use super::link::{self, remove}; use super::linker::LinkerInfo; use super::lto::{self, SerializedModule}; use super::symbol_export::symbol_name_for_instance_in_crate; use crate::{ CachedModuleCodegen, CodegenResults, CompiledModule, CrateInfo, ModuleCodegen, ModuleKind, }; use crate::traits::*; use jobserver::{Acquired, Client}; use rustc_data_structures::fx::FxHashMap; use rustc_data_structures::profiling::SelfProfilerRef; use rustc_data_structures::profiling::TimingGuard; use rustc_data_structures::profiling::VerboseTimingGuard; use rustc_data_structures::sync::Lrc; use rustc_errors::emitter::Emitter; use rustc_errors::{DiagnosticId, FatalError, Handler, Level}; use rustc_fs_util::link_or_copy; use rustc_hir::def_id::{CrateNum, LOCAL_CRATE}; use rustc_incremental::{ copy_cgu_workproduct_to_incr_comp_cache_dir, in_incr_comp_dir, in_incr_comp_dir_sess, }; use rustc_middle::dep_graph::{WorkProduct, WorkProductId}; use rustc_middle::middle::cstore::EncodedMetadata; use rustc_middle::middle::exported_symbols::SymbolExportLevel; use rustc_middle::ty::TyCtxt; use rustc_session::cgu_reuse_tracker::CguReuseTracker; use rustc_session::config::{self, CrateType, Lto, OutputFilenames, OutputType}; use rustc_session::config::{Passes, SanitizerSet, SwitchWithOptPath}; use rustc_session::Session; use rustc_span::source_map::SourceMap; use rustc_span::symbol::{sym, Symbol}; use rustc_span::{BytePos, FileName, InnerSpan, Pos, Span}; use rustc_target::spec::{MergeFunctions, PanicStrategy}; use std::any::Any; use std::fs; use std::io; use std::mem; use std::path::{Path, PathBuf}; use std::str; use std::sync::mpsc::{channel, Receiver, Sender}; use std::sync::Arc; use std::thread; const PRE_LTO_BC_EXT: &str = "pre-lto.bc"; /// What kind of object file to emit. #[derive(Clone, Copy, PartialEq)] pub enum EmitObj { // No object file. None, // Just uncompressed llvm bitcode. Provides easy compatibility with // emscripten's ecc compiler, when used as the linker. Bitcode, // Object code, possibly augmented with a bitcode section. ObjectCode(BitcodeSection), } /// What kind of llvm bitcode section to embed in an object file. #[derive(Clone, Copy, PartialEq)] pub enum BitcodeSection { // No bitcode section. None, // A full, uncompressed bitcode section. Full, } /// Module-specific configuration for `optimize_and_codegen`. pub struct ModuleConfig { /// Names of additional optimization passes to run. pub passes: Vec, /// Some(level) to optimize at a certain level, or None to run /// absolutely no optimizations (used for the metadata module). pub opt_level: Option, /// Some(level) to optimize binary size, or None to not affect program size. pub opt_size: Option, pub pgo_gen: SwitchWithOptPath, pub pgo_use: Option, pub sanitizer: SanitizerSet, pub sanitizer_recover: SanitizerSet, pub sanitizer_memory_track_origins: usize, // Flags indicating which outputs to produce. pub emit_pre_lto_bc: bool, pub emit_no_opt_bc: bool, pub emit_bc: bool, pub emit_ir: bool, pub emit_asm: bool, pub emit_obj: EmitObj, pub bc_cmdline: String, // 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_module: bool, pub vectorize_loop: bool, pub vectorize_slp: bool, pub merge_functions: bool, pub inline_threshold: Option, pub new_llvm_pass_manager: bool, pub emit_lifetime_markers: bool, } impl ModuleConfig { fn new( kind: ModuleKind, sess: &Session, no_builtins: bool, is_compiler_builtins: bool, ) -> ModuleConfig { // If it's a regular module, use `$regular`, otherwise use `$other`. // `$regular` and `$other` are evaluated lazily. macro_rules! if_regular { ($regular: expr, $other: expr) => { if let ModuleKind::Regular = kind { $regular } else { $other } }; } let opt_level_and_size = if_regular!(Some(sess.opts.optimize), None); let save_temps = sess.opts.cg.save_temps; let should_emit_obj = sess.opts.output_types.contains_key(&OutputType::Exe) || match kind { ModuleKind::Regular => sess.opts.output_types.contains_key(&OutputType::Object), ModuleKind::Allocator => false, ModuleKind::Metadata => sess.opts.output_types.contains_key(&OutputType::Metadata), }; let emit_obj = if !should_emit_obj { EmitObj::None } else if sess.target.obj_is_bitcode || (sess.opts.cg.linker_plugin_lto.enabled() && !no_builtins) { // This case is selected if the target uses objects as bitcode, or // if linker plugin LTO is enabled. In the linker plugin LTO case // the assumption is that the final link-step will read the bitcode // and convert it to object code. This may