use crate::back::write::{ self, save_temp_bitcode, to_llvm_opt_settings, with_llvm_pmb, DiagnosticHandlers, }; use crate::llvm::archive_ro::ArchiveRO; use crate::llvm::{self, False, True}; use crate::{LlvmCodegenBackend, ModuleLlvm}; use rustc_codegen_ssa::back::lto::{LtoModuleCodegen, SerializedModule, ThinModule, ThinShared}; use rustc_codegen_ssa::back::symbol_export; use rustc_codegen_ssa::back::write::{CodegenContext, FatLTOInput, ModuleConfig}; use rustc_codegen_ssa::traits::*; use rustc_codegen_ssa::{looks_like_rust_object_file, ModuleCodegen, ModuleKind}; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_errors::{FatalError, Handler}; use rustc_hir::def_id::LOCAL_CRATE; use rustc_middle::bug; use rustc_middle::dep_graph::WorkProduct; use rustc_middle::middle::exported_symbols::SymbolExportLevel; use rustc_session::cgu_reuse_tracker::CguReuse; use rustc_session::config::{self, CrateType, Lto}; use tracing::{debug, info}; use std::ffi::{CStr, CString}; use std::fs::File; use std::io; use std::mem; use std::path::Path; use std::ptr; use std::slice; use std::sync::Arc; /// We keep track of past LTO imports that were used to produce the current set /// of compiled object files that we might choose to reuse during this /// compilation session. pub const THIN_LTO_IMPORTS_INCR_COMP_FILE_NAME: &str = "thin-lto-past-imports.bin"; pub fn crate_type_allows_lto(crate_type: CrateType) -> bool { match crate_type { CrateType::Executable | CrateType::Staticlib | CrateType::Cdylib => true, CrateType::Dylib | CrateType::Rlib | CrateType::ProcMacro => false, } } fn prepare_lto( cgcx: &CodegenContext, diag_handler: &Handler, ) -> Result<(Vec, Vec<(SerializedModule, CString)>), FatalError> { let export_threshold = match cgcx.lto { // We're just doing LTO for our one crate Lto::ThinLocal => SymbolExportLevel::Rust, // We're doing LTO for the entire crate graph Lto::Fat | Lto::Thin => symbol_export::crates_export_threshold(&cgcx.crate_types), Lto::No => panic!("didn't request LTO but we're doing LTO"), }; let symbol_filter = &|&(ref name, level): &(String, SymbolExportLevel)| { if level.is_below_threshold(export_threshold) { Some(CString::new(name.as_str()).unwrap()) } else { None } }; let exported_symbols = cgcx.exported_symbols.as_ref().expect("needs exported symbols for LTO"); let mut symbols_below_threshold = { let _timer = cgcx.prof.generic_activity("LLVM_lto_generate_symbols_below_threshold"); exported_symbols[&LOCAL_CRATE].iter().filter_map(symbol_filter).collect::>() }; info!("{} symbols to preserve in this crate", symbols_below_threshold.len()); // If we're performing LTO for the entire crate graph, then for each of our // upstream dependencies, find the corresponding rlib and load the bitcode // from the archive. // // We save off all the bytecode and LLVM module ids for later processing // with either fat or thin LTO let mut upstream_modules = Vec::new(); if cgcx.lto != Lto::ThinLocal { if cgcx.opts.cg.prefer_dynamic { diag_handler .struct_err("cannot prefer dynamic linking when performing LTO") .note( "only 'staticlib', 'bin', and 'cdylib' outputs are \ supported with LTO", ) .emit(); return Err(FatalError); } // Make sure we actually can run LTO for crate_type in cgcx.crate_types.iter() { if !crate_type_allows_lto(*crate_type) { let e = diag_handler.fatal( "lto can only be run for executables, cdylibs and \ static library outputs", ); return Err(e); } } for &(cnum, ref path) in cgcx.each_linked_rlib_for_lto.iter() { let exported_symbols = cgcx.exported_symbols.as_ref().expect("needs exported symbols for LTO"); { let _timer = cgcx.prof.generic_activity("LLVM_lto_generate_symbols_below_threshold"); symbols_below_threshold .extend(exported_symbols[&cnum].iter().filter_map(symbol_filter)); } let archive = ArchiveRO::open(&path).expect("wanted an rlib"); let obj_files = archive .iter() .filter_map(|child| child.ok().and_then(|c| c.name().map(|name| (name, c)))) .filter(|&(name, _)| looks_like_rust_object_file(name)); for (name, child) in obj_files { info!("adding bitcode from {}", name); match get_bitcode_slice_from_object_data(child.data()) { Ok(data) => { let module = SerializedModule::FromRlib(data.to_vec()); upstream_modules.push((module, CString::new(name).unwrap())); } Err(msg) => return Err(diag_handler.fatal(&msg)), } } } } Ok((symbols_below_threshold, upstream_modules)) } fn get_bitcode_slice_from_object_data(obj: &[u8]) -> Result<&[u8], String> { let mut len = 0; let data = unsafe { llvm::LLVMRustGetBitcodeSliceFromObjectData(obj.as_ptr(), obj.len(), &mut len) }; if !data.is_null() { assert!