clang 10.0.0git

VTTBuilder.cpp
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1 //===- VTTBuilder.cpp - C++ VTT layout builder ----------------------------===//
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 generation of the layout of virtual table
10 // tables (VTT).
11 //
12 //===----------------------------------------------------------------------===//
13
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"
24 #include <cassert>
25 #include <cstdint>
26
27 using namespace clang;
28
29 #define DUMP_OVERRIDERS 0
30
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) {
37 // Lay out this VTT.
38 LayoutVTT(BaseSubobject(MostDerivedClass, CharUnits::Zero()),
39 /*BaseIsVirtual=*/false);
40 }
41
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();
49 }
50
51 if (!GenerateDefinition) {
52 VTTComponents.push_back(VTTComponent());
53 return;
54 }
55
56 VTTComponents.push_back(VTTComponent(VTableIndex, Base));
57 }
58
59 void VTTBuilder::LayoutSecondaryVTTs(BaseSubobject Base) {
60 const CXXRecordDecl *RD = Base.getBase();
61
62 for (const auto &I : RD->bases()) {
63 // Don't layout virtual bases.
64 if (I.isVirtual())
65 continue;
66
67 const auto *BaseDecl =
68 cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
69
70 const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
71 CharUnits BaseOffset = Base.getBaseOffset() +
72 Layout.getBaseClassOffset(BaseDecl);
73
74 // Layout the VTT for this base.
75 LayoutVTT(BaseSubobject(BaseDecl, BaseOffset), /*BaseIsVirtual=*/false);
76 }
77 }
78
79 void
80 VTTBuilder::LayoutSecondaryVirtualPointers(BaseSubobject Base,
81 bool BaseIsMorallyVirtual,
82 uint64_t VTableIndex,
83 const CXXRecordDecl *VTableClass,
84 VisitedVirtualBasesSetTy &VBases) {
85 const CXXRecordDecl *RD = Base.getBase();
86
87 // We're not interested in bases that don't have virtual bases, and not
88 // morally virtual bases.
89 if (!RD->getNumVBases() && !BaseIsMorallyVirtual)
90 return;
91
92 for (const auto &I : RD->bases()) {
93 const auto *BaseDecl =
94 cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
95
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
99 // virtual path.
100 //
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())
104 continue;
105
106 bool BaseDeclIsMorallyVirtual = BaseIsMorallyVirtual;
107 bool BaseDeclIsNonVirtualPrimaryBase = false;
108 CharUnits BaseOffset;
109 if (I.isVirtual()) {
110 // Ignore virtual bases that we've already visited.
111 if (!VBases.insert(BaseDecl).second)
112 continue;
113
114 BaseOffset = MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
115 BaseDeclIsMorallyVirtual = true;
116 } else {
117 const ASTRecordLayout &Layout = Ctx.getASTRecordLayout(RD);
118
119 BaseOffset = Base.getBaseOffset() +
120 Layout.getBaseClassOffset(BaseDecl);
121
122 if (!Layout.isPrimaryBaseVirtual() &&
123 Layout.getPrimaryBase() == BaseDecl)
124 BaseDeclIsNonVirtualPrimaryBase = true;
125 }
126
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,
136 VTableClass);
137 }
138
139 // And lay out the secondary virtual pointers for the base class.
140 LayoutSecondaryVirtualPointers(BaseSubobject(BaseDecl, BaseOffset),
141 BaseDeclIsMorallyVirtual, VTableIndex,
142 VTableClass, VBases);
143 }
144 }
145
146 void
147 VTTBuilder::LayoutSecondaryVirtualPointers(BaseSubobject Base,
148 uint64_t VTableIndex) {
149 VisitedVirtualBasesSetTy VBases;
150 LayoutSecondaryVirtualPointers(Base, /*BaseIsMorallyVirtual=*/false,
151 VTableIndex, Base.getBase(), VBases);
152 }
153
154 void VTTBuilder::LayoutVirtualVTTs(const CXXRecordDecl *RD,
155 VisitedVirtualBasesSetTy &VBases) {
156 for (const auto &I : RD->bases()) {
157 const auto *BaseDecl =
158 cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
159
160 // Check if this is a virtual base.
