1 //===- VTTBuilder.cpp - C++ VTT layout builder ----------------------------===//
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
7 //===----------------------------------------------------------------------===//
9 // This contains code dealing with generation of the layout of virtual table
12 //===----------------------------------------------------------------------===//
14 #include "clang/AST/VTTBuilder.h"
15 #include "clang/AST/ASTContext.h"
16 #include "clang/AST/BaseSubobject.h"
17 #include "clang/AST/CharUnits.h"
18 #include "clang/AST/Decl.h"
19 #include "clang/AST/DeclCXX.h"
20 #include "clang/AST/RecordLayout.h"
21 #include "clang/AST/Type.h"
22 #include "clang/Basic/LLVM.h"
23 #include "llvm/Support/Casting.h"
27 using namespace clang;
29 #define DUMP_OVERRIDERS 0
31 VTTBuilder::VTTBuilder(ASTContext &Ctx,
32 const CXXRecordDecl *MostDerivedClass,
33 bool GenerateDefinition)
34 : Ctx(Ctx), MostDerivedClass(MostDerivedClass),
35 MostDerivedClassLayout(Ctx.getASTRecordLayout(MostDerivedClass)),
36 GenerateDefinition(GenerateDefinition) {
38 LayoutVTT(BaseSubobject(MostDerivedClass, CharUnits::Zero()),
39 /*BaseIsVirtual=*/false);
42 void VTTBuilder::AddVTablePointer(BaseSubobject Base, uint64_t VTableIndex,
43 const CXXRecordDecl *VTableClass) {
44 // Store the vtable pointer index if we're generating the primary VTT.
45 if (VTableClass == MostDerivedClass) {
46 assert(!SecondaryVirtualPointerIndices.count(Base) &&
47 "A virtual pointer index already exists for this base subobject!");
48 SecondaryVirtualPointerIndices[Base] = VTTComponents.size();
51 if (!GenerateDefinition) {
52 VTTComponents.push_back(VTTComponent());
56 VTTComponents.push_back(VTTComponent(VTableIndex, Base));
59 void VTTBuilder::LayoutSecondaryVTTs(BaseSubobject Base) {
60 const CXXRecordDecl *RD = Base.getBase();
62 for (const auto &I : RD->bases()) {
63 // Don't layout virtual bases.
67 const CXXRecordDecl *BaseDecl =
68 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
70 const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
71 CharUnits BaseOffset = Base.getBaseOffset() +
72 Layout.getBaseClassOffset(BaseDecl);
74 // Layout the VTT for this base.
75 LayoutVTT(BaseSubobject(BaseDecl, BaseOffset), /*BaseIsVirtual=*/false);
80 VTTBuilder::LayoutSecondaryVirtualPointers(BaseSubobject Base,
81 bool BaseIsMorallyVirtual,
83 const CXXRecordDecl *VTableClass,
84 VisitedVirtualBasesSetTy &VBases) {
85 const CXXRecordDecl *RD = Base.getBase();
87 // We're not interested in bases that don't have virtual bases, and not
88 // morally virtual bases.
89 if (!RD->getNumVBases() && !BaseIsMorallyVirtual)
92 for (const auto &I : RD->bases()) {
93 const CXXRecordDecl *BaseDecl =
94 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
96 // Itanium C++ ABI 2.6.2:
97 // Secondary virtual pointers are present for all bases with either
98 // virtual bases or virtual function declarations overridden along a
101 // If the base class is not dynamic, we don't want to add it, nor any
102 // of its base classes.
103 if (!BaseDecl->isDynamicClass())
106 bool BaseDeclIsMorallyVirtual = BaseIsMorallyVirtual;
107 bool BaseDeclIsNonVirtualPrimaryBase = false;
108 CharUnits BaseOffset;
110 // Ignore virtual bases that we've already visited.
111 if (!VBases.insert(BaseDecl).second)
114 BaseOffset = MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
115 BaseDeclIsMorallyVirtual = true;
117 const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
119 BaseOffset = Base.getBaseOffset() +
120 Layout.getBaseClassOffset(BaseDecl);
122 if (!Layout.isPrimaryBaseVirtual() &&
123 Layout.getPrimaryBase() == BaseDecl)
124 BaseDeclIsNonVirtualPrimaryBase = true;
127 // Itanium C++ ABI 2.6.2:
128 // Secondary virtual pointers: for each base class X which (a) has virtual
129 // bases or is reachable along a virtual path from D, and (b) is not a
130 // non-virtual primary base, the address of the virtual table for X-in-D
131 // or an appropriate construction virtual table.
132 if (!BaseDeclIsNonVirtualPrimaryBase &&
133 (BaseDecl->getNumVBases() || BaseDeclIsMorallyVirtual)) {
134 // Add the vtable pointer.
135 AddVTablePointer(BaseSubobject(BaseDecl, BaseOffset), VTableIndex,
139 // And lay out the secondary virtual pointers for the base class.
140 LayoutSecondaryVirtualPointers(BaseSubobject(BaseDecl, BaseOffset),
141 BaseDeclIsMorallyVirtual, VTableIndex,
142 VTableClass, VBases);
147 VTTBuilder::LayoutSecondaryVirtualPointers(BaseSubobject Base,
148 uint64_t VTableIndex) {
149 VisitedVirtualBasesSetTy VBases;
150 LayoutSecondaryVirtualPointers(Base, /*BaseIsMorallyVirtual=*/false,
151 VTableIndex, Base.getBase(), VBases);
154 void VTTBuilder::LayoutVirtualVTTs(const CXXRecordDecl *RD,
155 VisitedVirtualBasesSetTy &VBases) {
156 for (const auto &I : RD->bases()) {
157 const CXXRecordDecl *BaseDecl =
158 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
160 // Check if this is a virtual base.
162 // Check if we've seen this base before.
163 if (!VBases.insert(BaseDecl).second)
166 CharUnits BaseOffset =
167 MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
169 LayoutVTT(BaseSubobject(BaseDecl, BaseOffset), /*BaseIsVirtual=*/true);
172 // We only need to layout virtual VTTs for this base if it actually has
174 if (BaseDecl->getNumVBases())
175 LayoutVirtualVTTs(BaseDecl, VBases);
179 void VTTBuilder::LayoutVTT(BaseSubobject Base, bool BaseIsVirtual) {
180 const CXXRecordDecl *RD = Base.getBase();
182 // Itanium C++ ABI 2.6.2:
183 // An array of virtual table addresses, called the VTT, is declared for
184 // each class type that has indirect or direct virtual base classes.
185 if (RD->getNumVBases() == 0)
188 bool IsPrimaryVTT = Base.getBase() == MostDerivedClass;
191 // Remember the sub-VTT index.
192 SubVTTIndicies[Base] = VTTComponents.size();
195 uint64_t VTableIndex = VTTVTables.size();
196 VTTVTables.push_back(VTTVTable(Base, BaseIsVirtual));
198 // Add the primary vtable pointer.
199 AddVTablePointer(Base, VTableIndex, RD);
201 // Add the secondary VTTs.
202 LayoutSecondaryVTTs(Base);
204 // Add the secondary virtual pointers.
205 LayoutSecondaryVirtualPointers(Base, VTableIndex);
207 // If this is the primary VTT, we want to lay out virtual VTTs as well.
209 VisitedVirtualBasesSetTy VBases;
210 LayoutVirtualVTTs(Base.getBase(), VBases);