1 //===- LTO.cpp ------------------------------------------------------------===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
11 #include "InputFiles.h"
12 #include "LinkerScript.h"
13 #include "SymbolTable.h"
15 #include "lld/Common/Args.h"
16 #include "lld/Common/ErrorHandler.h"
17 #include "lld/Common/TargetOptionsCommandFlags.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/SmallString.h"
20 #include "llvm/ADT/StringRef.h"
21 #include "llvm/ADT/Twine.h"
22 #include "llvm/BinaryFormat/ELF.h"
23 #include "llvm/Bitcode/BitcodeReader.h"
24 #include "llvm/Bitcode/BitcodeWriter.h"
25 #include "llvm/IR/DiagnosticPrinter.h"
26 #include "llvm/LTO/Caching.h"
27 #include "llvm/LTO/Config.h"
28 #include "llvm/LTO/LTO.h"
29 #include "llvm/Object/SymbolicFile.h"
30 #include "llvm/Support/CodeGen.h"
31 #include "llvm/Support/Error.h"
32 #include "llvm/Support/FileSystem.h"
33 #include "llvm/Support/MemoryBuffer.h"
38 #include <system_error>
42 using namespace llvm::object;
43 using namespace llvm::ELF;
45 using namespace lld::elf;
47 // Creates an empty file to store a list of object files for final
48 // linking of distributed ThinLTO.
49 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
52 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
54 error("cannot open " + file + ": " + ec.message());
60 static std::string getThinLTOOutputFile(StringRef modulePath) {
61 return lto::getThinLTOOutputFile(
62 std::string(modulePath), std::string(config->thinLTOPrefixReplace.first),
63 std::string(config->thinLTOPrefixReplace.second));
66 static lto::Config createConfig() {
69 // LLD supports the new relocations and address-significance tables.
70 c.Options = initTargetOptionsFromCodeGenFlags();
71 c.Options.RelaxELFRelocations = true;
72 c.Options.EmitAddrsig = true;
74 // Always emit a section per function/datum with LTO.
75 c.Options.FunctionSections = true;
76 c.Options.DataSections = true;
78 // Check if basic block sections must be used.
79 // Allowed values for --lto-basicblock-sections are "all", "labels",
80 // "<file name specifying basic block ids>", or none. This is the equivalent
81 // of -fbasic-block-sections= flag in clang.
82 if (!config->ltoBasicBlockSections.empty()) {
83 if (config->ltoBasicBlockSections == "all") {
84 c.Options.BBSections = BasicBlockSection::All;
85 } else if (config->ltoBasicBlockSections == "labels") {
86 c.Options.BBSections = BasicBlockSection::Labels;
87 } else if (config->ltoBasicBlockSections == "none") {
88 c.Options.BBSections = BasicBlockSection::None;
90 ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
91 MemoryBuffer::getFile(config->ltoBasicBlockSections.str());
93 error("cannot open " + config->ltoBasicBlockSections + ":" +
94 MBOrErr.getError().message());
96 c.Options.BBSectionsFuncListBuf = std::move(*MBOrErr);
98 c.Options.BBSections = BasicBlockSection::List;
102 c.Options.UniqueBasicBlockSectionNames =
103 config->ltoUniqueBasicBlockSectionNames;
105 if (auto relocModel = getRelocModelFromCMModel())
106 c.RelocModel = *relocModel;
107 else if (config->relocatable)
109 else if (config->isPic)
110 c.RelocModel = Reloc::PIC_;
112 c.RelocModel = Reloc::Static;
114 c.CodeModel = getCodeModelFromCMModel();
115 c.DisableVerify = config->disableVerify;
116 c.DiagHandler = diagnosticHandler;
117 c.OptLevel = config->ltoo;
119 c.MAttrs = getMAttrs();
120 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
122 c.PTO.LoopVectorization = c.OptLevel > 1;
123 c.PTO.SLPVectorization = c.OptLevel > 1;
125 // Set up a custom pipeline if we've been asked to.
126 c.OptPipeline = std::string(config->ltoNewPmPasses);
127 c.AAPipeline = std::string(config->ltoAAPipeline);
129 // Set up optimization remarks if we've been asked to.