(len != 0); let bc = unsafe { slice::from_raw_parts(data, len) }; // `bc` must be a sub-slice of `obj`. assert!(obj.as_ptr() <= bc.as_ptr()); assert!(bc[bc.len()..bc.len()].as_ptr() <= obj[obj.len()..obj.len()].as_ptr()); Ok(bc) } else { assert!(len == 0); let msg = llvm::last_error().unwrap_or_else(|| "unknown LLVM error".to_string()); Err(format!("failed to get bitcode from object file for LTO ({})", msg)) } } /// Performs fat LTO by merging all modules into a single one and returning it /// for further optimization. pub(crate) fn run_fat( cgcx: &CodegenContext, modules: Vec>, cached_modules: Vec<(SerializedModule, WorkProduct)>, ) -> Result, FatalError> { let diag_handler = cgcx.create_diag_handler(); let (symbols_below_threshold, upstream_modules) = prepare_lto(cgcx, &diag_handler)?; let symbols_below_threshold = symbols_below_threshold.iter().map(|c| c.as_ptr()).collect::>(); fat_lto( cgcx, &diag_handler, modules, cached_modules, upstream_modules, &symbols_below_threshold, ) } /// Performs thin LTO by performing necessary global analysis and returning two /// lists, one of the modules that need optimization and another for modules that /// can simply be copied over from the incr. comp. cache. pub(crate) fn run_thin( cgcx: &CodegenContext, modules: Vec<(String, ThinBuffer)>, cached_modules: Vec<(SerializedModule, WorkProduct)>, ) -> Result<(Vec>, Vec), FatalError> { let diag_handler = cgcx.create_diag_handler(); let (symbols_below_threshold, upstream_modules) = prepare_lto(cgcx, &diag_handler)?; let symbols_below_threshold = symbols_below_threshold.iter().map(|c| c.as_ptr()).collect::>(); if cgcx.opts.cg.linker_plugin_lto.enabled() { unreachable!( "We should never reach this case if the LTO step \ is deferred to the linker" ); } thin_lto( cgcx, &diag_handler, modules, upstream_modules, cached_modules, &symbols_below_threshold, ) } pub(crate) fn prepare_thin(module: ModuleCodegen) -> (String, ThinBuffer) { let name = module.name.clone(); let buffer = ThinBuffer::new(module.module_llvm.llmod()); (name, buffer) } fn fat_lto( cgcx: &CodegenContext, diag_handler: &Handler, modules: Vec>, cached_modules: Vec<(SerializedModule, WorkProduct)>, mut serialized_modules: Vec<(SerializedModule, CString)>, symbols_below_threshold: &[*const libc::c_char], ) -> Result, FatalError> { let _timer = cgcx.prof.generic_activity("LLVM_fat_lto_build_monolithic_module"); info!("going for a fat lto"); // Sort out all our lists of incoming modules into two lists. // // * `serialized_modules` (also and argument to this function) contains all // modules that are serialized in-memory. // * `in_memory` contains modules which are already parsed and in-memory, // such as from multi-CGU builds. // // All of `cached_modules` (cached from previous incremental builds) can // immediately go onto the `serialized_modules` modules list and then we can // split the `modules` array into these two lists. let mut in_memory = Vec::new(); serialized_modules.extend(cached_modules.into_iter().map(|(buffer, wp)| { info!("pushing cached module {:?}", wp.cgu_name); (buffer, CString::new(wp.cgu_name).unwrap()) })); for module in modules { match module { FatLTOInput::InMemory(m) => in_memory.push(m), FatLTOInput::Serialized { name, buffer } => { info!("pushing serialized module {:?}", name); let buffer = SerializedModule::Local(buffer); serialized_modules.push((buffer, CString::new(name).unwrap())); } } } // Find the "costliest" module and merge everything into that codegen unit. // All the other modules will be serialized and reparsed into the new // context, so this hopefully avoids serializing and parsing the largest // codegen unit. // // Additionally use a regular module as the base here to ensure that various // file copy operations in the backend work correctly. The only other kind // of module here should be an allocator one, and if your crate is smaller // than the allocator module then the size doesn't really matter anyway. let costliest_module = in_memory .iter() .enumerate() .filter(|&(_, module)| module.kind == ModuleKind::Regular) .map(|(i, module)| { let cost = unsafe { llvm::LLVMRustModuleCost(module.module_llvm.llmod()) }; (cost, i) }) .max(); // If we found a costliest module, we're good to go. Otherwise all our // inputs were serialized which could happen in the case, for example, that // all our inputs were incrementally reread from the cache and we're just // re-executing the LTO passes. If that's the case deserialize the first // module and create a linker with it. let module: ModuleCodegen = match costliest_module { Some((_cost, i)) => in_memory.remove(i), None => { assert!