clang/lib/CodeGen/CGVtable.cpp

//===--- CGVtable.cpp - Emit LLVM Code for C++ vtables --------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ code generation of virtual tables.
//
//===----------------------------------------------------------------------===//

#include "CodeGenModule.h"
#include "CodeGenFunction.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/RecordLayout.h"
#include "llvm/ADT/DenseSet.h"
#include <cstdio>

using namespace clang;
using namespace CodeGen;

namespace {
class VtableBuilder {
public:
  /// Index_t - Vtable index type.
  typedef uint64_t Index_t;
private:
  
  // VtableComponents - The components of the vtable being built.
  typedef llvm::SmallVector<llvm::Constant *, 64> VtableComponentsVectorTy;
  VtableComponentsVectorTy VtableComponents;
  
  const bool BuildVtable;

  llvm::Type *Ptr8Ty;
  
  /// MostDerivedClass - The most derived class that this vtable is being 
  /// built for.
  const CXXRecordDecl *MostDerivedClass;
  
  /// LayoutClass - The most derived class used for virtual base layout
  /// information.
  const CXXRecordDecl *LayoutClass;
  /// LayoutOffset - The offset for Class in LayoutClass.
  uint64_t LayoutOffset;
  /// BLayout - Layout for the most derived class that this vtable is being
  /// built for.
  const ASTRecordLayout &BLayout;
  llvm::SmallSet<const CXXRecordDecl *, 32> IndirectPrimary;
  llvm::SmallSet<const CXXRecordDecl *, 32> SeenVBase;
  llvm::Constant *rtti;
  llvm::LLVMContext &VMContext;
  CodeGenModule &CGM;  // Per-module state.
  
  llvm::DenseMap<GlobalDecl, Index_t> VCall;
  llvm::DenseMap<GlobalDecl, Index_t> VCallOffset;
  // This is the offset to the nearest virtual base
  llvm::DenseMap<GlobalDecl, Index_t> NonVirtualOffset;
  llvm::DenseMap<const CXXRecordDecl *, Index_t> VBIndex;

  /// PureVirtualFunction - Points to __cxa_pure_virtual.
  llvm::Constant *PureVirtualFn;
  
  /// VtableMethods - A data structure for keeping track of methods in a vtable.
  /// Can add methods, override methods and iterate in vtable order.
  class VtableMethods {
    // MethodToIndexMap - Maps from a global decl to the index it has in the
    // Methods vector.
    llvm::DenseMap<GlobalDecl, uint64_t> MethodToIndexMap;

    /// Methods - The methods, in vtable order.
    typedef llvm::SmallVector<GlobalDecl, 16> MethodsVectorTy;
    MethodsVectorTy Methods;
    MethodsVectorTy OrigMethods;

  public:
    /// AddMethod - Add a method to the vtable methods.
    void AddMethod(GlobalDecl GD) {
      assert(!MethodToIndexMap.count(GD) && 
             "Method has already been added!");
      
      MethodToIndexMap[GD] = Methods.size();
      Methods.push_back(GD);
      OrigMethods.push_back(GD);
    }
    
    /// OverrideMethod - Replace a method with another.
    void OverrideMethod(GlobalDecl OverriddenGD, GlobalDecl GD) {
      llvm::DenseMap<GlobalDecl, uint64_t>::iterator i 
        = MethodToIndexMap.find(OverriddenGD);
      assert(i != MethodToIndexMap.end() && "Did not find entry!");

      // Get the index of the old decl.
      uint64_t Index = i->second;
      
      // Replace the old decl with the new decl.
      Methods[Index] = GD;

      // And add the new.
      MethodToIndexMap[GD] = Index;
    }

    /// getIndex - Gives the index of a passed in GlobalDecl. Returns false if
    /// the index couldn't be found.
    bool getIndex(GlobalDecl GD, uint64_t &Index) const {
      llvm::DenseMap<GlobalDecl, uint64_t>::const_iterator i 
        = MethodToIndexMap.find(GD);

      if (i == MethodToIndexMap.end())
        return false;
      
      Index = i->second;
      return true;
    }

    GlobalDecl getOrigMethod(uint64_t Index) const {
      return OrigMethods[Index];
    }

    MethodsVectorTy::size_type size() const {
      return Methods.size();
    }

    void clear() {
      MethodToIndexMap.clear();
      Methods.clear();
      OrigMethods.clear();
    }
    
    GlobalDecl operator[](uint64_t Index) const {
      return Methods[Index];
    }
  };
  
  /// Methods - The vtable methods we're currently building.
  VtableMethods Methods;
  
  /// ThisAdjustments - For a given index in the vtable, contains the 'this'
  /// pointer adjustment needed for a method.
  typedef llvm::DenseMap<uint64_t, ThunkAdjustment> ThisAdjustmentsMapTy;
  ThisAdjustmentsMapTy ThisAdjustments;

  typedef std::vector<std::pair<std::pair<GlobalDecl, GlobalDecl>,
                                ThunkAdjustment> > SavedThisAdjustmentsVectorTy;
  SavedThisAdjustmentsVectorTy SavedThisAdjustments;

  /// BaseReturnTypes - Contains the base return types of methods who have been
  /// overridden with methods whose return types require adjustment. Used for
  /// generating covariant thunk information.
  typedef llvm::DenseMap<uint64_t, CanQualType> BaseReturnTypesMapTy;
  BaseReturnTypesMapTy BaseReturnTypes;
  
  std::vector<Index_t> VCalls;

  typedef std::pair<const CXXRecordDecl *, uint64_t> CtorVtable_t;
  // subAddressPoints - Used to hold the AddressPoints (offsets) into the built
  // vtable for use in computing the initializers for the VTT.
  llvm::DenseMap<CtorVtable_t, int64_t> &subAddressPoints;

  typedef CXXRecordDecl::method_iterator method_iter;
  const bool Extern;
  const uint32_t LLVMPointerWidth;
  Index_t extra;
  typedef std::vector<std::pair<const CXXRecordDecl *, int64_t> > Path_t;
  static llvm::DenseMap<CtorVtable_t, int64_t>&
  AllocAddressPoint(CodeGenModule &cgm, const CXXRecordDecl *l,
                    const CXXRecordDecl *c) {
    CodeGenModule::AddrMap_t *&oref = cgm.AddressPoints[l];
    if (oref == 0)
      oref = new CodeGenModule::AddrMap_t;

    llvm::DenseMap<CtorVtable_t, int64_t> *&ref = (*oref)[c];
    if (ref == 0)
      ref = new llvm::DenseMap<CtorVtable_t, int64_t>;
    return *ref;
  }
  
