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"
17using namespace clang;
18using namespace CodeGen;
19
20static llvm::GlobalVariable *
21GetAddrOfVTTVTable(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
40void
41CodeGenVTables::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
104llvm::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
128uint64_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
153uint64_t
154CodeGenVTables::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