(!serialized_modules.is_empty(), "must have at least one serialized module"); let (buffer, name) = serialized_modules.remove(0); info!("no in-memory regular modules to choose from, parsing {:?}", name); ModuleCodegen { module_llvm: ModuleLlvm::parse(cgcx, &name, buffer.data(), diag_handler)?, name: name.into_string().unwrap(), kind: ModuleKind::Regular, } } }; let mut serialized_bitcode = Vec::new(); { let (llcx, llmod) = { let llvm = &module.module_llvm; (&llvm.llcx, llvm.llmod()) }; info!("using {:?} as a base module", module.name); // The linking steps below may produce errors and diagnostics within LLVM // which we'd like to handle and print, so set up our diagnostic handlers // (which get unregistered when they go out of scope below). let _handler = DiagnosticHandlers::new(cgcx, diag_handler, llcx); // For all other modules we codegened we'll need to link them into our own // bitcode. All modules were codegened in their own LLVM context, however, // and we want to move everything to the same LLVM context. Currently the // way we know of to do that is to serialize them to a string and them parse // them later. Not great but hey, that's why it's "fat" LTO, right? for module in in_memory { let buffer = ModuleBuffer::new(module.module_llvm.llmod()); let llmod_id = CString::new(&module.name[..]).unwrap(); serialized_modules.push((SerializedModule::Local(buffer), llmod_id)); } // Sort the modules to ensure we produce deterministic results. serialized_modules.sort_by(|module1, module2| module1.1.cmp(&module2.1)); // For all serialized bitcode files we parse them and link them in as we did // above, this is all mostly handled in C++. Like above, though, we don't // know much about the memory management here so we err on the side of being // save and persist everything with the original module. let mut linker = Linker::new(llmod); for (bc_decoded, name) in serialized_modules { let _timer = cgcx .prof .generic_activity_with_arg("LLVM_fat_lto_link_module", format!("{:?}", name)); info!("linking {:?}", name); let data = bc_decoded.data(); linker.add(&data).map_err(|()| { let msg = format!("failed to load bc of {:?}", name); write::llvm_err(&diag_handler, &msg) })?; serialized_bitcode.push(bc_decoded); } drop(linker); save_temp_bitcode(&cgcx, &module, "lto.input"); // Internalize everything below threshold to help strip out more modules and such. unsafe { let ptr = symbols_below_threshold.as_ptr(); llvm::LLVMRustRunRestrictionPass( llmod, ptr as *const *const libc::c_char, symbols_below_threshold.len() as libc::size_t, ); save_temp_bitcode(&cgcx, &module, "lto.after-restriction"); } if cgcx.no_landing_pads { unsafe { llvm::LLVMRustMarkAllFunctionsNounwind(llmod); } save_temp_bitcode(&cgcx, &module, "lto.after-nounwind"); } } Ok(LtoModuleCodegen::Fat { module: Some(module), _serialized_bitcode: serialized_bitcode }) } struct Linker<'a>(&'a mut llvm::Linker<'a>); impl Linker<'a> { fn new(llmod: &'a llvm::Module) -> Self { unsafe { Linker(llvm::LLVMRustLinkerNew(llmod)) } } fn add(&mut self, bytecode: &[u8]) -> Result<(), ()> { unsafe { if llvm::LLVMRustLinkerAdd( self.0, bytecode.as_ptr() as *const libc::c_char, bytecode.len(), ) { Ok(()) } else { Err(()) } } } } impl Drop for Linker<'a> { fn drop(&mut self) { unsafe { llvm::LLVMRustLinkerFree(&mut *(self.0 as *mut _)); } } } /// Prepare "thin" LTO to get run on these modules. /// /// The general structure of ThinLTO is quite different from the structure of /// "fat" LTO above. With "fat" LTO all LLVM modules in question are merged into /// one giant LLVM module, and then we run more optimization passes over this /// big module after internalizing most symbols. Thin LTO, on the other hand, /// avoid this large bottleneck through more targeted optimization. /// /// At a high level Thin LTO looks like: /// /// 1. Prepare a "summary" of each LLVM module in question which describes /// the values inside, cost of the values, etc. /// 2. Merge the summaries of all modules in question into one "index" /// 3. Perform some global analysis on this index /// 4. For each module, use the index and analysis calculated previously to /// perform local transformations on the module, for example inlining /// small functions from other modules. /// 5. Run thin-specific optimization passes over each module, and then code /// generate everything at the end. /// /// The summary for each module is intended to be quite cheap, and the global /// index is relatively quite cheap to create as well. As a result, the goal of /// ThinLTO is to reduce the bottleneck on LTO and enable LTO to be used in more /// situations. For example one cheap optimization is that we can parallelize /// all codegen modules, easily making use of all the cores on a machine. /// /// With all that in mind, the function here is designed at specifically just /// calculating the *index* for ThinLTO. This index will then be shared amongst /// all of the `LtoModuleCodegen` units returned below and destroyed once /// they all go out of scope. fn thin_lto( cgcx: &CodegenContext, diag_handler: &Handler, modules: Vec<(String, ThinBuffer)>, serialized_modules: Vec<(SerializedModule, CString)>, cached_modules: Vec<(SerializedModule, WorkProduct)>, symbols_below_threshold: &[*const libc::c_char], ) -> Result<(Vec>, Vec), FatalError> { let _timer = cgcx.prof.generic_activity("LLVM_thin_lto_global_analysis"); unsafe { info!("going for that thin, thin LTO"); let green_modules: FxHashMap<_, _> = cached_modules.iter().map(|&(_, ref wp)| (wp.cgu_name.clone(), wp.clone())).collect(); let full_scope_len = modules.len() + serialized_modules.len() + cached_modules.len(); let mut thin_buffers = Vec::with_capacity(modules.len()); let mut module_names = Vec::with_capacity(full_scope_len); let mut thin_modules = Vec::with_capacity(full_scope_len); for (i, (name, buffer)) in modules.into_iter().enumerate() { info!("local module: {} - {}", i, name); let cname = CString::new(name.clone()).unwrap(); thin_modules.push(llvm::ThinLTOModule { identifier: cname.as_ptr(), data: buffer.data().as_ptr(), len: buffer.data().len(), }); thin_buffers.push(buffer); module_names.push(cname); } // FIXME: All upstream crates are deserialized internally in the // function below to extract their summary and modules. Note that // unlike the loop above we *must* decode and/or read something // here as these are all just serialized files on disk. An // improvement, however, to make here would be to store the // module summary separately from the actual module itself. Right // now this is store in one large bitcode file, and the entire // file is deflate-compressed. We could try to bypass some of the // decompression by storing the index uncompressed and only // lazily decompressing the bytecode if necessary. // // Note that truly taking advantage of this optimization will // likely be further down the road. We'd have to implement // incremental ThinLTO first where we could actually avoid // looking at upstream modules entirely sometimes (the contents, // we must always unconditionally look at the index). let mut serialized = Vec::with_capacity(serialized_modules.len() + cached_modules.len()); let cached_modules = cached_modules.into_iter().map(|(sm, wp)| (sm, CString::new(wp.cgu_name).unwrap())); for (module, name) in serialized_modules.into_iter().chain(cached_modules) { info!("upstream or cached module {:?}", name); thin_modules.push(llvm::ThinLTOModule { identifier: name.as_ptr(), data: module.data().as_ptr(), len: module.data().len(), }); serialized.push(module); module_names.push(name); } // Sanity check assert_eq!(thin_modules.len(), module_names.len()); // Delegate to the C++ bindings to create some data here. Once this is a // tried-and-true interface we may wish to try to upstream some of this // to LLVM itself, right now we reimplement a lot of what they do // upstream... let data = llvm::LLVMRustCreateThinLTOData( thin_modules.as_ptr(), thin_modules.len() as u32, symbols_below_threshold.as_ptr(), symbols_below_threshold.len() as u32, ) .ok_or_else(|| write::llvm_err(&diag_handler, "failed to prepare thin LTO context"))?; info!("thin LTO data created"); let (import_map_path, prev_import_map, curr_import_map) = if let Some(ref incr_comp_session_dir) = cgcx.incr_comp_session_dir { let path = incr_comp_session_dir.join(THIN_LTO_IMPORTS_INCR_COMP_FILE_NAME); // If previous imports have been deleted, or we get an IO error // reading the file storing them, then we'll just use `None` as the // prev_import_map, which will force the code to be recompiled. let prev = if path.exists() { ThinLTOImportMaps::load_from_file(&path).ok() } else { None }; let curr = ThinLTOImportMaps::from_thin_lto_data(data); (Some(path), prev, curr) } else { // If we don't compile incrementally, we don't need to load the // import data from LLVM. assert!(green_modules.is_empty()); let curr = ThinLTOImportMaps::default(); (None, None, curr) }; info!("thin LTO import map loaded"); let data = ThinData(data); // Throw our data in an `Arc` as we'll be sharing it across threads. We // also put all memory referenced by the C++ data (buffers, ids, etc) // into the arc as well. After this we'll create a thin module // codegen per module in this data. let shared = Arc::new(ThinShared { data, thin_buffers, serialized_modules: serialized, module_names, }); let mut copy_jobs = vec![]; let mut opt_jobs = vec![]; info!