C++ ArrayType::getElementType方法代码示例

/// computeTypeMapping - Loop over all of the linked values to compute type
/// mappings.  For example, if we link "extern Foo *x" and "Foo *x = NULL", then
/// we have two struct types 'Foo' but one got renamed when the module was
/// loaded into the same LLVMContext.
void ModuleLinker::computeTypeMapping() {
  // Incorporate globals.
  for (Module::global_iterator I = SrcM->global_begin(),
       E = SrcM->global_end(); I != E; ++I) {
    GlobalValue *DGV = getLinkedToGlobal(I);
    if (DGV == 0) continue;
    
    if (!DGV->hasAppendingLinkage() || !I->hasAppendingLinkage()) {
      TypeMap.addTypeMapping(DGV->getType(), I->getType());
      continue;      
    }
    
    // Unify the element type of appending arrays.
    ArrayType *DAT = cast<ArrayType>(DGV->getType()->getElementType());
    ArrayType *SAT = cast<ArrayType>(I->getType()->getElementType());
    TypeMap.addTypeMapping(DAT->getElementType(), SAT->getElementType());
  }
  
  // Incorporate functions.
  for (Module::iterator I = SrcM->begin(), E = SrcM->end(); I != E; ++I) {
    if (GlobalValue *DGV = getLinkedToGlobal(I))
      TypeMap.addTypeMapping(DGV->getType(), I->getType());
  }

  // Incorporate types by name, scanning all the types in the source module.
  // At this point, the destination module may have a type "%foo = { i32 }" for
  // example.  When the source module got loaded into the same LLVMContext, if
  // it had the same type, it would have been renamed to "%foo.42 = { i32 }".
  // Though it isn't required for correctness, attempt to link these up to clean
  // up the IR.
  std::vector<StructType*> SrcStructTypes;
  SrcM->findUsedStructTypes(SrcStructTypes);
  
  SmallPtrSet<StructType*, 32> SrcStructTypesSet(SrcStructTypes.begin(),
                                                 SrcStructTypes.end());
  
  for (unsigned i = 0, e = SrcStructTypes.size(); i != e; ++i) {
    StructType *ST = SrcStructTypes[i];
    if (!ST->hasName()) continue;
    
    // Check to see if there is a dot in the name followed by a digit.
    size_t DotPos = ST->getName().rfind('.');
    if (DotPos == 0 || DotPos == StringRef::npos ||
        ST->getName().back() == '.' || !isdigit(ST->getName()[DotPos+1]))
      continue;
    
    // Check to see if the destination module has a struct with the prefix name.
    if (StructType *DST = DstM->getTypeByName(ST->getName().substr(0, DotPos)))
      // Don't use it if this actually came from the source module.  They're in
      // the same LLVMContext after all.
      if (!SrcStructTypesSet.count(DST))
        TypeMap.addTypeMapping(DST, ST);
  }

  // Don't bother incorporating aliases, they aren't generally typed well.
  
  // Now that we have discovered all of the type equivalences, get a body for
  // any 'opaque' types in the dest module that are now resolved. 
  TypeMap.linkDefinedTypeBodies();
}

Constant *DevirtModule::getPointerAtOffset(Constant *I, uint64_t Offset) {
  if (I->getType()->isPointerTy()) {
    if (Offset == 0)
      return I;
    return nullptr;
  }

  const DataLayout &DL = M.getDataLayout();

  if (auto *C = dyn_cast<ConstantStruct>(I)) {
    const StructLayout *SL = DL.getStructLayout(C->getType());
    if (Offset >= SL->getSizeInBytes())
      return nullptr;

    unsigned Op = SL->getElementContainingOffset(Offset);
    return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
                              Offset - SL->getElementOffset(Op));
  }
  if (auto *C = dyn_cast<ConstantArray>(I)) {
    ArrayType *VTableTy = C->getType();
    uint64_t ElemSize = DL.getTypeAllocSize(VTableTy->getElementType());

    unsigned Op = Offset / ElemSize;
    if (Op >= C->getNumOperands())
      return nullptr;

    return getPointerAtOffset(cast<Constant>(I->getOperand(Op)),
                              Offset % ElemSize);
  }
  return nullptr;
}

  /* This routine extracts the filename of the file input to the open call
     This function has been borrowed from the LLPE toolchain by Smowton.
   */ 
  bool getConstantStringInfo(const Value *V, StringRef &Str) {

