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;
48 // Creates an empty file to store a list of object files for final
49 // linking of distributed ThinLTO.
50 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) {
53 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None);
55 error("cannot open " + file + ": " + ec.message());
61 static std::string getThinLTOOutputFile(StringRef modulePath) {
62 return lto::getThinLTOOutputFile(modulePath,
63 config->thinLTOPrefixReplace.first,
64 config->thinLTOPrefixReplace.second);
67 static lto::Config createConfig() {
70 // LLD supports the new relocations and address-significance tables.
71 c.Options = initTargetOptionsFromCodeGenFlags();
72 c.Options.RelaxELFRelocations = true;
73 c.Options.EmitAddrsig = true;
75 // Always emit a section per function/datum with LTO.
76 c.Options.FunctionSections = true;
77 c.Options.DataSections = true;
79 if (auto relocModel = getRelocModelFromCMModel())
80 c.RelocModel = *relocModel;
81 else if (config->relocatable)
83 else if (config->isPic)
84 c.RelocModel = Reloc::PIC_;
86 c.RelocModel = Reloc::Static;
88 c.CodeModel = getCodeModelFromCMModel();
89 c.DisableVerify = config->disableVerify;
90 c.DiagHandler = diagnosticHandler;
91 c.OptLevel = config->ltoo;
93 c.MAttrs = getMAttrs();
94 c.CGOptLevel = args::getCGOptLevel(config->ltoo);
96 c.PTO.LoopVectorization = c.OptLevel > 1;
97 c.PTO.SLPVectorization = c.OptLevel > 1;
99 // Set up a custom pipeline if we've been asked to.
100 c.OptPipeline = config->ltoNewPmPasses;
101 c.AAPipeline = config->ltoAAPipeline;
103 // Set up optimization remarks if we've been asked to.
104 c.RemarksFilename = config->optRemarksFilename;
105 c.RemarksPasses = config->optRemarksPasses;
106 c.RemarksWithHotness = config->optRemarksWithHotness;
107 c.RemarksFormat = config->optRemarksFormat;
109 c.SampleProfile = config->ltoSampleProfile;
110 c.UseNewPM = config->ltoNewPassManager;
111 c.DebugPassManager = config->ltoDebugPassManager;
112 c.DwoDir = config->dwoDir;
114 c.CSIRProfile = config->ltoCSProfileFile;
115 c.RunCSIRInstr = config->ltoCSProfileGenerate;
117 if (config->emitLLVM) {
118 c.PostInternalizeModuleHook = [](size_t task, const Module &m) {
119 if (std::unique_ptr<raw_fd_ostream> os = openFile(config->outputFile))
120 WriteBitcodeToFile(m, *os, false);
125 if (config->saveTemps)
126 checkError(c.addSaveTemps(config->outputFile.str() + ".",
127 /*UseInputModulePath*/ true));
131 BitcodeCompiler::BitcodeCompiler() {
132 // Initialize indexFile.
133 if (!config->thinLTOIndexOnlyArg.empty())
134 indexFile = openFile(config->thinLTOIndexOnlyArg);
136 // Initialize ltoObj.
137 lto::ThinBackend backend;
138 if (config->thinLTOIndexOnly) {
139 auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); };
140 backend = lto::createWriteIndexesThinBackend(
141 config->thinLTOPrefixReplace.first, config->thinLTOPrefixReplace.second,
142 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite);
143 } else if (config->thinLTOJobs != -1U) {
144 backend = lto::createInProcessThinBackend(config->thinLTOJobs);
147 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
148 config->ltoPartitions);
150 // Initialize usedStartStop.
151 for (Symbol *sym : symtab->symbols()) {
152 StringRef s = sym->getName();
153 for (StringRef prefix : {"__start_", "__stop_"})
154 if (s.startswith(prefix))
155 usedStartStop.insert(s.substr(prefix.size()));
159 BitcodeCompiler::~BitcodeCompiler() = default;
161 void BitcodeCompiler::add(BitcodeFile &f) {
162 lto::InputFile &obj = *f.obj;
163 bool isExec = !config->shared && !config->relocatable;
165 if (config->thinLTOIndexOnly)
166 thinIndices.insert(obj.getName());
168 ArrayRef<Symbol *> syms = f.getSymbols();
169 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols();
170 std::vector<lto::SymbolResolution> resols(syms.size());
172 // Provide a resolution to the LTO API for each symbol.
173 for (size_t i = 0, e = syms.size(); i != e; ++i) {
174 Symbol *sym = syms[i];
175 const lto::InputFile::Symbol &objSym = objSyms[i];
176 lto::SymbolResolution &r = resols[i];
178 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
179 // reports two symbols for module ASM defined. Without this check, lld
180 // flags an undefined in IR with a definition in ASM as prevailing.
