Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 874 insertions, 0 deletions

diff --git a/compiler/rustc_codegen_cranelift/src/driver/aot.rs b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
new file mode 100644
index 000000000..3cd1ef563
--- /dev/null
+++ b/compiler/rustc_codegen_cranelift/src/driver/aot.rs
@@ -0,0 +1,436 @@
+//! The AOT driver uses [`cranelift_object`] to write object files suitable for linking into a
+//! standalone executable.
+
+use std::path::PathBuf;
+
+use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
+use rustc_codegen_ssa::back::metadata::create_compressed_metadata_file;
+use rustc_codegen_ssa::{CodegenResults, CompiledModule, CrateInfo, ModuleKind};
+use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_metadata::EncodedMetadata;
+use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
+use rustc_middle::mir::mono::{CodegenUnit, MonoItem};
+use rustc_session::cgu_reuse_tracker::CguReuse;
+use rustc_session::config::{DebugInfo, OutputType};
+use rustc_session::Session;
+
+use cranelift_codegen::isa::TargetIsa;
+use cranelift_object::{ObjectBuilder, ObjectModule};
+
+use crate::{prelude::*, BackendConfig};
+
+struct ModuleCodegenResult(CompiledModule, Option<(WorkProductId, WorkProduct)>);
+
+impl<HCX> HashStable<HCX> for ModuleCodegenResult {
+    fn hash_stable(&self, _: &mut HCX, _: &mut StableHasher) {
+        // do nothing
+    }
+}
+
+fn make_module(sess: &Session, isa: Box<dyn TargetIsa>, name: String) -> ObjectModule {
+    let mut builder =
+        ObjectBuilder::new(isa, name + ".o", cranelift_module::default_libcall_names()).unwrap();
+    // Unlike cg_llvm, cg_clif defaults to disabling -Zfunction-sections. For cg_llvm binary size
+    // is important, while cg_clif cares more about compilation times. Enabling -Zfunction-sections
+    // can easily double the amount of time necessary to perform linking.
+    builder.per_function_section(sess.opts.unstable_opts.function_sections.unwrap_or(false));
+    ObjectModule::new(builder)
+}
+
+fn emit_module(
+    tcx: TyCtxt<'_>,
+    backend_config: &BackendConfig,
+    name: String,
+    kind: ModuleKind,
+    module: ObjectModule,
+    debug: Option<DebugContext<'_>>,
+    unwind_context: UnwindContext,
+) -> ModuleCodegenResult {
+    let mut product = module.finish();
+
+    if let Some(mut debug) = debug {
+        debug.emit(&mut product);
+    }
+
+    unwind_context.emit(&mut product);
+
+    let tmp_file = tcx.output_filenames(()).temp_path(OutputType::Object, Some(&name));
+    let obj = product.object.write().unwrap();
+
+    tcx.sess.prof.artifact_size("object_file", name.clone(), obj.len().try_into().unwrap());
+
+    if let Err(err) = std::fs::write(&tmp_file, obj) {
+        tcx.sess.fatal(&format!("error writing object file: {}", err));
+    }
+
+    let work_product = if backend_config.disable_incr_cache {
+        None
+    } else {
+        rustc_incremental::copy_cgu_workproduct_to_incr_comp_cache_dir(
+            tcx.sess,
+            &name,
+            &[("o", &tmp_file)],
+        )
+    };
+
+    ModuleCodegenResult(
+        CompiledModule { name, kind, object: Some(tmp_file), dwarf_object: None, bytecode: None },
+        work_product,
+    )
+}
+
+fn reuse_workproduct_for_cgu(
+    tcx: TyCtxt<'_>,
+    cgu: &CodegenUnit<'_>,
+    work_products: &mut FxHashMap<WorkProductId, WorkProduct>,
+) -> CompiledModule {
+    let work_product = cgu.previous_work_product(tcx);
+    let obj_out = tcx.output_filenames(()).temp_path(OutputType::Object, Some(cgu.name().as_str()));
+    let source_file = rustc_incremental::in_incr_comp_dir_sess(
+        &tcx.sess,
+        &work_product.saved_files.get("o").expect("no saved object file in work product"),
+    );
