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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 *
GetAddrOfVTTVTable(CodeGenVTables & CGVT,CodeGenModule & CGM,const CXXRecordDecl * MostDerivedClass,const VTTVTable & VTable,llvm::GlobalVariable::LinkageTypes Linkage,llvm::DenseMap<BaseSubobject,uint64_t> & AddressPoints)22 GetAddrOfVTTVTable(CodeGenVTables &CGVT, CodeGenModule &CGM,
23                    const CXXRecordDecl *MostDerivedClass,
24                    const VTTVTable &VTable,
25                    llvm::GlobalVariable::LinkageTypes Linkage,
26                    llvm::DenseMap<BaseSubobject, uint64_t> &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
EmitVTTDefinition(llvm::GlobalVariable * VTT,llvm::GlobalVariable::LinkageTypes Linkage,const CXXRecordDecl * RD)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, *Int64Ty = CGM.Int64Ty;
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     uint64_t 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       assert(AddressPoint != 0 && "Did not find vtable address point!");
72     } else {
73       AddressPoint = VTableAddressPoints[i->VTableIndex].lookup(i->VTableBase);
74       assert(AddressPoint != 0 && "Did not find ctor vtable address point!");
75     }
76 
77      llvm::Value *Idxs[] = {
78        llvm::ConstantInt::get(Int64Ty, 0),
79        llvm::ConstantInt::get(Int64Ty, AddressPoint)
80      };
81 
82      llvm::Constant *Init = llvm::ConstantExpr::getInBoundsGetElementPtr(
83          VTable->getValueType(), VTable, Idxs);
84 
85      Init = llvm::ConstantExpr::getBitCast(Init, 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.setGlobalVisibility(VTT, RD);
102 }
103 
GetAddrOfVTT(const CXXRecordDecl * RD)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 
121   llvm::GlobalVariable *GV =
122     CGM.CreateOrReplaceCXXRuntimeVariable(Name, ArrayType,
123                                           llvm::GlobalValue::ExternalLinkage);
124   GV->setUnnamedAddr(true);
125   return GV;
126 }
127 
getSubVTTIndex(const CXXRecordDecl * RD,BaseSubobject Base)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
getSecondaryVirtualPointerIndex(const CXXRecordDecl * RD,BaseSubobject Base)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