blob: cf981be0a4dde5b1bbd045bd2e43716dc8e592f7 [file] [log] [blame]
//=== RecordLayoutBuilder.cpp - Helper class for building record layouts ---==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "clang/AST/RecordLayout.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/CXXInheritance.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/Expr.h"
#include "clang/Basic/TargetInfo.h"
#include "clang/Sema/SemaDiagnostic.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/MathExtras.h"
using namespace clang;
namespace {
/// BaseSubobjectInfo - Represents a single base subobject in a complete class.
/// For a class hierarchy like
///
/// class A { };
/// class B : A { };
/// class C : A, B { };
///
/// The BaseSubobjectInfo graph for C will have three BaseSubobjectInfo
/// instances, one for B and two for A.
///
/// If a base is virtual, it will only have one BaseSubobjectInfo allocated.
struct BaseSubobjectInfo {
/// Class - The class for this base info.
const CXXRecordDecl *Class;
/// IsVirtual - Whether the BaseInfo represents a virtual base or not.
bool IsVirtual;
/// Bases - Information about the base subobjects.
SmallVector<BaseSubobjectInfo*, 4> Bases;
/// PrimaryVirtualBaseInfo - Holds the base info for the primary virtual base
/// of this base info (if one exists).
BaseSubobjectInfo *PrimaryVirtualBaseInfo;
// FIXME: Document.
const BaseSubobjectInfo *Derived;
};
/// \brief Externally provided layout. Typically used when the AST source, such
/// as DWARF, lacks all the information that was available at compile time, such
/// as alignment attributes on fields and pragmas in effect.
struct ExternalLayout {
ExternalLayout() : Size(0), Align(0) {}
/// \brief Overall record size in bits.
uint64_t Size;
/// \brief Overall record alignment in bits.
uint64_t Align;
/// \brief Record field offsets in bits.
llvm::DenseMap<const FieldDecl *, uint64_t> FieldOffsets;
/// \brief Direct, non-virtual base offsets.
llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsets;
/// \brief Virtual base offsets.
llvm::DenseMap<const CXXRecordDecl *, CharUnits> VirtualBaseOffsets;
/// Get the offset of the given field. The external source must provide
/// entries for all fields in the record.
uint64_t getExternalFieldOffset(const FieldDecl *FD) {
assert(FieldOffsets.count(FD) &&
"Field does not have an external offset");
return FieldOffsets[FD];
}
bool getExternalNVBaseOffset(const CXXRecordDecl *RD, CharUnits &BaseOffset) {
auto Known = BaseOffsets.find(RD);
if (Known == BaseOffsets.end())
return false;
BaseOffset = Known->second;
return true;
}
bool getExternalVBaseOffset(const CXXRecordDecl *RD, CharUnits &BaseOffset) {
auto Known = VirtualBaseOffsets.find(RD);
if (Known == VirtualBaseOffsets.end())
return false;
BaseOffset = Known->second;
return true;
}
};
/// EmptySubobjectMap - Keeps track of which empty subobjects exist at different
/// offsets while laying out a C++ class.
class EmptySubobjectMap {
const ASTContext &Context;
uint64_t CharWidth;
/// Class - The class whose empty entries we're keeping track of.
const CXXRecordDecl *Class;
/// EmptyClassOffsets - A map from offsets to empty record decls.
typedef llvm::TinyPtrVector<const CXXRecordDecl *> ClassVectorTy;
typedef llvm::DenseMap<CharUnits, ClassVectorTy> EmptyClassOffsetsMapTy;
EmptyClassOffsetsMapTy EmptyClassOffsets;
/// MaxEmptyClassOffset - The highest offset known to contain an empty
/// base subobject.
CharUnits MaxEmptyClassOffset;
/// ComputeEmptySubobjectSizes - Compute the size of the largest base or
/// member subobject that is empty.
void ComputeEmptySubobjectSizes();
void AddSubobjectAtOffset(const CXXRecordDecl *RD, CharUnits Offset);
void UpdateEmptyBaseSubobjects(const BaseSubobjectInfo *Info,
CharUnits Offset, bool PlacingEmptyBase);
void UpdateEmptyFieldSubobjects(const CXXRecordDecl *RD,
const CXXRecordDecl *Class,
CharUnits Offset);
void UpdateEmptyFieldSubobjects(const FieldDecl *FD, CharUnits Offset);
/// AnyEmptySubobjectsBeyondOffset - Returns whether there are any empty
/// subobjects beyond the given offset.
bool AnyEmptySubobjectsBeyondOffset(CharUnits Offset) const {
return Offset <= MaxEmptyClassOffset;
}
CharUnits
getFieldOffset(const ASTRecordLayout &Layout, unsigned FieldNo) const {
uint64_t FieldOffset = Layout.getFieldOffset(FieldNo);
assert(FieldOffset % CharWidth == 0 &&
"Field offset not at char boundary!");
return Context.toCharUnitsFromBits(FieldOffset);
}
protected:
bool CanPlaceSubobjectAtOffset(const CXXRecordDecl *RD,
CharUnits Offset) const;
bool CanPlaceBaseSubobjectAtOffset(const BaseSubobjectInfo *Info,
CharUnits Offset);
bool CanPlaceFieldSubobjectAtOffset(const CXXRecordDecl *RD,
const CXXRecordDecl *Class,
CharUnits Offset) const;
bool CanPlaceFieldSubobjectAtOffset(const FieldDecl *FD,
CharUnits Offset) const;
public:
/// This holds the size of the largest empty subobject (either a base
/// or a member). Will be zero if the record being built doesn't contain
/// any empty classes.
CharUnits SizeOfLargestEmptySubobject;
EmptySubobjectMap(const ASTContext &Context, const CXXRecordDecl *Class)
: Context(Context), CharWidth(Context.getCharWidth()), Class(Class) {
ComputeEmptySubobjectSizes();
}
/// CanPlaceBaseAtOffset - Return whether the given base class can be placed
/// at the given offset.
/// Returns false if placing the record will result in two components
/// (direct or indirect) of the same type having the same offset.
bool CanPlaceBaseAtOffset(const BaseSubobjectInfo *Info,
CharUnits Offset);
/// CanPlaceFieldAtOffset - Return whether a field can be placed at the given
/// offset.
bool CanPlaceFieldAtOffset(const FieldDecl *FD, CharUnits Offset);
};
void EmptySubobjectMap::ComputeEmptySubobjectSizes() {
// Check the bases.
for (const CXXBaseSpecifier &Base : Class->bases()) {
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
CharUnits EmptySize;
const ASTRecordLayout &Layout = Context.getASTRecordLayout(BaseDecl);
if (BaseDecl->isEmpty()) {
// If the class decl is empty, get its size.
EmptySize = Layout.getSize();
} else {
// Otherwise, we get the largest empty subobject for the decl.
EmptySize = Layout.getSizeOfLargestEmptySubobject();
}
if (EmptySize > SizeOfLargestEmptySubobject)
SizeOfLargestEmptySubobject = EmptySize;
}
// Check the fields.
for (const FieldDecl *FD : Class->fields()) {
const RecordType *RT =
Context.getBaseElementType(FD->getType())->getAs<RecordType>();
// We only care about record types.
if (!RT)
continue;
CharUnits EmptySize;
const CXXRecordDecl *MemberDecl = RT->getAsCXXRecordDecl();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(MemberDecl);
if (MemberDecl->isEmpty()) {
// If the class decl is empty, get its size.
EmptySize = Layout.getSize();
} else {
// Otherwise, we get the largest empty subobject for the decl.
EmptySize = Layout.getSizeOfLargestEmptySubobject();
}
if (EmptySize > SizeOfLargestEmptySubobject)
SizeOfLargestEmptySubobject = EmptySize;
}
}
bool
EmptySubobjectMap::CanPlaceSubobjectAtOffset(const CXXRecordDecl *RD,
CharUnits Offset) const {
// We only need to check empty bases.
if (!RD->isEmpty())
return true;
EmptyClassOffsetsMapTy::const_iterator I = EmptyClassOffsets.find(Offset);
if (I == EmptyClassOffsets.end())
return true;
const ClassVectorTy &Classes = I->second;
if (std::find(Classes.begin(), Classes.end(), RD) == Classes.end())
return true;
// There is already an empty class of the same type at this offset.
return false;
}
void EmptySubobjectMap::AddSubobjectAtOffset(const CXXRecordDecl *RD,
CharUnits Offset) {
// We only care about empty bases.
if (!RD->isEmpty())
return;
// If we have empty structures inside a union, we can assign both
// the same offset. Just avoid pushing them twice in the list.
ClassVectorTy &Classes = EmptyClassOffsets[Offset];
if (std::find(Classes.begin(), Classes.end(), RD) != Classes.end())
return;
Classes.push_back(RD);
// Update the empty class offset.
if (Offset > MaxEmptyClassOffset)
MaxEmptyClassOffset = Offset;
}
bool
EmptySubobjectMap::CanPlaceBaseSubobjectAtOffset(const BaseSubobjectInfo *Info,
CharUnits Offset) {
// We don't have to keep looking past the maximum offset that's known to
// contain an empty class.
if (!AnyEmptySubobjectsBeyondOffset(Offset))
return true;
if (!CanPlaceSubobjectAtOffset(Info->Class, Offset))
return false;
// Traverse all non-virtual bases.
const ASTRecordLayout &Layout = Context.getASTRecordLayout(Info->Class);
for (const BaseSubobjectInfo *Base : Info->Bases) {
if (Base->IsVirtual)
continue;
CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base->Class);
if (!CanPlaceBaseSubobjectAtOffset(Base, BaseOffset))
return false;
}
if (Info->PrimaryVirtualBaseInfo) {
BaseSubobjectInfo *PrimaryVirtualBaseInfo = Info->PrimaryVirtualBaseInfo;
if (Info == PrimaryVirtualBaseInfo->Derived) {
if (!CanPlaceBaseSubobjectAtOffset(PrimaryVirtualBaseInfo, Offset))
return false;
}
}
// Traverse all member variables.
unsigned FieldNo = 0;
for (CXXRecordDecl::field_iterator I = Info->Class->field_begin(),
E = Info->Class->field_end(); I != E; ++I, ++FieldNo) {
if (I->isBitField())
continue;
CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
if (!CanPlaceFieldSubobjectAtOffset(*I, FieldOffset))
return false;
}
return true;
}
void EmptySubobjectMap::UpdateEmptyBaseSubobjects(const BaseSubobjectInfo *Info,
CharUnits Offset,
bool PlacingEmptyBase) {
if (!PlacingEmptyBase && Offset >= SizeOfLargestEmptySubobject) {
// We know that the only empty subobjects that can conflict with empty
// subobject of non-empty bases, are empty bases that can be placed at
// offset zero. Because of this, we only need to keep track of empty base
// subobjects with offsets less than the size of the largest empty
// subobject for our class.
return;
}
AddSubobjectAtOffset(Info->Class, Offset);
// Traverse all non-virtual bases.
const ASTRecordLayout &Layout = Context.getASTRecordLayout(Info->Class);
for (const BaseSubobjectInfo *Base : Info->Bases) {
if (Base->IsVirtual)
continue;
CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base->Class);
UpdateEmptyBaseSubobjects(Base, BaseOffset, PlacingEmptyBase);
}
if (Info->PrimaryVirtualBaseInfo) {
BaseSubobjectInfo *PrimaryVirtualBaseInfo = Info->PrimaryVirtualBaseInfo;
if (Info == PrimaryVirtualBaseInfo->Derived)
UpdateEmptyBaseSubobjects(PrimaryVirtualBaseInfo, Offset,
PlacingEmptyBase);
}
// Traverse all member variables.
unsigned FieldNo = 0;
for (CXXRecordDecl::field_iterator I = Info->Class->field_begin(),
E = Info->Class->field_end(); I != E; ++I, ++FieldNo) {
if (I->isBitField())
continue;
CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
UpdateEmptyFieldSubobjects(*I, FieldOffset);
}
}
bool EmptySubobjectMap::CanPlaceBaseAtOffset(const BaseSubobjectInfo *Info,
CharUnits Offset) {
// If we know this class doesn't have any empty subobjects we don't need to
// bother checking.
if (SizeOfLargestEmptySubobject.isZero())
return true;
if (!CanPlaceBaseSubobjectAtOffset(Info, Offset))
return false;
// We are able to place the base at this offset. Make sure to update the
// empty base subobject map.
