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/ErrorHandler.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/Caching.h" 24 #include "llvm/LTO/Config.h" 25 #include "llvm/LTO/LTO.h" 26 #include "llvm/Object/SymbolicFile.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 66 // Always emit a section per function/datum with LTO. LLVM LTO should get most 67 // of the benefit of linker GC, but there are still opportunities for ICF. 68 c.Options.FunctionSections = true; 69 c.Options.DataSections = true; 70 71 // Use static reloc model on 32-bit x86 because it usually results in more 72 // compact code, and because there are also known code generation bugs when 73 // using the PIC model (see PR34306). 74 if (config->machine == COFF::IMAGE_FILE_MACHINE_I386) 75 c.RelocModel = Reloc::Static; 76 else 77 c.RelocModel = Reloc::PIC_; 78 c.DisableVerify = true; 79 c.DiagHandler = diagnosticHandler; 80 c.OptLevel = config->ltoo; 81 c.CPU = getCPUStr(); 82 c.MAttrs = getMAttrs(); 83 c.CGOptLevel = args::getCGOptLevel(config->ltoo); 84 c.AlwaysEmitRegularLTOObj = !config->ltoObjPath.empty(); 85 c.UseNewPM = config->ltoNewPassManager; 86 c.DebugPassManager = config->ltoDebugPassManager; 87 88 if (config->saveTemps) 89 checkError(c.addSaveTemps(std::string(config->outputFile) + ".", 90 /*UseInputModulePath*/ true)); 91 return c; 92 } 93 94 BitcodeCompiler::BitcodeCompiler() { 95 // Initialize indexFile. 96 if (!config->thinLTOIndexOnlyArg.empty()) 97 indexFile = openFile(config->thinLTOIndexOnlyArg); 98 99 // Initialize ltoObj. 100 lto::ThinBackend backend; 101 if (config->thinLTOIndexOnly) { 102 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); }; 103 backend = lto::createWriteIndexesThinBackend( 104 std::string(config->thinLTOPrefixReplace.first), 105 std::string(config->thinLTOPrefixReplace.second), 106 config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite); 107 } else { 108 backend = lto::createInProcessThinBackend( 109 llvm::heavyweight_hardware_concurrency(config->thinLTOJobs)); 110 } 111 112 ltoObj = std::make_unique<lto::LTO>(createConfig(), backend, 113 config->ltoPartitions); 114 } 115 116 BitcodeCompiler::~BitcodeCompiler() = default; 117 118 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); } 119 120 void BitcodeCompiler::add(BitcodeFile &f) { 121 lto::InputFile &obj = *f.obj; 122 unsigned symNum = 0; 123 std::vector<Symbol *> symBodies = f.getSymbols(); 124 std::vector<lto::SymbolResolution> resols(symBodies.size()); 125 126 if (config->thinLTOIndexOnly) 127 thinIndices.insert(obj.getName()); 128 129 // Provide a resolution to the LTO API for each symbol. 130 for (const lto::InputFile::Symbol &objSym : obj.symbols()) { 131 Symbol *sym = symBodies[symNum]; 132 lto::SymbolResolution &r = resols[symNum]; 133 ++symNum; 134 135 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 136 // reports two symbols for module ASM defined. Without this check, lld 137 // flags an undefined in IR with a definition in ASM as prevailing. 138 // Once IRObjectFile is fixed to report only one symbol this hack can 139 // be removed. 140 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 141 r.VisibleToRegularObj = sym->isUsedInRegularObj; 142 if (r.Prevailing) 143 undefine(sym); 144 145 // We tell LTO to not apply interprocedural optimization for wrapped 146 // (with -wrap) symbols because otherwise LTO would inline them while 147 // their values are still not final. 148 r.LinkerRedefined = !sym->canInline; 149 } 150 checkError(ltoObj->add(std::move(f.obj), resols)); 151 } 152 153 // Merge all the bitcode files we have seen, codegen the result 154 // and return the resulting objects. 155 std::vector<InputFile *> BitcodeCompiler::compile() { 156 unsigned maxTasks = ltoObj->getMaxTasks(); 157 buf.resize(maxTasks); 158 files.resize(maxTasks); 159 160 // The /lldltocache option specifies the path to a directory in which to cache 161 // native object files for ThinLTO incremental builds. If a path was 162 // specified, configure LTO to use it as the cache directory. 163 lto::NativeObjectCache cache; 164 if (!config->ltoCache.empty()) 165 cache = check(lto::localCache( 166 config->ltoCache, [&](size_t task, std::unique_ptr<MemoryBuffer> mb) { 167 files[task] = std::move(mb); 168 })); 169 170 checkError(ltoObj->run( 171 [&](size_t task) { 172 return std::make_unique<lto::NativeObjectStream>( 173 std::make_unique<raw_svector_ostream>(buf[task])); 174 }, 175 cache)); 176 177 // Emit empty index files for non-indexed files 178 for (StringRef s : thinIndices) { 179 std::string path = getThinLTOOutputFile(s); 180 openFile(path + ".thinlto.bc"); 181 if (config->thinLTOEmitImportsFiles) 182 openFile(path + ".imports"); 183 } 184 185 // ThinLTO with index only option is required to generate only the index 186 // files. After that, we exit from linker and ThinLTO backend runs in a 187 // distributed environment. 188 if (config->thinLTOIndexOnly) { 189 if (!config->ltoObjPath.empty()) 190 saveBuffer(buf[0], config->ltoObjPath); 191 if (indexFile) 192 indexFile->close(); 193 return {}; 194 } 195 196 if (!config->ltoCache.empty()) 197 pruneCache(config->ltoCache, config->ltoCachePolicy); 198 199 std::vector<InputFile *> ret; 200 for (unsigned i = 0; i != maxTasks; ++i) { 201 // Assign unique names to LTO objects. This ensures they have unique names 202 // in the PDB if one is produced. The names should look like: 203 // - foo.exe.lto.obj 204 // - foo.exe.lto.1.obj 205 // - ... 206 StringRef ltoObjName = 207 saver.save(Twine(config->outputFile) + ".lto" + 208 (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj"); 209 210 // Get the native object contents either from the cache or from memory. Do 211 // not use the cached MemoryBuffer directly, or the PDB will not be 212 // deterministic. 213 StringRef objBuf; 214 if (files[i]) 215 objBuf = files[i]->getBuffer(); 216 else 217 objBuf = buf[i]; 218 if (objBuf.empty()) 219 continue; 220 221 if (config->saveTemps) 222 saveBuffer(buf[i], ltoObjName); 223 ret.push_back(make<ObjFile>(MemoryBufferRef(objBuf, ltoObjName))); 224 } 225 226 return ret; 227 } 228