    // Look through bitcast instructions and geps.
    V = V->stripPointerCasts();
    // If the value is a GEP instruction or constant expression, treat it as an offset.
    if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
      // Make sure the GEP has exactly three arguments.
      if (GEP->getNumOperands() != 3)
	return false;

      // Make sure the index-ee is a pointer to array of i8.
      PointerType *PT = cast<PointerType>(GEP->getOperand(0)->getType());
      ArrayType *AT = dyn_cast<ArrayType>(PT->getElementType());
      if (AT == 0 || !AT->getElementType()->isIntegerTy(8))
	return false;

      // Check to make sure that the first operand of the GEP is an integer and
      // has value 0 so that we are sure we're indexing into the initializer.
      const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
      if (FirstIdx == 0 || !FirstIdx->isZero())
	return false;

      // If the second index isn't a ConstantInt, then this is a variable index
      // into the array.  If this occurs, we can't say anything meaningful about
      // the string.
      uint64_t StartIdx = 0;
      if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
	StartIdx = CI->getZExtValue();
      else
	return false;

    }

    // The GEP instruction, constant or instruction, must reference a global
    // variable that is a constant and is initialized. The referenced constant
    // initializer is the array that we'll use for optimization.
    const GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
    if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
      return false;

    // Handle the all-zeros case
    if (GV->getInitializer()->isNullValue()) {
      // This is a degenerate case. The initializer is constant zero so the
      // length of the string must be zero.
      Str = "";
      return true;
    }

    // Must be a Constant Array
    const ConstantDataArray *Array =
      dyn_cast<ConstantDataArray>(GV->getInitializer());

    if (Array == 0 || !Array->isString())
      return false;

    // Start out with the entire array in the StringRef.
    Str = Array->getAsString();
    return true;
  }

AllocaInst* Variables::changeLocal(Value* value, ArrayType* newType) {

  AllocaInst* oldTarget = dyn_cast<AllocaInst>(value);
  PointerType* oldPointerType = dyn_cast<PointerType>(oldTarget->getType());
  ArrayType* oldType = dyn_cast<ArrayType>(oldPointerType->getElementType());
  AllocaInst* newTarget = NULL;

  errs() << "Changing the precision of variable \"" << oldTarget->getName() << "\" from " << *oldType 
	 << " to " << *newType << ".\n";

  if (newType->getElementType()->getTypeID() != oldType->getElementType()->getTypeID()) {

    newTarget = new AllocaInst(newType, getInt32(1), "", oldTarget);
    
    // we are not calling getAlignment because in this case double requires 16. Investigate further.
    unsigned alignment;
    switch(newType->getElementType()->getTypeID()) {
    case Type::FloatTyID: 
      alignment = 4;
      break;
    case Type::DoubleTyID:
      alignment = 16;
      break;
    case Type::X86_FP80TyID:
      alignment = 16;
      break;
    default:
      alignment = 0;
    } 
    
    newTarget->setAlignment(alignment); // depends on type? 8 for float? 16 for double?
    newTarget->takeName(oldTarget);
    
    // iterating through instructions using old AllocaInst
    vector<Instruction*> erase;
    Value::use_iterator it = oldTarget->use_begin();
    for(; it != oldTarget->use_end(); it++) {
      bool is_erased = Transformer::transform(it, newTarget, oldTarget, newType, oldType, alignment);

      if (!is_erased)
        erase.push_back(dyn_cast<Instruction>(*it));
    }	  
    
    // erasing uses of old instructions
    for(unsigned int i = 0; i < erase.size(); i++) {
      erase[i]->eraseFromParent();
    }
    // erase old instruction
    //oldTarget->eraseFromParent();
  }
  else {
    errs() << "\tNo changes required.\n";    
  }