UpdateEmptyBaseSubobjects(Info, Offset, Info->Class->isEmpty());
return true;
}
bool
EmptySubobjectMap::CanPlaceFieldSubobjectAtOffset(const CXXRecordDecl *RD,
const CXXRecordDecl *Class,
CharUnits Offset) const {
// We don't have to keep looking past the maximum offset that's known to
// contain an empty class.
if (!AnyEmptySubobjectsBeyondOffset(Offset))
return true;
if (!CanPlaceSubobjectAtOffset(RD, Offset))
return false;
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
// Traverse all non-virtual bases.
for (const CXXBaseSpecifier &Base : RD->bases()) {
if (Base.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(BaseDecl);
if (!CanPlaceFieldSubobjectAtOffset(BaseDecl, Class, BaseOffset))
return false;
}
if (RD == Class) {
// This is the most derived class, traverse virtual bases as well.
for (const CXXBaseSpecifier &Base : RD->vbases()) {
const CXXRecordDecl *VBaseDecl = Base.getType()->getAsCXXRecordDecl();
CharUnits VBaseOffset = Offset + Layout.getVBaseClassOffset(VBaseDecl);
if (!CanPlaceFieldSubobjectAtOffset(VBaseDecl, Class, VBaseOffset))
return false;
}
}
// Traverse all member variables.
unsigned FieldNo = 0;
for (CXXRecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
I != E; ++I, ++FieldNo) {
if (I->isBitField())
continue;
CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
if (!CanPlaceFieldSubobjectAtOffset(*I, FieldOffset))
return false;
}
return true;
}
bool
EmptySubobjectMap::CanPlaceFieldSubobjectAtOffset(const FieldDecl *FD,
CharUnits Offset) const {
// We don't have to keep looking past the maximum offset that's known to
// contain an empty class.
if (!AnyEmptySubobjectsBeyondOffset(Offset))
return true;
QualType T = FD->getType();
if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl())
return CanPlaceFieldSubobjectAtOffset(RD, RD, Offset);
// If we have an array type we need to look at every element.
if (const ConstantArrayType *AT = Context.getAsConstantArrayType(T)) {
QualType ElemTy = Context.getBaseElementType(AT);
const RecordType *RT = ElemTy->getAs<RecordType>();
if (!RT)
return true;
const CXXRecordDecl *RD = RT->getAsCXXRecordDecl();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
uint64_t NumElements = Context.getConstantArrayElementCount(AT);
CharUnits ElementOffset = Offset;
for (uint64_t I = 0; I != NumElements; ++I) {
// We don't have to keep looking past the maximum offset that's known to
// contain an empty class.
if (!AnyEmptySubobjectsBeyondOffset(ElementOffset))
return true;
if (!CanPlaceFieldSubobjectAtOffset(RD, RD, ElementOffset))
return false;
ElementOffset += Layout.getSize();
}
}
return true;
}
bool
EmptySubobjectMap::CanPlaceFieldAtOffset(const FieldDecl *FD,
CharUnits Offset) {
if (!CanPlaceFieldSubobjectAtOffset(FD, Offset))
return false;
// We are able to place the member variable at this offset.
// Make sure to update the empty base subobject map.
UpdateEmptyFieldSubobjects(FD, Offset);
return true;
}
void EmptySubobjectMap::UpdateEmptyFieldSubobjects(const CXXRecordDecl *RD,
const CXXRecordDecl *Class,
CharUnits Offset) {
// We know that the only empty subobjects that can conflict with empty
// field subobjects are subobjects of empty bases that can be placed at offset
// zero. Because of this, we only need to keep track of empty field
// subobjects with offsets less than the size of the largest empty
// subobject for our class.
if (Offset >= SizeOfLargestEmptySubobject)
return;
AddSubobjectAtOffset(RD, Offset);
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
// Traverse all non-virtual bases.
for (const CXXBaseSpecifier &Base : RD->bases()) {
if (Base.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(BaseDecl);
UpdateEmptyFieldSubobjects(BaseDecl, Class, BaseOffset);
}
if (RD == Class) {
// This is the most derived class, traverse virtual bases as well.
for (const CXXBaseSpecifier &Base : RD->vbases()) {
const CXXRecordDecl *VBaseDecl = Base.getType()->getAsCXXRecordDecl();
CharUnits VBaseOffset = Offset + Layout.getVBaseClassOffset(VBaseDecl);
UpdateEmptyFieldSubobjects(VBaseDecl, Class, VBaseOffset);
}
}
// Traverse all member variables.
unsigned FieldNo = 0;
for (CXXRecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
I != E; ++I, ++FieldNo) {
if (I->isBitField())
continue;
CharUnits FieldOffset = Offset + getFieldOffset(Layout, FieldNo);
UpdateEmptyFieldSubobjects(*I, FieldOffset);
}
}
void EmptySubobjectMap::UpdateEmptyFieldSubobjects(const FieldDecl *FD,
CharUnits Offset) {
QualType T = FD->getType();
if (const CXXRecordDecl *RD = T->getAsCXXRecordDecl()) {
UpdateEmptyFieldSubobjects(RD, RD, Offset);
return;
}
// If we have an array type we need to update every element.
if (const ConstantArrayType *AT = Context.getAsConstantArrayType(T)) {
QualType ElemTy = Context.getBaseElementType(AT);
const RecordType *RT = ElemTy->getAs<RecordType>();
if (!RT)
return;
const CXXRecordDecl *RD = RT->getAsCXXRecordDecl();
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
uint64_t NumElements = Context.getConstantArrayElementCount(AT);
CharUnits ElementOffset = Offset;
for (uint64_t I = 0; I != NumElements; ++I) {
// We know that the only empty subobjects that can conflict with empty
// field subobjects are subobjects of empty bases that can be placed at
// offset zero. Because of this, we only need to keep track of empty field
// subobjects with offsets less than the size of the largest empty
// subobject for our class.
if (ElementOffset >= SizeOfLargestEmptySubobject)
return;
UpdateEmptyFieldSubobjects(RD, RD, ElementOffset);
ElementOffset += Layout.getSize();
}
}
}
typedef llvm::SmallPtrSet<const CXXRecordDecl*, 4> ClassSetTy;
class ItaniumRecordLayoutBuilder {
protected:
// FIXME: Remove this and make the appropriate fields public.
friend class clang::ASTContext;
const ASTContext &Context;
EmptySubobjectMap *EmptySubobjects;
/// Size - The current size of the record layout.
uint64_t Size;
/// Alignment - The current alignment of the record layout.
CharUnits Alignment;
/// \brief The alignment if attribute packed is not used.
CharUnits UnpackedAlignment;
SmallVector<uint64_t, 16> FieldOffsets;
/// \brief Whether the external AST source has provided a layout for this
/// record.
unsigned UseExternalLayout : 1;
/// \brief Whether we need to infer alignment, even when we have an
/// externally-provided layout.
unsigned InferAlignment : 1;
/// Packed - Whether the record is packed or not.
unsigned Packed : 1;
unsigned IsUnion : 1;
unsigned IsMac68kAlign : 1;
unsigned IsMsStruct : 1;
/// UnfilledBitsInLastUnit - If the last field laid out was a bitfield,
/// this contains the number of bits in the last unit that can be used for
/// an adjacent bitfield if necessary. The unit in question is usually
/// a byte, but larger units are used if IsMsStruct.
unsigned char UnfilledBitsInLastUnit;
/// LastBitfieldTypeSize - If IsMsStruct, represents the size of the type
/// of the previous field if it was a bitfield.
unsigned char LastBitfieldTypeSize;
/// MaxFieldAlignment - The maximum allowed field alignment. This is set by
/// #pragma pack.
CharUnits MaxFieldAlignment;
/// DataSize - The data size of the record being laid out.
uint64_t DataSize;
CharUnits NonVirtualSize;
CharUnits NonVirtualAlignment;
/// PrimaryBase - the primary base class (if one exists) of the class
/// we're laying out.
const CXXRecordDecl *PrimaryBase;
/// PrimaryBaseIsVirtual - Whether the primary base of the class we're laying
/// out is virtual.
bool PrimaryBaseIsVirtual;
/// HasOwnVFPtr - Whether the class provides its own vtable/vftbl
/// pointer, as opposed to inheriting one from a primary base class.
bool HasOwnVFPtr;
typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsetsMapTy;
/// Bases - base classes and their offsets in the record.
BaseOffsetsMapTy Bases;
// VBases - virtual base classes and their offsets in the record.
ASTRecordLayout::VBaseOffsetsMapTy VBases;
/// IndirectPrimaryBases - Virtual base classes, direct or indirect, that are
/// primary base classes for some other direct or indirect base class.
CXXIndirectPrimaryBaseSet IndirectPrimaryBases;
/// FirstNearlyEmptyVBase - The first nearly empty virtual base class in
/// inheritance graph order. Used for determining the primary base class.
const CXXRecordDecl *FirstNearlyEmptyVBase;
/// VisitedVirtualBases - A set of all the visited virtual bases, used to
/// avoid visiting virtual bases more than once.
llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBases;
/// Valid if UseExternalLayout is true.
ExternalLayout External;
ItaniumRecordLayoutBuilder(const ASTContext &Context,
EmptySubobjectMap *EmptySubobjects)
: Context(Context), EmptySubobjects(EmptySubobjects), Size(0),
Alignment(CharUnits::One()), UnpackedAlignment(CharUnits::One()),
UseExternalLayout(false), InferAlignment(false), Packed(false),
IsUnion(false), IsMac68kAlign(false), IsMsStruct(false),
UnfilledBitsInLastUnit(0), LastBitfieldTypeSize(0),
MaxFieldAlignment(CharUnits::Zero()), DataSize(0),
NonVirtualSize(CharUnits::Zero()),
NonVirtualAlignment(CharUnits::One()), PrimaryBase(nullptr),
PrimaryBaseIsVirtual(false), HasOwnVFPtr(false),
FirstNearlyEmptyVBase(nullptr) {}
void Layout(const RecordDecl *D);
void Layout(const CXXRecordDecl *D);
void Layout(const ObjCInterfaceDecl *D);
void LayoutFields(const RecordDecl *D);
void LayoutField(const FieldDecl *D, bool InsertExtraPadding);
void LayoutWideBitField(uint64_t FieldSize, uint64_t TypeSize,
bool FieldPacked, const FieldDecl *D);
void LayoutBitField(const FieldDecl *D);
TargetCXXABI getCXXABI() const {
return Context.getTargetInfo().getCXXABI();
}
/// BaseSubobjectInfoAllocator - Allocator for BaseSubobjectInfo objects.
llvm::SpecificBumpPtrAllocator<BaseSubobjectInfo> BaseSubobjectInfoAllocator;
typedef llvm::DenseMap<const CXXRecordDecl *, BaseSubobjectInfo *>
BaseSubobjectInfoMapTy;
/// VirtualBaseInfo - Map from all the (direct or indirect) virtual bases
/// of the class we're laying out to their base subobject info.
BaseSubobjectInfoMapTy VirtualBaseInfo;
/// NonVirtualBaseInfo - Map from all the direct non-virtual bases of the
/// class we're laying out to their base subobject info.
BaseSubobjectInfoMapTy NonVirtualBaseInfo;
/// ComputeBaseSubobjectInfo - Compute the base subobject information for the
/// bases of the given class.
void ComputeBaseSubobjectInfo(const CXXRecordDecl *RD);
/// ComputeBaseSubobjectInfo - Compute the base subobject information for a
/// single class and all of its base classes.
BaseSubobjectInfo *ComputeBaseSubobjectInfo(const CXXRecordDecl *RD,
bool IsVirtual,
BaseSubobjectInfo *Derived);
/// DeterminePrimaryBase - Determine the primary base of the given class.
void DeterminePrimaryBase(const CXXRecordDecl *RD);
void SelectPrimaryVBase(const CXXRecordDecl *RD);
void EnsureVTablePointerAlignment(CharUnits UnpackedBaseAlign);
/// LayoutNonVirtualBases - Determines the primary base class (if any) and
/// lays it out. Will then proceed to lay out all non-virtual base clasess.
void LayoutNonVirtualBases(const CXXRecordDecl *RD);
/// LayoutNonVirtualBase - Lays out a single non-virtual base.
void LayoutNonVirtualBase(const BaseSubobjectInfo *Base);
void AddPrimaryVirtualBaseOffsets(const BaseSubobjectInfo *Info,
CharUnits Offset);
/// LayoutVirtualBases - Lays out all the virtual bases.
void LayoutVirtualBases(const CXXRecordDecl *RD,
const CXXRecordDecl *MostDerivedClass);
/// LayoutVirtualBase - Lays out a single virtual base.
void LayoutVirtualBase(const BaseSubobjectInfo *Base);
/// LayoutBase - Will lay out a base and return the offset where it was
/// placed, in chars.
