C++ GlobalValue::setLinkage方法代码示例

/// Make sure GV is visible from both modules. Delete is true if it is
/// being deleted from this module.
/// This also makes sure GV cannot be dropped so that references from
/// the split module remain valid.
static void makeVisible(GlobalValue &GV, bool Delete, bool IsDeletePass) {
  bool Local = GV.hasLocalLinkage();
  if (Local || Delete) {
    // This changes members from private -> hidden -> causes linker errors when using llvm-link
    if (!IsDeletePass)
      GV.setLinkage(GlobalValue::ExternalLinkage);
    if (Local)
      GV.setVisibility(GlobalValue::HiddenVisibility);
    return;
  }

  if (!GV.hasLinkOnceLinkage()) {
    assert(!GV.isDiscardableIfUnused());
    return;
  }

  // Map linkonce* to weak* so that llvm doesn't drop this GV.
  switch(GV.getLinkage()) {
  default:
    llvm_unreachable("Unexpected linkage");
  case GlobalValue::LinkOnceAnyLinkage:
    GV.setLinkage(GlobalValue::WeakAnyLinkage);
    return;
  case GlobalValue::LinkOnceODRLinkage:
    GV.setLinkage(GlobalValue::WeakODRLinkage);
    return;
  }
}

GlobalValue *IRLinker::copyGlobalValueProto(const GlobalValue *SGV,
                                            bool ForDefinition) {
  GlobalValue *NewGV;
  if (auto *SGVar = dyn_cast<GlobalVariable>(SGV)) {
    NewGV = copyGlobalVariableProto(SGVar);
  } else if (auto *SF = dyn_cast<Function>(SGV)) {
    NewGV = copyFunctionProto(SF);
  } else {
    if (ForDefinition)
      NewGV = copyGlobalAliasProto(cast<GlobalAlias>(SGV));
    else
      NewGV = new GlobalVariable(
          DstM, TypeMap.get(SGV->getType()->getElementType()),
          /*isConstant*/ false, GlobalValue::ExternalLinkage,
          /*init*/ nullptr, SGV->getName(),
          /*insertbefore*/ nullptr, SGV->getThreadLocalMode(),
          SGV->getType()->getAddressSpace());
  }

  if (ForDefinition)
    NewGV->setLinkage(SGV->getLinkage());
  else if (SGV->hasExternalWeakLinkage() || SGV->hasWeakLinkage() ||
           SGV->hasLinkOnceLinkage())
    NewGV->setLinkage(GlobalValue::ExternalWeakLinkage);

  NewGV->copyAttributesFrom(SGV);
  return NewGV;
}

void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
  bool DoPromote = false;
  if (GV.hasLocalLinkage() &&
      ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
    // Once we change the name or linkage it is difficult to determine
    // again whether we should promote since shouldPromoteLocalToGlobal needs
    // to locate the summary (based on GUID from name and linkage). Therefore,
    // use DoPromote result saved above.
    GV.setName(getName(&GV, DoPromote));
    GV.setLinkage(getLinkage(&GV, DoPromote));
    if (!GV.hasLocalLinkage())
      GV.setVisibility(GlobalValue::HiddenVisibility);
  } else
    GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));

  // Remove functions imported as available externally defs from comdats,
  // as this is a declaration for the linker, and will be dropped eventually.
  // It is illegal for comdats to contain declarations.
  auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
  if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
    // The IRMover should not have placed any imported declarations in
    // a comdat, so the only declaration that should be in a comdat
    // at this point would be a definition imported as available_externally.
    assert(GO->hasAvailableExternallyLinkage() &&
           "Expected comdat on definition (possibly available external)");
    GO->setComdat(nullptr);
  }
}

/// Make sure GV is visible from both modules. Delete is true if it is
/// being deleted from this module.
/// This also makes sure GV cannot be dropped so that references from
/// the split module remain valid.
static void makeVisible(GlobalValue &GV, bool Delete) {
  bool Local = GV.hasLocalLinkage();
  if (Local)
    GV.setVisibility(GlobalValue::HiddenVisibility);

  if (Local || Delete) {
    GV.setLinkage(GlobalValue::ExternalLinkage);
    return;
  }

  if (!GV.hasLinkOnceLinkage()) {
    assert(!GV.isDiscardableIfUnused());
    return;
  }

