aggressive &&
-                            !sess.target.target.options.is_like_emscripten;
-
-        self.merge_functions = sess.opts.optimize == config::OptLevel::Default ||
-                               sess.opts.optimize == config::OptLevel::Aggressive;
-    }
-
-    pub fn bitcode_needed(&self) -> bool {
-        self.emit_bc || self.obj_is_bitcode
-            || self.emit_bc_compressed || self.embed_bitcode
-    }
-}
-
-/// Assembler name and command used by codegen when no_integrated_as is enabled
-struct AssemblerCommand {
-    name: PathBuf,
-    cmd: Command,
-}
-
-/// Additional resources used by optimize_and_codegen (not module specific)
-#[derive(Clone)]
-pub struct CodegenContext {
-    // Resources needed when running LTO
-    pub time_passes: bool,
-    pub lto: Lto,
-    pub no_landing_pads: bool,
-    pub save_temps: bool,
-    pub fewer_names: bool,
-    pub exported_symbols: Option<Arc<ExportedSymbols>>,
-    pub opts: Arc<config::Options>,
-    pub crate_types: Vec<config::CrateType>,
-    pub each_linked_rlib_for_lto: Vec<(CrateNum, PathBuf)>,
-    output_filenames: Arc<OutputFilenames>,
-    regular_module_config: Arc<ModuleConfig>,
-    metadata_module_config: Arc<ModuleConfig>,
-    allocator_module_config: Arc<ModuleConfig>,
-    pub tm_factory: Arc<dyn Fn() -> Result<&'static mut llvm::TargetMachine, String> + Send + Sync>,
-    pub msvc_imps_needed: bool,
-    pub target_pointer_width: String,
-    debuginfo: config::DebugInfo,
-
-    // Number of cgus excluding the allocator/metadata modules
-    pub total_cgus: usize,
-    // Handler to use for diagnostics produced during codegen.
-    pub diag_emitter: SharedEmitter,
-    // LLVM passes added by plugins.
-    pub plugin_passes: Vec<String>,
-    // LLVM optimizations for which we want to print remarks.
-    pub remark: Passes,
-    // Worker thread number
-    pub worker: usize,
-    // The incremental compilation session directory, or None if we are not
-    // compiling incrementally
-    pub incr_comp_session_dir: Option<PathBuf>,
-    // Used to update CGU re-use information during the thinlto phase.
-    pub cgu_reuse_tracker: CguReuseTracker,
-    // Channel back to the main control thread to send messages to
-    coordinator_send: Sender<Box<dyn Any + Send>>,
-    // A reference to the TimeGraph so we can register timings. None means that
-    // measuring is disabled.
-    time_graph: Option<TimeGraph>,
-    // The assembler command if no_integrated_as option is enabled, None otherwise
-    assembler_cmd: Option<Arc<AssemblerCommand>>
-}
-
-impl CodegenContext {
-    pub fn create_diag_handler(&self) -> Handler {
-        Handler::with_emitter(true, false, Box::new(self.diag_emitter.clone()))
-    }
-
-    pub(crate) fn config(&self, kind: ModuleKind) -> &ModuleConfig {
-        match kind {
-            ModuleKind::Regular => &self.regular_module_config,
-            ModuleKind::Metadata => &self.metadata_module_config,
-            ModuleKind::Allocator => &self.allocator_module_config,
-        }
+pub(crate) fn save_temp_bitcode(
+    cgcx: &CodegenContext<LlvmCodegenBackend>,
+    module: &ModuleCodegen<ModuleLlvm>,
+    name: &str
+) {
+    if !cgcx.save_temps {
+        return
     }
-
-    pub(crate) fn save_temp_bitcode(&self, module: &ModuleCodegen<ModuleLlvm>, name: &str) {
-        if !self.save_temps {
-            return
-        }
-        unsafe {
-            let ext = format!("{}.bc", name);
-            let cgu = Some(&module.name[..]);
-            let path = self.output_filenames.temp_path_ext(&ext, cgu);
-            let cstr = path2cstr(&path);
-            let llmod = module.module_llvm.llmod();
-            llvm::LLVMWriteBitcodeToFile(llmod, cstr.as_ptr());
-        }
+    unsafe {
+        let ext = format!("{}.bc", name);
+        let cgu = Some(&module.name[..]);
+        let path = cgcx.output_filenames.temp_path_ext(&ext, cgu);
+        let cstr = path2cstr(&path);
+        let llmod = module.module_llvm.llmod();
+        llvm::LLVMWriteBitcodeToFile(llmod, cstr.as_ptr());
     }
 }
 
 pub struct DiagnosticHandlers<'a> {
-    data: *mut (&'a CodegenContext, &'a Handler),
+    data: *mut (&'a CodegenContext<LlvmCodegenBackend>, &'a Handler),
     llcx: &'a llvm::Context,
 }
 
 impl<'a> DiagnosticHandlers<'a> {
-    pub fn new(cgcx: &'a CodegenContext,
+    pub fn new(cgcx: &'a CodegenContext<LlvmCodegenBackend>,
                handler: &'a Handler,
                llcx: &'a llvm::Context) -> Self {
         let data = Box::into_raw(Box::new((cgcx, handler)));
@@ -451,7 +246,7 @@ impl<'a> Drop for DiagnosticHandlers<'a> {
     }
 }
 
-unsafe extern "C" fn report_inline_asm<'a, 'b>(cgcx: &'a CodegenContext,
+unsafe extern "C" fn report_inline_asm<'a, 'b>(cgcx: &'a CodegenContext<LlvmCodegenBackend>,
                                                msg: &'b str,
                                                cookie: c_uint) {
     cgcx.diag_emitter.inline_asm_error(cookie as u32, msg.to_owned());
@@ -463,7 +258,7 @@ unsafe extern "C" fn inline_asm_handler(diag: &SMDiagnostic,
     if user.is_null() {
         return
     }
-    let (cgcx, _) = *(user as *const (&CodegenContext, &Handler));
+    let (cgcx, _) = *(user as *const (&CodegenContext<LlvmCodegenBackend>, &Handler));
 
     let msg = llvm::build_string(|s| llvm::LLVMRustWriteSMDiagnosticToString(diag, s))
         .expect("non-UTF8 SMDiagnostic");
@@ -475,7 +270,7 @@ unsafe extern "C" fn diagnostic_handler(info: &DiagnosticInfo, user: *mut c_void
     if user.is_null() {
         return
     }
-    let (cgcx, diag_handler) = *(user as *const (&CodegenContext, &Handler));
+    let (cgcx, diag_handler) = *(user as *const (&CodegenContext<LlvmCodegenBackend>, &Handler));
 
     match llvm::diagnostic::Diagnostic::unpack(info) {
         llvm::diagnostic::InlineAsm(inline) => {
@@ -512,7 +307,7 @@ unsafe extern "C" fn diagnostic_handler(info: &DiagnosticInfo, user: *mut c_void
 }
 
 // Unsafe due to LLVM calls.
-unsafe fn optimize(cgcx: &CodegenContext,
+pub(crate) unsafe fn optimize(cgcx: &CodegenContext<LlvmCodegenBackend>,
                    diag_handler: &Handler,
                    module: &ModuleCodegen<ModuleLlvm>,
                    config: &ModuleConfig,
@@ -572,7 +367,8 @@ unsafe fn optimize(cgcx: &CodegenContext,
             if !config.no_prepopulate_passes {
                 llvm::LLVMRustAddAnalysisPasses(tm, fpm, llmod);
                 llvm::LLVMRustAddAnalysisPasses(tm, mpm, llmod);
-                let opt_level = config.opt_level.unwrap_or(llvm::CodeGenOptLevel::None);
+                let opt_level = config.opt_level.map(get_llvm_opt_level)
+                    .unwrap_or(llvm::CodeGenOptLevel::None);
                 let prepare_for_thin_lto = cgcx.lto == Lto::Thin || cgcx.lto == Lto::ThinLocal ||
                     (cgcx.lto != Lto::Fat && cgcx.opts.debugging_opts.cross_lang_lto.enabled());
                 have_name_anon_globals_pass = have_name_anon_globals_pass || prepare_for_thin_lto;
@@ -644,35 +440,7 @@ unsafe fn optimize(cgcx: &CodegenContext,
     Ok(())
 }
 
-fn generate_lto_work(cgcx: &CodegenContext,
-                     modules: Vec<ModuleCodegen<ModuleLlvm>>,
-                     import_only_modules: Vec<(SerializedModule, WorkProduct)>)
-    -> Vec<(WorkItem, u64)>
-{
-    let mut timeline = cgcx.time_graph.as_ref().map(|tg| {
-        tg.start(CODEGEN_WORKER_TIMELINE,
-                 CODEGEN_WORK_PACKAGE_KIND,
-                 "generate lto")
-    }).unwrap_or(Timeline::noop());
-    let (lto_modules, copy_jobs) = lto::run(cgcx, modules, import_only_modules, &mut timeline)
-        .unwrap_or_else(|e| e.raise());
-
-    let lto_modules = lto_modules.into_iter().map(|module| {
-        let cost = module.cost();
-        (WorkItem::LTO(module), cost)
-    });
-
-    let copy_jobs = copy_jobs.into_iter().map(|wp| {
-        (WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen {
-            name: wp.cgu_name.clone(),
-            source: wp,
-        }), 0)
-    });
-
-    lto_modules.chain(copy_jobs).collect()
-}
-
-unsafe fn codegen(cgcx: &CodegenContext,
+pub(crate) unsafe fn codegen(cgcx: &CodegenContext<LlvmCodegenBackend>,
                   diag_handler: &Handler,
                   module: ModuleCodegen<ModuleLlvm>,
                   config: &ModuleConfig,
@@ -879,7 +647,7 @@ unsafe fn codegen(cgcx: &CodegenContext,
 ///
 /// Basically all of this is us attempting to follow in the footsteps of clang
 /// on iOS. See #35968 for lots more info.
-unsafe fn embed_bitcode(cgcx: &CodegenContext,
+unsafe fn embed_bitcode(cgcx: &CodegenContext<LlvmCodegenBackend>,
                         llcx: &llvm::Context,
                         llmod: &llvm::Module,
                         bitcode: Option<&[u8]>) {
@@ -919,1279 +687,6 @@ unsafe fn embed_bitcode(cgcx: &CodegenContext,
     llvm::LLVMRustSetLinkage(llglobal, llvm::Linkage::PrivateLinkage);
 }
 
