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 46 llvm::Type *Int8PtrTy = CGM.Int8PtrTy, *Int32Ty = CGM.Int32Ty; 47 llvm::ArrayType *ArrayType = 48 llvm::ArrayType::get(Int8PtrTy, Builder.getVTTComponents().size()); 49 50 SmallVector<llvm::GlobalVariable *, 8> VTables; 51 SmallVector<VTableAddressPointsMapTy, 8> VTableAddressPoints; 52 for (const VTTVTable *i = Builder.getVTTVTables().begin(), 53 *e = Builder.getVTTVTables().end(); i != e; ++i) { 54 VTableAddressPoints.push_back(VTableAddressPointsMapTy()); 55 VTables.push_back(GetAddrOfVTTVTable(*this, CGM, RD, *i, Linkage, 56 VTableAddressPoints.back())); 57 } 58 59 SmallVector<llvm::Constant *, 8> VTTComponents; 60 for (const VTTComponent *i = Builder.getVTTComponents().begin(), 61 *e = Builder.getVTTComponents().end(); i != e; ++i) { 62 const VTTVTable &VTTVT = Builder.getVTTVTables()[i->VTableIndex]; 63 llvm::GlobalVariable *VTable = VTables[i->VTableIndex]; 64 VTableLayout::AddressPointLocation AddressPoint; 65 if (VTTVT.getBase() == RD) { 66 // Just get the address point for the regular vtable. 67 AddressPoint = 68 getItaniumVTableContext().getVTableLayout(RD).getAddressPoint( 69 i->VTableBase); 70 } else { 71 AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(i->VTableBase); 72 assert(AddressPoint.AddressPointIndex != 0 && 73 "Did not find ctor vtable address point!"); 74 } 75 76 llvm::Value *Idxs[] = { 77 llvm::ConstantInt::get(Int32Ty, 0), 78 llvm::ConstantInt::get(Int32Ty, AddressPoint.VTableIndex), 79 llvm::ConstantInt::get(Int32Ty, AddressPoint.AddressPointIndex), 80 }; 81 82 llvm::Constant *Init = llvm::ConstantExpr::getGetElementPtr( 83 VTable->getValueType(), VTable, Idxs, /*InBounds=*/true, 84 /*InRangeIndex=*/1); 85 86 Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy); 87 88 VTTComponents.push_back(Init); 89 } 90 91 llvm::Constant *Init = llvm::ConstantArray::get(ArrayType, VTTComponents); 92 93 VTT->setInitializer(Init); 94 95 // Set the correct linkage. 96 VTT->setLinkage(Linkage); 97 98 if (CGM.supportsCOMDAT() && VTT->isWeakForLinker()) 99 VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName())); 100 101 // Set the right visibility. 102 CGM.setGVProperties(VTT, RD); 103 } 104 105 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) { 106 assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT"); 107 108 SmallString<256> OutName; 109 llvm::raw_svector_ostream Out(OutName); 110 cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext()) 111 .mangleCXXVTT(RD, Out); 112 StringRef Name = OutName.str(); 113 114 // This will also defer the definition of the VTT. 115 (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); 116 117 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false); 118 119 llvm::ArrayType *ArrayType = 120 llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size()); 121 unsigned Align = CGM.getDataLayout().getABITypeAlignment(CGM.Int8PtrTy); 122 123 llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable( 124 Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align); 125 GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global); 126 return GV; 127 } 128 129 uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD, 130 BaseSubobject Base) { 131 BaseSubobjectPairTy ClassSubobjectPair(RD, Base); 132 133 SubVTTIndiciesMapTy::iterator I = SubVTTIndicies.find(ClassSubobjectPair); 134 if (I != SubVTTIndicies.end()) 135 return I->second; 136 137 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false); 138 139 for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I = 140 Builder.getSubVTTIndicies().begin(), 141 E = Builder.getSubVTTIndicies().end(); I != E; ++I) { 142 // Insert all indices. 143 BaseSubobjectPairTy ClassSubobjectPair(RD, I->first); 144 145 SubVTTIndicies.insert(std::make_pair(ClassSubobjectPair, I->second)); 146 } 147 148 I = SubVTTIndicies.find(ClassSubobjectPair); 149 assert(I != SubVTTIndicies.end() && "Did not find index!"); 150 151 return I->second; 152 } 153 154 uint64_t 155 CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD, 156 BaseSubobject Base) { 157 SecondaryVirtualPointerIndicesMapTy::iterator I = 158 SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base)); 159 160 if (I != SecondaryVirtualPointerIndices.end()) 161 return I->second; 162 163 VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false); 164 165 // Insert all secondary vpointer indices. 166 for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I = 167 Builder.getSecondaryVirtualPointerIndices().begin(), 168 E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) { 169 std::pair<const CXXRecordDecl *, BaseSubobject> Pair = 170 std::make_pair(RD, I->first); 171 172 SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second)); 173 } 174 175 I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base)); 176 assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!"); 177 178 return I->second; 179 } 180