1 //===- LTO.cpp ------------------------------------------------------------===// 2 // 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 6 // 7 //===----------------------------------------------------------------------===// 8 9 #include "LTO.h" 10 #include "Config.h" 11 #include "Driver.h" 12 #include "InputFiles.h" 13 #include "Symbols.h" 14 #include "Target.h" 15 16 #include "lld/Common/Args.h" 17 #include "lld/Common/CommonLinkerContext.h" 18 #include "lld/Common/Strings.h" 19 #include "lld/Common/TargetOptionsCommandFlags.h" 20 #include "llvm/Bitcode/BitcodeWriter.h" 21 #include "llvm/LTO/Config.h" 22 #include "llvm/LTO/LTO.h" 23 #include "llvm/Support/Caching.h" 24 #include "llvm/Support/FileSystem.h" 25 #include "llvm/Support/Path.h" 26 #include "llvm/Support/raw_ostream.h" 27 #include "llvm/Transforms/ObjCARC.h" 28 29 using namespace lld; 30 using namespace lld::macho; 31 using namespace llvm; 32 using namespace llvm::MachO; 33 using namespace llvm::sys; 34 35 // Creates an empty file to store a list of object files for final 36 // linking of distributed ThinLTO. 37 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) { 38 std::error_code ec; 39 auto ret = 40 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None); 41 if (ec) { 42 error("cannot open " + file + ": " + ec.message()); 43 return nullptr; 44 } 45 return ret; 46 } 47 48 static std::string getThinLTOOutputFile(StringRef modulePath) { 49 return lto::getThinLTOOutputFile( 50 std::string(modulePath), std::string(config->thinLTOPrefixReplace.first), 51 std::string(config->thinLTOPrefixReplace.second)); 52 } 53 54 static lto::Config createConfig() { 55 lto::Config c; 56 c.Options = initTargetOptionsFromCodeGenFlags(); 57 c.Options.EmitAddrsig = config->icfLevel == ICFLevel::safe; 58 for (StringRef C : config->mllvmOpts) 59 c.MllvmArgs.emplace_back(C.str()); 60 c.CodeModel = getCodeModelFromCMModel(); 61 c.CPU = getCPUStr(); 62 c.MAttrs = getMAttrs(); 63 c.DiagHandler = diagnosticHandler; 64 c.PreCodeGenPassesHook = [](legacy::PassManager &pm) { 65 pm.add(createObjCARCContractPass()); 66 }; 67 68 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty(); 69 70 c.TimeTraceEnabled = config->timeTraceEnabled; 71 c.TimeTraceGranularity = config->timeTraceGranularity; 72 c.OptLevel = config->ltoo; 73 c.CGOptLevel = args::getCGOptLevel(config->ltoo); 74 if (config->saveTemps) 75 checkError(c.addSaveTemps(config->outputFile.str() + ".", 76 /*UseInputModulePath=*/true)); 77 return c; 78 } 79 80 // If `originalPath` exists, hardlinks `path` to `originalPath`. If that fails, 81 // or `originalPath` is not set, saves `buffer` to `path`. 82 static void saveOrHardlinkBuffer(StringRef buffer, const Twine &path, 83 std::optional<StringRef> originalPath) { 84 if (originalPath) { 85 auto err = fs::create_hard_link(*originalPath, path); 86 if (!err) 87 return; 88 } 89 saveBuffer(buffer, path); 90 } 91 92 BitcodeCompiler::BitcodeCompiler() { 93 // Initialize indexFile. 94 if (!config->thinLTOIndexOnlyArg.empty()) 95 indexFile = openFile(config->thinLTOIndexOnlyArg); 96 97 // Initialize ltoObj. 