+    if let Err(err) = rustc_fs_util::link_or_copy(&source_file, &obj_out) {
+        tcx.sess.err(&format!(
+            "unable to copy {} to {}: {}",
+            source_file.display(),
+            obj_out.display(),
+            err
+        ));
+    }
+
+    work_products.insert(cgu.work_product_id(), work_product);
+
+    CompiledModule {
+        name: cgu.name().to_string(),
+        kind: ModuleKind::Regular,
+        object: Some(obj_out),
+        dwarf_object: None,
+        bytecode: None,
+    }
+}
+
+fn module_codegen(
+    tcx: TyCtxt<'_>,
+    (backend_config, cgu_name): (BackendConfig, rustc_span::Symbol),
+) -> ModuleCodegenResult {
+    let cgu = tcx.codegen_unit(cgu_name);
+    let mono_items = cgu.items_in_deterministic_order(tcx);
+
+    let isa = crate::build_isa(tcx.sess, &backend_config);
+    let mut module = make_module(tcx.sess, isa, cgu_name.as_str().to_string());
+
+    let mut cx = crate::CodegenCx::new(
+        tcx,
+        backend_config.clone(),
+        module.isa(),
+        tcx.sess.opts.debuginfo != DebugInfo::None,
+        cgu_name,
+    );
+    super::predefine_mono_items(tcx, &mut module, &mono_items);
+    for (mono_item, _) in mono_items {
+        match mono_item {
+            MonoItem::Fn(inst) => {
+                cx.tcx
+                    .sess
+                    .time("codegen fn", || crate::base::codegen_fn(&mut cx, &mut module, inst));
+            }
+            MonoItem::Static(def_id) => crate::constant::codegen_static(tcx, &mut module, def_id),
+            MonoItem::GlobalAsm(item_id) => {
+                let item = cx.tcx.hir().item(item_id);
+                if let rustc_hir::ItemKind::GlobalAsm(asm) = item.kind {
+                    if !asm.options.contains(InlineAsmOptions::ATT_SYNTAX) {
+                        cx.global_asm.push_str("\n.intel_syntax noprefix\n");
+                    } else {
+                        cx.global_asm.push_str("\n.att_syntax\n");
+                    }
+                    for piece in asm.template {
+                        match *piece {
+                            InlineAsmTemplatePiece::String(ref s) => cx.global_asm.push_str(s),
+                            InlineAsmTemplatePiece::Placeholder { .. } => todo!(),
+                        }
+                    }
+                    cx.global_asm.push_str("\n.att_syntax\n\n");
+                } else {
+                    bug!("Expected GlobalAsm found {:?}", item);
+                }
+            }
+        }
+    }
+    crate::main_shim::maybe_create_entry_wrapper(
+        tcx,
+        &mut module,
+        &mut cx.unwind_context,
+        false,
+        cgu.is_primary(),
+    );
+
+    let debug_context = cx.debug_context;
+    let unwind_context = cx.unwind_context;
+    let codegen_result = tcx.sess.time("write object file", || {
+        emit_module(
+            tcx,
+            &backend_config,
+            cgu.name().as_str().to_string(),
+            ModuleKind::Regular,
+            module,
+            debug_context,
+            unwind_context,
+        )
+    });
+
+    codegen_global_asm(tcx, cgu.name().as_str(), &cx.global_asm);
+
+    codegen_result
+}
+
+pub(crate) fn run_aot(
+    tcx: TyCtxt<'_>,
+    backend_config: BackendConfig,
+    metadata: EncodedMetadata,
+    need_metadata_module: bool,
+) -> Box<(CodegenResults, FxHashMap<WorkProductId, WorkProduct>)> {
+    let mut work_products = FxHashMap::default();
+
+    let cgus = if tcx.sess.opts.output_types.should_codegen() {
+        tcx.collect_and_partition_mono_items(()).1
+    } else {
+        // If only `--emit metadata` is used, we shouldn't perform any codegen.
+        // Also `tcx.collect_and_partition_mono_items` may panic in that case.