CharUnits LayoutBase(const BaseSubobjectInfo *Base);
/// InitializeLayout - Initialize record layout for the given record decl.
void InitializeLayout(const Decl *D);
/// FinishLayout - Finalize record layout. Adjust record size based on the
/// alignment.
void FinishLayout(const NamedDecl *D);
void UpdateAlignment(CharUnits NewAlignment, CharUnits UnpackedNewAlignment);
void UpdateAlignment(CharUnits NewAlignment) {
UpdateAlignment(NewAlignment, NewAlignment);
}
/// \brief Retrieve the externally-supplied field offset for the given
/// field.
///
/// \param Field The field whose offset is being queried.
/// \param ComputedOffset The offset that we've computed for this field.
uint64_t updateExternalFieldOffset(const FieldDecl *Field,
uint64_t ComputedOffset);
void CheckFieldPadding(uint64_t Offset, uint64_t UnpaddedOffset,
uint64_t UnpackedOffset, unsigned UnpackedAlign,
bool isPacked, const FieldDecl *D);
DiagnosticBuilder Diag(SourceLocation Loc, unsigned DiagID);
CharUnits getSize() const {
assert(Size % Context.getCharWidth() == 0);
return Context.toCharUnitsFromBits(Size);
}
uint64_t getSizeInBits() const { return Size; }
void setSize(CharUnits NewSize) { Size = Context.toBits(NewSize); }
void setSize(uint64_t NewSize) { Size = NewSize; }
CharUnits getAligment() const { return Alignment; }
CharUnits getDataSize() const {
assert(DataSize % Context.getCharWidth() == 0);
return Context.toCharUnitsFromBits(DataSize);
}
uint64_t getDataSizeInBits() const { return DataSize; }
void setDataSize(CharUnits NewSize) { DataSize = Context.toBits(NewSize); }
void setDataSize(uint64_t NewSize) { DataSize = NewSize; }
ItaniumRecordLayoutBuilder(const ItaniumRecordLayoutBuilder &) = delete;
void operator=(const ItaniumRecordLayoutBuilder &) = delete;
};
} // end anonymous namespace
void ItaniumRecordLayoutBuilder::SelectPrimaryVBase(const CXXRecordDecl *RD) {
for (const auto &I : RD->bases()) {
assert(!I.getType()->isDependentType() &&
"Cannot layout class with dependent bases.");
const CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
// Check if this is a nearly empty virtual base.
if (I.isVirtual() && Context.isNearlyEmpty(Base)) {
// If it's not an indirect primary base, then we've found our primary
// base.
if (!IndirectPrimaryBases.count(Base)) {
PrimaryBase = Base;
PrimaryBaseIsVirtual = true;
return;
}
// Is this the first nearly empty virtual base?
if (!FirstNearlyEmptyVBase)
FirstNearlyEmptyVBase = Base;
}
SelectPrimaryVBase(Base);
if (PrimaryBase)
return;
}
}
/// DeterminePrimaryBase - Determine the primary base of the given class.
void ItaniumRecordLayoutBuilder::DeterminePrimaryBase(const CXXRecordDecl *RD) {
// If the class isn't dynamic, it won't have a primary base.
if (!RD->isDynamicClass())
return;
// Compute all the primary virtual bases for all of our direct and
// indirect bases, and record all their primary virtual base classes.
RD->getIndirectPrimaryBases(IndirectPrimaryBases);
// If the record has a dynamic base class, attempt to choose a primary base
// class. It is the first (in direct base class order) non-virtual dynamic
// base class, if one exists.
for (const auto &I : RD->bases()) {
// Ignore virtual bases.
if (I.isVirtual())
continue;
const CXXRecordDecl *Base = I.getType()->getAsCXXRecordDecl();
if (Base->isDynamicClass()) {
// We found it.
PrimaryBase = Base;
PrimaryBaseIsVirtual = false;
return;
}
}
// Under the Itanium ABI, if there is no non-virtual primary base class,
// try to compute the primary virtual base. The primary virtual base is
// the first nearly empty virtual base that is not an indirect primary
// virtual base class, if one exists.
if (RD->getNumVBases() != 0) {
SelectPrimaryVBase(RD);
if (PrimaryBase)
return;
}
// Otherwise, it is the first indirect primary base class, if one exists.
if (FirstNearlyEmptyVBase) {
PrimaryBase = FirstNearlyEmptyVBase;
PrimaryBaseIsVirtual = true;
return;
}
assert(!PrimaryBase && "Should not get here with a primary base!");
}
BaseSubobjectInfo *ItaniumRecordLayoutBuilder::ComputeBaseSubobjectInfo(
const CXXRecordDecl *RD, bool IsVirtual, BaseSubobjectInfo *Derived) {
BaseSubobjectInfo *Info;
if (IsVirtual) {
// Check if we already have info about this virtual base.
BaseSubobjectInfo *&InfoSlot = VirtualBaseInfo[RD];
if (InfoSlot) {
assert(InfoSlot->Class == RD && "Wrong class for virtual base info!");
return InfoSlot;
}
// We don't, create it.
InfoSlot = new (BaseSubobjectInfoAllocator.Allocate()) BaseSubobjectInfo;
Info = InfoSlot;
} else {
Info = new (BaseSubobjectInfoAllocator.Allocate()) BaseSubobjectInfo;
}
Info->Class = RD;
Info->IsVirtual = IsVirtual;
Info->Derived = nullptr;
Info->PrimaryVirtualBaseInfo = nullptr;
const CXXRecordDecl *PrimaryVirtualBase = nullptr;
BaseSubobjectInfo *PrimaryVirtualBaseInfo = nullptr;
// Check if this base has a primary virtual base.
if (RD->getNumVBases()) {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
if (Layout.isPrimaryBaseVirtual()) {
// This base does have a primary virtual base.
PrimaryVirtualBase = Layout.getPrimaryBase();
assert(PrimaryVirtualBase && "Didn't have a primary virtual base!");
// Now check if we have base subobject info about this primary base.
PrimaryVirtualBaseInfo = VirtualBaseInfo.lookup(PrimaryVirtualBase);
if (PrimaryVirtualBaseInfo) {
if (PrimaryVirtualBaseInfo->Derived) {
// We did have info about this primary base, and it turns out that it
// has already been claimed as a primary virtual base for another
// base.
PrimaryVirtualBase = nullptr;
} else {
// We can claim this base as our primary base.
Info->PrimaryVirtualBaseInfo = PrimaryVirtualBaseInfo;
PrimaryVirtualBaseInfo->Derived = Info;
}
}
}
}
// Now go through all direct bases.
for (const auto &I : RD->bases()) {
bool IsVirtual = I.isVirtual();
const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
Info->Bases.push_back(ComputeBaseSubobjectInfo(BaseDecl, IsVirtual, Info));
}
if (PrimaryVirtualBase && !PrimaryVirtualBaseInfo) {
// Traversing the bases must have created the base info for our primary
// virtual base.
PrimaryVirtualBaseInfo = VirtualBaseInfo.lookup(PrimaryVirtualBase);
assert(PrimaryVirtualBaseInfo &&
"Did not create a primary virtual base!");
// Claim the primary virtual base as our primary virtual base.
Info->PrimaryVirtualBaseInfo = PrimaryVirtualBaseInfo;
PrimaryVirtualBaseInfo->Derived = Info;
}
return Info;
}
void ItaniumRecordLayoutBuilder::ComputeBaseSubobjectInfo(
const CXXRecordDecl *RD) {
for (const auto &I : RD->bases()) {
bool IsVirtual = I.isVirtual();
const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
// Compute the base subobject info for this base.
BaseSubobjectInfo *Info = ComputeBaseSubobjectInfo(BaseDecl, IsVirtual,
nullptr);
if (IsVirtual) {
// ComputeBaseInfo has already added this base for us.
assert(VirtualBaseInfo.count(BaseDecl) &&
"Did not add virtual base!");
} else {
// Add the base info to the map of non-virtual bases.
assert(!NonVirtualBaseInfo.count(BaseDecl) &&
"Non-virtual base already exists!");
NonVirtualBaseInfo.insert(std::make_pair(BaseDecl, Info));
}
}
}
void ItaniumRecordLayoutBuilder::EnsureVTablePointerAlignment(
CharUnits UnpackedBaseAlign) {
CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
// The maximum field alignment overrides base align.
if (!MaxFieldAlignment.isZero()) {
BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
}
// Round up the current record size to pointer alignment.
setSize(getSize().alignTo(BaseAlign));
setDataSize(getSize());
// Update the alignment.
UpdateAlignment(BaseAlign, UnpackedBaseAlign);
}
void ItaniumRecordLayoutBuilder::LayoutNonVirtualBases(
const CXXRecordDecl *RD) {
// Then, determine the primary base class.
DeterminePrimaryBase(RD);
// Compute base subobject info.
ComputeBaseSubobjectInfo(RD);
// If we have a primary base class, lay it out.
if (PrimaryBase) {
if (PrimaryBaseIsVirtual) {
// If the primary virtual base was a primary virtual base of some other
// base class we'll have to steal it.
BaseSubobjectInfo *PrimaryBaseInfo = VirtualBaseInfo.lookup(PrimaryBase);
PrimaryBaseInfo->Derived = nullptr;
// We have a virtual primary base, insert it as an indirect primary base.
IndirectPrimaryBases.insert(PrimaryBase);
assert(!VisitedVirtualBases.count(PrimaryBase) &&
"vbase already visited!");
VisitedVirtualBases.insert(PrimaryBase);
LayoutVirtualBase(PrimaryBaseInfo);
} else {
BaseSubobjectInfo *PrimaryBaseInfo =
NonVirtualBaseInfo.lookup(PrimaryBase);
assert(PrimaryBaseInfo &&
"Did not find base info for non-virtual primary base!");
LayoutNonVirtualBase(PrimaryBaseInfo);
}
// If this class needs a vtable/vf-table and didn't get one from a
// primary base, add it in now.
} else if (RD->isDynamicClass()) {
assert(DataSize == 0 && "Vtable pointer must be at offset zero!");
CharUnits PtrWidth =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
CharUnits PtrAlign =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
EnsureVTablePointerAlignment(PtrAlign);
HasOwnVFPtr = true;
setSize(getSize() + PtrWidth);
setDataSize(getSize());
}
// Now lay out the non-virtual bases.
for (const auto &I : RD->bases()) {
// Ignore virtual bases.
if (I.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = I.getType()->getAsCXXRecordDecl();
// Skip the primary base, because we've already laid it out. The
// !PrimaryBaseIsVirtual check is required because we might have a
// non-virtual base of the same type as a primary virtual base.
if (BaseDecl == PrimaryBase && !PrimaryBaseIsVirtual)
continue;
// Lay out the base.
BaseSubobjectInfo *BaseInfo = NonVirtualBaseInfo.lookup(BaseDecl);
assert(BaseInfo && "Did not find base info for non-virtual base!");
LayoutNonVirtualBase(BaseInfo);
}
}
void ItaniumRecordLayoutBuilder::LayoutNonVirtualBase(
const BaseSubobjectInfo *Base) {
// Layout the base.
CharUnits Offset = LayoutBase(Base);
// Add its base class offset.
assert(!Bases.count(Base->Class) && "base offset already exists!");
Bases.insert(std::make_pair(Base->Class, Offset));
AddPrimaryVirtualBaseOffsets(Base, Offset);
}
void ItaniumRecordLayoutBuilder::AddPrimaryVirtualBaseOffsets(
const BaseSubobjectInfo *Info, CharUnits Offset) {
// This base isn't interesting, it has no virtual bases.
if (!Info->Class->getNumVBases())
return;
// First, check if we have a virtual primary base to add offsets for.
if (Info->PrimaryVirtualBaseInfo) {
assert(Info->PrimaryVirtualBaseInfo->IsVirtual &&
"Primary virtual base is not virtual!");
if (Info->PrimaryVirtualBaseInfo->Derived == Info) {
// Add the offset.
assert(!VBases.count(Info->PrimaryVirtualBaseInfo->Class) &&
"primary vbase offset already exists!");
VBases.insert(std::make_pair(Info->PrimaryVirtualBaseInfo->Class,
ASTRecordLayout::VBaseInfo(Offset, false)));
// Traverse the primary virtual base.