130 c.RemarksFilename = std::string(config->optRemarksFilename);
131 c.RemarksPasses = std::string(config->optRemarksPasses);
132 c.RemarksWithHotness = config->optRemarksWithHotness;
133 c.RemarksFormat = std::string(config->optRemarksFormat);
135 c.SampleProfile = std::string(config->ltoSampleProfile);
136 c.UseNewPM = config->ltoNewPassManager;
137 c.DebugPassManager = config->ltoDebugPassManager;
138 c.DwoDir = std::string(config->dwoDir);
140 c.HasWholeProgramVisibility = config->ltoWholeProgramVisibility;
141 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty();
143 for (const llvm::StringRef &name : config->thinLTOModulesToCompile)
144 c.ThinLTOModulesToCompile.emplace_back(name);
146 c.TimeTraceEnabled = config->timeTraceEnabled;
147 c.TimeTraceGranularity = config->timeTraceGranularity;
149 c.CSIRProfile = std::string(config->ltoCSProfileFile);
150 c.RunCSIRInstr = config->ltoCSProfileGenerate;
152 if (config->emitLLVM) {
153 c.PostInternalizeModuleHook = [](size_t task, const Module &m) {
154 if (std::unique_ptr<raw_fd_ostream> os = openFile(config->outputFile))
155 WriteBitcodeToFile(m, *os, false);
160 if (config->ltoEmitAsm)
161 c.CGFileType = CGFT_AssemblyFile;
163 if (config->saveTemps)
164 checkError(c.addSaveTemps(config->outputFile.str() + ".",
165 /*UseInputModulePath*/ true));
169 BitcodeCompiler::BitcodeCompiler() {
170 // Initialize indexFile.
171 if (!config->thinLTOIndexOnlyArg.empty())
172 indexFile = openFile(config->thinLTOIndexOnlyArg);
174 // Initialize ltoObj.
175 lto::ThinBackend backend;
176 if (config->thinLTOIndexOnly) {
177 auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); };
178 backend = lto::createWriteIndexesThinBackend(
179 std::string(config->thinLTOPrefixReplace.first),
180 std::string(config->thinLTOPrefixReplace.second),
181 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
183 backend = lto::createInProcessThinBackend(
184 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs));
187 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
188 config->ltoPartitions);
190 // Initialize usedStartStop.
191 for (Symbol *sym : symtab->symbols()) {
192 StringRef s = sym->getName();
193 for (StringRef prefix : {"__start_", "__stop_"})
194 if (s.startswith(prefix))
195 usedStartStop.insert(s.substr(prefix.size()));
199 BitcodeCompiler::~BitcodeCompiler() = default;
201 void BitcodeCompiler::add(BitcodeFile &f) {
202 lto::InputFile &obj = *f.obj;
203 bool isExec = !config->shared && !config->relocatable;
205 if (config->thinLTOIndexOnly)
206 thinIndices.insert(obj.getName());
208 ArrayRef<Symbol *> syms = f.getSymbols();
209 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
210 std::vector<lto::SymbolResolution> resols(syms.size());
212 // Provide a resolution to the LTO API for each symbol.
213 for (size_t i = 0, e = syms.size(); i != e; ++i) {
214 Symbol *sym = syms[i];
215 const lto::InputFile::Symbol &objSym = objSyms[i];
216 lto::SymbolResolution &r = resols[i];
218 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
219 // reports two symbols for module ASM defined. Without this check, lld
220 // flags an undefined in IR with a definition in ASM as prevailing.
221 // Once IRObjectFile is fixed to report only one symbol this hack can
223 r.Prevailing = !objSym.isUndefined() && sym->file == &f;
225 // We ask LTO to preserve following global symbols:
226 // 1) All symbols when doing relocatable link, so that them can be used
227 // for doing final link.
228 // 2) Symbols that are used in regular objects.
229 // 3) C named sections if we have corresponding __start_/__stop_ symbol.
230 // 4) Symbols that are defined in bitcode files and used for dynamic linking.
231 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
232 (r.Prevailing && sym->includeInDynsym()) ||
233 usedStartStop.count(objSym.getSectionName());
234 const auto *dr = dyn_cast<Defined>(sym);
235 r.FinalDefinitionInLinkageUnit =
236 (isExec || sym->visibility != STV_DEFAULT) && dr &&
237 // Skip absolute symbols from ELF objects, otherwise PC-rel relocations
238 // will be generated by for them, triggering linker errors.