("checking which modules can be-reused and which have to be re-optimized."); for (module_index, module_name) in shared.module_names.iter().enumerate() { let module_name = module_name_to_str(module_name); // If (1.) the module hasn't changed, and (2.) none of the modules // it imports from have changed, *and* (3.) the import and export // sets themselves have not changed from the previous compile when // it was last ThinLTO'ed, then we can re-use the post-ThinLTO // version of the module. Otherwise, freshly perform LTO // optimization. // // (Note that globally, the export set is just the inverse of the // import set.) // // For further justification of why the above is necessary and sufficient, // see the LLVM blog post on ThinLTO: // // http://blog.llvm.org/2016/06/thinlto-scalable-and-incremental-lto.html // // which states the following: // // ```quote // any particular ThinLTO backend must be redone iff: // // 1. The corresponding (primary) module’s bitcode changed // 2. The list of imports into or exports from the module changed // 3. The bitcode for any module being imported from has changed // 4. Any global analysis result affecting either the primary module // or anything it imports has changed. // ``` // // This strategy means we can always save the computed imports as // canon: when we reuse the post-ThinLTO version, condition (3.) // ensures that the current import set is the same as the previous // one. (And of course, when we don't reuse the post-ThinLTO // version, the current import set *is* the correct one, since we // are doing the ThinLTO in this current compilation cycle.) // // For more discussion, see rust-lang/rust#59535 (where the import // issue was discovered) and rust-lang/rust#69798 (where the // analogous export issue was discovered). if let (Some(prev_import_map), true) = (prev_import_map.as_ref(), green_modules.contains_key(module_name)) { assert!(cgcx.incr_comp_session_dir.is_some()); let prev_imports = prev_import_map.imports_of(module_name); let curr_imports = curr_import_map.imports_of(module_name); let prev_exports = prev_import_map.exports_of(module_name); let curr_exports = curr_import_map.exports_of(module_name); let imports_all_green = curr_imports .iter() .all(|imported_module| green_modules.contains_key(imported_module)); if imports_all_green && equivalent_as_sets(prev_imports, curr_imports) && equivalent_as_sets(prev_exports, curr_exports) { let work_product = green_modules[module_name].clone(); copy_jobs.push(work_product); info!(" - {}: re-used", module_name); assert!(cgcx.incr_comp_session_dir.is_some()); cgcx.cgu_reuse_tracker.set_actual_reuse(module_name, CguReuse::PostLto); continue; } } info!(" - {}: re-compiled", module_name); opt_jobs.push(LtoModuleCodegen::Thin(ThinModule { shared: shared.clone(), idx: module_index, })); } // Save the current ThinLTO import information for the next compilation // session, overwriting the previous serialized imports (if any). if let Some(path) = import_map_path { if let Err(err) = curr_import_map.save_to_file(&path) { let msg = format!("Error while writing ThinLTO import data: {}", err); return Err(write::llvm_err(&diag_handler, &msg)); } } Ok((opt_jobs, copy_jobs)) } } /// Given two slices, each with no repeat elements. returns true if and only if /// the two slices have the same contents when considered as sets (i.e. when /// element order is disregarded). fn equivalent_as_sets(a: &[String], b: &[String]) -> bool { // cheap path: unequal lengths means cannot possibly be set equivalent. if a.len() != b.len() { return false; } // fast path: before building new things, check if inputs are equivalent as is. if a == b { return true; } // slow path: general set comparison. let a: FxHashSet<&str> = a.iter().map(|s| s.as_str()).collect(); let b: FxHashSet<&str> = b.iter().map(|s| s.as_str()).collect(); a == b } pub(crate) fn run_pass_manager( cgcx: &CodegenContext, module: &ModuleCodegen, config: &ModuleConfig, thin: bool, ) { let _timer = cgcx.prof.extra_verbose_generic_activity("LLVM_lto_optimize", &module.name[..]); // Now we have one massive module inside of llmod. Time to run the // LTO-specific optimization passes that LLVM provides. // // This code is based off the code found in llvm's LTO code generator: // tools/lto/LTOCodeGenerator.cpp debug!