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