-pub(crate) struct CompiledModules {
-    pub modules: Vec<CompiledModule>,
-    pub metadata_module: CompiledModule,
-    pub allocator_module: Option<CompiledModule>,
-}
-
-fn need_crate_bitcode_for_rlib(sess: &Session) -> bool {
-    sess.crate_types.borrow().contains(&config::CrateType::Rlib) &&
-    sess.opts.output_types.contains_key(&OutputType::Exe)
-}
-
-fn need_pre_thin_lto_bitcode_for_incr_comp(sess: &Session) -> bool {
-    if sess.opts.incremental.is_none() {
-        return false
-    }
-
-    match sess.lto() {
-        Lto::Fat |
-        Lto::No => false,
-        Lto::Thin |
-        Lto::ThinLocal => true,
-    }
-}
-
-pub fn start_async_codegen(tcx: TyCtxt,
-                           time_graph: Option<TimeGraph>,
-                           metadata: EncodedMetadata,
-                           coordinator_receive: Receiver<Box<dyn Any + Send>>,
-                           total_cgus: usize)
-                           -> OngoingCodegen {
-    let sess = tcx.sess;
-    let crate_name = tcx.crate_name(LOCAL_CRATE);
-    let crate_hash = tcx.crate_hash(LOCAL_CRATE);
-    let no_builtins = attr::contains_name(&tcx.hir.krate().attrs, "no_builtins");
-    let subsystem = attr::first_attr_value_str_by_name(&tcx.hir.krate().attrs,
-                                                       "windows_subsystem");
-    let windows_subsystem = subsystem.map(|subsystem| {
-        if subsystem != "windows" && subsystem != "console" {
-            tcx.sess.fatal(&format!("invalid windows subsystem `{}`, only \
-                                     `windows` and `console` are allowed",
-                                    subsystem));
-        }
-        subsystem.to_string()
-    });
-
-    let linker_info = LinkerInfo::new(tcx);
-    let crate_info = CrateInfo::new(tcx);
-
-    // Figure out what we actually need to build.
-    let mut modules_config = ModuleConfig::new(sess.opts.cg.passes.clone());
-    let mut metadata_config = ModuleConfig::new(vec![]);
-    let mut allocator_config = ModuleConfig::new(vec![]);
-
-    if let Some(ref sanitizer) = sess.opts.debugging_opts.sanitizer {
-        match *sanitizer {
-            Sanitizer::Address => {
-                modules_config.passes.push("asan".to_owned());
-                modules_config.passes.push("asan-module".to_owned());
-            }
-            Sanitizer::Memory => {
-                modules_config.passes.push("msan".to_owned())
-            }
-            Sanitizer::Thread => {
-                modules_config.passes.push("tsan".to_owned())
-            }
-            _ => {}
-        }
-    }
-
-    if sess.opts.debugging_opts.profile {
-        modules_config.passes.push("insert-gcov-profiling".to_owned())
-    }
-
-    modules_config.pgo_gen = sess.opts.debugging_opts.pgo_gen.clone();
-    modules_config.pgo_use = sess.opts.debugging_opts.pgo_use.clone();
-
-    modules_config.opt_level = Some(get_llvm_opt_level(sess.opts.optimize));
-    modules_config.opt_size = Some(get_llvm_opt_size(sess.opts.optimize));
-
-    // Save all versions of the bytecode if we're saving our temporaries.
-    if sess.opts.cg.save_temps {
-        modules_config.emit_no_opt_bc = true;
-        modules_config.emit_pre_thin_lto_bc = true;
-        modules_config.emit_bc = true;
-        modules_config.emit_lto_bc = true;
-        metadata_config.emit_bc = true;
-        allocator_config.emit_bc = true;
-    }
-
-    // Emit compressed bitcode files for the crate if we're emitting an rlib.
-    // Whenever an rlib is created, the bitcode is inserted into the archive in
-    // order to allow LTO against it.
-    if need_crate_bitcode_for_rlib(sess) {
-        modules_config.emit_bc_compressed = true;
-        allocator_config.emit_bc_compressed = true;
-    }
-
-    modules_config.emit_pre_thin_lto_bc =
-        need_pre_thin_lto_bitcode_for_incr_comp(sess);
-
-    modules_config.no_integrated_as = tcx.sess.opts.cg.no_integrated_as ||
-        tcx.sess.target.target.options.no_integrated_as;
-
-    for output_type in sess.opts.output_types.keys() {
-        match *output_type {
-            OutputType::Bitcode => { modules_config.emit_bc = true; }
-            OutputType::LlvmAssembly => { modules_config.emit_ir = true; }
-            OutputType::Assembly => {
-                modules_config.emit_asm = true;
-                // If we're not using the LLVM assembler, this function
-                // could be invoked specially with output_type_assembly, so
-                // in this case we still want the metadata object file.
-                if !sess.opts.output_types.contains_key(&OutputType::Assembly) {
-                    metadata_config.emit_obj = true;
-                    allocator_config.emit_obj = true;
-                }
-            }
-            OutputType::Object => { modules_config.emit_obj = true; }
-            OutputType::Metadata => { metadata_config.emit_obj = true; }
-            OutputType::Exe => {
-                modules_config.emit_obj = true;
-                metadata_config.emit_obj = true;
-                allocator_config.emit_obj = true;
-            },
-            OutputType::Mir => {}
-            OutputType::DepInfo => {}
-        }
-    }
-
-    modules_config.set_flags(sess, no_builtins);
-    metadata_config.set_flags(sess, no_builtins);
-    allocator_config.set_flags(sess, no_builtins);
-
-    // Exclude metadata and allocator modules from time_passes output, since
-    // they throw off the "LLVM passes" measurement.
-    metadata_config.time_passes = false;
-    allocator_config.time_passes = false;
-
-    let (shared_emitter, shared_emitter_main) = SharedEmitter::new();
-    let (codegen_worker_send, codegen_worker_receive) = channel();
-
-    let coordinator_thread = start_executing_work(tcx,
-                                                  &crate_info,
-                                                  shared_emitter,
-                                                  codegen_worker_send,
-                                                  coordinator_receive,
-                                                  total_cgus,
-                                                  sess.jobserver.clone(),
-                                                  time_graph.clone(),
-                                                  Arc::new(modules_config),
-                                                  Arc::new(metadata_config),
-                                                  Arc::new(allocator_config));
-
-    OngoingCodegen {
-        crate_name,
-        crate_hash,
-        metadata,
-        windows_subsystem,
-        linker_info,
-        crate_info,
-
-        time_graph,
-        coordinator_send: tcx.tx_to_llvm_workers.lock().clone(),
-        codegen_worker_receive,
-        shared_emitter_main,
-        future: coordinator_thread,
-        output_filenames: tcx.output_filenames(LOCAL_CRATE),
-    }
-}
-
-fn copy_all_cgu_workproducts_to_incr_comp_cache_dir(
-    sess: &Session,
-    compiled_modules: &CompiledModules,
-) -> FxHashMap<WorkProductId, WorkProduct> {
-    let mut work_products = FxHashMap::default();
-
-    if sess.opts.incremental.is_none() {
-        return work_products;
-    }
-
-    for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) {
-        let mut files = vec![];
-
-        if let Some(ref path) = module.object {
-            files.push((WorkProductFileKind::Object, path.clone()));
-        }
-        if let Some(ref path) = module.bytecode {
-            files.push((WorkProductFileKind::Bytecode, path.clone()));
-        }
-        if let Some(ref path) = module.bytecode_compressed {
-            files.push((WorkProductFileKind::BytecodeCompressed, path.clone()));
-        }
-
-        if let Some((id, product)) =
-            copy_cgu_workproducts_to_incr_comp_cache_dir(sess, &module.name, &files)
-        {
-            work_products.insert(id, product);
-        }
-    }
-
-    work_products
-}
-
-fn produce_final_output_artifacts(sess: &Session,
-                                  compiled_modules: &CompiledModules,
-                                  crate_output: &OutputFilenames) {
-    let mut user_wants_bitcode = false;
-    let mut user_wants_objects = false;
-
-    // Produce final compile outputs.
-    let copy_gracefully = |from: &Path, to: &Path| {
-        if let Err(e) = fs::copy(from, to) {
-            sess.err(&format!("could not copy {:?} to {:?}: {}", from, to, e));
-        }
-    };
-
-    let copy_if_one_unit = |output_type: OutputType,
-                            keep_numbered: bool| {
-        if compiled_modules.modules.len() == 1 {
-            // 1) Only one codegen unit.  In this case it's no difficulty
-            //    to copy `foo.0.x` to `foo.x`.
-            let module_name = Some(&compiled_modules.modules[0].name[..]);
-            let path = crate_output.temp_path(output_type, module_name);
-            copy_gracefully(&path,
-                            &crate_output.path(output_type));
-            if !sess.opts.cg.save_temps && !keep_numbered {
-                // The user just wants `foo.x`, not `foo.#module-name#.x`.
-                remove(sess, &path);
-            }
-        } else {
-            let ext = crate_output.temp_path(output_type, None)
-                                  .extension()
-                                  .unwrap()
-                                  .to_str()
-                                  .unwrap()
-                                  .to_owned();
-
-            if crate_output.outputs.contains_key(&output_type) {
-                // 2) Multiple codegen units, with `--emit foo=some_name`.  We have
-                //    no good solution for this case, so warn the user.
-                sess.warn(&format!("ignoring emit path because multiple .{} files \
-                                    were produced", ext));
-            } else if crate_output.single_output_file.is_some() {
-                // 3) Multiple codegen units, with `-o some_name`.  We have
-                //    no good solution for this case, so warn the user.
-                sess.warn(&format!("ignoring -o because multiple .{} files \
-                                    were produced", ext));
-            } else {
-                // 4) Multiple codegen units, but no explicit name.  We
-                //    just leave the `foo.0.x` files in place.
-                // (We don't have to do any work in this case.)
-            }
-        }
-    };
-
-    // Flag to indicate whether the user explicitly requested bitcode.
-    // Otherwise, we produced it only as a temporary output, and will need
-    // to get rid of it.
-    for output_type in crate_output.outputs.keys() {
-        match *output_type {
-            OutputType::Bitcode => {
-                user_wants_bitcode = true;
-                // Copy to .bc, but always keep the .0.bc.  There is a later
-                // check to figure out if we should delete .0.bc files, or keep
-                // them for making an rlib.
-                copy_if_one_unit(OutputType::Bitcode, true);
-            }
-            OutputType::LlvmAssembly => {
-                copy_if_one_unit(OutputType::LlvmAssembly, false);
-            }
-            OutputType::Assembly => {
-                copy_if_one_unit(OutputType::Assembly, false);
-            }
-            OutputType::Object => {
-                user_wants_objects = true;
-                copy_if_one_unit(OutputType::Object, true);
-            }
-            OutputType::Mir |
-            OutputType::Metadata |
-            OutputType::Exe |
-            OutputType::DepInfo => {}
-        }
-    }
-
-    // Clean up unwanted temporary files.
-
-    // We create the following files by default:
-    //  - #crate#.#module-name#.bc
-    //  - #crate#.#module-name#.o
-    //  - #crate#.crate.metadata.bc
-    //  - #crate#.crate.metadata.o
-    //  - #crate#.o (linked from crate.##.o)
-    //  - #crate#.bc (copied from crate.##.bc)
-    // We may create additional files if requested by the user (through
-    // `-C save-temps` or `--emit=` flags).
-
-    if !sess.opts.cg.save_temps {
-        // Remove the temporary .#module-name#.o objects.  If the user didn't
-        // explicitly request bitcode (with --emit=bc), and the bitcode is not
-        // needed for building an rlib, then we must remove .#module-name#.bc as
-        // well.
-
-        // Specific rules for keeping .#module-name#.bc:
-        //  - If the user requested bitcode (`user_wants_bitcode`), and
-        //    codegen_units > 1, then keep it.
-        //  - If the user requested bitcode but codegen_units == 1, then we
-        //    can toss .#module-name#.bc because we copied it to .bc earlier.
-        //  - If we're not building an rlib and the user didn't request
-        //    bitcode, then delete .#module-name#.bc.
-        // If you change how this works, also update back::link::link_rlib,
-        // where .#module-name#.bc files are (maybe) deleted after making an
-        // rlib.
-        let needs_crate_object = crate_output.outputs.contains_key(&OutputType::Exe);
-
-        let keep_numbered_bitcode = user_wants_bitcode && sess.codegen_units() > 1;
-
-        let keep_numbered_objects = needs_crate_object ||
-                (user_wants_objects && sess.codegen_units() > 1);
-
-        for module in compiled_modules.modules.iter() {
-            if let Some(ref path) = module.object {
-                if !keep_numbered_objects {
-                    remove(sess, path);
-                }
-            }
-
-            if let Some(ref path) = module.bytecode {
-                if !keep_numbered_bitcode {
-                    remove(sess, path);
-                }
-            }
-        }
-
-        if !user_wants_bitcode {
-            if let Some(ref path) = compiled_modules.metadata_module.bytecode {
-                remove(sess, &path);
-            }
-
-            if let Some(ref allocator_module) = compiled_modules.allocator_module {
-                if let Some(ref path) = allocator_module.bytecode {
-                    remove(sess, path);
-                }
-            }
-        }
-    }
-
-    // We leave the following files around by default:
-    //  - #crate#.o
-    //  - #crate#.crate.metadata.o
-    //  - #crate#.bc
-    // These are used in linking steps and will be cleaned up afterward.
-}
-
-pub(crate) fn dump_incremental_data(_codegen_results: &CodegenResults) {
-    // FIXME(mw): This does not work at the moment because the situation has
-    //            become more complicated due to incremental LTO. Now a CGU
-    //            can have more than two caching states.
-    // println!("[incremental] Re-using {} out of {} modules",
-    //           codegen_results.modules.iter().filter(|m| m.pre_existing).count(),
-    //           codegen_results.modules.len());
-}
-
-enum WorkItem {
-    /// Optimize a newly codegened, totally unoptimized module.
-    Optimize(ModuleCodegen<ModuleLlvm>),
-    /// Copy the post-LTO artifacts from the incremental cache to the output
-    /// directory.
-    CopyPostLtoArtifacts(CachedModuleCodegen),
-    /// Perform (Thin)LTO on the given module.
-    LTO(lto::LtoModuleCodegen),
-}
-
-impl WorkItem {
-    fn module_kind(&self) -> ModuleKind {
-        match *self {
-            WorkItem::Optimize(ref m) => m.kind,
-            WorkItem::CopyPostLtoArtifacts(_) |
-            WorkItem::LTO(_) => ModuleKind::Regular,
-        }
-    }
-
-    fn name(&self) -> String {
-        match *self {
-            WorkItem::Optimize(ref m) => format!("optimize: {}", m.name),
-            WorkItem::CopyPostLtoArtifacts(ref m) => format!("copy post LTO artifacts: {}", m.name),
-            WorkItem::LTO(ref m) => format!("lto: {}", m.name()),
-        }
-    }
-}
-
-enum WorkItemResult {
-    Compiled(CompiledModule),
-    NeedsLTO(ModuleCodegen<ModuleLlvm>),
-}
-
-fn execute_work_item(cgcx: &CodegenContext,
-                     work_item: WorkItem,
-                     timeline: &mut Timeline)
-    -> Result<WorkItemResult, FatalError>
-{
-    let module_config = cgcx.config(work_item.module_kind());
-
-    match work_item {
-        WorkItem::Optimize(module) => {
-            execute_optimize_work_item(cgcx, module, module_config, timeline)
-        }
-        WorkItem::CopyPostLtoArtifacts(module) => {
-            execute_copy_from_cache_work_item(cgcx, module, module_config, timeline)
-        }
-        WorkItem::LTO(module) => {
-            execute_lto_work_item(cgcx, module, module_config, timeline)
-        }
-    }
-}
-
-fn execute_optimize_work_item(cgcx: &CodegenContext,
-                              module: ModuleCodegen<ModuleLlvm>,
-                              module_config: &ModuleConfig,
-                              timeline: &mut Timeline)
-    -> Result<WorkItemResult, FatalError>
-{
-    let diag_handler = cgcx.create_diag_handler();
-
-    unsafe {
-        optimize(cgcx, &diag_handler, &module, module_config, timeline)?;
-    }
-
-    let linker_does_lto = cgcx.opts.debugging_opts.cross_lang_lto.enabled();
-
-    // After we've done the initial round of optimizations we need to
-    // decide whether to synchronously codegen this module or ship it
-    // back to the coordinator thread for further LTO processing (which
-    // has to wait for all the initial modules to be optimized).
-    //
-    // Here we dispatch based on the `cgcx.lto` and kind of module we're
-    // codegenning...
-    let needs_lto = match cgcx.lto {
-        Lto::No => false,
-
-        // If the linker does LTO, we don't have to do it. Note that we
-        // keep doing full LTO, if it is requested, as not to break the
-        // assumption that the output will be a single module.
-        Lto::Thin | Lto::ThinLocal if linker_does_lto => false,
-
-        // Here we've got a full crate graph LTO requested. We ignore
-        // this, however, if the crate type is only an rlib as there's
-        // no full crate graph to process, that'll happen later.
-        //
-        // This use case currently comes up primarily for targets that
-        // require LTO so the request for LTO is always unconditionally
-        // passed down to the backend, but we don't actually want to do
-        // anything about it yet until we've got a final product.
-        Lto::Fat | Lto::Thin => {
-            cgcx.crate_types.len() != 1 ||
-                cgcx.crate_types[0] != config::CrateType::Rlib
-        }
-
-        // When we're automatically doing ThinLTO for multi-codegen-unit
-        // builds we don't actually want to LTO the allocator modules if
-        // it shows up. This is due to various linker shenanigans that
-        // we'll encounter later.
-        Lto::ThinLocal => {
-            module.kind != ModuleKind::Allocator
-        }
-    };
-
-    // Metadata modules never participate in LTO regardless of the lto
-    // settings.
-    let needs_lto = needs_lto && module.kind != ModuleKind::Metadata;
-
-    if needs_lto {
-        Ok(WorkItemResult::NeedsLTO(module))
-    } else {
-        let module = unsafe {
-            codegen(cgcx, &diag_handler, module, module_config, timeline)?
-        };
-        Ok(WorkItemResult::Compiled(module))
-    }
-}
-
-fn execute_copy_from_cache_work_item(cgcx: &CodegenContext,
-                                     module: CachedModuleCodegen,
-                                     module_config: &ModuleConfig,
-                                     _: &mut Timeline)
-    -> Result<WorkItemResult, FatalError>
-{
-    let incr_comp_session_dir = cgcx.incr_comp_session_dir
-                                    .as_ref()
-                                    .unwrap();
-    let mut object = None;
-    let mut bytecode = None;
-    let mut bytecode_compressed = None;
-    for (kind, saved_file) in &module.source.saved_files {
-        let obj_out = match kind {
-            WorkProductFileKind::Object => {
-                let path = cgcx.output_filenames.temp_path(OutputType::Object,
-                                                           Some(&module.name));
-                object = Some(path.clone());
-                path
-            }
-            WorkProductFileKind::Bytecode => {
-                let path = cgcx.output_filenames.temp_path(OutputType::Bitcode,
-                                                           Some(&module.name));
-                bytecode = Some(path.clone());
-                path
-            }
-            WorkProductFileKind::BytecodeCompressed => {
-                let path = cgcx.output_filenames.temp_path(OutputType::Bitcode,
-                                                           Some(&module.name))
-                    .with_extension(RLIB_BYTECODE_EXTENSION);
-                bytecode_compressed = Some(path.clone());
-                path
-            }
-        };
-        let source_file = in_incr_comp_dir(&incr_comp_session_dir,
-                                           &saved_file);
-        debug!("copying pre-existing module `{}` from {:?} to {}",
-               module.name,
-               source_file,
-               obj_out.display());
-        if let Err(err) = link_or_copy(&source_file, &obj_out) {
-            let diag_handler = cgcx.create_diag_handler();
-            diag_handler.err(&format!("unable to copy {} to {}: {}",
-                                      source_file.display(),
-                                      obj_out.display(),
-                                      err));
-        }
-    }
-
-    assert_eq!(object.is_some(), module_config.emit_obj);
-    assert_eq!(bytecode.is_some(), module_config.emit_bc);
-    assert_eq!(bytecode_compressed.is_some(), module_config.emit_bc_compressed);
-
-    Ok(WorkItemResult::Compiled(CompiledModule {
-        name: module.name,
-        kind: ModuleKind::Regular,
-        object,
-        bytecode,
-        bytecode_compressed,
-    }))
-}
-
-fn execute_lto_work_item(cgcx: &CodegenContext,
-                         mut module: lto::LtoModuleCodegen,
-                         module_config: &ModuleConfig,
-                         timeline: &mut Timeline)
-    -> Result<WorkItemResult, FatalError>
-{
-    let diag_handler = cgcx.create_diag_handler();
-
-    unsafe {
-        let module = module.optimize(cgcx, timeline)?;
-        let module = codegen(cgcx, &diag_handler, module, module_config, timeline)?;
-        Ok(WorkItemResult::Compiled(module))
-    }
-}
-
-enum Message {
-    Token(io::Result<Acquired>),
-    NeedsLTO {
-        result: ModuleCodegen<ModuleLlvm>,
-        worker_id: usize,
-    },
-    Done {
-        result: Result<CompiledModule, ()>,
-        worker_id: usize,
-    },
-    CodegenDone {
-        llvm_work_item: WorkItem,
-        cost: u64,
-    },
-    AddImportOnlyModule {
-        module_data: SerializedModule,
-        work_product: WorkProduct,
-    },
-    CodegenComplete,
-    CodegenItem,
-    CodegenAborted,
-}
-
-struct Diagnostic {
-    msg: String,
-    code: Option<DiagnosticId>,
-    lvl: Level,
-}
-
-#[derive(PartialEq, Clone, Copy, Debug)]
-enum MainThreadWorkerState {
-    Idle,
-    Codegenning,
-    LLVMing,
-}
-
-fn start_executing_work(tcx: TyCtxt,
-                        crate_info: &CrateInfo,
-                        shared_emitter: SharedEmitter,
-                        codegen_worker_send: Sender<Message>,
-                        coordinator_receive: Receiver<Box<dyn Any + Send>>,
-                        total_cgus: usize,
-                        jobserver: Client,
-                        time_graph: Option<TimeGraph>,
-                        modules_config: Arc<ModuleConfig>,
-                        metadata_config: Arc<ModuleConfig>,
-                        allocator_config: Arc<ModuleConfig>)
-                        -> thread::JoinHandle<Result<CompiledModules, ()>> {
-    let coordinator_send = tcx.tx_to_llvm_workers.lock().clone();
-    let sess = tcx.sess;
-
-    // Compute the set of symbols we need to retain when doing LTO (if we need to)
-    let exported_symbols = {
-        let mut exported_symbols = FxHashMap::default();
-
-        let copy_symbols = |cnum| {
-            let symbols = tcx.exported_symbols(cnum)
-                             .iter()
-                             .map(|&(s, lvl)| (s.symbol_name(tcx).to_string(), lvl))
-                             .collect();
-            Arc::new(symbols)
-        };
-
-        match sess.lto() {
-            Lto::No => None,
-            Lto::ThinLocal => {
-                exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
-                Some(Arc::new(exported_symbols))
-            }
-            Lto::Fat | Lto::Thin => {
-                exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
-                for &cnum in tcx.crates().iter() {
-                    exported_symbols.insert(cnum, copy_symbols(cnum));
-                }
-                Some(Arc::new(exported_symbols))
-            }
-        }
-    };
-
-    // First up, convert our jobserver into a helper thread so we can use normal
-    // mpsc channels to manage our messages and such.
-    // After we've requested tokens then we'll, when we can,
-    // get tokens on `coordinator_receive` which will
-    // get managed in the main loop below.
-    let coordinator_send2 = coordinator_send.clone();
-    let helper = jobserver.into_helper_thread(move |token| {
-        drop(coordinator_send2.send(Box::new(Message::Token(token))));
-    }).expect("failed to spawn helper thread");
-
-    let mut each_linked_rlib_for_lto = Vec::new();
-    drop(link::each_linked_rlib(sess, crate_info, &mut |cnum, path| {
-        if link::ignored_for_lto(sess, crate_info, cnum) {
-            return
-        }
-        each_linked_rlib_for_lto.push((cnum, path.to_path_buf()));
-    }));
-
-    let assembler_cmd = if modules_config.no_integrated_as {
-        // HACK: currently we use linker (gcc) as our assembler
-        let (linker, flavor) = link::linker_and_flavor(sess);
-
-        let (name, mut cmd) = get_linker(sess, &linker, flavor);
-        cmd.args(&sess.target.target.options.asm_args);
-
-        Some(Arc::new(AssemblerCommand { name, cmd }))
-    } else {
-        None
-    };
-
-    let cgcx = CodegenContext {
-        crate_types: sess.crate_types.borrow().clone(),
-        each_linked_rlib_for_lto,
-        lto: sess.lto(),
-        no_landing_pads: sess.no_landing_pads(),
-        fewer_names: sess.fewer_names(),
-        save_temps: sess.opts.cg.save_temps,
-        opts: Arc::new(sess.opts.clone()),
-        time_passes: sess.time_passes(),
-        exported_symbols,
-        plugin_passes: sess.plugin_llvm_passes.borrow().clone(),
-        remark: sess.opts.cg.remark.clone(),
-        worker: 0,
-        incr_comp_session_dir: sess.incr_comp_session_dir_opt().map(|r| r.clone()),
-        cgu_reuse_tracker: sess.cgu_reuse_tracker.clone(),
-        coordinator_send,
-        diag_emitter: shared_emitter.clone(),
-        time_graph,
-        output_filenames: tcx.output_filenames(LOCAL_CRATE),
-        regular_module_config: modules_config,
-        metadata_module_config: metadata_config,
-        allocator_module_config: allocator_config,
-        tm_factory: target_machine_factory(tcx.sess, false),
-        total_cgus,
-        msvc_imps_needed: msvc_imps_needed(tcx),
-        target_pointer_width: tcx.sess.target.target.target_pointer_width.clone(),
-        debuginfo: tcx.sess.opts.debuginfo,
-        assembler_cmd,
-    };
-
-    // This is the "main loop" of parallel work happening for parallel codegen.
-    // It's here that we manage parallelism, schedule work, and work with
-    // messages coming from clients.
-    //
-    // There are a few environmental pre-conditions that shape how the system
-    // is set up:
-    //
-    // - Error reporting only can happen on the main thread because that's the
-    //   only place where we have access to the compiler `Session`.
-    // - LLVM work can be done on any thread.
-    // - Codegen can only happen on the main thread.
-    // - Each thread doing substantial work most be in possession of a `Token`
-    //   from the `Jobserver`.
-    // - The compiler process always holds one `Token`. Any additional `Tokens`
-    //   have to be requested from the `Jobserver`.
-    //
-    // Error Reporting
-    // ===============
-    // The error reporting restriction is handled separately from the rest: We
-    // set up a `SharedEmitter` the holds an open channel to the main thread.
-    // When an error occurs on any thread, the shared emitter will send the
-    // error message to the receiver main thread (`SharedEmitterMain`). The
-    // main thread will periodically query this error message queue and emit
-    // any error messages it has received. It might even abort compilation if
-    // has received a fatal error. In this case we rely on all other threads
-    // being torn down automatically with the main thread.
-    // Since the main thread will often be busy doing codegen work, error
-    // reporting will be somewhat delayed, since the message queue can only be
-    // checked in between to work packages.
-    //
-    // Work Processing Infrastructure
-    // ==============================
-    // The work processing infrastructure knows three major actors:
-    //
-    // - the coordinator thread,
-    // - the main thread, and
-    // - LLVM worker threads
-    //
-    // The coordinator thread is running a message loop. It instructs the main
-    // thread about what work to do when, and it will spawn off LLVM worker
-    // threads as open LLVM WorkItems become available.
-    //
-    // The job of the main thread is to codegen CGUs into LLVM work package
-    // (since the main thread is the only thread that can do this). The main
-    // thread will block until it receives a message from the coordinator, upon
-    // which it will codegen one CGU, send it to the coordinator and block
-    // again. This way the coordinator can control what the main thread is
-    // doing.
-    //
-    // The coordinator keeps a queue of LLVM WorkItems, and when a `Token` is
-    // available, it will spawn off a new LLVM worker thread and let it process
-    // that a WorkItem. When a LLVM worker thread is done with its WorkItem,
-    // it will just shut down, which also frees all resources associated with
-    // the given LLVM module, and sends a message to the coordinator that the
-    // has been completed.
-    //
-    // Work Scheduling
-    // ===============
-    // The scheduler's goal is to minimize the time it takes to complete all
-    // work there is, however, we also want to keep memory consumption low
-    // if possible. These two goals are at odds with each other: If memory
-    // consumption were not an issue, we could just let the main thread produce
-    // LLVM WorkItems at full speed, assuring maximal utilization of
-    // Tokens/LLVM worker threads. However, since codegen usual is faster
-    // than LLVM processing, the queue of LLVM WorkItems would fill up and each
-    // WorkItem potentially holds on to a substantial amount of memory.
-    //
-    // So the actual goal is to always produce just enough LLVM WorkItems as
-    // not to starve our LLVM worker threads. That means, once we have enough
-    // WorkItems in our queue, we can block the main thread, so it does not
-    // produce more until we need them.
-    //
-    // Doing LLVM Work on the Main Thread
-    // ----------------------------------
-    // Since the main thread owns the compiler processes implicit `Token`, it is
-    // wasteful to keep it blocked without doing any work. Therefore, what we do
-    // in this case is: We spawn off an additional LLVM worker thread that helps
-    // reduce the queue. The work it is doing corresponds to the implicit
-    // `Token`. The coordinator will mark the main thread as being busy with
-    // LLVM work. (The actual work happens on another OS thread but we just care
-    // about `Tokens`, not actual threads).
-    //
-    // When any LLVM worker thread finishes while the main thread is marked as
-    // "busy with LLVM work", we can do a little switcheroo: We give the Token
-    // of the just finished thread to the LLVM worker thread that is working on
-    // behalf of the main thread's implicit Token, thus freeing up the main
-    // thread again. The coordinator can then again decide what the main thread
-    // should do. This allows the coordinator to make decisions at more points
-    // in time.
-    //
-    // Striking a Balance between Throughput and Memory Consumption
-    // ------------------------------------------------------------
-    // Since our two goals, (1) use as many Tokens as possible and (2) keep
-    // memory consumption as low as possible, are in conflict with each other,
-    // we have to find a trade off between them. Right now, the goal is to keep
-    // all workers busy, which means that no worker should find the queue empty
-    // when it is ready to start.
-    // How do we do achieve this? Good question :) We actually never know how
-    // many `Tokens` are potentially available so it's hard to say how much to
-    // fill up the queue before switching the main thread to LLVM work. Also we
-    // currently don't have a means to estimate how long a running LLVM worker
-    // will still be busy with it's current WorkItem. However, we know the
-    // maximal count of available Tokens that makes sense (=the number of CPU
-    // cores), so we can take a conservative guess. The heuristic we use here
-    // is implemented in the `queue_full_enough()` function.
-    //
-    // Some Background on Jobservers
-    // -----------------------------
-    // It's worth also touching on the management of parallelism here. We don't
-    // want to just spawn a thread per work item because while that's optimal
-    // parallelism it may overload a system with too many threads or violate our
-    // configuration for the maximum amount of cpu to use for this process. To
-    // manage this we use the `jobserver` crate.
-    //
-    // Job servers are an artifact of GNU make and are used to manage
-    // parallelism between processes. A jobserver is a glorified IPC semaphore
-    // basically. Whenever we want to run some work we acquire the semaphore,
-    // and whenever we're done with that work we release the semaphore. In this
-    // manner we can ensure that the maximum number of parallel workers is
-    // capped at any one point in time.
-    //
-    // LTO and the coordinator thread
-    // ------------------------------
-    //
-    // The final job the coordinator thread is responsible for is managing LTO
-    // and how that works. When LTO is requested what we'll to is collect all
-    // optimized LLVM modules into a local vector on the coordinator. Once all
-    // modules have been codegened and optimized we hand this to the `lto`
-    // module for further optimization. The `lto` module will return back a list
-    // of more modules to work on, which the coordinator will continue to spawn
-    // work for.
-    //
-    // Each LLVM module is automatically sent back to the coordinator for LTO if
-    // necessary. There's already optimizations in place to avoid sending work
-    // back to the coordinator if LTO isn't requested.
-    return thread::spawn(move || {
-        // We pretend to be within the top-level LLVM time-passes task here:
-        set_time_depth(1);
-
-        let max_workers = ::num_cpus::get();
-        let mut worker_id_counter = 0;
-        let mut free_worker_ids = Vec::new();
-        let mut get_worker_id = |free_worker_ids: &mut Vec<usize>| {
-            if let Some(id) = free_worker_ids.pop() {
-                id
-            } else {
-                let id = worker_id_counter;
-                worker_id_counter += 1;
-                id
-            }
-        };
-
-        // This is where we collect codegen units that have gone all the way
-        // through codegen and LLVM.
-        let mut compiled_modules = vec![];
-        let mut compiled_metadata_module = None;
-        let mut compiled_allocator_module = None;
-        let mut needs_lto = Vec::new();
-        let mut lto_import_only_modules = Vec::new();
-        let mut started_lto = false;
-        let mut codegen_aborted = false;
-
-        // This flag tracks whether all items have gone through codegens
-        let mut codegen_done = false;
-
-        // This is the queue of LLVM work items that still need processing.
-        let mut work_items = Vec::<(WorkItem, u64)>::new();
-
-        // This are the Jobserver Tokens we currently hold. Does not include
-        // the implicit Token the compiler process owns no matter what.
-        let mut tokens = Vec::new();
-
-        let mut main_thread_worker_state = MainThreadWorkerState::Idle;
-        let mut running = 0;
-
-        let mut llvm_start_time = None;
-
-        // Run the message loop while there's still anything that needs message
-        // processing. Note that as soon as codegen is aborted we simply want to
-        // wait for all existing work to finish, so many of the conditions here
-        // only apply if codegen hasn't been aborted as they represent pending
-        // work to be done.
-        while !codegen_done ||
-              running > 0 ||
-              (!codegen_aborted && (
-                  work_items.len() > 0 ||
-                  needs_lto.len() > 0 ||
-                  lto_import_only_modules.len() > 0 ||
-                  main_thread_worker_state != MainThreadWorkerState::Idle
-              ))
-        {
-
-            // While there are still CGUs to be codegened, the coordinator has
-            // to decide how to utilize the compiler processes implicit Token:
-            // For codegenning more CGU or for running them through LLVM.
-            if !codegen_done {
-                if main_thread_worker_state == MainThreadWorkerState::Idle {
-                    if !queue_full_enough(work_items.len(), running, max_workers) {
-                        // The queue is not full enough, codegen more items:
-                        if let Err(_) = codegen_worker_send.send(Message::CodegenItem) {
-                            panic!("Could not send Message::CodegenItem to main thread")
-                        }
-                        main_thread_worker_state = MainThreadWorkerState::Codegenning;
-                    } else {
-                        // The queue is full enough to not let the worker
-                        // threads starve. Use the implicit Token to do some
-                        // LLVM work too.
-                        let (item, _) = work_items.pop()
-                            .expect("queue empty - queue_full_enough() broken?");
-                        let cgcx = CodegenContext {
-                            worker: get_worker_id(&mut free_worker_ids),
-                            .. cgcx.clone()
-                        };
-                        maybe_start_llvm_timer(cgcx.config(item.module_kind()),
-                                               &mut llvm_start_time);
-                        main_thread_worker_state = MainThreadWorkerState::LLVMing;
-                        spawn_work(cgcx, item);
-                    }
-                }
-            } else if codegen_aborted {
-                // don't queue up any more work if codegen was aborted, we're
-                // just waiting for our existing children to finish
-            } else {
-                // If we've finished everything related to normal codegen
-                // then it must be the case that we've got some LTO work to do.
-                // Perform the serial work here of figuring out what we're
-                // going to LTO and then push a bunch of work items onto our
-                // queue to do LTO
-                if work_items.len() == 0 &&
-                   running == 0 &&
-                   main_thread_worker_state == MainThreadWorkerState::Idle {
-                    assert!(!started_lto);
-                    assert!(needs_lto.len() + lto_import_only_modules.len() > 0);
-                    started_lto = true;
-                    let modules = mem::replace(&mut needs_lto, Vec::new());
-                    let import_only_modules =
-                        mem::replace(&mut lto_import_only_modules, Vec::new());
-                    for (work, cost) in generate_lto_work(&cgcx, modules, import_only_modules) {
-                        let insertion_index = work_items
-                            .binary_search_by_key(&cost, |&(_, cost)| cost)
-                            .unwrap_or_else(|e| e);
-                        work_items.insert(insertion_index, (work, cost));
-                        if !cgcx.opts.debugging_opts.no_parallel_llvm {
-                            helper.request_token();
-                        }
-                    }
-                }
-
-                // In this branch, we know that everything has been codegened,
-                // so it's just a matter of determining whether the implicit
-                // Token is free to use for LLVM work.
-                match main_thread_worker_state {
-                    MainThreadWorkerState::Idle => {
-                        if let Some((item, _)) = work_items.pop() {
-                            let cgcx = CodegenContext {
-                                worker: get_worker_id(&mut free_worker_ids),
-                                .. cgcx.clone()
-                            };
-                            maybe_start_llvm_timer(cgcx.config(item.module_kind()),
-                                                   &mut llvm_start_time);
-                            main_thread_worker_state = MainThreadWorkerState::LLVMing;
-                            spawn_work(cgcx, item);
-                        } else {
-                            // There is no unstarted work, so let the main thread
-                            // take over for a running worker. Otherwise the
-                            // implicit token would just go to waste.
-                            // We reduce the `running` counter by one. The
-                            // `tokens.truncate()` below will take care of
-                            // giving the Token back.
-                            debug_assert!(running > 0);
-                            running -= 1;
-                            main_thread_worker_state = MainThreadWorkerState::LLVMing;
-                        }
-                    }
-                    MainThreadWorkerState::Codegenning => {
-                        bug!("codegen worker should not be codegenning after \
-                              codegen was already completed")
-                    }
-                    MainThreadWorkerState::LLVMing => {
-                        // Already making good use of that token
-                    }
-                }
-            }
-
-            // Spin up what work we can, only doing this while we've got available
-            // parallelism slots and work left to spawn.
-            while !codegen_aborted && work_items.len() > 0 && running < tokens.len() {
-                let (item, _) = work_items.pop().unwrap();
-
-                maybe_start_llvm_timer(cgcx.config(item.module_kind()),
-                                       &mut llvm_start_time);
-
-                let cgcx = CodegenContext {
-                    worker: get_worker_id(&mut free_worker_ids),
-                    .. cgcx.clone()
-                };
-
-                spawn_work(cgcx, item);
-                running += 1;
-            }
-
-            // Relinquish accidentally acquired extra tokens
-            tokens.truncate(running);
-
-            let msg = coordinator_receive.recv().unwrap();
-            match *msg.downcast::<Message>().ok().unwrap() {
-                // Save the token locally and the next turn of the loop will use
-                // this to spawn a new unit of work, or it may get dropped
-                // immediately if we have no more work to spawn.
-                Message::Token(token) => {
-                    match token {
-                        Ok(token) => {
-                            tokens.push(token);
-
-                            if main_thread_worker_state == MainThreadWorkerState::LLVMing {
-                                // If the main thread token is used for LLVM work
-                                // at the moment, we turn that thread into a regular
-                                // LLVM worker thread, so the main thread is free
-                                // to react to codegen demand.
-                                main_thread_worker_state = MainThreadWorkerState::Idle;
-                                running += 1;
-                            }
-                        }
-                        Err(e) => {
-                            let msg = &format!("failed to acquire jobserver token: {}", e);
-                            shared_emitter.fatal(msg);
-                            // Exit the coordinator thread
-                            panic!("{}", msg)
-                        }
-                    }
-                }
-
-                Message::CodegenDone { llvm_work_item, cost } => {
-                    // We keep the queue sorted by estimated processing cost,
-                    // so that more expensive items are processed earlier. This
-                    // is good for throughput as it gives the main thread more
-                    // time to fill up the queue and it avoids scheduling
-                    // expensive items to the end.
-                    // Note, however, that this is not ideal for memory
-                    // consumption, as LLVM module sizes are not evenly
-                    // distributed.
-                    let insertion_index =
-                        work_items.binary_search_by_key(&cost, |&(_, cost)| cost);
-                    let insertion_index = match insertion_index {
-                        Ok(idx) | Err(idx) => idx
-                    };
-                    work_items.insert(insertion_index, (llvm_work_item, cost));
-
-                    if !cgcx.opts.debugging_opts.no_parallel_llvm {
-                        helper.request_token();
-                    }
-                    assert!(!codegen_aborted);
-                    assert_eq!(main_thread_worker_state,
-                               MainThreadWorkerState::Codegenning);
-                    main_thread_worker_state = MainThreadWorkerState::Idle;
-                }
-
-                Message::CodegenComplete => {
-                    codegen_done = true;
-                    assert!(!codegen_aborted);
-                    assert_eq!(main_thread_worker_state,
-                               MainThreadWorkerState::Codegenning);
-                    main_thread_worker_state = MainThreadWorkerState::Idle;
-                }
-
-                // If codegen is aborted that means translation was aborted due
-                // to some normal-ish compiler error. In this situation we want
-                // to exit as soon as possible, but we want to make sure all
-                // existing work has finished. Flag codegen as being done, and
-                // then conditions above will ensure no more work is spawned but
-                // we'll keep executing this loop until `running` hits 0.
-                Message::CodegenAborted => {
-                    assert!(!codegen_aborted);
-                    codegen_done = true;
-                    codegen_aborted = true;
-                    assert_eq!(main_thread_worker_state,
-                               MainThreadWorkerState::Codegenning);
-                }
-
-                // If a thread exits successfully then we drop a token associated
-                // with that worker and update our `running` count. We may later
-                // re-acquire a token to continue running more work. We may also not
-                // actually drop a token here if the worker was running with an
-                // "ephemeral token"
-                //
-                // Note that if the thread failed that means it panicked, so we
-                // abort immediately.
-                Message::Done { result: Ok(compiled_module), worker_id } => {
-                    if main_thread_worker_state == MainThreadWorkerState::LLVMing {
-                        main_thread_worker_state = MainThreadWorkerState::Idle;
-                    } else {
-                        running -= 1;
-                    }
-
-                    free_worker_ids.push(worker_id);
-
-                    match compiled_module.kind {
-                        ModuleKind::Regular => {
-                            compiled_modules.push(compiled_module);
-                        }
-                        ModuleKind::Metadata => {
-                            assert!(compiled_metadata_module.is_none());
-                            compiled_metadata_module = Some(compiled_module);
-                        }
-                        ModuleKind::Allocator => {
-                            assert!(compiled_allocator_module.is_none());
-                            compiled_allocator_module = Some(compiled_module);
-                        }
-                    }
-                }
-                Message::NeedsLTO { result, worker_id } => {
-                    assert!(!started_lto);
-                    if main_thread_worker_state == MainThreadWorkerState::LLVMing {
-                        main_thread_worker_state = MainThreadWorkerState::Idle;
-                    } else {
-                        running -= 1;
-                    }
-                    free_worker_ids.push(worker_id);
-                    needs_lto.push(result);
-                }
-                Message::AddImportOnlyModule { module_data, work_product } => {
-                    assert!(!started_lto);
-                    assert!(!codegen_done);
-                    assert_eq!(main_thread_worker_state,
-                               MainThreadWorkerState::Codegenning);
-                    lto_import_only_modules.push((module_data, work_product));
-                    main_thread_worker_state = MainThreadWorkerState::Idle;
-                }
-                Message::Done { result: Err(()), worker_id: _ } => {
-                    bug!("worker thread panicked");
-                }
-                Message::CodegenItem => {
-                    bug!("the coordinator should not receive codegen requests")
-                }
-            }
-        }
-
-        if let Some(llvm_start_time) = llvm_start_time {
-            let total_llvm_time = Instant::now().duration_since(llvm_start_time);
-            // This is the top-level timing for all of LLVM, set the time-depth
-            // to zero.
-            set_time_depth(0);
-            print_time_passes_entry(cgcx.time_passes,
-                                    "LLVM passes",
-                                    total_llvm_time);
-        }
-
-        // Regardless of what order these modules completed in, report them to
-        // the backend in the same order every time to ensure that we're handing
-        // out deterministic results.
-        compiled_modules.sort_by(|a, b| a.name.cmp(&b.name));
-
-        let compiled_metadata_module = compiled_metadata_module
-            .expect("Metadata module not compiled?");
-
-        Ok(CompiledModules {
-            modules: compiled_modules,
-            metadata_module: compiled_metadata_module,
-            allocator_module: compiled_allocator_module,
-        })
-    });
-
-    // A heuristic that determines if we have enough LLVM WorkItems in the
-    // queue so that the main thread can do LLVM work instead of codegen
-    fn queue_full_enough(items_in_queue: usize,
-                         workers_running: usize,
-                         max_workers: usize) -> bool {
-        // Tune me, plz.
-        items_in_queue > 0 &&
-        items_in_queue >= max_workers.saturating_sub(workers_running / 2)
-    }
-
-    fn maybe_start_llvm_timer(config: &ModuleConfig,
-                              llvm_start_time: &mut Option<Instant>) {
-        // We keep track of the -Ztime-passes output manually,
-        // since the closure-based interface does not fit well here.
-        if config.time_passes {
-            if llvm_start_time.is_none() {
-                *llvm_start_time = Some(Instant::now());
-            }
-        }
-    }
-}
-
-pub const CODEGEN_WORKER_ID: usize = ::std::usize::MAX;
-pub const CODEGEN_WORKER_TIMELINE: time_graph::TimelineId =
-    time_graph::TimelineId(CODEGEN_WORKER_ID);
-pub const CODEGEN_WORK_PACKAGE_KIND: time_graph::WorkPackageKind =
-    time_graph::WorkPackageKind(&["#DE9597", "#FED1D3", "#FDC5C7", "#B46668", "#88494B"]);
-const LLVM_WORK_PACKAGE_KIND: time_graph::WorkPackageKind =
-    time_graph::WorkPackageKind(&["#7DB67A", "#C6EEC4", "#ACDAAA", "#579354", "#3E6F3C"]);
-
-fn spawn_work(cgcx: CodegenContext, work: WorkItem) {
-    let depth = time_depth();
-
-    thread::spawn(move || {
-        set_time_depth(depth);
-
-        // Set up a destructor which will fire off a message that we're done as
-        // we exit.
-        struct Bomb {
-            coordinator_send: Sender<Box<dyn Any + Send>>,
-            result: Option<WorkItemResult>,
-            worker_id: usize,
-        }
-        impl Drop for Bomb {
-            fn drop(&mut self) {
-                let worker_id = self.worker_id;
-                let msg = match self.result.take() {
-                    Some(WorkItemResult::Compiled(m)) => {
-                        Message::Done { result: Ok(m), worker_id }
-                    }
-                    Some(WorkItemResult::NeedsLTO(m)) => {
-                        Message::NeedsLTO { result: m, worker_id }
-                    }
-                    None => Message::Done { result: Err(()), worker_id }
-                };
-                drop(self.coordinator_send.send(Box::new(msg)));
-            }
-        }
-
-        let mut bomb = Bomb {
-            coordinator_send: cgcx.coordinator_send.clone(),
-            result: None,
-            worker_id: cgcx.worker,
-        };
-
-        // Execute the work itself, and if it finishes successfully then flag
-        // ourselves as a success as well.
-        //
-        // Note that we ignore any `FatalError` coming out of `execute_work_item`,
-        // as a diagnostic was already sent off to the main thread - just
-        // surface that there was an error in this worker.
-        bomb.result = {
-            let timeline = cgcx.time_graph.as_ref().map(|tg| {
-                tg.start(time_graph::TimelineId(cgcx.worker),
-                         LLVM_WORK_PACKAGE_KIND,
-                         &work.name())
-            });
-            let mut timeline = timeline.unwrap_or(Timeline::noop());
-            execute_work_item(&cgcx, work, &mut timeline).ok()
-        };
-    });
-}
-
-pub fn run_assembler(cgcx: &CodegenContext, handler: &Handler, assembly: &Path, object: &Path) {
-    let assembler = cgcx.assembler_cmd
-        .as_ref()
-        .expect("cgcx.assembler_cmd is missing?");
-
-    let pname = &assembler.name;
-    let mut cmd = assembler.cmd.clone();
-    cmd.arg("-c").arg("-o").arg(object).arg(assembly);
-    debug!("{:?}", cmd);
-
-    match cmd.output() {
-        Ok(prog) => {
-            if !prog.status.success() {
-                let mut note = prog.stderr.clone();
-                note.extend_from_slice(&prog.stdout);
-
-                handler.struct_err(&format!("linking with `{}` failed: {}",
-                                            pname.display(),
-                                            prog.status))
-                       .note(&format!("{:?}", &cmd))
-                       .note(str::from_utf8(&note[..]).unwrap())
-                       .emit();
-                handler.abort_if_errors();
-            }
-        },
-        Err(e) => {
-            handler.err(&format!("could not exec the linker `{}`: {}", pname.display(), e));
-            handler.abort_if_errors();
-        }
-    }
-}
-
 pub unsafe fn with_llvm_pmb(llmod: &llvm::Module,
                             config: &ModuleConfig,
                             opt_level: llvm::CodeGenOptLevel,
@@ -2203,7 +698,7 @@ pub unsafe fn with_llvm_pmb(llmod: &llvm::Module,
     // reasonable defaults and prepare it to actually populate the pass
     // manager.
     let builder = llvm::LLVMPassManagerBuilderCreate();
-    let opt_size = config.opt_size.unwrap_or(llvm::CodeGenOptSizeNone);
+    let opt_size = config.opt_size.map(get_llvm_opt_size).unwrap_or(llvm::CodeGenOptSizeNone);
     let inline_threshold = config.inline_threshold;
 
