1 //===--- CGVTT.cpp - Emit LLVM Code for C++ VTTs --------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This contains code dealing with C++ code generation of VTTs (vtable tables).
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "CodeGenModule.h"
15 #include "CGCXXABI.h"
16 #include "clang/AST/RecordLayout.h"
17 #include "clang/AST/VTTBuilder.h"
18 using namespace clang;
19 using namespace CodeGen;
20 
21 static llvm::GlobalVariable *
22 GetAddrOfVTTVTable(CodeGenVTables &CGVT, CodeGenModule &CGM,
23                    const CXXRecordDecl *MostDerivedClass,
24                    const VTTVTable &VTable,
25                    llvm::GlobalVariable::LinkageTypes Linkage,
26                    VTableLayout::AddressPointsMapTy &AddressPoints) {
27   if (VTable.getBase() == MostDerivedClass) {
28     assert(VTable.getBaseOffset().isZero() &&
29            "Most derived class vtable must have a zero offset!");
30     // This is a regular vtable.
31     return CGM.getCXXABI().getAddrOfVTable(MostDerivedClass, CharUnits());
32   }
33 
34   return CGVT.GenerateConstructionVTable(MostDerivedClass,
35                                          VTable.getBaseSubobject(),
36                                          VTable.isVirtual(),
37                                          Linkage,
38                                          AddressPoints);
39 }
40 
41 void
42 CodeGenVTables::EmitVTTDefinition(llvm::GlobalVariable *VTT,
43                                   llvm::GlobalVariable::LinkageTypes Linkage,
44                                   const CXXRecordDecl *RD) {
45   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/true);
46 
47   llvm::Type *Int8PtrTy = CGM.Int8PtrTy, *Int32Ty = CGM.Int32Ty;
48   llvm::ArrayType *ArrayType =
49     llvm::ArrayType::get(Int8PtrTy, Builder.getVTTComponents().size());
50 
51   SmallVector<llvm::GlobalVariable *, 8> VTables;
52   SmallVector<VTableAddressPointsMapTy, 8> VTableAddressPoints;
53   for (const VTTVTable *i = Builder.getVTTVTables().begin(),
54                        *e = Builder.getVTTVTables().end(); i != e; ++i) {
55     VTableAddressPoints.push_back(VTableAddressPointsMapTy());
56     VTables.push_back(GetAddrOfVTTVTable(*this, CGM, RD, *i, Linkage,
57                                          VTableAddressPoints.back()));
58   }
59 
60   SmallVector<llvm::Constant *, 8> VTTComponents;
61   for (const VTTComponent *i = Builder.getVTTComponents().begin(),
62                           *e = Builder.getVTTComponents().end(); i != e; ++i) {
63     const VTTVTable &VTTVT = Builder.getVTTVTables()[i->VTableIndex];
64     llvm::GlobalVariable *VTable = VTables[i->VTableIndex];
65     VTableLayout::AddressPointLocation AddressPoint;
66     if (VTTVT.getBase() == RD) {
67       // Just get the address point for the regular vtable.
68       AddressPoint =
69           getItaniumVTableContext().getVTableLayout(RD).getAddressPoint(
70               i->VTableBase);
71     } else {
72       AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(i->VTableBase);
73       assert(AddressPoint.AddressPointIndex != 0 &&
74              "Did not find ctor vtable address point!");
75     }
76 
77      llvm::Value *Idxs[] = {
78        llvm::ConstantInt::get(Int32Ty, 0),
79        llvm::ConstantInt::get(Int32Ty, AddressPoint.VTableIndex),
80        llvm::ConstantInt::get(Int32Ty, AddressPoint.AddressPointIndex),
81      };
82 
83      llvm::Constant *Init = llvm::ConstantExpr::getGetElementPtr(
84          VTable->getValueType(), VTable, Idxs, /*InBounds=*/true,
85          /*InRangeIndex=*/1);
86 
87      Init = llvm::ConstantExpr::getBitCast(Init, Int8PtrTy);
88 
89      VTTComponents.push_back(Init);
90   }
91 
92   llvm::Constant *Init = llvm::ConstantArray::get(ArrayType, VTTComponents);
93 
94   VTT->setInitializer(Init);
95 
96   // Set the correct linkage.
97   VTT->setLinkage(Linkage);
98 
99   if (CGM.supportsCOMDAT() && VTT->isWeakForLinker())
100     VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName()));
101 
102   // Set the right visibility.
103   CGM.setGlobalVisibility(VTT, RD);
104 }
105 
106 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
107   assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
108 
109   SmallString<256> OutName;
110   llvm::raw_svector_ostream Out(OutName);
111   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
112       .mangleCXXVTT(RD, Out);
113   StringRef Name = OutName.str();
114 
115   // This will also defer the definition of the VTT.
116   (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
117 
118   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
119 
120   llvm::ArrayType *ArrayType =
121     llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size());
122 
123   llvm::GlobalVariable *GV =
124     CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType,
125                                           llvm::GlobalValue::ExternalLinkage);
126   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
127   return GV;
128 }
129 
130 uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
131                                         BaseSubobject Base) {
132   BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
133 
134   SubVTTIndiciesMapTy::iterator I = SubVTTIndicies.find(ClassSubobjectPair);
135   if (I != SubVTTIndicies.end())
136     return I->second;
137 
138   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
139 
140   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
141        Builder.getSubVTTIndicies().begin(),
142        E = Builder.getSubVTTIndicies().end(); I != E; ++I) {
143     // Insert all indices.
144     BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
145 
146     SubVTTIndicies.insert(std::make_pair(ClassSubobjectPair, I->second));
147   }
148 
149   I = SubVTTIndicies.find(ClassSubobjectPair);
150   assert(I != SubVTTIndicies.end() && "Did not find index!");
151 
152   return I->second;
153 }
154 
155 uint64_t
156 CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
157                                                 BaseSubobject Base) {
158   SecondaryVirtualPointerIndicesMapTy::iterator I =
159     SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
160 
161   if (I != SecondaryVirtualPointerIndices.end())
162     return I->second;
163 
164   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
165 
166   // Insert all secondary vpointer indices.
167   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
168        Builder.getSecondaryVirtualPointerIndices().begin(),
169        E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
170     std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
171       std::make_pair(RD, I->first);
172 
173     SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second));
174   }
175 
176   I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
177   assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
178 
179   return I->second;
180 }
181