1 //===- LTO.cpp ------------------------------------------------------------===// 2 // 3 // The LLVM Linker 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #include "LTO.h" 11 #include "Config.h" 12 #include "InputFiles.h" 13 #include "Symbols.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/IR/DiagnosticPrinter.h" 22 #include "llvm/LTO/Caching.h" 23 #include "llvm/LTO/Config.h" 24 #include "llvm/LTO/LTO.h" 25 #include "llvm/Object/SymbolicFile.h" 26 #include "llvm/Support/CodeGen.h" 27 #include "llvm/Support/Error.h" 28 #include "llvm/Support/FileSystem.h" 29 #include "llvm/Support/MemoryBuffer.h" 30 #include "llvm/Support/raw_ostream.h" 31 #include <algorithm> 32 #include <cstddef> 33 #include <memory> 34 #include <string> 35 #include <system_error> 36 #include <vector> 37 38 using namespace llvm; 39 using namespace llvm::object; 40 41 using namespace lld; 42 using namespace lld::coff; 43 44 static std::unique_ptr<lto::LTO> createLTO() { 45 lto::Config C; 46 C.Options = InitTargetOptionsFromCodeGenFlags(); 47 48 // Always emit a section per function/datum with LTO. LLVM LTO should get most 49 // of the benefit of linker GC, but there are still opportunities for ICF. 50 C.Options.FunctionSections = true; 51 C.Options.DataSections = true; 52 53 // Use static reloc model on 32-bit x86 because it usually results in more 54 // compact code, and because there are also known code generation bugs when 55 // using the PIC model (see PR34306). 56 if (Config->Machine == COFF::IMAGE_FILE_MACHINE_I386) 57 C.RelocModel = Reloc::Static; 58 else 59 C.RelocModel = Reloc::PIC_; 60 C.DisableVerify = true; 61 C.DiagHandler = diagnosticHandler; 62 C.OptLevel = Config->LTOO; 63 C.CPU = GetCPUStr(); 64 C.MAttrs = GetMAttrs(); 65 66 if (Config->SaveTemps) 67 checkError(C.addSaveTemps(std::string(Config->OutputFile) + ".", 68 /*UseInputModulePath*/ true)); 69 lto::ThinBackend Backend; 70 if (Config->ThinLTOJobs != 0) 71 Backend = lto::createInProcessThinBackend(Config->ThinLTOJobs); 72 return llvm::make_unique<lto::LTO>(std::move(C), Backend, 73 Config->LTOPartitions); 74 } 75 76 BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {} 77 78 BitcodeCompiler::~BitcodeCompiler() = default; 79 80 static void undefine(Symbol *S) { replaceSymbol<Undefined>(S, S->getName()); } 81 82 void BitcodeCompiler::add(BitcodeFile &F) { 83 lto::InputFile &Obj = *F.Obj; 84 unsigned SymNum = 0; 85 std::vector<Symbol *> SymBodies = F.getSymbols(); 86 std::vector<lto::SymbolResolution> Resols(SymBodies.size()); 87 88 // Provide a resolution to the LTO API for each symbol. 89 for (const lto::InputFile::Symbol &ObjSym : Obj.symbols()) { 90 Symbol *Sym = SymBodies[SymNum]; 91 lto::SymbolResolution &R = Resols[SymNum]; 92 ++SymNum; 93 94 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile 95 // reports two symbols for module ASM defined. Without this check, lld 96 // flags an undefined in IR with a definition in ASM as prevailing. 97 // Once IRObjectFile is fixed to report only one symbol this hack can 98 // be removed. 99 R.Prevailing = !ObjSym.isUndefined() && Sym->getFile() == &F; 100 R.VisibleToRegularObj = Sym->IsUsedInRegularObj; 101 if (R.Prevailing) 102 undefine(Sym); 103 } 104 checkError(LTOObj->add(std::move(F.Obj), Resols)); 105 } 106 107 // Merge all the bitcode files we have seen, codegen the result 108 // and return the resulting objects. 109 std::vector<StringRef> BitcodeCompiler::compile() { 110 unsigned MaxTasks = LTOObj->getMaxTasks(); 111 Buf.resize(MaxTasks); 112 Files.resize(MaxTasks); 113 114 // The /lldltocache option specifies the path to a directory in which to cache 115 // native object files for ThinLTO incremental builds. If a path was 116 // specified, configure LTO to use it as the cache directory. 117 lto::NativeObjectCache Cache; 118 if (!Config->LTOCache.empty()) 119 Cache = check(lto::localCache( 120 Config->LTOCache, [&](size_t Task, std::unique_ptr<MemoryBuffer> MB) { 121 Files[Task] = std::move(MB); 122 })); 123 124 checkError(LTOObj->run( 125 [&](size_t Task) { 126 return llvm::make_unique<lto::NativeObjectStream>( 127 llvm::make_unique<raw_svector_ostream>(Buf[Task])); 128 }, 129 Cache)); 130 131 if (!Config->LTOCache.empty()) 132 pruneCache(Config->LTOCache, Config->LTOCachePolicy); 133 134 std::vector<StringRef> Ret; 135 for (unsigned I = 0; I != MaxTasks; ++I) { 136 if (Buf[I].empty()) 137 continue; 138 if (Config->SaveTemps) { 139 if (I == 0) 140 saveBuffer(Buf[I], Config->OutputFile + ".lto.obj"); 141 else 142 saveBuffer(Buf[I], Config->OutputFile + Twine(I) + ".lto.obj"); 143 } 144 Ret.emplace_back(Buf[I].data(), Buf[I].size()); 145 } 146 147 for (std::unique_ptr<MemoryBuffer> &File : Files) 148 if (File) 149 Ret.push_back(File->getBuffer()); 150 151 return Ret; 152 } 153