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llvm / llvm-project / 98dbcff19cfedb4e27d267310a76d616cd435447 / . / clang / lib / AST / VTableBuilder.cpp
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//===--- VTableBuilder.cpp - C++ vtable layout builder --------------------===//
//
// 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 generation of the layout of virtual tables.
//
//===----------------------------------------------------------------------===//
#include "clang/AST/VTableBuilder.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/RecordLayout.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/ADT/SetOperations.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cstdio>
using namespace clang;
#define DUMP_OVERRIDERS 0
namespace {
/// BaseOffset - Represents an offset from a derived class to a direct or
/// indirect base class.
struct BaseOffset {
/// DerivedClass - The derived class.
const CXXRecordDecl *DerivedClass;
/// VirtualBase - If the path from the derived class to the base class
/// involves virtual base classes, this holds the declaration of the last
/// virtual base in this path (i.e. closest to the base class).
const CXXRecordDecl *VirtualBase;
/// NonVirtualOffset - The offset from the derived class to the base class.
/// (Or the offset from the virtual base class to the base class, if the
/// path from the derived class to the base class involves a virtual base
/// class.
CharUnits NonVirtualOffset;
BaseOffset() : DerivedClass(nullptr), VirtualBase(nullptr),
NonVirtualOffset(CharUnits::Zero()) { }
BaseOffset(const CXXRecordDecl *DerivedClass,
const CXXRecordDecl *VirtualBase, CharUnits NonVirtualOffset)
: DerivedClass(DerivedClass), VirtualBase(VirtualBase),
NonVirtualOffset(NonVirtualOffset) { }
bool isEmpty() const { return NonVirtualOffset.isZero() && !VirtualBase; }
};
/// FinalOverriders - Contains the final overrider member functions for all
/// member functions in the base subobjects of a class.
class FinalOverriders {
public:
/// OverriderInfo - Information about a final overrider.
struct OverriderInfo {
/// Method - The method decl of the overrider.
const CXXMethodDecl *Method;
/// VirtualBase - The virtual base class subobject of this overrider.
/// Note that this records the closest derived virtual base class subobject.
const CXXRecordDecl *VirtualBase;
/// Offset - the base offset of the overrider's parent in the layout class.
CharUnits Offset;
OverriderInfo() : Method(nullptr), VirtualBase(nullptr),
Offset(CharUnits::Zero()) { }
};
private:
/// MostDerivedClass - The most derived class for which the final overriders
/// are stored.
const CXXRecordDecl *MostDerivedClass;
/// MostDerivedClassOffset - If we're building final overriders for a
/// construction vtable, this holds the offset from the layout class to the
/// most derived class.
const CharUnits MostDerivedClassOffset;
/// LayoutClass - The class we're using for layout information. Will be
/// different than the most derived class if the final overriders are for a
/// construction vtable.
const CXXRecordDecl *LayoutClass;
ASTContext &Context;
/// MostDerivedClassLayout - the AST record layout of the most derived class.
const ASTRecordLayout &MostDerivedClassLayout;
/// MethodBaseOffsetPairTy - Uniquely identifies a member function
/// in a base subobject.
typedef std::pair<const CXXMethodDecl *, CharUnits> MethodBaseOffsetPairTy;
typedef llvm::DenseMap<MethodBaseOffsetPairTy,
OverriderInfo> OverridersMapTy;
/// OverridersMap - The final overriders for all virtual member functions of
/// all the base subobjects of the most derived class.
OverridersMapTy OverridersMap;
/// SubobjectsToOffsetsMapTy - A mapping from a base subobject (represented
/// as a record decl and a subobject number) and its offsets in the most
/// derived class as well as the layout class.
typedef llvm::DenseMap<std::pair<const CXXRecordDecl *, unsigned>,
CharUnits> SubobjectOffsetMapTy;
typedef llvm::DenseMap<const CXXRecordDecl *, unsigned> SubobjectCountMapTy;
/// ComputeBaseOffsets - Compute the offsets for all base subobjects of the
/// given base.
void ComputeBaseOffsets(BaseSubobject Base, bool IsVirtual,
CharUnits OffsetInLayoutClass,
SubobjectOffsetMapTy &SubobjectOffsets,
SubobjectOffsetMapTy &SubobjectLayoutClassOffsets,
SubobjectCountMapTy &SubobjectCounts);
typedef llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBasesSetTy;
/// dump - dump the final overriders for a base subobject, and all its direct
/// and indirect base subobjects.
void dump(raw_ostream &Out, BaseSubobject Base,
VisitedVirtualBasesSetTy& VisitedVirtualBases);
public:
FinalOverriders(const CXXRecordDecl *MostDerivedClass,
CharUnits MostDerivedClassOffset,
const CXXRecordDecl *LayoutClass);
/// getOverrider - Get the final overrider for the given method declaration in
/// the subobject with the given base offset.
OverriderInfo getOverrider(const CXXMethodDecl *MD,
CharUnits BaseOffset) const {
assert(OverridersMap.count(std::make_pair(MD, BaseOffset)) &&
"Did not find overrider!");
return OverridersMap.lookup(std::make_pair(MD, BaseOffset));
}
/// dump - dump the final overriders.
void dump() {
VisitedVirtualBasesSetTy VisitedVirtualBases;
dump(llvm::errs(), BaseSubobject(MostDerivedClass, CharUnits::Zero()),
VisitedVirtualBases);
}
};
FinalOverriders::FinalOverriders(const CXXRecordDecl *MostDerivedClass,
CharUnits MostDerivedClassOffset,
const CXXRecordDecl *LayoutClass)
: MostDerivedClass(MostDerivedClass),
MostDerivedClassOffset(MostDerivedClassOffset), LayoutClass(LayoutClass),
Context(MostDerivedClass->getASTContext()),
MostDerivedClassLayout(Context.getASTRecordLayout(MostDerivedClass)) {
// Compute base offsets.
SubobjectOffsetMapTy SubobjectOffsets;
SubobjectOffsetMapTy SubobjectLayoutClassOffsets;
SubobjectCountMapTy SubobjectCounts;
ComputeBaseOffsets(BaseSubobject(MostDerivedClass, CharUnits::Zero()),
/*IsVirtual=*/false,
MostDerivedClassOffset,
SubobjectOffsets, SubobjectLayoutClassOffsets,
SubobjectCounts);
// Get the final overriders.
CXXFinalOverriderMap FinalOverriders;
MostDerivedClass->getFinalOverriders(FinalOverriders);
for (const auto &Overrider : FinalOverriders) {
const CXXMethodDecl *MD = Overrider.first;
const OverridingMethods &Methods = Overrider.second;
for (const auto &M : Methods) {
unsigned SubobjectNumber = M.first;
assert(SubobjectOffsets.count(std::make_pair(MD->getParent(),
SubobjectNumber)) &&
"Did not find subobject offset!");
CharUnits BaseOffset = SubobjectOffsets[std::make_pair(MD->getParent(),
SubobjectNumber)];
assert(M.second.size() == 1 && "Final overrider is not unique!");
const UniqueVirtualMethod &Method = M.second.front();
const CXXRecordDecl *OverriderRD = Method.Method->getParent();
assert(SubobjectLayoutClassOffsets.count(
std::make_pair(OverriderRD, Method.Subobject))
&& "Did not find subobject offset!");
CharUnits OverriderOffset =
SubobjectLayoutClassOffsets[std::make_pair(OverriderRD,
Method.Subobject)];
OverriderInfo& Overrider = OverridersMap[std::make_pair(MD, BaseOffset)];
assert(!Overrider.Method && "Overrider should not exist yet!");
Overrider.Offset = OverriderOffset;
Overrider.Method = Method.Method;
Overrider.VirtualBase = Method.InVirtualSubobject;
}
}
#if DUMP_OVERRIDERS
// And dump them (for now).
dump();
#endif
}
static BaseOffset ComputeBaseOffset(const ASTContext &Context,
const CXXRecordDecl *DerivedRD,
const CXXBasePath &Path) {
CharUnits NonVirtualOffset = CharUnits::Zero();
unsigned NonVirtualStart = 0;
const CXXRecordDecl *VirtualBase = nullptr;
// First, look for the virtual base class.
for (int I = Path.size(), E = 0; I != E; --I) {
const CXXBasePathElement &Element = Path[I - 1];
if (Element.Base->isVirtual()) {
NonVirtualStart = I;
QualType VBaseType = Element.Base->getType();
VirtualBase = VBaseType->getAsCXXRecordDecl();
break;
}
}
// Now compute the non-virtual offset.
for (unsigned I = NonVirtualStart, E = Path.size(); I != E; ++I) {
const CXXBasePathElement &Element = Path[I];
// Check the base class offset.
const ASTRecordLayout &Layout = Context.getASTRecordLayout(Element.Class);
const CXXRecordDecl *Base = Element.Base->getType()->getAsCXXRecordDecl();
NonVirtualOffset += Layout.getBaseClassOffset(Base);
}
// FIXME: This should probably use CharUnits or something. Maybe we should
// even change the base offsets in ASTRecordLayout to be specified in
// CharUnits.
return BaseOffset(DerivedRD, VirtualBase, NonVirtualOffset);
}
static BaseOffset ComputeBaseOffset(const ASTContext &Context,
const CXXRecordDecl *BaseRD,
const CXXRecordDecl *DerivedRD) {
CXXBasePaths Paths(/*FindAmbiguities=*/false,
/*RecordPaths=*/true, /*DetectVirtual=*/false);
if (!DerivedRD->isDerivedFrom(BaseRD, Paths))
llvm_unreachable("Class must be derived from the passed in base class!");
return ComputeBaseOffset(Context, DerivedRD, Paths.front());
}
static BaseOffset
ComputeReturnAdjustmentBaseOffset(ASTContext &Context,
const CXXMethodDecl *DerivedMD,
const CXXMethodDecl *BaseMD) {
const auto *BaseFT = BaseMD->getType()->castAs<FunctionType>();
const auto *DerivedFT = DerivedMD->getType()->castAs<FunctionType>();
// Canonicalize the return types.
CanQualType CanDerivedReturnType =
Context.getCanonicalType(DerivedFT->getReturnType());
CanQualType CanBaseReturnType =
Context.getCanonicalType(BaseFT->getReturnType());
assert(CanDerivedReturnType->getTypeClass() ==
CanBaseReturnType->getTypeClass() &&
"Types must have same type class!");
if (CanDerivedReturnType == CanBaseReturnType) {
// No adjustment needed.
return BaseOffset();
}
if (isa<ReferenceType>(CanDerivedReturnType)) {
CanDerivedReturnType =
CanDerivedReturnType->getAs<ReferenceType>()->getPointeeType();
CanBaseReturnType =
CanBaseReturnType->getAs<ReferenceType>()->getPointeeType();
} else if (isa<PointerType>(CanDerivedReturnType)) {
CanDerivedReturnType =
CanDerivedReturnType->getAs<PointerType>()->getPointeeType();
CanBaseReturnType =
CanBaseReturnType->getAs<PointerType>()->getPointeeType();
} else {
llvm_unreachable("Unexpected return type!");
}
// We need to compare unqualified types here; consider
// const T *Base::foo();
// T *Derived::foo();
if (CanDerivedReturnType.getUnqualifiedType() ==
CanBaseReturnType.getUnqualifiedType()) {
// No adjustment needed.
return BaseOffset();
}
const CXXRecordDecl *DerivedRD =
cast<CXXRecordDecl>(cast<RecordType>(CanDerivedReturnType)->getDecl());
const CXXRecordDecl *BaseRD =
cast<CXXRecordDecl>(cast<RecordType>(CanBaseReturnType)->getDecl());
return ComputeBaseOffset(Context, BaseRD, DerivedRD);
}
void
FinalOverriders::ComputeBaseOffsets(BaseSubobject Base, bool IsVirtual,
CharUnits OffsetInLayoutClass,
SubobjectOffsetMapTy &SubobjectOffsets,
SubobjectOffsetMapTy &SubobjectLayoutClassOffsets,
SubobjectCountMapTy &SubobjectCounts) {
const CXXRecordDecl *RD = Base.getBase();
unsigned SubobjectNumber = 0;
if (!IsVirtual)
SubobjectNumber = ++SubobjectCounts[RD];
// Set up the subobject to offset mapping.
assert(!SubobjectOffsets.count(std::make_pair(RD, SubobjectNumber))
&& "Subobject offset already exists!");
assert(!SubobjectLayoutClassOffsets.count(std::make_pair(RD, SubobjectNumber))
&& "Subobject offset already exists!");
SubobjectOffsets[std::make_pair(RD, SubobjectNumber)] = Base.getBaseOffset();
SubobjectLayoutClassOffsets[std::make_pair(RD, SubobjectNumber)] =
OffsetInLayoutClass;
// Traverse our bases.
for (const auto &B : RD->bases()) {
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
CharUnits BaseOffset;
CharUnits BaseOffsetInLayoutClass;
if (B.isVirtual()) {
// Check if we've visited this virtual base before.