+        &[]
+    };
+
+    if tcx.dep_graph.is_fully_enabled() {
+        for cgu in &*cgus {
+            tcx.ensure().codegen_unit(cgu.name());
+        }
+    }
+
+    let modules = super::time(tcx, backend_config.display_cg_time, "codegen mono items", || {
+        cgus.iter()
+            .map(|cgu| {
+                let cgu_reuse = determine_cgu_reuse(tcx, cgu);
+                tcx.sess.cgu_reuse_tracker.set_actual_reuse(cgu.name().as_str(), cgu_reuse);
+
+                match cgu_reuse {
+                    _ if backend_config.disable_incr_cache => {}
+                    CguReuse::No => {}
+                    CguReuse::PreLto => {
+                        return reuse_workproduct_for_cgu(tcx, &*cgu, &mut work_products);
+                    }
+                    CguReuse::PostLto => unreachable!(),
+                }
+
+                let dep_node = cgu.codegen_dep_node(tcx);
+                let (ModuleCodegenResult(module, work_product), _) = tcx.dep_graph.with_task(
+                    dep_node,
+                    tcx,
+                    (backend_config.clone(), cgu.name()),
+                    module_codegen,
+                    Some(rustc_middle::dep_graph::hash_result),
+                );
+
+                if let Some((id, product)) = work_product {
+                    work_products.insert(id, product);
+                }
+
+                module
+            })
+            .collect::<Vec<_>>()
+    });
+
+    tcx.sess.abort_if_errors();
+
+    let isa = crate::build_isa(tcx.sess, &backend_config);
+    let mut allocator_module = make_module(tcx.sess, isa, "allocator_shim".to_string());
+    assert_eq!(pointer_ty(tcx), allocator_module.target_config().pointer_type());
+    let mut allocator_unwind_context = UnwindContext::new(allocator_module.isa(), true);
+    let created_alloc_shim =
+        crate::allocator::codegen(tcx, &mut allocator_module, &mut allocator_unwind_context);
+
+    let allocator_module = if created_alloc_shim {
+        let ModuleCodegenResult(module, work_product) = emit_module(
+            tcx,
+            &backend_config,
+            "allocator_shim".to_string(),
+            ModuleKind::Allocator,
+            allocator_module,
+            None,
+            allocator_unwind_context,
+        );
+        if let Some((id, product)) = work_product {
+            work_products.insert(id, product);
+        }
+        Some(module)
+    } else {
+        None
+    };
+
+    let metadata_module = if need_metadata_module {
+        let _timer = tcx.prof.generic_activity("codegen crate metadata");
+        let (metadata_cgu_name, tmp_file) = tcx.sess.time("write compressed metadata", || {
+            use rustc_middle::mir::mono::CodegenUnitNameBuilder;
+
+            let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
+            let metadata_cgu_name = cgu_name_builder
+                .build_cgu_name(LOCAL_CRATE, &["crate"], Some("metadata"))
+                .as_str()
+                .to_string();
+
+            let tmp_file =
+                tcx.output_filenames(()).temp_path(OutputType::Metadata, Some(&metadata_cgu_name));
+
+            let symbol_name = rustc_middle::middle::exported_symbols::metadata_symbol_name(tcx);
+            let obj = create_compressed_metadata_file(tcx.sess, &metadata, &symbol_name);
+
+            if let Err(err) = std::fs::write(&tmp_file, obj) {
+                tcx.sess.fatal(&format!("error writing metadata object file: {}", err));
+            }
+
+            (metadata_cgu_name, tmp_file)
+        });
+
+        Some(CompiledModule {
+            name: metadata_cgu_name,
+            kind: ModuleKind::Metadata,
+            object: Some(tmp_file),
+            dwarf_object: None,
+            bytecode: None,
+        })
+    } else {
+        None
+    };
+
+    // FIXME handle `-Ctarget-cpu=native`
+    let target_cpu = match tcx.sess.opts.cg.target_cpu {
+        Some(ref name) => name,
+        None => tcx.sess.target.cpu.as_ref(),
+    }
+    .to_owned();
+
+    Box::new((
+        CodegenResults {
+            modules,
+            allocator_module,
+            metadata_module,
+            metadata,
+            crate_info: CrateInfo::new(tcx, target_cpu),
+        },
+        work_products,
+    ))
+}
+
+fn codegen_global_asm(tcx: TyCtxt<'_>, cgu_name: &str, global_asm: &str) {
+    use std::io::Write;
+    use std::process::{Command, Stdio};
+
+    if global_asm.is_empty() {
+        return;
+    }
+
+    if cfg!(not(feature = "inline_asm"))