  /// getPureVirtualFn - Return the __cxa_pure_virtual function.
  llvm::Constant* getPureVirtualFn() {
    if (!PureVirtualFn) {
      const llvm::FunctionType *Ty = 
        llvm::FunctionType::get(llvm::Type::getVoidTy(VMContext), 
                                /*isVarArg=*/false);
      PureVirtualFn = wrap(CGM.CreateRuntimeFunction(Ty, "__cxa_pure_virtual"));
    }
    
    return PureVirtualFn;
  }
  
public:
  VtableBuilder(const CXXRecordDecl *MostDerivedClass,
                const CXXRecordDecl *l, uint64_t lo, CodeGenModule &cgm,
                bool build)
    : BuildVtable(build), MostDerivedClass(MostDerivedClass), LayoutClass(l),
      LayoutOffset(lo), BLayout(cgm.getContext().getASTRecordLayout(l)),
      rtti(0), VMContext(cgm.getModule().getContext()),CGM(cgm),
      PureVirtualFn(0),
      subAddressPoints(AllocAddressPoint(cgm, l, MostDerivedClass)),
      Extern(!l->isInAnonymousNamespace()),
      LLVMPointerWidth(cgm.getContext().Target.getPointerWidth(0)) {
    Ptr8Ty = llvm::PointerType::get(llvm::Type::getInt8Ty(VMContext), 0);
    if (BuildVtable)
      rtti = cgm.GenerateRTTIRef(MostDerivedClass);
  }

  // getVtableComponents - Returns a reference to the vtable components.
  const VtableComponentsVectorTy &getVtableComponents() const {
    return VtableComponents;
  }
  
  llvm::DenseMap<const CXXRecordDecl *, Index_t> &getVBIndex()
    { return VBIndex; }

  SavedThisAdjustmentsVectorTy &getSavedThisAdjustments()
    { return SavedThisAdjustments; }

  llvm::Constant *wrap(Index_t i) {
    llvm::Constant *m;
    m = llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext), i);
    return llvm::ConstantExpr::getIntToPtr(m, Ptr8Ty);
  }

  llvm::Constant *wrap(llvm::Constant *m) {
    return llvm::ConstantExpr::getBitCast(m, Ptr8Ty);
  }

#define D1(x)
//#define D1(X) do { if (getenv("DEBUG")) { X; } } while (0)

  void GenerateVBaseOffsets(const CXXRecordDecl *RD, uint64_t Offset,
                            bool updateVBIndex, Index_t current_vbindex) {
    for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
           e = RD->bases_end(); i != e; ++i) {
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      Index_t next_vbindex = current_vbindex;
      if (i->isVirtual() && !SeenVBase.count(Base)) {
        SeenVBase.insert(Base);
        if (updateVBIndex) {
          next_vbindex = (ssize_t)(-(VCalls.size()*LLVMPointerWidth/8)
                                   - 3*LLVMPointerWidth/8);
          VBIndex[Base] = next_vbindex;
        }
        int64_t BaseOffset = -(Offset/8) + BLayout.getVBaseClassOffset(Base)/8;
        VCalls.push_back((0?700:0) + BaseOffset);
        D1(printf("  vbase for %s at %d delta %d most derived %s\n",
                  Base->getNameAsCString(),
                  (int)-VCalls.size()-3, (int)BaseOffset,
                  Class->getNameAsCString()));
      }
      // We also record offsets for non-virtual bases to closest enclosing
      // virtual base.  We do this so that we don't have to search
      // for the nearst virtual base class when generating thunks.
      if (updateVBIndex && VBIndex.count(Base) == 0)
        VBIndex[Base] = next_vbindex;
      GenerateVBaseOffsets(Base, Offset, updateVBIndex, next_vbindex);
    }
  }

  void StartNewTable() {
    SeenVBase.clear();
  }

  Index_t getNVOffset_1(const CXXRecordDecl *D, const CXXRecordDecl *B,
    Index_t Offset = 0) {

    if (B == D)
      return Offset;

    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(D);
    for (CXXRecordDecl::base_class_const_iterator i = D->bases_begin(),
           e = D->bases_end(); i != e; ++i) {
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      int64_t BaseOffset = 0;
      if (!i->isVirtual())
        BaseOffset = Offset + Layout.getBaseClassOffset(Base);
      int64_t o = getNVOffset_1(Base, B, BaseOffset);
      if (o >= 0)
        return o;
    }

    return -1;
  }

  /// getNVOffset - Returns the non-virtual offset for the given (B) base of the
  /// derived class D.
  Index_t getNVOffset(QualType qB, QualType qD) {
    qD = qD->getPointeeType();
    qB = qB->getPointeeType();
    CXXRecordDecl *D = cast<CXXRecordDecl>(qD->getAs<RecordType>()->getDecl());
    CXXRecordDecl *B = cast<CXXRecordDecl>(qB->getAs<RecordType>()->getDecl());
    int64_t o = getNVOffset_1(D, B);
    if (o >= 0)
      return o;

    assert(false && "FIXME: non-virtual base not found");
    return 0;
  }

  /// getVbaseOffset - Returns the index into the vtable for the virtual base
  /// offset for the given (B) virtual base of the derived class D.
  Index_t getVbaseOffset(QualType qB, QualType qD) {
    qD = qD->getPointeeType();
    qB = qB->getPointeeType();
    CXXRecordDecl *D = cast<CXXRecordDecl>(qD->getAs<RecordType>()->getDecl());
    CXXRecordDecl *B = cast<CXXRecordDecl>(qB->getAs<RecordType>()->getDecl());
    if (D != MostDerivedClass)
      return CGM.getVtableInfo().getVirtualBaseOffsetIndex(D, B);
    llvm::DenseMap<const CXXRecordDecl *, Index_t>::iterator i;
    i = VBIndex.find(B);
    if (i != VBIndex.end())
      return i->second;

    assert(false && "FIXME: Base not found");
    return 0;
  }

  bool OverrideMethod(GlobalDecl GD, bool MorallyVirtual,
                      Index_t OverrideOffset, Index_t Offset,
                      int64_t CurrentVBaseOffset);

  /// AppendMethods - Append the current methods to the vtable.
  void AppendMethodsToVtable();
  
  llvm::Constant *WrapAddrOf(GlobalDecl GD) {
    const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());

    const llvm::Type *Ty = CGM.getTypes().GetFunctionTypeForVtable(MD);

    return wrap(CGM.GetAddrOfFunction(GD, Ty));
  }

  void OverrideMethods(Path_t *Path, bool MorallyVirtual, int64_t Offset,
                       int64_t CurrentVBaseOffset) {
    for (Path_t::reverse_iterator i = Path->rbegin(),
           e = Path->rend(); i != e; ++i) {
      const CXXRecordDecl *RD = i->first;
      int64_t OverrideOffset = i->second;
      for (method_iter mi = RD->method_begin(), me = RD->method_end(); mi != me;
           ++mi) {
        const CXXMethodDecl *MD = *mi;

        if (!MD->isVirtual())
          continue;

        if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
          // Override both the complete and the deleting destructor.
          GlobalDecl CompDtor(DD, Dtor_Complete);
          OverrideMethod(CompDtor, MorallyVirtual, OverrideOffset, Offset,
                         CurrentVBaseOffset);

          GlobalDecl DeletingDtor(DD, Dtor_Deleting);
          OverrideMethod(DeletingDtor, MorallyVirtual, OverrideOffset, Offset,
                         CurrentVBaseOffset);
        } else {
          OverrideMethod(MD, MorallyVirtual, OverrideOffset, Offset,
                         CurrentVBaseOffset);
        }
      }
    }
  }

  void AddMethod(const GlobalDecl GD, bool MorallyVirtual, Index_t Offset,
                 int64_t CurrentVBaseOffset) {
    // If we can find a previously allocated slot for this, reuse it.
    if (OverrideMethod(GD, MorallyVirtual, Offset, Offset,
                       CurrentVBaseOffset))
      return;