  return newTarget;
}

bool EfficiencySanitizer::instrumentGetElementPtr(Instruction *I, Module &M) {
  GetElementPtrInst *GepInst = dyn_cast<GetElementPtrInst>(I);
  bool Res = false;
  if (GepInst == nullptr || GepInst->getNumIndices() == 1) {
    ++NumIgnoredGEPs;
    return false;
  }
  Type *SourceTy = GepInst->getSourceElementType();
  StructType *StructTy = nullptr;
  ConstantInt *Idx;
  // Check if GEP calculates address from a struct array.
  if (isa<StructType>(SourceTy)) {
    StructTy = cast<StructType>(SourceTy);
    Idx = dyn_cast<ConstantInt>(GepInst->getOperand(1));
    if ((Idx == nullptr || Idx->getSExtValue() != 0) &&
        !shouldIgnoreStructType(StructTy) && StructTyMap.count(StructTy) != 0)
      Res |= insertCounterUpdate(I, StructTy, getArrayCounterIdx(StructTy));
  }
  // Iterate all (except the first and the last) idx within each GEP instruction
  // for possible nested struct field address calculation.
  for (unsigned i = 1; i < GepInst->getNumIndices(); ++i) {
    SmallVector<Value *, 8> IdxVec(GepInst->idx_begin(),
                                   GepInst->idx_begin() + i);
    Type *Ty = GetElementPtrInst::getIndexedType(SourceTy, IdxVec);
    unsigned CounterIdx = 0;
    if (isa<ArrayType>(Ty)) {
      ArrayType *ArrayTy = cast<ArrayType>(Ty);
      StructTy = dyn_cast<StructType>(ArrayTy->getElementType());
      if (shouldIgnoreStructType(StructTy) || StructTyMap.count(StructTy) == 0)
        continue;
      // The last counter for struct array access.
      CounterIdx = getArrayCounterIdx(StructTy);
    } else if (isa<StructType>(Ty)) {
      StructTy = cast<StructType>(Ty);
      if (shouldIgnoreStructType(StructTy) || StructTyMap.count(StructTy) == 0)
        continue;
      // Get the StructTy's subfield index.
      Idx = cast<ConstantInt>(GepInst->getOperand(i+1));
      assert(Idx->getSExtValue() >= 0 &&
             Idx->getSExtValue() < StructTy->getNumElements());
      CounterIdx = getFieldCounterIdx(StructTy) + Idx->getSExtValue();
    }
    Res |= insertCounterUpdate(I, StructTy, CounterIdx);
  }
  if (Res)
    ++NumInstrumentedGEPs;
  else
    ++NumIgnoredGEPs;
  return Res;
}

static void appendToGlobalArray(const char *Array,
                                Module &M, Function *F, int Priority) {
  IRBuilder<> IRB(M.getContext());
  FunctionType *FnTy = FunctionType::get(IRB.getVoidTy(), false);

  // Get the current set of static global constructors and add the new ctor
  // to the list.
  SmallVector<Constant *, 16> CurrentCtors;
  StructType *EltTy;
  if (GlobalVariable *GVCtor = M.getNamedGlobal(Array)) {
    // If there is a global_ctors array, use the existing struct type, which can
    // have 2 or 3 fields.
    ArrayType *ATy = cast<ArrayType>(GVCtor->getType()->getElementType());
    EltTy = cast<StructType>(ATy->getElementType());
    if (Constant *Init = GVCtor->getInitializer()) {
      unsigned n = Init->getNumOperands();
      CurrentCtors.reserve(n + 1);
      for (unsigned i = 0; i != n; ++i)
        CurrentCtors.push_back(cast<Constant>(Init->getOperand(i)));
    }
    GVCtor->eraseFromParent();
  } else {
    // Use a simple two-field struct if there isn't one already.
    EltTy = StructType::get(IRB.getInt32Ty(), PointerType::getUnqual(FnTy),
                            nullptr);
  }

  // Build a 2 or 3 field global_ctor entry.  We don't take a comdat key.
  Constant *CSVals[3];
  CSVals[0] = IRB.getInt32(Priority);
  CSVals[1] = F;
  // FIXME: Drop support for the two element form in LLVM 4.0.
  if (EltTy->getNumElements() >= 3)
    CSVals[2] = llvm::Constant::getNullValue(IRB.getInt8PtrTy());
  Constant *RuntimeCtorInit =
      ConstantStruct::get(EltTy, makeArrayRef(CSVals, EltTy->getNumElements()));

  CurrentCtors.push_back(RuntimeCtorInit);

  // Create a new initializer.
  ArrayType *AT = ArrayType::get(EltTy, CurrentCtors.size());
  Constant *NewInit = ConstantArray::get(AT, CurrentCtors);

  // Create the new global variable and replace all uses of
  // the old global variable with the new one.
  (void)new GlobalVariable(M, NewInit->getType(), false,
                           GlobalValue::AppendingLinkage, NewInit, Array);
}

