text: //===-- LTOModule.cpp - LLVM Link Time Optimizer --------------------------===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file implements the Link Time Optimization library. This library is
  // intended to be used by linker to optimize code at link time.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/LTO/LTOModule.h"
  #include "llvm/ADT/Triple.h"
  #include "llvm/Bitcode/ReaderWriter.h"
  #include "llvm/CodeGen/Analysis.h"
  #include "llvm/IR/Constants.h"
  #include "llvm/IR/DiagnosticPrinter.h"
  #include "llvm/IR/LLVMContext.h"
  #include "llvm/IR/Mangler.h"
  #include "llvm/IR/Metadata.h"
  #include "llvm/IR/Module.h"
  #include "llvm/MC/MCExpr.h"
  #include "llvm/MC/MCInst.h"
  #include "llvm/MC/MCInstrInfo.h"
  #include "llvm/MC/MCParser/MCAsmParser.h"
  #include "llvm/MC/MCSection.h"
  #include "llvm/MC/MCSubtargetInfo.h"
  #include "llvm/MC/MCSymbol.h"
  #include "llvm/MC/MCTargetAsmParser.h"
  #include "llvm/MC/SubtargetFeature.h"
  #include "llvm/Object/IRObjectFile.h"
  #include "llvm/Object/ObjectFile.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/FileSystem.h"
  #include "llvm/Support/Host.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/Path.h"
  #include "llvm/Support/SourceMgr.h"
  #include "llvm/Support/TargetRegistry.h"
  #include "llvm/Support/TargetSelect.h"
  #include "llvm/Target/TargetLowering.h"
  #include "llvm/Target/TargetLoweringObjectFile.h"
  #include "llvm/Target/TargetRegisterInfo.h"
  #include "llvm/Target/TargetSubtargetInfo.h"
  #include "llvm/Transforms/Utils/GlobalStatus.h"
  #include <system_error>
  using namespace llvm;
  using namespace llvm::object;
  
  LTOModule::LTOModule(std::unique_ptr<object::IRObjectFile> Obj,
                       llvm::TargetMachine *TM)
      : IRFile(std::move(Obj)), _target(TM) {}
  
  LTOModule::LTOModule(std::unique_ptr<object::IRObjectFile> Obj,
                       llvm::TargetMachine *TM,
                       std::unique_ptr<LLVMContext> Context)
      : OwnedContext(std::move(Context)), IRFile(std::move(Obj)), _target(TM) {}
  
  LTOModule::~LTOModule() {}
  
  /// isBitcodeFile - Returns 'true' if the file (or memory contents) is LLVM
  /// bitcode.
  bool LTOModule::isBitcodeFile(const void *Mem, size_t Length) {
    ErrorOr<MemoryBufferRef> BCData = IRObjectFile::findBitcodeInMemBuffer(
        MemoryBufferRef(StringRef((const char *)Mem, Length), "<mem>"));
    return bool(BCData);
  }
  
  bool LTOModule::isBitcodeFile(const char *Path) {
    ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
        MemoryBuffer::getFile(Path);
    if (!BufferOrErr)
      return false;
  
    ErrorOr<MemoryBufferRef> BCData = IRObjectFile::findBitcodeInMemBuffer(
        BufferOrErr.get()->getMemBufferRef());
    return bool(BCData);
  }
  
  bool LTOModule::isBitcodeForTarget(MemoryBuffer *Buffer,
                                     StringRef TriplePrefix) {
    ErrorOr<MemoryBufferRef> BCOrErr =
        IRObjectFile::findBitcodeInMemBuffer(Buffer->getMemBufferRef());
    if (!BCOrErr)
      return false;
    LLVMContext Context;
    std::string Triple = getBitcodeTargetTriple(*BCOrErr, Context);
    return StringRef(Triple).startswith(TriplePrefix);
  }
  
  std::string LTOModule::getProducerString(MemoryBuffer *Buffer) {
    ErrorOr<MemoryBufferRef> BCOrErr =
        IRObjectFile::findBitcodeInMemBuffer(Buffer->getMemBufferRef());
    if (!BCOrErr)
      return "";
    LLVMContext Context;
    return getBitcodeProducerString(*BCOrErr, Context);
  }
  
