CGVTables.h

//===--- CGVTables.h - Emit LLVM Code for C++ vtables -----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ code generation of virtual tables.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_LIB_CODEGEN_CGVTABLES_H
#define LLVM_CLANG_LIB_CODEGEN_CGVTABLES_H

#include "clang/AST/BaseSubobject.h"
#include "clang/AST/CharUnits.h"
#include "clang/AST/GlobalDecl.h"
#include "clang/AST/VTableBuilder.h"
#include "clang/Basic/ABI.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/IR/GlobalVariable.h"

namespace clang {
  class CXXRecordDecl;

namespace CodeGen {
  class CodeGenModule;
  class ConstantArrayBuilder;
  class ConstantStructBuilder;

class CodeGenVTables {
  CodeGenModule &CGM;

  VTableContextBase *VTContext;

  /// VTableAddressPointsMapTy - Address points for a single vtable.
  typedef VTableLayout::AddressPointsMapTy VTableAddressPointsMapTy;

  typedef std::pair<const CXXRecordDecl *, BaseSubobject> BaseSubobjectPairTy;
  typedef llvm::DenseMap<BaseSubobjectPairTy, uint64_t> SubVTTIndiciesMapTy;

  /// SubVTTIndicies - Contains indices into the various sub-VTTs.
  SubVTTIndiciesMapTy SubVTTIndicies;

  typedef llvm::DenseMap<BaseSubobjectPairTy, uint64_t>
    SecondaryVirtualPointerIndicesMapTy;

  /// SecondaryVirtualPointerIndices - Contains the secondary virtual pointer
  /// indices.
  SecondaryVirtualPointerIndicesMapTy SecondaryVirtualPointerIndices;

  /// Cache for the pure virtual member call function.
  llvm::Constant *PureVirtualFn = nullptr;

  /// Cache for the deleted virtual member call function.
  llvm::Constant *DeletedVirtualFn = nullptr;

  /// Get the address of a thunk and emit it if necessary.
  llvm::Constant *maybeEmitThunk(GlobalDecl GD,
                                 const ThunkInfo &ThunkAdjustments,
                                 bool ForVTable);

  void addVTableComponent(ConstantArrayBuilder &builder,
                          const VTableLayout &layout, unsigned componentIndex,
                          llvm::Constant *rtti, unsigned &nextVTableThunkIndex,
                          unsigned vtableAddressPoint,
                          bool vtableHasLocalLinkage);

  /// Add a 32-bit offset to a component relative to the vtable when using the
  /// relative vtables ABI. The array builder points to the start of the vtable.
  void addRelativeComponent(ConstantArrayBuilder &builder,
                            llvm::Constant *component,
                            unsigned vtableAddressPoint,
                            bool vtableHasLocalLinkage,
                            bool isCompleteDtor) const;

  /// Create a dso_local stub that will be used for a relative reference in the
  /// relative vtable layout. This stub will just be a tail call to the original
  /// function and propagate any function attributes from the original. If the
  /// original function is already dso_local, the original is returned instead
  /// and a stub is not created.
  llvm::Function *
  getOrCreateRelativeStub(llvm::Function *func,
                          llvm::GlobalValue::LinkageTypes stubLinkage,
                          bool isCompleteDtor) const;

  bool useRelativeLayout() const;

  llvm::Type *getVTableComponentType() const;

public:
  /// Add vtable components for the given vtable layout to the given
  /// global initializer.
  void createVTableInitializer(ConstantStructBuilder &builder,
                               const VTableLayout &layout, llvm::Constant *rtti,
                               bool vtableHasLocalLinkage);

  CodeGenVTables(CodeGenModule &CGM);

  ItaniumVTableContext &getItaniumVTableContext() {
    return *cast<ItaniumVTableContext>(VTContext);
  }

  MicrosoftVTableContext &getMicrosoftVTableContext() {
    return *cast<MicrosoftVTableContext>(VTContext);
  }

  /// getSubVTTIndex - Return the index of the sub-VTT for the base class of the
  /// given record decl.
  uint64_t getSubVTTIndex(const CXXRecordDecl *RD, BaseSubobject Base);

  /// getSecondaryVirtualPointerIndex - Return the index in the VTT where the
  /// virtual pointer for the given subobject is located.
  uint64_t getSecondaryVirtualPointerIndex(const CXXRecordDecl *RD,
                                           BaseSubobject Base);

  /// GenerateConstructionVTable - Generate a construction vtable for the given
  /// base subobject.
  llvm::GlobalVariable *
  GenerateConstructionVTable(const CXXRecordDecl *RD, const BaseSubobject &Base,
                             bool BaseIsVirtual,
                             llvm::GlobalVariable::LinkageTypes Linkage,
                             VTableAddressPointsMapTy& AddressPoints);


  /// GetAddrOfVTT - Get the address of the VTT for the given record decl.
  llvm::GlobalVariable *GetAddrOfVTT(const CXXRecordDecl *RD);

  /// EmitVTTDefinition - Emit the definition of the given vtable.
  void EmitVTTDefinition(llvm::GlobalVariable *VTT,
                         llvm::GlobalVariable::LinkageTypes Linkage,
                         const CXXRecordDecl *RD);

  /// EmitThunks - Emit the associated thunks for the given global decl.
  void EmitThunks(GlobalDecl GD);

  /// GenerateClassData - Generate all the class data required to be
  /// generated upon definition of a KeyFunction.  This includes the
  /// vtable, the RTTI data structure (if RTTI is enabled) and the VTT
  /// (if the class has virtual bases).
  void GenerateClassData(const CXXRecordDecl *RD);

  bool isVTableExternal(const CXXRecordDecl *RD);

  /// Returns the type of a vtable with the given layout. Normally a struct of
  /// arrays of pointers, with one struct element for each vtable in the vtable
  /// group.
  llvm::Type *getVTableType(const VTableLayout &layout);

  /// Generate a public facing alias for the vtable and make the vtable either
  /// hidden or private. The alias will have the original linkage and visibility
  /// of the vtable. This is used for cases under the relative vtables ABI
  /// when a vtable may not be dso_local.
  void GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
                                   llvm::StringRef AliasNameRef);
};

} // end namespace CodeGen
} // end namespace clang
#endif