+        || tcx.sess.target.is_like_osx
+        || tcx.sess.target.is_like_windows
+    {
+        if global_asm.contains("__rust_probestack") {
+            return;
+        }
+
+        // FIXME fix linker error on macOS
+        if cfg!(not(feature = "inline_asm")) {
+            tcx.sess.fatal(
+                "asm! and global_asm! support is disabled while compiling rustc_codegen_cranelift",
+            );
+        } else {
+            tcx.sess.fatal("asm! and global_asm! are not yet supported on macOS and Windows");
+        }
+    }
+
+    let assembler = crate::toolchain::get_toolchain_binary(tcx.sess, "as");
+    let linker = crate::toolchain::get_toolchain_binary(tcx.sess, "ld");
+
+    // Remove all LLVM style comments
+    let global_asm = global_asm
+        .lines()
+        .map(|line| if let Some(index) = line.find("//") { &line[0..index] } else { line })
+        .collect::<Vec<_>>()
+        .join("\n");
+
+    let output_object_file = tcx.output_filenames(()).temp_path(OutputType::Object, Some(cgu_name));
+
+    // Assemble `global_asm`
+    let global_asm_object_file = add_file_stem_postfix(output_object_file.clone(), ".asm");
+    let mut child = Command::new(assembler)
+        .arg("-o")
+        .arg(&global_asm_object_file)
+        .stdin(Stdio::piped())
+        .spawn()
+        .expect("Failed to spawn `as`.");
+    child.stdin.take().unwrap().write_all(global_asm.as_bytes()).unwrap();
+    let status = child.wait().expect("Failed to wait for `as`.");
+    if !status.success() {
+        tcx.sess.fatal(&format!("Failed to assemble `{}`", global_asm));
+    }
+
+    // Link the global asm and main object file together
+    let main_object_file = add_file_stem_postfix(output_object_file.clone(), ".main");
+    std::fs::rename(&output_object_file, &main_object_file).unwrap();
+    let status = Command::new(linker)
+        .arg("-r") // Create a new object file
+        .arg("-o")
+        .arg(output_object_file)
+        .arg(&main_object_file)
+        .arg(&global_asm_object_file)
+        .status()
+        .unwrap();
+    if !status.success() {
+        tcx.sess.fatal(&format!(
+            "Failed to link `{}` and `{}` together",
+            main_object_file.display(),
+            global_asm_object_file.display(),
+        ));
+    }
+
+    std::fs::remove_file(global_asm_object_file).unwrap();
+    std::fs::remove_file(main_object_file).unwrap();
+}
+
+fn add_file_stem_postfix(mut path: PathBuf, postfix: &str) -> PathBuf {
+    let mut new_filename = path.file_stem().unwrap().to_owned();
+    new_filename.push(postfix);
+    if let Some(extension) = path.extension() {
+        new_filename.push(".");
+        new_filename.push(extension);
+    }
+    path.set_file_name(new_filename);
+    path
+}
+
+// Adapted from https://github.com/rust-lang/rust/blob/303d8aff6092709edd4dbd35b1c88e9aa40bf6d8/src/librustc_codegen_ssa/base.rs#L922-L953
+fn determine_cgu_reuse<'tcx>(tcx: TyCtxt<'tcx>, cgu: &CodegenUnit<'tcx>) -> CguReuse {
+    if !tcx.dep_graph.is_fully_enabled() {
+        return CguReuse::No;
+    }
+
+    let work_product_id = &cgu.work_product_id();
+    if tcx.dep_graph.previous_work_product(work_product_id).is_none() {
+        // We don't have anything cached for this CGU. This can happen
+        // if the CGU did not exist in the previous session.
+        return CguReuse::No;
+    }
+
+    // Try to mark the CGU as green. If it we can do so, it means that nothing
+    // affecting the LLVM module has changed and we can re-use a cached version.
+    // If we compile with any kind of LTO, this means we can re-use the bitcode
+    // of the Pre-LTO stage (possibly also the Post-LTO version but we'll only
+    // know that later). If we are not doing LTO, there is only one optimized
+    // version of each module, so we re-use that.
+    let dep_node = cgu.codegen_dep_node(tcx);
+    assert!(
+        !tcx.dep_graph.dep_node_exists(&dep_node),
+        "CompileCodegenUnit dep-node for CGU `{}` already exists before marking.",
+        cgu.name()
+    );
+
+    if tcx.try_mark_green(&dep_node) { CguReuse::PreLto } else { CguReuse::No }
+}
diff --git a/compiler/rustc_codegen_cranelift/src/driver/jit.rs b/compiler/rustc_codegen_cranelift/src/driver/jit.rs
new file mode 100644
index 000000000..a56a91000
--- /dev/null
+++ b/compiler/rustc_codegen_cranelift/src/driver/jit.rs
@@ -0,0 +1,385 @@
+//! The JIT driver uses [`cranelift_jit`] to JIT execute programs without writing any object
+//! files.
