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 } 177