AddPrimaryVirtualBaseOffsets(Info->PrimaryVirtualBaseInfo, Offset);
}
}
// Now go through all direct non-virtual bases.
const ASTRecordLayout &Layout = Context.getASTRecordLayout(Info->Class);
for (const BaseSubobjectInfo *Base : Info->Bases) {
if (Base->IsVirtual)
continue;
CharUnits BaseOffset = Offset + Layout.getBaseClassOffset(Base->Class);
AddPrimaryVirtualBaseOffsets(Base, BaseOffset);
}
}
void ItaniumRecordLayoutBuilder::LayoutVirtualBases(
const CXXRecordDecl *RD, const CXXRecordDecl *MostDerivedClass) {
const CXXRecordDecl *PrimaryBase;
bool PrimaryBaseIsVirtual;
if (MostDerivedClass == RD) {
PrimaryBase = this->PrimaryBase;
PrimaryBaseIsVirtual = this->PrimaryBaseIsVirtual;
} else {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
PrimaryBase = Layout.getPrimaryBase();
PrimaryBaseIsVirtual = Layout.isPrimaryBaseVirtual();
}
for (const CXXBaseSpecifier &Base : RD->bases()) {
assert(!Base.getType()->isDependentType() &&
"Cannot layout class with dependent bases.");
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
if (Base.isVirtual()) {
if (PrimaryBase != BaseDecl || !PrimaryBaseIsVirtual) {
bool IndirectPrimaryBase = IndirectPrimaryBases.count(BaseDecl);
// Only lay out the virtual base if it's not an indirect primary base.
if (!IndirectPrimaryBase) {
// Only visit virtual bases once.
if (!VisitedVirtualBases.insert(BaseDecl).second)
continue;
const BaseSubobjectInfo *BaseInfo = VirtualBaseInfo.lookup(BaseDecl);
assert(BaseInfo && "Did not find virtual base info!");
LayoutVirtualBase(BaseInfo);
}
}
}
if (!BaseDecl->getNumVBases()) {
// This base isn't interesting since it doesn't have any virtual bases.
continue;
}
LayoutVirtualBases(BaseDecl, MostDerivedClass);
}
}
void ItaniumRecordLayoutBuilder::LayoutVirtualBase(
const BaseSubobjectInfo *Base) {
assert(!Base->Derived && "Trying to lay out a primary virtual base!");
// Layout the base.
CharUnits Offset = LayoutBase(Base);
// Add its base class offset.
assert(!VBases.count(Base->Class) && "vbase offset already exists!");
VBases.insert(std::make_pair(Base->Class,
ASTRecordLayout::VBaseInfo(Offset, false)));
AddPrimaryVirtualBaseOffsets(Base, Offset);
}
CharUnits
ItaniumRecordLayoutBuilder::LayoutBase(const BaseSubobjectInfo *Base) {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(Base->Class);
CharUnits Offset;
// Query the external layout to see if it provides an offset.
bool HasExternalLayout = false;
if (UseExternalLayout) {
llvm::DenseMap<const CXXRecordDecl *, CharUnits>::iterator Known;
if (Base->IsVirtual)
HasExternalLayout = External.getExternalNVBaseOffset(Base->Class, Offset);
else
HasExternalLayout = External.getExternalVBaseOffset(Base->Class, Offset);
}
CharUnits UnpackedBaseAlign = Layout.getNonVirtualAlignment();
CharUnits BaseAlign = (Packed) ? CharUnits::One() : UnpackedBaseAlign;
// If we have an empty base class, try to place it at offset 0.
if (Base->Class->isEmpty() &&
(!HasExternalLayout || Offset == CharUnits::Zero()) &&
EmptySubobjects->CanPlaceBaseAtOffset(Base, CharUnits::Zero())) {
setSize(std::max(getSize(), Layout.getSize()));
UpdateAlignment(BaseAlign, UnpackedBaseAlign);
return CharUnits::Zero();
}
// The maximum field alignment overrides base align.
if (!MaxFieldAlignment.isZero()) {
BaseAlign = std::min(BaseAlign, MaxFieldAlignment);
UnpackedBaseAlign = std::min(UnpackedBaseAlign, MaxFieldAlignment);
}
if (!HasExternalLayout) {
// Round up the current record size to the base's alignment boundary.
Offset = getDataSize().alignTo(BaseAlign);
// Try to place the base.
while (!EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset))
Offset += BaseAlign;
} else {
bool Allowed = EmptySubobjects->CanPlaceBaseAtOffset(Base, Offset);
(void)Allowed;
assert(Allowed && "Base subobject externally placed at overlapping offset");
if (InferAlignment && Offset < getDataSize().alignTo(BaseAlign)) {
// The externally-supplied base offset is before the base offset we
// computed. Assume that the structure is packed.
Alignment = CharUnits::One();
InferAlignment = false;
}
}
if (!Base->Class->isEmpty()) {
// Update the data size.
setDataSize(Offset + Layout.getNonVirtualSize());
setSize(std::max(getSize(), getDataSize()));
} else
setSize(std::max(getSize(), Offset + Layout.getSize()));
// Remember max struct/class alignment.
UpdateAlignment(BaseAlign, UnpackedBaseAlign);
return Offset;
}
void ItaniumRecordLayoutBuilder::InitializeLayout(const Decl *D) {
if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
IsUnion = RD->isUnion();
IsMsStruct = RD->isMsStruct(Context);
}
Packed = D->hasAttr<PackedAttr>();
// Honor the default struct packing maximum alignment flag.
if (unsigned DefaultMaxFieldAlignment = Context.getLangOpts().PackStruct) {
MaxFieldAlignment = CharUnits::fromQuantity(DefaultMaxFieldAlignment);
}
// mac68k alignment supersedes maximum field alignment and attribute aligned,
// and forces all structures to have 2-byte alignment. The IBM docs on it
// allude to additional (more complicated) semantics, especially with regard
// to bit-fields, but gcc appears not to follow that.
if (D->hasAttr<AlignMac68kAttr>()) {
IsMac68kAlign = true;
MaxFieldAlignment = CharUnits::fromQuantity(2);
Alignment = CharUnits::fromQuantity(2);
} else {
if (const MaxFieldAlignmentAttr *MFAA = D->getAttr<MaxFieldAlignmentAttr>())
MaxFieldAlignment = Context.toCharUnitsFromBits(MFAA->getAlignment());
if (unsigned MaxAlign = D->getMaxAlignment())
UpdateAlignment(Context.toCharUnitsFromBits(MaxAlign));
}
// If there is an external AST source, ask it for the various offsets.
if (const RecordDecl *RD = dyn_cast<RecordDecl>(D))
if (ExternalASTSource *Source = Context.getExternalSource()) {
UseExternalLayout = Source->layoutRecordType(
RD, External.Size, External.Align, External.FieldOffsets,
External.BaseOffsets, External.VirtualBaseOffsets);
// Update based on external alignment.
if (UseExternalLayout) {
if (External.Align > 0) {
Alignment = Context.toCharUnitsFromBits(External.Align);
} else {
// The external source didn't have alignment information; infer it.
InferAlignment = true;
}
}
}
}
void ItaniumRecordLayoutBuilder::Layout(const RecordDecl *D) {
InitializeLayout(D);
LayoutFields(D);
// Finally, round the size of the total struct up to the alignment of the
// struct itself.
FinishLayout(D);
}
void ItaniumRecordLayoutBuilder::Layout(const CXXRecordDecl *RD) {
InitializeLayout(RD);
// Lay out the vtable and the non-virtual bases.
LayoutNonVirtualBases(RD);
LayoutFields(RD);
NonVirtualSize = Context.toCharUnitsFromBits(
llvm::alignTo(getSizeInBits(), Context.getTargetInfo().getCharAlign()));
NonVirtualAlignment = Alignment;
// Lay out the virtual bases and add the primary virtual base offsets.
LayoutVirtualBases(RD, RD);
// Finally, round the size of the total struct up to the alignment
// of the struct itself.
FinishLayout(RD);
#ifndef NDEBUG
// Check that we have base offsets for all bases.
for (const CXXBaseSpecifier &Base : RD->bases()) {
if (Base.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
assert(Bases.count(BaseDecl) && "Did not find base offset!");
}
// And all virtual bases.
for (const CXXBaseSpecifier &Base : RD->vbases()) {
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
assert(VBases.count(BaseDecl) && "Did not find base offset!");
}
#endif
}
void ItaniumRecordLayoutBuilder::Layout(const ObjCInterfaceDecl *D) {
if (ObjCInterfaceDecl *SD = D->getSuperClass()) {
const ASTRecordLayout &SL = Context.getASTObjCInterfaceLayout(SD);
UpdateAlignment(SL.getAlignment());
// We start laying out ivars not at the end of the superclass
// structure, but at the next byte following the last field.
setSize(SL.getDataSize());
setDataSize(getSize());
}
InitializeLayout(D);
// Layout each ivar sequentially.
for (const ObjCIvarDecl *IVD = D->all_declared_ivar_begin(); IVD;
IVD = IVD->getNextIvar())
LayoutField(IVD, false);
// Finally, round the size of the total struct up to the alignment of the
// struct itself.
FinishLayout(D);
}
void ItaniumRecordLayoutBuilder::LayoutFields(const RecordDecl *D) {
// Layout each field, for now, just sequentially, respecting alignment. In
// the future, this will need to be tweakable by targets.
bool InsertExtraPadding = D->mayInsertExtraPadding(/*EmitRemark=*/true);
bool HasFlexibleArrayMember = D->hasFlexibleArrayMember();
for (auto I = D->field_begin(), End = D->field_end(); I != End; ++I) {
auto Next(I);
++Next;
LayoutField(*I,
InsertExtraPadding && (Next != End || !HasFlexibleArrayMember));
}
}
// Rounds the specified size to have it a multiple of the char size.
static uint64_t
roundUpSizeToCharAlignment(uint64_t Size,
const ASTContext &Context) {
uint64_t CharAlignment = Context.getTargetInfo().getCharAlign();
return llvm::alignTo(Size, CharAlignment);
}
void ItaniumRecordLayoutBuilder::LayoutWideBitField(uint64_t FieldSize,
uint64_t TypeSize,
bool FieldPacked,
const FieldDecl *D) {
assert(Context.getLangOpts().CPlusPlus &&
"Can only have wide bit-fields in C++!");
// Itanium C++ ABI 2.4:
// If sizeof(T)*8 < n, let T' be the largest integral POD type with
// sizeof(T')*8 <= n.
QualType IntegralPODTypes[] = {
Context.UnsignedCharTy, Context.UnsignedShortTy, Context.UnsignedIntTy,
Context.UnsignedLongTy, Context.UnsignedLongLongTy
};
QualType Type;
for (const QualType &QT : IntegralPODTypes) {
uint64_t Size = Context.getTypeSize(QT);
if (Size > FieldSize)
break;
Type = QT;
}
assert(!Type.isNull() && "Did not find a type!");
CharUnits TypeAlign = Context.getTypeAlignInChars(Type);
// We're not going to use any of the unfilled bits in the last byte.
UnfilledBitsInLastUnit = 0;
LastBitfieldTypeSize = 0;
uint64_t FieldOffset;
uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
if (IsUnion) {
uint64_t RoundedFieldSize = roundUpSizeToCharAlignment(FieldSize,
Context);
setDataSize(std::max(getDataSizeInBits(), RoundedFieldSize));
FieldOffset = 0;
} else {
// The bitfield is allocated starting at the next offset aligned
// appropriately for T', with length n bits.
FieldOffset = llvm::alignTo(getDataSizeInBits(), Context.toBits(TypeAlign));
uint64_t NewSizeInBits = FieldOffset + FieldSize;
setDataSize(
llvm::alignTo(NewSizeInBits, Context.getTargetInfo().getCharAlign()));
UnfilledBitsInLastUnit = getDataSizeInBits() - NewSizeInBits;
}
// Place this field at the current location.