  LTOModule *LTOModule::createFromFile(const char *path, TargetOptions options,
                                       std::string &errMsg) {
    ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
        MemoryBuffer::getFile(path);
    if (std::error_code EC = BufferOrErr.getError()) {
      errMsg = EC.message();
      return nullptr;
    }
    std::unique_ptr<MemoryBuffer> Buffer = std::move(BufferOrErr.get());
    return makeLTOModule(Buffer->getMemBufferRef(), options, errMsg,
                         &getGlobalContext());
  }
  
  LTOModule *LTOModule::createFromOpenFile(int fd, const char *path, size_t size,
                                           TargetOptions options,
                                           std::string &errMsg) {
    return createFromOpenFileSlice(fd, path, size, 0, options, errMsg);
  }
  
  LTOModule *LTOModule::createFromOpenFileSlice(int fd, const char *path,
                                                size_t map_size, off_t offset,
                                                TargetOptions options,
                                                std::string &errMsg) {
    ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
        MemoryBuffer::getOpenFileSlice(fd, path, map_size, offset);
    if (std::error_code EC = BufferOrErr.getError()) {
      errMsg = EC.message();
      return nullptr;
    }
    std::unique_ptr<MemoryBuffer> Buffer = std::move(BufferOrErr.get());
    return makeLTOModule(Buffer->getMemBufferRef(), options, errMsg,
                         &getGlobalContext());
  }
  
  LTOModule *LTOModule::createFromBuffer(const void *mem, size_t length,
                                         TargetOptions options,
                                         std::string &errMsg, StringRef path) {
    return createInContext(mem, length, options, errMsg, path,
                           &getGlobalContext());
  }
  
  LTOModule *LTOModule::createInLocalContext(const void *mem, size_t length,
                                             TargetOptions options,
                                             std::string &errMsg,
                                             StringRef path) {
    return createInContext(mem, length, options, errMsg, path, nullptr);
  }
  
  LTOModule *LTOModule::createInContext(const void *mem, size_t length,
                                        TargetOptions options,
                                        std::string &errMsg, StringRef path,
                                        LLVMContext *Context) {
    StringRef Data((const char *)mem, length);
    MemoryBufferRef Buffer(Data, path);
    return makeLTOModule(Buffer, options, errMsg, Context);
  }
  
  static std::unique_ptr<Module> parseBitcodeFileImpl(MemoryBufferRef Buffer,
                                                      LLVMContext &Context,
                                                      bool ShouldBeLazy,
                                                      std::string &ErrMsg) {
  
    // Find the buffer.
    ErrorOr<MemoryBufferRef> MBOrErr =
        IRObjectFile::findBitcodeInMemBuffer(Buffer);
    if (std::error_code EC = MBOrErr.getError()) {
      ErrMsg = EC.message();
      return nullptr;
    }
  
    std::function<void(const DiagnosticInfo &)> DiagnosticHandler =
        [&ErrMsg](const DiagnosticInfo &DI) {
          raw_string_ostream Stream(ErrMsg);
          DiagnosticPrinterRawOStream DP(Stream);
          DI.print(DP);
        };
  
    if (!ShouldBeLazy) {
      // Parse the full file.
      ErrorOr<std::unique_ptr<Module>> M =
          parseBitcodeFile(*MBOrErr, Context, DiagnosticHandler);
      if (!M)
        return nullptr;
      return std::move(*M);
    }
  
    // Parse lazily.
    std::unique_ptr<MemoryBuffer> LightweightBuf =
        MemoryBuffer::getMemBuffer(*MBOrErr, false);
    ErrorOr<std::unique_ptr<Module>> M =
        getLazyBitcodeModule(std::move(LightweightBuf), Context,
                             DiagnosticHandler, true /*ShouldLazyLoadMetadata*/);
    if (!M)
      return nullptr;
    return std::move(*M);
  }
  
  LTOModule *LTOModule::makeLTOModule(MemoryBufferRef Buffer,
                                      TargetOptions options, std::string &errMsg,
                                      LLVMContext *Context) {
    std::unique_ptr<LLVMContext> OwnedContext;
    if (!Context) {
      OwnedContext = llvm::make_unique<LLVMContext>();
      Context = OwnedContext.get();
    }
  
