C++ GlobalAlias::setDLLStorageClass方法代码示例

bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
                          const BitVector &GlobalSet, Module &M, bool isConst,
                          unsigned AddrSpace) const {
  assert(Globals.size() > 1);

  Type *Int32Ty = Type::getInt32Ty(M.getContext());
  auto &DL = M.getDataLayout();

  LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #"
                    << GlobalSet.find_first() << "\n");

  bool Changed = false;
  ssize_t i = GlobalSet.find_first();
  while (i != -1) {
    ssize_t j = 0;
    uint64_t MergedSize = 0;
    std::vector<Type*> Tys;
    std::vector<Constant*> Inits;

    bool HasExternal = false;
    StringRef FirstExternalName;
    for (j = i; j != -1; j = GlobalSet.find_next(j)) {
      Type *Ty = Globals[j]->getValueType();
      MergedSize += DL.getTypeAllocSize(Ty);
      if (MergedSize > MaxOffset) {
        break;
      }
      Tys.push_back(Ty);
      Inits.push_back(Globals[j]->getInitializer());

      if (Globals[j]->hasExternalLinkage() && !HasExternal) {
        HasExternal = true;
        FirstExternalName = Globals[j]->getName();
      }
    }

    // Exit early if there is only one global to merge.
    if (Tys.size() < 2) {
      i = j;
      continue;
    }

    // If merged variables doesn't have external linkage, we needn't to expose
    // the symbol after merging.
    GlobalValue::LinkageTypes Linkage = HasExternal
                                            ? GlobalValue::ExternalLinkage
                                            : GlobalValue::InternalLinkage;
    StructType *MergedTy = StructType::get(M.getContext(), Tys);
    Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);

    // On Darwin external linkage needs to be preserved, otherwise
    // dsymutil cannot preserve the debug info for the merged
    // variables.  If they have external linkage, use the symbol name
    // of the first variable merged as the suffix of global symbol
    // name.  This avoids a link-time naming conflict for the
    // _MergedGlobals symbols.
    Twine MergedName =
        (IsMachO && HasExternal)
            ? "_MergedGlobals_" + FirstExternalName
            : "_MergedGlobals";
    auto MergedLinkage = IsMachO ? Linkage : GlobalValue::PrivateLinkage;
    auto *MergedGV = new GlobalVariable(
        M, MergedTy, isConst, MergedLinkage, MergedInit, MergedName, nullptr,
        GlobalVariable::NotThreadLocal, AddrSpace);

    const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);

    for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) {
      GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage();
      std::string Name = Globals[k]->getName();
      GlobalValue::DLLStorageClassTypes DLLStorage =
          Globals[k]->getDLLStorageClass();

      // Copy metadata while adjusting any debug info metadata by the original
      // global's offset within the merged global.
      MergedGV->copyMetadata(Globals[k], MergedLayout->getElementOffset(idx));

      Constant *Idx[2] = {
        ConstantInt::get(Int32Ty, 0),
        ConstantInt::get(Int32Ty, idx),
      };
      Constant *GEP =
          ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx);
      Globals[k]->replaceAllUsesWith(GEP);
      Globals[k]->eraseFromParent();

      // When the linkage is not internal we must emit an alias for the original
      // variable name as it may be accessed from another object. On non-Mach-O
      // we can also emit an alias for internal linkage as it's safe to do so.
      // It's not safe on Mach-O as the alias (and thus the portion of the
      // MergedGlobals variable) may be dead stripped at link time.
      if (Linkage != GlobalValue::InternalLinkage || !IsMachO) {
        GlobalAlias *GA =
            GlobalAlias::create(Tys[idx], AddrSpace, Linkage, Name, GEP, &M);
        GA->setDLLStorageClass(DLLStorage);
      }

      NumMerged++;
    }
    Changed = true;
//.........这里部分代码省略.........