FieldOffsets.push_back(FieldOffset);
CheckFieldPadding(FieldOffset, UnpaddedFieldOffset, FieldOffset,
Context.toBits(TypeAlign), FieldPacked, D);
// Update the size.
setSize(std::max(getSizeInBits(), getDataSizeInBits()));
// Remember max struct/class alignment.
UpdateAlignment(TypeAlign);
}
void ItaniumRecordLayoutBuilder::LayoutBitField(const FieldDecl *D) {
bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
uint64_t FieldSize = D->getBitWidthValue(Context);
TypeInfo FieldInfo = Context.getTypeInfo(D->getType());
uint64_t TypeSize = FieldInfo.Width;
unsigned FieldAlign = FieldInfo.Align;
// UnfilledBitsInLastUnit is the difference between the end of the
// last allocated bitfield (i.e. the first bit offset available for
// bitfields) and the end of the current data size in bits (i.e. the
// first bit offset available for non-bitfields). The current data
// size in bits is always a multiple of the char size; additionally,
// for ms_struct records it's also a multiple of the
// LastBitfieldTypeSize (if set).
// The struct-layout algorithm is dictated by the platform ABI,
// which in principle could use almost any rules it likes. In
// practice, UNIXy targets tend to inherit the algorithm described
// in the System V generic ABI. The basic bitfield layout rule in
// System V is to place bitfields at the next available bit offset
// where the entire bitfield would fit in an aligned storage unit of
// the declared type; it's okay if an earlier or later non-bitfield
// is allocated in the same storage unit. However, some targets
// (those that !useBitFieldTypeAlignment(), e.g. ARM APCS) don't
// require this storage unit to be aligned, and therefore always put
// the bitfield at the next available bit offset.
// ms_struct basically requests a complete replacement of the
// platform ABI's struct-layout algorithm, with the high-level goal
// of duplicating MSVC's layout. For non-bitfields, this follows
// the standard algorithm. The basic bitfield layout rule is to
// allocate an entire unit of the bitfield's declared type
// (e.g. 'unsigned long'), then parcel it up among successive
// bitfields whose declared types have the same size, making a new
// unit as soon as the last can no longer store the whole value.
// Since it completely replaces the platform ABI's algorithm,
// settings like !useBitFieldTypeAlignment() do not apply.
// A zero-width bitfield forces the use of a new storage unit for
// later bitfields. In general, this occurs by rounding up the
// current size of the struct as if the algorithm were about to
// place a non-bitfield of the field's formal type. Usually this
// does not change the alignment of the struct itself, but it does
// on some targets (those that useZeroLengthBitfieldAlignment(),
// e.g. ARM). In ms_struct layout, zero-width bitfields are
// ignored unless they follow a non-zero-width bitfield.
// A field alignment restriction (e.g. from #pragma pack) or
// specification (e.g. from __attribute__((aligned))) changes the
// formal alignment of the field. For System V, this alters the
// required alignment of the notional storage unit that must contain
// the bitfield. For ms_struct, this only affects the placement of
// new storage units. In both cases, the effect of #pragma pack is
// ignored on zero-width bitfields.
// On System V, a packed field (e.g. from #pragma pack or
// __attribute__((packed))) always uses the next available bit
// offset.
// In an ms_struct struct, the alignment of a fundamental type is
// always equal to its size. This is necessary in order to mimic
// the i386 alignment rules on targets which might not fully align
// all types (e.g. Darwin PPC32, where alignof(long long) == 4).
// First, some simple bookkeeping to perform for ms_struct structs.
if (IsMsStruct) {
// The field alignment for integer types is always the size.
FieldAlign = TypeSize;
// If the previous field was not a bitfield, or was a bitfield
// with a different storage unit size, we're done with that
// storage unit.
if (LastBitfieldTypeSize != TypeSize) {
// Also, ignore zero-length bitfields after non-bitfields.
if (!LastBitfieldTypeSize && !FieldSize)
FieldAlign = 1;
UnfilledBitsInLastUnit = 0;
LastBitfieldTypeSize = 0;
}
}
// If the field is wider than its declared type, it follows
// different rules in all cases.
if (FieldSize > TypeSize) {
LayoutWideBitField(FieldSize, TypeSize, FieldPacked, D);
return;
}
// Compute the next available bit offset.
uint64_t FieldOffset =
IsUnion ? 0 : (getDataSizeInBits() - UnfilledBitsInLastUnit);
// Handle targets that don't honor bitfield type alignment.
if (!IsMsStruct && !Context.getTargetInfo().useBitFieldTypeAlignment()) {
// Some such targets do honor it on zero-width bitfields.
if (FieldSize == 0 &&
Context.getTargetInfo().useZeroLengthBitfieldAlignment()) {
// The alignment to round up to is the max of the field's natural
// alignment and a target-specific fixed value (sometimes zero).
unsigned ZeroLengthBitfieldBoundary =
Context.getTargetInfo().getZeroLengthBitfieldBoundary();
FieldAlign = std::max(FieldAlign, ZeroLengthBitfieldBoundary);
// If that doesn't apply, just ignore the field alignment.
} else {
FieldAlign = 1;
}
}
// Remember the alignment we would have used if the field were not packed.
unsigned UnpackedFieldAlign = FieldAlign;
// Ignore the field alignment if the field is packed unless it has zero-size.
if (!IsMsStruct && FieldPacked && FieldSize != 0)
FieldAlign = 1;
// But, if there's an 'aligned' attribute on the field, honor that.
unsigned ExplicitFieldAlign = D->getMaxAlignment();
if (ExplicitFieldAlign) {
FieldAlign = std::max(FieldAlign, ExplicitFieldAlign);
UnpackedFieldAlign = std::max(UnpackedFieldAlign, ExplicitFieldAlign);
}
// But, if there's a #pragma pack in play, that takes precedent over
// even the 'aligned' attribute, for non-zero-width bitfields.
unsigned MaxFieldAlignmentInBits = Context.toBits(MaxFieldAlignment);
if (!MaxFieldAlignment.isZero() && FieldSize) {
UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignmentInBits);
if (FieldPacked)
FieldAlign = UnpackedFieldAlign;
else
FieldAlign = std::min(FieldAlign, MaxFieldAlignmentInBits);
}
// But, ms_struct just ignores all of that in unions, even explicit
// alignment attributes.
if (IsMsStruct && IsUnion) {
FieldAlign = UnpackedFieldAlign = 1;
}
// For purposes of diagnostics, we're going to simultaneously
// compute the field offsets that we would have used if we weren't
// adding any alignment padding or if the field weren't packed.
uint64_t UnpaddedFieldOffset = FieldOffset;
uint64_t UnpackedFieldOffset = FieldOffset;
// Check if we need to add padding to fit the bitfield within an
// allocation unit with the right size and alignment. The rules are
// somewhat different here for ms_struct structs.
if (IsMsStruct) {
// If it's not a zero-width bitfield, and we can fit the bitfield
// into the active storage unit (and we haven't already decided to
// start a new storage unit), just do so, regardless of any other
// other consideration. Otherwise, round up to the right alignment.
if (FieldSize == 0 || FieldSize > UnfilledBitsInLastUnit) {
FieldOffset = llvm::alignTo(FieldOffset, FieldAlign);
UnpackedFieldOffset =
llvm::alignTo(UnpackedFieldOffset, UnpackedFieldAlign);
UnfilledBitsInLastUnit = 0;
}
} else {
// #pragma pack, with any value, suppresses the insertion of padding.
bool AllowPadding = MaxFieldAlignment.isZero();
// Compute the real offset.
if (FieldSize == 0 ||
(AllowPadding &&
(FieldOffset & (FieldAlign-1)) + FieldSize > TypeSize)) {
FieldOffset = llvm::alignTo(FieldOffset, FieldAlign);
} else if (ExplicitFieldAlign &&
(MaxFieldAlignmentInBits == 0 ||
ExplicitFieldAlign <= MaxFieldAlignmentInBits) &&
Context.getTargetInfo().useExplicitBitFieldAlignment()) {
// TODO: figure it out what needs to be done on targets that don't honor
// bit-field type alignment like ARM APCS ABI.
FieldOffset = llvm::alignTo(FieldOffset, ExplicitFieldAlign);
}
// Repeat the computation for diagnostic purposes.
if (FieldSize == 0 ||
(AllowPadding &&
(UnpackedFieldOffset & (UnpackedFieldAlign-1)) + FieldSize > TypeSize))
UnpackedFieldOffset =
llvm::alignTo(UnpackedFieldOffset, UnpackedFieldAlign);
else if (ExplicitFieldAlign &&
(MaxFieldAlignmentInBits == 0 ||
ExplicitFieldAlign <= MaxFieldAlignmentInBits) &&
Context.getTargetInfo().useExplicitBitFieldAlignment())
UnpackedFieldOffset =
llvm::alignTo(UnpackedFieldOffset, ExplicitFieldAlign);
}
// If we're using external layout, give the external layout a chance
// to override this information.
if (UseExternalLayout)
FieldOffset = updateExternalFieldOffset(D, FieldOffset);
// Okay, place the bitfield at the calculated offset.
FieldOffsets.push_back(FieldOffset);
// Bookkeeping:
// Anonymous members don't affect the overall record alignment,
// except on targets where they do.
if (!IsMsStruct &&
!Context.getTargetInfo().useZeroLengthBitfieldAlignment() &&
!D->getIdentifier())
FieldAlign = UnpackedFieldAlign = 1;
// Diagnose differences in layout due to padding or packing.
if (!UseExternalLayout)
CheckFieldPadding(FieldOffset, UnpaddedFieldOffset, UnpackedFieldOffset,
UnpackedFieldAlign, FieldPacked, D);
// Update DataSize to include the last byte containing (part of) the bitfield.
// For unions, this is just a max operation, as usual.
if (IsUnion) {
// For ms_struct, allocate the entire storage unit --- unless this
// is a zero-width bitfield, in which case just use a size of 1.
uint64_t RoundedFieldSize;
if (IsMsStruct) {
RoundedFieldSize =
(FieldSize ? TypeSize : Context.getTargetInfo().getCharWidth());
// Otherwise, allocate just the number of bytes required to store
// the bitfield.
} else {
RoundedFieldSize = roundUpSizeToCharAlignment(FieldSize, Context);
}
setDataSize(std::max(getDataSizeInBits(), RoundedFieldSize));
// For non-zero-width bitfields in ms_struct structs, allocate a new
// storage unit if necessary.
} else if (IsMsStruct && FieldSize) {
// We should have cleared UnfilledBitsInLastUnit in every case
// where we changed storage units.
if (!UnfilledBitsInLastUnit) {
setDataSize(FieldOffset + TypeSize);
UnfilledBitsInLastUnit = TypeSize;
}
UnfilledBitsInLastUnit -= FieldSize;
LastBitfieldTypeSize = TypeSize;
// Otherwise, bump the data size up to include the bitfield,
// including padding up to char alignment, and then remember how
// bits we didn't use.
} else {
uint64_t NewSizeInBits = FieldOffset + FieldSize;
uint64_t CharAlignment = Context.getTargetInfo().getCharAlign();
setDataSize(llvm::alignTo(NewSizeInBits, CharAlignment));
UnfilledBitsInLastUnit = getDataSizeInBits() - NewSizeInBits;
// The only time we can get here for an ms_struct is if this is a
// zero-width bitfield, which doesn't count as anything for the
// purposes of unfilled bits.
LastBitfieldTypeSize = 0;
}
// Update the size.
setSize(std::max(getSizeInBits(), getDataSizeInBits()));
// Remember max struct/class alignment.
UpdateAlignment(Context.toCharUnitsFromBits(FieldAlign),
Context.toCharUnitsFromBits(UnpackedFieldAlign));
}
void ItaniumRecordLayoutBuilder::LayoutField(const FieldDecl *D,
bool InsertExtraPadding) {
if (D->isBitField()) {
LayoutBitField(D);
return;
}
uint64_t UnpaddedFieldOffset = getDataSizeInBits() - UnfilledBitsInLastUnit;
// Reset the unfilled bits.
UnfilledBitsInLastUnit = 0;
LastBitfieldTypeSize = 0;
bool FieldPacked = Packed || D->hasAttr<PackedAttr>();
CharUnits FieldOffset =
IsUnion ? CharUnits::Zero() : getDataSize();
CharUnits FieldSize;
CharUnits FieldAlign;
if (D->getType()->isIncompleteArrayType()) {
// This is a flexible array member; we can't directly
// query getTypeInfo about these, so we figure it out here.