if (SubobjectOffsets.count(std::make_pair(BaseDecl, 0)))
continue;
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
BaseOffset = MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
BaseOffsetInLayoutClass =
LayoutClassLayout.getVBaseClassOffset(BaseDecl);
} else {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
CharUnits Offset = Layout.getBaseClassOffset(BaseDecl);
BaseOffset = Base.getBaseOffset() + Offset;
BaseOffsetInLayoutClass = OffsetInLayoutClass + Offset;
}
ComputeBaseOffsets(BaseSubobject(BaseDecl, BaseOffset),
B.isVirtual(), BaseOffsetInLayoutClass,
SubobjectOffsets, SubobjectLayoutClassOffsets,
SubobjectCounts);
}
}
void FinalOverriders::dump(raw_ostream &Out, BaseSubobject Base,
VisitedVirtualBasesSetTy &VisitedVirtualBases) {
const CXXRecordDecl *RD = Base.getBase();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
for (const auto &B : RD->bases()) {
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
// Ignore bases that don't have any virtual member functions.
if (!BaseDecl->isPolymorphic())
continue;
CharUnits BaseOffset;
if (B.isVirtual()) {
if (!VisitedVirtualBases.insert(BaseDecl).second) {
// We've visited this base before.
continue;
}
BaseOffset = MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
} else {
BaseOffset = Layout.getBaseClassOffset(BaseDecl) + Base.getBaseOffset();
}
dump(Out, BaseSubobject(BaseDecl, BaseOffset), VisitedVirtualBases);
}
Out << "Final overriders for (";
RD->printQualifiedName(Out);
Out << ", ";
Out << Base.getBaseOffset().getQuantity() << ")\n";
// Now dump the overriders for this base subobject.
for (const auto *MD : RD->methods()) {
if (!VTableContextBase::hasVtableSlot(MD))
continue;
MD = MD->getCanonicalDecl();
OverriderInfo Overrider = getOverrider(MD, Base.getBaseOffset());
Out << " ";
MD->printQualifiedName(Out);
Out << " - (";
Overrider.Method->printQualifiedName(Out);
Out << ", " << Overrider.Offset.getQuantity() << ')';
BaseOffset Offset;
if (!Overrider.Method->isPure())
Offset = ComputeReturnAdjustmentBaseOffset(Context, Overrider.Method, MD);
if (!Offset.isEmpty()) {
Out << " [ret-adj: ";
if (Offset.VirtualBase) {
Offset.VirtualBase->printQualifiedName(Out);
Out << " vbase, ";
}
Out << Offset.NonVirtualOffset.getQuantity() << " nv]";
}
Out << "\n";
}
}
/// VCallOffsetMap - Keeps track of vcall offsets when building a vtable.
struct VCallOffsetMap {
typedef std::pair<const CXXMethodDecl *, CharUnits> MethodAndOffsetPairTy;
/// Offsets - Keeps track of methods and their offsets.
// FIXME: This should be a real map and not a vector.
SmallVector<MethodAndOffsetPairTy, 16> Offsets;
/// MethodsCanShareVCallOffset - Returns whether two virtual member functions
/// can share the same vcall offset.
static bool MethodsCanShareVCallOffset(const CXXMethodDecl *LHS,
const CXXMethodDecl *RHS);
public:
/// AddVCallOffset - Adds a vcall offset to the map. Returns true if the
/// add was successful, or false if there was already a member function with
/// the same signature in the map.
bool AddVCallOffset(const CXXMethodDecl *MD, CharUnits OffsetOffset);
/// getVCallOffsetOffset - Returns the vcall offset offset (relative to the
/// vtable address point) for the given virtual member function.
CharUnits getVCallOffsetOffset(const CXXMethodDecl *MD);
// empty - Return whether the offset map is empty or not.
bool empty() const { return Offsets.empty(); }
};
static bool HasSameVirtualSignature(const CXXMethodDecl *LHS,
const CXXMethodDecl *RHS) {
const FunctionProtoType *LT =
cast<FunctionProtoType>(LHS->getType().getCanonicalType());
const FunctionProtoType *RT =
cast<FunctionProtoType>(RHS->getType().getCanonicalType());
// Fast-path matches in the canonical types.
if (LT == RT) return true;
// Force the signatures to match. We can't rely on the overrides
// list here because there isn't necessarily an inheritance
// relationship between the two methods.
if (LT->getMethodQuals() != RT->getMethodQuals())
return false;
return LT->getParamTypes() == RT->getParamTypes();
}
bool VCallOffsetMap::MethodsCanShareVCallOffset(const CXXMethodDecl *LHS,
const CXXMethodDecl *RHS) {
assert(VTableContextBase::hasVtableSlot(LHS) && "LHS must be virtual!");
assert(VTableContextBase::hasVtableSlot(RHS) && "RHS must be virtual!");
// A destructor can share a vcall offset with another destructor.
if (isa<CXXDestructorDecl>(LHS))
return isa<CXXDestructorDecl>(RHS);
// FIXME: We need to check more things here.
// The methods must have the same name.
DeclarationName LHSName = LHS->getDeclName();
DeclarationName RHSName = RHS->getDeclName();
if (LHSName != RHSName)
return false;
// And the same signatures.
return HasSameVirtualSignature(LHS, RHS);
}
bool VCallOffsetMap::AddVCallOffset(const CXXMethodDecl *MD,
CharUnits OffsetOffset) {
// Check if we can reuse an offset.
for (const auto &OffsetPair : Offsets) {
if (MethodsCanShareVCallOffset(OffsetPair.first, MD))
return false;
}
// Add the offset.
Offsets.push_back(MethodAndOffsetPairTy(MD, OffsetOffset));
return true;
}
CharUnits VCallOffsetMap::getVCallOffsetOffset(const CXXMethodDecl *MD) {
// Look for an offset.
for (const auto &OffsetPair : Offsets) {
if (MethodsCanShareVCallOffset(OffsetPair.first, MD))
return OffsetPair.second;
}
llvm_unreachable("Should always find a vcall offset offset!");
}
/// VCallAndVBaseOffsetBuilder - Class for building vcall and vbase offsets.
class VCallAndVBaseOffsetBuilder {
public:
typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits>
VBaseOffsetOffsetsMapTy;
private:
const ItaniumVTableContext &VTables;
/// MostDerivedClass - The most derived class for which we're building vcall
/// and vbase offsets.
const CXXRecordDecl *MostDerivedClass;
/// LayoutClass - The class we're using for layout information. Will be
/// different than the most derived class if we're building a construction
/// vtable.
const CXXRecordDecl *LayoutClass;
/// Context - The ASTContext which we will use for layout information.
ASTContext &Context;
/// Components - vcall and vbase offset components
typedef SmallVector<VTableComponent, 64> VTableComponentVectorTy;
VTableComponentVectorTy Components;
/// VisitedVirtualBases - Visited virtual bases.
llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBases;
/// VCallOffsets - Keeps track of vcall offsets.
VCallOffsetMap VCallOffsets;
/// VBaseOffsetOffsets - Contains the offsets of the virtual base offsets,
/// relative to the address point.
VBaseOffsetOffsetsMapTy VBaseOffsetOffsets;
/// FinalOverriders - The final overriders of the most derived class.
/// (Can be null when we're not building a vtable of the most derived class).
const FinalOverriders *Overriders;
/// AddVCallAndVBaseOffsets - Add vcall offsets and vbase offsets for the
/// given base subobject.
void AddVCallAndVBaseOffsets(BaseSubobject Base, bool BaseIsVirtual,
CharUnits RealBaseOffset);
/// AddVCallOffsets - Add vcall offsets for the given base subobject.
void AddVCallOffsets(BaseSubobject Base, CharUnits VBaseOffset);
/// AddVBaseOffsets - Add vbase offsets for the given class.
void AddVBaseOffsets(const CXXRecordDecl *Base,
CharUnits OffsetInLayoutClass);
/// getCurrentOffsetOffset - Get the current vcall or vbase offset offset in
/// chars, relative to the vtable address point.
CharUnits getCurrentOffsetOffset() const;
public:
VCallAndVBaseOffsetBuilder(const ItaniumVTableContext &VTables,
const CXXRecordDecl *MostDerivedClass,
const CXXRecordDecl *LayoutClass,
const FinalOverriders *Overriders,
BaseSubobject Base, bool BaseIsVirtual,
CharUnits OffsetInLayoutClass)
: VTables(VTables), MostDerivedClass(MostDerivedClass),
LayoutClass(LayoutClass), Context(MostDerivedClass->getASTContext()),
Overriders(Overriders) {
// Add vcall and vbase offsets.
AddVCallAndVBaseOffsets(Base, BaseIsVirtual, OffsetInLayoutClass);
}
/// Methods for iterating over the components.
typedef VTableComponentVectorTy::const_reverse_iterator const_iterator;
const_iterator components_begin() const { return Components.rbegin(); }
const_iterator components_end() const { return Components.rend(); }
const VCallOffsetMap &getVCallOffsets() const { return VCallOffsets; }
const VBaseOffsetOffsetsMapTy &getVBaseOffsetOffsets() const {
return VBaseOffsetOffsets;
}
};
void
VCallAndVBaseOffsetBuilder::AddVCallAndVBaseOffsets(BaseSubobject Base,
bool BaseIsVirtual,
CharUnits RealBaseOffset) {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(Base.getBase());
// Itanium C++ ABI 2.5.2:
// ..in classes sharing a virtual table with a primary base class, the vcall
// and vbase offsets added by the derived class all come before the vcall
// and vbase offsets required by the base class, so that the latter may be
// laid out as required by the base class without regard to additions from
// the derived class(es).
// (Since we're emitting the vcall and vbase offsets in reverse order, we'll
// emit them for the primary base first).
if (const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase()) {
bool PrimaryBaseIsVirtual = Layout.isPrimaryBaseVirtual();
CharUnits PrimaryBaseOffset;
// Get the base offset of the primary base.
if (PrimaryBaseIsVirtual) {
assert(Layout.getVBaseClassOffset(PrimaryBase).isZero() &&
"Primary vbase should have a zero offset!");
const ASTRecordLayout &MostDerivedClassLayout =
Context.getASTRecordLayout(MostDerivedClass);
PrimaryBaseOffset =
MostDerivedClassLayout.getVBaseClassOffset(PrimaryBase);
} else {
assert(Layout.getBaseClassOffset(PrimaryBase).isZero() &&
"Primary base should have a zero offset!");
PrimaryBaseOffset = Base.getBaseOffset();
}
AddVCallAndVBaseOffsets(
BaseSubobject(PrimaryBase,PrimaryBaseOffset),
PrimaryBaseIsVirtual, RealBaseOffset);
}
AddVBaseOffsets(Base.getBase(), RealBaseOffset);
// We only want to add vcall offsets for virtual bases.
if (BaseIsVirtual)
AddVCallOffsets(Base, RealBaseOffset);
}
CharUnits VCallAndVBaseOffsetBuilder::getCurrentOffsetOffset() const {
// OffsetIndex is the index of this vcall or vbase offset, relative to the
// vtable address point. (We subtract 3 to account for the information just
// above the address point, the RTTI info, the offset to top, and the
// vcall offset itself).
int64_t OffsetIndex = -(int64_t)(3 + Components.size());
// Under the relative ABI, the offset widths are 32-bit ints instead of
// pointer widths.
CharUnits OffsetWidth = Context.toCharUnitsFromBits(
VTables.isRelativeLayout() ? 32
: Context.getTargetInfo().getPointerWidth(0));
CharUnits OffsetOffset = OffsetWidth * OffsetIndex;
return OffsetOffset;
}
void VCallAndVBaseOffsetBuilder::AddVCallOffsets(BaseSubobject Base,
CharUnits VBaseOffset) {
const CXXRecordDecl *RD = Base.getBase();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
// Handle the primary base first.
// We only want to add vcall offsets if the base is non-virtual; a virtual
// primary base will have its vcall and vbase offsets emitted already.
if (PrimaryBase && !Layout.isPrimaryBaseVirtual()) {
// Get the base offset of the primary base.
assert(Layout.getBaseClassOffset(PrimaryBase).isZero() &&
"Primary base should have a zero offset!");
AddVCallOffsets(BaseSubobject(PrimaryBase, Base.getBaseOffset()),
VBaseOffset);
}
// Add the vcall offsets.
for (const auto *MD : RD->methods()) {
if (!VTableContextBase::hasVtableSlot(MD))
continue;
MD = MD->getCanonicalDecl();
CharUnits OffsetOffset = getCurrentOffsetOffset();
// Don't add a vcall offset if we already have one for this member function
// signature.
if (!VCallOffsets.AddVCallOffset(MD, OffsetOffset))
continue;
CharUnits Offset = CharUnits::Zero();
if (Overriders) {
// Get the final overrider.
FinalOverriders::OverriderInfo Overrider =
Overriders->getOverrider(MD, Base.getBaseOffset());
/// The vcall offset is the offset from the virtual base to the object
/// where the function was overridden.
Offset = Overrider.Offset - VBaseOffset;
}
Components.push_back(
VTableComponent::MakeVCallOffset(Offset));
}
// And iterate over all non-virtual bases (ignoring the primary base).
for (const auto &B : RD->bases()) {
if (B.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
if (BaseDecl == PrimaryBase)
continue;
// Get the base offset of this base.