    // We didn't find an entry in the vtable that we could use, add a new
    // entry.
    Methods.AddMethod(GD);

    D1(printf("  vfn for %s at %d\n", MD->getNameAsString().c_str(),
              (int)Index[GD]));
    if (MorallyVirtual) {
      VCallOffset[GD] = Offset/8;
      Index_t &idx = VCall[GD];
      // Allocate the first one, after that, we reuse the previous one.
      if (idx == 0) {
        NonVirtualOffset[GD] = CurrentVBaseOffset/8 - Offset/8;
        idx = VCalls.size()+1;
        VCalls.push_back(0);
        D1(printf("  vcall for %s at %d with delta %d\n",
                  MD->getNameAsString().c_str(), (int)-VCalls.size()-3, 0));
      }
    }
  }

  void AddMethods(const CXXRecordDecl *RD, bool MorallyVirtual,
                  Index_t Offset, int64_t CurrentVBaseOffset) {
    for (method_iter mi = RD->method_begin(), me = RD->method_end(); mi != me;
         ++mi) {
      const CXXMethodDecl *MD = *mi;
      if (!MD->isVirtual())
        continue;
      
      if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
        // For destructors, add both the complete and the deleting destructor
        // to the vtable.
        AddMethod(GlobalDecl(DD, Dtor_Complete), MorallyVirtual, Offset, 
                  CurrentVBaseOffset);
        AddMethod(GlobalDecl(DD, Dtor_Deleting), MorallyVirtual, Offset, 
                  CurrentVBaseOffset);
      } else
        AddMethod(MD, MorallyVirtual, Offset, CurrentVBaseOffset);
    }
  }

  void NonVirtualBases(const CXXRecordDecl *RD, const ASTRecordLayout &Layout,
                       const CXXRecordDecl *PrimaryBase,
                       bool PrimaryBaseWasVirtual, bool MorallyVirtual,
                       int64_t Offset, int64_t CurrentVBaseOffset,
                       Path_t *Path) {
    Path->push_back(std::make_pair(RD, Offset));
    for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
           e = RD->bases_end(); i != e; ++i) {
      if (i->isVirtual())
        continue;
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      if (Base != PrimaryBase || PrimaryBaseWasVirtual) {
        uint64_t o = Offset + Layout.getBaseClassOffset(Base);
        StartNewTable();
        GenerateVtableForBase(Base, o, MorallyVirtual, false,
                              CurrentVBaseOffset, Path);
      }
    }
    Path->pop_back();
  }

// #define D(X) do { X; } while (0)
#define D(X)

  void insertVCalls(int InsertionPoint) {
    D1(printf("============= combining vbase/vcall\n"));
    D(VCalls.insert(VCalls.begin(), 673));
    D(VCalls.push_back(672));

    VtableComponents.insert(VtableComponents.begin() + InsertionPoint, 
                            VCalls.size(), 0);
    if (BuildVtable) {
      // The vcalls come first...
      for (std::vector<Index_t>::reverse_iterator i = VCalls.rbegin(),
             e = VCalls.rend();
           i != e; ++i)
        VtableComponents[InsertionPoint++] = wrap((0?600:0) + *i);
    }
    VCalls.clear();
    VCall.clear();
  }

  void AddAddressPoints(const CXXRecordDecl *RD, uint64_t Offset,
                       Index_t AddressPoint) {
    D1(printf("XXX address point for %s in %s layout %s at offset %d is %d\n",
              RD->getNameAsCString(), Class->getNameAsCString(),
              LayoutClass->getNameAsCString(), (int)Offset, (int)AddressPoint));
    subAddressPoints[std::make_pair(RD, Offset)] = AddressPoint;

    // Now also add the address point for all our primary bases.
    while (1) {
      const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
      RD = Layout.getPrimaryBase();
      const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();
      // FIXME: Double check this.
      if (RD == 0)
        break;
      if (PrimaryBaseWasVirtual &&
          BLayout.getVBaseClassOffset(RD) != Offset)
        break;
      D1(printf("XXX address point for %s in %s layout %s at offset %d is %d\n",
                RD->getNameAsCString(), Class->getNameAsCString(),
                LayoutClass->getNameAsCString(), (int)Offset, (int)AddressPoint));
      subAddressPoints[std::make_pair(RD, Offset)] = AddressPoint;
    }
  }


  Index_t FinishGenerateVtable(const CXXRecordDecl *RD,
                               const ASTRecordLayout &Layout,
                               const CXXRecordDecl *PrimaryBase,
                               bool PrimaryBaseWasVirtual,
                               bool MorallyVirtual, int64_t Offset,
                               bool ForVirtualBase, int64_t CurrentVBaseOffset,
                               Path_t *Path) {
    bool alloc = false;
    if (Path == 0) {
      alloc = true;
      Path = new Path_t;
    }

    StartNewTable();
    extra = 0;
    bool DeferVCalls = MorallyVirtual || ForVirtualBase;
    int VCallInsertionPoint = VtableComponents.size();
    if (!DeferVCalls) {
      insertVCalls(VCallInsertionPoint);
    } else
      // FIXME: just for extra, or for all uses of VCalls.size post this?
      extra = -VCalls.size();

    // Add the offset to top.
    VtableComponents.push_back(BuildVtable ? wrap(-((Offset-LayoutOffset)/8)) : 0);
    
    // Add the RTTI information.
    VtableComponents.push_back(rtti);
    
    Index_t AddressPoint = VtableComponents.size();

    AppendMethodsToVtable();

    // and then the non-virtual bases.
    NonVirtualBases(RD, Layout, PrimaryBase, PrimaryBaseWasVirtual,
                    MorallyVirtual, Offset, CurrentVBaseOffset, Path);

    if (ForVirtualBase) {
      // FIXME: We're adding to VCalls in callers, we need to do the overrides
      // in the inner part, so that we know the complete set of vcalls during
      // the build and don't have to insert into methods.  Saving out the
      // AddressPoint here, would need to be fixed, if we didn't do that.  Also
      // retroactively adding vcalls for overrides later wind up in the wrong
      // place, the vcall slot has to be alloted during the walk of the base
      // when the function is first introduces.
      AddressPoint += VCalls.size();
      insertVCalls(VCallInsertionPoint);
    }
    
    AddAddressPoints(RD, Offset, AddressPoint);

    if (alloc) {
      delete Path;
    }
    return AddressPoint;
  }

  void Primaries(const CXXRecordDecl *RD, bool MorallyVirtual, int64_t Offset,
                 bool updateVBIndex, Index_t current_vbindex,
                 int64_t CurrentVBaseOffset) {
    if (!RD->isDynamicClass())
      return;

    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
    const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
    const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();

    // vtables are composed from the chain of primaries.
    if (PrimaryBase && !PrimaryBaseWasVirtual) {
      D1(printf(" doing primaries for %s most derived %s\n",
                RD->getNameAsCString(), Class->getNameAsCString()));
      Primaries(PrimaryBase, PrimaryBaseWasVirtual|MorallyVirtual, Offset,
                updateVBIndex, current_vbindex, CurrentVBaseOffset);
    }

