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 "InputFiles.h" 12 #include "Symbols.h" 13 #include "lld/Common/Args.h" 14 #include "lld/Common/CommonLinkerContext.h" 15 #include "lld/Common/ErrorHandler.h" 16 #include "lld/Common/Filesystem.h" 17 #include "lld/Common/Strings.h" 18 #include "lld/Common/TargetOptionsCommandFlags.h" 19 #include "llvm/ADT/STLExtras.h" 20 #include "llvm/ADT/SmallString.h" 21 #include "llvm/ADT/StringRef.h" 22 #include "llvm/ADT/Twine.h" 23 #include "llvm/Bitcode/BitcodeWriter.h" 24 #include "llvm/IR/DiagnosticPrinter.h" 25 #include "llvm/LTO/Config.h" 26 #include "llvm/LTO/LTO.h" 27 #include "llvm/Object/SymbolicFile.h" 28 #include "llvm/Support/Caching.h" 29 #include "llvm/Support/CodeGen.h" 30 #include "llvm/Support/Error.h" 31 #include "llvm/Support/FileSystem.h" 32 #include "llvm/Support/MemoryBuffer.h" 33 #include "llvm/Support/Path.h" 34 #include "llvm/Support/raw_ostream.h" 35 #include <algorithm> 36 #include <cstddef> 37 #include <memory> 38 #include <string> 39 #include <system_error> 40 #include <vector> 41 42 using namespace llvm; 43 using namespace lld::wasm; 44 using namespace lld; 45 46 static std::string getThinLTOOutputFile(StringRef modulePath) { 47 return lto::getThinLTOOutputFile(modulePath, ctx.arg.thinLTOPrefixReplaceOld, 48 ctx.arg.thinLTOPrefixReplaceNew); 49 } 50 51 static lto::Config createConfig() { 52 lto::Config c; 53 c.Options = initTargetOptionsFromCodeGenFlags(); 54 55 // Always emit a section per function/data with LTO. 56 c.Options.FunctionSections = true; 57 c.Options.DataSections = true; 58 59 c.DisableVerify = ctx.arg.disableVerify; 60 c.DiagHandler = diagnosticHandler; 61 c.OptLevel = ctx.arg.ltoo; 62 c.MAttrs = getMAttrs(); 63 c.CGOptLevel = ctx.arg.ltoCgo; 64 c.DebugPassManager = ctx.arg.ltoDebugPassManager; 65 c.AlwaysEmitRegularLTOObj = !ctx.arg.ltoObjPath.empty(); 66 67 if (ctx.arg.relocatable) 68 c.RelocModel = std::nullopt; 69 else if (ctx.isPic) 70 c.RelocModel = Reloc::PIC_; 71 else 72 c.RelocModel = Reloc::Static; 73 74 if (ctx.arg.saveTemps) 75 checkError(c.addSaveTemps(ctx.arg.outputFile.str() + ".", 76 /*UseInputModulePath*/ true)); 77 return c; 78 } 79 80 namespace lld::wasm { 81 82 BitcodeCompiler::BitcodeCompiler() { 83 // Initialize indexFile. 84 if (!ctx.arg.thinLTOIndexOnlyArg.empty()) 85 indexFile = openFile(ctx.arg.thinLTOIndexOnlyArg); 86 87 // Initialize ltoObj. 88 lto::ThinBackend backend; 89 auto onIndexWrite = [&](StringRef s) { thinIndices.erase(s); }; 90 if (ctx.arg.thinLTOIndexOnly) { 91 backend = lto::createWriteIndexesThinBackend( 92 llvm::hardware_concurrency(ctx.arg.thinLTOJobs), 93 std::string(ctx.arg.thinLTOPrefixReplaceOld), 94 std::string(ctx.arg.thinLTOPrefixReplaceNew), 95 std::string(ctx.arg.thinLTOPrefixReplaceNativeObject), 96 ctx.arg.thinLTOEmitImportsFiles, indexFile.get(), onIndexWrite); 97 } else { 98 backend = lto::createInProcessThinBackend( 99 llvm::heavyweight_hardware_concurrency(ctx.arg.thinLTOJobs), 100 onIndexWrite, ctx.arg.thinLTOEmitIndexFiles, 101 ctx.arg.thinLTOEmitImportsFiles); 102 } 103 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend, 104 ctx.arg.ltoPartitions); 105 } 106 107 