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