("running the pass manager"); unsafe { if write::should_use_new_llvm_pass_manager(config) { let opt_stage = if thin { llvm::OptStage::ThinLTO } else { llvm::OptStage::FatLTO }; let opt_level = config.opt_level.unwrap_or(config::OptLevel::No); // See comment below for why this is necessary. let opt_level = if let config::OptLevel::No = opt_level { config::OptLevel::Less } else { opt_level }; write::optimize_with_new_llvm_pass_manager(cgcx, module, config, opt_level, opt_stage); debug!("lto done"); return; } let pm = llvm::LLVMCreatePassManager(); llvm::LLVMAddAnalysisPasses(module.module_llvm.tm, pm); if config.verify_llvm_ir { let pass = llvm::LLVMRustFindAndCreatePass("verify\0".as_ptr().cast()); llvm::LLVMRustAddPass(pm, pass.unwrap()); } // When optimizing for LTO we don't actually pass in `-O0`, but we force // it to always happen at least with `-O1`. // // With ThinLTO we mess around a lot with symbol visibility in a way // that will actually cause linking failures if we optimize at O0 which // notable is lacking in dead code elimination. To ensure we at least // get some optimizations and correctly link we forcibly switch to `-O1` // to get dead code elimination. // // Note that in general this shouldn't matter too much as you typically // only turn on ThinLTO when you're compiling with optimizations // otherwise. let opt_level = config .opt_level .map(|x| to_llvm_opt_settings(x).0) .unwrap_or(llvm::CodeGenOptLevel::None); let opt_level = match opt_level { llvm::CodeGenOptLevel::None => llvm::CodeGenOptLevel::Less, level => level, }; with_llvm_pmb(module.module_llvm.llmod(), config, opt_level, false, &mut |b| { if thin { llvm::LLVMRustPassManagerBuilderPopulateThinLTOPassManager(b, pm); } else { llvm::LLVMPassManagerBuilderPopulateLTOPassManager( b, pm, /* Internalize = */ False, /* RunInliner = */ True, ); } }); // We always generate bitcode through ThinLTOBuffers, // which do not support anonymous globals if config.bitcode_needed() { let pass = llvm::LLVMRustFindAndCreatePass("name-anon-globals\0".as_ptr().cast()); llvm::LLVMRustAddPass(pm, pass.unwrap()); } if config.verify_llvm_ir { let pass = llvm::LLVMRustFindAndCreatePass("verify\0".as_ptr().cast()); llvm::LLVMRustAddPass(pm, pass.unwrap()); } llvm::LLVMRunPassManager(pm, module.module_llvm.llmod()); llvm::LLVMDisposePassManager(pm); } debug!("lto done"); } pub struct ModuleBuffer(&'static mut llvm::ModuleBuffer); unsafe impl Send for ModuleBuffer {} unsafe impl Sync for ModuleBuffer {} impl ModuleBuffer { pub fn new(m: &llvm::Module) -> ModuleBuffer { ModuleBuffer(unsafe { llvm::LLVMRustModuleBufferCreate(m) }) } } impl ModuleBufferMethods for ModuleBuffer { fn data(&self) -> &[u8] { unsafe { let ptr = llvm::LLVMRustModuleBufferPtr(self.0); let len = llvm::LLVMRustModuleBufferLen(self.0); slice::from_raw_parts(ptr, len) } } } impl Drop for ModuleBuffer { fn drop(&mut self) { unsafe { llvm::LLVMRustModuleBufferFree(&mut *(self.0 as *mut _)); } } } pub struct ThinData(&'static mut llvm::ThinLTOData); unsafe impl Send for ThinData {} unsafe impl Sync for ThinData {} impl Drop for ThinData { fn drop(&mut self) { unsafe { llvm::LLVMRustFreeThinLTOData(&mut *(self.0 as *mut _)); } } } pub struct ThinBuffer(&'static mut llvm::ThinLTOBuffer); unsafe impl Send for ThinBuffer {} unsafe impl Sync for ThinBuffer {} impl ThinBuffer { pub fn new(m: &llvm::Module) -> ThinBuffer { unsafe { let buffer = llvm::LLVMRustThinLTOBufferCreate(m); ThinBuffer(buffer) } } } impl ThinBufferMethods for ThinBuffer { fn data(&self) -> &[u8] { unsafe { let ptr = llvm::LLVMRustThinLTOBufferPtr(self.0) as *const _; let len = llvm::LLVMRustThinLTOBufferLen(self.0); slice::from_raw_parts(ptr, len) } } } impl Drop for ThinBuffer { fn drop(&mut self) { unsafe { llvm::LLVMRustThinLTOBufferFree(&mut *(self.0 as *mut _)); } } } pub unsafe fn optimize_thin_module( thin_module: &mut ThinModule, cgcx: &CodegenContext, ) -> Result, FatalError> { let diag_handler = cgcx.create_diag_handler(); let tm = (cgcx.tm_factory.0)().map_err(|e| write::llvm_err(&diag_handler, &e))?; // Right now the implementation we've got only works over serialized // modules, so we create a fresh new LLVM context and parse the module // into that context. One day, however, we may do this for upstream // crates but for locally codegened modules we may be able to reuse // that LLVM Context and Module. let llcx = llvm::LLVMRustContextCreate(cgcx.fewer_names); let llmod_raw = parse_module( llcx, &thin_module.shared.module_names[thin_module.idx], thin_module.data(), &diag_handler, )? as *const _; let module = ModuleCodegen { module_llvm: ModuleLlvm { llmod_raw, llcx, tm }, name: thin_module.name().to_string(), kind: ModuleKind::Regular, }; { let target = &*module.module_llvm.tm; let llmod = module.module_llvm.llmod(); save_temp_bitcode(&cgcx, &module, "thin-lto-input"); // Before we do much else find the "main" `DICompileUnit` that we'll be // using below. If we find more than one though then rustc has changed // in a way we're not ready for, so generate an ICE by returning // an error. let mut cu1 = ptr::null_mut(); let mut cu2 = ptr::null_mut(); llvm::LLVMRustThinLTOGetDICompileUnit(llmod, &mut cu1, &mut cu2); if !cu2.is_null() { let msg = "multiple source DICompileUnits found"; return Err(write::llvm_err(&diag_handler, msg)); } // Like with "fat" LTO, get some better optimizations if landing pads // are disabled by removing all landing pads. if cgcx.no_landing_pads { let _timer = cgcx .prof .generic_activity_with_arg("LLVM_thin_lto_remove_landing_pads", thin_module.name()); llvm::LLVMRustMarkAllFunctionsNounwind(llmod); save_temp_bitcode(&cgcx, &module, "thin-lto-after-nounwind"); } // Up next comes the per-module local analyses that we do for Thin LTO. // Each of these functions is basically copied from the LLVM // implementation and then tailored to suit this implementation. Ideally // each of these would be supported by upstream LLVM but that's perhaps // a patch for another day! // // You can find some more comments about these functions in the LLVM // bindings we've got (currently `PassWrapper.cpp`) { let _timer = cgcx.prof.generic_activity_with_arg("LLVM_thin_lto_rename", thin_module.name()); if !llvm::LLVMRustPrepareThinLTORename(thin_module.shared.data.0, llmod, target) { let msg = "failed to prepare thin LTO module"; return Err(write::llvm_err(&diag_handler, msg)); } save_temp_bitcode(cgcx, &module, "thin-lto-after-rename"); } { let _timer = cgcx .prof .generic_activity_with_arg("LLVM_thin_lto_resolve_weak", thin_module.name()); if !llvm::LLVMRustPrepareThinLTOResolveWeak(thin_module.shared.data.0, llmod) { let msg = "failed to prepare thin LTO module"; return Err(write::llvm_err(&diag_handler, msg)); } save_temp_bitcode(cgcx, &module, "thin-lto-after-resolve"); } { let _timer = cgcx .prof .generic_activity_with_arg("LLVM_thin_lto_internalize", thin_module.name()); if !llvm::LLVMRustPrepareThinLTOInternalize(thin_module.shared.data.0, llmod) { let msg = "failed to prepare thin LTO module"; return Err(write::llvm_err(&diag_handler, msg)); } save_temp_bitcode(cgcx, &module, "thin-lto-after-internalize"); } { let _timer = cgcx.prof.generic_activity_with_arg("LLVM_thin_lto_import", thin_module.name()); if !llvm::LLVMRustPrepareThinLTOImport(thin_module.shared.data.0, llmod, target) { let msg = "failed to prepare thin LTO module"; return Err(write::llvm_err(&diag_handler, msg)); } save_temp_bitcode(cgcx, &module, "thin-lto-after-import"); } // Ok now this is a bit unfortunate. This is also something you won't // find upstream in LLVM's ThinLTO passes! This is a hack for now to // work around bugs in LLVM. // // First discovered in #45511 it was found that as part of ThinLTO // importing passes LLVM will import `DICompileUnit` metadata // information across modules. This means that we'll be working with one // LLVM module that has multiple `DICompileUnit` instances in it (a // bunch of `llvm.dbg.cu` members). Unfortunately there's a number of // bugs in LLVM's backend which generates invalid DWARF in a situation // like this: // // https://bugs.llvm.org/show_bug.cgi?id=35212 // https://bugs.llvm.org/show_bug.cgi?id=35562 // // While the first bug there is fixed the second ended up causing #46346 // which was basically a resurgence of #45511 after LLVM's bug 35212 was // fixed. // // This function below is a huge hack around this problem. The function // below is defined in `PassWrapper.cpp` and will basically "merge" // all `DICompileUnit` instances in a module. Basically it'll take all // the objects, rewrite all pointers of `DISubprogram` to point to the // first `DICompileUnit`, and then delete all the other units. // // This is probably mangling to the debug info slightly (but hopefully // not too much) but for now at least gets LLVM to emit valid DWARF (or // so it appears). Hopefully we can remove this once upstream bugs are // fixed in LLVM. { let _timer = cgcx .prof .generic_activity_with_arg("LLVM_thin_lto_patch_debuginfo", thin_module.name()); llvm::LLVMRustThinLTOPatchDICompileUnit(llmod, cu1); save_temp_bitcode(cgcx, &module, "thin-lto-after-patch"); } // Alright now that we've done everything related to the ThinLTO // analysis it's time to run some optimizations! Here we use the same // `run_pass_manager` as the "fat" LTO above except that we tell it to // populate a thin-specific pass manager, which presumably LLVM treats a // little differently. { info!