BitcodeCompiler::~BitcodeCompiler() = default; 108 109 static void undefine(Symbol *s) { 110 if (auto f = dyn_cast<DefinedFunction>(s)) 111 replaceSymbol<UndefinedFunction>(f, f->getName(), std::nullopt, 112 std::nullopt, 0, f->getFile(), 113 f->signature); 114 else if (isa<DefinedData>(s)) 115 replaceSymbol<UndefinedData>(s, s->getName(), 0, s->getFile()); 116 else 117 llvm_unreachable("unexpected symbol kind"); 118 } 119 120 void BitcodeCompiler::add(BitcodeFile &f) { 121 lto::InputFile &obj = *f.obj; 122 unsigned symNum = 0; 123 ArrayRef<Symbol *> syms = f.getSymbols(); 124 std::vector<lto::SymbolResolution> resols(syms.size()); 125 126 if (ctx.arg.thinLTOEmitIndexFiles) { 127 thinIndices.insert(obj.getName()); 128 } 129 130 // Provide a resolution to the LTO API for each symbol. 131 for (const lto::InputFile::Symbol &objSym : obj.symbols()) { 132 Symbol *sym = syms[symNum]; 133 lto::SymbolResolution &r = resols[symNum]; 134 ++symNum; 135 136 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 137 // reports two symbols for module ASM defined. Without this check, lld 138 // flags an undefined in IR with a definition in ASM as prevailing. 139 // Once IRObjectFile is fixed to report only one symbol this hack can 140 // be removed. 141 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 142 r.VisibleToRegularObj = ctx.arg.relocatable || sym->isUsedInRegularObj || 143 sym->isNoStrip() || 144 (r.Prevailing && sym->isExported()); 145 if (r.Prevailing) 146 undefine(sym); 147 148 // We tell LTO to not apply interprocedural optimization for wrapped 149 // (with --wrap) symbols because otherwise LTO would inline them while 150 // their values are still not final. 151 r.LinkerRedefined = !sym->canInline; 152 } 153 checkError(ltoObj->add(std::move(f.obj), resols)); 154 } 155 156 // If LazyObjFile has not been added to link, emit empty index files. 157 // This is needed because this is what GNU gold plugin does and we have a 158 // distributed build system that depends on that behavior. 159 static void thinLTOCreateEmptyIndexFiles() { 160 DenseSet<StringRef> linkedBitCodeFiles; 161 for (BitcodeFile *f : ctx.bitcodeFiles) 162 linkedBitCodeFiles.insert(f->getName()); 163 164 for (BitcodeFile *f : ctx.lazyBitcodeFiles) { 165 if (!f->lazy) 166 continue; 167 if (linkedBitCodeFiles.contains(f->getName())) 168 continue; 169 std::string path = 170 replaceThinLTOSuffix(getThinLTOOutputFile(f->obj->getName())); 171 std::unique_ptr<raw_fd_ostream> os = openFile(path + ".thinlto.bc"); 172 if (!os) 173 continue; 174 175 ModuleSummaryIndex m(/*HaveGVs*/ false); 176 m.setSkipModuleByDistributedBackend(); 177 writeIndexToFile(m, *os); 178 if (ctx.arg.thinLTOEmitImportsFiles) 179 openFile(path + ".imports"); 180 } 181 } 182 183 // Merge all the bitcode files we have seen, codegen the result 184 // and return the resulting objects. 185 std::vector<StringRef> BitcodeCompiler::compile() { 186 unsigned maxTasks = ltoObj->getMaxTasks(); 187 buf.resize(maxTasks); 188 files.resize(maxTasks); 189 190 // The --thinlto-cache-dir option specifies the path to a directory in which 191 // to cache native object files for ThinLTO incremental builds. If a path was 192 // specified, configure LTO to use it as the cache directory. 