path: root/lib/CodeGen/CGVTT.cpp

//===--- CGVTT.cpp - Emit LLVM Code for C++ VTTs --------------------------===//
//
//                     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 VTTs (vtable tables).
//
//===----------------------------------------------------------------------===//

#include "CodeGenModule.h"
#include "clang/AST/RecordLayout.h"
using namespace clang;
using namespace CodeGen;

#define D1(x)

namespace {

/// VTT builder - Class for building VTT layout information.
class VTTBuilder {
  /// MostDerivedClass - The most derived class for which we're building this
  /// vtable.
  const CXXRecordDecl *MostDerivedClass;

  /// Inits - The list of values built for the VTT.
  std::vector<llvm::Constant *> &Inits;
  
  /// MostDerivedClassLayout - the AST record layout of the most derived class.
  const ASTRecordLayout &MostDerivedClassLayout;

  CodeGenModule &CGM;  // Per-module state.

  CodeGenVTables::AddrMap_t &AddressPoints;
  // vtbl - A pointer to the vtable for Class.
  llvm::Constant *ClassVtbl;
  llvm::LLVMContext &VMContext;

  typedef llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBasesSetTy;

  typedef llvm::DenseMap<BaseSubobject, uint64_t> AddressPointsMapTy;

  /// SeenVBasesInSecondary - The seen virtual bases when building the 
  /// secondary virtual pointers.
  llvm::SmallPtrSet<const CXXRecordDecl *, 32> SeenVBasesInSecondary;

  llvm::DenseMap<const CXXRecordDecl *, uint64_t> SubVTTIndicies;
  
  bool GenerateDefinition;

  llvm::DenseMap<BaseSubobject, llvm::Constant *> CtorVtables;
  llvm::DenseMap<std::pair<const CXXRecordDecl *, BaseSubobject>, uint64_t> 
    CtorVtableAddressPoints;
  
  llvm::Constant *getCtorVtable(const BaseSubobject &Base,
                                bool BaseIsVirtual) {
    if (!GenerateDefinition)
      return 0;

    llvm::Constant *&CtorVtable = CtorVtables[Base];
    return CtorVtable;
  }
  
  
  /// 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) {
    if (!GenerateDefinition)
      return 0;

    uint64_t AddressPoint;
    
    if (VtableClass != MostDerivedClass) {
      // We have a ctor vtable, look for the address point in the ctor vtable
      // address points.
      AddressPoint = 
        CtorVtableAddressPoints[std::make_pair(VtableClass, 
                                               BaseSubobject(RD, Offset))];
    } else { 
      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,
                 bool MorallyVirtual) {
    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());

      // We only want to visit each virtual base once.
      if (i->isVirtual() && SeenVBasesInSecondary.count(Base))
        continue;
      
      // Itanium C++ ABI 2.6.2:
      //   Secondary virtual pointers are present for all bases with either
      //   virtual bases or virtual function declarations overridden along a 
      //   virtual path.
      //
      // If the base class is not dynamic, we don't want to add it, nor any
      // of its base classes.
      if (!Base->isDynamicClass())
        continue;

      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 = MostDerivedClassLayout.getVBaseClassOffset(Base);
      llvm::Constant *subvtbl = vtbl;
      const CXXRecordDecl *subVtblClass = VtblClass;
      if ((Base->getNumVBases() || BaseMorallyVirtual)
          && !NonVirtualPrimaryBase) {
        llvm::Constant *init;
        if (BaseMorallyVirtual || VtblClass == MostDerivedClass)
          init = BuildVtablePtr(vtbl, VtblClass, Base, BaseOffset);
        else {
          init = getCtorVtable(BaseSubobject(Base, BaseOffset), i->isVirtual());
          
          subvtbl = init;
          subVtblClass = Base;
          
          init = BuildVtablePtr(init, MostDerivedClass, Base, BaseOffset);
        }

        Inits.push_back(init);
      }
      
      if (i->isVirtual())
        SeenVBasesInSecondary.insert(Base);
      
      Secondary(Base, subvtbl, subVtblClass, BaseOffset, BaseMorallyVirtual);
    }
  }

  /// GetAddrOfVTable - Returns the address of the vtable for the base class in
  /// the given vtable class.
  ///
  /// \param AddressPoints - If the returned vtable is a construction vtable,
  /// this will hold the address points for it.
  llvm::Constant *GetAddrOfVTable(BaseSubobject Base, bool BaseIsVirtual,
                                  AddressPointsMapTy& AddressPoints);

  /// AddVTablePointer - Add a vtable pointer to the VTT currently being built.
  ///
  /// \param AddressPoints - If the vtable is a construction vtable, this has
  /// the address points for it.
  void AddVTablePointer(BaseSubobject Base, llvm::Constant *VTable,
                        const CXXRecordDecl *VTableClass,
                        const AddressPointsMapTy& AddressPoints);
                        
  /// LayoutSecondaryVTTs - Lay out the secondary VTTs of the given base 
  /// subobject.
  void LayoutSecondaryVTTs(BaseSubobject Base);
  
  /// LayoutSecondaryVirtualPointers - Lay out the secondary virtual pointers
  /// for the given base subobject.
  ///
  /// \param BaseIsMorallyVirtual whether the base subobject is a virtual base
  /// or a direct or indirect base of a virtual base.
  ///
  /// \param AddressPoints - If the vtable is a construction vtable, this has
  /// the address points for it.
  void LayoutSecondaryVirtualPointers(BaseSubobject Base, 
                                      bool BaseIsMorallyVirtual,
                                      llvm::Constant *VTable,
                                      const CXXRecordDecl *VTableClass,
                                      const AddressPointsMapTy& AddressPoints,
                                      VisitedVirtualBasesSetTy &VBases);
  
  /// LayoutSecondaryVirtualPointers - Lay out the secondary virtual pointers
  /// for the given base subobject.