1 //===--- CGVTables.h - Emit LLVM Code for C++ vtables -----------*- C++ -*-===//
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 virtual tables.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CLANG_LIB_CODEGEN_CGVTABLES_H
14 #define LLVM_CLANG_LIB_CODEGEN_CGVTABLES_H
15 
16 #include "clang/AST/BaseSubobject.h"
17 #include "clang/AST/CharUnits.h"
18 #include "clang/AST/GlobalDecl.h"
19 #include "clang/AST/VTableBuilder.h"
20 #include "clang/Basic/ABI.h"
21 #include "llvm/ADT/DenseMap.h"
22 #include "llvm/IR/GlobalVariable.h"
23 
24 namespace clang {
25   class CXXRecordDecl;
26 
27 namespace CodeGen {
28   class CodeGenModule;
29   class ConstantArrayBuilder;
30   class ConstantStructBuilder;
31 
32 class CodeGenVTables {
33   CodeGenModule &CGM;
34 
35   VTableContextBase *VTContext;
36 
37   /// VTableAddressPointsMapTy - Address points for a single vtable.
38   typedef VTableLayout::AddressPointsMapTy VTableAddressPointsMapTy;
39 
40   typedef std::pair<const CXXRecordDecl *, BaseSubobject> BaseSubobjectPairTy;
41   typedef llvm::DenseMap<BaseSubobjectPairTy, uint64_t> SubVTTIndiciesMapTy;
42 
43   /// SubVTTIndicies - Contains indices into the various sub-VTTs.
44   SubVTTIndiciesMapTy SubVTTIndicies;
45 
46   typedef llvm::DenseMap<BaseSubobjectPairTy, uint64_t>
47     SecondaryVirtualPointerIndicesMapTy;
48 
49   /// SecondaryVirtualPointerIndices - Contains the secondary virtual pointer
50   /// indices.
51   SecondaryVirtualPointerIndicesMapTy SecondaryVirtualPointerIndices;
52 
53   /// Cache for the pure virtual member call function.
54   llvm::Constant *PureVirtualFn = nullptr;
55 
56   /// Cache for the deleted virtual member call function.
57   llvm::Constant *DeletedVirtualFn = nullptr;
58 
59   /// Get the address of a thunk and emit it if necessary.
60   llvm::Constant *maybeEmitThunk(GlobalDecl GD,
61                                  const ThunkInfo &ThunkAdjustments,
62                                  bool ForVTable);
63 
64   void addVTableComponent(ConstantArrayBuilder &builder,
65                           const VTableLayout &layout, unsigned componentIndex,
66                           llvm::Constant *rtti, unsigned &nextVTableThunkIndex,
67                           unsigned vtableAddressPoint,
68                           bool vtableHasLocalLinkage);
69 
70   /// Add a 32-bit offset to a component relative to the vtable when using the
71   /// relative vtables ABI. The array builder points to the start of the vtable.
72   void addRelativeComponent(ConstantArrayBuilder &builder,
73                             llvm::Constant *component,
74                             unsigned vtableAddressPoint,
75                             bool vtableHasLocalLinkage,
76                             bool isCompleteDtor) const;
77 
78   /// Create a dso_local stub that will be used for a relative reference in the
79   /// relative vtable layout. This stub will just be a tail call to the original
80   /// function and propagate any function attributes from the original. If the
81   /// original function is already dso_local, the original is returned instead
82   /// and a stub is not created.
83   llvm::Function *
84   getOrCreateRelativeStub(llvm::Function *func,
85                           llvm::GlobalValue::LinkageTypes stubLinkage,
86                           bool isCompleteDtor) const;
87 
88   bool useRelativeLayout() const;
89 
90   llvm::Type *getVTableComponentType() const;
91 
92 public:
93   /// Add vtable components for the given vtable layout to the given
94   /// global initializer.
95   void createVTableInitializer(ConstantStructBuilder &builder,
96                                const VTableLayout &layout, llvm::Constant *rtti,
97                                bool vtableHasLocalLinkage);
98 
99   CodeGenVTables(CodeGenModule &CGM);
100 
101   ItaniumVTableContext &getItaniumVTableContext() {
102     return *cast<ItaniumVTableContext>(VTContext);
103   }
104 
105   MicrosoftVTableContext &getMicrosoftVTableContext() {
106     return *cast<MicrosoftVTableContext>(VTContext);
107   }
108 
109   /// getSubVTTIndex - Return the index of the sub-VTT for the base class of the
110   /// given record decl.
111   uint64_t getSubVTTIndex(const CXXRecordDecl *RD, BaseSubobject Base);
112 
113   /// getSecondaryVirtualPointerIndex - Return the index in the VTT where the
114   /// virtual pointer for the given subobject is located.
115   uint64_t getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
116                                            BaseSubobject Base);
117 
118   /// GenerateConstructionVTable - Generate a construction vtable for the given
119   /// base subobject.
120   llvm::GlobalVariable *
121   GenerateConstructionVTable(const CXXRecordDecl *RD, const BaseSubobject &Base,
122                              bool BaseIsVirtual,
123                              llvm::GlobalVariable::LinkageTypes Linkage,
124                              VTableAddressPointsMapTy& AddressPoints);
125 
126 
127   /// GetAddrOfVTT - Get the address of the VTT for the given record decl.
128   llvm::GlobalVariable *GetAddrOfVTT(const CXXRecordDecl *RD);
129 
130   /// EmitVTTDefinition - Emit the definition of the given vtable.
131   void EmitVTTDefinition(llvm::GlobalVariable *VTT,
132                          llvm::GlobalVariable::LinkageTypes Linkage,
133                          const CXXRecordDecl *RD);
134 
135   /// EmitThunks - Emit the associated thunks for the given global decl.
136   void EmitThunks(GlobalDecl GD);
137 
138   /// GenerateClassData - Generate all the class data required to be
139   /// generated upon definition of a KeyFunction.  This includes the
140   /// vtable, the RTTI data structure (if RTTI is enabled) and the VTT
141   /// (if the class has virtual bases).
142   void GenerateClassData(const CXXRecordDecl *RD);
143 
144   bool isVTableExternal(const CXXRecordDecl *RD);
145 
146   /// Returns the type of a vtable with the given layout. Normally a struct of
147   /// arrays of pointers, with one struct element for each vtable in the vtable
148   /// group.
149   llvm::Type *getVTableType(const VTableLayout &layout);
150 
151   /// Generate a public facing alias for the vtable and make the vtable either
152   /// hidden or private. The alias will have the original linkage and visibility
153   /// of the vtable. This is used for cases under the relative vtables ABI
154   /// when a vtable may not be dso_local.
155   void GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
156                                    llvm::StringRef AliasNameRef);
157 };
158 
159 } // end namespace CodeGen
160 } // end namespace clang
161 #endif
162