+
+use std::cell::RefCell;
+use std::ffi::CString;
+use std::os::raw::{c_char, c_int};
+use std::sync::{mpsc, Mutex};
+
+use rustc_codegen_ssa::CrateInfo;
+use rustc_middle::mir::mono::MonoItem;
+use rustc_session::Session;
+use rustc_span::Symbol;
+
+use cranelift_jit::{JITBuilder, JITModule};
+
+// FIXME use std::sync::OnceLock once it stabilizes
+use once_cell::sync::OnceCell;
+
+use crate::{prelude::*, BackendConfig};
+use crate::{CodegenCx, CodegenMode};
+
+struct JitState {
+    backend_config: BackendConfig,
+    jit_module: JITModule,
+}
+
+thread_local! {
+    static LAZY_JIT_STATE: RefCell<Option<JitState>> = const { RefCell::new(None) };
+}
+
+/// The Sender owned by the rustc thread
+static GLOBAL_MESSAGE_SENDER: OnceCell<Mutex<mpsc::Sender<UnsafeMessage>>> = OnceCell::new();
+
+/// A message that is sent from the jitted runtime to the rustc thread.
+/// Senders are responsible for upholding `Send` semantics.
+enum UnsafeMessage {
+    /// Request that the specified `Instance` be lazily jitted.
+    ///
+    /// Nothing accessible through `instance_ptr` may be moved or mutated by the sender after
+    /// this message is sent.
+    JitFn {
+        instance_ptr: *const Instance<'static>,
+        trampoline_ptr: *const u8,
+        tx: mpsc::Sender<*const u8>,
+    },
+}
+unsafe impl Send for UnsafeMessage {}
+
+impl UnsafeMessage {
+    /// Send the message.
+    fn send(self) -> Result<(), mpsc::SendError<UnsafeMessage>> {
+        thread_local! {
+            /// The Sender owned by the local thread
+            static LOCAL_MESSAGE_SENDER: mpsc::Sender<UnsafeMessage> =
+                GLOBAL_MESSAGE_SENDER
+                    .get().unwrap()
+                    .lock().unwrap()
+                    .clone();
+        }
+        LOCAL_MESSAGE_SENDER.with(|sender| sender.send(self))
+    }
+}
+
+fn create_jit_module<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    backend_config: &BackendConfig,
+    hotswap: bool,
+) -> (JITModule, CodegenCx<'tcx>) {
+    let crate_info = CrateInfo::new(tcx, "dummy_target_cpu".to_string());
+    let imported_symbols = load_imported_symbols_for_jit(tcx.sess, crate_info);
+
+    let isa = crate::build_isa(tcx.sess, backend_config);
+    let mut jit_builder = JITBuilder::with_isa(isa, cranelift_module::default_libcall_names());
+    jit_builder.hotswap(hotswap);
+    crate::compiler_builtins::register_functions_for_jit(&mut jit_builder);
+    jit_builder.symbols(imported_symbols);
+    jit_builder.symbol("__clif_jit_fn", clif_jit_fn as *const u8);
+    let mut jit_module = JITModule::new(jit_builder);
+
+    let mut cx = crate::CodegenCx::new(
+        tcx,
+        backend_config.clone(),
+        jit_module.isa(),
+        false,
+        Symbol::intern("dummy_cgu_name"),
+    );
+
+    crate::allocator::codegen(tcx, &mut jit_module, &mut cx.unwind_context);
+    crate::main_shim::maybe_create_entry_wrapper(
+        tcx,
+        &mut jit_module,
+        &mut cx.unwind_context,
+        true,
+        true,
+    );
+
+    (jit_module, cx)
+}
+
+pub(crate) fn run_jit(tcx: TyCtxt<'_>, backend_config: BackendConfig) -> ! {
+    if !tcx.sess.opts.output_types.should_codegen() {
+        tcx.sess.fatal("JIT mode doesn't work with `cargo check`");
+    }
+
+    if !tcx.sess.crate_types().contains(&rustc_session::config::CrateType::Executable) {
+        tcx.sess.fatal("can't jit non-executable crate");
+    }
+
+    let (mut jit_module, mut cx) = create_jit_module(
+        tcx,
+        &backend_config,
+        matches!(backend_config.codegen_mode, CodegenMode::JitLazy),
+    );
+
+    let (_, cgus) = tcx.collect_and_partition_mono_items(());
+    let mono_items = cgus
+        .iter()
+        .map(|cgu| cgu.items_in_deterministic_order(tcx).into_iter())
+        .flatten()
+        .collect::<FxHashMap<_, (_, _)>>()
+        .into_iter()
+        .collect::<Vec<(_, (_, _))>>();
+
+    super::time(tcx, backend_config.display_cg_time, "codegen mono items", || {
+        super::predefine_mono_items(tcx, &mut jit_module, &mono_items);
+        for (mono_item, _) in mono_items {
+            match mono_item {
+                MonoItem::Fn(inst) => match backend_config.codegen_mode {
