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 = llvm::ArrayType::get(
46       CGM.GlobalsInt8PtrTy, 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      VTTComponents.push_back(Init);
85   }
86 
87   llvm::Constant *Init = llvm::ConstantArray::get(ArrayType, VTTComponents);
88 
89   VTT->setInitializer(Init);
90 
91   // Set the correct linkage.
92   VTT->setLinkage(Linkage);
93 
94   if (CGM.supportsCOMDAT() && VTT->isWeakForLinker())
95     VTT->setComdat(CGM.getModule().getOrInsertComdat(VTT->getName()));
96 }
97 
98 llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
99   assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
100 
101   SmallString<256> OutName;
102   llvm::raw_svector_ostream Out(OutName);
103   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
104       .mangleCXXVTT(RD, Out);
105   StringRef Name = OutName.str();
106 
107   // This will also defer the definition of the VTT.
108   (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
109 
110   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
111 
112   llvm::ArrayType *ArrayType = llvm::ArrayType::get(
113       CGM.GlobalsInt8PtrTy, Builder.getVTTComponents().size());
114   llvm::Align Align = CGM.getDataLayout().getABITypeAlign(CGM.GlobalsInt8PtrTy);
115 
116   llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
117       Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
118   GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
119   CGM.setGVProperties(GV, RD);
120   return GV;
121 }
122 
123 uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
124                                         BaseSubobject Base) {
125   BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
126 
127   SubVTTIndiciesMapTy::iterator I = SubVTTIndicies.find(ClassSubobjectPair);
128   if (I != SubVTTIndicies.end())
129     return I->second;
130 
131   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
132 
133   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
134        Builder.getSubVTTIndicies().begin(),
135        E = Builder.getSubVTTIndicies().end(); I != E; ++I) {
136     // Insert all indices.
137     BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
138 
139     SubVTTIndicies.insert(std::make_pair(ClassSubobjectPair, I->second));
140   }
141 
142   I = SubVTTIndicies.find(ClassSubobjectPair);
143   assert(I != SubVTTIndicies.end() && "Did not find index!");
144 
145   return I->second;
146 }
147 
148 uint64_t
149 CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
150                                                 BaseSubobject Base) {
151   SecondaryVirtualPointerIndicesMapTy::iterator I =
152     SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
153 
154   if (I != SecondaryVirtualPointerIndices.end())
155     return I->second;
156 
157   VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
158 
159   // Insert all secondary vpointer indices.
160   for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
161        Builder.getSecondaryVirtualPointerIndices().begin(),
162        E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
163     std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
164       std::make_pair(RD, I->first);
165 
166     SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second));
167   }
168 
169   I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
170   assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
171 
172   return I->second;
173 }
174