CharUnits BaseOffset = Base.getBaseOffset() +
Layout.getBaseClassOffset(BaseDecl);
AddVCallOffsets(BaseSubobject(BaseDecl, BaseOffset),
VBaseOffset);
}
}
void
VCallAndVBaseOffsetBuilder::AddVBaseOffsets(const CXXRecordDecl *RD,
CharUnits OffsetInLayoutClass) {
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
// Add vbase offsets.
for (const auto &B : RD->bases()) {
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
// Check if this is a virtual base that we haven't visited before.
if (B.isVirtual() && VisitedVirtualBases.insert(BaseDecl).second) {
CharUnits Offset =
LayoutClassLayout.getVBaseClassOffset(BaseDecl) - OffsetInLayoutClass;
// Add the vbase offset offset.
assert(!VBaseOffsetOffsets.count(BaseDecl) &&
"vbase offset offset already exists!");
CharUnits VBaseOffsetOffset = getCurrentOffsetOffset();
VBaseOffsetOffsets.insert(
std::make_pair(BaseDecl, VBaseOffsetOffset));
Components.push_back(
VTableComponent::MakeVBaseOffset(Offset));
}
// Check the base class looking for more vbase offsets.
AddVBaseOffsets(BaseDecl, OffsetInLayoutClass);
}
}
/// ItaniumVTableBuilder - Class for building vtable layout information.
class ItaniumVTableBuilder {
public:
/// PrimaryBasesSetVectorTy - A set vector of direct and indirect
/// primary bases.
typedef llvm::SmallSetVector<const CXXRecordDecl *, 8>
PrimaryBasesSetVectorTy;
typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits>
VBaseOffsetOffsetsMapTy;
typedef VTableLayout::AddressPointsMapTy AddressPointsMapTy;
typedef llvm::DenseMap<GlobalDecl, int64_t> MethodVTableIndicesTy;
private:
/// VTables - Global vtable information.
ItaniumVTableContext &VTables;
/// MostDerivedClass - The most derived class for which we're building this
/// vtable.
const CXXRecordDecl *MostDerivedClass;
/// MostDerivedClassOffset - If we're building a construction vtable, this
/// holds the offset from the layout class to the most derived class.
const CharUnits MostDerivedClassOffset;
/// MostDerivedClassIsVirtual - Whether the most derived class is a virtual
/// base. (This only makes sense when building a construction vtable).
bool MostDerivedClassIsVirtual;
/// LayoutClass - The class we're using for layout information. Will be
/// different than the most derived class if we're building a construction
/// vtable.
const CXXRecordDecl *LayoutClass;
/// Context - The ASTContext which we will use for layout information.
ASTContext &Context;
/// FinalOverriders - The final overriders of the most derived class.
const FinalOverriders Overriders;
/// VCallOffsetsForVBases - Keeps track of vcall offsets for the virtual
/// bases in this vtable.
llvm::DenseMap<const CXXRecordDecl *, VCallOffsetMap> VCallOffsetsForVBases;
/// VBaseOffsetOffsets - Contains the offsets of the virtual base offsets for
/// the most derived class.
VBaseOffsetOffsetsMapTy VBaseOffsetOffsets;
/// Components - The components of the vtable being built.
SmallVector<VTableComponent, 64> Components;
/// AddressPoints - Address points for the vtable being built.
AddressPointsMapTy AddressPoints;
/// MethodInfo - Contains information about a method in a vtable.
/// (Used for computing 'this' pointer adjustment thunks.
struct MethodInfo {
/// BaseOffset - The base offset of this method.
const CharUnits BaseOffset;
/// BaseOffsetInLayoutClass - The base offset in the layout class of this
/// method.
const CharUnits BaseOffsetInLayoutClass;
/// VTableIndex - The index in the vtable that this method has.
/// (For destructors, this is the index of the complete destructor).
const uint64_t VTableIndex;
MethodInfo(CharUnits BaseOffset, CharUnits BaseOffsetInLayoutClass,
uint64_t VTableIndex)
: BaseOffset(BaseOffset),
BaseOffsetInLayoutClass(BaseOffsetInLayoutClass),
VTableIndex(VTableIndex) { }
MethodInfo()
: BaseOffset(CharUnits::Zero()),
BaseOffsetInLayoutClass(CharUnits::Zero()),
VTableIndex(0) { }
MethodInfo(MethodInfo const&) = default;
};
typedef llvm::DenseMap<const CXXMethodDecl *, MethodInfo> MethodInfoMapTy;
/// MethodInfoMap - The information for all methods in the vtable we're
/// currently building.
MethodInfoMapTy MethodInfoMap;
/// MethodVTableIndices - Contains the index (relative to the vtable address
/// point) where the function pointer for a virtual function is stored.
MethodVTableIndicesTy MethodVTableIndices;
typedef llvm::DenseMap<uint64_t, ThunkInfo> VTableThunksMapTy;
/// VTableThunks - The thunks by vtable index in the vtable currently being
/// built.
VTableThunksMapTy VTableThunks;
typedef SmallVector<ThunkInfo, 1> ThunkInfoVectorTy;
typedef llvm::DenseMap<const CXXMethodDecl *, ThunkInfoVectorTy> ThunksMapTy;
/// Thunks - A map that contains all the thunks needed for all methods in the
/// most derived class for which the vtable is currently being built.
ThunksMapTy Thunks;
/// AddThunk - Add a thunk for the given method.
void AddThunk(const CXXMethodDecl *MD, const ThunkInfo &Thunk);
/// ComputeThisAdjustments - Compute the 'this' pointer adjustments for the
/// part of the vtable we're currently building.
void ComputeThisAdjustments();
typedef llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBasesSetTy;
/// PrimaryVirtualBases - All known virtual bases who are a primary base of
/// some other base.
VisitedVirtualBasesSetTy PrimaryVirtualBases;
/// ComputeReturnAdjustment - Compute the return adjustment given a return
/// adjustment base offset.
ReturnAdjustment ComputeReturnAdjustment(BaseOffset Offset);
/// ComputeThisAdjustmentBaseOffset - Compute the base offset for adjusting
/// the 'this' pointer from the base subobject to the derived subobject.
BaseOffset ComputeThisAdjustmentBaseOffset(BaseSubobject Base,
BaseSubobject Derived) const;
/// ComputeThisAdjustment - Compute the 'this' pointer adjustment for the
/// given virtual member function, its offset in the layout class and its
/// final overrider.
ThisAdjustment
ComputeThisAdjustment(const CXXMethodDecl *MD,
CharUnits BaseOffsetInLayoutClass,
FinalOverriders::OverriderInfo Overrider);
/// AddMethod - Add a single virtual member function to the vtable
/// components vector.
void AddMethod(const CXXMethodDecl *MD, ReturnAdjustment ReturnAdjustment);
/// IsOverriderUsed - Returns whether the overrider will ever be used in this
/// part of the vtable.
///
/// Itanium C++ ABI 2.5.2:
///
/// struct A { virtual void f(); };
/// struct B : virtual public A { int i; };
/// struct C : virtual public A { int j; };
/// struct D : public B, public C {};
///
/// When B and C are declared, A is a primary base in each case, so although
/// vcall offsets are allocated in the A-in-B and A-in-C vtables, no this
/// adjustment is required and no thunk is generated. However, inside D
/// objects, A is no longer a primary base of C, so if we allowed calls to
/// C::f() to use the copy of A's vtable in the C subobject, we would need
/// to adjust this from C* to B::A*, which would require a third-party
/// thunk. Since we require that a call to C::f() first convert to A*,
/// C-in-D's copy of A's vtable is never referenced, so this is not
/// necessary.
bool IsOverriderUsed(const CXXMethodDecl *Overrider,
CharUnits BaseOffsetInLayoutClass,
const CXXRecordDecl *FirstBaseInPrimaryBaseChain,
CharUnits FirstBaseOffsetInLayoutClass) const;
/// AddMethods - Add the methods of this base subobject and all its
/// primary bases to the vtable components vector.
void AddMethods(BaseSubobject Base, CharUnits BaseOffsetInLayoutClass,
const CXXRecordDecl *FirstBaseInPrimaryBaseChain,
CharUnits FirstBaseOffsetInLayoutClass,
PrimaryBasesSetVectorTy &PrimaryBases);
// LayoutVTable - Layout the vtable for the given base class, including its
// secondary vtables and any vtables for virtual bases.
void LayoutVTable();
/// LayoutPrimaryAndSecondaryVTables - Layout the primary vtable for the
/// given base subobject, as well as all its secondary vtables.
///
/// \param BaseIsMorallyVirtual whether the base subobject is a virtual base
/// or a direct or indirect base of a virtual base.
///
/// \param BaseIsVirtualInLayoutClass - Whether the base subobject is virtual
/// in the layout class.
void LayoutPrimaryAndSecondaryVTables(BaseSubobject Base,
bool BaseIsMorallyVirtual,
bool BaseIsVirtualInLayoutClass,
CharUnits OffsetInLayoutClass);
/// LayoutSecondaryVTables - Layout the secondary vtables for the given base
/// subobject.
///
/// \param BaseIsMorallyVirtual whether the base subobject is a virtual base
/// or a direct or indirect base of a virtual base.
void LayoutSecondaryVTables(BaseSubobject Base, bool BaseIsMorallyVirtual,
CharUnits OffsetInLayoutClass);
/// DeterminePrimaryVirtualBases - Determine the primary virtual bases in this
/// class hierarchy.
void DeterminePrimaryVirtualBases(const CXXRecordDecl *RD,
CharUnits OffsetInLayoutClass,
VisitedVirtualBasesSetTy &VBases);
/// LayoutVTablesForVirtualBases - Layout vtables for all virtual bases of the
/// given base (excluding any primary bases).
void LayoutVTablesForVirtualBases(const CXXRecordDecl *RD,
VisitedVirtualBasesSetTy &VBases);
/// isBuildingConstructionVTable - Return whether this vtable builder is
/// building a construction vtable.
bool isBuildingConstructorVTable() const {
return MostDerivedClass != LayoutClass;
}
public:
/// Component indices of the first component of each of the vtables in the
/// vtable group.
SmallVector<size_t, 4> VTableIndices;
ItaniumVTableBuilder(ItaniumVTableContext &VTables,
const CXXRecordDecl *MostDerivedClass,
CharUnits MostDerivedClassOffset,
bool MostDerivedClassIsVirtual,
const CXXRecordDecl *LayoutClass)
: VTables(VTables), MostDerivedClass(MostDerivedClass),
MostDerivedClassOffset(MostDerivedClassOffset),
MostDerivedClassIsVirtual(MostDerivedClassIsVirtual),
LayoutClass(LayoutClass), Context(MostDerivedClass->getASTContext()),
Overriders(MostDerivedClass, MostDerivedClassOffset, LayoutClass) {
assert(!Context.getTargetInfo().getCXXABI().isMicrosoft());
LayoutVTable();
if (Context.getLangOpts().DumpVTableLayouts)
dumpLayout(llvm::outs());
}
uint64_t getNumThunks() const {
return Thunks.size();
}
ThunksMapTy::const_iterator thunks_begin() const {
return Thunks.begin();
}
ThunksMapTy::const_iterator thunks_end() const {
return Thunks.end();
}
const VBaseOffsetOffsetsMapTy &getVBaseOffsetOffsets() const {
return VBaseOffsetOffsets;
}
const AddressPointsMapTy &getAddressPoints() const {
return AddressPoints;
}
MethodVTableIndicesTy::const_iterator vtable_indices_begin() const {
return MethodVTableIndices.begin();
}
MethodVTableIndicesTy::const_iterator vtable_indices_end() const {
return MethodVTableIndices.end();
}
ArrayRef<VTableComponent> vtable_components() const { return Components; }
AddressPointsMapTy::const_iterator address_points_begin() const {
return AddressPoints.begin();
}
AddressPointsMapTy::const_iterator address_points_end() const {
return AddressPoints.end();
}
VTableThunksMapTy::const_iterator vtable_thunks_begin() const {
return VTableThunks.begin();
}
VTableThunksMapTy::const_iterator vtable_thunks_end() const {
return VTableThunks.end();
}
/// dumpLayout - Dump the vtable layout.
void dumpLayout(raw_ostream&);
};
void ItaniumVTableBuilder::AddThunk(const CXXMethodDecl *MD,
const ThunkInfo &Thunk) {
assert(!isBuildingConstructorVTable() &&
"Can't add thunks for construction vtable");
SmallVectorImpl<ThunkInfo> &ThunksVector = Thunks[MD];
// Check if we have this thunk already.
if (llvm::is_contained(ThunksVector, Thunk))
return;
ThunksVector.push_back(Thunk);
}
typedef llvm::SmallPtrSet<const CXXMethodDecl *, 8> OverriddenMethodsSetTy;
/// Visit all the methods overridden by the given method recursively,
/// in a depth-first pre-order. The Visitor's visitor method returns a bool
/// indicating whether to continue the recursion for the given overridden
/// method (i.e. returning false stops the iteration).
template <class VisitorTy>
static void
visitAllOverriddenMethods(const CXXMethodDecl *MD, VisitorTy &Visitor) {
assert(VTableContextBase::hasVtableSlot(MD) && "Method is not virtual!");
for (const CXXMethodDecl *OverriddenMD : MD->overridden_methods()) {
if (!Visitor(OverriddenMD))
continue;
visitAllOverriddenMethods(OverriddenMD, Visitor);
}
}
/// ComputeAllOverriddenMethods - Given a method decl, will return a set of all
/// the overridden methods that the function decl overrides.
static void
ComputeAllOverriddenMethods(const CXXMethodDecl *MD,
OverriddenMethodsSetTy& OverriddenMethods) {
auto OverriddenMethodsCollector = [&](const CXXMethodDecl *MD) {
// Don't recurse on this method if we've already collected it.
return OverriddenMethods.insert(MD).second;
};
visitAllOverriddenMethods(MD, OverriddenMethodsCollector);
}
void ItaniumVTableBuilder::ComputeThisAdjustments() {
// Now go through the method info map and see if any of the methods need
// 'this' pointer adjustments.
for (const auto &MI : MethodInfoMap) {
const CXXMethodDecl *MD = MI.first;
const MethodInfo &MethodInfo = MI.second;
// Ignore adjustments for unused function pointers.
uint64_t VTableIndex = MethodInfo.VTableIndex;
if (Components[VTableIndex].getKind() ==
VTableComponent::CK_UnusedFunctionPointer)
continue;
// Get the final overrider for this method.