("running thin lto passes over {}", module.name); let config = cgcx.config(module.kind); run_pass_manager(cgcx, &module, config, true); save_temp_bitcode(cgcx, &module, "thin-lto-after-pm"); } } Ok(module) } /// Summarizes module import/export relationships used by LLVM's ThinLTO pass. /// /// Note that we tend to have two such instances of `ThinLTOImportMaps` in use: /// one loaded from a file that represents the relationships used during the /// compilation associated with the incremetnal build artifacts we are /// attempting to reuse, and another constructed via `from_thin_lto_data`, which /// captures the relationships of ThinLTO in the current compilation. #[derive(Debug, Default)] pub struct ThinLTOImportMaps { // key = llvm name of importing module, value = list of modules it imports from imports: FxHashMap>, // key = llvm name of exporting module, value = list of modules it exports to exports: FxHashMap>, } impl ThinLTOImportMaps { /// Returns modules imported by `llvm_module_name` during some ThinLTO pass. fn imports_of(&self, llvm_module_name: &str) -> &[String] { self.imports.get(llvm_module_name).map(|v| &v[..]).unwrap_or(&[]) } /// Returns modules exported by `llvm_module_name` during some ThinLTO pass. fn exports_of(&self, llvm_module_name: &str) -> &[String] { self.exports.get(llvm_module_name).map(|v| &v[..]).unwrap_or(&[]) } fn save_to_file(&self, path: &Path) -> io::Result<()> { use std::io::Write; let file = File::create(path)?; let mut writer = io::BufWriter::new(file); for (importing_module_name, imported_modules) in &self.imports { writeln!(writer, "{}", importing_module_name)?; for imported_module in imported_modules { writeln!(writer, " {}", imported_module)?; } writeln!(writer)?; } Ok(()) } fn load_from_file(path: &Path) -> io::Result { use std::io::BufRead; let mut imports = FxHashMap::default(); let mut exports: FxHashMap<_, Vec<_>> = FxHashMap::default(); let mut current_module: Option = None; let mut current_imports: Vec = vec![]; let file = File::open(path)?; for line in io::BufReader::new(file).lines() { let line = line?; if line.is_empty() { let importing_module = current_module.take().expect("Importing module not set"); for imported in ¤t_imports { exports.entry(imported.clone()).or_default().push(importing_module.clone()); } imports.insert(importing_module, mem::replace(&mut current_imports, vec![])); } else if line.starts_with(' ') { // Space marks an imported module assert_ne!(current_module, None); current_imports.push(line.trim().to_string()); } else { // Otherwise, beginning of a new module (must be start or follow empty line) assert_eq!(current_module, None); current_module = Some(line.trim().to_string()); } } Ok(ThinLTOImportMaps { imports, exports }) } /// Loads the ThinLTO import map from ThinLTOData. unsafe fn from_thin_lto_data(data: *const llvm::ThinLTOData) -> ThinLTOImportMaps { unsafe extern "C" fn imported_module_callback( payload: *mut libc::c_void, importing_module_name: *const libc::c_char, imported_module_name: *const libc::c_char, ) { let map = &mut *(payload as *mut ThinLTOImportMaps); let importing_module_name = CStr::from_ptr(importing_module_name); let importing_module_name = module_name_to_str(&importing_module_name); let imported_module_name = CStr::from_ptr(imported_module_name); let imported_module_name = module_name_to_str(&imported_module_name); if !map.imports.contains_key(importing_module_name) { map.imports.insert(importing_module_name.to_owned(), vec![]); } map.imports .get_mut(importing_module_name) .unwrap() .push(imported_module_name.to_owned()); if !map.exports.contains_key(imported_module_name) { map.exports.insert(imported_module_name.to_owned(), vec![]); } map.exports .get_mut(imported_module_name) .unwrap() .push(importing_module_name.to_owned()); } let mut map = ThinLTOImportMaps::default(); llvm::LLVMRustGetThinLTOModuleImports( data, imported_module_callback, &mut map as *mut _ as *mut libc::c_void, ); map } } fn module_name_to_str(c_str: &CStr) -> &str { c_str.to_str().unwrap_or_else(|e| { bug!("Encountered non-utf8 LLVM module name `{}`: {}", c_str.to_string_lossy(), e) }) } pub fn parse_module<'a>( cx: &'a llvm::Context, name: &CStr, data: &[u8], diag_handler: &Handler, ) -> Result<&'a llvm::Module, FatalError> { unsafe { llvm::LLVMRustParseBitcodeForLTO(cx, data.as_ptr(), data.len(), name.as_ptr()).ok_or_else( || { let msg = "failed to parse bitcode for LTO module"; write::llvm_err(&diag_handler, msg) }, ) } }