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/Strings.h" 16 #include "lld/Common/TargetOptionsCommandFlags.h" 17 #include "llvm/ADT/STLExtras.h" 18 #include "llvm/ADT/SmallString.h" 19 #include "llvm/ADT/StringRef.h" 20 #include "llvm/ADT/Twine.h" 21 #include "llvm/Bitcode/BitcodeWriter.h" 22 #include "llvm/IR/DiagnosticPrinter.h" 23 #include "llvm/LTO/Config.h" 24 #include "llvm/LTO/LTO.h" 25 #include "llvm/Object/SymbolicFile.h" 26 #include "llvm/Support/Caching.h" 27 #include "llvm/Support/CodeGen.h" 28 #include "llvm/Support/Error.h" 29 #include "llvm/Support/FileSystem.h" 30 #include "llvm/Support/MemoryBuffer.h" 31 #include "llvm/Support/raw_ostream.h" 32 #include <algorithm> 33 #include <cstddef> 34 #include <memory> 35 #include <string> 36 #include <system_error> 37 #include <vector> 38 39 using namespace llvm; 40 using namespace llvm::object; 41 using namespace lld; 42 using namespace lld::coff; 43 44 // Creates an empty file to and returns a raw_fd_ostream to write to it. 45 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) { 46 std::error_code ec; 47 auto ret = 48 std::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::OF_None); 49 if (ec) { 50 error("cannot open " + file + ": " + ec.message()); 51 return nullptr; 52 } 53 return ret; 54 } 55 56 static std::string getThinLTOOutputFile(StringRef path) { 57 return lto::getThinLTOOutputFile( 58 std::string(path), std::string(config->thinLTOPrefixReplace.first), 59 std::string(config->thinLTOPrefixReplace.second)); 60 } 61 62 static lto::Config createConfig() { 63 lto::Config c; 64 c.Options = initTargetOptionsFromCodeGenFlags(); 65 c.Options.EmitAddrsig = true; 66 67 // Always emit a section per function/datum with LTO. LLVM LTO should get most 68 // of the benefit of linker GC, but there are still opportunities for ICF. 69 c.Options.FunctionSections = true; 70 c.Options.DataSections = true; 71 72 // Use static reloc model on 32-bit x86 because it usually results in more 73 // compact code, and because there are also known code generation bugs when 74 // using the PIC model (see PR34306). 75 if (config->machine == COFF::IMAGE_FILE_MACHINE_I386) 76 c.RelocModel = Reloc::Static; 77 else 78 c.RelocModel = Reloc::PIC_; 79 c.DisableVerify = true; 80 c.DiagHandler = diagnosticHandler; 81 c.OptLevel = config->ltoo; 82 c.CPU = getCPUStr(); 83 c.MAttrs = getMAttrs(); 84 c.CGOptLevel = args::getCGOptLevel(config->ltoo); 85 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty(); 86 c.DebugPassManager = config->ltoDebugPassManager; 87 c.CSIRProfile = std::string(config->ltoCSProfileFile); 88 c.RunCSIRInstr = config->ltoCSProfileGenerate; 89 c.PGOWarnMismatch = config->ltoPGOWarnMismatch; 90 91 if (config->saveTemps) 92 checkError(c.addSaveTemps(std::string(config->outputFile) + ".", 93 /*UseInputModulePath*/ true)); 94 return c; 95 } 96 97 BitcodeCompiler::BitcodeCompiler() { 98 // Initialize indexFile. 99 if (!config->thinLTOIndexOnlyArg.empty()) 100 indexFile = openFile(config->thinLTOIndexOnlyArg); 101 102 // Initialize ltoObj. 103 lto::ThinBackend backend; 104 if (config->thinLTOIndexOnly) { 105 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); }; 106 backend = lto::createWriteIndexesThinBackend( 107 std::string(config->thinLTOPrefixReplace.first), 108 std::string(config->thinLTOPrefixReplace.second), 109 config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite); 110 } else { 111 backend = lto::createInProcessThinBackend( 112 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs)); 113 } 114 115 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend, 116 config->ltoPartitions); 117 } 118 119 BitcodeCompiler::~BitcodeCompiler() = default; 120 121 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); } 122 123 void BitcodeCompiler::add(BitcodeFile &f) { 124 lto::InputFile &obj = *f.obj; 125 unsigned symNum = 0; 126 std::vector<Symbol *> symBodies = f.getSymbols(); 127 std::vector<lto::SymbolResolution> resols(symBodies.size()); 128 129 if (config->thinLTOIndexOnly) 130 thinIndices.insert(obj.getName()); 131 132 // Provide a resolution to the LTO API for each symbol. 