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.UseNewPM = config->ltoNewPassManager; 87 c.DebugPassManager = config->ltoDebugPassManager; 88 c.CSIRProfile = std::string(config->ltoCSProfileFile); 89 c.RunCSIRInstr = config->ltoCSProfileGenerate; 90 c.PGOWarnMismatch = config->ltoPGOWarnMismatch; 91 92 if (config->saveTemps) 93 checkError(c.addSaveTemps(std::string(config->outputFile) + ".", 94 /*UseInputModulePath*/ true)); 95 return c; 96 } 97 98 BitcodeCompiler::BitcodeCompiler() { 99 // Initialize indexFile. 100 if (!config->thinLTOIndexOnlyArg.empty()) 101 indexFile = openFile(config->thinLTOIndexOnlyArg); 102 103 // Initialize ltoObj. 104 lto::ThinBackend backend; 105 if (config->thinLTOIndexOnly) { 106 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); }; 107 backend = lto::createWriteIndexesThinBackend( 108 std::string(config->thinLTOPrefixReplace.first), 109 std::string(config->thinLTOPrefixReplace.second), 110 config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite); 111 } else { 112 backend = lto::createInProcessThinBackend( 113 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs)); 114 } 115 116 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend, 117 config->ltoPartitions); 118 } 119 120 BitcodeCompiler::~BitcodeCompiler() = default; 121 122 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); } 123 124 void BitcodeCompiler::add(BitcodeFile &f) { 125 lto::InputFile &obj = *f.obj; 126 unsigned symNum = 0; 127 std::vector<Symbol *> symBodies = f.getSymbols(); 128 std::vector<lto::SymbolResolution> resols(symBodies.size()); 129 130 if (config->thinLTOIndexOnly) 131 thinIndices.insert(obj.getName()); 132 133 // Provide a resolution to the LTO API for each symbol. 134 for (const lto::InputFile::Symbol &objSym : obj.symbols()) { 135 Symbol *sym = symBodies[symNum]; 136 lto::SymbolResolution &r = resols[symNum]; 137 ++symNum; 138 139 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 140 // reports two symbols for module ASM defined. Without this check, lld 141 // flags an undefined in IR with a definition in ASM as prevailing. 142 // Once IRObjectFile is fixed to report only one symbol this hack can 143 // be removed. 144 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 145 r.VisibleToRegularObj = sym->isUsedInRegularObj; 146 if (r.Prevailing) 147 undefine(sym); 148 149 // We tell LTO to not apply interprocedural optimization for wrapped 150 // (with -wrap) symbols because otherwise LTO would inline them while 151 // their values are still not final. 152 r.LinkerRedefined = !sym->canInline; 153 } 154 checkError(ltoObj->add(std::move(f.obj), resols)); 155 } 156 157 // Merge all the bitcode files we have seen, codegen the result 158 // and return the resulting objects. 159 std::vector<InputFile *> BitcodeCompiler::compile(COFFLinkerContext &ctx) { 160 unsigned maxTasks = ltoObj->getMaxTasks(); 161 buf.resize(maxTasks); 162 files.resize(maxTasks); 163 164 // The /lldltocache option specifies the path to a directory in which to cache 165 // native object files for ThinLTO incremental builds. If a path was 166 // specified, configure LTO to use it as the cache directory. 167 FileCache cache; 168 if (!config->ltoCache.empty()) 169 cache = 170 check(localCache("ThinLTO", "Thin", config->ltoCache, 171 [&](size_t task, std::unique_ptr<MemoryBuffer> mb) { 172 files[task] = std::move(mb); 173 })); 174 175 checkError(ltoObj->run( 176 [&](size_t task) { 177 return std::make_unique<CachedFileStream>( 178 std::make_unique<raw_svector_ostream>(buf[task])); 179 }, 180 cache)); 181 182 // Emit empty index files for non-indexed files 183 for (StringRef s : thinIndices) { 184 std::string path = getThinLTOOutputFile(s); 185 openFile(path + ".thinlto.bc"); 186 if (config->thinLTOEmitImportsFiles) 187 openFile(path + ".imports"); 188 } 189 190 // ThinLTO with index only option is required to generate only the index 191 // files. After that, we exit from linker and ThinLTO backend runs in a 192 // distributed environment. 193 if (config->thinLTOIndexOnly) { 194 if (!config->ltoObjPath.empty()) 195 saveBuffer(buf[0], config->ltoObjPath); 196 if (indexFile) 197 indexFile->close(); 198 return {}; 199 } 200 201 if (!config->ltoCache.empty()) 202 pruneCache(config->ltoCache, config->ltoCachePolicy); 203 204 std::vector<InputFile *> ret; 205 for (unsigned i = 0; i != maxTasks; ++i) { 206 // Assign unique names to LTO objects. This ensures they have unique names 207 // in the PDB if one is produced. The names should look like: 208 // - foo.exe.lto.obj 209 // - foo.exe.lto.1.obj 210 // - ... 211 StringRef ltoObjName = 212 saver().save(Twine(config->outputFile) + ".lto" + 213 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj"); 214 215 // Get the native object contents either from the cache or from memory. Do 216 // not use the cached MemoryBuffer directly, or the PDB will not be 217 // deterministic. 218 StringRef objBuf; 219 if (files[i]) 220 objBuf = files[i]->getBuffer(); 221 else 222 objBuf = buf[i]; 223 if (objBuf.empty()) 224 continue; 225 226 if (config->saveTemps) 227 saveBuffer(buf[i], ltoObjName); 228 ret.push_back(make<ObjFile>(ctx, MemoryBufferRef(objBuf, ltoObjName))); 229 } 230 231 return ret; 232 } 233