FinalOverriders::OverriderInfo Overrider =
Overriders.getOverrider(MD, MethodInfo.BaseOffset);
// Check if we need an adjustment at all.
if (MethodInfo.BaseOffsetInLayoutClass == Overrider.Offset) {
// When a return thunk is needed by a derived class that overrides a
// virtual base, gcc uses a virtual 'this' adjustment as well.
// While the thunk itself might be needed by vtables in subclasses or
// in construction vtables, there doesn't seem to be a reason for using
// the thunk in this vtable. Still, we do so to match gcc.
if (VTableThunks.lookup(VTableIndex).Return.isEmpty())
continue;
}
ThisAdjustment ThisAdjustment =
ComputeThisAdjustment(MD, MethodInfo.BaseOffsetInLayoutClass, Overrider);
if (ThisAdjustment.isEmpty())
continue;
// Add it.
VTableThunks[VTableIndex].This = ThisAdjustment;
if (isa<CXXDestructorDecl>(MD)) {
// Add an adjustment for the deleting destructor as well.
VTableThunks[VTableIndex + 1].This = ThisAdjustment;
}
}
/// Clear the method info map.
MethodInfoMap.clear();
if (isBuildingConstructorVTable()) {
// We don't need to store thunk information for construction vtables.
return;
}
for (const auto &TI : VTableThunks) {
const VTableComponent &Component = Components[TI.first];
const ThunkInfo &Thunk = TI.second;
const CXXMethodDecl *MD;
switch (Component.getKind()) {
default:
llvm_unreachable("Unexpected vtable component kind!");
case VTableComponent::CK_FunctionPointer:
MD = Component.getFunctionDecl();
break;
case VTableComponent::CK_CompleteDtorPointer:
MD = Component.getDestructorDecl();
break;
case VTableComponent::CK_DeletingDtorPointer:
// We've already added the thunk when we saw the complete dtor pointer.
continue;
}
if (MD->getParent() == MostDerivedClass)
AddThunk(MD, Thunk);
}
}
ReturnAdjustment
ItaniumVTableBuilder::ComputeReturnAdjustment(BaseOffset Offset) {
ReturnAdjustment Adjustment;
if (!Offset.isEmpty()) {
if (Offset.VirtualBase) {
// Get the virtual base offset offset.
if (Offset.DerivedClass == MostDerivedClass) {
// We can get the offset offset directly from our map.
Adjustment.Virtual.Itanium.VBaseOffsetOffset =
VBaseOffsetOffsets.lookup(Offset.VirtualBase).getQuantity();
} else {
Adjustment.Virtual.Itanium.VBaseOffsetOffset =
VTables.getVirtualBaseOffsetOffset(Offset.DerivedClass,
Offset.VirtualBase).getQuantity();
}
}
Adjustment.NonVirtual = Offset.NonVirtualOffset.getQuantity();
}
return Adjustment;
}
BaseOffset ItaniumVTableBuilder::ComputeThisAdjustmentBaseOffset(
BaseSubobject Base, BaseSubobject Derived) const {
const CXXRecordDecl *BaseRD = Base.getBase();
const CXXRecordDecl *DerivedRD = Derived.getBase();
CXXBasePaths Paths(/*FindAmbiguities=*/true,
/*RecordPaths=*/true, /*DetectVirtual=*/true);
if (!DerivedRD->isDerivedFrom(BaseRD, Paths))
llvm_unreachable("Class must be derived from the passed in base class!");
// We have to go through all the paths, and see which one leads us to the
// right base subobject.
for (const CXXBasePath &Path : Paths) {
BaseOffset Offset = ComputeBaseOffset(Context, DerivedRD, Path);
CharUnits OffsetToBaseSubobject = Offset.NonVirtualOffset;
if (Offset.VirtualBase) {
// If we have a virtual base class, the non-virtual offset is relative
// to the virtual base class offset.
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
/// Get the virtual base offset, relative to the most derived class
/// layout.
OffsetToBaseSubobject +=
LayoutClassLayout.getVBaseClassOffset(Offset.VirtualBase);
} else {
// Otherwise, the non-virtual offset is relative to the derived class
// offset.
OffsetToBaseSubobject += Derived.getBaseOffset();
}
// Check if this path gives us the right base subobject.
if (OffsetToBaseSubobject == Base.getBaseOffset()) {
// Since we're going from the base class _to_ the derived class, we'll
// invert the non-virtual offset here.
Offset.NonVirtualOffset = -Offset.NonVirtualOffset;
return Offset;
}
}
return BaseOffset();
}
ThisAdjustment ItaniumVTableBuilder::ComputeThisAdjustment(
const CXXMethodDecl *MD, CharUnits BaseOffsetInLayoutClass,
FinalOverriders::OverriderInfo Overrider) {
// Ignore adjustments for pure virtual member functions.
if (Overrider.Method->isPure())
return ThisAdjustment();
BaseSubobject OverriddenBaseSubobject(MD->getParent(),
BaseOffsetInLayoutClass);
BaseSubobject OverriderBaseSubobject(Overrider.Method->getParent(),
Overrider.Offset);
// Compute the adjustment offset.
BaseOffset Offset = ComputeThisAdjustmentBaseOffset(OverriddenBaseSubobject,
OverriderBaseSubobject);
if (Offset.isEmpty())
return ThisAdjustment();
ThisAdjustment Adjustment;
if (Offset.VirtualBase) {
// Get the vcall offset map for this virtual base.
VCallOffsetMap &VCallOffsets = VCallOffsetsForVBases[Offset.VirtualBase];
if (VCallOffsets.empty()) {
// We don't have vcall offsets for this virtual base, go ahead and
// build them.
VCallAndVBaseOffsetBuilder Builder(
VTables, MostDerivedClass, MostDerivedClass,
/*Overriders=*/nullptr,
BaseSubobject(Offset.VirtualBase, CharUnits::Zero()),
/*BaseIsVirtual=*/true,
/*OffsetInLayoutClass=*/
CharUnits::Zero());
VCallOffsets = Builder.getVCallOffsets();
}
Adjustment.Virtual.Itanium.VCallOffsetOffset =
VCallOffsets.getVCallOffsetOffset(MD).getQuantity();
}
// Set the non-virtual part of the adjustment.
Adjustment.NonVirtual = Offset.NonVirtualOffset.getQuantity();
return Adjustment;
}
void ItaniumVTableBuilder::AddMethod(const CXXMethodDecl *MD,
ReturnAdjustment ReturnAdjustment) {
if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
assert(ReturnAdjustment.isEmpty() &&
"Destructor can't have return adjustment!");
// Add both the complete destructor and the deleting destructor.
Components.push_back(VTableComponent::MakeCompleteDtor(DD));
Components.push_back(VTableComponent::MakeDeletingDtor(DD));
} else {
// Add the return adjustment if necessary.
if (!ReturnAdjustment.isEmpty())
VTableThunks[Components.size()].Return = ReturnAdjustment;
// Add the function.
Components.push_back(VTableComponent::MakeFunction(MD));
}
}
/// OverridesIndirectMethodInBase - Return whether the given member function
/// overrides any methods in the set of given bases.
/// Unlike OverridesMethodInBase, this checks "overriders of overriders".
/// For example, if we have:
///
/// struct A { virtual void f(); }
/// struct B : A { virtual void f(); }
/// struct C : B { virtual void f(); }
///
/// OverridesIndirectMethodInBase will return true if given C::f as the method
/// and { A } as the set of bases.
static bool OverridesIndirectMethodInBases(
const CXXMethodDecl *MD,
ItaniumVTableBuilder::PrimaryBasesSetVectorTy &Bases) {
if (Bases.count(MD->getParent()))
return true;
for (const CXXMethodDecl *OverriddenMD : MD->overridden_methods()) {
// Check "indirect overriders".
if (OverridesIndirectMethodInBases(OverriddenMD, Bases))
return true;
}
return false;
}
bool ItaniumVTableBuilder::IsOverriderUsed(
const CXXMethodDecl *Overrider, CharUnits BaseOffsetInLayoutClass,
const CXXRecordDecl *FirstBaseInPrimaryBaseChain,
CharUnits FirstBaseOffsetInLayoutClass) const {
// If the base and the first base in the primary base chain have the same
// offsets, then this overrider will be used.
if (BaseOffsetInLayoutClass == FirstBaseOffsetInLayoutClass)
return true;
// We know now that Base (or a direct or indirect base of it) is a primary
// base in part of the class hierarchy, but not a primary base in the most
// derived class.
// If the overrider is the first base in the primary base chain, we know
// that the overrider will be used.
if (Overrider->getParent() == FirstBaseInPrimaryBaseChain)
return true;
ItaniumVTableBuilder::PrimaryBasesSetVectorTy PrimaryBases;
const CXXRecordDecl *RD = FirstBaseInPrimaryBaseChain;
PrimaryBases.insert(RD);
// Now traverse the base chain, starting with the first base, until we find
// the base that is no longer a primary base.
while (true) {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
if (!PrimaryBase)
break;
if (Layout.isPrimaryBaseVirtual()) {
assert(Layout.getVBaseClassOffset(PrimaryBase).isZero() &&
"Primary base should always be at offset 0!");
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
// Now check if this is the primary base that is not a primary base in the
// most derived class.
if (LayoutClassLayout.getVBaseClassOffset(PrimaryBase) !=
FirstBaseOffsetInLayoutClass) {
// We found it, stop walking the chain.
break;
}
} else {
assert(Layout.getBaseClassOffset(PrimaryBase).isZero() &&
"Primary base should always be at offset 0!");
}
if (!PrimaryBases.insert(PrimaryBase))
llvm_unreachable("Found a duplicate primary base!");
RD = PrimaryBase;
}
// If the final overrider is an override of one of the primary bases,
// then we know that it will be used.
return OverridesIndirectMethodInBases(Overrider, PrimaryBases);
}
typedef llvm::SmallSetVector<const CXXRecordDecl *, 8> BasesSetVectorTy;
/// FindNearestOverriddenMethod - Given a method, returns the overridden method
/// from the nearest base. Returns null if no method was found.
/// The Bases are expected to be sorted in a base-to-derived order.
static const CXXMethodDecl *
FindNearestOverriddenMethod(const CXXMethodDecl *MD,
BasesSetVectorTy &Bases) {
OverriddenMethodsSetTy OverriddenMethods;
ComputeAllOverriddenMethods(MD, OverriddenMethods);
for (const CXXRecordDecl *PrimaryBase : llvm::reverse(Bases)) {
// Now check the overridden methods.
for (const CXXMethodDecl *OverriddenMD : OverriddenMethods) {
// We found our overridden method.
if (OverriddenMD->getParent() == PrimaryBase)
return OverriddenMD;
}
}
return nullptr;
}
void ItaniumVTableBuilder::AddMethods(
BaseSubobject Base, CharUnits BaseOffsetInLayoutClass,
const CXXRecordDecl *FirstBaseInPrimaryBaseChain,
CharUnits FirstBaseOffsetInLayoutClass,
PrimaryBasesSetVectorTy &PrimaryBases) {
// Itanium C++ ABI 2.5.2:
// The order of the virtual function pointers in a virtual table is the
// order of declaration of the corresponding member functions in the class.
//
// There is an entry for any virtual function declared in a class,
// whether it is a new function or overrides a base class function,
// unless it overrides a function from the primary base, and conversion
// between their return types does not require an adjustment.
const CXXRecordDecl *RD = Base.getBase();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
if (const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase()) {
CharUnits PrimaryBaseOffset;
CharUnits PrimaryBaseOffsetInLayoutClass;
if (Layout.isPrimaryBaseVirtual()) {
assert(Layout.getVBaseClassOffset(PrimaryBase).isZero() &&
"Primary vbase should have a zero offset!");
const ASTRecordLayout &MostDerivedClassLayout =
Context.getASTRecordLayout(MostDerivedClass);
PrimaryBaseOffset =
MostDerivedClassLayout.getVBaseClassOffset(PrimaryBase);
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
PrimaryBaseOffsetInLayoutClass =
LayoutClassLayout.getVBaseClassOffset(PrimaryBase);
} else {
assert(Layout.getBaseClassOffset(PrimaryBase).isZero() &&
"Primary base should have a zero offset!");
PrimaryBaseOffset = Base.getBaseOffset();
PrimaryBaseOffsetInLayoutClass = BaseOffsetInLayoutClass;
}
AddMethods(BaseSubobject(PrimaryBase, PrimaryBaseOffset),
PrimaryBaseOffsetInLayoutClass, FirstBaseInPrimaryBaseChain,
FirstBaseOffsetInLayoutClass, PrimaryBases);
if (!PrimaryBases.insert(PrimaryBase))
llvm_unreachable("Found a duplicate primary base!");
}
typedef llvm::SmallVector<const CXXMethodDecl *, 8> NewVirtualFunctionsTy;
NewVirtualFunctionsTy NewVirtualFunctions;
llvm::SmallVector<const CXXMethodDecl*, 4> NewImplicitVirtualFunctions;
// Now go through all virtual member functions and add them.
for (const auto *MD : RD->methods()) {
if (!ItaniumVTableContext::hasVtableSlot(MD))
continue;
MD = MD->getCanonicalDecl();
// Get the final overrider.