be done by either the // native linker or rustc itself. // // Note, however, that the linker-plugin-lto requested here is // explicitly ignored for `#![no_builtins]` crates. These crates are // specifically ignored by rustc's LTO passes and wouldn't work if // loaded into the linker. These crates define symbols that LLVM // lowers intrinsics to, and these symbol dependencies aren't known // until after codegen. As a result any crate marked // `#![no_builtins]` is assumed to not participate in LTO and // instead goes on to generate object code. EmitObj::Bitcode } else if need_bitcode_in_object(sess) { EmitObj::ObjectCode(BitcodeSection::Full) } else { EmitObj::ObjectCode(BitcodeSection::None) }; ModuleConfig { passes: if_regular!( { let mut passes = sess.opts.cg.passes.clone(); // compiler_builtins overrides the codegen-units settings, // which is incompatible with -Zprofile which requires that // only a single codegen unit is used per crate. if sess.opts.debugging_opts.profile && !is_compiler_builtins { passes.push("insert-gcov-profiling".to_owned()); } // The rustc option `-Zinstrument_coverage` injects intrinsic calls to // `llvm.instrprof.increment()`, which requires the LLVM `instrprof` pass. if sess.opts.debugging_opts.instrument_coverage { passes.push("instrprof".to_owned()); } passes }, vec![] ), opt_level: opt_level_and_size, opt_size: opt_level_and_size, pgo_gen: if_regular!( sess.opts.cg.profile_generate.clone(), SwitchWithOptPath::Disabled ), pgo_use: if_regular!(sess.opts.cg.profile_use.clone(), None), sanitizer: if_regular!(sess.opts.debugging_opts.sanitizer, SanitizerSet::empty()), sanitizer_recover: if_regular!( sess.opts.debugging_opts.sanitizer_recover, SanitizerSet::empty() ), sanitizer_memory_track_origins: if_regular!( sess.opts.debugging_opts.sanitizer_memory_track_origins, 0 ), emit_pre_lto_bc: if_regular!( save_temps || need_pre_lto_bitcode_for_incr_comp(sess), false ), emit_no_opt_bc: if_regular!(save_temps, false), emit_bc: if_regular!( save_temps || sess.opts.output_types.contains_key(&OutputType::Bitcode), save_temps ), emit_ir: if_regular!( sess.opts.output_types.contains_key(&OutputType::LlvmAssembly), false ), emit_asm: if_regular!( sess.opts.output_types.contains_key(&OutputType::Assembly), false ), emit_obj, bc_cmdline: sess.target.bitcode_llvm_cmdline.clone(), verify_llvm_ir: sess.verify_llvm_ir(), no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes, no_builtins: no_builtins || sess.target.no_builtins, // Exclude metadata and allocator modules from time_passes output, // since they throw off the "LLVM passes" measurement. time_module: if_regular!(true, false), // Copy what clang does by turning on loop vectorization at O2 and // slp vectorization at O3. vectorize_loop: !sess.opts.cg.no_vectorize_loops && (sess.opts.optimize == config::OptLevel::Default || sess.opts.optimize == config::OptLevel::Aggressive), vectorize_slp: !sess.opts.cg.no_vectorize_slp && sess.opts.optimize == config::OptLevel::Aggressive, // Some targets (namely, NVPTX) interact badly with the // MergeFunctions pass. This is because MergeFunctions can generate // new function calls which may interfere with the target calling // convention; e.g. for the NVPTX target, PTX kernels should not // call other PTX kernels. MergeFunctions can also be configured to // generate aliases instead, but aliases are not supported by some // backends (again, NVPTX). Therefore, allow targets to opt out of // the MergeFunctions pass, but otherwise keep the pass enabled (at // O2 and O3) since it can be useful for reducing code size. merge_functions: match sess .opts .debugging_opts .merge_functions .unwrap_or(sess.target.merge_functions) { MergeFunctions::Disabled => false, MergeFunctions::Trampolines | MergeFunctions::Aliases => { sess.opts.optimize == config::OptLevel::Default || sess.opts.optimize == config::OptLevel::Aggressive } }, inline_threshold: sess.opts.cg.inline_threshold, new_llvm_pass_manager: sess.opts.debugging_opts.new_llvm_pass_manager, emit_lifetime_markers: sess.emit_lifetime_markers(), } } pub fn bitcode_needed(&self) -> bool { self.emit_bc || self.emit_obj == EmitObj::Bitcode || self.emit_obj == EmitObj::ObjectCode(BitcodeSection::Full) } } /// Configuration passed to the function returned by the `target_machine_factory`. pub struct TargetMachineFactoryConfig { /// Split DWARF is enabled in LLVM by checking that `TM.MCOptions.SplitDwarfFile` isn't empty, /// so the path to the