ConstantInt* Variables::getAlignmentInBits(Type *type) {
  ConstantInt *alignment = NULL;
  ArrayType *arrayType = dyn_cast<ArrayType>(type);
  switch (arrayType->getElementType()->getTypeID()) {
  case Type::FloatTyID:
    alignment = getInt64(32);
    break;
  case Type::DoubleTyID:
    alignment = getInt64(64);
    break;
  default:
    errs() << "WARNING: Unhandled type @ getAlignmentInBits\n";
    exit(1);
  }
  return alignment;
}

ConstantInt* Variables::getSizeInBits(Type *type) {
  ConstantInt *size = NULL;
  ArrayType *arrayType = dyn_cast<ArrayType>(type);
  switch (arrayType->getElementType()->getTypeID()) {
  case Type::FloatTyID: {
    int isize = arrayType->getNumElements() * 32;
    size = getInt64(isize);
    break;
  }
  case Type::DoubleTyID: {
    int isize = arrayType->getNumElements() * 64;
    size = getInt64(isize);
    break;
  }
  default:
    errs() << "WARNING: Unhandled type @ getSizeInBits\n";
    exit(1);
  }
  return size;
}

bool DevirtModule::tryFindVirtualCallTargets(
    std::vector<VirtualCallTarget> &TargetsForSlot,
    const std::set<BitSetInfo> &BitSetInfos, uint64_t ByteOffset) {
  for (const BitSetInfo &BS : BitSetInfos) {
    if (!BS.Bits->GV->isConstant())
      return false;

    auto Init = dyn_cast<ConstantArray>(BS.Bits->GV->getInitializer());
    if (!Init)
      return false;
    ArrayType *VTableTy = Init->getType();

    uint64_t ElemSize =
        M.getDataLayout().getTypeAllocSize(VTableTy->getElementType());
    uint64_t GlobalSlotOffset = BS.Offset + ByteOffset;
    if (GlobalSlotOffset % ElemSize != 0)
      return false;

    unsigned Op = GlobalSlotOffset / ElemSize;
    if (Op >= Init->getNumOperands())
      return false;

    auto Fn = dyn_cast<Function>(Init->getOperand(Op)->stripPointerCasts());
    if (!Fn)
      return false;

    // We can disregard __cxa_pure_virtual as a possible call target, as
    // calls to pure virtuals are UB.
    if (Fn->getName() == "__cxa_pure_virtual")
      continue;

    TargetsForSlot.push_back({Fn, &BS});
  }

  // Give up if we couldn't find any targets.
  return !TargetsForSlot.empty();
}

uint64_t TargetData::getTypeSizeInBits(Type *Ty) const {
  assert(Ty->isSized() && "Cannot getTypeInfo() on a type that is unsized!");
  switch (Ty->getTypeID()) {
  case Type::LabelTyID:
  case Type::PointerTyID:
    return getPointerSizeInBits();
  case Type::ArrayTyID: {
    ArrayType *ATy = cast<ArrayType>(Ty);
    return getTypeAllocSizeInBits(ATy->getElementType())*ATy->getNumElements();
  }
  case Type::StructTyID:
    // Get the layout annotation... which is lazily created on demand.
    return getStructLayout(cast<StructType>(Ty))->getSizeInBits();
  case Type::IntegerTyID:
    return cast<IntegerType>(Ty)->getBitWidth();
  case Type::VoidTyID:
    return 8;
  case Type::HalfTyID:
    return 16;
  case Type::FloatTyID:
    return 32;
  case Type::DoubleTyID:
  case Type::X86_MMXTyID:
    return 64;
  case Type::PPC_FP128TyID:
  case Type::FP128TyID:
    return 128;
  // In memory objects this is always aligned to a higher boundary, but
  // only 80 bits contain information.
  case Type::X86_FP80TyID:
    return 80;
  case Type::VectorTyID:
    return cast<VectorType>(Ty)->getBitWidth();
  default:
    llvm_unreachable("TargetData::getTypeSizeInBits(): Unsupported type");
  }
}

static bool tryPromoteAllocaToVector(AllocaInst *Alloca, AMDGPUAS AS) {
  ArrayType *AllocaTy = dyn_cast<ArrayType>(Alloca->getAllocatedType());

  DEBUG(dbgs() << "Alloca candidate for vectorization\n");

