rust/src/driver/aot.rs

//! The AOT driver uses [`cranelift_object`] to write object files suitable for linking into a
//! standalone executable.

use std::sync::Arc;

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::global_asm::GlobalAsmConfig;
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
    }
}

pub(crate) struct OngoingCodegen {
    modules: Vec<ModuleCodegenResult>,
    allocator_module: Option<CompiledModule>,
    metadata_module: Option<CompiledModule>,
    metadata: EncodedMetadata,
    crate_info: CrateInfo,
    work_products: FxHashMap<WorkProductId, WorkProduct>,
}

impl OngoingCodegen {
    pub(crate) fn join(self) -> (CodegenResults, FxHashMap<WorkProductId, WorkProduct>) {
        let mut work_products = self.work_products;
        let mut modules = vec![];

        for module_codegen_result in self.modules {
            let ModuleCodegenResult(module, work_product) = module_codegen_result;
            if let Some((work_product_id, work_product)) = work_product {
                work_products.insert(work_product_id, work_product);
            }
            modules.push(module);
        }

        (
            CodegenResults {
                modules,
                allocator_module: self.allocator_module,
                metadata_module: self.metadata_module,
                metadata: self.metadata,
                crate_info: self.crate_info,
            },
            work_products,
        )
    }
}

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<'_>) -> ModuleCodegenResult {
    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
        ));
    }

    ModuleCodegenResult(
        CompiledModule {
            name: cgu.name().to_string(),
            kind: ModuleKind::Regular,
            object: Some(obj_out),
            dwarf_object: None,
            bytecode: None,
        },
        Some((cgu.work_product_id(), work_product)),
    )
}

fn module_codegen(
    tcx: TyCtxt<'_>,
    (backend_config, global_asm_config, cgu_name): (
        BackendConfig,
        Arc<GlobalAsmConfig>,
        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);
    let mut cached_context = Context::new();
    for (mono_item, _) in mono_items {
        match mono_item {
            MonoItem::Fn(inst) => {
                cx.tcx.sess.time("codegen fn", || {
                    crate::base::codegen_and_compile_fn(
                        &mut cx,
                        &mut cached_context,
                        &mut module,
                        inst,
                    )
                });
            }
            MonoItem::Static(def_id) => crate::constant::codegen_static(tcx, &mut module, def_id),
            MonoItem::GlobalAsm(item_id) => {
                crate::global_asm::codegen_global_asm_item(tcx, &mut cx.global_asm, item_id);
            }
        }
    }
    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,
        )
    });

    match crate::global_asm::compile_global_asm(
        &global_asm_config,
        cgu.name().as_str(),
        &cx.global_asm,
    ) {
        Ok(()) => {}
        Err(err) => tcx.sess.fatal(&err),
    }

    codegen_result
}

pub(crate) fn run_aot(
    tcx: TyCtxt<'_>,
    backend_config: BackendConfig,
    metadata: EncodedMetadata,
    need_metadata_module: bool,
) -> Box<OngoingCodegen> {
    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 global_asm_config = Arc::new(crate::global_asm::GlobalAsmConfig::new(tcx));

    let modules = super::time(tcx, backend_config.display_cg_time, "codegen mono items", || {
        cgus.iter()
            .map(|cgu| {
                let cgu_reuse = if backend_config.disable_incr_cache {
                    CguReuse::No
                } else {
                    determine_cgu_reuse(tcx, cgu)
                };
                tcx.sess.cgu_reuse_tracker.set_actual_reuse(cgu.name().as_str(), cgu_reuse);

                match cgu_reuse {
                    CguReuse::No => {
                        let dep_node = cgu.codegen_dep_node(tcx);
                        tcx.dep_graph
                            .with_task(
                                dep_node,
                                tcx,
                                (backend_config.clone(), global_asm_config.clone(), cgu.name()),
                                module_codegen,
                                Some(rustc_middle::dep_graph::hash_result),
                            )
                            .0
                    }
                    CguReuse::PreLto => reuse_workproduct_for_cgu(tcx, &*cgu),
                    CguReuse::PostLto => unreachable!(),
                }
            })
            .collect::<Vec<_>>()
    });

    tcx.sess.abort_if_errors();

    let mut work_products = FxHashMap::default();

    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(OngoingCodegen {
        modules,
        allocator_module,
        metadata_module,
        metadata,
        crate_info: CrateInfo::new(tcx, target_cpu),
        work_products,
    })
}

// 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 }
}