  // Map linkonce* to weak* so that llvm doesn't drop this GV.
  switch(GV.getLinkage()) {
  default:
    llvm_unreachable("Unexpected linkage");
  case GlobalValue::LinkOnceAnyLinkage:
    GV.setLinkage(GlobalValue::WeakAnyLinkage);
    return;
  case GlobalValue::LinkOnceODRLinkage:
    GV.setLinkage(GlobalValue::WeakODRLinkage);
    return;
  }
}

void ThinLTOGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {
  if (GV.hasLocalLinkage() &&
      (doPromoteLocalToGlobal(&GV) || isPerformingImport())) {
    GV.setName(getName(&GV));
    GV.setLinkage(getLinkage(&GV));
    if (!GV.hasLocalLinkage())
      GV.setVisibility(GlobalValue::HiddenVisibility);
    if (isModuleExporting())
      NewExportedValues.insert(&GV);
    return;
  }
  GV.setLinkage(getLinkage(&GV));
}

// llvm_mark_decl_weak - Used by varasm.c, called when a decl is found to be
// weak, but it already had an llvm object created for it. This marks the LLVM
// object weak as well.
void llvm_mark_decl_weak(tree decl) {
  assert(DECL_LLVM_SET_P(decl) && DECL_WEAK(decl) &&
         isa<GlobalValue>(DECL_LLVM(decl)) && "Decl isn't marked weak!");
  GlobalValue *GV = cast<GlobalValue>(DECL_LLVM(decl));

  // Do not mark something that is already known to be linkonce or internal.
  if (GV->hasExternalLinkage()) {
    if (GV->isDeclaration())
      GV->setLinkage(GlobalValue::ExternalWeakLinkage);
    else
      GV->setLinkage(GlobalValue::WeakLinkage);
  }
}

/// gold informs us that all symbols have been read. At this point, we use
/// get_symbols to see if any of our definitions have been overridden by a
/// native object file. Then, perform optimization and codegen.
static ld_plugin_status allSymbolsReadHook(raw_fd_ostream *ApiFile) {
  if (Modules.empty())
    return LDPS_OK;

  LLVMContext Context;
  std::unique_ptr<Module> Combined(new Module("ld-temp.o", Context));
  Linker L(Combined.get());

  std::string DefaultTriple = sys::getDefaultTargetTriple();

  StringSet<> Internalize;
  StringSet<> Maybe;
  for (claimed_file &F : Modules) {
    std::unique_ptr<Module> M =
        getModuleForFile(Context, F, ApiFile, Internalize, Maybe);
    if (!options::triple.empty())
      M->setTargetTriple(options::triple.c_str());
    else if (M->getTargetTriple().empty()) {
      M->setTargetTriple(DefaultTriple);
    }

    if (L.linkInModule(M.get()))
      message(LDPL_FATAL, "Failed to link module");
  }

  for (const auto &Name : Internalize) {
    GlobalValue *GV = Combined->getNamedValue(Name.first());
    if (GV)
      internalize(*GV);
  }

  for (const auto &Name : Maybe) {
    GlobalValue *GV = Combined->getNamedValue(Name.first());
    if (!GV)
      continue;
    GV->setLinkage(GlobalValue::LinkOnceODRLinkage);
    if (canBeOmittedFromSymbolTable(GV))
      internalize(*GV);
  }

  if (options::generate_bc_file != options::BC_NO) {
    std::string path;
    if (options::generate_bc_file == options::BC_ONLY)
      path = output_name;
    else
      path = output_name + ".bc";
    saveBCFile(path, *L.getModule());
    if (options::generate_bc_file == options::BC_ONLY)
      return LDPS_OK;
  }

  codegen(*L.getModule());

  if (!options::extra_library_path.empty() &&
      set_extra_library_path(options::extra_library_path.c_str()) != LDPS_OK)
    message(LDPL_FATAL, "Unable to set the extra library path.");