  // FIXME: There is no reason why we can't support larger arrays, we
  // are just being conservative for now.
  // FIXME: We also reject alloca's of the form [ 2 x [ 2 x i32 ]] or equivalent. Potentially these
  // could also be promoted but we don't currently handle this case
  if (!AllocaTy ||
      AllocaTy->getNumElements() > 4 ||
      AllocaTy->getNumElements() < 2 ||
      !VectorType::isValidElementType(AllocaTy->getElementType())) {
    DEBUG(dbgs() << "  Cannot convert type to vector\n");
    return false;
  }

  std::map<GetElementPtrInst*, Value*> GEPVectorIdx;
  std::vector<Value*> WorkList;
  for (User *AllocaUser : Alloca->users()) {
    GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(AllocaUser);
    if (!GEP) {
      if (!canVectorizeInst(cast<Instruction>(AllocaUser), Alloca))
        return false;

      WorkList.push_back(AllocaUser);
      continue;
    }

    Value *Index = GEPToVectorIndex(GEP);

    // If we can't compute a vector index from this GEP, then we can't
    // promote this alloca to vector.
    if (!Index) {
      DEBUG(dbgs() << "  Cannot compute vector index for GEP " << *GEP << '\n');
      return false;
    }

    GEPVectorIdx[GEP] = Index;
    for (User *GEPUser : AllocaUser->users()) {
      if (!canVectorizeInst(cast<Instruction>(GEPUser), AllocaUser))
        return false;

      WorkList.push_back(GEPUser);
    }
  }

  VectorType *VectorTy = arrayTypeToVecType(AllocaTy);

  DEBUG(dbgs() << "  Converting alloca to vector "
        << *AllocaTy << " -> " << *VectorTy << '\n');

  for (Value *V : WorkList) {
    Instruction *Inst = cast<Instruction>(V);
    IRBuilder<> Builder(Inst);
    switch (Inst->getOpcode()) {
    case Instruction::Load: {
      Type *VecPtrTy = VectorTy->getPointerTo(AS.PRIVATE_ADDRESS);
      Value *Ptr = cast<LoadInst>(Inst)->getPointerOperand();
      Value *Index = calculateVectorIndex(Ptr, GEPVectorIdx);

      Value *BitCast = Builder.CreateBitCast(Alloca, VecPtrTy);
      Value *VecValue = Builder.CreateLoad(BitCast);
      Value *ExtractElement = Builder.CreateExtractElement(VecValue, Index);
      Inst->replaceAllUsesWith(ExtractElement);
      Inst->eraseFromParent();
      break;
    }
    case Instruction::Store: {
      Type *VecPtrTy = VectorTy->getPointerTo(AS.PRIVATE_ADDRESS);

      StoreInst *SI = cast<StoreInst>(Inst);
      Value *Ptr = SI->getPointerOperand();
      Value *Index = calculateVectorIndex(Ptr, GEPVectorIdx);
      Value *BitCast = Builder.CreateBitCast(Alloca, VecPtrTy);
      Value *VecValue = Builder.CreateLoad(BitCast);
      Value *NewVecValue = Builder.CreateInsertElement(VecValue,
                                                       SI->getValueOperand(),
                                                       Index);
      Builder.CreateStore(NewVecValue, BitCast);
      Inst->eraseFromParent();
      break;
    }
    case Instruction::BitCast:
    case Instruction::AddrSpaceCast:
      break;

    default:
      llvm_unreachable("Inconsistency in instructions promotable to vector");
    }
  }
  return true;
}

/// If there were any appending global variables, link them together now.
/// Return true on error.
Constant *IRLinker::linkAppendingVarProto(GlobalVariable *DstGV,
                                          const GlobalVariable *SrcGV) {
  Type *EltTy = cast<ArrayType>(TypeMap.get(SrcGV->getType()->getElementType()))
                    ->getElementType();

  StringRef Name = SrcGV->getName();
  bool IsNewStructor = false;
  bool IsOldStructor = false;
  if (Name == "llvm.global_ctors" || Name == "llvm.global_dtors") {
    if (cast<StructType>(EltTy)->getNumElements() == 3)
      IsNewStructor = true;
    else
      IsOldStructor = true;
  }

  PointerType *VoidPtrTy = Type::getInt8Ty(SrcGV->getContext())->getPointerTo();
  if (IsOldStructor) {
    auto &ST = *cast<StructType>(EltTy);
    Type *Tys[3] = {ST.getElementType(0), ST.getElementType(1), VoidPtrTy};
    EltTy = StructType::get(SrcGV->getContext(), Tys, false);
  }

  if (DstGV) {
    ArrayType *DstTy = cast<ArrayType>(DstGV->getType()->getElementType());

    if (!SrcGV->hasAppendingLinkage() || !DstGV->hasAppendingLinkage()) {
      emitError(
          "Linking globals named '" + SrcGV->getName() +
          "': can only link appending global with another appending global!");
      return nullptr;
    }