133 for (const lto::InputFile::Symbol &objSym : obj.symbols()) { 134 Symbol *sym = symBodies[symNum]; 135 lto::SymbolResolution &r = resols[symNum]; 136 ++symNum; 137 138 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 139 // reports two symbols for module ASM defined. Without this check, lld 140 // flags an undefined in IR with a definition in ASM as prevailing. 141 // Once IRObjectFile is fixed to report only one symbol this hack can 142 // be removed. 143 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 144 r.VisibleToRegularObj = sym->isUsedInRegularObj; 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 // Merge all the bitcode files we have seen, codegen the result 157 // and return the resulting objects. 158 std::vector<InputFile *> BitcodeCompiler::compile(COFFLinkerContext &ctx) { 159 unsigned maxTasks = ltoObj->getMaxTasks(); 160 buf.resize(maxTasks); 161 files.resize(maxTasks); 162 163 // The /lldltocache option specifies the path to a directory in which to cache 164 // native object files for ThinLTO incremental builds. If a path was 165 // specified, configure LTO to use it as the cache directory. 166 FileCache cache; 167 if (!config->ltoCache.empty()) 168 cache = 169 check(localCache("ThinLTO", "Thin", config->ltoCache, 170 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) { 171 files[task] = std::move(mb); 172 })); 173 174 checkError(ltoObj->run( 175 [&](size_t task) { 176 return std::make_unique<CachedFileStream>( 177 std::make_unique<raw_svector_ostream>(buf[task])); 178 }, 179 cache)); 180 181 // Emit empty index files for non-indexed files 182 for (StringRef s : thinIndices) { 183 std::string path = getThinLTOOutputFile(s); 184 openFile(path + ".thinlto.bc"); 185 if (config->thinLTOEmitImportsFiles) 186 openFile(path + ".imports"); 187 } 188 189 // ThinLTO with index only option is required to generate only the index 190 // files. After that, we exit from linker and ThinLTO backend runs in a 191 // distributed environment. 192 if (config->thinLTOIndexOnly) { 193 if (!config->ltoObjPath.empty()) 194 saveBuffer(buf[0], config->ltoObjPath); 195 if (indexFile) 196 indexFile->close(); 197 return {}; 198 } 199 200 if (!config->ltoCache.empty()) 201 pruneCache(config->ltoCache, config->ltoCachePolicy); 202 203 std::vector<InputFile *> ret; 204 for (unsigned i = 0; i != maxTasks; ++i) { 205 // Assign unique names to LTO objects. This ensures they have unique names 206 // in the PDB if one is produced. The names should look like: 207 // - foo.exe.lto.obj 208 // - foo.exe.lto.1.obj 209 // - ... 210 StringRef ltoObjName = 211 saver().save(Twine(config->outputFile) + ".lto" + 212 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj"); 213 214 // Get the native object contents either from the cache or from memory. Do 215 // not use the cached MemoryBuffer directly, or the PDB will not be 216 // deterministic. 217 StringRef objBuf; 218 if (files[i]) 219 objBuf = files[i]->getBuffer(); 220 else 221 objBuf = buf[i]; 222 if (objBuf.empty()) 223 continue; 224 225 if (config->saveTemps) 226 saveBuffer(buf[i], ltoObjName); 227 ret.push_back(make<ObjFile>(ctx, MemoryBufferRef(objBuf, ltoObjName))); 228 } 229 230 return ret; 231 } 232