     let pgo_gen_path = config.pgo_gen.as_ref().map(|s| {
@@ -2271,295 +766,16 @@ pub unsafe fn with_llvm_pmb(llmod: &llvm::Module,
     llvm::LLVMPassManagerBuilderDispose(builder);
 }
 
-
-enum SharedEmitterMessage {
-    Diagnostic(Diagnostic),
-    InlineAsmError(u32, String),
-    AbortIfErrors,
-    Fatal(String),
-}
-
-#[derive(Clone)]
-pub struct SharedEmitter {
-    sender: Sender<SharedEmitterMessage>,
-}
-
-pub struct SharedEmitterMain {
-    receiver: Receiver<SharedEmitterMessage>,
-}
-
-impl SharedEmitter {
-    pub fn new() -> (SharedEmitter, SharedEmitterMain) {
-        let (sender, receiver) = channel();
-
-        (SharedEmitter { sender }, SharedEmitterMain { receiver })
-    }
-
-    fn inline_asm_error(&self, cookie: u32, msg: String) {
-        drop(self.sender.send(SharedEmitterMessage::InlineAsmError(cookie, msg)));
-    }
-
-    fn fatal(&self, msg: &str) {
-        drop(self.sender.send(SharedEmitterMessage::Fatal(msg.to_string())));
-    }
-}
-
-impl Emitter for SharedEmitter {
-    fn emit(&mut self, db: &DiagnosticBuilder) {
-        drop(self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic {
-            msg: db.message(),
-            code: db.code.clone(),
-            lvl: db.level,
-        })));
-        for child in &db.children {
-            drop(self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic {
-                msg: child.message(),
-                code: None,
-                lvl: child.level,
-            })));
-        }
-        drop(self.sender.send(SharedEmitterMessage::AbortIfErrors));
-    }
-}
-
-impl SharedEmitterMain {
-    pub fn check(&self, sess: &Session, blocking: bool) {
-        loop {
-            let message = if blocking {
-                match self.receiver.recv() {
-                    Ok(message) => Ok(message),
-                    Err(_) => Err(()),
-                }
-            } else {
-                match self.receiver.try_recv() {
-                    Ok(message) => Ok(message),
-                    Err(_) => Err(()),
-                }
-            };
-
-            match message {
-                Ok(SharedEmitterMessage::Diagnostic(diag)) => {
-                    let handler = sess.diagnostic();
-                    match diag.code {
-                        Some(ref code) => {
-                            handler.emit_with_code(&MultiSpan::new(),
-                                                   &diag.msg,
-                                                   code.clone(),
-                                                   diag.lvl);
-                        }
-                        None => {
-                            handler.emit(&MultiSpan::new(),
-                                         &diag.msg,
-                                         diag.lvl);
-                        }
-                    }
-                }
-                Ok(SharedEmitterMessage::InlineAsmError(cookie, msg)) => {
-                    match Mark::from_u32(cookie).expn_info() {
-                        Some(ei) => sess.span_err(ei.call_site, &msg),
-                        None     => sess.err(&msg),
-                    }
-                }
-                Ok(SharedEmitterMessage::AbortIfErrors) => {
-                    sess.abort_if_errors();
-                }
-                Ok(SharedEmitterMessage::Fatal(msg)) => {
-                    sess.fatal(&msg);
-                }
-                Err(_) => {
-                    break;
-                }
-            }
-
-        }
-    }
-}
-
-pub struct OngoingCodegen {
-    crate_name: Symbol,
-    crate_hash: Svh,
-    metadata: EncodedMetadata,
-    windows_subsystem: Option<String>,
-    linker_info: LinkerInfo,
-    crate_info: CrateInfo,
-    time_graph: Option<TimeGraph>,
-    coordinator_send: Sender<Box<dyn Any + Send>>,
-    codegen_worker_receive: Receiver<Message>,
-    shared_emitter_main: SharedEmitterMain,
-    future: thread::JoinHandle<Result<CompiledModules, ()>>,
-    output_filenames: Arc<OutputFilenames>,
-}
-
-impl OngoingCodegen {
-    pub(crate) fn join(
-        self,
-        sess: &Session
-    ) -> (CodegenResults, FxHashMap<WorkProductId, WorkProduct>) {
-        self.shared_emitter_main.check(sess, true);
-        let compiled_modules = match self.future.join() {
-            Ok(Ok(compiled_modules)) => compiled_modules,
-            Ok(Err(())) => {
-                sess.abort_if_errors();
-                panic!("expected abort due to worker thread errors")
-            },
-            Err(_) => {
-                bug!("panic during codegen/LLVM phase");
-            }
-        };
-
-        sess.cgu_reuse_tracker.check_expected_reuse(sess);
-
-        sess.abort_if_errors();
-
-        if let Some(time_graph) = self.time_graph {
-            time_graph.dump(&format!("{}-timings", self.crate_name));
-        }
-
-        let work_products =
-            copy_all_cgu_workproducts_to_incr_comp_cache_dir(sess,
-                                                             &compiled_modules);
-        produce_final_output_artifacts(sess,
-                                       &compiled_modules,
-                                       &self.output_filenames);
-
-        // FIXME: time_llvm_passes support - does this use a global context or
-        // something?
-        if sess.codegen_units() == 1 && sess.time_llvm_passes() {
-            unsafe { llvm::LLVMRustPrintPassTimings(); }
-        }
-
-        (CodegenResults {
-            crate_name: self.crate_name,
-            crate_hash: self.crate_hash,
-            metadata: self.metadata,
-            windows_subsystem: self.windows_subsystem,
-            linker_info: self.linker_info,
-            crate_info: self.crate_info,
-
-            modules: compiled_modules.modules,
-            allocator_module: compiled_modules.allocator_module,
-            metadata_module: compiled_modules.metadata_module,
-        }, work_products)
-    }
-
-    pub(crate) fn submit_pre_codegened_module_to_llvm(&self,
-                                                      tcx: TyCtxt,
-                                                      module: ModuleCodegen<ModuleLlvm>) {
-        self.wait_for_signal_to_codegen_item();
-        self.check_for_errors(tcx.sess);
-
-        // These are generally cheap and won't through off scheduling.
-        let cost = 0;
-        submit_codegened_module_to_llvm(tcx, module, cost);
-    }
-
-    pub fn codegen_finished(&self, tcx: TyCtxt) {
-        self.wait_for_signal_to_codegen_item();
-        self.check_for_errors(tcx.sess);
-        drop(self.coordinator_send.send(Box::new(Message::CodegenComplete)));
-    }
-
-    /// Consume this context indicating that codegen was entirely aborted, and
-    /// we need to exit as quickly as possible.
-    ///
-    /// This method blocks the current thread until all worker threads have
-    /// finished, and all worker threads should have exited or be real close to
-    /// exiting at this point.
-    pub fn codegen_aborted(self) {
-        // Signal to the coordinator it should spawn no more work and start
-        // shutdown.
-        drop(self.coordinator_send.send(Box::new(Message::CodegenAborted)));
-        drop(self.future.join());
-    }
-
-    pub fn check_for_errors(&self, sess: &Session) {
-        self.shared_emitter_main.check(sess, false);
-    }
-
-    pub fn wait_for_signal_to_codegen_item(&self) {
-        match self.codegen_worker_receive.recv() {
-            Ok(Message::CodegenItem) => {
-                // Nothing to do
-            }
-            Ok(_) => panic!("unexpected message"),
-            Err(_) => {
-                // One of the LLVM threads must have panicked, fall through so
-                // error handling can be reached.
-            }
-        }
-    }
-}
-
-// impl Drop for OngoingCodegen {
-//     fn drop(&mut self) {
-//     }
-// }
-
-pub(crate) fn submit_codegened_module_to_llvm(tcx: TyCtxt,
-                                              module: ModuleCodegen<ModuleLlvm>,
-                                              cost: u64) {
-    let llvm_work_item = WorkItem::Optimize(module);
-    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::CodegenDone {
-        llvm_work_item,
-        cost,
-    })));
-}
-
-pub(crate) fn submit_post_lto_module_to_llvm(tcx: TyCtxt,
-                                             module: CachedModuleCodegen) {
-    let llvm_work_item = WorkItem::CopyPostLtoArtifacts(module);
-    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::CodegenDone {
-        llvm_work_item,
-        cost: 0,
-    })));
-}
-
-pub(crate) fn submit_pre_lto_module_to_llvm(tcx: TyCtxt,
-                                            module: CachedModuleCodegen) {
-    let filename = pre_lto_bitcode_filename(&module.name);
-    let bc_path = in_incr_comp_dir_sess(tcx.sess, &filename);
-    let file = fs::File::open(&bc_path).unwrap_or_else(|e| {
-        panic!("failed to open bitcode file `{}`: {}", bc_path.display(), e)
-    });
-
-    let mmap = unsafe {
-        memmap::Mmap::map(&file).unwrap_or_else(|e| {
-            panic!("failed to mmap bitcode file `{}`: {}", bc_path.display(), e)
-        })
-    };
-
-    // Schedule the module to be loaded
-    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::AddImportOnlyModule {
-        module_data: SerializedModule::FromUncompressedFile(mmap),
-        work_product: module.source,
-    })));
-}
-
-pub(super) fn pre_lto_bitcode_filename(module_name: &str) -> String {
-    format!("{}.{}", module_name, PRE_THIN_LTO_BC_EXT)
-}
-
-fn msvc_imps_needed(tcx: TyCtxt) -> bool {
-    // This should never be true (because it's not supported). If it is true,
-    // something is wrong with commandline arg validation.
-    assert!(!(tcx.sess.opts.debugging_opts.cross_lang_lto.enabled() &&
-              tcx.sess.target.target.options.is_like_msvc &&
-              tcx.sess.opts.cg.prefer_dynamic));
-
-    tcx.sess.target.target.options.is_like_msvc &&
-        tcx.sess.crate_types.borrow().iter().any(|ct| *ct == config::CrateType::Rlib) &&
-    // ThinLTO can't handle this workaround in all cases, so we don't
-    // emit the `__imp_` symbols. Instead we make them unnecessary by disallowing
-    // dynamic linking when cross-language LTO is enabled.
-    !tcx.sess.opts.debugging_opts.cross_lang_lto.enabled()
-}
-
 // Create a `__imp_<symbol> = &symbol` global for every public static `symbol`.
 // This is required to satisfy `dllimport` references to static data in .rlibs
 // when using MSVC linker.  We do this only for data, as linker can fix up
 // code references on its own.
 // See #26591, #27438
-fn create_msvc_imps(cgcx: &CodegenContext, llcx: &llvm::Context, llmod: &llvm::Module) {
+fn create_msvc_imps(
+    cgcx: &CodegenContext<LlvmCodegenBackend>,
+    llcx: &llvm::Context,
+    llmod: &llvm::Module
+) {
     if !cgcx.msvc_imps_needed {
         return
     }
diff --git a/src/librustc_codegen_llvm/base.rs b/src/librustc_codegen_llvm/base.rs
index 5f8601cb6da..529639bf033 100644
--- a/src/librustc_codegen_llvm/base.rs
+++ b/src/librustc_codegen_llvm/base.rs
@@ -28,7 +28,6 @@ use rustc_codegen_ssa::{ModuleCodegen, ModuleKind};
 use rustc_codegen_ssa::base::maybe_create_entry_wrapper;
 use super::LlvmCodegenBackend;
 
-use back::write;
 use llvm;
 use metadata;
 use rustc::mir::mono::{Linkage, Visibility, Stats};
@@ -44,6 +43,7 @@ use rustc_codegen_ssa::mono_item::MonoItemExt;
 use rustc_data_structures::small_c_str::SmallCStr;
 
 use rustc_codegen_ssa::interfaces::*;
+use rustc_codegen_ssa::back::write::submit_codegened_module_to_llvm;
 
 use std::ffi::CString;
 use std::time::Instant;
@@ -53,7 +53,7 @@ use rustc::hir::CodegenFnAttrs;
 use value::Value;
 
 
-pub(crate) fn write_metadata<'a, 'gcx>(
+pub fn write_metadata<'a, 'gcx>(
     tcx: TyCtxt<'a, 'gcx, 'gcx>,
     llvm_module: &ModuleLlvm
 ) -> EncodedMetadata {
@@ -163,9 +163,7 @@ pub fn compile_codegen_unit<'ll, 'tcx>(tcx: TyCtxt<'ll, 'tcx, 'tcx>,
     let cost = time_to_codegen.as_secs() * 1_000_000_000 +
                time_to_codegen.subsec_nanos() as u64;
 