// Flexible array members don't have any size, but they
// have to be aligned appropriately for their element type.
FieldSize = CharUnits::Zero();
const ArrayType* ATy = Context.getAsArrayType(D->getType());
FieldAlign = Context.getTypeAlignInChars(ATy->getElementType());
} else if (const ReferenceType *RT = D->getType()->getAs<ReferenceType>()) {
unsigned AS = RT->getPointeeType().getAddressSpace();
FieldSize =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(AS));
FieldAlign =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(AS));
} else {
std::pair<CharUnits, CharUnits> FieldInfo =
Context.getTypeInfoInChars(D->getType());
FieldSize = FieldInfo.first;
FieldAlign = FieldInfo.second;
if (IsMsStruct) {
// If MS bitfield layout is required, figure out what type is being
// laid out and align the field to the width of that type.
// Resolve all typedefs down to their base type and round up the field
// alignment if necessary.
QualType T = Context.getBaseElementType(D->getType());
if (const BuiltinType *BTy = T->getAs<BuiltinType>()) {
CharUnits TypeSize = Context.getTypeSizeInChars(BTy);
if (TypeSize > FieldAlign)
FieldAlign = TypeSize;
}
}
}
// The align if the field is not packed. This is to check if the attribute
// was unnecessary (-Wpacked).
CharUnits UnpackedFieldAlign = FieldAlign;
CharUnits UnpackedFieldOffset = FieldOffset;
if (FieldPacked)
FieldAlign = CharUnits::One();
CharUnits MaxAlignmentInChars =
Context.toCharUnitsFromBits(D->getMaxAlignment());
FieldAlign = std::max(FieldAlign, MaxAlignmentInChars);
UnpackedFieldAlign = std::max(UnpackedFieldAlign, MaxAlignmentInChars);
// The maximum field alignment overrides the aligned attribute.
if (!MaxFieldAlignment.isZero()) {
FieldAlign = std::min(FieldAlign, MaxFieldAlignment);
UnpackedFieldAlign = std::min(UnpackedFieldAlign, MaxFieldAlignment);
}
// Round up the current record size to the field's alignment boundary.
FieldOffset = FieldOffset.alignTo(FieldAlign);
UnpackedFieldOffset = UnpackedFieldOffset.alignTo(UnpackedFieldAlign);
if (UseExternalLayout) {
FieldOffset = Context.toCharUnitsFromBits(
updateExternalFieldOffset(D, Context.toBits(FieldOffset)));
if (!IsUnion && EmptySubobjects) {
// Record the fact that we're placing a field at this offset.
bool Allowed = EmptySubobjects->CanPlaceFieldAtOffset(D, FieldOffset);
(void)Allowed;
assert(Allowed && "Externally-placed field cannot be placed here");
}
} else {
if (!IsUnion && EmptySubobjects) {
// Check if we can place the field at this offset.
while (!EmptySubobjects->CanPlaceFieldAtOffset(D, FieldOffset)) {
// We couldn't place the field at the offset. Try again at a new offset.
FieldOffset += FieldAlign;
}
}
}
// Place this field at the current location.
FieldOffsets.push_back(Context.toBits(FieldOffset));
if (!UseExternalLayout)
CheckFieldPadding(Context.toBits(FieldOffset), UnpaddedFieldOffset,
Context.toBits(UnpackedFieldOffset),
Context.toBits(UnpackedFieldAlign), FieldPacked, D);
if (InsertExtraPadding) {
CharUnits ASanAlignment = CharUnits::fromQuantity(8);
CharUnits ExtraSizeForAsan = ASanAlignment;
if (FieldSize % ASanAlignment)
ExtraSizeForAsan +=
ASanAlignment - CharUnits::fromQuantity(FieldSize % ASanAlignment);
FieldSize += ExtraSizeForAsan;
}
// Reserve space for this field.
uint64_t FieldSizeInBits = Context.toBits(FieldSize);
if (IsUnion)
setDataSize(std::max(getDataSizeInBits(), FieldSizeInBits));
else
setDataSize(FieldOffset + FieldSize);
// Update the size.
setSize(std::max(getSizeInBits(), getDataSizeInBits()));
// Remember max struct/class alignment.
UpdateAlignment(FieldAlign, UnpackedFieldAlign);
}
void ItaniumRecordLayoutBuilder::FinishLayout(const NamedDecl *D) {
// In C++, records cannot be of size 0.
if (Context.getLangOpts().CPlusPlus && getSizeInBits() == 0) {
if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
// Compatibility with gcc requires a class (pod or non-pod)
// which is not empty but of size 0; such as having fields of
// array of zero-length, remains of Size 0
if (RD->isEmpty())
setSize(CharUnits::One());
}
else
setSize(CharUnits::One());
}
// Finally, round the size of the record up to the alignment of the
// record itself.
uint64_t UnpaddedSize = getSizeInBits() - UnfilledBitsInLastUnit;
uint64_t UnpackedSizeInBits =
llvm::alignTo(getSizeInBits(), Context.toBits(UnpackedAlignment));
CharUnits UnpackedSize = Context.toCharUnitsFromBits(UnpackedSizeInBits);
uint64_t RoundedSize =
llvm::alignTo(getSizeInBits(), Context.toBits(Alignment));
if (UseExternalLayout) {
// If we're inferring alignment, and the external size is smaller than
// our size after we've rounded up to alignment, conservatively set the
// alignment to 1.
if (InferAlignment && External.Size < RoundedSize) {
Alignment = CharUnits::One();
InferAlignment = false;
}
setSize(External.Size);
return;
}
// Set the size to the final size.
setSize(RoundedSize);
unsigned CharBitNum = Context.getTargetInfo().getCharWidth();
if (const RecordDecl *RD = dyn_cast<RecordDecl>(D)) {
// Warn if padding was introduced to the struct/class/union.
if (getSizeInBits() > UnpaddedSize) {
unsigned PadSize = getSizeInBits() - UnpaddedSize;
bool InBits = true;
if (PadSize % CharBitNum == 0) {
PadSize = PadSize / CharBitNum;
InBits = false;
}
Diag(RD->getLocation(), diag::warn_padded_struct_size)
<< Context.getTypeDeclType(RD)
<< PadSize
<< (InBits ? 1 : 0); // (byte|bit)
}
// Warn if we packed it unnecessarily. If the alignment is 1 byte don't
// bother since there won't be alignment issues.
if (Packed && UnpackedAlignment > CharUnits::One() &&
getSize() == UnpackedSize)
Diag(D->getLocation(), diag::warn_unnecessary_packed)
<< Context.getTypeDeclType(RD);
}
}
void ItaniumRecordLayoutBuilder::UpdateAlignment(
CharUnits NewAlignment, CharUnits UnpackedNewAlignment) {
// The alignment is not modified when using 'mac68k' alignment or when
// we have an externally-supplied layout that also provides overall alignment.
if (IsMac68kAlign || (UseExternalLayout && !InferAlignment))
return;
if (NewAlignment > Alignment) {
assert(llvm::isPowerOf2_64(NewAlignment.getQuantity()) &&
"Alignment not a power of 2");
Alignment = NewAlignment;
}
if (UnpackedNewAlignment > UnpackedAlignment) {
assert(llvm::isPowerOf2_64(UnpackedNewAlignment.getQuantity()) &&
"Alignment not a power of 2");
UnpackedAlignment = UnpackedNewAlignment;
}
}
uint64_t
ItaniumRecordLayoutBuilder::updateExternalFieldOffset(const FieldDecl *Field,
uint64_t ComputedOffset) {
uint64_t ExternalFieldOffset = External.getExternalFieldOffset(Field);
if (InferAlignment && ExternalFieldOffset < ComputedOffset) {
// The externally-supplied field offset is before the field offset we
// computed. Assume that the structure is packed.
Alignment = CharUnits::One();
InferAlignment = false;
}
// Use the externally-supplied field offset.
return ExternalFieldOffset;
}
/// \brief Get diagnostic %select index for tag kind for
/// field padding diagnostic message.
/// WARNING: Indexes apply to particular diagnostics only!
///
/// \returns diagnostic %select index.
static unsigned getPaddingDiagFromTagKind(TagTypeKind Tag) {
switch (Tag) {
case TTK_Struct: return 0;
case TTK_Interface: return 1;
case TTK_Class: return 2;
default: llvm_unreachable("Invalid tag kind for field padding diagnostic!");
}
}
void ItaniumRecordLayoutBuilder::CheckFieldPadding(
uint64_t Offset, uint64_t UnpaddedOffset, uint64_t UnpackedOffset,
unsigned UnpackedAlign, bool isPacked, const FieldDecl *D) {
// We let objc ivars without warning, objc interfaces generally are not used
// for padding tricks.
if (isa<ObjCIvarDecl>(D))
return;
// Don't warn about structs created without a SourceLocation. This can
// be done by clients of the AST, such as codegen.
if (D->getLocation().isInvalid())
return;
unsigned CharBitNum = Context.getTargetInfo().getCharWidth();
// Warn if padding was introduced to the struct/class.
if (!IsUnion && Offset > UnpaddedOffset) {
unsigned PadSize = Offset - UnpaddedOffset;
bool InBits = true;
if (PadSize % CharBitNum == 0) {
PadSize = PadSize / CharBitNum;
InBits = false;
}
if (D->getIdentifier())
Diag(D->getLocation(), diag::warn_padded_struct_field)
<< getPaddingDiagFromTagKind(D->getParent()->getTagKind())
<< Context.getTypeDeclType(D->getParent())
<< PadSize
<< (InBits ? 1 : 0) // (byte|bit)
<< D->getIdentifier();
else
Diag(D->getLocation(), diag::warn_padded_struct_anon_field)
<< getPaddingDiagFromTagKind(D->getParent()->getTagKind())
<< Context.getTypeDeclType(D->getParent())
<< PadSize
<< (InBits ? 1 : 0); // (byte|bit)
}
// Warn if we packed it unnecessarily. If the alignment is 1 byte don't
// bother since there won't be alignment issues.
if (isPacked && UnpackedAlign > CharBitNum && Offset == UnpackedOffset)
Diag(D->getLocation(), diag::warn_unnecessary_packed)
<< D->getIdentifier();
}
static const CXXMethodDecl *computeKeyFunction(ASTContext &Context,
const CXXRecordDecl *RD) {
// If a class isn't polymorphic it doesn't have a key function.
if (!RD->isPolymorphic())
return nullptr;
// A class that is not externally visible doesn't have a key function. (Or
// at least, there's no point to assigning a key function to such a class;
// this doesn't affect the ABI.)
if (!RD->isExternallyVisible())
return nullptr;
// Template instantiations don't have key functions per Itanium C++ ABI 5.2.6.
// Same behavior as GCC.