dwarf object has to be provided when we create the target machine. /// This can be ignored by backends which do not need it for their Split DWARF support. pub split_dwarf_file: Option, } impl TargetMachineFactoryConfig { pub fn new( cgcx: &CodegenContext, module_name: &str, ) -> TargetMachineFactoryConfig { let split_dwarf_file = if cgcx.target_can_use_split_dwarf { cgcx.output_filenames.split_dwarf_filename(cgcx.split_debuginfo, Some(module_name)) } else { None }; TargetMachineFactoryConfig { split_dwarf_file } } } pub type TargetMachineFactoryFn = Arc< dyn Fn(TargetMachineFactoryConfig) -> Result<::TargetMachine, String> + Send + Sync, >; pub type ExportedSymbols = FxHashMap>>; /// Additional resources used by optimize_and_codegen (not module specific) #[derive(Clone)] pub struct CodegenContext { // Resources needed when running LTO pub backend: B, pub prof: SelfProfilerRef, pub lto: Lto, pub no_landing_pads: bool, pub save_temps: bool, pub fewer_names: bool, pub exported_symbols: Option>, pub opts: Arc, pub crate_types: Vec, pub each_linked_rlib_for_lto: Vec<(CrateNum, PathBuf)>, pub output_filenames: Arc, pub regular_module_config: Arc, pub metadata_module_config: Arc, pub allocator_module_config: Arc, pub tm_factory: TargetMachineFactoryFn, pub msvc_imps_needed: bool, pub is_pe_coff: bool, pub target_can_use_split_dwarf: bool, pub target_pointer_width: u32, pub target_arch: String, pub debuginfo: config::DebugInfo, pub split_debuginfo: rustc_target::spec::SplitDebuginfo, // 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 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, // 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>, } impl CodegenContext { pub fn create_diag_handler(&self) -> Handler { Handler::with_emitter(true, None, 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( cgcx: &CodegenContext, needs_fat_lto: Vec>, needs_thin_lto: Vec<(String, B::ThinBuffer)>, import_only_modules: Vec<(SerializedModule, WorkProduct)>, ) -> Vec<(WorkItem, u64)> { let _prof_timer = cgcx.prof.generic_activity("codegen_generate_lto_work"); let (lto_modules, copy_jobs) = if !needs_fat_lto.is_empty() { assert!(needs_thin_lto.is_empty()); let lto_module = B::run_fat_lto(cgcx, needs_fat_lto, import_only_modules).unwrap_or_else(|e| e.raise()); (vec![lto_module], vec![]) } else { assert!(needs_fat_lto.is_empty()); B::run_thin_lto(cgcx, needs_thin_lto, import_only_modules).unwrap_or_else(|e| e.raise()) }; lto_modules .into_iter() .map(|module| { let cost = module.cost(); (WorkItem::LTO(module), cost) }) .chain(copy_jobs.into_iter().map(|wp| { ( WorkItem::CopyPostLtoArtifacts(CachedModuleCodegen { name: wp.cgu_name.clone(), source: wp, }), 0, ) })) .collect() } pub struct CompiledModules { pub modules: Vec, pub metadata_module: Option, pub allocator_module: Option, } fn need_bitcode_in_object(sess: &Session) -> bool { let requested_for_rlib = sess.opts.cg.embed_bitcode && sess.crate_types().contains(&CrateType::Rlib) && sess.opts.output_types.contains_key(&OutputType::Exe); let forced_by_target = sess.target.forces_embed_bitcode; requested_for_rlib || forced_by_target } fn need_pre_lto_bitcode_for_incr_comp(sess: &Session) -> bool { if sess.opts.incremental.is_none() { return false; } match sess.lto() { Lto::No => false, Lto::Fat | Lto::Thin | Lto::ThinLocal => true, } } pub fn start_async_codegen( backend: B, tcx: TyCtxt<'_>, metadata: EncodedMetadata, total_cgus: usize, ) -> OngoingCodegen { let (coordinator_send, coordinator_receive) = channel(); let sess = tcx.sess; let crate_name = tcx.crate_name(LOCAL_CRATE); let no_builtins = tcx.sess.contains_name(&tcx.hir().krate().item.attrs, sym::no_builtins); let is_compiler_builtins = tcx.sess.contains_name(&tcx.hir().krate().item.attrs, sym::compiler_builtins); let subsystem = tcx .sess .first_attr_value_str_by_name(&tcx.hir().krate().item.attrs, sym::windows_subsystem); let windows_subsystem = subsystem.map(|subsystem| { if subsystem != sym::windows && subsystem != sym::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); let regular_config = ModuleConfig::new(ModuleKind::Regular, sess, no_builtins, is_compiler_builtins); let metadata_config = ModuleConfig::new(ModuleKind::Metadata, sess, no_builtins, is_compiler_builtins); let allocator_config = ModuleConfig::new(ModuleKind::Allocator, sess, no_builtins, is_compiler_builtins); 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(), Arc::new(regular_config), Arc::new(metadata_config), Arc::new(allocator_config), coordinator_send.clone(), ); OngoingCodegen { backend, crate_name, metadata, windows_subsystem, linker_info, crate_info, coordinator_send, 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 { let mut work_products = FxHashMap::default(); if sess.opts.incremental.is_none() { return work_products; } let _timer = sess.timer("copy_all_cgu_workproducts_to_incr_comp_cache_dir"); for module in compiled_modules.modules.iter().filter(|m| m.kind == ModuleKind::Regular) { let path = module.object.as_ref().cloned(); if let Some((id, product)) = copy_cgu_workproduct_to_incr_comp_cache_dir(sess, &module.name, &path) { 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.dwarf_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 metadata_module) = compiled_modules.metadata_module { if let Some(ref path) = 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 enum WorkItem { /// Optimize a newly codegened, totally unoptimized module. Optimize(ModuleCodegen), /// Copy the post-LTO artifacts from the incremental cache to the output /// directory. CopyPostLtoArtifacts(CachedModuleCodegen), /// Performs (Thin)LTO on the given module. LTO(lto::LtoModuleCodegen), } impl WorkItem { pub fn module_kind(&self) -> ModuleKind { match *self { WorkItem::Optimize(ref m) => m.kind, WorkItem::CopyPostLtoArtifacts(_) | WorkItem::LTO(_) => ModuleKind::Regular, } } fn start_profiling<'a>(&self, cgcx: &'a CodegenContext) -> TimingGuard<'a> { match *self { WorkItem::Optimize(ref m) => { cgcx.prof.generic_activity_with_arg("codegen_module_optimize", &m.name[..]) } WorkItem::CopyPostLtoArtifacts(ref m) => cgcx .prof .generic_activity_with_arg("codegen_copy_artifacts_from_incr_cache", &m.name[..]), WorkItem::LTO(ref m) => { cgcx.prof.generic_activity_with_arg("codegen_module_perform_lto", m.name()) } } } } enum WorkItemResult { Compiled(CompiledModule), NeedsLink(ModuleCodegen), NeedsFatLTO(FatLTOInput), NeedsThinLTO(String, B::ThinBuffer), } pub enum FatLTOInput { Serialized { name: String, buffer: B::ModuleBuffer }, InMemory(ModuleCodegen), } fn execute_work_item( cgcx: &CodegenContext, work_item: WorkItem, ) -> Result, FatalError> { let module_config = cgcx.config(work_item.module_kind()); match work_item { WorkItem::Optimize(module) => execute_optimize_work_item(cgcx, module, module_config), WorkItem::CopyPostLtoArtifacts(module) => { execute_copy_from_cache_work_item(cgcx, module, module_config) } WorkItem::LTO(module) => execute_lto_work_item(cgcx, module, module_config), } } // Actual LTO type we end up choosing based on multiple factors. pub enum ComputedLtoType { No, Thin, Fat, } pub fn compute_per_cgu_lto_type( sess_lto: &Lto, opts: &config::Options, sess_crate_types: &[CrateType], module_kind: ModuleKind, ) -> ComputedLtoType { // Metadata modules never participate in LTO regardless of the lto // settings. if module_kind == ModuleKind::Metadata { return ComputedLtoType::No; } // 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. let linker_does_lto = opts.cg.linker_plugin_lto.enabled(); // 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. let is_allocator = module_kind == ModuleKind::Allocator; // We ignore a request for full crate grath LTO if the cate type // is only an rlib, as there is 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. let is_rlib = sess_crate_types.len() == 1 && sess_crate_types[0] == CrateType::Rlib; match sess_lto { Lto::ThinLocal if !linker_does_lto && !is_allocator => ComputedLtoType::Thin, Lto::Thin if !linker_does_lto && !is_rlib => ComputedLtoType::Thin, Lto::Fat if !is_rlib => ComputedLtoType::Fat, _ => ComputedLtoType::No, } } fn execute_optimize_work_item( cgcx: &CodegenContext, module: ModuleCodegen, module_config: &ModuleConfig, ) -> Result, FatalError> { let diag_handler = cgcx.create_diag_handler(); unsafe { B::optimize(cgcx, &diag_handler, &module, module_config)?; } // 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). let lto_type = compute_per_cgu_lto_type(&cgcx.lto, &cgcx.opts, &cgcx.crate_types, module.kind); // If we're doing some form of incremental LTO then we need to be sure to // save our module to disk first. let bitcode = if cgcx.config(module.kind).emit_pre_lto_bc { let filename = pre_lto_bitcode_filename(&module.name); cgcx.incr_comp_session_dir.as_ref().map(|path| path.join(&filename)) } else { None }; match lto_type { ComputedLtoType::No => finish_intra_module_work(cgcx, module, module_config), ComputedLtoType::Thin => { let (name, thin_buffer) = B::prepare_thin(module); if let Some(path) = bitcode { fs::write(&path, thin_buffer.data()).unwrap_or_else(|e| { panic!