-    write::submit_codegened_module_to_llvm(tcx,
-                                           module,
-                                           cost);
+    submit_codegened_module_to_llvm(&LlvmCodegenBackend(()), tcx, module, cost);
     return stats;
 
     fn module_codegen<'ll, 'tcx>(
diff --git a/src/librustc_codegen_llvm/lib.rs b/src/librustc_codegen_llvm/lib.rs
index 85a9e551abb..8f14637d6f1 100644
--- a/src/librustc_codegen_llvm/lib.rs
+++ b/src/librustc_codegen_llvm/lib.rs
@@ -68,15 +68,17 @@ extern crate tempfile;
 extern crate memmap;
 
 use rustc_codegen_ssa::interfaces::*;
-use time_graph::TimeGraph;
-use std::sync::mpsc::Receiver;
-use back::write::{self, OngoingCodegen};
+use rustc_codegen_ssa::back::write::{CodegenContext, ModuleConfig};
+use rustc_codegen_ssa::back::lto::{SerializedModule, LtoModuleCodegen, ThinModule};
+use rustc_codegen_ssa::CompiledModule;
+use errors::{FatalError, Handler};
+use rustc::dep_graph::WorkProduct;
+use rustc::util::time_graph::Timeline;
 use syntax_pos::symbol::InternedString;
 use rustc::mir::mono::Stats;
-
 pub use llvm_util::target_features;
 use std::any::Any;
-use std::sync::mpsc;
+use std::sync::{mpsc, Arc};
 
 use rustc::dep_graph::DepGraph;
 use rustc::middle::allocator::AllocatorKind;
@@ -87,9 +89,8 @@ use rustc::ty::{self, TyCtxt};
 use rustc::util::time_graph;
 use rustc::util::profiling::ProfileCategory;
 use rustc_mir::monomorphize;
-use rustc_codegen_ssa::{ModuleCodegen, CompiledModule, CachedModuleCodegen, CrateInfo};
+use rustc_codegen_ssa::ModuleCodegen;
 use rustc_codegen_utils::codegen_backend::CodegenBackend;
-use rustc_data_structures::svh::Svh;
 
 mod diagnostics;
 
@@ -127,12 +128,10 @@ mod type_;
 mod type_of;
 mod value;
 
+#[derive(Clone)]
 pub struct LlvmCodegenBackend(());
 
 impl ExtraBackendMethods for LlvmCodegenBackend {
-    type Module = ModuleLlvm;
-    type OngoingCodegen = OngoingCodegen;
-
     fn new_metadata(&self, sess: &Session, mod_name: &str) -> ModuleLlvm {
         ModuleLlvm::new(sess, mod_name)
     }
@@ -143,57 +142,95 @@ impl ExtraBackendMethods for LlvmCodegenBackend {
     ) -> EncodedMetadata {
         base::write_metadata(tcx, metadata)
     }
-    fn start_async_codegen(
+    fn codegen_allocator(&self, tcx: TyCtxt, mods: &ModuleLlvm, kind: AllocatorKind) {
+        unsafe { allocator::codegen(tcx, mods, kind) }
+    }
+    fn compile_codegen_unit<'a, 'tcx: 'a>(
         &self,
-        tcx: TyCtxt,
-        time_graph: Option<TimeGraph>,
-        metadata: EncodedMetadata,
-        coordinator_receive: Receiver<Box<dyn Any + Send>>,
-        total_cgus: usize
-    ) -> OngoingCodegen {
-        write::start_async_codegen(tcx, time_graph, metadata, coordinator_receive, total_cgus)
+        tcx: TyCtxt<'a, 'tcx, 'tcx>,
+        cgu_name: InternedString,
+    ) -> Stats {
+        base::compile_codegen_unit(tcx, cgu_name)
     }
-    fn submit_pre_codegened_module_to_backend(
+    fn target_machine_factory(
         &self,
-        codegen: &OngoingCodegen,
-        tcx: TyCtxt,
-        module: ModuleCodegen<ModuleLlvm>
-    ) {
-        codegen.submit_pre_codegened_module_to_llvm(tcx, module)
+        sess: &Session,
+        find_features: bool
+    ) -> Arc<dyn Fn() ->
+        Result<&'static mut llvm::TargetMachine, String> + Send + Sync> {
+        back::write::target_machine_factory(sess, find_features)
     }
-    fn submit_pre_lto_module_to_backend(&self, tcx: TyCtxt, module: CachedModuleCodegen) {
-        write::submit_pre_lto_module_to_llvm(tcx, module)
+    fn target_cpu<'b>(&self, sess: &'b Session) -> &'b str {
+        llvm_util::target_cpu(sess)
     }
-    fn submit_post_lto_module_to_backend(&self, tcx: TyCtxt, module: CachedModuleCodegen) {
-        write::submit_post_lto_module_to_llvm(tcx, module)
+}
+
+impl Clone for &'static mut llvm::TargetMachine {
+    fn clone(&self) -> Self {
+        // This method should never be called. It is put here because in
+        // rustc_codegen_ssa::back::write::CodegenContext, the TargetMachine is contained in a
+        // closure returned by a function under an Arc. The clone-deriving algorithm works when the
+        // struct contains the original LLVM TargetMachine type but not any more when supplied with
+        // a generic type. Hence this dummy Clone implementation.
+        panic!()
     }
-    fn codegen_aborted(codegen: OngoingCodegen) {
-        codegen.codegen_aborted();
+}
+
+impl WriteBackendMethods for LlvmCodegenBackend {
+    type Module = ModuleLlvm;
+    type ModuleBuffer = back::lto::ModuleBuffer;
+    type Context = llvm::Context;
+    type TargetMachine = &'static mut llvm::TargetMachine;
+    type ThinData = back::lto::ThinData;
+    type ThinBuffer = back::lto::ThinBuffer;
+    fn print_pass_timings(&self) {
+            unsafe { llvm::LLVMRustPrintPassTimings(); }
     }
-    fn codegen_finished(&self, codegen: &OngoingCodegen, tcx: TyCtxt) {
-        codegen.codegen_finished(tcx)
+    fn run_lto(
+        cgcx: &CodegenContext<Self>,
+        modules: Vec<ModuleCodegen<Self::Module>>,
+        cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
+        timeline: &mut Timeline
+    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError> {
+        back::lto::run(cgcx, modules, cached_modules, timeline)
     }
-    fn check_for_errors(&self, codegen: &OngoingCodegen, sess: &Session) {
-        codegen.check_for_errors(sess)
+    unsafe fn optimize(
+        cgcx: &CodegenContext<Self>,
+        diag_handler: &Handler,
+        module: &ModuleCodegen<Self::Module>,
+        config: &ModuleConfig,
+        timeline: &mut Timeline
+    ) -> Result<(), FatalError> {
+        back::write::optimize(cgcx, diag_handler, module, config, timeline)
     }
-    fn codegen_allocator(&self, tcx: TyCtxt, mods: &ModuleLlvm, kind: AllocatorKind) {
-        unsafe { allocator::codegen(tcx, mods, kind) }
+    unsafe fn optimize_thin(
+        cgcx: &CodegenContext<Self>,
+        thin: &mut ThinModule<Self>,
+        timeline: &mut Timeline
+    ) -> Result<ModuleCodegen<Self::Module>, FatalError> {
+        back::lto::optimize_thin_module(thin, cgcx, timeline)
     }
-    fn wait_for_signal_to_codegen_item(&self, codegen: &OngoingCodegen) {
-        codegen.wait_for_signal_to_codegen_item()
+    unsafe fn codegen(
+        cgcx: &CodegenContext<Self>,
+        diag_handler: &Handler,
+        module: ModuleCodegen<Self::Module>,
+        config: &ModuleConfig,
+        timeline: &mut Timeline
+    ) -> Result<CompiledModule, FatalError> {
+        back::write::codegen(cgcx, diag_handler, module, config, timeline)
     }
-    fn compile_codegen_unit<'a, 'tcx: 'a>(
-        &self,
-        tcx: TyCtxt<'a, 'tcx, 'tcx>,
-        cgu_name: InternedString,
-    ) -> Stats {
-        base::compile_codegen_unit(tcx, cgu_name)
+    fn run_lto_pass_manager(
+        cgcx: &CodegenContext<Self>,
+        module: &ModuleCodegen<Self::Module>,
+        config: &ModuleConfig,
+        thin: bool
+    ) {
+        back::lto::run_pass_manager(cgcx, module, config, thin)
     }
 }
 
-
-impl !Send for LlvmCodegenBackend {} // Llvm is on a per-thread basis
-impl !Sync for LlvmCodegenBackend {}
+unsafe impl<'a> Send for LlvmCodegenBackend {} // Llvm is on a per-thread basis
+unsafe impl<'a> Sync for LlvmCodegenBackend {}
 
 impl LlvmCodegenBackend {
     pub fn new() -> Box<dyn CodegenBackend> {
@@ -201,7 +238,7 @@ impl LlvmCodegenBackend {
     }
 }
 
-impl CodegenBackend for LlvmCodegenBackend {
+impl<'a> CodegenBackend for LlvmCodegenBackend {
     fn init(&self, sess: &Session) {
         llvm_util::init(sess); // Make sure llvm is inited
     }
@@ -254,21 +291,21 @@ impl CodegenBackend for LlvmCodegenBackend {
     }
 
     fn provide(&self, providers: &mut ty::query::Providers) {
-        rustc_codegen_utils::symbol_export::provide(providers);
         rustc_codegen_utils::symbol_names::provide(providers);
+        rustc_codegen_ssa::back::symbol_export::provide(providers);
         rustc_codegen_ssa::base::provide_both(providers);
         attributes::provide(providers);
     }
 
     fn provide_extern(&self, providers: &mut ty::query::Providers) {
-        rustc_codegen_utils::symbol_export::provide_extern(providers);
+        rustc_codegen_ssa::back::symbol_export::provide_extern(providers);
         rustc_codegen_ssa::base::provide_both(providers);
         attributes::provide_extern(providers);
     }
 
-    fn codegen_crate<'a, 'tcx>(
+    fn codegen_crate<'b, 'tcx>(
         &self,
-        tcx: TyCtxt<'a, 'tcx, 'tcx>,
+        tcx: TyCtxt<'b, 'tcx, 'tcx>,
         rx: mpsc::Receiver<Box<dyn Any + Send>>
     ) -> Box<dyn Any> {
         box rustc_codegen_ssa::base::codegen_crate(LlvmCodegenBackend(()), tcx, rx)
@@ -282,12 +319,13 @@ impl CodegenBackend for LlvmCodegenBackend {
         outputs: &OutputFilenames,
     ) -> Result<(), CompileIncomplete>{
         use rustc::util::common::time;
-        let (ongoing_codegen, work_products) =
-            ongoing_codegen.downcast::<::back::write::OngoingCodegen>()
+        let (codegen_results, work_products) =
+            ongoing_codegen.downcast::
+                <rustc_codegen_ssa::back::write::OngoingCodegen<LlvmCodegenBackend>>()
                 .expect("Expected LlvmCodegenBackend's OngoingCodegen, found Box<Any>")
                 .join(sess);
         if sess.opts.debugging_opts.incremental_info {
-            back::write::dump_incremental_data(&ongoing_codegen);
+            rustc_codegen_ssa::back::write::dump_incremental_data(&codegen_results);
         }
 
         time(sess,
@@ -305,14 +343,14 @@ impl CodegenBackend for LlvmCodegenBackend {
         // This should produce either a finished executable or library.
         sess.profiler(|p| p.start_activity(ProfileCategory::Linking));
         time(sess, "linking", || {
-            back::link::link_binary(sess, &ongoing_codegen,
-                                    outputs, &ongoing_codegen.crate_name.as_str());
+            back::link::link_binary(sess, &codegen_results,
+                                    outputs, &codegen_results.crate_name.as_str());
         });
         sess.profiler(|p| p.end_activity(ProfileCategory::Linking));
 
         // Now that we won't touch anything in the incremental compilation directory
         // any more, we can finalize it (which involves renaming it)
-        rustc_incremental::finalize_session_directory(sess, ongoing_codegen.crate_hash);
+        rustc_incremental::finalize_session_directory(sess, codegen_results.crate_hash);
 
         Ok(())
     }
@@ -363,15 +401,4 @@ impl Drop for ModuleLlvm {
     }
 }
 
-struct CodegenResults {
-    crate_name: Symbol,
-    modules: Vec<CompiledModule>,
-    allocator_module: Option<CompiledModule>,
-    metadata_module: CompiledModule,
-    crate_hash: Svh,
-    metadata: rustc::middle::cstore::EncodedMetadata,
-    windows_subsystem: Option<String>,
-    linker_info: rustc_codegen_utils::linker::LinkerInfo,
-    crate_info: CrateInfo,
-}
 __build_diagnostic_array! { librustc_codegen_llvm, DIAGNOSTICS }
diff --git a/src/librustc_codegen_ssa/Cargo.toml b/src/librustc_codegen_ssa/Cargo.toml
index ae187c5e3e0..a158c34f9d1 100644
--- a/src/librustc_codegen_ssa/Cargo.toml
+++ b/src/librustc_codegen_ssa/Cargo.toml
@@ -9,3 +9,7 @@ path = "lib.rs"
 test = false
 
 [dependencies]
+cc = "1.0.1"
+num_cpus = "1.0"
+rustc-demangle = "0.1.4"
+memmap = "0.6"
diff --git a/src/librustc_codegen_ssa/back/archive.rs b/src/librustc_codegen_ssa/back/archive.rs
new file mode 100644
index 00000000000..b5e1deb0d5d
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/archive.rs
@@ -0,0 +1,36 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use rustc::session::Session;
+
+use std::path::PathBuf;
+
+pub fn find_library(name: &str, search_paths: &[PathBuf], sess: &Session)
+                    -> PathBuf {
+    // On Windows, static libraries sometimes show up as libfoo.a and other
+    // times show up as foo.lib
+    let oslibname = format!("{}{}{}",
+                            sess.target.target.options.staticlib_prefix,
+                            name,
+                            sess.target.target.options.staticlib_suffix);
+    let unixlibname = format!("lib{}.a", name);
+
+    for path in search_paths {
+        debug!("looking for {} inside {:?}", name, path);
+        let test = path.join(&oslibname);
+        if test.exists() { return test }
+        if oslibname != unixlibname {
+            let test = path.join(&unixlibname);
+            if test.exists() { return test }
+        }
+    }
+    sess.fatal(&format!("could not find native static library `{}`, \
+                         perhaps an -L flag is missing?", name));
+}
diff --git a/src/librustc_codegen_utils/command.rs b/src/librustc_codegen_ssa/back/command.rs
index 9ebbdd7c3c9..9ebbdd7c3c9 100644
--- a/src/librustc_codegen_utils/command.rs
+++ b/src/librustc_codegen_ssa/back/command.rs
diff --git a/src/librustc_codegen_ssa/back/link.rs b/src/librustc_codegen_ssa/back/link.rs
new file mode 100644
index 00000000000..b0575b841d5
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -0,0 +1,208 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+/// For all the linkers we support, and information they might
+/// need out of the shared crate context before we get rid of it.
+
+use rustc::session::{Session, config};
+use rustc::session::search_paths::PathKind;
+use rustc::middle::dependency_format::Linkage;
+use rustc::middle::cstore::LibSource;
+use rustc_target::spec::LinkerFlavor;
+use rustc::hir::def_id::CrateNum;
+
+use super::command::Command;
+use CrateInfo;
+
+use cc::windows_registry;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::env;
+
+pub fn remove(sess: &Session, path: &Path) {
+    if let Err(e) = fs::remove_file(path) {
+        sess.err(&format!("failed to remove {}: {}",
+                          path.display(),
+                          e));
+    }
+}
+
+// The third parameter is for env vars, used on windows to set up the
+// path for MSVC to find its DLLs, and gcc to find its bundled
+// toolchain
+pub fn get_linker(sess: &Session, linker: &Path, flavor: LinkerFlavor) -> (PathBuf, Command) {
+    let msvc_tool = windows_registry::find_tool(&sess.opts.target_triple.triple(), "link.exe");
+
+    // If our linker looks like a batch script on Windows then to execute this
+    // we'll need to spawn `cmd` explicitly. This is primarily done to handle
+    // emscripten where the linker is `emcc.bat` and needs to be spawned as
+    // `cmd /c emcc.bat ...`.
+    //
+    // This worked historically but is needed manually since #42436 (regression
+    // was tagged as #42791) and some more info can be found on #44443 for
+    // emscripten itself.
+    let mut cmd = match linker.to_str() {
+        Some(linker) if cfg!(windows) && linker.ends_with(".bat") => Command::bat_script(linker),
+        _ => match flavor {
+            LinkerFlavor::Lld(f) => Command::lld(linker, f),
+            LinkerFlavor::Msvc
+                if sess.opts.cg.linker.is_none() && sess.target.target.options.linker.is_none() =>
+            {
+                Command::new(msvc_tool.as_ref().map(|t| t.path()).unwrap_or(linker))
+            },
+            _ => Command::new(linker),
+        }
+    };
+
+    // The compiler's sysroot often has some bundled tools, so add it to the
+    // PATH for the child.
+    let mut new_path = sess.host_filesearch(PathKind::All)
+                           .get_tools_search_paths();
+    let mut msvc_changed_path = false;
+    if sess.target.target.options.is_like_msvc {
+        if let Some(ref tool) = msvc_tool {
+            cmd.args(tool.args());
+            for &(ref k, ref v) in tool.env() {
+                if k == "PATH" {
+                    new_path.extend(env::split_paths(v));
+                    msvc_changed_path = true;
+                } else {
+                    cmd.env(k, v);
+                }
+            }
+        }
+    }
+
+    if !msvc_changed_path {
+        if let Some(path) = env::var_os("PATH") {
+            new_path.extend(env::split_paths(&path));
+        }
+    }
+    cmd.env("PATH", env::join_paths(new_path).unwrap());
+
+    (linker.to_path_buf(), cmd)
+}
+
+pub fn each_linked_rlib(sess: &Session,
+                               info: &CrateInfo,
+                               f: &mut dyn FnMut(CrateNum, &Path)) -> Result<(), String> {
+    let crates = info.used_crates_static.iter();
+    let fmts = sess.dependency_formats.borrow();
+    let fmts = fmts.get(&config::CrateType::Executable)
+                   .or_else(|| fmts.get(&config::CrateType::Staticlib))
+                   .or_else(|| fmts.get(&config::CrateType::Cdylib))
+                   .or_else(|| fmts.get(&config::CrateType::ProcMacro));
+    let fmts = match fmts {
+        Some(f) => f,
+        None => return Err("could not find formats for rlibs".to_string())
+    };
+    for &(cnum, ref path) in crates {
+        match fmts.get(cnum.as_usize() - 1) {
+            Some(&Linkage::NotLinked) |
+            Some(&Linkage::IncludedFromDylib) => continue,
+            Some(_) => {}
+            None => return Err("could not find formats for rlibs".to_string())
+        }
+        let name = &info.crate_name[&cnum];
+        let path = match *path {
+            LibSource::Some(ref p) => p,
+            LibSource::MetadataOnly => {
+                return Err(format!("could not find rlib for: `{}`, found rmeta (metadata) file",
+                                   name))
+            }
+            LibSource::None => {
+                return Err(format!("could not find rlib for: `{}`", name))
+            }
+        };
+        f(cnum, &path);
+    }
+    Ok(())
+}
+
+/// Returns a boolean indicating whether the specified crate should be ignored
+/// during LTO.
+///
+/// Crates ignored during LTO are not lumped together in the "massive object
+/// file" that we create and are linked in their normal rlib states. See
+/// comments below for what crates do not participate in LTO.
+///
+/// It's unusual for a crate to not participate in LTO. Typically only
+/// compiler-specific and unstable crates have a reason to not participate in
+/// LTO.
+pub fn ignored_for_lto(sess: &Session, info: &CrateInfo, cnum: CrateNum) -> bool {
+    // If our target enables builtin function lowering in LLVM then the
+    // crates providing these functions don't participate in LTO (e.g.
+    // no_builtins or compiler builtins crates).
+    !sess.target.target.options.no_builtins &&
+        (info.compiler_builtins == Some(cnum) || info.is_no_builtins.contains(&cnum))
+}
+
+pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
+    fn infer_from(
+        sess: &Session,
+        linker: Option<PathBuf>,
+        flavor: Option<LinkerFlavor>,
+    ) -> Option<(PathBuf, LinkerFlavor)> {
+        match (linker, flavor) {
+            (Some(linker), Some(flavor)) => Some((linker, flavor)),
+            // only the linker flavor is known; use the default linker for the selected flavor
+            (None, Some(flavor)) => Some((PathBuf::from(match flavor {
+                LinkerFlavor::Em  => if cfg!(windows) { "emcc.bat" } else { "emcc" },
+                LinkerFlavor::Gcc => "cc",
+                LinkerFlavor::Ld => "ld",
+                LinkerFlavor::Msvc => "link.exe",
+                LinkerFlavor::Lld(_) => "lld",
+            }), flavor)),
+            (Some(linker), None) => {
+                let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
+                    sess.fatal("couldn't extract file stem from specified linker");
+                }).to_owned();
+
+                let flavor = if stem == "emcc" {
+                    LinkerFlavor::Em
+                } else if stem == "gcc" || stem.ends_with("-gcc") {
+                    LinkerFlavor::Gcc
+                } else if stem == "ld" || stem == "ld.lld" || stem.ends_with("-ld") {
+                    LinkerFlavor::Ld
+                } else if stem == "link" || stem == "lld-link" {
+                    LinkerFlavor::Msvc
+                } else if stem == "lld" || stem == "rust-lld" {
+                    LinkerFlavor::Lld(sess.target.target.options.lld_flavor)
+                } else {
+                    // fall back to the value in the target spec
+                    sess.target.target.linker_flavor
+                };
+
+                Some((linker, flavor))
+            },
+            (None, None) => None,
+        }
+    }
+
+    // linker and linker flavor specified via command line have precedence over what the target
+    // specification specifies
+    if let Some(ret) = infer_from(
+        sess,
+        sess.opts.cg.linker.clone(),
+        sess.opts.debugging_opts.linker_flavor,
+    ) {
+        return ret;
+    }
+
+    if let Some(ret) = infer_from(
+        sess,
+        sess.target.target.options.linker.clone().map(PathBuf::from),
+        Some(sess.target.target.linker_flavor),
+    ) {
+        return ret;
+    }
+
+    bug!("Not enough information provided to determine how to invoke the linker");
+}
diff --git a/src/librustc_codegen_utils/linker.rs b/src/librustc_codegen_ssa/back/linker.rs
index 219bf256638..da9cfbb94d1 100644
--- a/src/librustc_codegen_utils/linker.rs
+++ b/src/librustc_codegen_ssa/back/linker.rs
@@ -8,6 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use super::symbol_export;
+use super::command::Command;
+use super::archive;
+
 use rustc_data_structures::fx::FxHashMap;
 use std::ffi::{OsStr, OsString};
 use std::fs::{self, File};
@@ -15,7 +19,6 @@ use std::io::prelude::*;
 use std::io::{self, BufWriter};
 use std::path::{Path, PathBuf};
 
-use command::Command;
 use rustc::hir::def_id::{LOCAL_CRATE, CrateNum};
 use rustc::middle::dependency_format::Linkage;
 use rustc::session::Session;
@@ -256,7 +259,7 @@ impl<'a> Linker for GccLinker<'a> {
             // -force_load is the macOS equivalent of --whole-archive, but it
             // involves passing the full path to the library to link.
             self.linker_arg("-force_load");
-            let lib = ::find_library(lib, search_path, &self.sess);
+            let lib = archive::find_library(lib, search_path, &self.sess);
             self.linker_arg(&lib);
         }
     }
@@ -878,36 +881,6 @@ impl<'a> Linker for EmLinker<'a> {
     }
 }
 