+                    CodegenMode::Aot => unreachable!(),
+                    CodegenMode::Jit => {
+                        cx.tcx.sess.time("codegen fn", || {
+                            crate::base::codegen_fn(&mut cx, &mut jit_module, inst)
+                        });
+                    }
+                    CodegenMode::JitLazy => codegen_shim(&mut cx, &mut jit_module, inst),
+                },
+                MonoItem::Static(def_id) => {
+                    crate::constant::codegen_static(tcx, &mut jit_module, def_id);
+                }
+                MonoItem::GlobalAsm(item_id) => {
+                    let item = tcx.hir().item(item_id);
+                    tcx.sess.span_fatal(item.span, "Global asm is not supported in JIT mode");
+                }
+            }
+        }
+    });
+
+    if !cx.global_asm.is_empty() {
+        tcx.sess.fatal("Inline asm is not supported in JIT mode");
+    }
+
+    tcx.sess.abort_if_errors();
+
+    jit_module.finalize_definitions();
+    unsafe { cx.unwind_context.register_jit(&jit_module) };
+
+    println!(
+        "Rustc codegen cranelift will JIT run the executable, because -Cllvm-args=mode=jit was passed"
+    );
+
+    let args = std::iter::once(&*tcx.crate_name(LOCAL_CRATE).as_str().to_string())
+        .chain(backend_config.jit_args.iter().map(|arg| &**arg))
+        .map(|arg| CString::new(arg).unwrap())
+        .collect::<Vec<_>>();
+
+    let start_sig = Signature {
+        params: vec![
+            AbiParam::new(jit_module.target_config().pointer_type()),
+            AbiParam::new(jit_module.target_config().pointer_type()),
+        ],
+        returns: vec![AbiParam::new(jit_module.target_config().pointer_type() /*isize*/)],
+        call_conv: jit_module.target_config().default_call_conv,
+    };
+    let start_func_id = jit_module.declare_function("main", Linkage::Import, &start_sig).unwrap();
+    let finalized_start: *const u8 = jit_module.get_finalized_function(start_func_id);
+
+    LAZY_JIT_STATE.with(|lazy_jit_state| {
+        let mut lazy_jit_state = lazy_jit_state.borrow_mut();
+        assert!(lazy_jit_state.is_none());
+        *lazy_jit_state = Some(JitState { backend_config, jit_module });
+    });
+
+    let f: extern "C" fn(c_int, *const *const c_char) -> c_int =
+        unsafe { ::std::mem::transmute(finalized_start) };
+
+    let (tx, rx) = mpsc::channel();
+    GLOBAL_MESSAGE_SENDER.set(Mutex::new(tx)).unwrap();
+
+    // Spawn the jitted runtime in a new thread so that this rustc thread can handle messages
+    // (eg to lazily JIT further functions as required)
+    std::thread::spawn(move || {
+        let mut argv = args.iter().map(|arg| arg.as_ptr()).collect::<Vec<_>>();
+
+        // Push a null pointer as a terminating argument. This is required by POSIX and
+        // useful as some dynamic linkers use it as a marker to jump over.
+        argv.push(std::ptr::null());
+
+        let ret = f(args.len() as c_int, argv.as_ptr());
+        std::process::exit(ret);
+    });
+
+    // Handle messages
+    loop {
+        match rx.recv().unwrap() {
+            // lazy JIT compilation request - compile requested instance and return pointer to result
+            UnsafeMessage::JitFn { instance_ptr, trampoline_ptr, tx } => {
+                tx.send(jit_fn(instance_ptr, trampoline_ptr))
+                    .expect("jitted runtime hung up before response to lazy JIT request was sent");
+            }
+        }
+    }
+}
+
+extern "C" fn clif_jit_fn(
+    instance_ptr: *const Instance<'static>,
+    trampoline_ptr: *const u8,
+) -> *const u8 {
+    // send the JIT request to the rustc thread, with a channel for the response
+    let (tx, rx) = mpsc::channel();
+    UnsafeMessage::JitFn { instance_ptr, trampoline_ptr, tx }
+        .send()
+        .expect("rustc thread hung up before lazy JIT request was sent");
+
+    // block on JIT compilation result
+    rx.recv().expect("rustc thread hung up before responding to sent lazy JIT request")
+}
+
+fn jit_fn(instance_ptr: *const Instance<'static>, trampoline_ptr: *const u8) -> *const u8 {
+    rustc_middle::ty::tls::with(|tcx| {
+        // lift is used to ensure the correct lifetime for instance.