("Error writing pre-lto-bitcode file `{}`: {}", path.display(), e); }); } Ok(WorkItemResult::NeedsThinLTO(name, thin_buffer)) } ComputedLtoType::Fat => match bitcode { Some(path) => { let (name, buffer) = B::serialize_module(module); fs::write(&path, buffer.data()).unwrap_or_else(|e| { panic!("Error writing pre-lto-bitcode file `{}`: {}", path.display(), e); }); Ok(WorkItemResult::NeedsFatLTO(FatLTOInput::Serialized { name, buffer })) } None => Ok(WorkItemResult::NeedsFatLTO(FatLTOInput::InMemory(module))), }, } } fn execute_copy_from_cache_work_item( cgcx: &CodegenContext, module: CachedModuleCodegen, module_config: &ModuleConfig, ) -> Result, FatalError> { let incr_comp_session_dir = cgcx.incr_comp_session_dir.as_ref().unwrap(); let mut object = None; if let Some(saved_file) = module.source.saved_file { let obj_out = cgcx.output_filenames.temp_path(OutputType::Object, Some(&module.name)); object = Some(obj_out.clone()); 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 != EmitObj::None); Ok(WorkItemResult::Compiled(CompiledModule { name: module.name, kind: ModuleKind::Regular, object, dwarf_object: None, bytecode: None, })) } fn execute_lto_work_item( cgcx: &CodegenContext, mut module: lto::LtoModuleCodegen, module_config: &ModuleConfig, ) -> Result, FatalError> { let module = unsafe { module.optimize(cgcx)? }; finish_intra_module_work(cgcx, module, module_config) } fn finish_intra_module_work( cgcx: &CodegenContext, module: ModuleCodegen, module_config: &ModuleConfig, ) -> Result, FatalError> { let diag_handler = cgcx.create_diag_handler(); if !cgcx.opts.debugging_opts.combine_cgu || module.kind == ModuleKind::Metadata || module.kind == ModuleKind::Allocator { let module = unsafe { B::codegen(cgcx, &diag_handler, module, module_config)? }; Ok(WorkItemResult::Compiled(module)) } else { Ok(WorkItemResult::NeedsLink(module)) } } pub enum Message { Token(io::Result), NeedsFatLTO { result: FatLTOInput, worker_id: usize, }, NeedsThinLTO { name: String, thin_buffer: B::ThinBuffer, worker_id: usize, }, NeedsLink { module: ModuleCodegen, worker_id: usize, }, Done { result: Result>, 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, lvl: Level, } #[derive(PartialEq, Clone, Copy, Debug)] enum MainThreadWorkerState { Idle, Codegenning, LLVMing, } fn start_executing_work( backend: B, tcx: TyCtxt<'_>, crate_info: &CrateInfo, shared_emitter: SharedEmitter, codegen_worker_send: Sender>, coordinator_receive: Receiver>, total_cgus: usize, jobserver: Client, regular_config: Arc, metadata_config: Arc, allocator_config: Arc, tx_to_llvm_workers: Sender>, ) -> thread::JoinHandle> { let coordinator_send = tx_to_llvm_workers; 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)| (symbol_name_for_instance_in_crate(tcx, s, cnum), 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(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 ol = if tcx.sess.opts.debugging_opts.no_codegen || !tcx.sess.opts.output_types.should_codegen() { // If we know that we won’t be doing codegen, create target machines without optimisation. config::OptLevel::No } else { tcx.backend_optimization_level(LOCAL_CRATE) }; let cgcx = CodegenContext:: { backend: backend.clone(), crate_types: sess.crate_types().to_vec(), each_linked_rlib_for_lto, lto: sess.lto(), no_landing_pads: sess.panic_strategy() == PanicStrategy::Abort, fewer_names: sess.fewer_names(), save_temps: sess.opts.cg.save_temps, opts: Arc::new(sess.opts.clone()), prof: sess.prof.clone(), exported_symbols, 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(), output_filenames: tcx.output_filenames(LOCAL_CRATE), regular_module_config: regular_config, metadata_module_config: metadata_config, allocator_module_config: allocator_config, tm_factory: backend.target_machine_factory(tcx.sess, ol), total_cgus, msvc_imps_needed: msvc_imps_needed(tcx), is_pe_coff: tcx.sess.target.is_like_windows, target_can_use_split_dwarf: tcx.sess.target_can_use_split_dwarf(), target_pointer_width: tcx.sess.target.pointer_width, target_arch: tcx.sess.target.arch.clone(), debuginfo: tcx.sess.opts.debuginfo, split_debuginfo: tcx.sess.split_debuginfo(), }; // 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 || { let mut worker_id_counter = 0; let mut free_worker_ids = Vec::new(); let mut get_worker_id = |free_worker_ids: &mut Vec| { 