  return LDPS_OK;
}

void FunctionImportGlobalProcessing::processGlobalForThinLTO(GlobalValue &GV) {

  // Check the summaries to see if the symbol gets resolved to a known local
  // definition.
  if (GV.hasName()) {
    ValueInfo VI = ImportIndex.getValueInfo(GV.getGUID());
    if (VI) {
      // Need to check all summaries are local in case of hash collisions.
      bool IsLocal = VI.getSummaryList().size() &&
          llvm::all_of(VI.getSummaryList(),
                       [](const std::unique_ptr<GlobalValueSummary> &Summary) {
                         return Summary->isDSOLocal();
                       });
      if (IsLocal)
        GV.setDSOLocal(true);
    }
  }

  bool DoPromote = false;
  if (GV.hasLocalLinkage() &&
      ((DoPromote = shouldPromoteLocalToGlobal(&GV)) || isPerformingImport())) {
    // Once we change the name or linkage it is difficult to determine
    // again whether we should promote since shouldPromoteLocalToGlobal needs
    // to locate the summary (based on GUID from name and linkage). Therefore,
    // use DoPromote result saved above.
    GV.setName(getName(&GV, DoPromote));
    GV.setLinkage(getLinkage(&GV, DoPromote));
    if (!GV.hasLocalLinkage())
      GV.setVisibility(GlobalValue::HiddenVisibility);
  } else
    GV.setLinkage(getLinkage(&GV, /* DoPromote */ false));

  // Remove functions imported as available externally defs from comdats,
  // as this is a declaration for the linker, and will be dropped eventually.
  // It is illegal for comdats to contain declarations.
  auto *GO = dyn_cast_or_null<GlobalObject>(&GV);
  if (GO && GO->isDeclarationForLinker() && GO->hasComdat()) {
    // The IRMover should not have placed any imported declarations in
    // a comdat, so the only declaration that should be in a comdat
    // at this point would be a definition imported as available_externally.
    assert(GO->hasAvailableExternallyLinkage() &&
           "Expected comdat on definition (possibly available external)");
    GO->setComdat(nullptr);
  }
}

static void raiseVisibilityOnValue(GlobalValue &V, GlobalRenamer &R) {
  if (V.hasLocalLinkage()) {
    if (R.needsRenaming(V))
      V.setName(R.getRename(V));
    V.setLinkage(GlobalValue::ExternalLinkage);
    V.setVisibility(GlobalValue::HiddenVisibility);
  }
  V.setUnnamedAddr(GlobalValue::UnnamedAddr::None);
  assert(!R.needsRenaming(V) && "Invalid global name.");
}

GlobalValue *IRLinker::copyGlobalValueProto(const GlobalValue *SGV,
                                            bool ForDefinition) {
  GlobalValue *NewGV;
  if (auto *SGVar = dyn_cast<GlobalVariable>(SGV)) {
    NewGV = copyGlobalVariableProto(SGVar);
  } else if (auto *SF = dyn_cast<Function>(SGV)) {
    NewGV = copyFunctionProto(SF);
  } else {
    if (ForDefinition)
      NewGV = copyGlobalAliasProto(cast<GlobalAlias>(SGV));
    else
      NewGV = new GlobalVariable(
          DstM, TypeMap.get(SGV->getValueType()),
          /*isConstant*/ false, GlobalValue::ExternalLinkage,
          /*init*/ nullptr, SGV->getName(),
          /*insertbefore*/ nullptr, SGV->getThreadLocalMode(),
          SGV->getType()->getAddressSpace());
  }

  if (ForDefinition)
    NewGV->setLinkage(SGV->getLinkage());
  else if (SGV->hasExternalWeakLinkage())
    NewGV->setLinkage(GlobalValue::ExternalWeakLinkage);

  NewGV->copyAttributesFrom(SGV);

  if (auto *NewGO = dyn_cast<GlobalObject>(NewGV)) {
    // Metadata for global variables and function declarations is copied eagerly.
    if (isa<GlobalVariable>(SGV) || SGV->isDeclaration())
      NewGO->copyMetadata(cast<GlobalObject>(SGV), 0);
  }

