clang 8.0.0

VTTBuilder.cpp
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1 //===- VTTBuilder.cpp - C++ VTT layout builder ----------------------------===//
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 generation of the layout of virtual table
11 // tables (VTT).
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "clang/AST/VTTBuilder.h"
16 #include "clang/AST/ASTContext.h"
17 #include "clang/AST/BaseSubobject.h"
18 #include "clang/AST/CharUnits.h"
19 #include "clang/AST/Decl.h"
20 #include "clang/AST/DeclCXX.h"
21 #include "clang/AST/RecordLayout.h"
22 #include "clang/AST/Type.h"
23 #include "clang/Basic/LLVM.h"
24 #include "llvm/Support/Casting.h"
25 #include <cassert>
26 #include <cstdint>
27
28 using namespace clang;
29
30 #define DUMP_OVERRIDERS 0
31
32 VTTBuilder::VTTBuilder(ASTContext &Ctx,
33 const CXXRecordDecl *MostDerivedClass,
34 bool GenerateDefinition)
35 : Ctx(Ctx), MostDerivedClass(MostDerivedClass),
36 MostDerivedClassLayout(Ctx.getASTRecordLayout(MostDerivedClass)),
37 GenerateDefinition(GenerateDefinition) {
38 // Lay out this VTT.
39 LayoutVTT(BaseSubobject(MostDerivedClass, CharUnits::Zero()),
40 /*BaseIsVirtual=*/false);
41 }
42
43 void VTTBuilder::AddVTablePointer(BaseSubobject Base, uint64_t VTableIndex,
44 const CXXRecordDecl *VTableClass) {
45 // Store the vtable pointer index if we're generating the primary VTT.
46 if (VTableClass == MostDerivedClass) {
47 assert(!SecondaryVirtualPointerIndices.count(Base) &&
48 "A virtual pointer index already exists for this base subobject!");
49 SecondaryVirtualPointerIndices[Base] = VTTComponents.size();
50 }
51
52 if (!GenerateDefinition) {
53 VTTComponents.push_back(VTTComponent());
54 return;
55 }
56
57 VTTComponents.push_back(VTTComponent(VTableIndex, Base));
58 }
59
60 void VTTBuilder::LayoutSecondaryVTTs(BaseSubobject Base) {
61 const CXXRecordDecl *RD = Base.getBase();
62
63 for (const auto &I : RD->bases()) {
64 // Don't layout virtual bases.
65 if (I.isVirtual())
66 continue;
67
68 const CXXRecordDecl *BaseDecl =
69 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
70
71 const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
72 CharUnits BaseOffset = Base.getBaseOffset() +
73 Layout.getBaseClassOffset(BaseDecl);
74
75 // Layout the VTT for this base.
76 LayoutVTT(BaseSubobject(BaseDecl, BaseOffset), /*BaseIsVirtual=*/false);
77 }
78 }
79
80 void
81 VTTBuilder::LayoutSecondaryVirtualPointers(BaseSubobject Base,
82 bool BaseIsMorallyVirtual,
83 uint64_t VTableIndex,
84 const CXXRecordDecl *VTableClass,
85 VisitedVirtualBasesSetTy &VBases) {
86 const CXXRecordDecl *RD = Base.getBase();
87
88 // We're not interested in bases that don't have virtual bases, and not
89 // morally virtual bases.
90 if (!RD->getNumVBases() && !BaseIsMorallyVirtual)
91 return;
92
93 for (const auto &I : RD->bases()) {
94 const CXXRecordDecl *BaseDecl =
95 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
96
97 // Itanium C++ ABI 2.6.2:
98 // Secondary virtual pointers are present for all bases with either
99 // virtual bases or virtual function declarations overridden along a
100 // virtual path.
101 //
102 // If the base class is not dynamic, we don't want to add it, nor any
103 // of its base classes.