-fn exported_symbols(tcx: TyCtxt, crate_type: CrateType) -> Vec<String> {
-    let mut symbols = Vec::new();
-
-    let export_threshold =
-        ::symbol_export::crates_export_threshold(&[crate_type]);
-    for &(symbol, level) in tcx.exported_symbols(LOCAL_CRATE).iter() {
-        if level.is_below_threshold(export_threshold) {
-            symbols.push(symbol.symbol_name(tcx).to_string());
-        }
-    }
-
-    let formats = tcx.sess.dependency_formats.borrow();
-    let deps = formats[&crate_type].iter();
-
-    for (index, dep_format) in deps.enumerate() {
-        let cnum = CrateNum::new(index + 1);
-        // For each dependency that we are linking to statically ...
-        if *dep_format == Linkage::Static {
-            // ... we add its symbol list to our export list.
-            for &(symbol, level) in tcx.exported_symbols(cnum).iter() {
-                if level.is_below_threshold(export_threshold) {
-                    symbols.push(symbol.symbol_name(tcx).to_string());
-                }
-            }
-        }
-    }
-
-    symbols
-}
-
 pub struct WasmLd<'a> {
     cmd: Command,
     sess: &'a Session,
@@ -1075,3 +1048,32 @@ impl<'a> Linker for WasmLd<'a> {
         // Do nothing for now
     }
 }
+
+fn exported_symbols(tcx: TyCtxt, crate_type: CrateType) -> Vec<String> {
+    let mut symbols = Vec::new();
+
+    let export_threshold = symbol_export::crates_export_threshold(&[crate_type]);
+    for &(symbol, level) in tcx.exported_symbols(LOCAL_CRATE).iter() {
+        if level.is_below_threshold(export_threshold) {
+            symbols.push(symbol.symbol_name(tcx).to_string());
+        }
+    }
+
+    let formats = tcx.sess.dependency_formats.borrow();
+    let deps = formats[&crate_type].iter();
+
+    for (index, dep_format) in deps.enumerate() {
+        let cnum = CrateNum::new(index + 1);
+        // For each dependency that we are linking to statically ...
+        if *dep_format == Linkage::Static {
+            // ... we add its symbol list to our export list.
+            for &(symbol, level) in tcx.exported_symbols(cnum).iter() {
+                if level.is_below_threshold(export_threshold) {
+                    symbols.push(symbol.symbol_name(tcx).to_string());
+                }
+            }
+        }
+    }
+
+    symbols
+}
diff --git a/src/librustc_codegen_ssa/back/lto.rs b/src/librustc_codegen_ssa/back/lto.rs
new file mode 100644
index 00000000000..f68a82d8780
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/lto.rs
@@ -0,0 +1,122 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use super::write::CodegenContext;
+use interfaces::*;
+use ModuleCodegen;
+
+use rustc::util::time_graph::Timeline;
+use rustc_errors::FatalError;
+
+use std::sync::Arc;
+use std::ffi::CString;
+
+pub struct ThinModule<B: WriteBackendMethods> {
+    pub shared: Arc<ThinShared<B>>,
+    pub idx: usize,
+}
+
+impl<B: WriteBackendMethods> ThinModule<B> {
+    pub fn name(&self) -> &str {
+        self.shared.module_names[self.idx].to_str().unwrap()
+    }
+
+    pub fn cost(&self) -> u64 {
+        // Yes, that's correct, we're using the size of the bytecode as an
+        // indicator for how costly this codegen unit is.
+        self.data().len() as u64
+    }
+
+    pub fn data(&self) -> &[u8] {
+        let a = self.shared.thin_buffers.get(self.idx).map(|b| b.data());
+        a.unwrap_or_else(|| {
+            let len = self.shared.thin_buffers.len();
+            self.shared.serialized_modules[self.idx - len].data()
+        })
+    }
+}
+
+pub struct ThinShared<B: WriteBackendMethods> {
+    pub data: B::ThinData,
+    pub thin_buffers: Vec<B::ThinBuffer>,
+    pub serialized_modules: Vec<SerializedModule<B::ModuleBuffer>>,
+    pub module_names: Vec<CString>,
+}
+
+
+pub enum LtoModuleCodegen<B: WriteBackendMethods> {
+    Fat {
+        module: Option<ModuleCodegen<B::Module>>,
+        _serialized_bitcode: Vec<SerializedModule<B::ModuleBuffer>>,
+    },
+
+    Thin(ThinModule<B>),
+}
+
+impl<B: WriteBackendMethods> LtoModuleCodegen<B> {
+    pub fn name(&self) -> &str {
+        match *self {
+            LtoModuleCodegen::Fat { .. } => "everything",
+            LtoModuleCodegen::Thin(ref m) => m.name(),
+        }
+    }
+
+    /// Optimize this module within the given codegen context.
+    ///
+    /// This function is unsafe as it'll return a `ModuleCodegen` still
+    /// points to LLVM data structures owned by this `LtoModuleCodegen`.
+    /// It's intended that the module returned is immediately code generated and
+    /// dropped, and then this LTO module is dropped.
+    pub unsafe fn optimize(
+        &mut self,
+        cgcx: &CodegenContext<B>,
+        timeline: &mut Timeline
+    ) -> Result<ModuleCodegen<B::Module>, FatalError> {
+        match *self {
+            LtoModuleCodegen::Fat { ref mut module, .. } => {
+                let module = module.take().unwrap();
+                {
+                    let config = cgcx.config(module.kind);
+                    B::run_lto_pass_manager(cgcx, &module, config, false);
+                    timeline.record("fat-done");
+                }
+                Ok(module)
+            }
+            LtoModuleCodegen::Thin(ref mut thin) => B::optimize_thin(cgcx, thin, timeline),
+        }
+    }
+
+    /// A "gauge" of how costly it is to optimize this module, used to sort
+    /// biggest modules first.
+    pub fn cost(&self) -> u64 {
+        match *self {
+            // Only one module with fat LTO, so the cost doesn't matter.
+            LtoModuleCodegen::Fat { .. } => 0,
+            LtoModuleCodegen::Thin(ref m) => m.cost(),
+        }
+    }
+}
+
+
+pub enum SerializedModule<M: ModuleBufferMethods> {
+    Local(M),
+    FromRlib(Vec<u8>),
+    FromUncompressedFile(memmap::Mmap),
+}
+
+impl<M: ModuleBufferMethods> SerializedModule<M> {
+    pub fn data(&self) -> &[u8] {
+        match *self {
+            SerializedModule::Local(ref m) => m.data(),
+            SerializedModule::FromRlib(ref m) => m,
+            SerializedModule::FromUncompressedFile(ref m) => m,
+        }
+    }
+}
diff --git a/src/librustc_codegen_ssa/back/mod.rs b/src/librustc_codegen_ssa/back/mod.rs
new file mode 100644
index 00000000000..3d7ead74d1c
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/mod.rs
@@ -0,0 +1,17 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub mod write;
+pub mod linker;
+pub mod lto;
+pub mod link;
+pub mod command;
+pub mod symbol_export;
+pub mod archive;
diff --git a/src/librustc_codegen_utils/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index dff7e518630..dff7e518630 100644
--- a/src/librustc_codegen_utils/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
diff --git a/src/librustc_codegen_ssa/back/write.rs b/src/librustc_codegen_ssa/back/write.rs
new file mode 100644
index 00000000000..e958b5441f2
--- /dev/null
+++ b/src/librustc_codegen_ssa/back/write.rs
@@ -0,0 +1,1843 @@
+// Copyright 2013-2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use {ModuleCodegen, ModuleKind, CachedModuleCodegen, CompiledModule, CrateInfo, CodegenResults,
+    RLIB_BYTECODE_EXTENSION};
+use super::linker::LinkerInfo;
+use super::lto::{self, SerializedModule};
+use super::link::{self, remove, get_linker};
+use super::command::Command;
+use super::symbol_export::ExportedSymbols;
+
+use memmap;
+use rustc_incremental::{copy_cgu_workproducts_to_incr_comp_cache_dir,
+                        in_incr_comp_dir, in_incr_comp_dir_sess};
+use rustc::dep_graph::{WorkProduct, WorkProductId, WorkProductFileKind};
+use rustc::dep_graph::cgu_reuse_tracker::CguReuseTracker;
+use rustc::middle::cstore::EncodedMetadata;
+use rustc::session::config::{self, OutputFilenames, OutputType, Passes, Sanitizer, Lto};
+use rustc::session::Session;
+use rustc::util::nodemap::FxHashMap;
+use rustc::util::time_graph::{self, TimeGraph, Timeline};
+use interfaces::*;
+use rustc::hir::def_id::{CrateNum, LOCAL_CRATE};
+use rustc::ty::TyCtxt;
+use rustc::util::common::{time_depth, set_time_depth, print_time_passes_entry};
+use rustc_fs_util::link_or_copy;
+use rustc_data_structures::svh::Svh;
+use rustc_errors::{Handler, Level, DiagnosticBuilder, FatalError, DiagnosticId};
+use rustc_errors::emitter::{Emitter};
+use syntax::attr;
+use syntax::ext::hygiene::Mark;
+use syntax_pos::MultiSpan;
+use syntax_pos::symbol::Symbol;
+use jobserver::{Client, Acquired};
+
+use std::any::Any;
+use std::fs;
+use std::io;
+use std::mem;
+use std::path::{Path, PathBuf};
+use std::str;
+use std::sync::Arc;
+use std::sync::mpsc::{channel, Sender, Receiver};
+use std::time::Instant;
+use std::thread;
+
+const PRE_THIN_LTO_BC_EXT: &str = "pre-thin-lto.bc";
+
+/// Module-specific configuration for `optimize_and_codegen`.
+pub struct ModuleConfig {
+    /// Names of additional optimization passes to run.
+    pub passes: Vec<String>,
+    /// Some(level) to optimize at a certain level, or None to run
+    /// absolutely no optimizations (used for the metadata module).
+    pub opt_level: Option<config::OptLevel>,
+
+    /// Some(level) to optimize binary size, or None to not affect program size.
+    pub opt_size: Option<config::OptLevel>,
+
+    pub pgo_gen: Option<String>,
+    pub pgo_use: String,
+
+    // Flags indicating which outputs to produce.
+    pub emit_pre_thin_lto_bc: bool,
+    pub emit_no_opt_bc: bool,
+    pub emit_bc: bool,
+    pub emit_bc_compressed: bool,
+    pub emit_lto_bc: bool,
+    pub emit_ir: bool,
+    pub emit_asm: bool,
+    pub emit_obj: bool,
+    // Miscellaneous flags.  These are mostly copied from command-line
+    // options.
+    pub verify_llvm_ir: bool,
+    pub no_prepopulate_passes: bool,
+    pub no_builtins: bool,
+    pub time_passes: bool,
+    pub vectorize_loop: bool,
+    pub vectorize_slp: bool,
+    pub merge_functions: bool,
+    pub inline_threshold: Option<usize>,
+    // Instead of creating an object file by doing LLVM codegen, just
+    // make the object file bitcode. Provides easy compatibility with
+    // emscripten's ecc compiler, when used as the linker.
+    pub obj_is_bitcode: bool,
+    pub no_integrated_as: bool,
+    pub embed_bitcode: bool,
+    pub embed_bitcode_marker: bool,
+}
+
+impl ModuleConfig {
+    fn new(passes: Vec<String>) -> ModuleConfig {
+        ModuleConfig {
+            passes,
+            opt_level: None,
+            opt_size: None,
+
+            pgo_gen: None,
+            pgo_use: String::new(),
+
+            emit_no_opt_bc: false,
+            emit_pre_thin_lto_bc: false,
+            emit_bc: false,
+            emit_bc_compressed: false,
+            emit_lto_bc: false,
+            emit_ir: false,
+            emit_asm: false,
+            emit_obj: false,
+            obj_is_bitcode: false,
+            embed_bitcode: false,
+            embed_bitcode_marker: false,
+            no_integrated_as: false,
+
+            verify_llvm_ir: false,
+            no_prepopulate_passes: false,
+            no_builtins: false,
+            time_passes: false,
+            vectorize_loop: false,
+            vectorize_slp: false,
+            merge_functions: false,
+            inline_threshold: None
+        }
+    }
+
+    fn set_flags(&mut self, sess: &Session, no_builtins: bool) {
+        self.verify_llvm_ir = sess.verify_llvm_ir();
+        self.no_prepopulate_passes = sess.opts.cg.no_prepopulate_passes;
+        self.no_builtins = no_builtins || sess.target.target.options.no_builtins;
+        self.time_passes = sess.time_passes();
+        self.inline_threshold = sess.opts.cg.inline_threshold;
+        self.obj_is_bitcode = sess.target.target.options.obj_is_bitcode ||
+                              sess.opts.debugging_opts.cross_lang_lto.enabled();
+        let embed_bitcode = sess.target.target.options.embed_bitcode ||
+                            sess.opts.debugging_opts.embed_bitcode;
+        if embed_bitcode {
+            match sess.opts.optimize {
+                config::OptLevel::No |
+                config::OptLevel::Less => {
+                    self.embed_bitcode_marker = embed_bitcode;
+                }
+                _ => self.embed_bitcode = embed_bitcode,
+            }
+        }
+
+        // Copy what clang does by turning on loop vectorization at O2 and
+        // slp vectorization at O3. Otherwise configure other optimization aspects
+        // of this pass manager builder.
+        // Turn off vectorization for emscripten, as it's not very well supported.
+        self.vectorize_loop = !sess.opts.cg.no_vectorize_loops &&
+                             (sess.opts.optimize == config::OptLevel::Default ||
+                              sess.opts.optimize == config::OptLevel::Aggressive) &&
+                             !sess.target.target.options.is_like_emscripten;
+
+        self.vectorize_slp = !sess.opts.cg.no_vectorize_slp &&
+                            sess.opts.optimize == config::OptLevel::Aggressive &&
+                            !sess.target.target.options.is_like_emscripten;
+
+        self.merge_functions = sess.opts.optimize == config::OptLevel::Default ||
+                               sess.opts.optimize == config::OptLevel::Aggressive;
+    }
+
+    pub fn bitcode_needed(&self) -> bool {
+        self.emit_bc || self.obj_is_bitcode
+            || self.emit_bc_compressed || self.embed_bitcode
+    }
+}
+
+/// Assembler name and command used by codegen when no_integrated_as is enabled
+pub struct AssemblerCommand {
+    name: PathBuf,
+    cmd: Command,
+}
+
+/// Additional resources used by optimize_and_codegen (not module specific)
+#[derive(Clone)]
+pub struct CodegenContext<B: WriteBackendMethods> {
+    // Resources needed when running LTO
+    pub backend: B,
+    pub time_passes: bool,
+    pub lto: Lto,
+    pub no_landing_pads: bool,
+    pub save_temps: bool,
+    pub fewer_names: bool,
+    pub exported_symbols: Option<Arc<ExportedSymbols>>,
+    pub opts: Arc<config::Options>,
+    pub crate_types: Vec<config::CrateType>,
+    pub each_linked_rlib_for_lto: Vec<(CrateNum, PathBuf)>,
+    pub output_filenames: Arc<OutputFilenames>,
+    pub regular_module_config: Arc<ModuleConfig>,
+    pub metadata_module_config: Arc<ModuleConfig>,
+    pub allocator_module_config: Arc<ModuleConfig>,
+    pub tm_factory: Arc<dyn Fn()
+        -> Result<B::TargetMachine, String> + Send + Sync>,
+    pub msvc_imps_needed: bool,
+    pub target_pointer_width: String,
+    pub debuginfo: config::DebugInfo,
+
+    // Number of cgus excluding the allocator/metadata modules
+    pub total_cgus: usize,
+    // Handler to use for diagnostics produced during codegen.
+    pub diag_emitter: SharedEmitter,
+    // LLVM passes added by plugins.
+    pub plugin_passes: Vec<String>,
+    // LLVM optimizations for which we want to print remarks.
+    pub remark: Passes,
+    // Worker thread number
+    pub worker: usize,
+    // The incremental compilation session directory, or None if we are not
+    // compiling incrementally
+    pub incr_comp_session_dir: Option<PathBuf>,
+    // Used to update CGU re-use information during the thinlto phase.
+    pub cgu_reuse_tracker: CguReuseTracker,
+    // Channel back to the main control thread to send messages to
+    pub coordinator_send: Sender<Box<dyn Any + Send>>,
+    // A reference to the TimeGraph so we can register timings. None means that
+    // measuring is disabled.
+    pub time_graph: Option<TimeGraph>,
+    // The assembler command if no_integrated_as option is enabled, None otherwise
+    pub assembler_cmd: Option<Arc<AssemblerCommand>>
+}
+
+impl<B: WriteBackendMethods> CodegenContext<B> {
+    pub fn create_diag_handler(&self) -> Handler {
+        Handler::with_emitter(true, false, Box::new(self.diag_emitter.clone()))
+    }
+
+    pub fn config(&self, kind: ModuleKind) -> &ModuleConfig {
+        match kind {
+            ModuleKind::Regular => &self.regular_module_config,
+            ModuleKind::Metadata => &self.metadata_module_config,
+            ModuleKind::Allocator => &self.allocator_module_config,
+        }
+    }
+}
+
+fn generate_lto_work<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    modules: Vec<ModuleCodegen<B::Module>>,
+    import_only_modules: Vec<(SerializedModule<B::ModuleBuffer>, WorkProduct)>
+) -> Vec<(WorkItem<B>, u64)> {
+    let mut timeline = cgcx.time_graph.as_ref().map(|tg| {
+        tg.start(CODEGEN_WORKER_TIMELINE,
+                 CODEGEN_WORK_PACKAGE_KIND,
+                 "generate lto")
+    }).unwrap_or(Timeline::noop());
+    let (lto_modules, copy_jobs) = B::run_lto(cgcx, modules, import_only_modules, &mut timeline)
+        .unwrap_or_else(|e| e.raise());
+
+    let lto_modules = lto_modules.into_iter().map(|module| {
+        let cost = module.cost();
+        (WorkItem::LTO(module), cost)
+    });
+
+    let copy_jobs = copy_jobs.into_iter().map(|wp| {
+        (WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen {
+            name: wp.cgu_name.clone(),
+            source: wp,
+        }), 0)
+    });
+
+    lto_modules.chain(copy_jobs).collect()
+}
+
+pub struct CompiledModules {
+    pub modules: Vec<CompiledModule>,
+    pub metadata_module: CompiledModule,
+    pub allocator_module: Option<CompiledModule>,
+}
+
+fn need_crate_bitcode_for_rlib(sess: &Session) -> bool {
+    sess.crate_types.borrow().contains(&config::CrateType::Rlib) &&
+    sess.opts.output_types.contains_key(&OutputType::Exe)
+}
+
+fn need_pre_thin_lto_bitcode_for_incr_comp(sess: &Session) -> bool {
+    if sess.opts.incremental.is_none() {
+        return false
+    }
+
+    match sess.lto() {
+        Lto::Fat |
+        Lto::No => false,
+        Lto::Thin |
+        Lto::ThinLocal => true,
+    }
+}
+
+pub fn start_async_codegen<B: ExtraBackendMethods>(
+    backend: B,
+    tcx: TyCtxt,
+    time_graph: Option<TimeGraph>,
+    metadata: EncodedMetadata,
+    coordinator_receive: Receiver<Box<dyn Any + Send>>,
+    total_cgus: usize
+) -> OngoingCodegen<B> {
+    let sess = tcx.sess;
+    let crate_name = tcx.crate_name(LOCAL_CRATE);
+    let crate_hash = tcx.crate_hash(LOCAL_CRATE);
+    let no_builtins = attr::contains_name(&tcx.hir.krate().attrs, "no_builtins");
+    let subsystem = attr::first_attr_value_str_by_name(&tcx.hir.krate().attrs,
+                                                       "windows_subsystem");
+    let windows_subsystem = subsystem.map(|subsystem| {
+        if subsystem != "windows" && subsystem != "console" {
+            tcx.sess.fatal(&format!("invalid windows subsystem `{}`, only \
+                                     `windows` and `console` are allowed",
+                                    subsystem));
+        }
+        subsystem.to_string()
+    });
+
+    let linker_info = LinkerInfo::new(tcx);
+    let crate_info = CrateInfo::new(tcx);
+
+    // Figure out what we actually need to build.
+    let mut modules_config = ModuleConfig::new(sess.opts.cg.passes.clone());
+    let mut metadata_config = ModuleConfig::new(vec![]);
+    let mut allocator_config = ModuleConfig::new(vec![]);
+
+    if let Some(ref sanitizer) = sess.opts.debugging_opts.sanitizer {
+        match *sanitizer {
+            Sanitizer::Address => {
+                modules_config.passes.push("asan".to_owned());
+                modules_config.passes.push("asan-module".to_owned());
+            }
+            Sanitizer::Memory => {
+                modules_config.passes.push("msan".to_owned())
+            }
+            Sanitizer::Thread => {
+                modules_config.passes.push("tsan".to_owned())
+            }
+            _ => {}
+        }
+    }
+
+    if sess.opts.debugging_opts.profile {
+        modules_config.passes.push("insert-gcov-profiling".to_owned())
+    }
+
+    modules_config.pgo_gen = sess.opts.debugging_opts.pgo_gen.clone();
+    modules_config.pgo_use = sess.opts.debugging_opts.pgo_use.clone();
+
+    modules_config.opt_level = Some(sess.opts.optimize);
+    modules_config.opt_size = Some(sess.opts.optimize);
+
+    // Save all versions of the bytecode if we're saving our temporaries.
+    if sess.opts.cg.save_temps {
+        modules_config.emit_no_opt_bc = true;
+        modules_config.emit_pre_thin_lto_bc = true;
+        modules_config.emit_bc = true;
+        modules_config.emit_lto_bc = true;
+        metadata_config.emit_bc = true;
+        allocator_config.emit_bc = true;
+    }
+
+    // Emit compressed bitcode files for the crate if we're emitting an rlib.
+    // Whenever an rlib is created, the bitcode is inserted into the archive in
+    // order to allow LTO against it.
+    if need_crate_bitcode_for_rlib(sess) {
+        modules_config.emit_bc_compressed = true;
+        allocator_config.emit_bc_compressed = true;
+    }
+
+    modules_config.emit_pre_thin_lto_bc =
+        need_pre_thin_lto_bitcode_for_incr_comp(sess);
+
+    modules_config.no_integrated_as = tcx.sess.opts.cg.no_integrated_as ||
+        tcx.sess.target.target.options.no_integrated_as;
+
+    for output_type in sess.opts.output_types.keys() {
+        match *output_type {
+            OutputType::Bitcode => { modules_config.emit_bc = true; }
+            OutputType::LlvmAssembly => { modules_config.emit_ir = true; }
+            OutputType::Assembly => {
+                modules_config.emit_asm = true;
+                // If we're not using the LLVM assembler, this function
+                // could be invoked specially with output_type_assembly, so
+                // in this case we still want the metadata object file.
+                if !sess.opts.output_types.contains_key(&OutputType::Assembly) {
+                    metadata_config.emit_obj = true;
+                    allocator_config.emit_obj = true;
+                }
+            }
+            OutputType::Object => { modules_config.emit_obj = true; }
+            OutputType::Metadata => { metadata_config.emit_obj = true; }
+            OutputType::Exe => {
+                modules_config.emit_obj = true;
+                metadata_config.emit_obj = true;
+                allocator_config.emit_obj = true;
+            },
+            OutputType::Mir => {}
+            OutputType::DepInfo => {}
+        }
+    }
+
+    modules_config.set_flags(sess, no_builtins);
+    metadata_config.set_flags(sess, no_builtins);
+    allocator_config.set_flags(sess, no_builtins);
+
+    // Exclude metadata and allocator modules from time_passes output, since
+    // they throw off the "LLVM passes" measurement.
+    metadata_config.time_passes = false;
+    allocator_config.time_passes = false;
+
+    let (shared_emitter, shared_emitter_main) = SharedEmitter::new();
+    let (codegen_worker_send, codegen_worker_receive) = channel();
+
+    let coordinator_thread = start_executing_work(backend.clone(),
+                                                  tcx,
+                                                  &crate_info,
+                                                  shared_emitter,
+                                                  codegen_worker_send,
+                                                  coordinator_receive,
+                                                  total_cgus,
+                                                  sess.jobserver.clone(),
+                                                  time_graph.clone(),
+                                                  Arc::new(modules_config),
+                                                  Arc::new(metadata_config),
+                                                  Arc::new(allocator_config));
+
+    OngoingCodegen {
+        backend,
+        crate_name,
+        crate_hash,
+        metadata,
+        windows_subsystem,
+        linker_info,
+        crate_info,
+
+        time_graph,
+        coordinator_send: tcx.tx_to_llvm_workers.lock().clone(),
+        codegen_worker_receive,
+        shared_emitter_main,
+        future: coordinator_thread,
+        output_filenames: tcx.output_filenames(LOCAL_CRATE),
+    }
+}
+
+fn copy_all_cgu_workproducts_to_incr_comp_cache_dir(
+    sess: &Session,
+    compiled_modules: &CompiledModules,
+) -> FxHashMap<WorkProductId, WorkProduct> {
+    let mut work_products = FxHashMap::default();
+
+    if sess.opts.incremental.is_none() {
+        return work_products;
+    }
+
+    for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) {
+        let mut files = vec![];
+
+        if let Some(ref path) = module.object {
+            files.push((WorkProductFileKind::Object, path.clone()));
+        }
+        if let Some(ref path) = module.bytecode {
+            files.push((WorkProductFileKind::Bytecode, path.clone()));
+        }
+        if let Some(ref path) = module.bytecode_compressed {
+            files.push((WorkProductFileKind::BytecodeCompressed, path.clone()));
+        }
+
+        if let Some((id, product)) =
+                copy_cgu_workproducts_to_incr_comp_cache_dir(sess, &module.name, &files) {
+            work_products.insert(id, product);
+        }
+    }
+
+    work_products
+}
+
+fn produce_final_output_artifacts(sess: &Session,
+                                  compiled_modules: &CompiledModules,
+                                  crate_output: &OutputFilenames) {
+    let mut user_wants_bitcode = false;
+    let mut user_wants_objects = false;
+
+    // Produce final compile outputs.
+    let copy_gracefully = |from: &Path, to: &Path| {
+        if let Err(e) = fs::copy(from, to) {
+            sess.err(&format!("could not copy {:?} to {:?}: {}", from, to, e));
+        }
+    };
+
+    let copy_if_one_unit = |output_type: OutputType,
+                            keep_numbered: bool| {
+        if compiled_modules.modules.len() == 1 {
+            // 1) Only one codegen unit.  In this case it's no difficulty
+            //    to copy `foo.0.x` to `foo.x`.
+            let module_name = Some(&compiled_modules.modules[0].name[..]);
+            let path = crate_output.temp_path(output_type, module_name);
+            copy_gracefully(&path,
+                            &crate_output.path(output_type));
+            if !sess.opts.cg.save_temps && !keep_numbered {
+                // The user just wants `foo.x`, not `foo.#module-name#.x`.
+                remove(sess, &path);
+            }
+        } else {
+            let ext = crate_output.temp_path(output_type, None)
+                                  .extension()
+                                  .unwrap()
+                                  .to_str()
+                                  .unwrap()
+                                  .to_owned();
+
+            if crate_output.outputs.contains_key(&output_type) {
+                // 2) Multiple codegen units, with `--emit foo=some_name`.  We have
+                //    no good solution for this case, so warn the user.
+                sess.warn(&format!("ignoring emit path because multiple .{} files \
+                                    were produced", ext));
+            } else if crate_output.single_output_file.is_some() {
+                // 3) Multiple codegen units, with `-o some_name`.  We have
+                //    no good solution for this case, so warn the user.
+                sess.warn(&format!("ignoring -o because multiple .{} files \
+                                    were produced", ext));
+            } else {
+                // 4) Multiple codegen units, but no explicit name.  We
+                //    just leave the `foo.0.x` files in place.
+                // (We don't have to do any work in this case.)
+            }
+        }
+    };
+
+    // Flag to indicate whether the user explicitly requested bitcode.
+    // Otherwise, we produced it only as a temporary output, and will need
+    // to get rid of it.
+    for output_type in crate_output.outputs.keys() {
+        match *output_type {
+            OutputType::Bitcode => {
+                user_wants_bitcode = true;
+                // Copy to .bc, but always keep the .0.bc.  There is a later
+                // check to figure out if we should delete .0.bc files, or keep
+                // them for making an rlib.
+                copy_if_one_unit(OutputType::Bitcode, true);
+            }
+            OutputType::LlvmAssembly => {