  // Remove these copied constants in case this stays a declaration, since
  // they point to the source module. If the def is linked the values will
  // be mapped in during linkFunctionBody.
  if (auto *NewF = dyn_cast<Function>(NewGV)) {
    NewF->setPersonalityFn(nullptr);
    NewF->setPrefixData(nullptr);
    NewF->setPrologueData(nullptr);
  }

  return NewGV;
}

static void keepGlobalValue(GlobalValue &GV,
                            std::vector<GlobalAlias *> &KeptAliases) {
  assert(!GV.hasLocalLinkage());

  if (auto *GA = dyn_cast<GlobalAlias>(&GV))
    KeptAliases.push_back(GA);

  switch (GV.getLinkage()) {
  default:
    break;
  case GlobalValue::LinkOnceAnyLinkage:
    GV.setLinkage(GlobalValue::WeakAnyLinkage);
    break;
  case GlobalValue::LinkOnceODRLinkage:
    GV.setLinkage(GlobalValue::WeakODRLinkage);
    break;
  }

  assert(!GV.isDiscardableIfUnused());
}

/// linkFunctionProto - Link the function in the source module into the
/// destination module if needed, setting up mapping information.
bool ModuleLinker::linkFunctionProto(Function *SF) {
  GlobalValue *DGV = getLinkedToGlobal(SF);
  llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;

  if (DGV) {
    GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
    bool LinkFromSrc = false;
    GlobalValue::VisibilityTypes NV;
    if (getLinkageResult(DGV, SF, NewLinkage, NV, LinkFromSrc))
      return true;
    NewVisibility = NV;

    if (!LinkFromSrc) {
      // Set calculated linkage
      DGV->setLinkage(NewLinkage);
      DGV->setVisibility(*NewVisibility);

      // Make sure to remember this mapping.
      ValueMap[SF] = ConstantExpr::getBitCast(DGV, TypeMap.get(SF->getType()));
      
      // Track the function from the source module so we don't attempt to remap 
      // it.
      DoNotLinkFromSource.insert(SF);
      
      return false;
    }
  }
  
  // If there is no linkage to be performed or we are linking from the source,
  // bring SF over.
  Function *NewDF = Function::Create(TypeMap.get(SF->getFunctionType()),
                                     SF->getLinkage(), SF->getName(), DstM);
  CopyGVAttributes(NewDF, SF);
  if (NewVisibility)
    NewDF->setVisibility(*NewVisibility);

  if (DGV) {
    // Any uses of DF need to change to NewDF, with cast.
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDF, DGV->getType()));
    DGV->eraseFromParent();
  } else {
    // Internal, LO_ODR, or LO linkage - stick in set to ignore and lazily link.
    if (SF->hasLocalLinkage() || SF->hasLinkOnceLinkage() ||
        SF->hasAvailableExternallyLinkage()) {
      DoNotLinkFromSource.insert(SF);
      LazilyLinkFunctions.push_back(SF);
    }
  }
  
  ValueMap[SF] = NewDF;
  return false;
}

/// LinkAliasProto - Set up prototypes for any aliases that come over from the
/// source module.
bool ModuleLinker::linkAliasProto(GlobalAlias *SGA) {
  GlobalValue *DGV = getLinkedToGlobal(SGA);
  llvm::Optional<GlobalValue::VisibilityTypes> NewVisibility;

  if (DGV) {
    GlobalValue::LinkageTypes NewLinkage = GlobalValue::InternalLinkage;
    GlobalValue::VisibilityTypes NV;
    bool LinkFromSrc = false;
    if (getLinkageResult(DGV, SGA, NewLinkage, NV, LinkFromSrc))
      return true;
    NewVisibility = NV;

    if (!LinkFromSrc) {
      // Set calculated linkage.
      DGV->setLinkage(NewLinkage);
      DGV->setVisibility(*NewVisibility);

      // Make sure to remember this mapping.
      ValueMap[SGA] = ConstantExpr::getBitCast(DGV,TypeMap.get(SGA->getType()));
      