104 if (!BaseDecl->isDynamicClass())
105 continue;
106
107 bool BaseDeclIsMorallyVirtual = BaseIsMorallyVirtual;
108 bool BaseDeclIsNonVirtualPrimaryBase = false;
109 CharUnits BaseOffset;
110 if (I.isVirtual()) {
111 // Ignore virtual bases that we've already visited.
112 if (!VBases.insert(BaseDecl).second)
113 continue;
114
115 BaseOffset = MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
116 BaseDeclIsMorallyVirtual = true;
117 } else {
118 const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
119
120 BaseOffset = Base.getBaseOffset() +
121 Layout.getBaseClassOffset(BaseDecl);
122
123 if (!Layout.isPrimaryBaseVirtual() &&
124 Layout.getPrimaryBase() == BaseDecl)
125 BaseDeclIsNonVirtualPrimaryBase = true;
126 }
127
128 // Itanium C++ ABI 2.6.2:
129 // Secondary virtual pointers: for each base class X which (a) has virtual
130 // bases or is reachable along a virtual path from D, and (b) is not a
131 // non-virtual primary base, the address of the virtual table for X-in-D
132 // or an appropriate construction virtual table.
133 if (!BaseDeclIsNonVirtualPrimaryBase &&
134 (BaseDecl->getNumVBases() || BaseDeclIsMorallyVirtual)) {
135 // Add the vtable pointer.
136 AddVTablePointer(BaseSubobject(BaseDecl, BaseOffset), VTableIndex,
137 VTableClass);
138 }
139
140 // And lay out the secondary virtual pointers for the base class.
141 LayoutSecondaryVirtualPointers(BaseSubobject(BaseDecl, BaseOffset),
142 BaseDeclIsMorallyVirtual, VTableIndex,
143 VTableClass, VBases);
144 }
145 }
146
147 void
148 VTTBuilder::LayoutSecondaryVirtualPointers(BaseSubobject Base,
149 uint64_t VTableIndex) {
150 VisitedVirtualBasesSetTy VBases;
151 LayoutSecondaryVirtualPointers(Base, /*BaseIsMorallyVirtual=*/false,
152 VTableIndex, Base.getBase(), VBases);
153 }
154
155 void VTTBuilder::LayoutVirtualVTTs(const CXXRecordDecl *RD,
156 VisitedVirtualBasesSetTy &VBases) {
157 for (const auto &I : RD->bases()) {
158 const CXXRecordDecl *BaseDecl =
159 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
160
161 // Check if this is a virtual base.
162 if (I.isVirtual()) {
163 // Check if we've seen this base before.
164 if (!VBases.insert(BaseDecl).second)
165 continue;
166
167 CharUnits BaseOffset =
168 MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
169
170 LayoutVTT(BaseSubobject(BaseDecl, BaseOffset), /*BaseIsVirtual=*/true);
171 }
172
173 // We only need to layout virtual VTTs for this base if it actually has
174 // virtual bases.
175 if (BaseDecl->getNumVBases())
176 LayoutVirtualVTTs(BaseDecl, VBases);
177 }
178 }
179
180 void VTTBuilder::LayoutVTT(BaseSubobject Base, bool BaseIsVirtual) {
181 const CXXRecordDecl *RD = Base.getBase();
182
183 // Itanium C++ ABI 2.6.2:
184 // An array of virtual table addresses, called the VTT, is declared for
185 // each class type that has indirect or direct virtual base classes.
186 if (RD->getNumVBases() == 0)
187 return;
188
189 bool IsPrimaryVTT = Base.getBase() == MostDerivedClass;
190
191 if (!IsPrimaryVTT) {
192 // Remember the sub-VTT index.
193 SubVTTIndicies[Base] = VTTComponents.size();
194 }
195
196 uint64_t VTableIndex = VTTVTables.size();
197 VTTVTables.push_back(VTTVTable(Base, BaseIsVirtual));
198
199 // Add the primary vtable pointer.
200 AddVTablePointer(Base, VTableIndex, RD);
201
202 // Add the secondary VTTs.