+        let instance = tcx.lift(unsafe { *instance_ptr }).unwrap();
+
+        LAZY_JIT_STATE.with(|lazy_jit_state| {
+            let mut lazy_jit_state = lazy_jit_state.borrow_mut();
+            let lazy_jit_state = lazy_jit_state.as_mut().unwrap();
+            let jit_module = &mut lazy_jit_state.jit_module;
+            let backend_config = lazy_jit_state.backend_config.clone();
+
+            let name = tcx.symbol_name(instance).name;
+            let sig = crate::abi::get_function_sig(tcx, jit_module.isa().triple(), instance);
+            let func_id = jit_module.declare_function(name, Linkage::Export, &sig).unwrap();
+
+            let current_ptr = jit_module.read_got_entry(func_id);
+
+            // If the function's GOT entry has already been updated to point at something other
+            // than the shim trampoline, don't re-jit but just return the new pointer instead.
+            // This does not need synchronization as this code is executed only by a sole rustc
+            // thread.
+            if current_ptr != trampoline_ptr {
+                return current_ptr;
+            }
+
+            jit_module.prepare_for_function_redefine(func_id).unwrap();
+
+            let mut cx = crate::CodegenCx::new(
+                tcx,
+                backend_config,
+                jit_module.isa(),
+                false,
+                Symbol::intern("dummy_cgu_name"),
+            );
+            tcx.sess.time("codegen fn", || crate::base::codegen_fn(&mut cx, jit_module, instance));
+
+            assert!(cx.global_asm.is_empty());
+            jit_module.finalize_definitions();
+            unsafe { cx.unwind_context.register_jit(&jit_module) };
+            jit_module.get_finalized_function(func_id)
+        })
+    })
+}
+
+fn load_imported_symbols_for_jit(
+    sess: &Session,
+    crate_info: CrateInfo,
+) -> Vec<(String, *const u8)> {
+    use rustc_middle::middle::dependency_format::Linkage;
+
+    let mut dylib_paths = Vec::new();
+
+    let data = &crate_info
+        .dependency_formats
+        .iter()
+        .find(|(crate_type, _data)| *crate_type == rustc_session::config::CrateType::Executable)
+        .unwrap()
+        .1;
+    for &cnum in &crate_info.used_crates {
+        let src = &crate_info.used_crate_source[&cnum];
+        match data[cnum.as_usize() - 1] {
+            Linkage::NotLinked | Linkage::IncludedFromDylib => {}
+            Linkage::Static => {
+                let name = crate_info.crate_name[&cnum];
+                let mut err = sess.struct_err(&format!("Can't load static lib {}", name));
+                err.note("rustc_codegen_cranelift can only load dylibs in JIT mode.");
+                err.emit();
+            }
+            Linkage::Dynamic => {
+                dylib_paths.push(src.dylib.as_ref().unwrap().0.clone());
+            }
+        }
+    }
+
+    let mut imported_symbols = Vec::new();
+    for path in dylib_paths {
+        use object::{Object, ObjectSymbol};
+        let lib = libloading::Library::new(&path).unwrap();
+        let obj = std::fs::read(path).unwrap();
+        let obj = object::File::parse(&*obj).unwrap();
+        imported_symbols.extend(obj.dynamic_symbols().filter_map(|symbol| {
+            let name = symbol.name().unwrap().to_string();
+            if name.is_empty() || !symbol.is_global() || symbol.is_undefined() {
+                return None;
+            }
+            if name.starts_with("rust_metadata_") {
+                // The metadata is part of a section that is not loaded by the dynamic linker in
+                // case of cg_llvm.
+                return None;
+            }
+            let dlsym_name = if cfg!(target_os = "macos") {
+                // On macOS `dlsym` expects the name without leading `_`.
+                assert!(name.starts_with('_'), "{:?}", name);
+                &name[1..]
