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   // Set the right visibility.
101   CGM.setGVProperties(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   unsigned Align = CGM.getDataLayout().getABITypeAlignment(CGM.Int8PtrTy);
121 
122   llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
123       Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
124   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
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