    D1(printf(" doing vcall entries for %s most derived %s\n",
              RD->getNameAsCString(), Class->getNameAsCString()));

    // And add the virtuals for the class to the primary vtable.
    AddMethods(RD, MorallyVirtual, Offset, CurrentVBaseOffset);
  }

  void VBPrimaries(const CXXRecordDecl *RD, bool MorallyVirtual, int64_t Offset,
                   bool updateVBIndex, Index_t current_vbindex,
                   bool RDisVirtualBase, int64_t CurrentVBaseOffset,
                   bool bottom) {
    if (!RD->isDynamicClass())
      return;

    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
    const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
    const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();

    // vtables are composed from the chain of primaries.
    if (PrimaryBase) {
      int BaseCurrentVBaseOffset = CurrentVBaseOffset;
      if (PrimaryBaseWasVirtual) {
        IndirectPrimary.insert(PrimaryBase);
        BaseCurrentVBaseOffset = BLayout.getVBaseClassOffset(PrimaryBase);
      }

      D1(printf(" doing primaries for %s most derived %s\n",
                RD->getNameAsCString(), Class->getNameAsCString()));
      
      VBPrimaries(PrimaryBase, PrimaryBaseWasVirtual|MorallyVirtual, Offset,
                  updateVBIndex, current_vbindex, PrimaryBaseWasVirtual,
                  BaseCurrentVBaseOffset, false);
    }

    D1(printf(" doing vbase entries for %s most derived %s\n",
              RD->getNameAsCString(), Class->getNameAsCString()));
    GenerateVBaseOffsets(RD, Offset, updateVBIndex, current_vbindex);

    if (RDisVirtualBase || bottom) {
      Primaries(RD, MorallyVirtual, Offset, updateVBIndex, current_vbindex,
                CurrentVBaseOffset);
    }
  }

  int64_t GenerateVtableForBase(const CXXRecordDecl *RD, int64_t Offset = 0,
                                bool MorallyVirtual = false, 
                                bool ForVirtualBase = false,
                                int CurrentVBaseOffset = 0,
                                Path_t *Path = 0) {
    if (!RD->isDynamicClass())
      return 0;

    // Construction vtable don't need parts that have no virtual bases and
    // aren't morally virtual.
    if ((LayoutClass != MostDerivedClass) && 
        RD->getNumVBases() == 0 && !MorallyVirtual)
      return 0;

    const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
    const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
    const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();

    extra = 0;
    D1(printf("building entries for base %s most derived %s\n",
              RD->getNameAsCString(), Class->getNameAsCString()));

    if (ForVirtualBase)
      extra = VCalls.size();

    VBPrimaries(RD, MorallyVirtual, Offset, !ForVirtualBase, 0, ForVirtualBase,
                CurrentVBaseOffset, true);

    if (Path)
      OverrideMethods(Path, MorallyVirtual, Offset, CurrentVBaseOffset);

    return FinishGenerateVtable(RD, Layout, PrimaryBase, PrimaryBaseWasVirtual,
                                MorallyVirtual, Offset, ForVirtualBase,
                                CurrentVBaseOffset, Path);
  }

  void GenerateVtableForVBases(const CXXRecordDecl *RD,
                               int64_t Offset = 0,
                               Path_t *Path = 0) {
    bool alloc = false;
    if (Path == 0) {
      alloc = true;
      Path = new Path_t;
    }
    // FIXME: We also need to override using all paths to a virtual base,
    // right now, we just process the first path
    Path->push_back(std::make_pair(RD, Offset));
    for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
           e = RD->bases_end(); i != e; ++i) {
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      if (i->isVirtual() && !IndirectPrimary.count(Base)) {
        // Mark it so we don't output it twice.
        IndirectPrimary.insert(Base);
        StartNewTable();
        VCall.clear();
        int64_t BaseOffset = BLayout.getVBaseClassOffset(Base);
        int64_t CurrentVBaseOffset = BaseOffset;
        D1(printf("vtable %s virtual base %s\n",
                  Class->getNameAsCString(), Base->getNameAsCString()));
        GenerateVtableForBase(Base, BaseOffset, true, true, CurrentVBaseOffset,
                              Path);
      }
      int64_t BaseOffset;
      if (i->isVirtual())
        BaseOffset = BLayout.getVBaseClassOffset(Base);
      else {
        const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
        BaseOffset = Offset + Layout.getBaseClassOffset(Base);
      }
        
      if (Base->getNumVBases()) {
        GenerateVtableForVBases(Base, BaseOffset, Path);
      }
    }
    Path->pop_back();
    if (alloc)
      delete Path;
  }
};
} // end anonymous namespace

/// TypeConversionRequiresAdjustment - Returns whether conversion from a 
/// derived type to a base type requires adjustment.
static bool
TypeConversionRequiresAdjustment(ASTContext &Ctx,
                                 const CXXRecordDecl *DerivedDecl,
                                 const CXXRecordDecl *BaseDecl) {
  CXXBasePaths Paths(/*FindAmbiguities=*/false,
                     /*RecordPaths=*/true, /*DetectVirtual=*/true);
  if (!const_cast<CXXRecordDecl *>(DerivedDecl)->
      isDerivedFrom(const_cast<CXXRecordDecl *>(BaseDecl), Paths)) {
    assert(false && "Class must be derived from the passed in base class!");
    return false;
  }
  
  // If we found a virtual base we always want to require adjustment.
  if (Paths.getDetectedVirtual())
    return true;
  
  const CXXBasePath &Path = Paths.front();
  
  for (size_t Start = 0, End = Path.size(); Start != End; ++Start) {
    const CXXBasePathElement &Element = Path[Start];
    
    // Check the base class offset.
    const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(Element.Class);
    
    const RecordType *BaseType = Element.Base->getType()->getAs<RecordType>();
    const CXXRecordDecl *Base = cast<CXXRecordDecl>(BaseType->getDecl());
    
    if (Layout.getBaseClassOffset(Base) != 0) {
      // This requires an adjustment.
      return true;
    }
  }
  
  return false;
}

static bool 
TypeConversionRequiresAdjustment(ASTContext &Ctx,
                                 QualType DerivedType, QualType BaseType) {
  // Canonicalize the types.
  QualType CanDerivedType = Ctx.getCanonicalType(DerivedType);
  QualType CanBaseType = Ctx.getCanonicalType(BaseType);
  
  assert(CanDerivedType->getTypeClass() == CanBaseType->getTypeClass() && 
         "Types must have same type class!");
  
  if (CanDerivedType == CanBaseType) {
    // No adjustment needed.
    return false;
  }
  
  if (const ReferenceType *RT = dyn_cast<ReferenceType>(CanDerivedType)) {
    CanDerivedType = RT->getPointeeType();
    CanBaseType = cast<ReferenceType>(CanBaseType)->getPointeeType();
  } else if (const PointerType *PT = dyn_cast<PointerType>(CanDerivedType)) {
    CanDerivedType = PT->getPointeeType();
    CanBaseType = cast<PointerType>(CanBaseType)->getPointeeType();
  } else {
    assert(false && "Unexpected return type!");
  }
  
  if (CanDerivedType == CanBaseType) {
    // No adjustment needed.
    return false;
  }
  
  const CXXRecordDecl *DerivedDecl = 
  cast<CXXRecordDecl>(cast<RecordType>(CanDerivedType)->getDecl());
  
  const CXXRecordDecl *BaseDecl = 
  cast<CXXRecordDecl>(cast<RecordType>(CanBaseType)->getDecl());
  
  return TypeConversionRequiresAdjustment(Ctx, DerivedDecl, BaseDecl);
}

bool VtableBuilder::OverrideMethod(GlobalDecl GD, bool MorallyVirtual,
                                   Index_t OverrideOffset, Index_t Offset,
                                   int64_t CurrentVBaseOffset) {
  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());

  const bool isPure = MD->isPure();
  