+            } else {
+                &name
+            };
+            let symbol: libloading::Symbol<'_, *const u8> =
+                unsafe { lib.get(dlsym_name.as_bytes()) }.unwrap();
+            Some((name, *symbol))
+        }));
+        std::mem::forget(lib)
+    }
+
+    sess.abort_if_errors();
+
+    imported_symbols
+}
+
+fn codegen_shim<'tcx>(cx: &mut CodegenCx<'tcx>, module: &mut JITModule, inst: Instance<'tcx>) {
+    let tcx = cx.tcx;
+
+    let pointer_type = module.target_config().pointer_type();
+
+    let name = tcx.symbol_name(inst).name;
+    let sig = crate::abi::get_function_sig(tcx, module.isa().triple(), inst);
+    let func_id = module.declare_function(name, Linkage::Export, &sig).unwrap();
+
+    let instance_ptr = Box::into_raw(Box::new(inst));
+
+    let jit_fn = module
+        .declare_function(
+            "__clif_jit_fn",
+            Linkage::Import,
+            &Signature {
+                call_conv: module.target_config().default_call_conv,
+                params: vec![AbiParam::new(pointer_type), AbiParam::new(pointer_type)],
+                returns: vec![AbiParam::new(pointer_type)],
+            },
+        )
+        .unwrap();
+
+    cx.cached_context.clear();
+    let trampoline = &mut cx.cached_context.func;
+    trampoline.signature = sig.clone();
+
+    let mut builder_ctx = FunctionBuilderContext::new();
+    let mut trampoline_builder = FunctionBuilder::new(trampoline, &mut builder_ctx);
+
+    let trampoline_fn = module.declare_func_in_func(func_id, trampoline_builder.func);
+    let jit_fn = module.declare_func_in_func(jit_fn, trampoline_builder.func);
+    let sig_ref = trampoline_builder.func.import_signature(sig);
+
+    let entry_block = trampoline_builder.create_block();
+    trampoline_builder.append_block_params_for_function_params(entry_block);
+    let fn_args = trampoline_builder.func.dfg.block_params(entry_block).to_vec();
+
+    trampoline_builder.switch_to_block(entry_block);
+    let instance_ptr = trampoline_builder.ins().iconst(pointer_type, instance_ptr as u64 as i64);
+    let trampoline_ptr = trampoline_builder.ins().func_addr(pointer_type, trampoline_fn);
+    let jitted_fn = trampoline_builder.ins().call(jit_fn, &[instance_ptr, trampoline_ptr]);
+    let jitted_fn = trampoline_builder.func.dfg.inst_results(jitted_fn)[0];
+    let call_inst = trampoline_builder.ins().call_indirect(sig_ref, jitted_fn, &fn_args);
+    let ret_vals = trampoline_builder.func.dfg.inst_results(call_inst).to_vec();
+    trampoline_builder.ins().return_(&ret_vals);
+
+    module.define_function(func_id, &mut cx.cached_context).unwrap();
+}
diff --git a/compiler/rustc_codegen_cranelift/src/driver/mod.rs b/compiler/rustc_codegen_cranelift/src/driver/mod.rs
new file mode 100644
index 000000000..8f5714ecb
--- /dev/null
+++ b/compiler/rustc_codegen_cranelift/src/driver/mod.rs
@@ -0,0 +1,53 @@
+//! Drivers are responsible for calling [`codegen_fn`] or [`codegen_static`] for each mono item and
+//! performing any further actions like JIT executing or writing object files.
+//!
+//! [`codegen_fn`]: crate::base::codegen_fn
+//! [`codegen_static`]: crate::constant::codegen_static
+
+use rustc_middle::mir::mono::{Linkage as RLinkage, MonoItem, Visibility};
+
+use crate::prelude::*;
+
+pub(crate) mod aot;
+#[cfg(feature = "jit")]
+pub(crate) mod jit;
+
+fn predefine_mono_items<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    module: &mut dyn Module,
+    mono_items: &[(MonoItem<'tcx>, (RLinkage, Visibility))],
+) {
+    tcx.sess.time("predefine functions", || {
+        let is_compiler_builtins = tcx.is_compiler_builtins(LOCAL_CRATE);
+        for &(mono_item, (linkage, visibility)) in mono_items {
+            match mono_item {
+                MonoItem::Fn(instance) => {
+                    let name = tcx.symbol_name(instance).name;
+                    let _inst_guard = crate::PrintOnPanic(|| format!("{:?} {}", instance, name));
+                    let sig = get_function_sig(tcx, module.isa().triple(), instance);
+                    let linkage = crate::linkage::get_clif_linkage(
+                        mono_item,
+                        linkage,
+                        visibility,
+                        is_compiler_builtins,
+                    );
+                    module.declare_function(name, linkage, &sig).unwrap();
+                }
+                MonoItem::Static(_) | MonoItem::GlobalAsm(_) => {}
+            }
+        }
+    });
+}
+
+fn time<R>(tcx: TyCtxt<'_>, display: bool, name: &'static str, f: impl FnOnce() -> R) -> R {
+    if display {
+        println!("[{:<30}: {}] start", tcx.crate_name(LOCAL_CRATE), name);
+        let before = std::time::Instant::now();
+        let res = tcx.sess.time(name, f);
+        let after = std::time::Instant::now();
+        println!("[{:<30}: {}] end time: {:?}", tcx.crate_name(LOCAL_CRATE), name, after - before);
+        res
+    } else {
+        tcx.sess.time(name, f)
+    }
+}