    // If we own a context, we know this is being used only for symbol
    // extraction, not linking.  Be lazy in that case.
    std::unique_ptr<Module> M = parseBitcodeFileImpl(
        Buffer, *Context,
        /* ShouldBeLazy */ static_cast<bool>(OwnedContext), errMsg);
    if (!M)
      return nullptr;
  
    std::string TripleStr = M->getTargetTriple();
    if (TripleStr.empty())
      TripleStr = sys::getDefaultTargetTriple();
    llvm::Triple Triple(TripleStr);
  
    // find machine architecture for this module
    const Target *march = TargetRegistry::lookupTarget(TripleStr, errMsg);
    if (!march)
      return nullptr;
  
    // construct LTOModule, hand over ownership of module and target
    SubtargetFeatures Features;
    Features.getDefaultSubtargetFeatures(Triple);
    std::string FeatureStr = Features.getString();
    // Set a default CPU for Darwin triples.
    std::string CPU;
    if (Triple.isOSDarwin()) {
      if (Triple.getArch() == llvm::Triple::x86_64)
        CPU = "core2";
      else if (Triple.getArch() == llvm::Triple::x86)
        CPU = "yonah";
      else if (Triple.getArch() == llvm::Triple::aarch64)
        CPU = "cyclone";
    }
  
    TargetMachine *target = march->createTargetMachine(TripleStr, CPU, FeatureStr,
                                                       options);
    M->setDataLayout(target->createDataLayout());
  
    std::unique_ptr<object::IRObjectFile> IRObj(
        new object::IRObjectFile(Buffer, std::move(M)));
  
    LTOModule *Ret;
    if (OwnedContext)
      Ret = new LTOModule(std::move(IRObj), target, std::move(OwnedContext));
    else
      Ret = new LTOModule(std::move(IRObj), target);
  
    if (Ret->parseSymbols(errMsg)) {
      delete Ret;
      return nullptr;
    }
  
    Ret->parseMetadata();
  
    return Ret;
  }
  
  /// Create a MemoryBuffer from a memory range with an optional name.
  std::unique_ptr<MemoryBuffer>
  LTOModule::makeBuffer(const void *mem, size_t length, StringRef name) {
    const char *startPtr = (const char*)mem;
    return MemoryBuffer::getMemBuffer(StringRef(startPtr, length), name, false);
  }
  
  /// objcClassNameFromExpression - Get string that the data pointer points to.
  bool
  LTOModule::objcClassNameFromExpression(const Constant *c, std::string &name) {
    if (const ConstantExpr *ce = dyn_cast<ConstantExpr>(c)) {
      Constant *op = ce->getOperand(0);
      if (GlobalVariable *gvn = dyn_cast<GlobalVariable>(op)) {
        Constant *cn = gvn->getInitializer();
        if (ConstantDataArray *ca = dyn_cast<ConstantDataArray>(cn)) {
          if (ca->isCString()) {
            name = (".objc_class_name_" + ca->getAsCString()).str();
            return true;
          }
        }
      }
    }
    return false;
  }
  
  /// addObjCClass - Parse i386/ppc ObjC class data structure.
  void LTOModule::addObjCClass(const GlobalVariable *clgv) {
    const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
    if (!c) return;
  
    // second slot in __OBJC,__class is pointer to superclass name
    std::string superclassName;
    if (objcClassNameFromExpression(c->getOperand(1), superclassName)) {
      auto IterBool =
          _undefines.insert(std::make_pair(superclassName, NameAndAttributes()));
      if (IterBool.second) {
        NameAndAttributes &info = IterBool.first->second;
        info.name = IterBool.first->first().data();
        info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
        info.isFunction = false;
        info.symbol = clgv;
      }
    }
  
    // third slot in __OBJC,__class is pointer to class name
    std::string className;
    if (objcClassNameFromExpression(c->getOperand(2), className)) {
      auto Iter = _defines.insert(className).first;
  
      NameAndAttributes info;
      info.name = Iter->first().data();
      info.attributes = LTO_SYMBOL_PERMISSIONS_DATA |
        LTO_SYMBOL_DEFINITION_REGULAR | LTO_SYMBOL_SCOPE_DEFAULT;
      info.isFunction = false;
      info.symbol = clgv;
      _symbols.push_back(info);
    }
  }
  
