1 //===- LTO.cpp ------------------------------------------------------------===//
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
12 #include "InputFiles.h"
13 #include "LinkerScript.h"
14 #include "SymbolTable.h"
16 #include "lld/Common/ErrorHandler.h"
17 #include "lld/Common/TargetOptionsCommandFlags.h"
18 #include "llvm/ADT/STLExtras.h"
19 #include "llvm/ADT/SmallString.h"
20 #include "llvm/ADT/StringRef.h"
21 #include "llvm/ADT/Twine.h"
22 #include "llvm/BinaryFormat/ELF.h"
23 #include "llvm/IR/DiagnosticPrinter.h"
24 #include "llvm/LTO/Caching.h"
25 #include "llvm/LTO/Config.h"
26 #include "llvm/LTO/LTO.h"
27 #include "llvm/Object/SymbolicFile.h"
28 #include "llvm/Support/CodeGen.h"
29 #include "llvm/Support/Error.h"
30 #include "llvm/Support/FileSystem.h"
31 #include "llvm/Support/MemoryBuffer.h"
32 #include "llvm/Support/raw_ostream.h"
37 #include <system_error>
41 using namespace llvm::object;
42 using namespace llvm::ELF;
45 using namespace lld::elf;
47 // This is for use when debugging LTO.
48 static void saveBuffer(StringRef Buffer, const Twine &Path) {
50 raw_fd_ostream OS(Path.str(), EC, sys::fs::OpenFlags::F_None);
52 error("cannot create " + Path + ": " + EC.message());
56 static void diagnosticHandler(const DiagnosticInfo &DI) {
57 SmallString<128> ErrStorage;
58 raw_svector_ostream OS(ErrStorage);
59 DiagnosticPrinterRawOStream DP(OS);
64 static void checkError(Error E) {
65 handleAllErrors(std::move(E),
66 [&](ErrorInfoBase &EIB) { error(EIB.message()); });
69 static std::unique_ptr<lto::LTO> createLTO() {
72 // LLD supports the new relocations.
73 Conf.Options = InitTargetOptionsFromCodeGenFlags();
74 Conf.Options.RelaxELFRelocations = true;
76 // Always emit a section per function/datum with LTO.
77 Conf.Options.FunctionSections = true;
78 Conf.Options.DataSections = true;
80 if (Config->Relocatable)
81 Conf.RelocModel = None;
83 Conf.RelocModel = Reloc::PIC_;
85 Conf.RelocModel = Reloc::Static;
86 Conf.CodeModel = GetCodeModelFromCMModel();
87 Conf.DisableVerify = Config->DisableVerify;
88 Conf.DiagHandler = diagnosticHandler;
89 Conf.OptLevel = Config->LTOO;
91 // Set up a custom pipeline if we've been asked to.
92 Conf.OptPipeline = Config->LTONewPmPasses;
93 Conf.AAPipeline = Config->LTOAAPipeline;
95 // Set up optimization remarks if we've been asked to.
96 Conf.RemarksFilename = Config->OptRemarksFilename;
97 Conf.RemarksWithHotness = Config->OptRemarksWithHotness;
99 if (Config->SaveTemps)
100 checkError(Conf.addSaveTemps(std::string(Config->OutputFile) + ".",
101 /*UseInputModulePath*/ true));
103 lto::ThinBackend Backend;
104 if (Config->ThinLTOJobs != -1u)
105 Backend = lto::createInProcessThinBackend(Config->ThinLTOJobs);
106 return llvm::make_unique<lto::LTO>(std::move(Conf), Backend,
107 Config->LTOPartitions);
110 BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {
111 for (Symbol *Sym : Symtab->getSymbols()) {
112 StringRef Name = Sym->getName();
113 for (StringRef Prefix : {"__start_", "__stop_"})
114 if (Name.startswith(Prefix))
115 UsedStartStop.insert(Name.substr(Prefix.size()));
119 BitcodeCompiler::~BitcodeCompiler() = default;
121 static void undefine(Symbol *S) {
122 replaceSymbol<Undefined>(S, nullptr, S->getName(), STB_GLOBAL, STV_DEFAULT,
126 void BitcodeCompiler::add(BitcodeFile &F) {
127 lto::InputFile &Obj = *F.Obj;
129 std::vector<Symbol *> Syms = F.getSymbols();
130 std::vector<lto::SymbolResolution> Resols(Syms.size());
132 DenseSet<StringRef> ScriptSymbols;
133 for (BaseCommand *Base : Script->SectionCommands)
134 if (auto *Cmd = dyn_cast<SymbolAssignment>(Base))
135 ScriptSymbols.insert(Cmd->Name);
137 // Provide a resolution to the LTO API for each symbol.