+                copy_if_one_unit(OutputType::LlvmAssembly, false);
+            }
+            OutputType::Assembly => {
+                copy_if_one_unit(OutputType::Assembly, false);
+            }
+            OutputType::Object => {
+                user_wants_objects = true;
+                copy_if_one_unit(OutputType::Object, true);
+            }
+            OutputType::Mir |
+            OutputType::Metadata |
+            OutputType::Exe |
+            OutputType::DepInfo => {}
+        }
+    }
+
+    // Clean up unwanted temporary files.
+
+    // We create the following files by default:
+    //  - #crate#.#module-name#.bc
+    //  - #crate#.#module-name#.o
+    //  - #crate#.crate.metadata.bc
+    //  - #crate#.crate.metadata.o
+    //  - #crate#.o (linked from crate.##.o)
+    //  - #crate#.bc (copied from crate.##.bc)
+    // We may create additional files if requested by the user (through
+    // `-C save-temps` or `--emit=` flags).
+
+    if !sess.opts.cg.save_temps {
+        // Remove the temporary .#module-name#.o objects.  If the user didn't
+        // explicitly request bitcode (with --emit=bc), and the bitcode is not
+        // needed for building an rlib, then we must remove .#module-name#.bc as
+        // well.
+
+        // Specific rules for keeping .#module-name#.bc:
+        //  - If the user requested bitcode (`user_wants_bitcode`), and
+        //    codegen_units > 1, then keep it.
+        //  - If the user requested bitcode but codegen_units == 1, then we
+        //    can toss .#module-name#.bc because we copied it to .bc earlier.
+        //  - If we're not building an rlib and the user didn't request
+        //    bitcode, then delete .#module-name#.bc.
+        // If you change how this works, also update back::link::link_rlib,
+        // where .#module-name#.bc files are (maybe) deleted after making an
+        // rlib.
+        let needs_crate_object = crate_output.outputs.contains_key(&OutputType::Exe);
+
+        let keep_numbered_bitcode = user_wants_bitcode && sess.codegen_units() > 1;
+
+        let keep_numbered_objects = needs_crate_object ||
+                (user_wants_objects && sess.codegen_units() > 1);
+
+        for module in compiled_modules.modules.iter() {
+            if let Some(ref path) = module.object {
+                if !keep_numbered_objects {
+                    remove(sess, path);
+                }
+            }
+
+            if let Some(ref path) = module.bytecode {
+                if !keep_numbered_bitcode {
+                    remove(sess, path);
+                }
+            }
+        }
+
+        if !user_wants_bitcode {
+            if let Some(ref path) = compiled_modules.metadata_module.bytecode {
+                remove(sess, &path);
+            }
+
+            if let Some(ref allocator_module) = compiled_modules.allocator_module {
+                if let Some(ref path) = allocator_module.bytecode {
+                    remove(sess, path);
+                }
+            }
+        }
+    }
+
+    // We leave the following files around by default:
+    //  - #crate#.o
+    //  - #crate#.crate.metadata.o
+    //  - #crate#.bc
+    // These are used in linking steps and will be cleaned up afterward.
+}
+
+pub fn dump_incremental_data(_codegen_results: &CodegenResults) {
+    // FIXME(mw): This does not work at the moment because the situation has
+    //            become more complicated due to incremental LTO. Now a CGU
+    //            can have more than two caching states.
+    // println!("[incremental] Re-using {} out of {} modules",
+    //           codegen_results.modules.iter().filter(|m| m.pre_existing).count(),
+    //           codegen_results.modules.len());
+}
+
+pub enum WorkItem<B: WriteBackendMethods> {
+    /// Optimize a newly codegened, totally unoptimized module.
+    Optimize(ModuleCodegen<B::Module>),
+    /// Copy the post-LTO artifacts from the incremental cache to the output
+    /// directory.
+    CopyPostLtoArtifacts(CachedModuleCodegen),
+    /// Perform (Thin)LTO on the given module.
+    LTO(lto::LtoModuleCodegen<B>),
+}
+
+impl<B: WriteBackendMethods> WorkItem<B> {
+    pub fn module_kind(&self) -> ModuleKind {
+        match *self {
+            WorkItem::Optimize(ref m) => m.kind,
+            WorkItem::CopyPostLtoArtifacts(_) |
+            WorkItem::LTO(_) => ModuleKind::Regular,
+        }
+    }
+
+    pub fn name(&self) -> String {
+        match *self {
+            WorkItem::Optimize(ref m) => format!("optimize: {}", m.name),
+            WorkItem::CopyPostLtoArtifacts(ref m) => format!("copy post LTO artifacts: {}", m.name),
+            WorkItem::LTO(ref m) => format!("lto: {}", m.name()),
+        }
+    }
+}
+
+enum WorkItemResult<M> {
+    Compiled(CompiledModule),
+    NeedsLTO(ModuleCodegen<M>),
+}
+
+fn execute_work_item<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    work_item: WorkItem<B>,
+    timeline: &mut Timeline
+) -> Result<WorkItemResult<B::Module>, FatalError> {
+    let module_config = cgcx.config(work_item.module_kind());
+
+    match work_item {
+        WorkItem::Optimize(module) => {
+            execute_optimize_work_item(cgcx, module, module_config, timeline)
+        }
+        WorkItem::CopyPostLtoArtifacts(module) => {
+            execute_copy_from_cache_work_item(cgcx, module, module_config, timeline)
+        }
+        WorkItem::LTO(module) => {
+            execute_lto_work_item(cgcx, module, module_config, timeline)
+        }
+    }
+}
+
+fn execute_optimize_work_item<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    module: ModuleCodegen<B::Module>,
+    module_config: &ModuleConfig,
+    timeline: &mut Timeline
+) -> Result<WorkItemResult<B::Module>, FatalError> {
+    let diag_handler = cgcx.create_diag_handler();
+
+    unsafe {
+        B::optimize(cgcx, &diag_handler, &module, module_config, timeline)?;
+    }
+
+    let linker_does_lto = cgcx.opts.debugging_opts.cross_lang_lto.enabled();
+
+    // After we've done the initial round of optimizations we need to
+    // decide whether to synchronously codegen this module or ship it
+    // back to the coordinator thread for further LTO processing (which
+    // has to wait for all the initial modules to be optimized).
+    //
+    // Here we dispatch based on the `cgcx.lto` and kind of module we're
+    // codegenning...
+    let needs_lto = match cgcx.lto {
+        Lto::No => false,
+
+        // If the linker does LTO, we don't have to do it. Note that we
+        // keep doing full LTO, if it is requested, as not to break the
+        // assumption that the output will be a single module.
+        Lto::Thin | Lto::ThinLocal if linker_does_lto => false,
+
+        // Here we've got a full crate graph LTO requested. We ignore
+        // this, however, if the crate type is only an rlib as there's
+        // no full crate graph to process, that'll happen later.
+        //
+        // This use case currently comes up primarily for targets that
+        // require LTO so the request for LTO is always unconditionally
+        // passed down to the backend, but we don't actually want to do
+        // anything about it yet until we've got a final product.
+        Lto::Fat | Lto::Thin => {
+            cgcx.crate_types.len() != 1 ||
+                cgcx.crate_types[0] != config::CrateType::Rlib
+        }
+
+        // When we're automatically doing ThinLTO for multi-codegen-unit
+        // builds we don't actually want to LTO the allocator modules if
+        // it shows up. This is due to various linker shenanigans that
+        // we'll encounter later.
+        Lto::ThinLocal => {
+            module.kind != ModuleKind::Allocator
+        }
+    };
+
+    // Metadata modules never participate in LTO regardless of the lto
+    // settings.
+    let needs_lto = needs_lto && module.kind != ModuleKind::Metadata;
+
+    if needs_lto {
+        Ok(WorkItemResult::NeedsLTO(module))
+    } else {
+        let module = unsafe { B::codegen(cgcx, &diag_handler, module, module_config, timeline)? };
+        Ok(WorkItemResult::Compiled(module))
+    }
+}
+
+fn execute_copy_from_cache_work_item<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    module: CachedModuleCodegen,
+    module_config: &ModuleConfig,
+    _: &mut Timeline
+) -> Result<WorkItemResult<B::Module>, FatalError> {
+    let incr_comp_session_dir = cgcx.incr_comp_session_dir
+                                    .as_ref()
+                                    .unwrap();
+    let mut object = None;
+    let mut bytecode = None;
+    let mut bytecode_compressed = None;
+    for (kind, saved_file) in &module.source.saved_files {
+        let obj_out = match kind {
+            WorkProductFileKind::Object => {
+                let path = cgcx.output_filenames.temp_path(OutputType::Object,
+                                                           Some(&module.name));
+                object = Some(path.clone());
+                path
+            }
+            WorkProductFileKind::Bytecode => {
+                let path = cgcx.output_filenames.temp_path(OutputType::Bitcode,
+                                                           Some(&module.name));
+                bytecode = Some(path.clone());
+                path
+            }
+            WorkProductFileKind::BytecodeCompressed => {
+                let path = cgcx.output_filenames.temp_path(OutputType::Bitcode,
+                                                           Some(&module.name))
+                    .with_extension(RLIB_BYTECODE_EXTENSION);
+                bytecode_compressed = Some(path.clone());
+                path
+            }
+        };
+        let source_file = in_incr_comp_dir(&incr_comp_session_dir,
+                                           &saved_file);
+        debug!("copying pre-existing module `{}` from {:?} to {}",
+               module.name,
+               source_file,
+               obj_out.display());
+        if let Err(err) = link_or_copy(&source_file, &obj_out) {
+            let diag_handler = cgcx.create_diag_handler();
+            diag_handler.err(&format!("unable to copy {} to {}: {}",
+                                      source_file.display(),
+                                      obj_out.display(),
+                                      err));
+        }
+    }
+
+    assert_eq!(object.is_some(), module_config.emit_obj);
+    assert_eq!(bytecode.is_some(), module_config.emit_bc);
+    assert_eq!(bytecode_compressed.is_some(), module_config.emit_bc_compressed);
+
+    Ok(WorkItemResult::Compiled(CompiledModule {
+        name: module.name,
+        kind: ModuleKind::Regular,
+        object,
+        bytecode,
+        bytecode_compressed,
+    }))
+}
+
+fn execute_lto_work_item<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    mut module: lto::LtoModuleCodegen<B>,
+    module_config: &ModuleConfig,
+    timeline: &mut Timeline
+) -> Result<WorkItemResult<B::Module>, FatalError> {
+    let diag_handler = cgcx.create_diag_handler();
+
+    unsafe {
+        let module = module.optimize(cgcx, timeline)?;
+        let module = B::codegen(cgcx, &diag_handler, module, module_config, timeline)?;
+        Ok(WorkItemResult::Compiled(module))
+    }
+}
+
+pub enum Message<B: WriteBackendMethods> {
+    Token(io::Result<Acquired>),
+    NeedsLTO {
+        result: ModuleCodegen<B::Module>,
+        worker_id: usize,
+    },
+    Done {
+        result: Result<CompiledModule, ()>,
+        worker_id: usize,
+    },
+    CodegenDone {
+        llvm_work_item: WorkItem<B>,
+        cost: u64,
+    },
+    AddImportOnlyModule {
+        module_data: SerializedModule<B::ModuleBuffer>,
+        work_product: WorkProduct,
+    },
+    CodegenComplete,
+    CodegenItem,
+    CodegenAborted,
+}
+
+struct Diagnostic {
+    msg: String,
+    code: Option<DiagnosticId>,
+    lvl: Level,
+}
+
+#[derive(PartialEq, Clone, Copy, Debug)]
+enum MainThreadWorkerState {
+    Idle,
+    Codegenning,
+    LLVMing,
+}
+
+fn start_executing_work<B: ExtraBackendMethods>(
+    backend: B,
+    tcx: TyCtxt,
+    crate_info: &CrateInfo,
+    shared_emitter: SharedEmitter,
+    codegen_worker_send: Sender<Message<B>>,
+    coordinator_receive: Receiver<Box<dyn Any + Send>>,
+    total_cgus: usize,
+    jobserver: Client,
+    time_graph: Option<TimeGraph>,
+    modules_config: Arc<ModuleConfig>,
+    metadata_config: Arc<ModuleConfig>,
+    allocator_config: Arc<ModuleConfig>
+) -> thread::JoinHandle<Result<CompiledModules, ()>> {
+    let coordinator_send = tcx.tx_to_llvm_workers.lock().clone();
+    let sess = tcx.sess;
+
+    // Compute the set of symbols we need to retain when doing LTO (if we need to)
+    let exported_symbols = {
+        let mut exported_symbols = FxHashMap::default();
+
+        let copy_symbols = |cnum| {
+            let symbols = tcx.exported_symbols(cnum)
+                             .iter()
+                             .map(|&(s, lvl)| (s.symbol_name(tcx).to_string(), lvl))
+                             .collect();
+            Arc::new(symbols)
+        };
+
+        match sess.lto() {
+            Lto::No => None,
+            Lto::ThinLocal => {
+                exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
+                Some(Arc::new(exported_symbols))
+            }
+            Lto::Fat | Lto::Thin => {
+                exported_symbols.insert(LOCAL_CRATE, copy_symbols(LOCAL_CRATE));
+                for &cnum in tcx.crates().iter() {
+                    exported_symbols.insert(cnum, copy_symbols(cnum));
+                }
+                Some(Arc::new(exported_symbols))
+            }
+        }
+    };
+
+    // First up, convert our jobserver into a helper thread so we can use normal
+    // mpsc channels to manage our messages and such.
+    // After we've requested tokens then we'll, when we can,
+    // get tokens on `coordinator_receive` which will
+    // get managed in the main loop below.
+    let coordinator_send2 = coordinator_send.clone();
+    let helper = jobserver.into_helper_thread(move |token| {
+        drop(coordinator_send2.send(Box::new(Message::Token::<B>(token))));
+    }).expect("failed to spawn helper thread");
+
+    let mut each_linked_rlib_for_lto = Vec::new();
+    drop(link::each_linked_rlib(sess, crate_info, &mut |cnum, path| {
+        if link::ignored_for_lto(sess, crate_info, cnum) {
+            return
+        }
+        each_linked_rlib_for_lto.push((cnum, path.to_path_buf()));
+    }));
+
+    let assembler_cmd = if modules_config.no_integrated_as {
+        // HACK: currently we use linker (gcc) as our assembler
+        let (linker, flavor) = link::linker_and_flavor(sess);
+
+        let (name, mut cmd) = get_linker(sess, &linker, flavor);
+        cmd.args(&sess.target.target.options.asm_args);
+        Some(Arc::new(AssemblerCommand {
+            name,
+            cmd,
+        }))
+    } else {
+        None
+    };
+
+    let cgcx = CodegenContext::<B> {
+        backend: backend.clone(),
+        crate_types: sess.crate_types.borrow().clone(),
+        each_linked_rlib_for_lto,
+        lto: sess.lto(),
+        no_landing_pads: sess.no_landing_pads(),
+        fewer_names: sess.fewer_names(),
+        save_temps: sess.opts.cg.save_temps,
+        opts: Arc::new(sess.opts.clone()),
+        time_passes: sess.time_passes(),
+        exported_symbols,
+        plugin_passes: sess.plugin_llvm_passes.borrow().clone(),
+        remark: sess.opts.cg.remark.clone(),
+        worker: 0,
+        incr_comp_session_dir: sess.incr_comp_session_dir_opt().map(|r| r.clone()),
+        cgu_reuse_tracker: sess.cgu_reuse_tracker.clone(),
+        coordinator_send,
+        diag_emitter: shared_emitter.clone(),
+        time_graph,
+        output_filenames: tcx.output_filenames(LOCAL_CRATE),
+        regular_module_config: modules_config,
+        metadata_module_config: metadata_config,
+        allocator_module_config: allocator_config,
+        tm_factory: backend.target_machine_factory(tcx.sess, false),
+        total_cgus,
+        msvc_imps_needed: msvc_imps_needed(tcx),
+        target_pointer_width: tcx.sess.target.target.target_pointer_width.clone(),
+        debuginfo: tcx.sess.opts.debuginfo,
+        assembler_cmd,
+    };
+
+    // This is the "main loop" of parallel work happening for parallel codegen.
+    // It's here that we manage parallelism, schedule work, and work with
+    // messages coming from clients.
+    //
+    // There are a few environmental pre-conditions that shape how the system
+    // is set up:
+    //
+    // - Error reporting only can happen on the main thread because that's the
+    //   only place where we have access to the compiler `Session`.
+    // - LLVM work can be done on any thread.
+    // - Codegen can only happen on the main thread.
+    // - Each thread doing substantial work most be in possession of a `Token`
+    //   from the `Jobserver`.
+    // - The compiler process always holds one `Token`. Any additional `Tokens`
+    //   have to be requested from the `Jobserver`.
+    //
+    // Error Reporting
+    // ===============
+    // The error reporting restriction is handled separately from the rest: We
+    // set up a `SharedEmitter` the holds an open channel to the main thread.
+    // When an error occurs on any thread, the shared emitter will send the
+    // error message to the receiver main thread (`SharedEmitterMain`). The
+    // main thread will periodically query this error message queue and emit
+    // any error messages it has received. It might even abort compilation if
+    // has received a fatal error. In this case we rely on all other threads
+    // being torn down automatically with the main thread.
+    // Since the main thread will often be busy doing codegen work, error
+    // reporting will be somewhat delayed, since the message queue can only be
+    // checked in between to work packages.
+    //
+    // Work Processing Infrastructure
+    // ==============================
+    // The work processing infrastructure knows three major actors:
+    //
+    // - the coordinator thread,
+    // - the main thread, and
+    // - LLVM worker threads
+    //
+    // The coordinator thread is running a message loop. It instructs the main
+    // thread about what work to do when, and it will spawn off LLVM worker
+    // threads as open LLVM WorkItems become available.
+    //
+    // The job of the main thread is to codegen CGUs into LLVM work package
+    // (since the main thread is the only thread that can do this). The main
+    // thread will block until it receives a message from the coordinator, upon
+    // which it will codegen one CGU, send it to the coordinator and block
+    // again. This way the coordinator can control what the main thread is
+    // doing.
+    //
+    // The coordinator keeps a queue of LLVM WorkItems, and when a `Token` is
+    // available, it will spawn off a new LLVM worker thread and let it process
+    // that a WorkItem. When a LLVM worker thread is done with its WorkItem,
+    // it will just shut down, which also frees all resources associated with
+    // the given LLVM module, and sends a message to the coordinator that the
+    // has been completed.
+    //
+    // Work Scheduling
+    // ===============
+    // The scheduler's goal is to minimize the time it takes to complete all
+    // work there is, however, we also want to keep memory consumption low
+    // if possible. These two goals are at odds with each other: If memory
+    // consumption were not an issue, we could just let the main thread produce
+    // LLVM WorkItems at full speed, assuring maximal utilization of
+    // Tokens/LLVM worker threads. However, since codegen usual is faster
+    // than LLVM processing, the queue of LLVM WorkItems would fill up and each
+    // WorkItem potentially holds on to a substantial amount of memory.
+    //
+    // So the actual goal is to always produce just enough LLVM WorkItems as
+    // not to starve our LLVM worker threads. That means, once we have enough
+    // WorkItems in our queue, we can block the main thread, so it does not
+    // produce more until we need them.
+    //
+    // Doing LLVM Work on the Main Thread
+    // ----------------------------------
+    // Since the main thread owns the compiler processes implicit `Token`, it is
+    // wasteful to keep it blocked without doing any work. Therefore, what we do
+    // in this case is: We spawn off an additional LLVM worker thread that helps
+    // reduce the queue. The work it is doing corresponds to the implicit
+    // `Token`. The coordinator will mark the main thread as being busy with
+    // LLVM work. (The actual work happens on another OS thread but we just care
+    // about `Tokens`, not actual threads).
+    //
+    // When any LLVM worker thread finishes while the main thread is marked as
+    // "busy with LLVM work", we can do a little switcheroo: We give the Token
+    // of the just finished thread to the LLVM worker thread that is working on
+    // behalf of the main thread's implicit Token, thus freeing up the main
+    // thread again. The coordinator can then again decide what the main thread
+    // should do. This allows the coordinator to make decisions at more points
+    // in time.
+    //
+    // Striking a Balance between Throughput and Memory Consumption
+    // ------------------------------------------------------------
+    // Since our two goals, (1) use as many Tokens as possible and (2) keep
+    // memory consumption as low as possible, are in conflict with each other,
+    // we have to find a trade off between them. Right now, the goal is to keep
+    // all workers busy, which means that no worker should find the queue empty
+    // when it is ready to start.
+    // How do we do achieve this? Good question :) We actually never know how
+    // many `Tokens` are potentially available so it's hard to say how much to
+    // fill up the queue before switching the main thread to LLVM work. Also we
+    // currently don't have a means to estimate how long a running LLVM worker
+    // will still be busy with it's current WorkItem. However, we know the
+    // maximal count of available Tokens that makes sense (=the number of CPU
+    // cores), so we can take a conservative guess. The heuristic we use here
+    // is implemented in the `queue_full_enough()` function.
+    //
+    // Some Background on Jobservers
+    // -----------------------------
+    // It's worth also touching on the management of parallelism here. We don't
+    // want to just spawn a thread per work item because while that's optimal
+    // parallelism it may overload a system with too many threads or violate our
+    // configuration for the maximum amount of cpu to use for this process. To
+    // manage this we use the `jobserver` crate.
+    //
+    // Job servers are an artifact of GNU make and are used to manage
+    // parallelism between processes. A jobserver is a glorified IPC semaphore
+    // basically. Whenever we want to run some work we acquire the semaphore,
+    // and whenever we're done with that work we release the semaphore. In this
+    // manner we can ensure that the maximum number of parallel workers is
+    // capped at any one point in time.
+    //
+    // LTO and the coordinator thread
+    // ------------------------------
+    //
+    // The final job the coordinator thread is responsible for is managing LTO
+    // and how that works. When LTO is requested what we'll to is collect all
+    // optimized LLVM modules into a local vector on the coordinator. Once all
+    // modules have been codegened and optimized we hand this to the `lto`
+    // module for further optimization. The `lto` module will return back a list
+    // of more modules to work on, which the coordinator will continue to spawn
+    // work for.
+    //
+    // Each LLVM module is automatically sent back to the coordinator for LTO if
+    // necessary. There's already optimizations in place to avoid sending work
+    // back to the coordinator if LTO isn't requested.
+    return thread::spawn(move || {
+        // We pretend to be within the top-level LLVM time-passes task here:
+        set_time_depth(1);
+
+        let max_workers = ::num_cpus::get();
+        let mut worker_id_counter = 0;
+        let mut free_worker_ids = Vec::new();
+        let mut get_worker_id = |free_worker_ids: &mut Vec<usize>| {
+            if let Some(id) = free_worker_ids.pop() {
+                id
+            } else {
+                let id = worker_id_counter;
+                worker_id_counter += 1;
+                id
+            }
+        };
+
+        // This is where we collect codegen units that have gone all the way
+        // through codegen and LLVM.
+        let mut compiled_modules = vec![];
+        let mut compiled_metadata_module = None;
+        let mut compiled_allocator_module = None;
+        let mut needs_lto = Vec::new();
+        let mut lto_import_only_modules = Vec::new();
+        let mut started_lto = false;
+        let mut codegen_aborted = false;
+
+        // This flag tracks whether all items have gone through codegens
+        let mut codegen_done = false;
+
+        // This is the queue of LLVM work items that still need processing.
+        let mut work_items = Vec::<(WorkItem<B>, u64)>::new();
+
+        // This are the Jobserver Tokens we currently hold. Does not include
+        // the implicit Token the compiler process owns no matter what.
+        let mut tokens = Vec::new();
+
+        let mut main_thread_worker_state = MainThreadWorkerState::Idle;
+        let mut running = 0;
+
+        let mut llvm_start_time = None;
+
+        // Run the message loop while there's still anything that needs message
+        // processing. Note that as soon as codegen is aborted we simply want to
+        // wait for all existing work to finish, so many of the conditions here
+        // only apply if codegen hasn't been aborted as they represent pending
+        // work to be done.
+        while !codegen_done ||
+              running > 0 ||
+              (!codegen_aborted && (
+                  work_items.len() > 0 ||
+                  needs_lto.len() > 0 ||
+                  lto_import_only_modules.len() > 0 ||
+                  main_thread_worker_state != MainThreadWorkerState::Idle
+              ))
+        {
+
+            // While there are still CGUs to be codegened, the coordinator has
+            // to decide how to utilize the compiler processes implicit Token:
+            // For codegenning more CGU or for running them through LLVM.
+            if !codegen_done {
+                if main_thread_worker_state == MainThreadWorkerState::Idle {
+                    if !queue_full_enough(work_items.len(), running, max_workers) {
+                        // The queue is not full enough, codegen more items:
+                        if let Err(_) = codegen_worker_send.send(Message::CodegenItem) {
+                            panic!("Could not send Message::CodegenItem to main thread")
+                        }
+                        main_thread_worker_state = MainThreadWorkerState::Codegenning;
+                    } else {
+                        // The queue is full enough to not let the worker
+                        // threads starve. Use the implicit Token to do some
+                        // LLVM work too.
+                        let (item, _) = work_items.pop()
+                            .expect("queue empty - queue_full_enough() broken?");
+                        let cgcx = CodegenContext {
+                            worker: get_worker_id(&mut free_worker_ids),
+                            .. cgcx.clone()
+                        };
+                        maybe_start_llvm_timer(cgcx.config(item.module_kind()),
+                                               &mut llvm_start_time);
+                        main_thread_worker_state = MainThreadWorkerState::LLVMing;
+                        spawn_work(cgcx, item);
+                    }