      // Track the alias from the source module so we don't attempt to remap it.
      DoNotLinkFromSource.insert(SGA);
      
      return false;
    }
  }
  
  // If there is no linkage to be performed or we're linking from the source,
  // bring over SGA.
  GlobalAlias *NewDA = new GlobalAlias(TypeMap.get(SGA->getType()),
                                       SGA->getLinkage(), SGA->getName(),
                                       /*aliasee*/0, DstM);
  CopyGVAttributes(NewDA, SGA);
  if (NewVisibility)
    NewDA->setVisibility(*NewVisibility);

  if (DGV) {
    // Any uses of DGV need to change to NewDA, with cast.
    DGV->replaceAllUsesWith(ConstantExpr::getBitCast(NewDA, DGV->getType()));
    DGV->eraseFromParent();
  }
  
  ValueMap[SGA] = NewDA;
  return false;
}

//.........这里部分代码省略.........
    const Comdat &C = SMEC.getValue();
    if (ComdatsChosen.count(&C))
      continue;
    Comdat::SelectionKind SK;
    bool LinkFromSrc;
    if (getComdatResult(&C, SK, LinkFromSrc))
      return true;
    ComdatsChosen[&C] = std::make_pair(SK, LinkFromSrc);

    if (!LinkFromSrc)
      continue;

    Module::ComdatSymTabType &ComdatSymTab = DstM.getComdatSymbolTable();
    Module::ComdatSymTabType::iterator DstCI = ComdatSymTab.find(C.getName());
    if (DstCI == ComdatSymTab.end())
      continue;

    // The source comdat is replacing the dest one.
    const Comdat *DstC = &DstCI->second;
    ReplacedDstComdats.insert(DstC);
  }

  // Alias have to go first, since we are not able to find their comdats
  // otherwise.
  for (auto I = DstM.alias_begin(), E = DstM.alias_end(); I != E;) {
    GlobalAlias &GV = *I++;
    dropReplacedComdat(GV, ReplacedDstComdats);
  }

  for (auto I = DstM.global_begin(), E = DstM.global_end(); I != E;) {
    GlobalVariable &GV = *I++;
    dropReplacedComdat(GV, ReplacedDstComdats);
  }

  for (auto I = DstM.begin(), E = DstM.end(); I != E;) {
    Function &GV = *I++;
    dropReplacedComdat(GV, ReplacedDstComdats);
  }

  for (GlobalVariable &GV : SrcM->globals())
    if (GV.hasLinkOnceLinkage())
      if (const Comdat *SC = GV.getComdat())
        LazyComdatMembers[SC].push_back(&GV);

  for (Function &SF : *SrcM)
    if (SF.hasLinkOnceLinkage())
      if (const Comdat *SC = SF.getComdat())
        LazyComdatMembers[SC].push_back(&SF);

  for (GlobalAlias &GA : SrcM->aliases())
    if (GA.hasLinkOnceLinkage())
      if (const Comdat *SC = GA.getComdat())
        LazyComdatMembers[SC].push_back(&GA);

  // Insert all of the globals in src into the DstM module... without linking
  // initializers (which could refer to functions not yet mapped over).
  for (GlobalVariable &GV : SrcM->globals())
    if (linkIfNeeded(GV))
      return true;

  for (Function &SF : *SrcM)
    if (linkIfNeeded(SF))
      return true;

  for (GlobalAlias &GA : SrcM->aliases())
    if (linkIfNeeded(GA))
      return true;

  for (unsigned I = 0; I < ValuesToLink.size(); ++I) {
    GlobalValue *GV = ValuesToLink[I];
    const Comdat *SC = GV->getComdat();
    if (!SC)
      continue;
    for (GlobalValue *GV2 : LazyComdatMembers[SC]) {
      GlobalValue *DGV = getLinkedToGlobal(GV2);
      bool LinkFromSrc = true;
      if (DGV && shouldLinkFromSource(LinkFromSrc, *DGV, *GV2))
        return true;
      if (LinkFromSrc)
        ValuesToLink.insert(GV2);
    }
  }

  if (shouldInternalizeLinkedSymbols()) {
    for (GlobalValue *GV : ValuesToLink)
      Internalize.insert(GV->getName());
  }

