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
101llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
102  assert(RD->getNumVBases() && "Only classes with virtual bases need a VTT");
103
104  SmallString<256> OutName;
105  llvm::raw_svector_ostream Out(OutName);
106  cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
107      .mangleCXXVTT(RD, Out);
108  StringRef Name = OutName.str();
109
110  // This will also defer the definition of the VTT.
111  (void) CGM.getCXXABI().getAddrOfVTable(RD, CharUnits());
112
113  VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
114
115  llvm::ArrayType *ArrayType =
116    llvm::ArrayType::get(CGM.Int8PtrTy, Builder.getVTTComponents().size());
117  llvm::Align Align = CGM.getDataLayout().getABITypeAlign(CGM.Int8PtrTy);
118
119  llvm::GlobalVariable *GV = CGM.CreateOrReplaceCXXRuntimeVariable(
120      Name, ArrayType, llvm::GlobalValue::ExternalLinkage, Align);
121  GV->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
122  CGM.setGVProperties(GV, RD);
123  return GV;
124}
125
126uint64_t CodeGenVTables::getSubVTTIndex(const CXXRecordDecl *RD,
127                                        BaseSubobject Base) {
128  BaseSubobjectPairTy ClassSubobjectPair(RD, Base);
129
130  SubVTTIndiciesMapTy::iterator I = SubVTTIndicies.find(ClassSubobjectPair);
131  if (I != SubVTTIndicies.end())
132    return I->second;
133
134  VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
135
136  for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
137       Builder.getSubVTTIndicies().begin(),
138       E = Builder.getSubVTTIndicies().end(); I != E; ++I) {
139    // Insert all indices.
140    BaseSubobjectPairTy ClassSubobjectPair(RD, I->first);
141
142    SubVTTIndicies.insert(std::make_pair(ClassSubobjectPair, I->second));
143  }
144
145  I = SubVTTIndicies.find(ClassSubobjectPair);
146  assert(I != SubVTTIndicies.end() && "Did not find index!");
147
148  return I->second;
149}
150
151uint64_t
152CodeGenVTables::getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
153                                                BaseSubobject Base) {
154  SecondaryVirtualPointerIndicesMapTy::iterator I =
155    SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
156
157  if (I != SecondaryVirtualPointerIndices.end())
158    return I->second;
159
160  VTTBuilder Builder(CGM.getContext(), RD, /*GenerateDefinition=*/false);
161
162  // Insert all secondary vpointer indices.
163  for (llvm::DenseMap<BaseSubobject, uint64_t>::const_iterator I =
164       Builder.getSecondaryVirtualPointerIndices().begin(),
165       E = Builder.getSecondaryVirtualPointerIndices().end(); I != E; ++I) {
166    std::pair<const CXXRecordDecl *, BaseSubobject> Pair =
167      std::make_pair(RD, I->first);
168
169    SecondaryVirtualPointerIndices.insert(std::make_pair(Pair, I->second));
170  }
171
172  I = SecondaryVirtualPointerIndices.find(std::make_pair(RD, Base));
173  assert(I != SecondaryVirtualPointerIndices.end() && "Did not find index!");
174
175  return I->second;
176}
177