+                }
+            } else if codegen_aborted {
+                // don't queue up any more work if codegen was aborted, we're
+                // just waiting for our existing children to finish
+            } else {
+                // If we've finished everything related to normal codegen
+                // then it must be the case that we've got some LTO work to do.
+                // Perform the serial work here of figuring out what we're
+                // going to LTO and then push a bunch of work items onto our
+                // queue to do LTO
+                if work_items.len() == 0 &&
+                   running == 0 &&
+                   main_thread_worker_state == MainThreadWorkerState::Idle {
+                    assert!(!started_lto);
+                    assert!(needs_lto.len() + lto_import_only_modules.len() > 0);
+                    started_lto = true;
+                    let modules = mem::replace(&mut needs_lto, Vec::new());
+                    let import_only_modules =
+                        mem::replace(&mut lto_import_only_modules, Vec::new());
+                    for (work, cost) in generate_lto_work(&cgcx, modules, import_only_modules) {
+                        let insertion_index = work_items
+                            .binary_search_by_key(&cost, |&(_, cost)| cost)
+                            .unwrap_or_else(|e| e);
+                        work_items.insert(insertion_index, (work, cost));
+                        if !cgcx.opts.debugging_opts.no_parallel_llvm {
+                            helper.request_token();
+                        }
+                    }
+                }
+
+                // In this branch, we know that everything has been codegened,
+                // so it's just a matter of determining whether the implicit
+                // Token is free to use for LLVM work.
+                match main_thread_worker_state {
+                    MainThreadWorkerState::Idle => {
+                        if let Some((item, _)) = work_items.pop() {
+                            let cgcx = CodegenContext {
+                                worker: get_worker_id(&mut free_worker_ids),
+                                .. cgcx.clone()
+                            };
+                            maybe_start_llvm_timer(cgcx.config(item.module_kind()),
+                                                   &mut llvm_start_time);
+                            main_thread_worker_state = MainThreadWorkerState::LLVMing;
+                            spawn_work(cgcx, item);
+                        } else {
+                            // There is no unstarted work, so let the main thread
+                            // take over for a running worker. Otherwise the
+                            // implicit token would just go to waste.
+                            // We reduce the `running` counter by one. The
+                            // `tokens.truncate()` below will take care of
+                            // giving the Token back.
+                            debug_assert!(running > 0);
+                            running -= 1;
+                            main_thread_worker_state = MainThreadWorkerState::LLVMing;
+                        }
+                    }
+                    MainThreadWorkerState::Codegenning => {
+                        bug!("codegen worker should not be codegenning after \
+                              codegen was already completed")
+                    }
+                    MainThreadWorkerState::LLVMing => {
+                        // Already making good use of that token
+                    }
+                }
+            }
+
+            // Spin up what work we can, only doing this while we've got available
+            // parallelism slots and work left to spawn.
+            while !codegen_aborted && work_items.len() > 0 && running < tokens.len() {
+                let (item, _) = work_items.pop().unwrap();
+
+                maybe_start_llvm_timer(cgcx.config(item.module_kind()),
+                                       &mut llvm_start_time);
+
+                let cgcx = CodegenContext {
+                    worker: get_worker_id(&mut free_worker_ids),
+                    .. cgcx.clone()
+                };
+
+                spawn_work(cgcx, item);
+                running += 1;
+            }
+
+            // Relinquish accidentally acquired extra tokens
+            tokens.truncate(running);
+
+            let msg = coordinator_receive.recv().unwrap();
+            match *msg.downcast::<Message<B>>().ok().unwrap() {
+                // Save the token locally and the next turn of the loop will use
+                // this to spawn a new unit of work, or it may get dropped
+                // immediately if we have no more work to spawn.
+                Message::Token(token) => {
+                    match token {
+                        Ok(token) => {
+                            tokens.push(token);
+
+                            if main_thread_worker_state == MainThreadWorkerState::LLVMing {
+                                // If the main thread token is used for LLVM work
+                                // at the moment, we turn that thread into a regular
+                                // LLVM worker thread, so the main thread is free
+                                // to react to codegen demand.
+                                main_thread_worker_state = MainThreadWorkerState::Idle;
+                                running += 1;
+                            }
+                        }
+                        Err(e) => {
+                            let msg = &format!("failed to acquire jobserver token: {}", e);
+                            shared_emitter.fatal(msg);
+                            // Exit the coordinator thread
+                            panic!("{}", msg)
+                        }
+                    }
+                }
+
+                Message::CodegenDone { llvm_work_item, cost } => {
+                    // We keep the queue sorted by estimated processing cost,
+                    // so that more expensive items are processed earlier. This
+                    // is good for throughput as it gives the main thread more
+                    // time to fill up the queue and it avoids scheduling
+                    // expensive items to the end.
+                    // Note, however, that this is not ideal for memory
+                    // consumption, as LLVM module sizes are not evenly
+                    // distributed.
+                    let insertion_index =
+                        work_items.binary_search_by_key(&cost, |&(_, cost)| cost);
+                    let insertion_index = match insertion_index {
+                        Ok(idx) | Err(idx) => idx
+                    };
+                    work_items.insert(insertion_index, (llvm_work_item, cost));
+
+                    if !cgcx.opts.debugging_opts.no_parallel_llvm {
+                        helper.request_token();
+                    }
+                    assert!(!codegen_aborted);
+                    assert_eq!(main_thread_worker_state,
+                               MainThreadWorkerState::Codegenning);
+                    main_thread_worker_state = MainThreadWorkerState::Idle;
+                }
+
+                Message::CodegenComplete => {
+                    codegen_done = true;
+                    assert!(!codegen_aborted);
+                    assert_eq!(main_thread_worker_state,
+                               MainThreadWorkerState::Codegenning);
+                    main_thread_worker_state = MainThreadWorkerState::Idle;
+                }
+
+                // If codegen is aborted that means translation was aborted due
+                // to some normal-ish compiler error. In this situation we want
+                // to exit as soon as possible, but we want to make sure all
+                // existing work has finished. Flag codegen as being done, and
+                // then conditions above will ensure no more work is spawned but
+                // we'll keep executing this loop until `running` hits 0.
+                Message::CodegenAborted => {
+                    assert!(!codegen_aborted);
+                    codegen_done = true;
+                    codegen_aborted = true;
+                    assert_eq!(main_thread_worker_state,
+                               MainThreadWorkerState::Codegenning);
+                }
+
+                // If a thread exits successfully then we drop a token associated
+                // with that worker and update our `running` count. We may later
+                // re-acquire a token to continue running more work. We may also not
+                // actually drop a token here if the worker was running with an
+                // "ephemeral token"
+                //
+                // Note that if the thread failed that means it panicked, so we
+                // abort immediately.
+                Message::Done { result: Ok(compiled_module), worker_id } => {
+                    if main_thread_worker_state == MainThreadWorkerState::LLVMing {
+                        main_thread_worker_state = MainThreadWorkerState::Idle;
+                    } else {
+                        running -= 1;
+                    }
+
+                    free_worker_ids.push(worker_id);
+
+                    match compiled_module.kind {
+                        ModuleKind::Regular => {
+                            compiled_modules.push(compiled_module);
+                        }
+                        ModuleKind::Metadata => {
+                            assert!(compiled_metadata_module.is_none());
+                            compiled_metadata_module = Some(compiled_module);
+                        }
+                        ModuleKind::Allocator => {
+                            assert!(compiled_allocator_module.is_none());
+                            compiled_allocator_module = Some(compiled_module);
+                        }
+                    }
+                }
+                Message::NeedsLTO { result, worker_id } => {
+                    assert!(!started_lto);
+                    if main_thread_worker_state == MainThreadWorkerState::LLVMing {
+                        main_thread_worker_state = MainThreadWorkerState::Idle;
+                    } else {
+                        running -= 1;
+                    }
+                    free_worker_ids.push(worker_id);
+                    needs_lto.push(result);
+                }
+                Message::AddImportOnlyModule { module_data, work_product } => {
+                    assert!(!started_lto);
+                    assert!(!codegen_done);
+                    assert_eq!(main_thread_worker_state,
+                               MainThreadWorkerState::Codegenning);
+                    lto_import_only_modules.push((module_data, work_product));
+                    main_thread_worker_state = MainThreadWorkerState::Idle;
+                }
+                Message::Done { result: Err(()), worker_id: _ } => {
+                    bug!("worker thread panicked");
+                }
+                Message::CodegenItem => {
+                    bug!("the coordinator should not receive codegen requests")
+                }
+            }
+        }
+
+        if let Some(llvm_start_time) = llvm_start_time {
+            let total_llvm_time = Instant::now().duration_since(llvm_start_time);
+            // This is the top-level timing for all of LLVM, set the time-depth
+            // to zero.
+            set_time_depth(0);
+            print_time_passes_entry(cgcx.time_passes,
+                                    "LLVM passes",
+                                    total_llvm_time);
+        }
+
+        // Regardless of what order these modules completed in, report them to
+        // the backend in the same order every time to ensure that we're handing
+        // out deterministic results.
+        compiled_modules.sort_by(|a, b| a.name.cmp(&b.name));
+
+        let compiled_metadata_module = compiled_metadata_module
+            .expect("Metadata module not compiled?");
+
+        Ok(CompiledModules {
+            modules: compiled_modules,
+            metadata_module: compiled_metadata_module,
+            allocator_module: compiled_allocator_module,
+        })
+    });
+
+    // A heuristic that determines if we have enough LLVM WorkItems in the
+    // queue so that the main thread can do LLVM work instead of codegen
+    fn queue_full_enough(items_in_queue: usize,
+                         workers_running: usize,
+                         max_workers: usize) -> bool {
+        // Tune me, plz.
+        items_in_queue > 0 &&
+        items_in_queue >= max_workers.saturating_sub(workers_running / 2)
+    }
+
+    fn maybe_start_llvm_timer(config: &ModuleConfig,
+                              llvm_start_time: &mut Option<Instant>) {
+        // We keep track of the -Ztime-passes output manually,
+        // since the closure-based interface does not fit well here.
+        if config.time_passes {
+            if llvm_start_time.is_none() {
+                *llvm_start_time = Some(Instant::now());
+            }
+        }
+    }
+}
+
+pub const CODEGEN_WORKER_ID: usize = ::std::usize::MAX;
+pub const CODEGEN_WORKER_TIMELINE: time_graph::TimelineId =
+    time_graph::TimelineId(CODEGEN_WORKER_ID);
+pub const CODEGEN_WORK_PACKAGE_KIND: time_graph::WorkPackageKind =
+    time_graph::WorkPackageKind(&["#DE9597", "#FED1D3", "#FDC5C7", "#B46668", "#88494B"]);
+const LLVM_WORK_PACKAGE_KIND: time_graph::WorkPackageKind =
+    time_graph::WorkPackageKind(&["#7DB67A", "#C6EEC4", "#ACDAAA", "#579354", "#3E6F3C"]);
+
+fn spawn_work<B: ExtraBackendMethods>(
+    cgcx: CodegenContext<B>,
+    work: WorkItem<B>
+) {
+    let depth = time_depth();
+
+    thread::spawn(move || {
+        set_time_depth(depth);
+
+        // Set up a destructor which will fire off a message that we're done as
+        // we exit.
+        struct Bomb<B: ExtraBackendMethods> {
+            coordinator_send: Sender<Box<dyn Any + Send>>,
+            result: Option<WorkItemResult<B::Module>>,
+            worker_id: usize,
+        }
+        impl<B: ExtraBackendMethods> Drop for Bomb<B> {
+            fn drop(&mut self) {
+                let worker_id = self.worker_id;
+                let msg = match self.result.take() {
+                    Some(WorkItemResult::Compiled(m)) => {
+                        Message::Done::<B> { result: Ok(m), worker_id }
+                    }
+                    Some(WorkItemResult::NeedsLTO(m)) => {
+                        Message::NeedsLTO::<B> { result: m, worker_id }
+                    }
+                    None => Message::Done::<B> { result: Err(()), worker_id }
+                };
+                drop(self.coordinator_send.send(Box::new(msg)));
+            }
+        }
+
+        let mut bomb = Bomb::<B> {
+            coordinator_send: cgcx.coordinator_send.clone(),
+            result: None,
+            worker_id: cgcx.worker,
+        };
+
+        // Execute the work itself, and if it finishes successfully then flag
+        // ourselves as a success as well.
+        //
+        // Note that we ignore any `FatalError` coming out of `execute_work_item`,
+        // as a diagnostic was already sent off to the main thread - just
+        // surface that there was an error in this worker.
+        bomb.result = {
+            let timeline = cgcx.time_graph.as_ref().map(|tg| {
+                tg.start(time_graph::TimelineId(cgcx.worker),
+                         LLVM_WORK_PACKAGE_KIND,
+                         &work.name())
+            });
+            let mut timeline = timeline.unwrap_or(Timeline::noop());
+            execute_work_item(&cgcx, work, &mut timeline).ok()
+        };
+    });
+}
+
+pub fn run_assembler<B: ExtraBackendMethods>(
+    cgcx: &CodegenContext<B>,
+    handler: &Handler,
+    assembly: &Path,
+    object: &Path
+) {
+    let assembler = cgcx.assembler_cmd
+        .as_ref()
+        .expect("cgcx.assembler_cmd is missing?");
+
+    let pname = &assembler.name;
+    let mut cmd = assembler.cmd.clone();
+    cmd.arg("-c").arg("-o").arg(object).arg(assembly);
+    debug!("{:?}", cmd);
+
+    match cmd.output() {
+        Ok(prog) => {
+            if !prog.status.success() {
+                let mut note = prog.stderr.clone();
+                note.extend_from_slice(&prog.stdout);
+
+                handler.struct_err(&format!("linking with `{}` failed: {}",
+                                            pname.display(),
+                                            prog.status))
+                    .note(&format!("{:?}", &cmd))
+                    .note(str::from_utf8(&note[..]).unwrap())
+                    .emit();
+                handler.abort_if_errors();
+            }
+        },
+        Err(e) => {
+            handler.err(&format!("could not exec the linker `{}`: {}", pname.display(), e));
+            handler.abort_if_errors();
+        }
+    }
+}
+
+
+enum SharedEmitterMessage {
+    Diagnostic(Diagnostic),
+    InlineAsmError(u32, String),
+    AbortIfErrors,
+    Fatal(String),
+}
+
+#[derive(Clone)]
+pub struct SharedEmitter {
+    sender: Sender<SharedEmitterMessage>,
+}
+
+pub struct SharedEmitterMain {
+    receiver: Receiver<SharedEmitterMessage>,
+}
+
+impl SharedEmitter {
+    pub fn new() -> (SharedEmitter, SharedEmitterMain) {
+        let (sender, receiver) = channel();
+
+        (SharedEmitter { sender }, SharedEmitterMain { receiver })
+    }
+
+    pub fn inline_asm_error(&self, cookie: u32, msg: String) {
+        drop(self.sender.send(SharedEmitterMessage::InlineAsmError(cookie, msg)));
+    }
+
+    pub fn fatal(&self, msg: &str) {
+        drop(self.sender.send(SharedEmitterMessage::Fatal(msg.to_string())));
+    }
+}
+
+impl Emitter for SharedEmitter {
+    fn emit(&mut self, db: &DiagnosticBuilder) {
+        drop(self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic {
+            msg: db.message(),
+            code: db.code.clone(),
+            lvl: db.level,
+        })));
+        for child in &db.children {
+            drop(self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic {
+                msg: child.message(),
+                code: None,
+                lvl: child.level,
+            })));
+        }
+        drop(self.sender.send(SharedEmitterMessage::AbortIfErrors));
+    }
+}
+
+impl SharedEmitterMain {
+    pub fn check(&self, sess: &Session, blocking: bool) {
+        loop {
+            let message = if blocking {
+                match self.receiver.recv() {
+                    Ok(message) => Ok(message),
+                    Err(_) => Err(()),
+                }
+            } else {
+                match self.receiver.try_recv() {
+                    Ok(message) => Ok(message),
+                    Err(_) => Err(()),
+                }
+            };
+
+            match message {
+                Ok(SharedEmitterMessage::Diagnostic(diag)) => {
+                    let handler = sess.diagnostic();
+                    match diag.code {
+                        Some(ref code) => {
+                            handler.emit_with_code(&MultiSpan::new(),
+                                                   &diag.msg,
+                                                   code.clone(),
+                                                   diag.lvl);
+                        }
+                        None => {
+                            handler.emit(&MultiSpan::new(),
+                                         &diag.msg,
+                                         diag.lvl);
+                        }
+                    }
+                }
+                Ok(SharedEmitterMessage::InlineAsmError(cookie, msg)) => {
+                    match Mark::from_u32(cookie).expn_info() {
+                        Some(ei) => sess.span_err(ei.call_site, &msg),
+                        None     => sess.err(&msg),
+                    }
+                }
+                Ok(SharedEmitterMessage::AbortIfErrors) => {
+                    sess.abort_if_errors();
+                }
+                Ok(SharedEmitterMessage::Fatal(msg)) => {
+                    sess.fatal(&msg);
+                }
+                Err(_) => {
+                    break;
+                }
+            }
+
+        }
+    }
+}
+
+pub struct OngoingCodegen<B: ExtraBackendMethods> {
+    pub backend: B,
+    pub crate_name: Symbol,
+    pub crate_hash: Svh,
+    pub metadata: EncodedMetadata,
+    pub windows_subsystem: Option<String>,
+    pub linker_info: LinkerInfo,
+    pub crate_info: CrateInfo,
+    pub time_graph: Option<TimeGraph>,
+    pub coordinator_send: Sender<Box<dyn Any + Send>>,
+    pub codegen_worker_receive: Receiver<Message<B>>,
+    pub shared_emitter_main: SharedEmitterMain,
+    pub future: thread::JoinHandle<Result<CompiledModules, ()>>,
+    pub output_filenames: Arc<OutputFilenames>,
+}
+
+impl<B: ExtraBackendMethods> OngoingCodegen<B> {
+    pub fn join(
+        self,
+        sess: &Session
+    ) -> (CodegenResults, FxHashMap<WorkProductId, WorkProduct>) {
+        self.shared_emitter_main.check(sess, true);
+        let compiled_modules = match self.future.join() {
+            Ok(Ok(compiled_modules)) => compiled_modules,
+            Ok(Err(())) => {
+                sess.abort_if_errors();
+                panic!("expected abort due to worker thread errors")
+            },
+            Err(_) => {
+                bug!("panic during codegen/LLVM phase");
+            }
+        };
+
+        sess.cgu_reuse_tracker.check_expected_reuse(sess);
+
+        sess.abort_if_errors();
+
+        if let Some(time_graph) = self.time_graph {
+            time_graph.dump(&format!("{}-timings", self.crate_name));
+        }
+
+        let work_products =
+            copy_all_cgu_workproducts_to_incr_comp_cache_dir(sess,
+                                                             &compiled_modules);
+        produce_final_output_artifacts(sess,
+                                       &compiled_modules,
+                                       &self.output_filenames);
+
+        // FIXME: time_llvm_passes support - does this use a global context or
+        // something?
+        if sess.codegen_units() == 1 && sess.time_llvm_passes() {
+            self.backend.print_pass_timings()
+        }
+
+        (CodegenResults {
+            crate_name: self.crate_name,
+            crate_hash: self.crate_hash,
+            metadata: self.metadata,
+            windows_subsystem: self.windows_subsystem,
+            linker_info: self.linker_info,
+            crate_info: self.crate_info,
+
+            modules: compiled_modules.modules,
+            allocator_module: compiled_modules.allocator_module,
+            metadata_module: compiled_modules.metadata_module,
+        }, work_products)
+    }
+
+    pub fn submit_pre_codegened_module_to_llvm(&self,
+                                                       tcx: TyCtxt,
+                                                       module: ModuleCodegen<B::Module>) {
+        self.wait_for_signal_to_codegen_item();
+        self.check_for_errors(tcx.sess);
+
+        // These are generally cheap and won't through off scheduling.
+        let cost = 0;
+        submit_codegened_module_to_llvm(&self.backend, tcx, module, cost);
+    }
+
+    pub fn codegen_finished(&self, tcx: TyCtxt) {
+        self.wait_for_signal_to_codegen_item();
+        self.check_for_errors(tcx.sess);
+        drop(self.coordinator_send.send(Box::new(Message::CodegenComplete::<B>)));
+    }
+
+    /// Consume this context indicating that codegen was entirely aborted, and
+    /// we need to exit as quickly as possible.
+    ///
+    /// This method blocks the current thread until all worker threads have
+    /// finished, and all worker threads should have exited or be real close to
+    /// exiting at this point.
+    pub fn codegen_aborted(self) {
+        // Signal to the coordinator it should spawn no more work and start
+        // shutdown.
+        drop(self.coordinator_send.send(Box::new(Message::CodegenAborted::<B>)));
+        drop(self.future.join());
+    }
+
+    pub fn check_for_errors(&self, sess: &Session) {
+        self.shared_emitter_main.check(sess, false);
+    }
+
+    pub fn wait_for_signal_to_codegen_item(&self) {
+        match self.codegen_worker_receive.recv() {
+            Ok(Message::CodegenItem) => {
+                // Nothing to do
+            }
+            Ok(_) => panic!("unexpected message"),
+            Err(_) => {
+                // One of the LLVM threads must have panicked, fall through so
+                // error handling can be reached.
+            }
+        }
+    }
+}
+
+pub fn submit_codegened_module_to_llvm<B: ExtraBackendMethods>(
+    _backend: &B,
+    tcx: TyCtxt,
+    module: ModuleCodegen<B::Module>,
+    cost: u64
+) {
+    let llvm_work_item = WorkItem::Optimize(module);
+    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::CodegenDone::<B> {
+        llvm_work_item,
+        cost,
+    })));
+}
+
+pub fn submit_post_lto_module_to_llvm<B: ExtraBackendMethods>(
+    _backend: &B,
+    tcx: TyCtxt,
+    module: CachedModuleCodegen
+) {
+    let llvm_work_item = WorkItem::CopyPostLtoArtifacts(module);
+    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::CodegenDone::<B> {
+        llvm_work_item,
+        cost: 0,
+    })));
+}
+
+pub fn submit_pre_lto_module_to_llvm<B: ExtraBackendMethods>(
+    _backend: &B,
+    tcx: TyCtxt,
+    module: CachedModuleCodegen
+) {
+    let filename = pre_lto_bitcode_filename(&module.name);
+    let bc_path = in_incr_comp_dir_sess(tcx.sess, &filename);
+    let file = fs::File::open(&bc_path).unwrap_or_else(|e| {
+        panic!("failed to open bitcode file `{}`: {}", bc_path.display(), e)
+    });
+
+    let mmap = unsafe {
+        memmap::Mmap::map(&file).unwrap_or_else(|e| {
+            panic!("failed to mmap bitcode file `{}`: {}", bc_path.display(), e)
+        })
+    };
+    // Schedule the module to be loaded
+    drop(tcx.tx_to_llvm_workers.lock().send(Box::new(Message::AddImportOnlyModule::<B> {
+        module_data: SerializedModule::FromUncompressedFile(mmap),
+        work_product: module.source,
+    })));
+}
+
+pub fn pre_lto_bitcode_filename(module_name: &str) -> String {
+    format!("{}.{}", module_name, PRE_THIN_LTO_BC_EXT)
+}
+
+fn msvc_imps_needed(tcx: TyCtxt) -> bool {
+    // This should never be true (because it's not supported). If it is true,
+    // something is wrong with commandline arg validation.
+    assert!(!(tcx.sess.opts.debugging_opts.cross_lang_lto.enabled() &&
+              tcx.sess.target.target.options.is_like_msvc &&
+              tcx.sess.opts.cg.prefer_dynamic));
+
+    tcx.sess.target.target.options.is_like_msvc &&
+        tcx.sess.crate_types.borrow().iter().any(|ct| *ct == config::CrateType::Rlib) &&
+    // ThinLTO can't handle this workaround in all cases, so we don't
+    // emit the `__imp_` symbols. Instead we make them unnecessary by disallowing
+    // dynamic linking when cross-language LTO is enabled.
+    !tcx.sess.opts.debugging_opts.cross_lang_lto.enabled()
+}
diff --git a/src/librustc_codegen_ssa/base.rs b/src/librustc_codegen_ssa/base.rs
index 81a2d0a5389..a590dcd3ea8 100644
--- a/src/librustc_codegen_ssa/base.rs
+++ b/src/librustc_codegen_ssa/base.rs
@@ -39,6 +39,8 @@ use rustc::util::profiling::ProfileCategory;
 use rustc::session::config::{self, EntryFnType, Lto};
 use rustc::session::Session;
 use mir::place::PlaceRef;
+use back::write::{OngoingCodegen, start_async_codegen, submit_pre_lto_module_to_llvm,
+    submit_post_lto_module_to_llvm};
 use {MemFlags, CrateInfo};
 use callee;
 use rustc_mir::monomorphize::item::DefPathBasedNames;
@@ -556,7 +558,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     backend: B,
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     rx: mpsc::Receiver<Box<dyn Any + Send>>
-) -> B::OngoingCodegen {
+) -> OngoingCodegen<B> {
 