FinalOverriders::OverriderInfo Overrider =
Overriders.getOverrider(MD, Base.getBaseOffset());
// Check if this virtual member function overrides a method in a primary
// base. If this is the case, and the return type doesn't require adjustment
// then we can just use the member function from the primary base.
if (const CXXMethodDecl *OverriddenMD =
FindNearestOverriddenMethod(MD, PrimaryBases)) {
if (ComputeReturnAdjustmentBaseOffset(Context, MD,
OverriddenMD).isEmpty()) {
// Replace the method info of the overridden method with our own
// method.
assert(MethodInfoMap.count(OverriddenMD) &&
"Did not find the overridden method!");
MethodInfo &OverriddenMethodInfo = MethodInfoMap[OverriddenMD];
MethodInfo MethodInfo(Base.getBaseOffset(), BaseOffsetInLayoutClass,
OverriddenMethodInfo.VTableIndex);
assert(!MethodInfoMap.count(MD) &&
"Should not have method info for this method yet!");
MethodInfoMap.insert(std::make_pair(MD, MethodInfo));
MethodInfoMap.erase(OverriddenMD);
// If the overridden method exists in a virtual base class or a direct
// or indirect base class of a virtual base class, we need to emit a
// thunk if we ever have a class hierarchy where the base class is not
// a primary base in the complete object.
if (!isBuildingConstructorVTable() && OverriddenMD != MD) {
// Compute the this adjustment.
ThisAdjustment ThisAdjustment =
ComputeThisAdjustment(OverriddenMD, BaseOffsetInLayoutClass,
Overrider);
if (ThisAdjustment.Virtual.Itanium.VCallOffsetOffset &&
Overrider.Method->getParent() == MostDerivedClass) {
// There's no return adjustment from OverriddenMD and MD,
// but that doesn't mean there isn't one between MD and
// the final overrider.
BaseOffset ReturnAdjustmentOffset =
ComputeReturnAdjustmentBaseOffset(Context, Overrider.Method, MD);
ReturnAdjustment ReturnAdjustment =
ComputeReturnAdjustment(ReturnAdjustmentOffset);
// This is a virtual thunk for the most derived class, add it.
AddThunk(Overrider.Method,
ThunkInfo(ThisAdjustment, ReturnAdjustment));
}
}
continue;
}
}
if (MD->isImplicit())
NewImplicitVirtualFunctions.push_back(MD);
else
NewVirtualFunctions.push_back(MD);
}
std::stable_sort(
NewImplicitVirtualFunctions.begin(), NewImplicitVirtualFunctions.end(),
[](const CXXMethodDecl *A, const CXXMethodDecl *B) {
if (A->isCopyAssignmentOperator() != B->isCopyAssignmentOperator())
return A->isCopyAssignmentOperator();
if (A->isMoveAssignmentOperator() != B->isMoveAssignmentOperator())
return A->isMoveAssignmentOperator();
if (isa<CXXDestructorDecl>(A) != isa<CXXDestructorDecl>(B))
return isa<CXXDestructorDecl>(A);
assert(A->getOverloadedOperator() == OO_EqualEqual &&
B->getOverloadedOperator() == OO_EqualEqual &&
"unexpected or duplicate implicit virtual function");
// We rely on Sema to have declared the operator== members in the
// same order as the corresponding operator<=> members.
return false;
});
NewVirtualFunctions.append(NewImplicitVirtualFunctions.begin(),
NewImplicitVirtualFunctions.end());
for (const CXXMethodDecl *MD : NewVirtualFunctions) {
// Get the final overrider.
FinalOverriders::OverriderInfo Overrider =
Overriders.getOverrider(MD, Base.getBaseOffset());
// Insert the method info for this method.
MethodInfo MethodInfo(Base.getBaseOffset(), BaseOffsetInLayoutClass,
Components.size());
assert(!MethodInfoMap.count(MD) &&
"Should not have method info for this method yet!");
MethodInfoMap.insert(std::make_pair(MD, MethodInfo));
// Check if this overrider is going to be used.
const CXXMethodDecl *OverriderMD = Overrider.Method;
if (!IsOverriderUsed(OverriderMD, BaseOffsetInLayoutClass,
FirstBaseInPrimaryBaseChain,
FirstBaseOffsetInLayoutClass)) {
Components.push_back(VTableComponent::MakeUnusedFunction(OverriderMD));
continue;
}
// Check if this overrider needs a return adjustment.
// We don't want to do this for pure virtual member functions.
BaseOffset ReturnAdjustmentOffset;
if (!OverriderMD->isPure()) {
ReturnAdjustmentOffset =
ComputeReturnAdjustmentBaseOffset(Context, OverriderMD, MD);
}
ReturnAdjustment ReturnAdjustment =
ComputeReturnAdjustment(ReturnAdjustmentOffset);
AddMethod(Overrider.Method, ReturnAdjustment);
}
}
void ItaniumVTableBuilder::LayoutVTable() {
LayoutPrimaryAndSecondaryVTables(BaseSubobject(MostDerivedClass,
CharUnits::Zero()),
/*BaseIsMorallyVirtual=*/false,
MostDerivedClassIsVirtual,
MostDerivedClassOffset);
VisitedVirtualBasesSetTy VBases;
// Determine the primary virtual bases.
DeterminePrimaryVirtualBases(MostDerivedClass, MostDerivedClassOffset,
VBases);
VBases.clear();
LayoutVTablesForVirtualBases(MostDerivedClass, VBases);
// -fapple-kext adds an extra entry at end of vtbl.
bool IsAppleKext = Context.getLangOpts().AppleKext;
if (IsAppleKext)
Components.push_back(VTableComponent::MakeVCallOffset(CharUnits::Zero()));
}
void ItaniumVTableBuilder::LayoutPrimaryAndSecondaryVTables(
BaseSubobject Base, bool BaseIsMorallyVirtual,
bool BaseIsVirtualInLayoutClass, CharUnits OffsetInLayoutClass) {
assert(Base.getBase()->isDynamicClass() && "class does not have a vtable!");
unsigned VTableIndex = Components.size();
VTableIndices.push_back(VTableIndex);
// Add vcall and vbase offsets for this vtable.
VCallAndVBaseOffsetBuilder Builder(
VTables, MostDerivedClass, LayoutClass, &Overriders, Base,
BaseIsVirtualInLayoutClass, OffsetInLayoutClass);
Components.append(Builder.components_begin(), Builder.components_end());
// Check if we need to add these vcall offsets.
if (BaseIsVirtualInLayoutClass && !Builder.getVCallOffsets().empty()) {
VCallOffsetMap &VCallOffsets = VCallOffsetsForVBases[Base.getBase()];
if (VCallOffsets.empty())
VCallOffsets = Builder.getVCallOffsets();
}
// If we're laying out the most derived class we want to keep track of the
// virtual base class offset offsets.
if (Base.getBase() == MostDerivedClass)
VBaseOffsetOffsets = Builder.getVBaseOffsetOffsets();
// Add the offset to top.
CharUnits OffsetToTop = MostDerivedClassOffset - OffsetInLayoutClass;
Components.push_back(VTableComponent::MakeOffsetToTop(OffsetToTop));
// Next, add the RTTI.
Components.push_back(VTableComponent::MakeRTTI(MostDerivedClass));
uint64_t AddressPoint = Components.size();
// Now go through all virtual member functions and add them.
PrimaryBasesSetVectorTy PrimaryBases;
AddMethods(Base, OffsetInLayoutClass,
Base.getBase(), OffsetInLayoutClass,
PrimaryBases);
const CXXRecordDecl *RD = Base.getBase();
if (RD == MostDerivedClass) {
assert(MethodVTableIndices.empty());
for (const auto &I : MethodInfoMap) {
const CXXMethodDecl *MD = I.first;
const MethodInfo &MI = I.second;
if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
MethodVTableIndices[GlobalDecl(DD, Dtor_Complete)]
= MI.VTableIndex - AddressPoint;
MethodVTableIndices[GlobalDecl(DD, Dtor_Deleting)]
= MI.VTableIndex + 1 - AddressPoint;
} else {
MethodVTableIndices[MD] = MI.VTableIndex - AddressPoint;
}
}
}
// Compute 'this' pointer adjustments.
ComputeThisAdjustments();
// Add all address points.
while (true) {
AddressPoints.insert(
std::make_pair(BaseSubobject(RD, OffsetInLayoutClass),
VTableLayout::AddressPointLocation{
unsigned(VTableIndices.size() - 1),
unsigned(AddressPoint - VTableIndex)}));
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
if (!PrimaryBase)
break;
if (Layout.isPrimaryBaseVirtual()) {
// Check if this virtual primary base is a primary base in the layout
// class. If it's not, we don't want to add it.
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
if (LayoutClassLayout.getVBaseClassOffset(PrimaryBase) !=
OffsetInLayoutClass) {
// We don't want to add this class (or any of its primary bases).
break;
}
}
RD = PrimaryBase;
}
// Layout secondary vtables.
LayoutSecondaryVTables(Base, BaseIsMorallyVirtual, OffsetInLayoutClass);
}
void
ItaniumVTableBuilder::LayoutSecondaryVTables(BaseSubobject Base,
bool BaseIsMorallyVirtual,
CharUnits OffsetInLayoutClass) {
// Itanium C++ ABI 2.5.2:
// Following the primary virtual table of a derived class are secondary
// virtual tables for each of its proper base classes, except any primary
// base(s) with which it shares its primary virtual table.
const CXXRecordDecl *RD = Base.getBase();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase();
for (const auto &B : RD->bases()) {
// Ignore virtual bases, we'll emit them later.
if (B.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
// Ignore bases that don't have a vtable.
if (!BaseDecl->isDynamicClass())
continue;
if (isBuildingConstructorVTable()) {
// Itanium C++ ABI 2.6.4:
// Some of the base class subobjects may not need construction virtual
// tables, which will therefore not be present in the construction
// virtual table group, even though the subobject virtual tables are
// present in the main virtual table group for the complete object.
if (!BaseIsMorallyVirtual && !BaseDecl->getNumVBases())
continue;
}
// Get the base offset of this base.
CharUnits RelativeBaseOffset = Layout.getBaseClassOffset(BaseDecl);
CharUnits BaseOffset = Base.getBaseOffset() + RelativeBaseOffset;
CharUnits BaseOffsetInLayoutClass =
OffsetInLayoutClass + RelativeBaseOffset;
// Don't emit a secondary vtable for a primary base. We might however want
// to emit secondary vtables for other bases of this base.
if (BaseDecl == PrimaryBase) {
LayoutSecondaryVTables(BaseSubobject(BaseDecl, BaseOffset),
BaseIsMorallyVirtual, BaseOffsetInLayoutClass);
continue;
}
// Layout the primary vtable (and any secondary vtables) for this base.
LayoutPrimaryAndSecondaryVTables(
BaseSubobject(BaseDecl, BaseOffset),
BaseIsMorallyVirtual,
/*BaseIsVirtualInLayoutClass=*/false,
BaseOffsetInLayoutClass);
}
}
void ItaniumVTableBuilder::DeterminePrimaryVirtualBases(
const CXXRecordDecl *RD, CharUnits OffsetInLayoutClass,
VisitedVirtualBasesSetTy &VBases) {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
// Check if this base has a primary base.
if (const CXXRecordDecl *PrimaryBase = Layout.getPrimaryBase()) {
// Check if it's virtual.
if (Layout.isPrimaryBaseVirtual()) {
bool IsPrimaryVirtualBase = true;
if (isBuildingConstructorVTable()) {
// Check if the base is actually a primary base in the class we use for
// layout.