193 FileCache cache; 194 if (!ctx.arg.thinLTOCacheDir.empty()) 195 cache = check(localCache("ThinLTO", "Thin", ctx.arg.thinLTOCacheDir, 196 [&](size_t task, const Twine &moduleName, 197 std::unique_ptr<MemoryBuffer> mb) { 198 files[task] = std::move(mb); 199 })); 200 201 checkError(ltoObj->run( 202 [&](size_t task, const Twine &moduleName) { 203 buf[task].first = moduleName.str(); 204 return std::make_unique<CachedFileStream>( 205 std::make_unique<raw_svector_ostream>(buf[task].second)); 206 }, 207 cache)); 208 209 // Emit empty index files for non-indexed files but not in single-module mode. 210 for (StringRef s : thinIndices) { 211 std::string path(s); 212 openFile(path + ".thinlto.bc"); 213 if (ctx.arg.thinLTOEmitImportsFiles) 214 openFile(path + ".imports"); 215 } 216 217 if (ctx.arg.thinLTOEmitIndexFiles) 218 thinLTOCreateEmptyIndexFiles(); 219 220 if (ctx.arg.thinLTOIndexOnly) { 221 if (!ctx.arg.ltoObjPath.empty()) 222 saveBuffer(buf[0].second, ctx.arg.ltoObjPath); 223 224 // ThinLTO with index only option is required to generate only the index 225 // files. After that, we exit from linker and ThinLTO backend runs in a 226 // distributed environment. 227 if (indexFile) 228 indexFile->close(); 229 return {}; 230 } 231 232 if (!ctx.arg.thinLTOCacheDir.empty()) 233 pruneCache(ctx.arg.thinLTOCacheDir, ctx.arg.thinLTOCachePolicy, files); 234 235 std::vector<StringRef> ret; 236 for (unsigned i = 0; i != maxTasks; ++i) { 237 StringRef objBuf = buf[i].second; 238 StringRef bitcodeFilePath = buf[i].first; 239 if (objBuf.empty()) 240 continue; 241 ret.emplace_back(objBuf.data(), objBuf.size()); 242 if (!ctx.arg.saveTemps) 243 continue; 244 245 // If the input bitcode file is path/to/x.o and -o specifies a.out, the 246 // corresponding native relocatable file path will look like: 247 // path/to/a.out.lto.x.o. 248 StringRef ltoObjName; 249 if (bitcodeFilePath == "ld-temp.o") { 250 ltoObjName = 251 saver().save(Twine(ctx.arg.outputFile) + ".lto" + 252 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".o"); 253 } else { 254 StringRef directory = sys::path::parent_path(bitcodeFilePath); 255 // For an archive member, which has an identifier like "d/a.a(coll.o at 256 // 8)" (see BitcodeFile::BitcodeFile), use the filename; otherwise, use 257 // the stem (d/a.o => a). 258 StringRef baseName = bitcodeFilePath.ends_with(")") 259 ? sys::path::filename(bitcodeFilePath) 260 : sys::path::stem(bitcodeFilePath); 261 StringRef outputFileBaseName = sys::path::filename(ctx.arg.outputFile); 262 SmallString<256> path; 263 sys::path::append(path, directory, 264 outputFileBaseName + ".lto." + baseName + ".o"); 265 sys::path::remove_dots(path, true); 266 ltoObjName = saver().save(path.str()); 267 } 268 saveBuffer(objBuf, ltoObjName); 269 } 270 271 if (!ctx.arg.ltoObjPath.empty()) { 272 saveBuffer(buf[0].second, ctx.arg.ltoObjPath); 273 for (unsigned i = 1; i != maxTasks; ++i) 274 saveBuffer(buf[i].second, ctx.arg.ltoObjPath + Twine(i)); 275 } 276 277 for (std::unique_ptr<MemoryBuffer> &file : files) 278 if (file) 279 ret.push_back(file->getBuffer()); 280 281 return ret; 282 } 283 284 } // namespace lld::wasm 285