clang/lib/CodeGen/CGVTT.cpp

   1 //===--- CGVTT.cpp - Emit LLVM Code for C++ VTTs --------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This contains code dealing with C++ code generation of VTTs (vtable tables).
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "CodeGenModule.h"
  14 #include "CGCXXABI.h"
  15 #include "clang/AST/RecordLayout.h"
  16 #include "clang/AST/VTTBuilder.h"
  17 using namespace clang;
  18 using namespace CodeGen;
  19
  20 static llvm::GlobalVariable *
  21 GetAddrOfVTTVTable(CodeGenVTables &CGVT, CodeGenModule &CGM,
  22                    const CXXRecordDecl *MostDerivedClass,
  23                    const VTTVTable &VTable,
  24                    llvm::GlobalVariable::LinkageTypes Linkage,
  25                    VTableLayout::AddressPointsMapTy &AddressPoints) {
  26   if (VTable.getBase() == MostDerivedClass) {
  27     assert(VTable.getBaseOffset().isZero() &&
  28            "Most derived class vtable must have a zero offset!");
  29     // This is a regular vtable.
  30     return CGM.getCXXABI().getAddrOfVTable(MostDerivedClass, CharUnits());
  31   }
  32
  33   return CGVT.GenerateConstructionVTable(MostDerivedClass,
  34                                          VTable.getBaseSubobject(),
  35                                          VTable.isVirtual(),
  36                                          Linkage,
  37                                          AddressPoints);
  38 }
  39
  40 void
  41 CodeGenVTables::EmitVTTDefinition(llvm::GlobalVariable *VTT,
  42                                   llvm::GlobalVariable::LinkageTypes Linkage,
  43                                   const CXXRecordDecl *RD) {
  44   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/true);
  45   llvm::ArrayType *ArrayType =
  46       llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size());
  47
  48   SmallVector<llvm::GlobalVariable *, 8> VTables;
  49   SmallVector<VTableAddressPointsMapTy, 8> VTableAddressPoints;
  50   for (const VTTVTable *i = Builder.getVTTVTables().begin(),
  51                        *e = Builder.getVTTVTables().end(); i != e; ++i) {
  52     VTableAddressPoints.push_back(VTableAddressPointsMapTy());
  53     VTables.push_back(GetAddrOfVTTVTable(*this, CGM, RD, *i, Linkage,
  54                                          VTableAddressPoints.back()));
  55   }
  56
  57   SmallVector<llvm::Constant *, 8> VTTComponents;
  58   for (const VTTComponent *i = Builder.getVTTComponents().begin(),
  59                           *e = Builder.getVTTComponents().end(); i != e; ++i) {
  60     const VTTVTable &VTTVT = Builder.getVTTVTables()[i->VTableIndex];
  61     llvm::GlobalVariable *VTable = VTables[i->VTableIndex];
  62     VTableLayout::AddressPointLocation AddressPoint;
  63     if (VTTVT.getBase() == RD) {
  64       // Just get the address point for the regular vtable.
  65       AddressPoint =
  66           getItaniumVTableContext().getVTableLayout(RD).getAddressPoint(
  67               i->VTableBase);
  68     } else {
  69       AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(i->VTableBase);
  70       assert(AddressPoint.AddressPointIndex != 0 &&
  71              "Did not find ctor vtable address point!");
  72     }
  73
  74      llvm::Value *Idxs[] = {
  75        llvm::ConstantInt::get(CGM.Int32Ty, 0),
  76        llvm::ConstantInt::get(CGM.Int32Ty, AddressPoint.VTableIndex),
  77        llvm::ConstantInt::get(CGM.Int32Ty, AddressPoint.AddressPointIndex),
  78      };
  79
  80      llvm::Constant *Init = llvm::ConstantExpr::getGetElementPtr(
  81          VTable->getValueType(), VTable, Idxs, /*InBounds=*/true,
  82          /*InRangeIndex=*/1);
  83
  84      Init = llvm::ConstantExpr::getPointerBitCastOrAddrSpaceCast(Init,
  85                                                                  CGM.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
 101 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
 102   assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
 103
 104   SmallString<256> OutName;
 105   llvm::raw_svector_ostream Out(OutName);
 106   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
 107       .mangleCXXVTT(RD, Out);
 108   StringRef Name = OutName.str();
 109
 110   // This will also defer the definition of the VTT.
 111   (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
 112
 113   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
 114
 115   llvm::ArrayType *ArrayType =
 116     llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size());
 117   unsigned Align = CGM.getDataLayout().getABITypeAlignment(CGM.Int8PtrTy);
 118
 119   llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
 120       Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
 121   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
 122   CGM.setGVProperties(GV, RD);
 123   return GV;
 124 }
 125
 126 uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
 127                                         BaseSubobject Base) {
 128   BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
 129
 130   SubVTTIndiciesMapTy::iterator I = SubVTTIndicies.find(ClassSubobjectPair);
 131   if (I != SubVTTIndicies.end())
 132     return I->second;
 133
 134   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
 135
 136   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
 137        Builder.getSubVTTIndicies().begin(),
 138        E = Builder.getSubVTTIndicies().end(); I != E; ++I) {
 139     // Insert all indices.
 140     BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
 141
 142     SubVTTIndicies.insert(std::make_pair(ClassSubobjectPair, I->second));
 143   }
 144
 145   I = SubVTTIndicies.find(ClassSubobjectPair);
 146   assert(I != SubVTTIndicies.end() && "Did not find index!");
 147
 148   return I->second;
 149 }
 150
 151 uint64_t
 152 CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
 153                                                 BaseSubobject Base) {
 154   SecondaryVirtualPointerIndicesMapTy::iterator I =
 155     SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
 156
 157   if (I != SecondaryVirtualPointerIndices.end())
 158     return I->second;
 159
 160   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
 161
 162   // Insert all secondary vpointer indices.
 163   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
 164        Builder.getSecondaryVirtualPointerIndices().begin(),
 165        E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
 166     std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
 167       std::make_pair(RD, I->first);
 168
 169     SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second));
 170   }
 171
 172   I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
 173   assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
 174
 175   return I->second;
 176 }