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
CharUnits PrimaryBaseOffsetInLayoutClass =
LayoutClassLayout.getVBaseClassOffset(PrimaryBase);
// We know that the base is not a primary base in the layout class if
// the base offsets are different.
if (PrimaryBaseOffsetInLayoutClass != OffsetInLayoutClass)
IsPrimaryVirtualBase = false;
}
if (IsPrimaryVirtualBase)
PrimaryVirtualBases.insert(PrimaryBase);
}
}
// Traverse bases, looking for more primary virtual bases.
for (const auto &B : RD->bases()) {
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
CharUnits BaseOffsetInLayoutClass;
if (B.isVirtual()) {
if (!VBases.insert(BaseDecl).second)
continue;
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
BaseOffsetInLayoutClass =
LayoutClassLayout.getVBaseClassOffset(BaseDecl);
} else {
BaseOffsetInLayoutClass =
OffsetInLayoutClass + Layout.getBaseClassOffset(BaseDecl);
}
DeterminePrimaryVirtualBases(BaseDecl, BaseOffsetInLayoutClass, VBases);
}
}
void ItaniumVTableBuilder::LayoutVTablesForVirtualBases(
const CXXRecordDecl *RD, VisitedVirtualBasesSetTy &VBases) {
// Itanium C++ ABI 2.5.2:
// Then come the virtual base virtual tables, also in inheritance graph
// order, and again excluding primary bases (which share virtual tables with
// the classes for which they are primary).
for (const auto &B : RD->bases()) {
const CXXRecordDecl *BaseDecl = B.getType()->getAsCXXRecordDecl();
// Check if this base needs a vtable. (If it's virtual, not a primary base
// of some other class, and we haven't visited it before).
if (B.isVirtual() && BaseDecl->isDynamicClass() &&
!PrimaryVirtualBases.count(BaseDecl) &&
VBases.insert(BaseDecl).second) {
const ASTRecordLayout &MostDerivedClassLayout =
Context.getASTRecordLayout(MostDerivedClass);
CharUnits BaseOffset =
MostDerivedClassLayout.getVBaseClassOffset(BaseDecl);
const ASTRecordLayout &LayoutClassLayout =
Context.getASTRecordLayout(LayoutClass);
CharUnits BaseOffsetInLayoutClass =
LayoutClassLayout.getVBaseClassOffset(BaseDecl);
LayoutPrimaryAndSecondaryVTables(
BaseSubobject(BaseDecl, BaseOffset),
/*BaseIsMorallyVirtual=*/true,
/*BaseIsVirtualInLayoutClass=*/true,
BaseOffsetInLayoutClass);
}
// We only need to check the base for virtual base vtables if it actually
// has virtual bases.
if (BaseDecl->getNumVBases())
LayoutVTablesForVirtualBases(BaseDecl, VBases);
}
}
/// dumpLayout - Dump the vtable layout.
void ItaniumVTableBuilder::dumpLayout(raw_ostream &Out) {
// FIXME: write more tests that actually use the dumpLayout output to prevent
// ItaniumVTableBuilder regressions.
if (isBuildingConstructorVTable()) {
Out << "Construction vtable for ('";
MostDerivedClass->printQualifiedName(Out);
Out << "', ";
Out << MostDerivedClassOffset.getQuantity() << ") in '";
LayoutClass->printQualifiedName(Out);
} else {
Out << "Vtable for '";
MostDerivedClass->printQualifiedName(Out);
}
Out << "' (" << Components.size() << " entries).\n";
// Iterate through the address points and insert them into a new map where
// they are keyed by the index and not the base object.
// Since an address point can be shared by multiple subobjects, we use an
// STL multimap.
std::multimap<uint64_t, BaseSubobject> AddressPointsByIndex;
for (const auto &AP : AddressPoints) {
const BaseSubobject &Base = AP.first;
uint64_t Index =
VTableIndices[AP.second.VTableIndex] + AP.second.AddressPointIndex;
AddressPointsByIndex.insert(std::make_pair(Index, Base));
}
for (unsigned I = 0, E = Components.size(); I != E; ++I) {
uint64_t Index = I;
Out << llvm::format("%4d | ", I);
const VTableComponent &Component = Components[I];
// Dump the component.
switch (Component.getKind()) {
case VTableComponent::CK_VCallOffset:
Out << "vcall_offset ("
<< Component.getVCallOffset().getQuantity()
<< ")";
break;
case VTableComponent::CK_VBaseOffset:
Out << "vbase_offset ("
<< Component.getVBaseOffset().getQuantity()
<< ")";
break;
case VTableComponent::CK_OffsetToTop:
Out << "offset_to_top ("
<< Component.getOffsetToTop().getQuantity()
<< ")";
break;
case VTableComponent::CK_RTTI:
Component.getRTTIDecl()->printQualifiedName(Out);
Out << " RTTI";
break;
case VTableComponent::CK_FunctionPointer: {
const CXXMethodDecl *MD = Component.getFunctionDecl();
std::string Str =
PredefinedExpr::ComputeName(PredefinedExpr::PrettyFunctionNoVirtual,
MD);
Out << Str;
if (MD->isPure())
Out << " [pure]";
if (MD->isDeleted())
Out << " [deleted]";
ThunkInfo Thunk = VTableThunks.lookup(I);
if (!Thunk.isEmpty()) {
// If this function pointer has a return adjustment, dump it.
if (!Thunk.Return.isEmpty()) {
Out << "\n [return adjustment: ";
Out << Thunk.Return.NonVirtual << " non-virtual";
if (Thunk.Return.Virtual.Itanium.VBaseOffsetOffset) {
Out << ", " << Thunk.Return.Virtual.Itanium.VBaseOffsetOffset;
Out << " vbase offset offset";
}
Out << ']';
}
// If this function pointer has a 'this' pointer adjustment, dump it.
if (!Thunk.This.isEmpty()) {
Out << "\n [this adjustment: ";
Out << Thunk.This.NonVirtual << " non-virtual";
if (Thunk.This.Virtual.Itanium.VCallOffsetOffset) {
Out << ", " << Thunk.This.Virtual.Itanium.VCallOffsetOffset;
Out << " vcall offset offset";
}
Out << ']';
}
}
break;
}
case VTableComponent::CK_CompleteDtorPointer:
case VTableComponent::CK_DeletingDtorPointer: {
bool IsComplete =
Component.getKind() == VTableComponent::CK_CompleteDtorPointer;
const CXXDestructorDecl *DD = Component.getDestructorDecl();
DD->printQualifiedName(Out);
if (IsComplete)
Out << "() [complete]";
else
Out << "() [deleting]";
if (DD->isPure())
Out << " [pure]";
ThunkInfo Thunk = VTableThunks.lookup(I);
if (!Thunk.isEmpty()) {
// If this destructor has a 'this' pointer adjustment, dump it.
if (!Thunk.This.isEmpty()) {
Out << "\n [this adjustment: ";
Out << Thunk.This.NonVirtual << " non-virtual";
if (Thunk.This.Virtual.Itanium.VCallOffsetOffset) {
Out << ", " << Thunk.This.Virtual.Itanium.VCallOffsetOffset;
Out << " vcall offset offset";
}
Out << ']';
}
}
break;
}
case VTableComponent::CK_UnusedFunctionPointer: {
const CXXMethodDecl *MD = Component.getUnusedFunctionDecl();
std::string Str =
PredefinedExpr::ComputeName(PredefinedExpr::PrettyFunctionNoVirtual,
MD);
Out << "[unused] " << Str;
if (MD->isPure())
Out << " [pure]";
}
}
Out << '\n';
// Dump the next address point.
uint64_t NextIndex = Index + 1;
if (AddressPointsByIndex.count(NextIndex)) {
if (AddressPointsByIndex.count(NextIndex) == 1) {
const BaseSubobject &Base =
AddressPointsByIndex.find(NextIndex)->second;
Out << " -- (";
Base.getBase()->printQualifiedName(Out);
Out << ", " << Base.getBaseOffset().getQuantity();
Out << ") vtable address --\n";
} else {
CharUnits BaseOffset =
AddressPointsByIndex.lower_bound(NextIndex)->second.getBaseOffset();
// We store the class names in a set to get a stable order.
std::set<std::string> ClassNames;
for (const auto &I :
llvm::make_range(AddressPointsByIndex.equal_range(NextIndex))) {
assert(I.second.getBaseOffset() == BaseOffset &&
"Invalid base offset!");
const CXXRecordDecl *RD = I.second.getBase();
ClassNames.insert(RD->getQualifiedNameAsString());
}
for (const std::string &Name : ClassNames) {
Out << " -- (" << Name;
Out << ", " << BaseOffset.getQuantity() << ") vtable address --\n";
}
}
}
}
Out << '\n';
if (isBuildingConstructorVTable())
return;
if (MostDerivedClass->getNumVBases()) {
// We store the virtual base class names and their offsets in a map to get
// a stable order.
std::map<std::string, CharUnits> ClassNamesAndOffsets;
for (const auto &I : VBaseOffsetOffsets) {
std::string ClassName = I.first->getQualifiedNameAsString();
CharUnits OffsetOffset = I.second;
ClassNamesAndOffsets.insert(std::make_pair(ClassName, OffsetOffset));
}
Out << "Virtual base offset offsets for '";
MostDerivedClass->printQualifiedName(Out);
Out << "' (";
Out << ClassNamesAndOffsets.size();
Out << (ClassNamesAndOffsets.size() == 1 ? " entry" : " entries") << ").\n";
for (const auto &I : ClassNamesAndOffsets)
Out << " " << I.first << " | " << I.second.getQuantity() << '\n';
Out << "\n";
}
if (!Thunks.empty()) {
// We store the method names in a map to get a stable order.
std::map<std::string, const CXXMethodDecl *> MethodNamesAndDecls;
for (const auto &I : Thunks) {
const CXXMethodDecl *MD = I.first;
std::string MethodName =
PredefinedExpr::ComputeName(PredefinedExpr::PrettyFunctionNoVirtual,
MD);
MethodNamesAndDecls.insert(std::make_pair(MethodName, MD));
}
for (const auto &I : MethodNamesAndDecls) {
const std::string &MethodName = I.first;
const CXXMethodDecl *MD = I.second;
ThunkInfoVectorTy ThunksVector = Thunks[MD];
llvm::sort(ThunksVector, [](const ThunkInfo &LHS, const ThunkInfo &RHS) {
assert(LHS.Method == nullptr && RHS.Method == nullptr);
return std::tie(LHS.This, LHS.Return) < std::tie(RHS.This, RHS.Return);
});
Out << "Thunks for '" << MethodName << "' (" << ThunksVector.size();
Out << (ThunksVector.size() == 1 ? " entry" : " entries") << ").\n";
for (unsigned I = 0, E = ThunksVector.size(); I != E; ++I) {
const ThunkInfo &Thunk = ThunksVector[I];
Out << llvm::format("%4d | ", I);
// If this function pointer has a return pointer adjustment, dump it.
if (!Thunk.Return.isEmpty()) {
Out << "return adjustment: " << Thunk.Return.NonVirtual;
Out << " non-virtual";
if (Thunk.Return.Virtual.Itanium.VBaseOffsetOffset) {
Out << ", " << Thunk.Return.Virtual.Itanium.VBaseOffsetOffset;
Out << " vbase offset offset";
}
if (!Thunk.This.isEmpty())
Out << "\n ";
}
// If this function pointer has a 'this' pointer adjustment, dump it.
if (!Thunk.This.isEmpty()) {
Out << "this adjustment: ";
Out << Thunk.This.NonVirtual << " non-virtual";
if (Thunk.This.Virtual.Itanium.VCallOffsetOffset) {
Out << ", " << Thunk.This.Virtual.Itanium.VCallOffsetOffset;
Out << " vcall offset offset";
}
}
Out << '\n';
}
Out << '\n';
}
}
// Compute the vtable indices for all the member functions.
// Store them in a map keyed by the index so we'll get a sorted table.
std::map<uint64_t, std::string> IndicesMap;
for (const auto *MD : MostDerivedClass->methods()) {
// We only want virtual member functions.
if (!ItaniumVTableContext::hasVtableSlot(MD))
continue;
MD = MD->getCanonicalDecl();
std::string MethodName =
PredefinedExpr::ComputeName(PredefinedExpr::PrettyFunctionNoVirtual,
MD);
if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
GlobalDecl GD(DD, Dtor_Complete);
assert(MethodVTableIndices.count(GD));
uint64_t VTableIndex = MethodVTableIndices[GD];
IndicesMap[VTableIndex] = MethodName + " [complete]";
IndicesMap[VTableIndex + 1] = MethodName + " [deleting]";
} else {
assert(MethodVTableIndices.count(MD));
IndicesMap[MethodVTableIndices[MD]] = MethodName;
}
}
// Print the vtable indices for all the member functions.
if (!IndicesMap.empty()) {
Out << "VTable indices for '";
MostDerivedClass->printQualifiedName(Out);
Out << "' (" << IndicesMap.size() << " entries).\n";
for (const auto &I : IndicesMap) {
uint64_t VTableIndex = I.first;
const std::string &MethodName = I.second;
Out << llvm::format("%4" PRIu64 " | ", VTableIndex) << MethodName
<< '\n';
}
}
Out << '\n';
}
}
static VTableLayout::AddressPointsIndexMapTy
MakeAddressPointIndices(const VTableLayout::AddressPointsMapTy &addressPoints,
unsigned numVTables) {
VTableLayout::AddressPointsIndexMapTy indexMap(numVTables);
for (auto it = addressPoints.begin(); it != addressPoints.end(); ++it) {
const auto &addressPointLoc = it->second;
unsigned vtableIndex = addressPointLoc.VTableIndex;
unsigned addressPoint = addressPointLoc.AddressPointIndex;
if (indexMap[vtableIndex]) {
// Multiple BaseSubobjects can map to the same AddressPointLocation, but
// every vtable index should have a unique address point.
assert(indexMap[vtableIndex] == addressPoint &&
"Every vtable index should have a unique address point. Found a "
"vtable that has two different address points.");
} else {
indexMap[vtableIndex] = addressPoint;
}
}
// Note that by this point, not all the address may be initialized if the
// AddressPoints map is empty. This is ok if the map isn't needed. See
// MicrosoftVTableContext::computeVTableRelatedInformation() which uses an
// emprt map.