181 // Once IRObjectFile is fixed to report only one symbol this hack can
183 r.Prevailing = !objSym.isUndefined() && sym->file == &f;
185 // We ask LTO to preserve following global symbols:
186 // 1) All symbols when doing relocatable link, so that them can be used
187 // for doing final link.
188 // 2) Symbols that are used in regular objects.
189 // 3) C named sections if we have corresponding __start_/__stop_ symbol.
190 // 4) Symbols that are defined in bitcode files and used for dynamic linking.
191 r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
192 (r.Prevailing && sym->includeInDynsym()) ||
193 usedStartStop.count(objSym.getSectionName());
194 const auto *dr = dyn_cast<Defined>(sym);
195 r.FinalDefinitionInLinkageUnit =
196 (isExec || sym->visibility != STV_DEFAULT) && dr &&
197 // Skip absolute symbols from ELF objects, otherwise PC-rel relocations
198 // will be generated by for them, triggering linker errors.
199 // Symbol section is always null for bitcode symbols, hence the check
200 // for isElf(). Skip linker script defined symbols as well: they have
202 !(dr->section == nullptr && (!sym->file || sym->file->isElf()));
205 sym->replace(Undefined{nullptr, sym->getName(), STB_GLOBAL, STV_DEFAULT,
208 // We tell LTO to not apply interprocedural optimization for wrapped
209 // (with --wrap) symbols because otherwise LTO would inline them while
210 // their values are still not final.
211 r.LinkerRedefined = !sym->canInline;
213 checkError(ltoObj->add(std::move(f.obj), resols));
216 // If LazyObjFile has not been added to link, emit empty index files.
217 // This is needed because this is what GNU gold plugin does and we have a
218 // distributed build system that depends on that behavior.
219 static void thinLTOCreateEmptyIndexFiles() {
220 for (LazyObjFile *f : lazyObjFiles) {
221 if (!isBitcode(f->mb))
223 std::string path = replaceThinLTOSuffix(getThinLTOOutputFile(f->getName()));
224 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc");
228 ModuleSummaryIndex m(/*HaveGVs*/ false);
229 m.setSkipModuleByDistributedBackend();
230 WriteIndexToFile(m, *os);
231 if (config->thinLTOEmitImportsFiles)
232 openFile(path + ".imports");
236 // Merge all the bitcode files we have seen, codegen the result
237 // and return the resulting ObjectFile(s).
238 std::vector<InputFile *> BitcodeCompiler::compile() {
239 unsigned maxTasks = ltoObj->getMaxTasks();
240 buf.resize(maxTasks);
241 files.resize(maxTasks);
243 // The --thinlto-cache-dir option specifies the path to a directory in which
244 // to cache native object files for ThinLTO incremental builds. If a path was
245 // specified, configure LTO to use it as the cache directory.
246 lto::NativeObjectCache cache;
247 if (!config->thinLTOCacheDir.empty())
249 lto::localCache(config->thinLTOCacheDir,
250 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) {
251 files[task] = std::move(mb);
254 if (!bitcodeFiles.empty())
255 checkError(ltoObj->run(
257 return std::make_unique<lto::NativeObjectStream>(
258 std::make_unique<raw_svector_ostream>(buf[task]));
262 // Emit empty index files for non-indexed files
263 for (StringRef s : thinIndices) {
264 std::string path = getThinLTOOutputFile(s);
265 openFile(path + ".thinlto.bc");
266 if (config->thinLTOEmitImportsFiles)
267 openFile(path + ".imports");
270 if (config->thinLTOIndexOnly) {
271 thinLTOCreateEmptyIndexFiles();
273 if (!config->ltoObjPath.empty())
274 saveBuffer(buf[0], config->ltoObjPath);
276 // ThinLTO with index only option is required to generate only the index
277 // files. After that, we exit from linker and ThinLTO backend runs in a
278 // distributed environment.
284 if (!config->thinLTOCacheDir.empty())
285 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy);
287 if (!config->ltoObjPath.empty()) {
288 saveBuffer(buf[0], config->ltoObjPath);
289 for (unsigned i = 1; i != maxTasks; ++i)
290 saveBuffer(buf[i], config->ltoObjPath + Twine(i));
293 if (config->saveTemps) {
294 saveBuffer(buf[0], config->outputFile + ".lto.o");
295 for (unsigned i = 1; i != maxTasks; ++i)
296 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.o");
299 std::vector<InputFile *> ret;
300 for (unsigned i = 0; i != maxTasks; ++i)
302 ret.push_back(createObjectFile(MemoryBufferRef(buf[i], "lto.tmp")));
304 for (std::unique_ptr<MemoryBuffer> &file : files)
306 ret.push_back(createObjectFile(*file));