161 if (I.isVirtual()) {
162 // Check if we've seen this base before.
163 if (!VBases.insert(BaseDecl).second)
164 continue;
165
166 CharUnits BaseOffset =
167 MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
168
169 LayoutVTT(BaseSubobject(BaseDecl, BaseOffset), /*BaseIsVirtual=*/true);
170 }
171
172 // We only need to layout virtual VTTs for this base if it actually has
173 // virtual bases.
174 if (BaseDecl->getNumVBases())
175 LayoutVirtualVTTs(BaseDecl, VBases);
176 }
177 }
178
179 void VTTBuilder::LayoutVTT(BaseSubobject Base, bool BaseIsVirtual) {
180 const CXXRecordDecl *RD = Base.getBase();
181
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)
186 return;
187
188 bool IsPrimaryVTT = Base.getBase() == MostDerivedClass;
189
190 if (!IsPrimaryVTT) {
191 // Remember the sub-VTT index.
192 SubVTTIndicies[Base] = VTTComponents.size();
193 }
194
195 uint64_t VTableIndex = VTTVTables.size();
196 VTTVTables.push_back(VTTVTable(Base, BaseIsVirtual));
197
198 // Add the primary vtable pointer.
199 AddVTablePointer(Base, VTableIndex, RD);
200
201 // Add the secondary VTTs.
202 LayoutSecondaryVTTs(Base);
203
204 // Add the secondary virtual pointers.
205 LayoutSecondaryVirtualPointers(Base, VTableIndex);
206
207 // If this is the primary VTT, we want to lay out virtual VTTs as well.
208 if (IsPrimaryVTT) {
209 VisitedVirtualBasesSetTy VBases;
210 LayoutVirtualVTTs(Base.getBase(), VBases);
211 }
212 }
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:225
clang::CXXRecordDecl::bases
base_class_range bases()
Definition: DeclCXX.h:587
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:3023
clang::ASTRecordLayout::getBaseClassOffset
CharUnits getBaseClassOffset(const CXXRecordDecl *Base) const
getBaseClassOffset - Get the offset, in chars, for the given base class.
Definition: RecordLayout.h:232
clang::CXXRecordDecl::getNumVBases
unsigned getNumVBases() const
Retrieves the number of virtual base classes of this class.
Definition: DeclCXX.h:602
Base
Type.h
C Language Family Type Representation.
clang::VTTVTable
Definition: VTTBuilder.h:32
clang::VTTComponent
Definition: VTTBuilder.h:61
clang::BaseSubobject::getBaseOffset
CharUnits getBaseOffset() const
getBaseOffset - Returns the base class offset.
Definition: BaseSubobject.h:46
clang::ASTContext
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:168
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:240
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::ASTRecordLayout
ASTRecordLayout - This class contains layout information for one RecordDecl, which is a struct/union/...
Definition: RecordLayout.h:38
clang::ASTRecordLayout::getPrimaryBase
const CXXRecordDecl * getPrimaryBase() const
getPrimaryBase - Get the primary base for this record.
Definition: RecordLayout.h:217
clang::BaseSubobject::getBase
const CXXRecordDecl * getBase() const
getBase - Returns the base class declaration.
Definition: BaseSubobject.h:43
clang::BaseSubobject
Definition: BaseSubobject.h:30
VTTBuilder.h
Decl.h
clang
Dataflow Directional Tag Classes.
Definition: CFGReachabilityAnalysis.h:21
clang::VTTBuilder::VTTBuilder
VTTBuilder(ASTContext &Ctx, const CXXRecordDecl *MostDerivedClass, bool GenerateDefinition)
Definition: VTTBuilder.cpp:31
clang::RecordType
A helper class that allows the use of isa/cast/dyncast to detect TagType objects of structs/unions/cl...
Definition: Type.h:4495
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:253
RecordLayout.h