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_link = Vec::new(); let mut needs_fat_lto = Vec::new(); let mut needs_thin_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 prof = &cgcx.prof; let mut llvm_start_time: Option> = 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.is_empty() && needs_fat_lto.is_empty() && needs_thin_lto.is_empty() && lto_import_only_modules.is_empty() && 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 { // Compute the number of workers that will be running once we've taken as many // items from the work queue as we can, plus one for the main thread. It's not // critically important that we use this instead of just `running`, but it // prevents the `queue_full_enough` heuristic from fluctuating just because a // worker finished up and we decreased the `running` count, even though we're // just going to increase it right after this when we put a new worker to work. let extra_tokens = tokens.len().checked_sub(running).unwrap(); let additional_running = std::cmp::min(extra_tokens, work_items.len()); let anticipated_running = running + additional_running + 1; if !queue_full_enough(work_items.len(), anticipated_running) { // The queue is not full enough, codegen more items: if codegen_worker_send.send(Message::CodegenItem).is_err() { 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( prof, 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.is_empty() && running == 0 && main_thread_worker_state == MainThreadWorkerState::Idle { assert!(!started_lto); started_lto = true; let needs_fat_lto = mem::take(&mut needs_fat_lto); let needs_thin_lto = mem::take(&mut needs_thin_lto); let import_only_modules = mem::take(&mut lto_import_only_modules); for (work, cost) in generate_lto_work(&cgcx, needs_fat_lto, needs_thin_lto, 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( prof, 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.is_empty() && running < tokens.len() { let (item, _) = work_items.pop().unwrap(); maybe_start_llvm_timer(prof, 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); // 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" let mut free_worker = |worker_id| { if main_thread_worker_state == MainThreadWorkerState::LLVMing { main_thread_worker_state = MainThreadWorkerState::Idle; } else { running -= 1; } free_worker_ids.push(worker_id); }; let msg = coordinator_receive.recv().unwrap(); match *msg.downcast::>().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); } Message::Done { result: Ok(compiled_module), worker_id } => { free_worker(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::NeedsLink { module, worker_id } => { free_worker(worker_id); needs_link.push(module); } Message::NeedsFatLTO { result, worker_id } => { assert!(!started_lto); free_worker(worker_id); needs_fat_lto.push(result); } Message::NeedsThinLTO { name, thin_buffer, worker_id } => { assert!(!started_lto); free_worker(worker_id); needs_thin_lto.push((name, thin_buffer)); } 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; } // If the thread failed that means it panicked, so we abort immediately. Message::Done { result: Err(None), worker_id: _ } => { bug!("worker thread panicked"); } Message::Done { result: Err(Some(WorkerFatalError)), worker_id: _ } => { return Err(()); } Message::CodegenItem => bug!("the coordinator should not receive codegen requests"), } } let needs_link = mem::take(&mut needs_link); if !needs_link.is_empty() { assert!(compiled_modules.is_empty()); let diag_handler = cgcx.create_diag_handler(); let module = B::run_link(&cgcx, &diag_handler, needs_link).map_err(|_| ())?; let module = unsafe { B::codegen(&cgcx, &diag_handler, module, cgcx.config(ModuleKind::Regular)) .map_err(|_| ())? }; compiled_modules.push(module); } // Drop to print timings drop(llvm_start_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)); 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) -> bool { // This heuristic scales ahead-of-time codegen according to available // concurrency, as measured by `workers_running`. The idea is that the // more concurrency we have available, the more demand there will be for // work items, and the fuller the queue should be kept to meet demand. // An important property of this approach is that we codegen ahead of // time only as much as necessary, so as to keep fewer LLVM modules in // memory at once, thereby reducing memory consumption. // // When the number of workers running is less than the max concurrency // available to us, this heuristic can cause us to instruct the main // thread to work on an LLVM item (that is, tell it to "LLVM") instead // of codegen, even though it seems like it *should* be codegenning so // that we can create more work items and spawn more LLVM workers. // // But this is not a problem. When the main thread is told to LLVM, // according to this heuristic and how work is scheduled, there is // always at least one item in the queue, and therefore at least one // pending jobserver token request. If there *is* more concurrency // available, we will immediately receive a token, which will upgrade // the main thread's LLVM worker to a real one (conceptually), and free // up the main thread to codegen if necessary. On the other hand, if // there isn't more concurrency, then the main thread working on an LLVM // item is appropriate, as long as the queue is full enough for demand. // // Speaking of which, how full should we keep the queue? Probably less // full than you'd think. A lot has to go wrong for the queue not to be // full enough and for that to have a negative effect on compile times. // // Workers are unlikely to finish at exactly the same time, so when one // finishes and takes another work item off the queue, we often have // ample time to codegen at that point before the next worker finishes. // But suppose that codegen takes so long that the workers exhaust the // queue, and we have one or more workers that have nothing to work on. // Well, it might not be so bad. Of all the LLVM modules we create and // optimize, one has to finish last. It's not necessarily the case that // by losing some concurrency for a moment, we delay the point at which // that last LLVM module is finished and the rest of compilation can // proceed. Also, when we can't take advantage of some concurrency, we // give tokens back to the job server. That enables some other rustc to // potentially make use of the available concurrency. That could even // *decrease* overall compile time if we're lucky. But yes, if no other // rustc can make use of the concurrency, then we've squandered it. // // However, keeping the queue full is also beneficial when we have a // surge in available concurrency. Then items can be taken from the // queue immediately, without having to wait for codegen. // // So, the heuristic below tries to keep one item in the queue for every // four running workers. Based on limited benchmarking, this appears to // be more than sufficient to avoid increasing compilation times. let quarter_of_workers = workers_running - 3 * workers_running / 4; items_in_queue > 0 && items_in_queue >= quarter_of_workers } fn maybe_start_llvm_timer<'a>( prof: &'a SelfProfilerRef, config: &ModuleConfig, llvm_start_time: &mut Option>, ) { if config.time_module && llvm_start_time.is_none() { *llvm_start_time = Some(prof.extra_verbose_generic_activity("LLVM_passes", "crate")); } } } /// `FatalError` is explicitly not `Send`. #[must_use] pub struct WorkerFatalError; fn spawn_work(cgcx: CodegenContext, work: WorkItem) { thread::spawn(move || { // Set up a destructor which will fire off a message that we're done as // we exit. struct Bomb { coordinator_send: Sender>, result: Option, FatalError>>, worker_id: usize, } impl Drop for Bomb { fn drop(&mut self) { let worker_id = self.worker_id; let msg = match self.result.take() { Some(Ok(WorkItemResult::Compiled(m))) => { Message::Done:: { result: Ok(m), worker_id } } Some(Ok(WorkItemResult::NeedsLink(m))) => { Message::NeedsLink:: { module: m, worker_id } } Some(Ok(WorkItemResult::NeedsFatLTO(m))) => { Message::NeedsFatLTO:: { result: m, worker_id } } Some(Ok(WorkItemResult::NeedsThinLTO(name, thin_buffer))) => { Message::NeedsThinLTO:: { name, thin_buffer, worker_id } } Some(Err(FatalError)) => { Message::Done:: { result: Err(Some(WorkerFatalError)), worker_id } } None => Message::Done:: { result: Err(None), 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 _prof_timer = work.start_profiling(&cgcx); Some(execute_work_item(&cgcx, work)) }; }); } enum SharedEmitterMessage { Diagnostic(Diagnostic), InlineAsmError(u32, String, Level, Option<(String, Vec)>), AbortIfErrors, Fatal(String), } #[derive(Clone)] pub struct SharedEmitter { sender: Sender, } pub struct SharedEmitterMain { receiver: Receiver, } 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, level: Level, source: Option<(String, Vec)>, ) { drop(self.sender.send(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source))); } pub