203 LayoutSecondaryVTTs(Base);
204
205 // Add the secondary virtual pointers.
206 LayoutSecondaryVirtualPointers(Base, VTableIndex);
207
208 // If this is the primary VTT, we want to lay out virtual VTTs as well.
209 if (IsPrimaryVTT) {
210 VisitedVirtualBasesSetTy VBases;
211 LayoutVirtualVTTs(Base.getBase(), VBases);
212 }
213 }
ASTContext.h
Defines the clang::ASTContext interface.
clang::ASTRecordLayout::isPrimaryBaseVirtual
bool isPrimaryBaseVirtual() const
isPrimaryBaseVirtual - Get whether the primary base for this record is virtual or not...
Definition: RecordLayout.h:226
clang::CXXRecordDecl::bases
base_class_range bases()
Definition: DeclCXX.h:823
clang::ASTContext::getASTRecordLayout
const ASTRecordLayout & getASTRecordLayout(const RecordDecl *D) const
Get or compute information about the layout of the specified record (struct/union/class) D...
Definition: RecordLayoutBuilder.cpp:2966
clang::ASTRecordLayout::getBaseClassOffset
CharUnits getBaseClassOffset(const CXXRecordDecl *Base) const
getBaseClassOffset - Get the offset, in chars, for the given base class.
Definition: RecordLayout.h:233
clang::CXXRecordDecl::getNumVBases
unsigned getNumVBases() const
Retrieves the number of virtual base classes of this class.
Definition: DeclCXX.h:838
Base
Type.h
C Language Family Type Representation.
clang::VTTVTable
Definition: VTTBuilder.h:33
clang::VTTComponent
Definition: VTTBuilder.h:62
clang::BaseSubobject::getBaseOffset
CharUnits getBaseOffset() const
getBaseOffset - Returns the base class offset.
Definition: BaseSubobject.h:47
clang::ASTContext
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:155
BaseSubobject.h
clang::CharUnits::Zero
static CharUnits Zero()
Zero - Construct a CharUnits quantity of zero.
Definition: CharUnits.h:53
clang::ASTRecordLayout::getVBaseClassOffset
CharUnits getVBaseClassOffset(const CXXRecordDecl *VBase) const
getVBaseClassOffset - Get the offset, in chars, for the given base class.
Definition: RecordLayout.h:241
CharUnits.h
clang::CharUnits
CharUnits - This is an opaque type for sizes expressed in character units.
Definition: CharUnits.h:38
LLVM.h
Forward-declares and imports various common LLVM datatypes that clang wants to use unqualified...
clang::CXXRecordDecl::isDynamicClass
bool isDynamicClass() const
Definition: DeclCXX.h:789
clang::ASTRecordLayout
ASTRecordLayout - This class contains layout information for one RecordDecl, which is a struct/union/...
Definition: RecordLayout.h:39
clang::ASTRecordLayout::getPrimaryBase
const CXXRecordDecl * getPrimaryBase() const
getPrimaryBase - Get the primary base for this record.
Definition: RecordLayout.h:218
clang::BaseSubobject::getBase
const CXXRecordDecl * getBase() const
getBase - Returns the base class declaration.
Definition: BaseSubobject.h:44
clang::BaseSubobject
Definition: BaseSubobject.h:31
VTTBuilder.h
Decl.h
clang
Dataflow Directional Tag Classes.
Definition: CFGReachabilityAnalysis.h:22
clang::VTTBuilder::VTTBuilder
VTTBuilder(ASTContext &Ctx, const CXXRecordDecl *MostDerivedClass, bool GenerateDefinition)
Definition: VTTBuilder.cpp:32
clang::RecordType
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4370
DeclCXX.h
Defines the C++ Decl subclasses, other than those for templates (found in DeclTemplate.h) and friends (in DeclFriend.h).
clang::CXXRecordDecl
Represents a C++ struct/union/class.
Definition: DeclCXX.h:300
RecordLayout.h