    // Check to see that they two arrays agree on type.
    if (EltTy != DstTy->getElementType()) {
      emitError("Appending variables with different element types!");
      return nullptr;
    }
    if (DstGV->isConstant() != SrcGV->isConstant()) {
      emitError("Appending variables linked with different const'ness!");
      return nullptr;
    }

    if (DstGV->getAlignment() != SrcGV->getAlignment()) {
      emitError(
          "Appending variables with different alignment need to be linked!");
      return nullptr;
    }

    if (DstGV->getVisibility() != SrcGV->getVisibility()) {
      emitError(
          "Appending variables with different visibility need to be linked!");
      return nullptr;
    }

    if (DstGV->hasUnnamedAddr() != SrcGV->hasUnnamedAddr()) {
      emitError(
          "Appending variables with different unnamed_addr need to be linked!");
      return nullptr;
    }

    if (StringRef(DstGV->getSection()) != SrcGV->getSection()) {
      emitError(
          "Appending variables with different section name need to be linked!");
      return nullptr;
    }
  }

  SmallVector<Constant *, 16> DstElements;
  if (DstGV)
    getArrayElements(DstGV->getInitializer(), DstElements);

  SmallVector<Constant *, 16> SrcElements;
  getArrayElements(SrcGV->getInitializer(), SrcElements);

  if (IsNewStructor)
    SrcElements.erase(
        std::remove_if(SrcElements.begin(), SrcElements.end(),
                       [this](Constant *E) {
                         auto *Key = dyn_cast<GlobalValue>(
                             E->getAggregateElement(2)->stripPointerCasts());
                         if (!Key)
                           return false;
                         GlobalValue *DGV = getLinkedToGlobal(Key);
                         return !shouldLink(DGV, *Key);
                       }),
        SrcElements.end());
  uint64_t NewSize = DstElements.size() + SrcElements.size();
  ArrayType *NewType = ArrayType::get(EltTy, NewSize);

  // Create the new global variable.
  GlobalVariable *NG = new GlobalVariable(
      DstM, NewType, SrcGV->isConstant(), SrcGV->getLinkage(),
      /*init*/ nullptr, /*name*/ "", DstGV, SrcGV->getThreadLocalMode(),
      SrcGV->getType()->getAddressSpace());

  NG->copyAttributesFrom(SrcGV);
  forceRenaming(NG, SrcGV->getName());

//.........这里部分代码省略.........

/// linkAppendingVarProto - If there were any appending global variables, link
/// them together now.  Return true on error.
bool ModuleLinker::linkAppendingVarProto(GlobalVariable *DstGV,
                                         GlobalVariable *SrcGV) {
 
  if (!SrcGV->hasAppendingLinkage() || !DstGV->hasAppendingLinkage())
    return emitError("Linking globals named '" + SrcGV->getName() +
           "': can only link appending global with another appending global!");
  
  ArrayType *DstTy = cast<ArrayType>(DstGV->getType()->getElementType());
  ArrayType *SrcTy =
    cast<ArrayType>(TypeMap.get(SrcGV->getType()->getElementType()));
  Type *EltTy = DstTy->getElementType();
  
  // Check to see that they two arrays agree on type.
  if (EltTy != SrcTy->getElementType())
    return emitError("Appending variables with different element types!");
  if (DstGV->isConstant() != SrcGV->isConstant())
    return emitError("Appending variables linked with different const'ness!");
  
  if (DstGV->getAlignment() != SrcGV->getAlignment())
    return emitError(
             "Appending variables with different alignment need to be linked!");
  
  if (DstGV->getVisibility() != SrcGV->getVisibility())
    return emitError(
            "Appending variables with different visibility need to be linked!");
  
  if (DstGV->getSection() != SrcGV->getSection())
    return emitError(
          "Appending variables with different section name need to be linked!");
  
  uint64_t NewSize = DstTy->getNumElements() + SrcTy->getNumElements();
  ArrayType *NewType = ArrayType::get(EltTy, NewSize);
  
  // Create the new global variable.
  GlobalVariable *NG =
    new GlobalVariable(*DstGV->getParent(), NewType, SrcGV->isConstant(),
                       DstGV->getLinkage(), /*init*/0, /*name*/"", DstGV,
                       DstGV->isThreadLocal(),
                       DstGV->getType()->getAddressSpace());
  