239 // Symbol section is always null for bitcode symbols, hence the check
240 // for isElf(). Skip linker script defined symbols as well: they have
242 !(dr->section == nullptr && (!sym->file || sym->file->isElf()));
245 sym->replace(Undefined{nullptr, sym->getName(), STB_GLOBAL, STV_DEFAULT,
248 // We tell LTO to not apply interprocedural optimization for wrapped
249 // (with --wrap) symbols because otherwise LTO would inline them while
250 // their values are still not final.
251 r.LinkerRedefined = !sym->canInline;
253 checkError(ltoObj->add(std::move(f.obj), resols));
256 // If LazyObjFile has not been added to link, emit empty index files.
257 // This is needed because this is what GNU gold plugin does and we have a
258 // distributed build system that depends on that behavior.
259 static void thinLTOCreateEmptyIndexFiles() {
260 for (LazyObjFile *f : lazyObjFiles) {
261 if (f->fetched || !isBitcode(f->mb))
263 std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName()));
264 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
268 ModuleSummaryIndex m(/*HaveGVs*/ false);
269 m.setSkipModuleByDistributedBackend();
270 WriteIndexToFile(m, *os);
271 if (config->thinLTOEmitImportsFiles)
272 openFile(path + ".imports");
276 // Merge all the bitcode files we have seen, codegen the result
277 // and return the resulting ObjectFile(s).
278 std::vector<InputFile *> BitcodeCompiler::compile() {
279 unsigned maxTasks = ltoObj->getMaxTasks();
280 buf.resize(maxTasks);
281 files.resize(maxTasks);
283 // The --thinlto-cache-dir option specifies the path to a directory in which
284 // to cache native object files for ThinLTO incremental builds. If a path was
285 // specified, configure LTO to use it as the cache directory.
286 lto::NativeObjectCache cache;
287 if (!config->thinLTOCacheDir.empty())
289 lto::localCache(config->thinLTOCacheDir,
290 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
291 files[task] = std::move(mb);
294 if (!bitcodeFiles.empty())
295 checkError(ltoObj->run(
297 return std::make_unique<lto::NativeObjectStream>(
298 std::make_unique<raw_svector_ostream>(buf[task]));
302 // Emit empty index files for non-indexed files but not in single-module mode.
303 if (config->thinLTOModulesToCompile.empty()) {
304 for (StringRef s : thinIndices) {
305 std::string path = getThinLTOOutputFile(s);
306 openFile(path + ".thinlto.bc");
307 if (config->thinLTOEmitImportsFiles)
308 openFile(path + ".imports");
312 if (config->thinLTOIndexOnly) {
313 thinLTOCreateEmptyIndexFiles();
315 if (!config->ltoObjPath.empty())
316 saveBuffer(buf[0], config->ltoObjPath);
318 // ThinLTO with index only option is required to generate only the index
319 // files. After that, we exit from linker and ThinLTO backend runs in a
320 // distributed environment.
326 if (!config->thinLTOCacheDir.empty())
327 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy);
329 if (!config->ltoObjPath.empty()) {
330 saveBuffer(buf[0], config->ltoObjPath);
331 for (unsigned i = 1; i != maxTasks; ++i)
332 saveBuffer(buf[i], config->ltoObjPath + Twine(i));
335 if (config->saveTemps) {
337 saveBuffer(buf[0], config->outputFile + ".lto.o");
338 for (unsigned i = 1; i != maxTasks; ++i)
339 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
342 if (config->ltoEmitAsm) {
343 saveBuffer(buf[0], config->outputFile);
344 for (unsigned i = 1; i != maxTasks; ++i)
345 saveBuffer(buf[i], config->outputFile + Twine(i));
349 std::vector<InputFile *> ret;
350 for (unsigned i = 0; i != maxTasks; ++i)
352 ret.push_back(createObjectFile(MemoryBufferRef(buf[i], "lto.tmp")));
354 for (std::unique_ptr<MemoryBuffer> &file : files)
356 ret.push_back(createObjectFile(*file));