  /// addObjCCategory - Parse i386/ppc ObjC category data structure.
  void LTOModule::addObjCCategory(const GlobalVariable *clgv) {
    const ConstantStruct *c = dyn_cast<ConstantStruct>(clgv->getInitializer());
    if (!c) return;
  
    // second slot in __OBJC,__category is pointer to target class name
    std::string targetclassName;
    if (!objcClassNameFromExpression(c->getOperand(1), targetclassName))
      return;
  
    auto IterBool =
        _undefines.insert(std::make_pair(targetclassName, NameAndAttributes()));
  
    if (!IterBool.second)
      return;
  
    NameAndAttributes &info = IterBool.first->second;
    info.name = IterBool.first->first().data();
    info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
    info.isFunction = false;
    info.symbol = clgv;
  }
  
  /// addObjCClassRef - Parse i386/ppc ObjC class list data structure.
  void LTOModule::addObjCClassRef(const GlobalVariable *clgv) {
    std::string targetclassName;
    if (!objcClassNameFromExpression(clgv->getInitializer(), targetclassName))
      return;
  
    auto IterBool =
        _undefines.insert(std::make_pair(targetclassName, NameAndAttributes()));
  
    if (!IterBool.second)
      return;
  
    NameAndAttributes &info = IterBool.first->second;
    info.name = IterBool.first->first().data();
    info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
    info.isFunction = false;
    info.symbol = clgv;
  }
  
  void LTOModule::addDefinedDataSymbol(const object::BasicSymbolRef &Sym) {
    SmallString<64> Buffer;
    {
      raw_svector_ostream OS(Buffer);
      Sym.printName(OS);
    }
  
    const GlobalValue *V = IRFile->getSymbolGV(Sym.getRawDataRefImpl());
    addDefinedDataSymbol(Buffer.c_str(), V);
  }
  
  void LTOModule::addDefinedDataSymbol(const char *Name, const GlobalValue *v) {
    // Add to list of defined symbols.
    addDefinedSymbol(Name, v, false);
  
    if (!v->hasSection() /* || !isTargetDarwin */)
      return;
  
    // Special case i386/ppc ObjC data structures in magic sections:
    // The issue is that the old ObjC object format did some strange
    // contortions to avoid real linker symbols.  For instance, the
    // ObjC class data structure is allocated statically in the executable
    // that defines that class.  That data structures contains a pointer to
    // its superclass.  But instead of just initializing that part of the
    // struct to the address of its superclass, and letting the static and
    // dynamic linkers do the rest, the runtime works by having that field
    // instead point to a C-string that is the name of the superclass.
    // At runtime the objc initialization updates that pointer and sets
    // it to point to the actual super class.  As far as the linker
    // knows it is just a pointer to a string.  But then someone wanted the
    // linker to issue errors at build time if the superclass was not found.
    // So they figured out a way in mach-o object format to use an absolute
    // symbols (.objc_class_name_Foo = 0) and a floating reference
    // (.reference .objc_class_name_Bar) to cause the linker into erroring when
    // a class was missing.
    // The following synthesizes the implicit .objc_* symbols for the linker
    // from the ObjC data structures generated by the front end.
  
    // special case if this data blob is an ObjC class definition
    std::string Section = v->getSection();
    if (Section.compare(0, 15, "__OBJC,__class,") == 0) {
      if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
        addObjCClass(gv);
      }
    }
  
    // special case if this data blob is an ObjC category definition
    else if (Section.compare(0, 18, "__OBJC,__category,") == 0) {
      if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
        addObjCCategory(gv);
      }
    }
  
    // special case if this data blob is the list of referenced classes
    else if (Section.compare(0, 18, "__OBJC,__cls_refs,") == 0) {
      if (const GlobalVariable *gv = dyn_cast<GlobalVariable>(v)) {
        addObjCClassRef(gv);
      }
    }
  }
  
  void LTOModule::addDefinedFunctionSymbol(const object::BasicSymbolRef &Sym) {
    SmallString<64> Buffer;
    {
      raw_svector_ostream OS(Buffer);
      Sym.printName(OS);
    }
  
    const Function *F =
        cast<Function>(IRFile->getSymbolGV(Sym.getRawDataRefImpl()));
    addDefinedFunctionSymbol(Buffer.c_str(), F);
  }
  
  void LTOModule::addDefinedFunctionSymbol(const char *Name, const Function *F) {
    // add to list of defined symbols
    addDefinedSymbol(Name, F, true);
  }
  
  void LTOModule::addDefinedSymbol(const char *Name, const GlobalValue *def,
                                   bool isFunction) {
    // set alignment part log2() can have rounding errors
    uint32_t align = def->getAlignment();
    uint32_t attr = align ? countTrailingZeros(align) : 0;
  