  // Propagate alignment, visibility and section info.
  CopyGVAttributes(NG, DstGV);
  
  AppendingVarInfo AVI;
  AVI.NewGV = NG;
  AVI.DstInit = DstGV->getInitializer();
  AVI.SrcInit = SrcGV->getInitializer();
  AppendingVars.push_back(AVI);

  // Replace any uses of the two global variables with uses of the new
  // global.
  ValueMap[SrcGV] = ConstantExpr::getBitCast(NG, TypeMap.get(SrcGV->getType()));

  DstGV->replaceAllUsesWith(ConstantExpr::getBitCast(NG, DstGV->getType()));
  DstGV->eraseFromParent();
  
  // Track the source variable so we don't try to link it.
  DoNotLinkFromSource.insert(SrcGV);
  
  return false;
}

static Constant *julia_const_to_llvm(const void *ptr, jl_datatype_t *bt)
{
    // assumes `jl_isbits(bt)`.
    // `ptr` can point to a inline field, do not read the tag from it.
    // make sure to return exactly the type specified by
    // julia_type_to_llvm as this will be assumed by the callee.
    if (bt == jl_bool_type)
        return ConstantInt::get(T_int8, (*(const uint8_t*)ptr) ? 1 : 0);

    if (jl_is_vecelement_type((jl_value_t*)bt))
        bt = (jl_datatype_t*)jl_tparam0(bt);

    Type *lt = julia_struct_to_llvm((jl_value_t*)bt, NULL, NULL);

    if (type_is_ghost(lt))
        return UndefValue::get(NoopType);

    if (jl_is_primitivetype(bt)) {
        if (lt->isFloatTy()) {
            uint32_t data32 = *(const uint32_t*)ptr;
            return ConstantFP::get(jl_LLVMContext,
                    APFloat(lt->getFltSemantics(), APInt(32, data32)));
        }
        if (lt->isDoubleTy()) {
            uint64_t data64 = *(const uint64_t*)ptr;
            return ConstantFP::get(jl_LLVMContext,
                    APFloat(lt->getFltSemantics(), APInt(64, data64)));
        }
        int nb = jl_datatype_size(bt);
        APInt val(8 * nb, 0);
        void *bits = const_cast<uint64_t*>(val.getRawData());
        assert(sys::IsLittleEndianHost);
        memcpy(bits, ptr, nb);
        if (lt->isFloatingPointTy()) {
            return ConstantFP::get(jl_LLVMContext,
                    APFloat(lt->getFltSemantics(), val));
        }
        assert(cast<IntegerType>(lt)->getBitWidth() == 8u * nb);
        return ConstantInt::get(lt, val);
    }

    CompositeType *lct = cast<CompositeType>(lt);
    size_t nf = jl_datatype_nfields(bt);
    std::vector<Constant*> fields(nf);
    for (size_t i = 0; i < nf; i++) {
        size_t offs = jl_field_offset(bt, i);
        assert(!jl_field_isptr(bt, i));
        jl_value_t *ft = jl_field_type(bt, i);
        Type *lft = lct->getTypeAtIndex(i);
        const uint8_t *ov = (const uint8_t*)ptr + offs;
        Constant *val;
        if (jl_is_uniontype(ft)) {
            // compute the same type layout as julia_struct_to_llvm
            size_t fsz = jl_field_size(bt, i);
            size_t al = jl_field_align(bt, i);
            uint8_t sel = ((const uint8_t*)ptr)[offs + fsz - 1];
            jl_value_t *active_ty = jl_nth_union_component(ft, sel);
            size_t active_sz = jl_datatype_size(active_ty);
            ArrayType *aty = cast<ArrayType>(cast<StructType>(lft)->getTypeAtIndex(0u));
            assert(aty->getElementType() == IntegerType::get(jl_LLVMContext, 8 * al) &&
                   aty->getNumElements() == (fsz - 1) / al);
            std::vector<Constant*> ArrayElements(0);
            for (unsigned j = 0; j < aty->getNumElements(); j++) {
                APInt Elem(8 * al, 0);
                void *bits = const_cast<uint64_t*>(Elem.getRawData());
                if (active_sz > al) {
                    memcpy(bits, ov, al);
                    active_sz -= al;
                }
                else if (active_sz > 0) {
                    memcpy(bits, ov, active_sz);
                    active_sz = 0;
                }
                ov += al;
                ArrayElements.push_back(ConstantInt::get(aty->getElementType(), Elem));
            }
            std::vector<Constant*> Elements(0);
            Elements.push_back(ConstantArray::get(aty, ArrayElements));
            unsigned remainder = (fsz - 1) % al;
            while (remainder--) {
                uint8_t byte;
                if (active_sz > 0) {
                    byte = *ov;
                    active_sz -= 1;
                }
                else {
                    byte = 0;
                }
                ov += 1;
                APInt Elem(8, byte);
                Elements.push_back(ConstantInt::get(T_int8, Elem));
            }
            Elements.push_back(ConstantInt::get(T_int8, sel));
            val = ConstantStruct::get(cast<StructType>(lft), Elements);
        }
        else {
            val = julia_const_to_llvm(ov, (jl_datatype_t*)ft);
        }
        fields[i] = val;
    }
//.........这里部分代码省略.........

