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 42 using namespace lld; 43 using namespace lld::coff; 44 45 // Creates an empty file to and returns a raw_fd_ostream to write to it. 46 static std::unique_ptr<raw_fd_ostream> openFile(StringRef file) { 47 std::error_code ec; 48 auto ret = 49 llvm::make_unique<raw_fd_ostream>(file, ec, sys::fs::OpenFlags::F_None); 50 if (ec) { 51 error("cannot open " + file + ": " + ec.message()); 52 return nullptr; 53 } 54 return ret; 55 } 56 57 static std::string getThinLTOOutputFile(StringRef path) { 58 return lto::getThinLTOOutputFile(path, 59 config->thinLTOPrefixReplace.first, 60 config->thinLTOPrefixReplace.second); 61 } 62 63 static lto::Config createConfig() { 64 lto::Config c; 65 c.Options = initTargetOptionsFromCodeGenFlags(); 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 86 if (config->saveTemps) 87 checkError(c.addSaveTemps(std::string(config->outputFile) + ".", 88 /*UseInputModulePath*/ true)); 89 return c; 90 } 91 92 BitcodeCompiler::BitcodeCompiler() { 93 // Initialize indexFile. 94 if (!config->thinLTOIndexOnlyArg.empty()) 95 indexFile = openFile(config->thinLTOIndexOnlyArg); 96 97 // Initialize ltoObj. 98 lto::ThinBackend backend; 99 if (config->thinLTOIndexOnly) { 100 auto OnIndexWrite = [&](StringRef S) { thinIndices.erase(S); }; 101 backend = lto::createWriteIndexesThinBackend( 102 config->thinLTOPrefixReplace.first, config->thinLTOPrefixReplace.second, 103 config->thinLTOEmitImportsFiles, indexFile.get(), OnIndexWrite); 104 } else if (config->thinLTOJobs != 0) { 105 backend = lto::createInProcessThinBackend(config->thinLTOJobs); 106 } 107 108 ltoObj = llvm::make_unique<lto::LTO>(createConfig(), backend, 109 config->ltoPartitions); 110 } 111 112 BitcodeCompiler::~BitcodeCompiler() = default; 113 114 static void undefine(Symbol *s) { replaceSymbol<Undefined>(s, s->getName()); } 115 116 void BitcodeCompiler::add(BitcodeFile &f) { 117 lto::InputFile &obj = *f.obj; 118 unsigned symNum = 0; 119 std::vector<Symbol *> symBodies = f.getSymbols(); 120 std::vector<lto::SymbolResolution> resols(symBodies.size()); 121 122 if (config->thinLTOIndexOnly) 123 thinIndices.insert(obj.getName()); 124 125 // Provide a resolution to the LTO API for each symbol. 126 for (const lto::InputFile::Symbol &objSym : obj.symbols()) { 127 Symbol *sym = symBodies[symNum]; 128 lto::SymbolResolution &r = resols[symNum]; 129 ++symNum; 130 131 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 132 // reports two symbols for module ASM defined. Without this check, lld 133 // flags an undefined in IR with a definition in ASM as prevailing. 134 // Once IRObjectFile is fixed to report only one symbol this hack can 135 // be removed. 136 r.Prevailing = !objSym.isUndefined() && sym->getFile() == &f; 137 r.VisibleToRegularObj = sym->isUsedInRegularObj; 138 if (r.Prevailing) 139 undefine(sym); 140 } 141 checkError(ltoObj->add(std::move(f.obj), resols)); 142 } 143 144 // Merge all the bitcode files we have seen, codegen the result 145 // and return the resulting objects. 146 std::vector<StringRef> BitcodeCompiler::compile() { 147 unsigned maxTasks = ltoObj->getMaxTasks(); 148 buf.resize(maxTasks); 149 files.resize(maxTasks); 150 151 // The /lldltocache option specifies the path to a directory in which to cache 152 // native object files for ThinLTO incremental builds. If a path was 153 // specified, configure LTO to use it as the cache directory. 154 lto::NativeObjectCache cache; 155 if (!config->ltoCache.empty()) 156 cache = check(lto::localCache( 157 config->ltoCache, [&](size_t task, std::unique_ptr<MemoryBuffer> mb) { 158 files[task] = std::move(mb); 159 })); 160 161 checkError(ltoObj->run( 162 [&](size_t task) { 163 return llvm::make_unique<lto::NativeObjectStream>( 164 llvm::make_unique<raw_svector_ostream>(buf[task])); 165 }, 166 cache)); 167 168 // Emit empty index files for non-indexed files 169 for (StringRef s : thinIndices) { 170 std::string path = getThinLTOOutputFile(s); 171 openFile(path + ".thinlto.bc"); 172 if (config->thinLTOEmitImportsFiles) 173 openFile(path + ".imports"); 174 } 175 176 // ThinLTO with index only option is required to generate only the index 177 // files. After that, we exit from linker and ThinLTO backend runs in a 178 // distributed environment. 179 if (config->thinLTOIndexOnly) { 180 if (indexFile) 181 indexFile->close(); 182 return {}; 183 } 184 185 if (!config->ltoCache.empty()) 186 pruneCache(config->ltoCache, config->ltoCachePolicy); 187 188 std::vector<StringRef> ret; 189 for (unsigned i = 0; i != maxTasks; ++i) { 190 if (buf[i].empty()) 191 continue; 192 if (config->saveTemps) { 193 if (i == 0) 194 saveBuffer(buf[i], config->outputFile + ".lto.obj"); 195 else 196 saveBuffer(buf[i], config->outputFile + Twine(i) + ".lto.obj"); 197 } 198 ret.emplace_back(buf[i].data(), buf[i].size()); 199 } 200 201 for (std::unique_ptr<MemoryBuffer> &file : files) 202 if (file) 203 ret.push_back(file->getBuffer()); 204 205 return ret; 206 } 207