TemplateSpecializationKind TSK = RD->getTemplateSpecializationKind();
if (TSK == TSK_ImplicitInstantiation ||
TSK == TSK_ExplicitInstantiationDeclaration ||
TSK == TSK_ExplicitInstantiationDefinition)
return nullptr;
bool allowInlineFunctions =
Context.getTargetInfo().getCXXABI().canKeyFunctionBeInline();
for (const CXXMethodDecl *MD : RD->methods()) {
if (!MD->isVirtual())
continue;
if (MD->isPure())
continue;
// Ignore implicit member functions, they are always marked as inline, but
// they don't have a body until they're defined.
if (MD->isImplicit())
continue;
if (MD->isInlineSpecified())
continue;
if (MD->hasInlineBody())
continue;
// Ignore inline deleted or defaulted functions.
if (!MD->isUserProvided())
continue;
// In certain ABIs, ignore functions with out-of-line inline definitions.
if (!allowInlineFunctions) {
const FunctionDecl *Def;
if (MD->hasBody(Def) && Def->isInlineSpecified())
continue;
}
if (Context.getLangOpts().CUDA) {
// While compiler may see key method in this TU, during CUDA
// compilation we should ignore methods that are not accessible
// on this side of compilation.
if (Context.getLangOpts().CUDAIsDevice) {
// In device mode ignore methods without __device__ attribute.
if (!MD->hasAttr<CUDADeviceAttr>())
continue;
} else {
// In host mode ignore __device__-only methods.
if (!MD->hasAttr<CUDAHostAttr>() && MD->hasAttr<CUDADeviceAttr>())
continue;
}
}
// If the key function is dllimport but the class isn't, then the class has
// no key function. The DLL that exports the key function won't export the
// vtable in this case.
if (MD->hasAttr<DLLImportAttr>() && !RD->hasAttr<DLLImportAttr>())
return nullptr;
// We found it.
return MD;
}
return nullptr;
}
DiagnosticBuilder ItaniumRecordLayoutBuilder::Diag(SourceLocation Loc,
unsigned DiagID) {
return Context.getDiagnostics().Report(Loc, DiagID);
}
/// Does the target C++ ABI require us to skip over the tail-padding
/// of the given class (considering it as a base class) when allocating
/// objects?
static bool mustSkipTailPadding(TargetCXXABI ABI, const CXXRecordDecl *RD) {
switch (ABI.getTailPaddingUseRules()) {
case TargetCXXABI::AlwaysUseTailPadding:
return false;
case TargetCXXABI::UseTailPaddingUnlessPOD03:
// FIXME: To the extent that this is meant to cover the Itanium ABI
// rules, we should implement the restrictions about over-sized
// bitfields:
//
// http://mentorembedded.github.com/cxx-abi/abi.html#POD :
// In general, a type is considered a POD for the purposes of
// layout if it is a POD type (in the sense of ISO C++
// [basic.types]). However, a POD-struct or POD-union (in the
// sense of ISO C++ [class]) with a bitfield member whose
// declared width is wider than the declared type of the
// bitfield is not a POD for the purpose of layout. Similarly,
// an array type is not a POD for the purpose of layout if the
// element type of the array is not a POD for the purpose of
// layout.
//
// Where references to the ISO C++ are made in this paragraph,
// the Technical Corrigendum 1 version of the standard is
// intended.
return RD->isPOD();
case TargetCXXABI::UseTailPaddingUnlessPOD11:
// This is equivalent to RD->getTypeForDecl().isCXX11PODType(),
// but with a lot of abstraction penalty stripped off. This does
// assume that these properties are set correctly even in C++98
// mode; fortunately, that is true because we want to assign
// consistently semantics to the type-traits intrinsics (or at
// least as many of them as possible).
return RD->isTrivial() && RD->isStandardLayout();
}
llvm_unreachable("bad tail-padding use kind");
}
static bool isMsLayout(const ASTContext &Context) {
return Context.getTargetInfo().getCXXABI().isMicrosoft();
}
// This section contains an implementation of struct layout that is, up to the
// included tests, compatible with cl.exe (2013). The layout produced is
// significantly different than those produced by the Itanium ABI. Here we note
// the most important differences.
//
// * The alignment of bitfields in unions is ignored when computing the
// alignment of the union.
// * The existence of zero-width bitfield that occurs after anything other than
// a non-zero length bitfield is ignored.
// * There is no explicit primary base for the purposes of layout. All bases
// with vfptrs are laid out first, followed by all bases without vfptrs.
// * The Itanium equivalent vtable pointers are split into a vfptr (virtual
// function pointer) and a vbptr (virtual base pointer). They can each be
// shared with a, non-virtual bases. These bases need not be the same. vfptrs
// always occur at offset 0. vbptrs can occur at an arbitrary offset and are
// placed after the lexicographically last non-virtual base. This placement
// is always before fields but can be in the middle of the non-virtual bases
// due to the two-pass layout scheme for non-virtual-bases.
// * Virtual bases sometimes require a 'vtordisp' field that is laid out before
// the virtual base and is used in conjunction with virtual overrides during
// construction and destruction. This is always a 4 byte value and is used as
// an alternative to constructor vtables.
// * vtordisps are allocated in a block of memory with size and alignment equal
// to the alignment of the completed structure (before applying __declspec(
// align())). The vtordisp always occur at the end of the allocation block,
// immediately prior to the virtual base.
// * vfptrs are injected after all bases and fields have been laid out. In
// order to guarantee proper alignment of all fields, the vfptr injection
// pushes all bases and fields back by the alignment imposed by those bases
// and fields. This can potentially add a significant amount of padding.
// vfptrs are always injected at offset 0.
// * vbptrs are injected after all bases and fields have been laid out. In
// order to guarantee proper alignment of all fields, the vfptr injection
// pushes all bases and fields back by the alignment imposed by those bases
// and fields. This can potentially add a significant amount of padding.
// vbptrs are injected immediately after the last non-virtual base as
// lexicographically ordered in the code. If this site isn't pointer aligned
// the vbptr is placed at the next properly aligned location. Enough padding
// is added to guarantee a fit.
// * The last zero sized non-virtual base can be placed at the end of the
// struct (potentially aliasing another object), or may alias with the first
// field, even if they are of the same type.
// * The last zero size virtual base may be placed at the end of the struct
// potentially aliasing another object.
// * The ABI attempts to avoid aliasing of zero sized bases by adding padding
// between bases or vbases with specific properties. The criteria for
// additional padding between two bases is that the first base is zero sized
// or ends with a zero sized subobject and the second base is zero sized or
// trails with a zero sized base or field (sharing of vfptrs can reorder the
// layout of the so the leading base is not always the first one declared).
// This rule does take into account fields that are not records, so padding
// will occur even if the last field is, e.g. an int. The padding added for
// bases is 1 byte. The padding added between vbases depends on the alignment
// of the object but is at least 4 bytes (in both 32 and 64 bit modes).
// * There is no concept of non-virtual alignment, non-virtual alignment and
// alignment are always identical.
// * There is a distinction between alignment and required alignment.
// __declspec(align) changes the required alignment of a struct. This
// alignment is _always_ obeyed, even in the presence of #pragma pack. A
// record inherits required alignment from all of its fields and bases.
// * __declspec(align) on bitfields has the effect of changing the bitfield's
// alignment instead of its required alignment. This is the only known way
// to make the alignment of a struct bigger than 8. Interestingly enough
// this alignment is also immune to the effects of #pragma pack and can be
// used to create structures with large alignment under #pragma pack.
// However, because it does not impact required alignment, such a structure,
// when used as a field or base, will not be aligned if #pragma pack is
// still active at the time of use.
//
// Known incompatibilities:
// * all: #pragma pack between fields in a record
// * 2010 and back: If the last field in a record is a bitfield, every object
// laid out after the record will have extra padding inserted before it. The
// extra padding will have size equal to the size of the storage class of the
// bitfield. 0 sized bitfields don't exhibit this behavior and the extra
// padding can be avoided by adding a 0 sized bitfield after the non-zero-
// sized bitfield.
// * 2012 and back: In 64-bit mode, if the alignment of a record is 16 or
// greater due to __declspec(align()) then a second layout phase occurs after
// The locations of the vf and vb pointers are known. This layout phase
// suffers from the "last field is a bitfield" bug in 2010 and results in
// _every_ field getting padding put in front of it, potentially including the
// vfptr, leaving the vfprt at a non-zero location which results in a fault if
// anything tries to read the vftbl. The second layout phase also treats
// bitfields as separate entities and gives them each storage rather than
// packing them. Additionally, because this phase appears to perform a
// (an unstable) sort on the members before laying them out and because merged
// bitfields have the same address, the bitfields end up in whatever order
// the sort left them in, a behavior we could never hope to replicate.
namespace {
struct MicrosoftRecordLayoutBuilder {
struct ElementInfo {
CharUnits Size;
CharUnits Alignment;
};
typedef llvm::DenseMap<const CXXRecordDecl *, CharUnits> BaseOffsetsMapTy;
MicrosoftRecordLayoutBuilder(const ASTContext &Context) : Context(Context) {}
private:
MicrosoftRecordLayoutBuilder(const MicrosoftRecordLayoutBuilder &) = delete;
void operator=(const MicrosoftRecordLayoutBuilder &) = delete;
public:
void layout(const RecordDecl *RD);
void cxxLayout(const CXXRecordDecl *RD);
/// \brief Initializes size and alignment and honors some flags.
void initializeLayout(const RecordDecl *RD);
/// \brief Initialized C++ layout, compute alignment and virtual alignment and
/// existence of vfptrs and vbptrs. Alignment is needed before the vfptr is
/// laid out.
void initializeCXXLayout(const CXXRecordDecl *RD);
void layoutNonVirtualBases(const CXXRecordDecl *RD);
void layoutNonVirtualBase(const CXXRecordDecl *RD,
const CXXRecordDecl *BaseDecl,
const ASTRecordLayout &BaseLayout,
const ASTRecordLayout *&PreviousBaseLayout);
void injectVFPtr(const CXXRecordDecl *RD);
void injectVBPtr(const CXXRecordDecl *RD);
/// \brief Lays out the fields of the record. Also rounds size up to
/// alignment.
void layoutFields(const RecordDecl *RD);
void layoutField(const FieldDecl *FD);
void layoutBitField(const FieldDecl *FD);
/// \brief Lays out a single zero-width bit-field in the record and handles
/// special cases associated with zero-width bit-fields.
void layoutZeroWidthBitField(const FieldDecl *FD);
void layoutVirtualBases(const CXXRecordDecl *RD);
void finalizeLayout(const RecordDecl *RD);
/// \brief Gets the size and alignment of a base taking pragma pack and
/// __declspec(align) into account.
ElementInfo getAdjustedElementInfo(const ASTRecordLayout &Layout);
/// \brief Gets the size and alignment of a field taking pragma pack and
/// __declspec(align) into account. It also updates RequiredAlignment as a
/// side effect because it is most convenient to do so here.
ElementInfo getAdjustedElementInfo(const FieldDecl *FD);
/// \brief Places a field at an offset in CharUnits.
void placeFieldAtOffset(CharUnits FieldOffset) {
FieldOffsets.push_back(Context.toBits(FieldOffset));
}
/// \brief Places a bitfield at a bit offset.
void placeFieldAtBitOffset(uint64_t FieldOffset) {
FieldOffsets.push_back(FieldOffset);
}
/// \brief Compute the set of virtual bases for which vtordisps are required.
void computeVtorDispSet(
llvm::SmallPtrSetImpl<const CXXRecordDecl *> &HasVtorDispSet,
const CXXRecordDecl *RD) const;
const ASTContext &Context;
/// \brief The size of the record being laid out.
CharUnits Size;
/// \brief The non-virtual size of the record layout.
CharUnits NonVirtualSize;
/// \brief The data size of the record layout.
CharUnits DataSize;
/// \brief The current alignment of the record layout.
CharUnits Alignment;
/// \brief The maximum allowed field alignment. This is set by #pragma pack.
CharUnits MaxFieldAlignment;
/// \brief The alignment that this record must obey. This is imposed by
/// __declspec(align()) on the record itself or one of its fields or bases.
CharUnits RequiredAlignment;
/// \brief The size of the allocation of the currently active bitfield.
/// This value isn't meaningful unless LastFieldIsNonZeroWidthBitfield
/// is true.
CharUnits CurrentBitfieldSize;
/// \brief Offset to the virtual base table pointer (if one exists).
CharUnits VBPtrOffset;
/// \brief Minimum record size possible.
CharUnits MinEmptyStructSize;
/// \brief The size and alignment info of a pointer.
ElementInfo PointerInfo;
/// \brief The primary base class (if one exists).
const CXXRecordDecl *PrimaryBase;
/// \brief The class we share our vb-pointer with.
const CXXRecordDecl *SharedVBPtrBase;
/// \brief The collection of field offsets.
SmallVector<uint64_t, 16> FieldOffsets;
/// \brief Base classes and their offsets in the record.
BaseOffsetsMapTy Bases;
/// \brief virtual base classes and their offsets in the record.
ASTRecordLayout::VBaseOffsetsMapTy VBases;
/// \brief The number of remaining bits in our last bitfield allocation.
/// This value isn't meaningful unless LastFieldIsNonZeroWidthBitfield is
/// true.
unsigned RemainingBitsInField;
bool IsUnion : 1;
/// \brief True if the last field laid out was a bitfield and was not 0
/// width.
bool LastFieldIsNonZeroWidthBitfield : 1;
/// \brief True if the class has its own vftable pointer.
bool HasOwnVFPtr : 1;
/// \brief True if the class has a vbtable pointer.
bool HasVBPtr : 1;
/// \brief True if the last sub-object within the type is zero sized or the
/// object itself is zero sized. This *does not* count members that are not
/// records. Only used for MS-ABI.
bool EndsWithZeroSizedObject : 1;
/// \brief True if this class is zero sized or first base is zero sized or
/// has this property. Only used for MS-ABI.
bool LeadsWithZeroSizedBase : 1;
/// \brief True if the external AST source provided a layout for this record.
bool UseExternalLayout : 1;
/// \brief The layout provided by the external AST source. Only active if
/// UseExternalLayout is true.