    // set permissions part
    if (isFunction) {
      attr |= LTO_SYMBOL_PERMISSIONS_CODE;
    } else {
      const GlobalVariable *gv = dyn_cast<GlobalVariable>(def);
      if (gv && gv->isConstant())
        attr |= LTO_SYMBOL_PERMISSIONS_RODATA;
      else
        attr |= LTO_SYMBOL_PERMISSIONS_DATA;
    }
  
    // set definition part
    if (def->hasWeakLinkage() || def->hasLinkOnceLinkage())
      attr |= LTO_SYMBOL_DEFINITION_WEAK;
    else if (def->hasCommonLinkage())
      attr |= LTO_SYMBOL_DEFINITION_TENTATIVE;
    else
      attr |= LTO_SYMBOL_DEFINITION_REGULAR;
  
    // set scope part
    if (def->hasLocalLinkage())
      // Ignore visibility if linkage is local.
      attr |= LTO_SYMBOL_SCOPE_INTERNAL;
    else if (def->hasHiddenVisibility())
      attr |= LTO_SYMBOL_SCOPE_HIDDEN;
    else if (def->hasProtectedVisibility())
      attr |= LTO_SYMBOL_SCOPE_PROTECTED;
    else if (canBeOmittedFromSymbolTable(def))
      attr |= LTO_SYMBOL_SCOPE_DEFAULT_CAN_BE_HIDDEN;
    else
      attr |= LTO_SYMBOL_SCOPE_DEFAULT;
  
    if (def->hasComdat())
      attr |= LTO_SYMBOL_COMDAT;
  
    if (isa<GlobalAlias>(def))
      attr |= LTO_SYMBOL_ALIAS;
  
    auto Iter = _defines.insert(Name).first;
  
    // fill information structure
    NameAndAttributes info;
    StringRef NameRef = Iter->first();
    info.name = NameRef.data();
    assert(info.name[NameRef.size()] == '\0');
    info.attributes = attr;
    info.isFunction = isFunction;
    info.symbol = def;
  
    // add to table of symbols
    _symbols.push_back(info);
  }
  
  /// addAsmGlobalSymbol - Add a global symbol from module-level ASM to the
  /// defined list.
  void LTOModule::addAsmGlobalSymbol(const char *name,
                                     lto_symbol_attributes scope) {
    auto IterBool = _defines.insert(name);
  
    // only add new define if not already defined
    if (!IterBool.second)
      return;
  
    NameAndAttributes &info = _undefines[IterBool.first->first().data()];
  
    if (info.symbol == nullptr) {
      // FIXME: This is trying to take care of module ASM like this:
      //
      //   module asm ".zerofill __FOO, __foo, _bar_baz_qux, 0"
      //
      // but is gross and its mother dresses it funny. Have the ASM parser give us
      // more details for this type of situation so that we're not guessing so
      // much.
  
      // fill information structure
      info.name = IterBool.first->first().data();
      info.attributes =
        LTO_SYMBOL_PERMISSIONS_DATA | LTO_SYMBOL_DEFINITION_REGULAR | scope;
      info.isFunction = false;
      info.symbol = nullptr;
  
      // add to table of symbols
      _symbols.push_back(info);
      return;
    }
  
    if (info.isFunction)
      addDefinedFunctionSymbol(info.name, cast<Function>(info.symbol));
    else
      addDefinedDataSymbol(info.name, info.symbol);
  
    _symbols.back().attributes &= ~LTO_SYMBOL_SCOPE_MASK;
    _symbols.back().attributes |= scope;
  }
  
  /// addAsmGlobalSymbolUndef - Add a global symbol from module-level ASM to the
  /// undefined list.
  void LTOModule::addAsmGlobalSymbolUndef(const char *name) {
    auto IterBool = _undefines.insert(std::make_pair(name, NameAndAttributes()));
  
    _asm_undefines.push_back(IterBool.first->first().data());
  