  // FIXME: Should OverrideOffset's be Offset?

  for (CXXMethodDecl::method_iterator mi = MD->begin_overridden_methods(),
       e = MD->end_overridden_methods(); mi != e; ++mi) {
    GlobalDecl OGD;
    
    const CXXMethodDecl *OMD = *mi;
    if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(OMD))
      OGD = GlobalDecl(DD, GD.getDtorType());
    else
      OGD = OMD;

    // Check whether this is the method being overridden in this section of
    // the vtable.
    uint64_t Index;
    if (!Methods.getIndex(OGD, Index))
      continue;

    // Get the original method, which we should be computing thunks, etc,
    // against.
    OGD = Methods.getOrigMethod(Index);
    OMD = cast<CXXMethodDecl>(OGD.getDecl());

    QualType ReturnType = 
      MD->getType()->getAs<FunctionType>()->getResultType();
    QualType OverriddenReturnType = 
      OMD->getType()->getAs<FunctionType>()->getResultType();
    
    // Check if we need a return type adjustment.
    if (TypeConversionRequiresAdjustment(CGM.getContext(), ReturnType, 
                                          OverriddenReturnType)) {
      CanQualType &BaseReturnType = BaseReturnTypes[Index];

      // Insert the base return type.
      if (BaseReturnType.isNull())
        BaseReturnType =
          CGM.getContext().getCanonicalType(OverriddenReturnType);
    }

    Methods.OverrideMethod(OGD, GD);

    ThisAdjustments.erase(Index);
    if (MorallyVirtual || VCall.count(OGD)) {
      Index_t &idx = VCall[OGD];
      if (idx == 0) {
        NonVirtualOffset[GD] = -OverrideOffset/8 + CurrentVBaseOffset/8;
        VCallOffset[GD] = OverrideOffset/8;
        idx = VCalls.size()+1;
        VCalls.push_back(0);
        D1(printf("  vcall for %s at %d with delta %d most derived %s\n",
                  MD->getNameAsString().c_str(), (int)-idx-3,
                  (int)VCalls[idx-1], Class->getNameAsCString()));
      } else {
        NonVirtualOffset[GD] = NonVirtualOffset[OGD];
        VCallOffset[GD] = VCallOffset[OGD];
        VCalls[idx-1] = -VCallOffset[OGD] + OverrideOffset/8;
        D1(printf("  vcall patch for %s at %d with delta %d most derived %s\n",
                  MD->getNameAsString().c_str(), (int)-idx-3,
                  (int)VCalls[idx-1], Class->getNameAsCString()));
      }
      VCall[GD] = idx;
      int64_t NonVirtualAdjustment = NonVirtualOffset[GD];
      int64_t VirtualAdjustment = 
        -((idx + extra + 2) * LLVMPointerWidth / 8);
      
      // Optimize out virtual adjustments of 0.
      if (VCalls[idx-1] == 0)
        VirtualAdjustment = 0;
      
      ThunkAdjustment ThisAdjustment(NonVirtualAdjustment,
                                      VirtualAdjustment);

      if (!isPure && !ThisAdjustment.isEmpty()) {
        ThisAdjustments[Index] = ThisAdjustment;
        // FIXME: Might this end up inserting some false adjustments?
        SavedThisAdjustments.push_back(std::make_pair(std::make_pair(GD, OGD),
                                                      ThisAdjustment));
      }
      return true;
    }

    // FIXME: finish off
    int64_t NonVirtualAdjustment = VCallOffset[OGD] - OverrideOffset/8;

    if (NonVirtualAdjustment) {
      ThunkAdjustment ThisAdjustment(NonVirtualAdjustment, 0);
      
      if (!isPure)
        ThisAdjustments[Index] = ThisAdjustment;
    }
    return true;
  }

  return false;
}

void VtableBuilder::AppendMethodsToVtable() {
  if (!BuildVtable) {
    VtableComponents.insert(VtableComponents.end(), Methods.size(), 
                            (llvm::Constant *)0);
    ThisAdjustments.clear();
    BaseReturnTypes.clear();
    Methods.clear();
    return;
  }

  // Reserve room in the vtable for our new methods.
  VtableComponents.reserve(VtableComponents.size() + Methods.size());

  for (unsigned i = 0, e = Methods.size(); i != e; ++i) {
    GlobalDecl GD = Methods[i];
    const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
  
    // Get the 'this' pointer adjustment.
    ThunkAdjustment ThisAdjustment = ThisAdjustments.lookup(i);
  
    // Construct the return type adjustment.
    ThunkAdjustment ReturnAdjustment;

    QualType BaseReturnType = BaseReturnTypes.lookup(i);
    if (!BaseReturnType.isNull() && !MD->isPure()) {
      QualType DerivedType = 
        MD->getType()->getAs<FunctionType>()->getResultType();
      
      int64_t NonVirtualAdjustment = 
      getNVOffset(BaseReturnType, DerivedType) / 8;
      
      int64_t VirtualAdjustment = 
      getVbaseOffset(BaseReturnType, DerivedType);
      
      ReturnAdjustment = ThunkAdjustment(NonVirtualAdjustment, 
                                         VirtualAdjustment);
    }

    llvm::Constant *Method = 0;
    if (!ReturnAdjustment.isEmpty()) {
      // Build a covariant thunk.
      CovariantThunkAdjustment Adjustment(ThisAdjustment, ReturnAdjustment);
      Method = wrap(CGM.GetAddrOfCovariantThunk(GD, Adjustment));
    } else if (!ThisAdjustment.isEmpty()) {
      // Build a "regular" thunk.
      Method = wrap(CGM.GetAddrOfThunk(GD, ThisAdjustment));
    } else if (MD->isPure()) {
      // We have a pure virtual method.
      Method = getPureVirtualFn();
    } else {
      // We have a good old regular method.
      Method = WrapAddrOf(GD);
    }

    // Add the method to the vtable.
    VtableComponents.push_back(Method);
  }
  
  
  ThisAdjustments.clear();
  BaseReturnTypes.clear();
  
  Methods.clear();
}

void CGVtableInfo::ComputeMethodVtableIndices(const CXXRecordDecl *RD) {
  
  // Itanium C++ ABI 2.5.2:
  // The order of the virtual function pointers in a virtual table is the 
  // order of declaration of the corresponding member functions in the class.
  //
  // There is an entry for any virtual function declared in a class, 
  // whether it is a new function or overrides a base class function, 
  // unless it overrides a function from the primary base, and conversion
  // between their return types does not require an adjustment. 

  int64_t CurrentIndex = 0;
  