98 lto::ThinBackend backend; 99 auto onIndexWrite = [&](StringRef S) { thinIndices.erase(S); }; 100 if (config->thinLTOIndexOnly) { 101 backend = lto::createWriteIndexesThinBackend( 102 std::string(config->thinLTOPrefixReplace.first), 103 std::string(config->thinLTOPrefixReplace.second), 104 config->thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite); 105 } else { 106 backend = lto::createInProcessThinBackend( 107 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs), 108 onIndexWrite, config->thinLTOEmitIndexFiles, 109 config->thinLTOEmitImportsFiles); 110 } 111 112 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend); 113 } 114 115 void BitcodeCompiler::add(BitcodeFile &f) { 116 lto::InputFile &obj = *f.obj; 117 118 if (config->thinLTOEmitIndexFiles) 119 thinIndices.insert(obj.getName()); 120 121 ArrayRef<lto::InputFile::Symbol> objSyms = obj.symbols(); 122 std::vector<lto::SymbolResolution> resols; 123 resols.reserve(objSyms.size()); 124 125 // Provide a resolution to the LTO API for each symbol. 126 bool exportDynamic = 127 config->outputType != MH_EXECUTE || config->exportDynamic; 128 auto symIt = f.symbols.begin(); 129 for (const lto::InputFile::Symbol &objSym : objSyms) { 130 resols.emplace_back(); 131 lto::SymbolResolution &r = resols.back(); 132 Symbol *sym = *symIt++; 133 134 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 135 // reports two symbols for module ASM defined. Without this check, lld 136 // flags an undefined in IR with a definition in ASM as prevailing. 137 // Once IRObjectFile is fixed to report only one symbol this hack can 138 // be removed. 139 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 140 141 if (const auto *defined = dyn_cast<Defined>(sym)) { 142 r.ExportDynamic = 143 defined->isExternal() && !defined->privateExtern && exportDynamic; 144 r.FinalDefinitionInLinkageUnit = 145 !defined->isExternalWeakDef() && !defined->interposable; 146 } else if (const auto *common = dyn_cast<CommonSymbol>(sym)) { 147 r.ExportDynamic = !common->privateExtern && exportDynamic; 148 r.FinalDefinitionInLinkageUnit = true; 149 } 150 151 r.VisibleToRegularObj = 152 sym->isUsedInRegularObj || (r.Prevailing && r.ExportDynamic); 153 154 // Un-define the symbol so that we don't get duplicate symbol errors when we 155 // load the ObjFile emitted by LTO compilation. 156 if (r.Prevailing) 157 replaceSymbol<Undefined>(sym, sym->getName(), sym->getFile(), 158 RefState::Strong, /*wasBitcodeSymbol=*/true); 159 160 // TODO: set the other resolution configs properly 161 } 162 checkError(ltoObj->add(std::move(f.obj), resols)); 163 } 164 165 // If LazyObjFile has not been added to link, emit empty index files. 166 // This is needed because this is what GNU gold plugin does and we have a 167 // distributed build system that depends on that behavior. 168 static void thinLTOCreateEmptyIndexFiles() { 169 DenseSet<StringRef> linkedBitCodeFiles; 170 for (InputFile *file : inputFiles) 171 if (auto *f = dyn_cast<BitcodeFile>(file)) 172 if (!f->lazy) 173 linkedBitCodeFiles.insert(f->getName()); 174 175 for (InputFile *file : inputFiles) { 176 if (auto *f = dyn_cast<BitcodeFile>(file)) { 177 if (!f->lazy) 178 continue; 179 if (linkedBitCodeFiles.contains(f->getName())) 180 continue; 181 std::string path = 182 replaceThinLTOSuffix(getThinLTOOutputFile(f->obj->getName())); 183 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc"); 184 if (!os) 185 continue; 186 187 ModuleSummaryIndex m(/*HaveGVs=*/false); 188 m.setSkipModuleByDistributedBackend(); 189 writeIndexToFile(m, *os); 190 if (config->thinLTOEmitImportsFiles) 191 openFile(path + ".imports"); 192 } 193 } 194 } 195 196 // Merge all the bitcode files we have seen, codegen the result 197 // and return the resulting ObjectFile(s). 198 std::vector<ObjFile *> BitcodeCompiler::compile() { 199 unsigned maxTasks = ltoObj->getMaxTasks(); 200 buf.resize(maxTasks); 201 files.resize(maxTasks); 202 203 // The -cache_path_lto option specifies the path to a directory in which 204 // to cache native object files for ThinLTO incremental builds. If a path was 205 // specified, configure LTO to use it as the cache directory. 