fn fatal(&self, msg: &str) { drop(self.sender.send(SharedEmitterMessage::Fatal(msg.to_string()))); } } impl Emitter for SharedEmitter { fn emit_diagnostic(&mut self, diag: &rustc_errors::Diagnostic) { drop(self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic { msg: diag.message(), code: diag.code.clone(), lvl: diag.level, }))); for child in &diag.children { drop(self.sender.send(SharedEmitterMessage::Diagnostic(Diagnostic { msg: child.message(), code: None, lvl: child.level, }))); } drop(self.sender.send(SharedEmitterMessage::AbortIfErrors)); } fn source_map(&self) -> Option<&Lrc> { None } } 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(); let mut d = rustc_errors::Diagnostic::new(diag.lvl, &diag.msg); if let Some(code) = diag.code { d.code(code); } handler.emit_diagnostic(&d); } Ok(SharedEmitterMessage::InlineAsmError(cookie, msg, level, source)) => { let msg = msg.strip_prefix("error: ").unwrap_or(&msg); let mut err = match level { Level::Error => sess.struct_err(&msg), Level::Warning => sess.struct_warn(&msg), Level::Note => sess.struct_note_without_error(&msg), _ => bug!("Invalid inline asm diagnostic level"), }; // If the cookie is 0 then we don't have span information. if cookie != 0 { let pos = BytePos::from_u32(cookie); let span = Span::with_root_ctxt(pos, pos); err.set_span(span); }; // Point to the generated assembly if it is available. if let Some((buffer, spans)) = source { let source = sess .source_map() .new_source_file(FileName::inline_asm_source_code(&buffer), buffer); let source_span = Span::with_root_ctxt(source.start_pos, source.end_pos); let spans: Vec<_> = spans.iter().map(|sp| source_span.from_inner(*sp)).collect(); err.span_note(spans, "instantiated into assembly here"); } err.emit(); } Ok(SharedEmitterMessage::AbortIfErrors) => { sess.abort_if_errors(); } Ok(SharedEmitterMessage::Fatal(msg)) => { sess.fatal(&msg); } Err(_) => { break; } } } } } pub struct OngoingCodegen { pub backend: B, pub crate_name: Symbol, pub metadata: EncodedMetadata, pub windows_subsystem: Option, pub linker_info: LinkerInfo, pub crate_info: CrateInfo, pub coordinator_send: Sender>, pub codegen_worker_receive: Receiver>, pub shared_emitter_main: SharedEmitterMain, pub future: thread::JoinHandle>, pub output_filenames: Arc, } impl OngoingCodegen { pub fn join(self, sess: &Session) -> (CodegenResults, FxHashMap) { let _timer = sess.timer("finish_ongoing_codegen"); self.shared_emitter_main.check(sess, true); let future = self.future; let compiled_modules = sess.time("join_worker_thread", || match 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.diagnostic()); sess.abort_if_errors(); 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, 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, ) { self.wait_for_signal_to_codegen_item(); self.check_for_errors(tcx.sess); // These are generally cheap and won't throw off scheduling. let cost = 0; submit_codegened_module_to_llvm(&self.backend, &self.coordinator_send, 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::))); } /// Consumes 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. } } } } pub fn submit_codegened_module_to_llvm( _backend: &B, tx_to_llvm_workers: &Sender>, module: ModuleCodegen, cost: u64, ) { let llvm_work_item = WorkItem::Optimize(module); drop(tx_to_llvm_workers.send(Box::new(Message::CodegenDone:: { llvm_work_item, cost }))); } pub fn submit_post_lto_module_to_llvm( _backend: &B, tx_to_llvm_workers: &Sender>, module: CachedModuleCodegen, ) { let llvm_work_item = WorkItem::CopyPostLtoArtifacts(module); drop(tx_to_llvm_workers.send(Box::new(Message::CodegenDone:: { llvm_work_item, cost: 0 }))); } pub fn submit_pre_lto_module_to_llvm( _backend: &B, tcx: TyCtxt<'_>, tx_to_llvm_workers: &Sender>, 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(tx_to_llvm_workers.send(Box::new(Message::AddImportOnlyModule:: { module_data: SerializedModule::FromUncompressedFile(mmap), work_product: module.source, }))); } pub fn pre_lto_bitcode_filename(module_name: &str) -> String { format!("{}.{}", module_name, PRE_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.cg.linker_plugin_lto.enabled() && tcx.sess.target.is_like_windows && tcx.sess.opts.cg.prefer_dynamic) ); tcx.sess.target.is_like_windows && tcx.sess.crate_types().iter().any(|ct| *ct == 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 linker plugin LTO is enabled. !tcx.sess.opts.cg.linker_plugin_lto.enabled() }