ExternalLayout External;
};
} // namespace
MicrosoftRecordLayoutBuilder::ElementInfo
MicrosoftRecordLayoutBuilder::getAdjustedElementInfo(
const ASTRecordLayout &Layout) {
ElementInfo Info;
Info.Alignment = Layout.getAlignment();
// Respect pragma pack.
if (!MaxFieldAlignment.isZero())
Info.Alignment = std::min(Info.Alignment, MaxFieldAlignment);
// Track zero-sized subobjects here where it's already available.
EndsWithZeroSizedObject = Layout.endsWithZeroSizedObject();
// Respect required alignment, this is necessary because we may have adjusted
// the alignment in the case of pragam pack. Note that the required alignment
// doesn't actually apply to the struct alignment at this point.
Alignment = std::max(Alignment, Info.Alignment);
RequiredAlignment = std::max(RequiredAlignment, Layout.getRequiredAlignment());
Info.Alignment = std::max(Info.Alignment, Layout.getRequiredAlignment());
Info.Size = Layout.getNonVirtualSize();
return Info;
}
MicrosoftRecordLayoutBuilder::ElementInfo
MicrosoftRecordLayoutBuilder::getAdjustedElementInfo(
const FieldDecl *FD) {
// Get the alignment of the field type's natural alignment, ignore any
// alignment attributes.
ElementInfo Info;
std::tie(Info.Size, Info.Alignment) =
Context.getTypeInfoInChars(FD->getType()->getUnqualifiedDesugaredType());
// Respect align attributes on the field.
CharUnits FieldRequiredAlignment =
Context.toCharUnitsFromBits(FD->getMaxAlignment());
// Respect align attributes on the type.
if (Context.isAlignmentRequired(FD->getType()))
FieldRequiredAlignment = std::max(
Context.getTypeAlignInChars(FD->getType()), FieldRequiredAlignment);
// Respect attributes applied to subobjects of the field.
if (FD->isBitField())
// For some reason __declspec align impacts alignment rather than required
// alignment when it is applied to bitfields.
Info.Alignment = std::max(Info.Alignment, FieldRequiredAlignment);
else {
if (auto RT =
FD->getType()->getBaseElementTypeUnsafe()->getAs<RecordType>()) {
auto const &Layout = Context.getASTRecordLayout(RT->getDecl());
EndsWithZeroSizedObject = Layout.endsWithZeroSizedObject();
FieldRequiredAlignment = std::max(FieldRequiredAlignment,
Layout.getRequiredAlignment());
}
// Capture required alignment as a side-effect.
RequiredAlignment = std::max(RequiredAlignment, FieldRequiredAlignment);
}
// Respect pragma pack, attribute pack and declspec align
if (!MaxFieldAlignment.isZero())
Info.Alignment = std::min(Info.Alignment, MaxFieldAlignment);
if (FD->hasAttr<PackedAttr>())
Info.Alignment = CharUnits::One();
Info.Alignment = std::max(Info.Alignment, FieldRequiredAlignment);
return Info;
}
void MicrosoftRecordLayoutBuilder::layout(const RecordDecl *RD) {
// For C record layout, zero-sized records always have size 4.
MinEmptyStructSize = CharUnits::fromQuantity(4);
initializeLayout(RD);
layoutFields(RD);
DataSize = Size = Size.alignTo(Alignment);
RequiredAlignment = std::max(
RequiredAlignment, Context.toCharUnitsFromBits(RD->getMaxAlignment()));
finalizeLayout(RD);
}
void MicrosoftRecordLayoutBuilder::cxxLayout(const CXXRecordDecl *RD) {
// The C++ standard says that empty structs have size 1.
MinEmptyStructSize = CharUnits::One();
initializeLayout(RD);
initializeCXXLayout(RD);
layoutNonVirtualBases(RD);
layoutFields(RD);
injectVBPtr(RD);
injectVFPtr(RD);
if (HasOwnVFPtr || (HasVBPtr && !SharedVBPtrBase))
Alignment = std::max(Alignment, PointerInfo.Alignment);
auto RoundingAlignment = Alignment;
if (!MaxFieldAlignment.isZero())
RoundingAlignment = std::min(RoundingAlignment, MaxFieldAlignment);
NonVirtualSize = Size = Size.alignTo(RoundingAlignment);
RequiredAlignment = std::max(
RequiredAlignment, Context.toCharUnitsFromBits(RD->getMaxAlignment()));
layoutVirtualBases(RD);
finalizeLayout(RD);
}
void MicrosoftRecordLayoutBuilder::initializeLayout(const RecordDecl *RD) {
IsUnion = RD->isUnion();
Size = CharUnits::Zero();
Alignment = CharUnits::One();
// In 64-bit mode we always perform an alignment step after laying out vbases.
// In 32-bit mode we do not. The check to see if we need to perform alignment
// checks the RequiredAlignment field and performs alignment if it isn't 0.
RequiredAlignment = Context.getTargetInfo().getTriple().isArch64Bit()
? CharUnits::One()
: CharUnits::Zero();
// Compute the maximum field alignment.
MaxFieldAlignment = CharUnits::Zero();
// Honor the default struct packing maximum alignment flag.
if (unsigned DefaultMaxFieldAlignment = Context.getLangOpts().PackStruct)
MaxFieldAlignment = CharUnits::fromQuantity(DefaultMaxFieldAlignment);
// Honor the packing attribute. The MS-ABI ignores pragma pack if its larger
// than the pointer size.
if (const MaxFieldAlignmentAttr *MFAA = RD->getAttr<MaxFieldAlignmentAttr>()){
unsigned PackedAlignment = MFAA->getAlignment();
if (PackedAlignment <= Context.getTargetInfo().getPointerWidth(0))
MaxFieldAlignment = Context.toCharUnitsFromBits(PackedAlignment);
}
// Packed attribute forces max field alignment to be 1.
if (RD->hasAttr<PackedAttr>())
MaxFieldAlignment = CharUnits::One();
// Try to respect the external layout if present.
UseExternalLayout = false;
if (ExternalASTSource *Source = Context.getExternalSource())
UseExternalLayout = Source->layoutRecordType(
RD, External.Size, External.Align, External.FieldOffsets,
External.BaseOffsets, External.VirtualBaseOffsets);
}
void
MicrosoftRecordLayoutBuilder::initializeCXXLayout(const CXXRecordDecl *RD) {
EndsWithZeroSizedObject = false;
LeadsWithZeroSizedBase = false;
HasOwnVFPtr = false;
HasVBPtr = false;
PrimaryBase = nullptr;
SharedVBPtrBase = nullptr;
// Calculate pointer size and alignment. These are used for vfptr and vbprt
// injection.
PointerInfo.Size =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerWidth(0));
PointerInfo.Alignment =
Context.toCharUnitsFromBits(Context.getTargetInfo().getPointerAlign(0));
// Respect pragma pack.
if (!MaxFieldAlignment.isZero())
PointerInfo.Alignment = std::min(PointerInfo.Alignment, MaxFieldAlignment);
}
void
MicrosoftRecordLayoutBuilder::layoutNonVirtualBases(const CXXRecordDecl *RD) {
// The MS-ABI lays out all bases that contain leading vfptrs before it lays
// out any bases that do not contain vfptrs. We implement this as two passes
// over the bases. This approach guarantees that the primary base is laid out
// first. We use these passes to calculate some additional aggregated
// information about the bases, such as required alignment and the presence of
// zero sized members.
const ASTRecordLayout *PreviousBaseLayout = nullptr;
// Iterate through the bases and lay out the non-virtual ones.
for (const CXXBaseSpecifier &Base : RD->bases()) {
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
// Mark and skip virtual bases.
if (Base.isVirtual()) {
HasVBPtr = true;
continue;
}
// Check for a base to share a VBPtr with.
if (!SharedVBPtrBase && BaseLayout.hasVBPtr()) {
SharedVBPtrBase = BaseDecl;
HasVBPtr = true;
}
// Only lay out bases with extendable VFPtrs on the first pass.
if (!BaseLayout.hasExtendableVFPtr())
continue;
// If we don't have a primary base, this one qualifies.
if (!PrimaryBase) {
PrimaryBase = BaseDecl;
LeadsWithZeroSizedBase = BaseLayout.leadsWithZeroSizedBase();
}
// Lay out the base.
layoutNonVirtualBase(RD, BaseDecl, BaseLayout, PreviousBaseLayout);
}
// Figure out if we need a fresh VFPtr for this class.
if (!PrimaryBase && RD->isDynamicClass())
for (CXXRecordDecl::method_iterator i = RD->method_begin(),
e = RD->method_end();
!HasOwnVFPtr && i != e; ++i)
HasOwnVFPtr = i->isVirtual() && i->size_overridden_methods() == 0;
// If we don't have a primary base then we have a leading object that could
// itself lead with a zero-sized object, something we track.
bool CheckLeadingLayout = !PrimaryBase;
// Iterate through the bases and lay out the non-virtual ones.
for (const CXXBaseSpecifier &Base : RD->bases()) {
if (Base.isVirtual())
continue;
const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl();
const ASTRecordLayout &BaseLayout = Context.getASTRecordLayout(BaseDecl);
// Only lay out bases without extendable VFPtrs on the second pass.
if (BaseLayout.hasExtendableVFPtr()) {
VBPtrOffset = Bases[BaseDecl] + BaseLayout.getNonVirtualSize();
continue;
}
// If this is the first layout, check to see if it leads with a zero sized
// object. If it does, so do we.
if (CheckLeadingLayout) {
CheckLeadingLayout = false;
LeadsWithZeroSizedBase = BaseLayout.leadsWithZeroSizedBase();
}
// Lay out the base.
layoutNonVirtualBase(RD, BaseDecl, BaseLayout, PreviousBaseLayout);
VBPtrOffset = Bases[BaseDecl] + BaseLayout.getNonVirtualSize();
}
// Set our VBPtroffset if we know it at this point.
if (!HasVBPtr)
VBPtrOffset = CharUnits::fromQuantity(-1);
else if (SharedVBPtrBase) {
const ASTRecordLayout &Layout = Context.getASTRecordLayout(SharedVBPtrBase);
VBPtrOffset = Bases[SharedVBPtrBase] + Layout.getVBPtrOffset();
}
}
static bool recordUsesEBO(const RecordDecl *RD) {
if (!isa<CXXRecordDecl>(RD))
return false;
if (RD->hasAttr<EmptyBasesAttr>())
return true;
if (auto *LVA = RD->getAttr<LayoutVersionAttr>())
// TODO: Double check with the next version of MSVC.
if (LVA->getVersion() <= LangOptions::MSVC2015)
return false;
// TODO: Some later version of MSVC will change the default behavior of the
// compiler to enable EBO by default. When this happens, we will need an
// additional isCompatibleWithMSVC check.
return false;
}
void MicrosoftRecordLayoutBuilder::layoutNonVirtualBase(
const CXXRecordDecl *RD,
const CXXRecordDecl *BaseDecl,
const ASTRecordLayout &BaseLayout,
const ASTRecordLayout *&PreviousBaseLayout) {
// Insert padding between two bases if the left first one is zero sized or
// contains a zero sized subobject and the right is zero sized or one leads
// with a zero sized base.
bool MDCUsesEBO = recordUsesEBO(RD);
if (PreviousBaseLayout && PreviousBaseLayout->endsWithZeroSizedObject() &&
BaseLayout.leadsWithZeroSizedBase() && !MDCUsesEBO)
Size++;
ElementInfo Info = getAdjustedElementInfo(BaseLayout);
CharUnits BaseOffset;
// Respect the external AST source base offset, if present.
bool FoundBase = false;
if (UseExternalLayout) {
FoundBase = External.getExternalNVBaseOffset(BaseDecl, BaseOffset);
if (FoundBase) {
assert(BaseOffset >= Size && "base offset already allocated");
Size = BaseOffset;
}
}
if (!FoundBase) {
if (MDCUsesEBO && BaseDecl->isEmpty() &&
BaseLayout.getNonVirtualSize() == CharUnits::Zero()) {
BaseOffset = CharUnits::Zero