    // we already have the symbol
    if (!IterBool.second)
      return;
  
    uint32_t attr = LTO_SYMBOL_DEFINITION_UNDEFINED;
    attr |= LTO_SYMBOL_SCOPE_DEFAULT;
    NameAndAttributes &info = IterBool.first->second;
    info.name = IterBool.first->first().data();
    info.attributes = attr;
    info.isFunction = false;
    info.symbol = nullptr;
  }
  
  /// Add a symbol which isn't defined just yet to a list to be resolved later.
  void LTOModule::addPotentialUndefinedSymbol(const object::BasicSymbolRef &Sym,
                                              bool isFunc) {
    SmallString<64> name;
    {
      raw_svector_ostream OS(name);
      Sym.printName(OS);
    }
  
    auto IterBool = _undefines.insert(std::make_pair(name, NameAndAttributes()));
  
    // we already have the symbol
    if (!IterBool.second)
      return;
  
    NameAndAttributes &info = IterBool.first->second;
  
    info.name = IterBool.first->first().data();
  
    const GlobalValue *decl = IRFile->getSymbolGV(Sym.getRawDataRefImpl());
  
    if (decl->hasExternalWeakLinkage())
      info.attributes = LTO_SYMBOL_DEFINITION_WEAKUNDEF;
    else
      info.attributes = LTO_SYMBOL_DEFINITION_UNDEFINED;
  
    info.isFunction = isFunc;
    info.symbol = decl;
  }
  
  /// parseSymbols - Parse the symbols from the module and model-level ASM and add
  /// them to either the defined or undefined lists.
  bool LTOModule::parseSymbols(std::string &errMsg) {
    for (auto &Sym : IRFile->symbols()) {
      const GlobalValue *GV = IRFile->getSymbolGV(Sym.getRawDataRefImpl());
      uint32_t Flags = Sym.getFlags();
      if (Flags & object::BasicSymbolRef::SF_FormatSpecific)
        continue;
  
      bool IsUndefined = Flags & object::BasicSymbolRef::SF_Undefined;
  
      if (!GV) {
        SmallString<64> Buffer;
        {
          raw_svector_ostream OS(Buffer);
          Sym.printName(OS);
        }
        const char *Name = Buffer.c_str();
  
        if (IsUndefined)
          addAsmGlobalSymbolUndef(Name);
        else if (Flags & object::BasicSymbolRef::SF_Global)
          addAsmGlobalSymbol(Name, LTO_SYMBOL_SCOPE_DEFAULT);
        else
          addAsmGlobalSymbol(Name, LTO_SYMBOL_SCOPE_INTERNAL);
        continue;
      }
  
      auto *F = dyn_cast<Function>(GV);
      if (IsUndefined) {
        addPotentialUndefinedSymbol(Sym, F != nullptr);
        continue;
      }
  
      if (F) {
        addDefinedFunctionSymbol(Sym);
        continue;
      }
  
      if (isa<GlobalVariable>(GV)) {
        addDefinedDataSymbol(Sym);
        continue;
      }
  
      assert(isa<GlobalAlias>(GV));
      addDefinedDataSymbol(Sym);
    }
  
    // make symbols for all undefines
    for (StringMap<NameAndAttributes>::iterator u =_undefines.begin(),
           e = _undefines.end(); u != e; ++u) {
      // If this symbol also has a definition, then don't make an undefine because
      // it is a tentative definition.
      if (_defines.count(u->getKey())) continue;
      NameAndAttributes info = u->getValue();
      _symbols.push_back(info);
    }
  
    return false;
  }
  
  /// parseMetadata - Parse metadata from the module
  void LTOModule::parseMetadata() {
    raw_string_ostream OS(LinkerOpts);
  
    // Linker Options
    if (Metadata *Val = getModule().getModuleFlag("Linker Options")) {
      MDNode *LinkerOptions = cast<MDNode>(Val);
      for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
        MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
        for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
          MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
          OS << " " << MDOption->getString();
        }
      }
    }
  
    // Globals
    Mangler Mang;
    for (const NameAndAttributes &Sym : _symbols) {
      if (!Sym.symbol)
        continue;
      _target->getObjFileLowering()->emitLinkerFlagsForGlobal(OS, Sym.symbol,
                                                              Mang);
    }
  
    // Add other interesting metadata here.
  }
  