     check_for_rustc_errors_attr(tcx);
 
@@ -590,19 +592,20 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     // Skip crate items and just output metadata in -Z no-codegen mode.
     if tcx.sess.opts.debugging_opts.no_codegen ||
        !tcx.sess.opts.output_types.should_codegen() {
-        let ongoing_codegen = backend.start_async_codegen(
+        let ongoing_codegen = start_async_codegen(
+            backend,
             tcx,
             time_graph,
             metadata,
             rx,
             1);
 
-        backend.submit_pre_codegened_module_to_backend(&ongoing_codegen, tcx, metadata_module);
-        backend.codegen_finished(&ongoing_codegen, tcx);
+        ongoing_codegen.submit_pre_codegened_module_to_llvm(tcx, metadata_module);
+        ongoing_codegen.codegen_finished(tcx);
 
         assert_and_save_dep_graph(tcx);
 
-        backend.check_for_errors(&ongoing_codegen, tcx.sess);
+        ongoing_codegen.check_for_errors(tcx.sess);
 
         return ongoing_codegen;
     }
@@ -623,7 +626,8 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         }
     }
 
-    let ongoing_codegen = backend.start_async_codegen(
+    let ongoing_codegen = start_async_codegen(
+        backend.clone(),
         tcx,
         time_graph.clone(),
         metadata,
@@ -667,10 +671,10 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     };
 
     if let Some(allocator_module) = allocator_module {
-        backend.submit_pre_codegened_module_to_backend(&ongoing_codegen, tcx, allocator_module);
+        ongoing_codegen.submit_pre_codegened_module_to_llvm(tcx, allocator_module);
     }
 
-    backend.submit_pre_codegened_module_to_backend(&ongoing_codegen, tcx, metadata_module);
+    ongoing_codegen.submit_pre_codegened_module_to_llvm(tcx, metadata_module);
 
     // We sort the codegen units by size. This way we can schedule work for LLVM
     // a bit more efficiently.
@@ -684,8 +688,8 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
     let mut all_stats = Stats::default();
 
     for cgu in codegen_units.into_iter() {
-        backend.wait_for_signal_to_codegen_item(&ongoing_codegen);
-        backend.check_for_errors(&ongoing_codegen, tcx.sess);
+        ongoing_codegen.wait_for_signal_to_codegen_item();
+        ongoing_codegen.check_for_errors(tcx.sess);
 
         let cgu_reuse = determine_cgu_reuse(tcx, &cgu);
         tcx.sess.cgu_reuse_tracker.set_actual_reuse(&cgu.name().as_str(), cgu_reuse);
@@ -704,14 +708,14 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
                 false
             }
             CguReuse::PreLto => {
-                backend.submit_pre_lto_module_to_backend(tcx, CachedModuleCodegen {
+                submit_pre_lto_module_to_llvm(&backend, tcx, CachedModuleCodegen {
                     name: cgu.name().to_string(),
                     source: cgu.work_product(tcx),
                 });
                 true
             }
             CguReuse::PostLto => {
-                backend.submit_post_lto_module_to_backend(tcx, CachedModuleCodegen {
+                submit_post_lto_module_to_llvm(&backend, tcx, CachedModuleCodegen {
                     name: cgu.name().to_string(),
                     source: cgu.work_product(tcx),
                 });
@@ -720,7 +724,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         };
     }
 
-    backend.codegen_finished(&ongoing_codegen, tcx);
+    ongoing_codegen.codegen_finished(tcx);
 
     // Since the main thread is sometimes blocked during codegen, we keep track
     // -Ztime-passes output manually.
@@ -754,7 +758,7 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
         }
     }
 
-    backend.check_for_errors(&ongoing_codegen, tcx.sess);
+    ongoing_codegen.check_for_errors(tcx.sess);
 
     assert_and_save_dep_graph(tcx);
     ongoing_codegen.into_inner()
@@ -777,24 +781,24 @@ pub fn codegen_crate<B: ExtraBackendMethods>(
 /// If you see this comment in the code, then it means that this workaround
 /// worked! We may yet one day track down the mysterious cause of that
 /// segfault...
-struct AbortCodegenOnDrop<B: ExtraBackendMethods>(Option<B::OngoingCodegen>);
+struct AbortCodegenOnDrop<B: ExtraBackendMethods>(Option<OngoingCodegen<B>>);
 
 impl<B: ExtraBackendMethods> AbortCodegenOnDrop<B> {
-    fn into_inner(mut self) -> B::OngoingCodegen {
+    fn into_inner(mut self) -> OngoingCodegen<B> {
         self.0.take().unwrap()
     }
 }
 
 impl<B: ExtraBackendMethods> Deref for AbortCodegenOnDrop<B> {
-    type Target = B::OngoingCodegen;
+    type Target = OngoingCodegen<B>;
 
-    fn deref(&self) -> &B::OngoingCodegen {
+    fn deref(&self) -> &OngoingCodegen<B> {
         self.0.as_ref().unwrap()
     }
 }
 
 impl<B: ExtraBackendMethods> DerefMut for AbortCodegenOnDrop<B> {
-    fn deref_mut(&mut self) -> &mut B::OngoingCodegen {
+    fn deref_mut(&mut self) -> &mut OngoingCodegen<B> {
         self.0.as_mut().unwrap()
     }
 }
@@ -802,7 +806,7 @@ impl<B: ExtraBackendMethods> DerefMut for AbortCodegenOnDrop<B> {
 impl<B: ExtraBackendMethods> Drop for AbortCodegenOnDrop<B> {
     fn drop(&mut self) {
         if let Some(codegen) = self.0.take() {
-            B::codegen_aborted(codegen);
+            codegen.codegen_aborted();
         }
     }
 }
diff --git a/src/librustc_codegen_ssa/interfaces/backend.rs b/src/librustc_codegen_ssa/interfaces/backend.rs
index 6e8233bcb88..b4d376cf5f0 100644
--- a/src/librustc_codegen_ssa/interfaces/backend.rs
+++ b/src/librustc_codegen_ssa/interfaces/backend.rs
@@ -11,18 +11,16 @@
 use rustc::ty::layout::{HasTyCtxt, LayoutOf, TyLayout};
 use rustc::ty::Ty;
 
+use super::write::WriteBackendMethods;
 use super::CodegenObject;
 use rustc::middle::allocator::AllocatorKind;
 use rustc::middle::cstore::EncodedMetadata;
 use rustc::mir::mono::Stats;
 use rustc::session::Session;
 use rustc::ty::TyCtxt;
-use rustc::util::time_graph::TimeGraph;
 use rustc_codegen_utils::codegen_backend::CodegenBackend;
-use std::any::Any;
-use std::sync::mpsc::Receiver;
+use std::sync::Arc;
 use syntax_pos::symbol::InternedString;
-use {CachedModuleCodegen, ModuleCodegen};
 
 pub trait BackendTypes {
     type Value: CodegenObject;
@@ -43,10 +41,7 @@ impl<'tcx, T> Backend<'tcx> for T where
     Self: BackendTypes + HasTyCtxt<'tcx> + LayoutOf<Ty = Ty<'tcx>, TyLayout = TyLayout<'tcx>>
 {}
 
-pub trait ExtraBackendMethods: CodegenBackend {
-    type Module;
-    type OngoingCodegen;
-
+pub trait ExtraBackendMethods: CodegenBackend + WriteBackendMethods + Sized + Send {
     fn new_metadata(&self, sess: &Session, mod_name: &str) -> Self::Module;
     fn write_metadata<'b, 'gcx>(
         &self,
@@ -54,30 +49,18 @@ pub trait ExtraBackendMethods: CodegenBackend {
         metadata: &Self::Module,
     ) -> EncodedMetadata;
     fn codegen_allocator(&self, tcx: TyCtxt, mods: &Self::Module, kind: AllocatorKind);
-
-    fn start_async_codegen(
-        &self,
-        tcx: TyCtxt,
-        time_graph: Option<TimeGraph>,
-        metadata: EncodedMetadata,
-        coordinator_receive: Receiver<Box<dyn Any + Send>>,
-        total_cgus: usize,
-    ) -> Self::OngoingCodegen;
-    fn submit_pre_codegened_module_to_backend(
-        &self,
-        codegen: &Self::OngoingCodegen,
-        tcx: TyCtxt,
-        module: ModuleCodegen<Self::Module>,
-    );
-    fn submit_pre_lto_module_to_backend(&self, tcx: TyCtxt, module: CachedModuleCodegen);
-    fn submit_post_lto_module_to_backend(&self, tcx: TyCtxt, module: CachedModuleCodegen);
-    fn codegen_aborted(codegen: Self::OngoingCodegen);
-    fn codegen_finished(&self, codegen: &Self::OngoingCodegen, tcx: TyCtxt);
-    fn check_for_errors(&self, codegen: &Self::OngoingCodegen, sess: &Session);
-    fn wait_for_signal_to_codegen_item(&self, codegen: &Self::OngoingCodegen);
     fn compile_codegen_unit<'a, 'tcx: 'a>(
         &self,
         tcx: TyCtxt<'a, 'tcx, 'tcx>,
         cgu_name: InternedString,
     ) -> Stats;
+    // If find_features is true this won't access `sess.crate_types` by assuming
+    // that `is_pie_binary` is false. When we discover LLVM target features
+    // `sess.crate_types` is uninitialized so we cannot access it.
+    fn target_machine_factory(
+        &self,
+        sess: &Session,
+        find_features: bool,
+    ) -> Arc<dyn Fn() -> Result<Self::TargetMachine, String> + Send + Sync>;
+    fn target_cpu<'b>(&self, sess: &'b Session) -> &'b str;
 }
diff --git a/src/librustc_codegen_ssa/interfaces/mod.rs b/src/librustc_codegen_ssa/interfaces/mod.rs
index 1797060f6a4..5cff31e17b5 100644
--- a/src/librustc_codegen_ssa/interfaces/mod.rs
+++ b/src/librustc_codegen_ssa/interfaces/mod.rs
@@ -35,6 +35,7 @@ mod intrinsic;
 mod misc;
 mod statics;
 mod type_;
+mod write;
 
 pub use self::abi::{AbiBuilderMethods, AbiMethods};
 pub use self::asm::{AsmBuilderMethods, AsmMethods};
@@ -49,6 +50,7 @@ pub use self::statics::StaticMethods;
 pub use self::type_::{
     ArgTypeMethods, BaseTypeMethods, DerivedTypeMethods, LayoutTypeMethods, TypeMethods,
 };
+pub use self::write::{ModuleBufferMethods, ThinBufferMethods, WriteBackendMethods};
 
 use std::fmt;
 
diff --git a/src/librustc_codegen_ssa/interfaces/write.rs b/src/librustc_codegen_ssa/interfaces/write.rs
new file mode 100644
index 00000000000..3419e1c59ed
--- /dev/null
+++ b/src/librustc_codegen_ssa/interfaces/write.rs
@@ -0,0 +1,72 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use back::lto::{LtoModuleCodegen, SerializedModule, ThinModule};
+use back::write::{CodegenContext, ModuleConfig};
+use {CompiledModule, ModuleCodegen};
+
+use rustc::dep_graph::WorkProduct;
+use rustc::util::time_graph::Timeline;
+use rustc_errors::{FatalError, Handler};
+
+pub trait WriteBackendMethods: 'static + Sized + Clone {
+    type Module: Send + Sync;
+    type TargetMachine: Clone;
+    type ModuleBuffer: ModuleBufferMethods;
+    type Context: ?Sized;
+    type ThinData: Send + Sync;
+    type ThinBuffer: ThinBufferMethods;
+
+    /// Performs LTO, which in the case of full LTO means merging all modules into
+    /// a single one and returning it for further optimizing. For ThinLTO, it will
+    /// do the global analysis necessary and return two lists, one of the modules
+    /// the need optimization and another for modules that can simply be copied over
+    /// from the incr. comp. cache.
+    fn run_lto(
+        cgcx: &CodegenContext<Self>,
+        modules: Vec<ModuleCodegen<Self::Module>>,
+        cached_modules: Vec<(SerializedModule<Self::ModuleBuffer>, WorkProduct)>,
+        timeline: &mut Timeline,
+    ) -> Result<(Vec<LtoModuleCodegen<Self>>, Vec<WorkProduct>), FatalError>;
+    fn print_pass_timings(&self);
+    unsafe fn optimize(
+        cgcx: &CodegenContext<Self>,
+        diag_handler: &Handler,
+        module: &ModuleCodegen<Self::Module>,
+        config: &ModuleConfig,
+        timeline: &mut Timeline,
+    ) -> Result<(), FatalError>;
+    unsafe fn optimize_thin(
+        cgcx: &CodegenContext<Self>,
+        thin: &mut ThinModule<Self>,
+        timeline: &mut Timeline,
+    ) -> Result<ModuleCodegen<Self::Module>, FatalError>;
+    unsafe fn codegen(
+        cgcx: &CodegenContext<Self>,
+        diag_handler: &Handler,
+        module: ModuleCodegen<Self::Module>,
+        config: &ModuleConfig,
+        timeline: &mut Timeline,
+    ) -> Result<CompiledModule, FatalError>;
+    fn run_lto_pass_manager(
+        cgcx: &CodegenContext<Self>,
+        llmod: &ModuleCodegen<Self::Module>,
+        config: &ModuleConfig,
+        thin: bool,
+    );
+}
+
+pub trait ThinBufferMethods: Send + Sync {
+    fn data(&self) -> &[u8];
+}
+
+pub trait ModuleBufferMethods: Send + Sync {
+    fn data(&self) -> &[u8];
+}
diff --git a/src/librustc_codegen_ssa/lib.rs b/src/librustc_codegen_ssa/lib.rs
index 2a42ad91e3d..e779d8f1469 100644
--- a/src/librustc_codegen_ssa/lib.rs
+++ b/src/librustc_codegen_ssa/lib.rs
@@ -39,7 +39,16 @@ extern crate syntax_pos;
 extern crate rustc_incremental;
 extern crate rustc_codegen_utils;
 extern crate rustc_data_structures;
+extern crate rustc_allocator;
+extern crate rustc_fs_util;
+extern crate serialize;
+extern crate rustc_errors;
+extern crate rustc_demangle;
+extern crate cc;
 extern crate libc;
+extern crate jobserver;
+extern crate memmap;
+extern crate num_cpus;
 
 use std::path::PathBuf;
 use rustc::dep_graph::WorkProduct;
@@ -48,7 +57,9 @@ use rustc::middle::lang_items::LangItem;
 use rustc::hir::def_id::CrateNum;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::Lrc;
+use rustc_data_structures::svh::Svh;
 use rustc::middle::cstore::{LibSource, CrateSource, NativeLibrary};
+use syntax_pos::symbol::Symbol;
 
 // NB: This module needs to be declared first so diagnostics are
 // registered before they are used.
@@ -63,6 +74,7 @@ pub mod callee;
 pub mod glue;
 pub mod meth;
 pub mod mono_item;
+pub mod back;
 
 pub struct ModuleCodegen<M> {
     /// The name of the module. When the crate may be saved between
@@ -159,4 +171,17 @@ pub struct CrateInfo {
     pub missing_lang_items: FxHashMap<CrateNum, Vec<LangItem>>,
 }
 
+
+pub struct CodegenResults {
+    pub crate_name: Symbol,
+    pub modules: Vec<CompiledModule>,
+    pub allocator_module: Option<CompiledModule>,
+    pub metadata_module: CompiledModule,
+    pub crate_hash: Svh,
+    pub metadata: rustc::middle::cstore::EncodedMetadata,
+    pub windows_subsystem: Option<String>,
+    pub linker_info: back::linker::LinkerInfo,
+    pub crate_info: CrateInfo,
+}
+
 __build_diagnostic_array! { librustc_codegen_ssa, DIAGNOSTICS }
diff --git a/src/librustc_codegen_utils/Cargo.toml b/src/librustc_codegen_utils/Cargo.toml
index 4c57e978414..34a09f30b64 100644
--- a/src/librustc_codegen_utils/Cargo.toml
+++ b/src/librustc_codegen_utils/Cargo.toml
@@ -13,11 +13,9 @@ test = false
 flate2 = "1.0"
 log = "0.4"
 
-serialize = { path = "../libserialize" }
 syntax = { path = "../libsyntax" }
 syntax_pos = { path = "../libsyntax_pos" }
 rustc = { path = "../librustc" }
-rustc_allocator = { path = "../librustc_allocator" }
 rustc_target = { path = "../librustc_target" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_metadata = { path = "../librustc_metadata" }
diff --git a/src/librustc_codegen_utils/lib.rs b/src/librustc_codegen_utils/lib.rs
index 8d85c6691c2..96b319481a7 100644
--- a/src/librustc_codegen_utils/lib.rs
+++ b/src/librustc_codegen_utils/lib.rs
@@ -31,10 +31,8 @@ extern crate flate2;
 #[macro_use]
 extern crate log;
 
-extern crate serialize;
 #[macro_use]
 extern crate rustc;
-extern crate rustc_allocator;
 extern crate rustc_target;
 extern crate rustc_metadata;
 extern crate rustc_mir;
@@ -43,16 +41,10 @@ extern crate syntax;
 extern crate syntax_pos;
 #[macro_use] extern crate rustc_data_structures;
 
-use std::path::PathBuf;
-
-use rustc::session::Session;
 use rustc::ty::TyCtxt;
 
-pub mod command;
 pub mod link;
-pub mod linker;
 pub mod codegen_backend;
-pub mod symbol_export;
 pub mod symbol_names;
 pub mod symbol_names_test;
 
@@ -70,27 +62,4 @@ pub fn check_for_rustc_errors_attr(tcx: TyCtxt) {
     }
 }
 
-pub fn find_library(name: &str, search_paths: &[PathBuf], sess: &Session)
-                    -> PathBuf {
-    // On Windows, static libraries sometimes show up as libfoo.a and other
-    // times show up as foo.lib
-    let oslibname = format!("{}{}{}",
-                            sess.target.target.options.staticlib_prefix,
-                            name,
-                            sess.target.target.options.staticlib_suffix);
-    let unixlibname = format!("lib{}.a", name);
-
-    for path in search_paths {
-        debug!("looking for {} inside {:?}", name, path);
-        let test = path.join(&oslibname);
-        if test.exists() { return test }
-        if oslibname != unixlibname {
-            let test = path.join(&unixlibname);
-            if test.exists() { return test }
-        }
-    }
-    sess.fatal(&format!("could not find native static library `{}`, \
-                         perhaps an -L flag is missing?", name));
-}
-
 __build_diagnostic_array! { librustc_codegen_utils, DIAGNOSTICS }