  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
  const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
  
  if (PrimaryBase) {
    assert(PrimaryBase->isDefinition() && 
           "Should have the definition decl of the primary base!");

    // Since the record decl shares its vtable pointer with the primary base
    // we need to start counting at the end of the primary base's vtable.
    CurrentIndex = getNumVirtualFunctionPointers(PrimaryBase);
  }
  
  const CXXDestructorDecl *ImplicitVirtualDtor = 0;
  
  for (CXXRecordDecl::method_iterator i = RD->method_begin(),
       e = RD->method_end(); i != e; ++i) {
    const CXXMethodDecl *MD = *i;

    // We only want virtual methods.
    if (!MD->isVirtual())
      continue;

    bool ShouldAddEntryForMethod = true;
    
    // Check if this method overrides a method in the primary base.
    for (CXXMethodDecl::method_iterator i = MD->begin_overridden_methods(),
         e = MD->end_overridden_methods(); i != e; ++i) {
      const CXXMethodDecl *OverriddenMD = *i;
      const CXXRecordDecl *OverriddenRD = OverriddenMD->getParent();
      assert(OverriddenMD->isCanonicalDecl() &&
             "Should have the canonical decl of the overridden RD!");
      
      if (OverriddenRD == PrimaryBase) {
        // Check if converting from the return type of the method to the 
        // return type of the overridden method requires conversion.
        QualType ReturnType = 
          MD->getType()->getAs<FunctionType>()->getResultType();
        QualType OverriddenReturnType =
          OverriddenMD->getType()->getAs<FunctionType>()->getResultType();
        
        if (!TypeConversionRequiresAdjustment(CGM.getContext(), 
                                            ReturnType, OverriddenReturnType)) {
          // This index is shared between the index in the vtable of the primary
          // base class.
          if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
            const CXXDestructorDecl *OverriddenDD = 
              cast<CXXDestructorDecl>(OverriddenMD);
            
            // Add both the complete and deleting entries.
            MethodVtableIndices[GlobalDecl(DD, Dtor_Complete)] = 
              getMethodVtableIndex(GlobalDecl(OverriddenDD, Dtor_Complete));
            MethodVtableIndices[GlobalDecl(DD, Dtor_Deleting)] = 
              getMethodVtableIndex(GlobalDecl(OverriddenDD, Dtor_Deleting));
          } else {
            MethodVtableIndices[MD] = getMethodVtableIndex(OverriddenMD);
          }
          
          // We don't need to add an entry for this method.
          ShouldAddEntryForMethod = false;
          break;
        }        
      }
    }
    
    if (!ShouldAddEntryForMethod)
      continue;
    
    if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
      if (MD->isImplicit()) {
        assert(!ImplicitVirtualDtor && 
               "Did already see an implicit virtual dtor!");
        ImplicitVirtualDtor = DD;
        continue;
      } 

      // Add the complete dtor.
      MethodVtableIndices[GlobalDecl(DD, Dtor_Complete)] = CurrentIndex++;
      
      // Add the deleting dtor.
      MethodVtableIndices[GlobalDecl(DD, Dtor_Deleting)] = CurrentIndex++;
    } else {
      // Add the entry.
      MethodVtableIndices[MD] = CurrentIndex++;
    }
  }

  if (ImplicitVirtualDtor) {
    // Itanium C++ ABI 2.5.2:
    // If a class has an implicitly-defined virtual destructor, 
    // its entries come after the declared virtual function pointers.

    // Add the complete dtor.
    MethodVtableIndices[GlobalDecl(ImplicitVirtualDtor, Dtor_Complete)] = 
      CurrentIndex++;
    
    // Add the deleting dtor.
    MethodVtableIndices[GlobalDecl(ImplicitVirtualDtor, Dtor_Deleting)] = 
      CurrentIndex++;
  }
  
  NumVirtualFunctionPointers[RD] = CurrentIndex;
}

uint64_t CGVtableInfo::getNumVirtualFunctionPointers(const CXXRecordDecl *RD) {
  llvm::DenseMap<const CXXRecordDecl *, uint64_t>::iterator I = 
    NumVirtualFunctionPointers.find(RD);
  if (I != NumVirtualFunctionPointers.end())
    return I->second;

  ComputeMethodVtableIndices(RD);

  I = NumVirtualFunctionPointers.find(RD);
  assert(I != NumVirtualFunctionPointers.end() && "Did not find entry!");
  return I->second;
}
      
uint64_t CGVtableInfo::getMethodVtableIndex(GlobalDecl GD) {
  MethodVtableIndicesTy::iterator I = MethodVtableIndices.find(GD);
  if (I != MethodVtableIndices.end())
    return I->second;
  
  const CXXRecordDecl *RD = cast<CXXMethodDecl>(GD.getDecl())->getParent();

  ComputeMethodVtableIndices(RD);

  I = MethodVtableIndices.find(GD);
  assert(I != MethodVtableIndices.end() && "Did not find index!");
  return I->second;
}

ThunkAdjustment CGVtableInfo::getThisAdjustment(GlobalDecl GD,
                                                GlobalDecl OGD) {
  SavedThisAdjustmentsTy::iterator I =
    SavedThisAdjustments.find(std::make_pair(GD, OGD));
  if (I != SavedThisAdjustments.end())
    return I->second;

  const CXXRecordDecl *RD = cast<CXXRecordDecl>(GD.getDecl()->getDeclContext());
  if (!SavedThisAdjustmentRecords.insert(RD).second)
    return ThunkAdjustment();

  VtableBuilder b(RD, RD, 0, CGM, false);
  D1(printf("vtable %s\n", RD->getNameAsCString()));
  b.GenerateVtableForBase(RD);
  b.GenerateVtableForVBases(RD);
  
  SavedThisAdjustments.insert(b.getSavedThisAdjustments().begin(),
                              b.getSavedThisAdjustments().end());

  I = SavedThisAdjustments.find(std::make_pair(GD, OGD));
  if (I != SavedThisAdjustments.end())
    return I->second;

  return ThunkAdjustment();
}

int64_t CGVtableInfo::getVirtualBaseOffsetIndex(const CXXRecordDecl *RD, 
                                                const CXXRecordDecl *VBase) {
  ClassPairTy ClassPair(RD, VBase);
  
  VirtualBaseClassIndiciesTy::iterator I = 
    VirtualBaseClassIndicies.find(ClassPair);
  if (I != VirtualBaseClassIndicies.end())
    return I->second;
  
  // FIXME: This seems expensive.  Can we do a partial job to get
  // just this data.
  VtableBuilder b(RD, RD, 0, CGM, false);
  D1(printf("vtable %s\n", RD->getNameAsCString()));
  b.GenerateVtableForBase(RD);
  b.GenerateVtableForVBases(RD);
  
  for (llvm::DenseMap<const CXXRecordDecl *, uint64_t>::iterator I =
       b.getVBIndex().begin(), E = b.getVBIndex().end(); I != E; ++I) {
    // Insert all types.
    ClassPairTy ClassPair(RD, I->first);
    