return indexMap;
}
VTableLayout::VTableLayout(ArrayRef<size_t> VTableIndices,
ArrayRef<VTableComponent> VTableComponents,
ArrayRef<VTableThunkTy> VTableThunks,
const AddressPointsMapTy &AddressPoints)
: VTableComponents(VTableComponents), VTableThunks(VTableThunks),
AddressPoints(AddressPoints), AddressPointIndices(MakeAddressPointIndices(
AddressPoints, VTableIndices.size())) {
if (VTableIndices.size() <= 1)
assert(VTableIndices.size() == 1 && VTableIndices[0] == 0);
else
this->VTableIndices = OwningArrayRef<size_t>(VTableIndices);
llvm::sort(this->VTableThunks, [](const VTableLayout::VTableThunkTy &LHS,
const VTableLayout::VTableThunkTy &RHS) {
assert((LHS.first != RHS.first || LHS.second == RHS.second) &&
"Different thunks should have unique indices!");
return LHS.first < RHS.first;
});
}
VTableLayout::~VTableLayout() { }
bool VTableContextBase::hasVtableSlot(const CXXMethodDecl *MD) {
return MD->isVirtual() && !MD->isConsteval();
}
ItaniumVTableContext::ItaniumVTableContext(
ASTContext &Context, VTableComponentLayout ComponentLayout)
: VTableContextBase(/*MS=*/false), ComponentLayout(ComponentLayout) {}
ItaniumVTableContext::~ItaniumVTableContext() {}
uint64_t ItaniumVTableContext::getMethodVTableIndex(GlobalDecl GD) {
GD = GD.getCanonicalDecl();
MethodVTableIndicesTy::iterator I = MethodVTableIndices.find(GD);
if (I != MethodVTableIndices.end())
return I->second;
const CXXRecordDecl *RD = cast<CXXMethodDecl>(GD.getDecl())->getParent();
computeVTableRelatedInformation(RD);
I = MethodVTableIndices.find(GD);
assert(I != MethodVTableIndices.end() && "Did not find index!");
return I->second;
}
CharUnits
ItaniumVTableContext::getVirtualBaseOffsetOffset(const CXXRecordDecl *RD,
const CXXRecordDecl *VBase) {
ClassPairTy ClassPair(RD, VBase);
VirtualBaseClassOffsetOffsetsMapTy::iterator I =
VirtualBaseClassOffsetOffsets.find(ClassPair);
if (I != VirtualBaseClassOffsetOffsets.end())
return I->second;
VCallAndVBaseOffsetBuilder Builder(*this, RD, RD, /*Overriders=*/nullptr,
BaseSubobject(RD, CharUnits::Zero()),
/*BaseIsVirtual=*/false,
/*OffsetInLayoutClass=*/CharUnits::Zero());
for (const auto &I : Builder.getVBaseOffsetOffsets()) {
// Insert all types.
ClassPairTy ClassPair(RD, I.first);
VirtualBaseClassOffsetOffsets.insert(std::make_pair(ClassPair, I.second));
}
I = VirtualBaseClassOffsetOffsets.find(ClassPair);
assert(I != VirtualBaseClassOffsetOffsets.end() && "Did not find index!");
return I->second;
}
static std::unique_ptr<VTableLayout>
CreateVTableLayout(const ItaniumVTableBuilder &Builder) {
SmallVector<VTableLayout::VTableThunkTy, 1>
VTableThunks(Builder.vtable_thunks_begin(), Builder.vtable_thunks_end());
return std::make_unique<VTableLayout>(
Builder.VTableIndices, Builder.vtable_components(), VTableThunks,
Builder.getAddressPoints());
}
void
ItaniumVTableContext::computeVTableRelatedInformation(const CXXRecordDecl *RD) {
std::unique_ptr<const VTableLayout> &Entry = VTableLayouts[RD];
// Check if we've computed this information before.
if (Entry)
return;
ItaniumVTableBuilder Builder(*this, RD, CharUnits::Zero(),
/*MostDerivedClassIsVirtual=*/0, RD);
Entry = CreateVTableLayout(Builder);
MethodVTableIndices.insert(Builder.vtable_indices_begin(),
Builder.vtable_indices_end());
// Add the known thunks.
Thunks.insert(Builder.thunks_begin(), Builder.thunks_end());
// If we don't have the vbase information for this class, insert it.
// getVirtualBaseOffsetOffset will compute it separately without computing
// the rest of the vtable related information.
if (!RD->getNumVBases())
return;
const CXXRecordDecl *VBase =
RD->vbases_begin()->getType()->getAsCXXRecordDecl();
if (VirtualBaseClassOffsetOffsets.count(std::make_pair(RD, VBase)))
return;
for (const auto &I : Builder.getVBaseOffsetOffsets()) {
// Insert all types.
ClassPairTy ClassPair(RD, I.first);
VirtualBaseClassOffsetOffsets.insert(std::make_pair(ClassPair, I.second));
}
}
std::unique_ptr<VTableLayout>
ItaniumVTableContext::createConstructionVTableLayout(
const CXXRecordDecl *MostDerivedClass, CharUnits MostDerivedClassOffset,
bool MostDerivedClassIsVirtual, const CXXRecordDecl *LayoutClass) {
ItaniumVTableBuilder Builder(*this, MostDerivedClass, MostDerivedClassOffset,
MostDerivedClassIsVirtual, LayoutClass);
return CreateVTableLayout(Builder);
}
namespace {
// Vtables in the Microsoft ABI are different from the Itanium ABI.
//
// The main differences are:
// 1. Separate vftable and vbtable.
//
// 2. Each subobject with a vfptr gets its own vftable rather than an address
// point in a single vtable shared between all the subobjects.
// Each vftable is represented by a separate section and virtual calls
// must be done using the vftable which has a slot for the function to be
// called.
//
// 3. Virtual method definitions expect their 'this' parameter to point to the
// first vfptr whose table provides a compatible overridden method. In many
// cases, this permits the original vf-table entry to directly call
// the method instead of passing through a thunk.
// See example before VFTableBuilder::ComputeThisOffset below.
//
// A compatible overridden method is one which does not have a non-trivial
// covariant-return adjustment.
//
// The first vfptr is the one with the lowest offset in the complete-object
// layout of the defining class, and the method definition will subtract
// that constant offset from the parameter value to get the real 'this'
// value. Therefore, if the offset isn't really constant (e.g. if a virtual
// function defined in a virtual base is overridden in a more derived
// virtual base and these bases have a reverse order in the complete
// object), the vf-table may require a this-adjustment thunk.
//
// 4. vftables do not contain new entries for overrides that merely require
// this-adjustment. Together with #3, this keeps vf-tables smaller and
// eliminates the need for this-adjustment thunks in many cases, at the cost
// of often requiring redundant work to adjust the "this" pointer.
//
// 5. Instead of VTT and constructor vtables, vbtables and vtordisps are used.
// Vtordisps are emitted into the class layout if a class has
// a) a user-defined ctor/dtor
// and
// b) a method overriding a method in a virtual base.
//
// To get a better understanding of this code,
// you might want to see examples in test/CodeGenCXX/microsoft-abi-vtables-*.cpp
class VFTableBuilder {
public:
typedef llvm::DenseMap<GlobalDecl, MethodVFTableLocation>
MethodVFTableLocationsTy;
typedef llvm::iterator_range<MethodVFTableLocationsTy::const_iterator>
method_locations_range;
private:
/// VTables - Global vtable information.
MicrosoftVTableContext &VTables;
/// Context - The ASTContext which we will use for layout information.
ASTContext &Context;
/// MostDerivedClass - The most derived class for which we're building this
/// vtable.
const CXXRecordDecl *MostDerivedClass;
const ASTRecordLayout &MostDerivedClassLayout;
const VPtrInfo &WhichVFPtr;
/// FinalOverriders - The final overriders of the most derived class.
const FinalOverriders Overriders;
/// Components - The components of the vftable being built.
SmallVector<VTableComponent, 64> Components;
MethodVFTableLocationsTy MethodVFTableLocations;
/// Does this class have an RTTI component?
bool HasRTTIComponent = false;
/// MethodInfo - Contains information about a method in a vtable.
/// (Used for computing 'this' pointer adjustment thunks.
struct MethodInfo {
/// VBTableIndex - The nonzero index in the vbtable that
/// this method's base has, or zero.
const uint64_t VBTableIndex;
/// VFTableIndex - The index in the vftable that this method has.
const uint64_t VFTableIndex;
/// Shadowed - Indicates if this vftable slot is shadowed by
/// a slot for a covariant-return override. If so, it shouldn't be printed
/// or used for vcalls in the most derived class.
bool Shadowed;
/// UsesExtraSlot - Indicates if this vftable slot was created because
/// any of the overridden slots required a return adjusting thunk.
bool UsesExtraSlot;
MethodInfo(uint64_t VBTableIndex, uint64_t VFTableIndex,
bool UsesExtraSlot = false)
: VBTableIndex(VBTableIndex), VFTableIndex(VFTableIndex),
Shadowed(false), UsesExtraSlot(UsesExtraSlot) {}
MethodInfo()
: VBTableIndex(0), VFTableIndex(0), Shadowed(false),
UsesExtraSlot(false) {}
};
typedef llvm::DenseMap<const CXXMethodDecl *, MethodInfo> MethodInfoMapTy;
/// MethodInfoMap - The information for all methods in the vftable we're
/// currently building.
MethodInfoMapTy MethodInfoMap;
typedef llvm::DenseMap<uint64_t, ThunkInfo> VTableThunksMapTy;
/// VTableThunks - The thunks by vftable index in the vftable currently being
/// built.
VTableThunksMapTy VTableThunks;
typedef SmallVector<ThunkInfo, 1> ThunkInfoVectorTy;
typedef llvm::DenseMap<const CXXMethodDecl *, ThunkInfoVectorTy> ThunksMapTy;
/// Thunks - A map that contains all the thunks needed for all methods in the
/// most derived class for which the vftable is currently being built.
ThunksMapTy Thunks;
/// AddThunk - Add a thunk for the given method.
void AddThunk(const CXXMethodDecl *MD, const ThunkInfo &Thunk) {
SmallVector<ThunkInfo, 1> &ThunksVector = Thunks[MD];
// Check if we have this thunk already.
if (llvm::is_contained(ThunksVector, Thunk))
return;
ThunksVector.push_back(Thunk);
}
/// ComputeThisOffset - Returns the 'this' argument offset for the given
/// method, relative to the beginning of the MostDerivedClass.
CharUnits ComputeThisOffset(FinalOverriders::OverriderInfo Overrider);
void CalculateVtordispAdjustment(FinalOverriders::OverriderInfo Overrider,
CharUnits ThisOffset, ThisAdjustment &TA);
/// AddMethod - Add a single virtual member function to the vftable
/// components vector.
void AddMethod(const CXXMethodDecl *MD, ThunkInfo TI) {
if (!TI.isEmpty()) {
VTableThunks[Components.size()] = TI;
AddThunk(MD, TI);
}
if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
assert(TI.Return.isEmpty() &&
"Destructor can't have return adjustment!");
Components.push_back(VTableComponent::MakeDeletingDtor(DD));
} else {
Components.push_back(VTableComponent::MakeFunction(MD));
}
}
/// AddMethods - Add the methods of this base subobject and the relevant
/// subbases to the vftable we're currently laying out.
void AddMethods(BaseSubobject Base, unsigned BaseDepth,
const CXXRecordDecl *LastVBase,
BasesSetVectorTy &VisitedBases);
void LayoutVFTable() {
// RTTI data goes before all other entries.
if (HasRTTIComponent)
Components.push_back(VTableComponent::MakeRTTI(MostDerivedClass));
BasesSetVectorTy VisitedBases;
AddMethods(BaseSubobject(MostDerivedClass, CharUnits::Zero()), 0, nullptr,
VisitedBases);
// Note that it is possible for the vftable to contain only an RTTI
// pointer, if all virtual functions are constewval.
assert(!Components.empty() && "vftable can't be empty");
assert(MethodVFTableLocations.empty());
for (const auto &I : MethodInfoMap) {
const CXXMethodDecl *MD = I.first;
const MethodInfo &MI = I.second;
assert(MD == MD->getCanonicalDecl());
// Skip the methods that the MostDerivedClass didn't override
// and the entries shadowed by return adjusting thunks.
if (MD->getParent() != MostDerivedClass || MI.Shadowed)
continue;
MethodVFTableLocation Loc(MI.VBTableIndex, WhichVFPtr.getVBaseWithVPtr(),
WhichVFPtr.NonVirtualOffset, MI.VFTableIndex);
if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) {
MethodVFTableLocations[GlobalDecl(DD, Dtor_Deleting)] = Loc;
} else {
MethodVFTableLocations[MD] = Loc;
}
}
}
public:
VFTableBuilder(MicrosoftVTableContext &VTables,
const CXXRecordDecl *MostDerivedClass, const VPtrInfo &Which)
: VTables(VTables),
Context(MostDerivedClass->getASTContext()),
MostDerivedClass(MostDerivedClass),
MostDerivedClassLayout(Context.getASTRecordLayout(MostDerivedClass)),
WhichVFPtr(Which),
Overriders(MostDerivedClass, CharUnits(), MostDerivedClass) {
// Provide the RTTI component if RTTIData is enabled. If the vftable would
// be available externally, we should not provide the RTTI componenent. It
// is currently impossible to get available externally vftables with either
// dllimport or extern template instantiations, but eventually we may add a
// flag to support additional devirtualization that needs this.
if (Context.getLangOpts().RTTIData)
HasRTTIComponent = true;
LayoutVFTable();
if (Context.getLangOpts().DumpVTableLayouts)
dumpLayout(llvm::outs());
}
uint64_t getNumThunks() const { return Thunks.size(); }
ThunksMapTy::const_iterator thunks_begin() const { return Thunks.begin(); }
ThunksMapTy::const_iterator thunks_end() const { return Thunks.end(); }
method_locations_range vtable_locations() const {
return method_locations_range(MethodVFTableLocations.begin(),
MethodVFTableLocations.end());
}
ArrayRef<VTableComponent> vtable_components() const { return Components; }
VTableThunksMapTy::const_iterator vtable_thunks_begin() const {
return VTableThunks.begin();
}
VTableThunksMapTy::const_iterator vtable_thunks_end() const {
return VTableThunks.end();
}
void dumpLayout(raw_ostream &);
};
} // end namespace
// Let's study one class hierarchy as an example:
// struct A {
// virtual void f();
// int x;
// };
//
// struct B : virtual A {
// virtual void f();
// };
//
// Record layouts:
// struct A:
// 0 | (A vftable pointer)
// 4 | int x
//
// struct B:
// 0 | (B vbtable pointer)
// 4 | struct A (virtual base)
// 4 | (A vftable pointer)
// 8 | int x
//
// Let's assume we have a pointer to the A part of an object of dynamic type B:
// B b;
// A *a = (A*)&b;
// a->f();
//
// In this hierarchy, f() belongs to the vftable of A, so B::f() expects
// "this" parameter to point at the A subobject, which is B+4.