138 for (const lto::InputFile::Symbol &ObjSym : Obj.symbols()) {
139 Symbol *Sym = Syms[SymNum];
140 lto::SymbolResolution &R = Resols[SymNum];
143 // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
144 // reports two symbols for module ASM defined. Without this check, lld
145 // flags an undefined in IR with a definition in ASM as prevailing.
146 // Once IRObjectFile is fixed to report only one symbol this hack can
148 R.Prevailing = !ObjSym.isUndefined() && Sym->File == &F;
150 // We ask LTO to preserve following global symbols:
151 // 1) All symbols when doing relocatable link, so that them can be used
152 // for doing final link.
153 // 2) Symbols that are used in regular objects.
154 // 3) C named sections if we have corresponding __start_/__stop_ symbol.
155 // 4) Symbols that are defined in bitcode files and used for dynamic linking.
156 R.VisibleToRegularObj = Config->Relocatable || Sym->IsUsedInRegularObj ||
157 (R.Prevailing && Sym->includeInDynsym()) ||
158 UsedStartStop.count(ObjSym.getSectionName());
162 // We tell LTO to not apply interprocedural optimization for following
163 // symbols because otherwise LTO would inline them while their values are
165 // 1) Aliased (with --defsym) or wrapped (with --wrap) symbols.
166 // 2) Symbols redefined in linker script.
167 R.LinkerRedefined = !Sym->CanInline || ScriptSymbols.count(Sym->getName());
169 checkError(LTOObj->add(std::move(F.Obj), Resols));
172 // Merge all the bitcode files we have seen, codegen the result
173 // and return the resulting ObjectFile(s).
174 std::vector<InputFile *> BitcodeCompiler::compile() {
175 std::vector<InputFile *> Ret;
176 unsigned MaxTasks = LTOObj->getMaxTasks();
177 Buff.resize(MaxTasks);
178 Files.resize(MaxTasks);
180 // The --thinlto-cache-dir option specifies the path to a directory in which
181 // to cache native object files for ThinLTO incremental builds. If a path was
182 // specified, configure LTO to use it as the cache directory.
183 lto::NativeObjectCache Cache;
184 if (!Config->ThinLTOCacheDir.empty())
186 lto::localCache(Config->ThinLTOCacheDir,
187 [&](size_t Task, std::unique_ptr<MemoryBuffer> MB,
188 StringRef Path) { Files[Task] = std::move(MB); }));
190 checkError(LTOObj->run(
192 return llvm::make_unique<lto::NativeObjectStream>(
193 llvm::make_unique<raw_svector_ostream>(Buff[Task]));
197 if (!Config->ThinLTOCacheDir.empty())
198 pruneCache(Config->ThinLTOCacheDir, Config->ThinLTOCachePolicy);
200 for (unsigned I = 0; I != MaxTasks; ++I) {
203 if (Config->SaveTemps) {
205 saveBuffer(Buff[I], Config->OutputFile + ".lto.o");
207 saveBuffer(Buff[I], Config->OutputFile + Twine(I) + ".lto.o");
209 InputFile *Obj = createObjectFile(MemoryBufferRef(Buff[I], "lto.tmp"));
213 for (std::unique_ptr<MemoryBuffer> &File : Files)
215 Ret.push_back(createObjectFile(*File));