    VirtualBaseClassIndicies.insert(std::make_pair(ClassPair, I->second));
  }
  
  I = VirtualBaseClassIndicies.find(ClassPair);
  assert(I != VirtualBaseClassIndicies.end() && "Did not find index!");
  
  return I->second;
}

uint64_t CGVtableInfo::getVtableAddressPoint(const CXXRecordDecl *RD) {
  uint64_t AddressPoint = 
    (*(*(CGM.AddressPoints[RD]))[RD])[std::make_pair(RD, 0)];
  
  return AddressPoint;
}

llvm::GlobalVariable *
CGVtableInfo::GenerateVtable(llvm::GlobalVariable::LinkageTypes Linkage,
                             bool GenerateDefinition,
                             const CXXRecordDecl *LayoutClass,
                             const CXXRecordDecl *RD, uint64_t Offset) {
  llvm::SmallString<256> OutName;
  if (LayoutClass != RD)
    CGM.getMangleContext().mangleCXXCtorVtable(LayoutClass, Offset / 8, 
                                               RD, OutName);
  else
    CGM.getMangleContext().mangleCXXVtable(RD, OutName);
  llvm::StringRef Name = OutName.str();

  int64_t AddressPoint;

  llvm::GlobalVariable *GV = CGM.getModule().getGlobalVariable(Name);
  if (GV && CGM.AddressPoints[LayoutClass] && !GV->isDeclaration()) {
    AddressPoint=(*(*(CGM.AddressPoints[LayoutClass]))[RD])[std::make_pair(RD,
                                                                       Offset)];
    // FIXME: We can never have 0 address point.  Do this for now so gepping
    // retains the same structure.  Later, we'll just assert.
    if (AddressPoint == 0)
      AddressPoint = 1;
  } else {
    VtableBuilder b(RD, LayoutClass, Offset, CGM, GenerateDefinition);

    D1(printf("vtable %s\n", RD->getNameAsCString()));
    // First comes the vtables for all the non-virtual bases...
    AddressPoint = b.GenerateVtableForBase(RD, Offset);

    // then the vtables for all the virtual bases.
    b.GenerateVtableForVBases(RD, Offset);

    llvm::Constant *Init = 0;
    const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGM.getLLVMContext());
    llvm::ArrayType *ArrayType = 
      llvm::ArrayType::get(Int8PtrTy, b.getVtableComponents().size());

    if (GenerateDefinition)
      Init = llvm::ConstantArray::get(ArrayType, &b.getVtableComponents()[0], 
                                      b.getVtableComponents().size());

    llvm::GlobalVariable *OGV = GV;
    
    GV = new llvm::GlobalVariable(CGM.getModule(), ArrayType, 
                                  /*isConstant=*/true, Linkage, Init, Name);
    CGM.setGlobalVisibility(GV, RD);
  
    if (OGV) {
      GV->takeName(OGV);
      llvm::Constant *NewPtr = 
        llvm::ConstantExpr::getBitCast(GV, OGV->getType());
      OGV->replaceAllUsesWith(NewPtr);
      OGV->eraseFromParent();
    }
  }
  
  return GV;
}

namespace {
class VTTBuilder {
  /// Inits - The list of values built for the VTT.
  std::vector<llvm::Constant *> &Inits;
  /// Class - The most derived class that this vtable is being built for.
  const CXXRecordDecl *Class;
  CodeGenModule &CGM;  // Per-module state.
  llvm::SmallSet<const CXXRecordDecl *, 32> SeenVBase;
  /// BLayout - Layout for the most derived class that this vtable is being
  /// built for.
  const ASTRecordLayout &BLayout;
  CodeGenModule::AddrMap_t &AddressPoints;
  // vtbl - A pointer to the vtable for Class.
  llvm::Constant *ClassVtbl;
  llvm::LLVMContext &VMContext;

  /// BuildVtablePtr - Build up a referene to the given secondary vtable
  llvm::Constant *BuildVtablePtr(llvm::Constant *Vtable,
                                 const CXXRecordDecl *VtableClass,
                                 const CXXRecordDecl *RD,
                                 uint64_t Offset) {
    int64_t AddressPoint = 
      (*AddressPoints[VtableClass])[std::make_pair(RD, Offset)];
    
    // FIXME: We can never have 0 address point.  Do this for now so gepping
    // retains the same structure.  Later we'll just assert.
    if (AddressPoint == 0)
      AddressPoint = 1;
    D1(printf("XXX address point for %s in %s layout %s at offset %d was %d\n",
              RD->getNameAsCString(), VtblClass->getNameAsCString(),
              Class->getNameAsCString(), (int)Offset, (int)AddressPoint));

    llvm::Value *Idxs[] = {
      llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext), 0),
      llvm::ConstantInt::get(llvm::Type::getInt64Ty(VMContext), AddressPoint)
    };
    
    llvm::Constant *Init = 
      llvm::ConstantExpr::getInBoundsGetElementPtr(Vtable, Idxs, 2);

    const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(VMContext);
    return llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
  }

  /// Secondary - Add the secondary vtable pointers to Inits.  Offset is the
  /// current offset in bits to the object we're working on.
  void Secondary(const CXXRecordDecl *RD, llvm::Constant *vtbl,
                 const CXXRecordDecl *VtblClass, uint64_t Offset=0,
                 bool MorallyVirtual=false) {
    if (RD->getNumVBases() == 0 && ! MorallyVirtual)
      return;

    for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
           e = RD->bases_end(); i != e; ++i) {
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
      const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
      const bool PrimaryBaseWasVirtual = Layout.getPrimaryBaseWasVirtual();
      bool NonVirtualPrimaryBase;
      NonVirtualPrimaryBase = !PrimaryBaseWasVirtual && Base == PrimaryBase;
      bool BaseMorallyVirtual = MorallyVirtual | i->isVirtual();
      uint64_t BaseOffset;
      if (!i->isVirtual()) {
        const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
        BaseOffset = Offset + Layout.getBaseClassOffset(Base);
      } else
        BaseOffset = BLayout.getVBaseClassOffset(Base);
      llvm::Constant *subvtbl = vtbl;
      const CXXRecordDecl *subVtblClass = VtblClass;
      if ((Base->getNumVBases() || BaseMorallyVirtual)
          && !NonVirtualPrimaryBase) {
        // FIXME: Slightly too many of these for __ZTT8test8_B2
        llvm::Constant *init;
        if (BaseMorallyVirtual)
          init = BuildVtablePtr(vtbl, VtblClass, RD, Offset);
        else {
          init = CGM.getVtableInfo().getCtorVtable(Class, Base, BaseOffset);
          
          subvtbl = init;
          subVtblClass = Base;
          
          init = BuildVtablePtr(init, Class, Base, BaseOffset);
        }
        Inits.push_back(init);
      }
      Secondary(Base, subvtbl, subVtblClass, BaseOffset, BaseMorallyVirtual);
    }
  }

  /// BuiltVTT - Add the VTT to Inits.  Offset is the offset in bits to the
  /// currnet object we're working on.
  void BuildVTT(const CXXRecordDecl *RD, uint64_t Offset, bool MorallyVirtual) {
    if (RD->getNumVBases() == 0 && !MorallyVirtual)
      return;

    llvm::Constant *Vtable;
    const CXXRecordDecl *VtableClass;