206 FileCache cache; 207 if (!config->thinLTOCacheDir.empty()) 208 cache = check(localCache("ThinLTO", "Thin", config->thinLTOCacheDir, 209 [&](size_t task, const Twine &moduleName, 210 std::unique_ptr<MemoryBuffer> mb) { 211 files[task] = std::move(mb); 212 })); 213 214 checkError(ltoObj->run( 215 [&](size_t task, const Twine &moduleName) { 216 return std::make_unique<CachedFileStream>( 217 std::make_unique<raw_svector_ostream>(buf[task])); 218 }, 219 cache)); 220 221 // Emit empty index files for non-indexed files 222 for (StringRef s : thinIndices) { 223 std::string path = getThinLTOOutputFile(s); 224 openFile(path + ".thinlto.bc"); 225 if (config->thinLTOEmitImportsFiles) 226 openFile(path + ".imports"); 227 } 228 229 if (config->thinLTOEmitIndexFiles) 230 thinLTOCreateEmptyIndexFiles(); 231 232 // In ThinLTO mode, Clang passes a temporary directory in -object_path_lto, 233 // while the argument is a single file in FullLTO mode. 234 bool objPathIsDir = true; 235 if (!config->ltoObjPath.empty()) { 236 if (std::error_code ec = fs::create_directories(config->ltoObjPath)) 237 fatal("cannot create LTO object path " + config->ltoObjPath + ": " + 238 ec.message()); 239 240 if (!fs::is_directory(config->ltoObjPath)) { 241 objPathIsDir = false; 242 unsigned objCount = 243 count_if(buf, [](const SmallString<0> &b) { return !b.empty(); }); 244 if (objCount > 1) 245 fatal("-object_path_lto must specify a directory when using ThinLTO"); 246 } 247 } 248 249 auto outputFilePath = [objPathIsDir](int i) { 250 SmallString<261> filePath("/tmp/lto.tmp"); 251 if (!config->ltoObjPath.empty()) { 252 filePath = config->ltoObjPath; 253 if (objPathIsDir) 254 path::append(filePath, Twine(i) + "." + 255 getArchitectureName(config->arch()) + 256 ".lto.o"); 257 } 258 return filePath; 259 }; 260 261 // ThinLTO with index only option is required to generate only the index 262 // files. After that, we exit from linker and ThinLTO backend runs in a 263 // distributed environment. 264 if (config->thinLTOIndexOnly) { 265 if (!config->ltoObjPath.empty()) 266 saveBuffer(buf[0], outputFilePath(0)); 267 if (indexFile) 268 indexFile->close(); 269 return {}; 270 } 271 272 if (!config->thinLTOCacheDir.empty()) 273 pruneCache(config->thinLTOCacheDir, config->thinLTOCachePolicy, files); 274 275 std::vector<ObjFile *> ret; 276 for (unsigned i = 0; i < maxTasks; ++i) { 277 // Get the native object contents either from the cache or from memory. Do 278 // not use the cached MemoryBuffer directly to ensure dsymutil does not 279 // race with the cache pruner. 280 StringRef objBuf; 281 std::optional<StringRef> cachePath; 282 if (files[i]) { 283 objBuf = files[i]->getBuffer(); 284 cachePath = files[i]->getBufferIdentifier(); 285 } else { 286 objBuf = buf[i]; 287 } 288 if (objBuf.empty()) 289 continue; 290 291 // FIXME: should `saveTemps` and `ltoObjPath` use the same file name? 292 if (config->saveTemps) 293 saveBuffer(objBuf, 294 config->outputFile + ((i == 0) ? "" : Twine(i)) + ".lto.o"); 295 296 auto filePath = outputFilePath(i); 297 uint32_t modTime = 0; 298 if (!config->ltoObjPath.empty()) { 299 saveOrHardlinkBuffer(objBuf, filePath, cachePath); 300 modTime = getModTime(filePath); 301 } 302 ret.push_back(make<ObjFile>( 303 MemoryBufferRef(objBuf, saver().save(filePath.str())), modTime, "")); 304 } 305 306 return ret; 307 } 308