// In the B::f() prologue, it adjusts "this" back to B by subtracting 4,
// performed as a *static* adjustment.
//
// Interesting thing happens when we alter the relative placement of A and B
// subobjects in a class:
// struct C : virtual B { };
//
// C c;
// A *a = (A*)&c;
// a->f();
//
// Respective record layout is:
// 0 | (C vbtable pointer)
// 4 | struct A (virtual base)
// 4 | (A vftable pointer)
// 8 | int x
// 12 | struct B (virtual base)
// 12 | (B vbtable pointer)
//
// The final overrider of f() in class C is still B::f(), so B+4 should be
// passed as "this" to that code. However, "a" points at B-8, so the respective
// vftable entry should hold a thunk that adds 12 to the "this" argument before
// performing a tail call to B::f().
//
// With this example in mind, we can now calculate the 'this' argument offset
// for the given method, relative to the beginning of the MostDerivedClass.
CharUnits
VFTableBuilder::ComputeThisOffset(FinalOverriders::OverriderInfo Overrider) {
BasesSetVectorTy Bases;
{
// Find the set of least derived bases that define the given method.
OverriddenMethodsSetTy VisitedOverriddenMethods;
auto InitialOverriddenDefinitionCollector = [&](
const CXXMethodDecl *OverriddenMD) {
if (OverriddenMD->size_overridden_methods() == 0)
Bases.insert(OverriddenMD->getParent());
// Don't recurse on this method if we've already collected it.
return VisitedOverriddenMethods.insert(OverriddenMD).second;
};
visitAllOverriddenMethods(Overrider.Method,
InitialOverriddenDefinitionCollector);
}
// If there are no overrides then 'this' is located
// in the base that defines the method.
if (Bases.size() == 0)
return Overrider.Offset;
CXXBasePaths Paths;
Overrider.Method->getParent()->lookupInBases(
[&Bases](const CXXBaseSpecifier *Specifier, CXXBasePath &) {
return Bases.count(Specifier->getType()->getAsCXXRecordDecl());
},
Paths);
// This will hold the smallest this offset among overridees of MD.
// This implies that an offset of a non-virtual base will dominate an offset
// of a virtual base to potentially reduce the number of thunks required
// in the derived classes that inherit this method.
CharUnits Ret;
bool First = true;
const ASTRecordLayout &OverriderRDLayout =
Context.getASTRecordLayout(Overrider.Method->getParent());
for (const CXXBasePath &Path : Paths) {
CharUnits ThisOffset = Overrider.Offset;
CharUnits LastVBaseOffset;
// For each path from the overrider to the parents of the overridden
// methods, traverse the path, calculating the this offset in the most
// derived class.
for (const CXXBasePathElement &Element : Path) {
QualType CurTy = Element.Base->getType();
const CXXRecordDecl *PrevRD = Element.Class,
*CurRD = CurTy->getAsCXXRecordDecl();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(PrevRD);
if (Element.Base->isVirtual()) {
// The interesting things begin when you have virtual inheritance.
// The final overrider will use a static adjustment equal to the offset
// of the vbase in the final overrider class.
// For example, if the final overrider is in a vbase B of the most
// derived class and it overrides a method of the B's own vbase A,
// it uses A* as "this". In its prologue, it can cast A* to B* with
// a static offset. This offset is used regardless of the actual
// offset of A from B in the most derived class, requiring an
// this-adjusting thunk in the vftable if A and B are laid out
// differently in the most derived class.
LastVBaseOffset = ThisOffset =
Overrider.Offset + OverriderRDLayout.getVBaseClassOffset(CurRD);
} else {
ThisOffset += Layout.getBaseClassOffset(CurRD);
}
}
if (isa<CXXDestructorDecl>(Overrider.Method)) {
if (LastVBaseOffset.isZero()) {
// If a "Base" class has at least one non-virtual base with a virtual
// destructor, the "Base" virtual destructor will take the address
// of the "Base" subobject as the "this" argument.
ThisOffset = Overrider.Offset;
} else {
// A virtual destructor of a virtual base takes the address of the
// virtual base subobject as the "this" argument.
ThisOffset = LastVBaseOffset;
}
}
if (Ret > ThisOffset || First) {
First = false;
Ret = ThisOffset;
}
}
assert(!First && "Method not found in the given subobject?");
return Ret;
}
// Things are getting even more complex when the "this" adjustment has to
// use a dynamic offset instead of a static one, or even two dynamic offsets.
// This is sometimes required when a virtual call happens in the middle of
// a non-most-derived class construction or destruction.
//
// Let's take a look at the following example:
// struct A {
// virtual void f();
// };
//
// void foo(A *a) { a->f(); } // Knows nothing about siblings of A.
//
// struct B : virtual A {
// virtual void f();
// B() {
// foo(this);
// }
// };
//
// struct C : virtual B {
// virtual void f();
// };
//
// Record layouts for these classes are:
// struct A
// 0 | (A vftable pointer)
//
// struct B
// 0 | (B vbtable pointer)
// 4 | (vtordisp for vbase A)
// 8 | struct A (virtual base)
// 8 | (A vftable pointer)
//
// struct C
// 0 | (C vbtable pointer)
// 4 | (vtordisp for vbase A)
// 8 | struct A (virtual base) // A precedes B!
// 8 | (A vftable pointer)
// 12 | struct B (virtual base)
// 12 | (B vbtable pointer)
//
// When one creates an object of type C, the C constructor:
// - initializes all the vbptrs, then
// - calls the A subobject constructor
// (initializes A's vfptr with an address of A vftable), then
// - calls the B subobject constructor
// (initializes A's vfptr with an address of B vftable and vtordisp for A),
// that in turn calls foo(), then
// - initializes A's vfptr with an address of C vftable and zeroes out the
// vtordisp
// FIXME: if a structor knows it belongs to MDC, why doesn't it use a vftable
// without vtordisp thunks?
// FIXME: how are vtordisp handled in the presence of nooverride/final?
//
// When foo() is called, an object with a layout of class C has a vftable
// referencing B::f() that assumes a B layout, so the "this" adjustments are
// incorrect, unless an extra adjustment is done. This adjustment is called
// "vtordisp adjustment". Vtordisp basically holds the difference between the
// actual location of a vbase in the layout class and the location assumed by
// the vftable of the class being constructed/destructed. Vtordisp is only
// needed if "this" escapes a
// structor (or we can't prove otherwise).
// [i.e. vtordisp is a dynamic adjustment for a static adjustment, which is an
// estimation of a dynamic adjustment]
//
// foo() gets a pointer to the A vbase and doesn't know anything about B or C,
// so it just passes that pointer as "this" in a virtual call.
// If there was no vtordisp, that would just dispatch to B::f().
// However, B::f() assumes B+8 is passed as "this",
// yet the pointer foo() passes along is B-4 (i.e. C+8).
// An extra adjustment is needed, so we emit a thunk into the B vftable.
// This vtordisp thunk subtracts the value of vtordisp
// from the "this" argument (-12) before making a tailcall to B::f().
//
// Let's consider an even more complex example:
// struct D : virtual B, virtual C {
// D() {
// foo(this);
// }
// };
//
// struct D
// 0 | (D vbtable pointer)
// 4 | (vtordisp for vbase A)
// 8 | struct A (virtual base) // A precedes both B and C!
// 8 | (A vftable pointer)
// 12 | struct B (virtual base) // B precedes C!
// 12 | (B vbtable pointer)
// 16 | struct C (virtual base)
// 16 | (C vbtable pointer)
//
// When D::D() calls foo(), we find ourselves in a thunk that should tailcall
// to C::f(), which assumes C+8 as its "this" parameter. This time, foo()
// passes along A, which is C-8. The A vtordisp holds
// "D.vbptr[index_of_A] - offset_of_A_in_D"
// and we statically know offset_of_A_in_D, so can get a pointer to D.
// When we know it, we can make an extra vbtable lookup to locate the C vbase
// and one extra static adjustment to calculate the expected value of C+8.
void VFTableBuilder::CalculateVtordispAdjustment(
FinalOverriders::OverriderInfo Overrider, CharUnits ThisOffset,
ThisAdjustment &TA) {
const ASTRecordLayout::VBaseOffsetsMapTy &VBaseMap =
MostDerivedClassLayout.getVBaseOffsetsMap();
const ASTRecordLayout::VBaseOffsetsMapTy::const_iterator &VBaseMapEntry =
VBaseMap.find(WhichVFPtr.getVBaseWithVPtr());
assert(VBaseMapEntry != VBaseMap.end());
// If there's no vtordisp or the final overrider is defined in the same vbase
// as the initial declaration, we don't need any vtordisp adjustment.
if (!VBaseMapEntry->second.hasVtorDisp() ||
Overrider.VirtualBase == WhichVFPtr.getVBaseWithVPtr())
return;
// OK, now we know we need to use a vtordisp thunk.
// The implicit vtordisp field is located right before the vbase.
CharUnits OffsetOfVBaseWithVFPtr = VBaseMapEntry->second.VBaseOffset;
TA.Virtual.Microsoft.VtordispOffset =
(OffsetOfVBaseWithVFPtr - WhichVFPtr.FullOffsetInMDC).getQuantity() - 4;
// A simple vtordisp thunk will suffice if the final overrider is defined
// in either the most derived class or its non-virtual base.
if (Overrider.Method->getParent() == MostDerivedClass ||
!Overrider.VirtualBase)
return;
// Otherwise, we need to do use the dynamic offset of the final overrider
// in order to get "this" adjustment right.
TA.Virtual.Microsoft.VBPtrOffset =
(OffsetOfVBaseWithVFPtr + WhichVFPtr.NonVirtualOffset -
MostDerivedClassLayout.getVBPtrOffset()).getQuantity();
TA.Virtual.Microsoft.VBOffsetOffset =
Context.getTypeSizeInChars(Context.IntTy).getQuantity() *
VTables.getVBTableIndex(MostDerivedClass, Overrider.VirtualBase);
TA.NonVirtual = (ThisOffset - Overrider.Offset).getQuantity();
}
static void GroupNewVirtualOverloads(
const CXXRecordDecl *RD,
SmallVector<const CXXMethodDecl *, 10> &VirtualMethods) {
// Put the virtual methods into VirtualMethods in the proper order:
// 1) Group overloads by declaration name. New groups are added to the
// vftable in the order of their first declarations in this class
// (including overrides, non-virtual methods and any other named decl that
// might be nested within the class).
// 2) In each group, new overloads appear in the reverse order of declaration.
typedef SmallVector<const CXXMethodDecl *, 1> MethodGroup;
SmallVector<MethodGroup, 10> Groups;
typedef llvm::DenseMap<DeclarationName, unsigned> VisitedGroupIndicesTy;
VisitedGroupIndicesTy VisitedGroupIndices;
for (const auto *D : RD->decls()) {
const auto *ND = dyn_cast<NamedDecl>(D);
if (!ND)
continue;
VisitedGroupIndicesTy::iterator J;
bool Inserted;
std::tie(J, Inserted) = VisitedGroupIndices.insert(
std::make_pair(ND->getDeclName(), Groups.size()));
if (Inserted)
Groups.push_back(MethodGroup());
if (const auto *MD = dyn_cast<CXXMethodDecl>(ND))
if (MicrosoftVTableContext::hasVtableSlot(MD))
Groups[J->second].push_back(MD->getCanonicalDecl());
}
for (const MethodGroup &Group : Groups)
VirtualMethods.append(Group.rbegin(), Group.rend());
}
static bool isDirectVBase(const CXXRecordDecl *Base, const CXXRecordDecl *RD) {
for (const auto &B : RD->bases()) {
if (B.isVirtual() && B.getType()->getAsCXXRecordDecl() == Base)
return true;
}
return false;
}