  if (Mover.move(std::move(SrcM), ValuesToLink.getArrayRef(),
                 [this](GlobalValue &GV, IRMover::ValueAdder Add) {
                   addLazyFor(GV, Add);
                 }))
    return true;
  for (auto &P : Internalize) {
    GlobalValue *GV = DstM.getNamedValue(P.first());
    GV->setLinkage(GlobalValue::InternalLinkage);
  }

  return false;
}

//.........这里部分代码省略.........
    // IRONLY handling for internalization, which isn't performed in ThinLTO
    // mode currently anyway.
    if (options::thinlto && (Resolution == LDPR_PREVAILING_DEF_IRONLY_EXP ||
                             Resolution == LDPR_PREVAILING_DEF_IRONLY))
      Resolution = LDPR_PREVAILING_DEF;

    GV->setUnnamedAddr(Res.UnnamedAddr);
    GV->setVisibility(Res.Visibility);

    // Override gold's resolution for common symbols. We want the largest
    // one to win.
    if (GV->hasCommonLinkage()) {
      if (Resolution == LDPR_PREVAILING_DEF_IRONLY)
        Res.CommonInternal = true;

      if (Resolution == LDPR_PREVAILING_DEF_IRONLY ||
          Resolution == LDPR_PREVAILING_DEF)
        Res.UseCommon = true;

      const DataLayout &DL = GV->getParent()->getDataLayout();
      uint64_t Size = DL.getTypeAllocSize(GV->getType()->getElementType());
      unsigned Align = GV->getAlignment();

      if (Res.UseCommon && Size >= Res.CommonSize) {
        // Take GV.
        if (Res.CommonInternal)
          Resolution = LDPR_PREVAILING_DEF_IRONLY;
        else
          Resolution = LDPR_PREVAILING_DEF;
        cast<GlobalVariable>(GV)->setAlignment(
            std::max(Res.CommonAlign, Align));
      } else {
        // Do not take GV, it's smaller than what we already have in the
        // combined module.
        Resolution = LDPR_PREEMPTED_IR;
        if (Align > Res.CommonAlign)
          // Need to raise the alignment though.
          Realign[Sym.name] = Align;
      }

      Res.CommonSize = std::max(Res.CommonSize, Size);
      Res.CommonAlign = std::max(Res.CommonAlign, Align);
    }

    switch (Resolution) {
    case LDPR_UNKNOWN:
      llvm_unreachable("Unexpected resolution");

    case LDPR_RESOLVED_IR:
    case LDPR_RESOLVED_EXEC:
    case LDPR_RESOLVED_DYN:
    case LDPR_PREEMPTED_IR:
    case LDPR_PREEMPTED_REG:
      break;

    case LDPR_UNDEF:
      if (!GV->isDeclarationForLinker())
        assert(GV->hasComdat());
      break;

    case LDPR_PREVAILING_DEF_IRONLY: {
      Keep.push_back(GV);
      // The IR linker has to be able to map this value to a declaration,
      // so we can only internalize after linking.
      if (!Used.count(GV))
        Internalize.insert(GV->getName());
      break;
    }

    case LDPR_PREVAILING_DEF:
      Keep.push_back(GV);
      // There is a non IR use, so we have to force optimizations to keep this.
      switch (GV->getLinkage()) {
      default:
        break;
      case GlobalValue::LinkOnceAnyLinkage:
        GV->setLinkage(GlobalValue::WeakAnyLinkage);
        break;
      case GlobalValue::LinkOnceODRLinkage:
        GV->setLinkage(GlobalValue::WeakODRLinkage);
        break;
      }
      break;

    case LDPR_PREVAILING_DEF_IRONLY_EXP: {
      // We can only check for address uses after we merge the modules. The
      // reason is that this GV might have a copy in another module
      // and in that module the address might be significant, but that
      // copy will be LDPR_PREEMPTED_IR.
      Maybe.insert(GV->getName());
      Keep.push_back(GV);
      break;
    }
    }

    freeSymName(Sym);
  }

  return Obj.takeModule();
}