/// Loop over all of the linked values to compute type mappings.  For example,
/// if we link "extern Foo *x" and "Foo *x = NULL", then we have two struct
/// types 'Foo' but one got renamed when the module was loaded into the same
/// LLVMContext.
void IRLinker::computeTypeMapping() {
  for (GlobalValue &SGV : SrcM->globals()) {
    GlobalValue *DGV = getLinkedToGlobal(&SGV);
    if (!DGV)
      continue;

    if (!DGV->hasAppendingLinkage() || !SGV.hasAppendingLinkage()) {
      TypeMap.addTypeMapping(DGV->getType(), SGV.getType());
      continue;
    }

    // Unify the element type of appending arrays.
    ArrayType *DAT = cast<ArrayType>(DGV->getValueType());
    ArrayType *SAT = cast<ArrayType>(SGV.getValueType());
    TypeMap.addTypeMapping(DAT->getElementType(), SAT->getElementType());
  }

  for (GlobalValue &SGV : *SrcM)
    if (GlobalValue *DGV = getLinkedToGlobal(&SGV))
      TypeMap.addTypeMapping(DGV->getType(), SGV.getType());

  for (GlobalValue &SGV : SrcM->aliases())
    if (GlobalValue *DGV = getLinkedToGlobal(&SGV))
      TypeMap.addTypeMapping(DGV->getType(), SGV.getType());

  // Incorporate types by name, scanning all the types in the source module.
  // At this point, the destination module may have a type "%foo = { i32 }" for
  // example.  When the source module got loaded into the same LLVMContext, if
  // it had the same type, it would have been renamed to "%foo.42 = { i32 }".
  std::vector<StructType *> Types = SrcM->getIdentifiedStructTypes();
  for (StructType *ST : Types) {
    if (!ST->hasName())
      continue;

    // Check to see if there is a dot in the name followed by a digit.
    size_t DotPos = ST->getName().rfind('.');
    if (DotPos == 0 || DotPos == StringRef::npos ||
        ST->getName().back() == '.' ||
        !isdigit(static_cast<unsigned char>(ST->getName()[DotPos + 1])))
      continue;

    // Check to see if the destination module has a struct with the prefix name.
    StructType *DST = DstM.getTypeByName(ST->getName().substr(0, DotPos));
    if (!DST)
      continue;

    // Don't use it if this actually came from the source module. They're in
    // the same LLVMContext after all. Also don't use it unless the type is
    // actually used in the destination module. This can happen in situations
    // like this:
    //
    //      Module A                         Module B
    //      --------                         --------
    //   %Z = type { %A }                %B = type { %C.1 }
    //   %A = type { %B.1, [7 x i8] }    %C.1 = type { i8* }
    //   %B.1 = type { %C }              %A.2 = type { %B.3, [5 x i8] }
    //   %C = type { i8* }               %B.3 = type { %C.1 }
    //
    // When we link Module B with Module A, the '%B' in Module B is
    // used. However, that would then use '%C.1'. But when we process '%C.1',
    // we prefer to take the '%C' version. So we are then left with both
    // '%C.1' and '%C' being used for the same types. This leads to some
    // variables using one type and some using the other.
    if (TypeMap.DstStructTypesSet.hasType(DST))
      TypeMap.addTypeMapping(DST, ST);
  }

  // Now that we have discovered all of the type equivalences, get a body for
  // any 'opaque' types in the dest module that are now resolved.
  TypeMap.linkDefinedTypeBodies();
}