    // First comes the primary virtual table pointer...
    if (MorallyVirtual) {
      Vtable = ClassVtbl;
      VtableClass = Class;
    } else {
      Vtable = CGM.getVtableInfo().getCtorVtable(Class, RD, Offset);
      VtableClass = RD;
    }
    
    llvm::Constant *Init = BuildVtablePtr(Vtable, VtableClass, RD, Offset);
    Inits.push_back(Init);

    // then the secondary VTTs....
    SecondaryVTTs(RD, Offset, MorallyVirtual);

    // and last the secondary vtable pointers.
    Secondary(RD, Vtable, VtableClass, Offset, MorallyVirtual);
  }

  /// SecondaryVTTs - Add the secondary VTTs to Inits.  The secondary VTTs are
  /// built from each direct non-virtual proper base that requires a VTT in
  /// declaration order.
  void SecondaryVTTs(const CXXRecordDecl *RD, uint64_t Offset=0,
                     bool MorallyVirtual=false) {
    for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
           e = RD->bases_end(); i != e; ++i) {
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      if (i->isVirtual())
        continue;
      const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
      uint64_t BaseOffset = Offset + Layout.getBaseClassOffset(Base);
      BuildVTT(Base, BaseOffset, MorallyVirtual);
    }
  }

  /// VirtualVTTs - Add the VTT for each proper virtual base in inheritance
  /// graph preorder.
  void VirtualVTTs(const CXXRecordDecl *RD) {
    for (CXXRecordDecl::base_class_const_iterator i = RD->bases_begin(),
           e = RD->bases_end(); i != e; ++i) {
      const CXXRecordDecl *Base =
        cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
      if (i->isVirtual() && !SeenVBase.count(Base)) {
        SeenVBase.insert(Base);
        uint64_t BaseOffset = BLayout.getVBaseClassOffset(Base);
        BuildVTT(Base, BaseOffset, true);
      }
      VirtualVTTs(Base);
    }
  }

public:
  VTTBuilder(std::vector<llvm::Constant *> &inits, const CXXRecordDecl *c,
             CodeGenModule &cgm)
    : Inits(inits), Class(c), CGM(cgm),
      BLayout(cgm.getContext().getASTRecordLayout(c)),
      AddressPoints(*cgm.AddressPoints[c]),
      VMContext(cgm.getModule().getContext()) {
    
    // First comes the primary virtual table pointer for the complete class...
    ClassVtbl = CGM.getVtableInfo().getVtable(Class);
    Inits.push_back(BuildVtablePtr(ClassVtbl, Class, Class, 0));
    
    // then the secondary VTTs...
    SecondaryVTTs(Class);

    // then the secondary vtable pointers...
    Secondary(Class, ClassVtbl, Class);

    // and last, the virtual VTTs.
    VirtualVTTs(Class);
  }
};
}

llvm::GlobalVariable *
CGVtableInfo::GenerateVTT(llvm::GlobalVariable::LinkageTypes Linkage,
                          const CXXRecordDecl *RD) {
  // Only classes that have virtual bases need a VTT.
  if (RD->getNumVBases() == 0)
    return 0;

  llvm::SmallString<256> OutName;
  CGM.getMangleContext().mangleCXXVTT(RD, OutName);
  llvm::StringRef Name = OutName.str();


  D1(printf("vtt %s\n", RD->getNameAsCString()));

  std::vector<llvm::Constant *> inits;
  VTTBuilder b(inits, RD, CGM);

  const llvm::Type *Int8PtrTy = llvm::Type::getInt8PtrTy(CGM.getLLVMContext());
  const llvm::ArrayType *Type = llvm::ArrayType::get(Int8PtrTy, inits.size());
  
  llvm::Constant *Init = llvm::ConstantArray::get(Type, inits);
  
  llvm::GlobalVariable *VTT = 
    new llvm::GlobalVariable(CGM.getModule(), Type, /*isConstant=*/true, 
                             Linkage, Init, Name);
  CGM.setGlobalVisibility(VTT, RD);
  
  return VTT;
}

void CGVtableInfo::GenerateClassData(llvm::GlobalVariable::LinkageTypes Linkage,
                                     const CXXRecordDecl *RD) {
  assert(!Vtables.count(RD) && "Vtable has already been generated!");
  Vtables[RD] = GenerateVtable(Linkage, /*GenerateDefinition=*/true, RD, RD, 0);
  
  CGM.GenerateRTTI(RD);
  GenerateVTT(Linkage, RD);  
}

llvm::GlobalVariable *CGVtableInfo::getVtable(const CXXRecordDecl *RD) {
  llvm::GlobalVariable *Vtable = Vtables.lookup(RD);
  
  if (!Vtable)
    Vtable = GenerateVtable(llvm::GlobalValue::ExternalLinkage, 
                            /*GenerateDefinition=*/false, RD, RD, 0);

  return Vtable;
}

llvm::GlobalVariable *
CGVtableInfo::getCtorVtable(const CXXRecordDecl *LayoutClass,
                            const CXXRecordDecl *RD, uint64_t Offset) {
  return GenerateVtable(llvm::GlobalValue::InternalLinkage, 
                        /*GenerateDefinition=*/true,
                        LayoutClass, RD, Offset);
}

void CGVtableInfo::MaybeEmitVtable(GlobalDecl GD) {
  const CXXMethodDecl *MD = cast<CXXMethodDecl>(GD.getDecl());
  const CXXRecordDecl *RD = MD->getParent();

  // If the class doesn't have a vtable we don't need to emit one.
  if (!RD->isDynamicClass())
    return;
  
  const ASTRecordLayout &Layout = CGM.getContext().getASTRecordLayout(RD);
  
  // Get the key function.
  const CXXMethodDecl *KeyFunction = Layout.getKeyFunction();
  
  if (KeyFunction) {
    // We don't have the right key function.
    if (KeyFunction->getCanonicalDecl() != MD->getCanonicalDecl())
      return;
    
    // If the key function is a destructor, we only want to emit the vtable 
    // once, so do it for the complete destructor.
    if (isa<CXXDestructorDecl>(MD) && GD.getDtorType() != Dtor_Complete)
      return;
  } else {
    // If there is no key function, we only want to emit the vtable if we are
    // emitting a constructor.
    if (!isa<CXXConstructorDecl>(MD) || GD.getCtorType() != Ctor_Complete)
      return;
  }

  llvm::GlobalVariable::LinkageTypes Linkage;
  if (RD->isInAnonymousNamespace())
    Linkage = llvm::GlobalVariable::InternalLinkage;
  else if (KeyFunction)
    Linkage = llvm::GlobalVariable::ExternalLinkage;
  else
    Linkage = llvm::GlobalVariable::WeakODRLinkage;
  
  // Emit the data.
  GenerateClassData(Linkage, RD);

  for (CXXRecordDecl::method_iterator i = RD->method_begin(),
       e = RD->method_end(); i != e; ++i) {
    if ((*i)->isVirtual() && (*i)->hasInlineBody()) {
      if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(*i)) {
        CGM.BuildThunksForVirtual(GlobalDecl(DD, Dtor_Complete));
        CGM.BuildThunksForVirtual(GlobalDecl(DD, Dtor_Deleting));
      } else {
        CGM.BuildThunksForVirtual(GlobalDecl(*i));
      }
    }
  }
}