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      1 //===--- CGVTT.cpp - Emit LLVM Code for C++ VTTs --------------------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This contains code dealing with C++ code generation of VTTs (vtable tables).
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "CodeGenModule.h"
     15 #include "CGCXXABI.h"
     16 #include "clang/AST/RecordLayout.h"
     17 #include "clang/AST/VTTBuilder.h"
     18 using namespace clang;
     19 using namespace CodeGen;
     20 
     21 static llvm::GlobalVariable *
     22 GetAddrOfVTTVTable(CodeGenVTables &CGVT, CodeGenModule &CGM,
     23                    const CXXRecordDecl *MostDerivedClass,
     24                    const VTTVTable &VTable,
     25                    llvm::GlobalVariable::LinkageTypes Linkage,
     26                    llvm::DenseMap<BaseSubobject, uint64_t> &AddressPoints) {
     27   if (VTable.getBase() == MostDerivedClass) {
     28     assert(VTable.getBaseOffset().isZero() &&
     29            "Most derived class vtable must have a zero offset!");
     30     // This is a regular vtable.
     31     return CGM.getCXXABI().getAddrOfVTable(MostDerivedClass, CharUnits());
     32   }
     33 
     34   return CGVT.GenerateConstructionVTable(MostDerivedClass,
     35                                          VTable.getBaseSubobject(),
     36                                          VTable.isVirtual(),
     37                                          Linkage,
     38                                          AddressPoints);
     39 }
     40 
     41 void
     42 CodeGenVTables::EmitVTTDefinition(llvm::GlobalVariable *VTT,
     43                                   llvm::GlobalVariable::LinkageTypes Linkage,
     44                                   const CXXRecordDecl *RD) {
     45   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/true);
     46 
     47   llvm::Type *Int8PtrTy = CGM.Int8PtrTy, *Int64Ty = CGM.Int64Ty;
     48   llvm::ArrayType *ArrayType =
     49     llvm::ArrayType::get(Int8PtrTy, Builder.getVTTComponents().size());
     50 
     51   SmallVector<llvm::GlobalVariable *, 8> VTables;
     52   SmallVector<VTableAddressPointsMapTy, 8> VTableAddressPoints;
     53   for (const VTTVTable *i = Builder.getVTTVTables().begin(),
     54                        *e = Builder.getVTTVTables().end(); i != e; ++i) {
     55     VTableAddressPoints.push_back(VTableAddressPointsMapTy());
     56     VTables.push_back(GetAddrOfVTTVTable(*this, CGM, RD, *i, Linkage,
     57                                          VTableAddressPoints.back()));
     58   }
     59 
     60   SmallVector<llvm::Constant *, 8> VTTComponents;
     61   for (const VTTComponent *i = Builder.getVTTComponents().begin(),
     62                           *e = Builder.getVTTComponents().end(); i != e; ++i) {
     63     const VTTVTable &VTTVT = Builder.getVTTVTables()[i->VTableIndex];
     64     llvm::GlobalVariable *VTable = VTables[i->VTableIndex];
     65     uint64_t AddressPoint;
     66     if (VTTVT.getBase() == RD) {
     67       // Just get the address point for the regular vtable.
     68       AddressPoint =
     69           getItaniumVTableContext().getVTableLayout(RD).getAddressPoint(
     70               i->VTableBase);
     71       assert(AddressPoint != 0 && "Did not find vtable address point!");
     72     } else {
     73       AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(i->VTableBase);
     74       assert(AddressPoint != 0 && "Did not find ctor vtable address point!");
     75     }
     76 
     77      llvm::Value *Idxs[] = {
     78        llvm::ConstantInt::get(Int64Ty, 0),
     79        llvm::ConstantInt::get(Int64Ty, AddressPoint)
     80      };
     81 
     82      llvm::Constant *Init = llvm::ConstantExpr::getInBoundsGetElementPtr(
     83          VTable->getValueType(), VTable, Idxs);
     84 
     85      Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
     86 
     87      VTTComponents.push_back(Init);
     88   }
     89 
     90   llvm::Constant *Init = llvm::ConstantArray::get(ArrayType, VTTComponents);
     91 
     92   VTT->setInitializer(Init);
     93 
     94   // Set the correct linkage.
     95   VTT->setLinkage(Linkage);
     96 
     97   if (CGM.supportsCOMDAT() && VTT->isWeakForLinker())
     98     VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName()));
     99 
    100   // Set the right visibility.
    101   CGM.setGlobalVisibility(VTT, RD);
    102 }
    103 
    104 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
    105   assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
    106 
    107   SmallString<256> OutName;
    108   llvm::raw_svector_ostream Out(OutName);
    109   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
    110       .mangleCXXVTT(RD, Out);
    111   StringRef Name = OutName.str();
    112 
    113   // This will also defer the definition of the VTT.
    114   (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
    115 
    116   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
    117 
    118   llvm::ArrayType *ArrayType =
    119     llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size());
    120 
    121   llvm::GlobalVariable *GV =
    122     CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType,
    123                                           llvm::GlobalValue::ExternalLinkage);
    124   GV->setUnnamedAddr(true);
    125   return GV;
    126 }
    127 
    128 uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
    129                                         BaseSubobject Base) {
    130   BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
    131 
    132   SubVTTIndiciesMapTy::iterator I = SubVTTIndicies.find(ClassSubobjectPair);
    133   if (I != SubVTTIndicies.end())
    134     return I->second;
    135 
    136   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
    137 
    138   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
    139        Builder.getSubVTTIndicies().begin(),
    140        E = Builder.getSubVTTIndicies().end(); I != E; ++I) {
    141     // Insert all indices.
    142     BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
    143 
    144     SubVTTIndicies.insert(std::make_pair(ClassSubobjectPair, I->second));
    145   }
    146 
    147   I = SubVTTIndicies.find(ClassSubobjectPair);
    148   assert(I != SubVTTIndicies.end() && "Did not find index!");
    149 
    150   return I->second;
    151 }
    152 
    153 uint64_t
    154 CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
    155                                                 BaseSubobject Base) {
    156   SecondaryVirtualPointerIndicesMapTy::iterator I =
    157     SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
    158 
    159   if (I != SecondaryVirtualPointerIndices.end())
    160     return I->second;
    161 
    162   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
    163 
    164   // Insert all secondary vpointer indices.
    165   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
    166        Builder.getSecondaryVirtualPointerIndices().begin(),
    167        E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
    168     std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
    169       std::make_pair(RD, I->first);
    170 
    171     SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second));
    172   }
    173 
    174   I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
    175   assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
    176 
    177   return I->second;
    178 }
    179