//===--- CGRecordLayoutBuilder.cpp - CGRecordLayout builder ----*- C++ -*-===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // Builder implementation for CGRecordLayout objects. // //===----------------------------------------------------------------------===// #include "CGRecordLayout.h" #include "CGCXXABI.h" #include "CodeGenTypes.h" #include "clang/AST/ASTContext.h" #include "clang/AST/Attr.h" #include "clang/AST/CXXInheritance.h" #include "clang/AST/DeclCXX.h" #include "clang/AST/Expr.h" #include "clang/AST/RecordLayout.h" #include "clang/Frontend/CodeGenOptions.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/DerivedTypes.h" #include "llvm/IR/Type.h" #include "llvm/Support/Debug.h" #include "llvm/Support/MathExtras.h" #include "llvm/Support/raw_ostream.h" using namespace clang; using namespace CodeGen; namespace { /// The CGRecordLowering is responsible for lowering an ASTRecordLayout to an /// llvm::Type. Some of the lowering is straightforward, some is not. Here we /// detail some of the complexities and weirdnesses here. /// * LLVM does not have unions - Unions can, in theory be represented by any /// llvm::Type with correct size. We choose a field via a specific heuristic /// and add padding if necessary. /// * LLVM does not have bitfields - Bitfields are collected into contiguous /// runs and allocated as a single storage type for the run. ASTRecordLayout /// contains enough information to determine where the runs break. Microsoft /// and Itanium follow different rules and use different codepaths. /// * It is desired that, when possible, bitfields use the appropriate iN type /// when lowered to llvm types. For example unsigned x : 24 gets lowered to /// i24. This isn't always possible because i24 has storage size of 32 bit /// and if it is possible to use that extra byte of padding we must use /// [i8 x 3] instead of i24. The function clipTailPadding does this. /// C++ examples that require clipping: /// struct { int a : 24; char b; }; // a must be clipped, b goes at offset 3 /// struct A { int a : 24; }; // a must be clipped because a struct like B // could exist: struct B : A { char b; }; // b goes at offset 3 /// * Clang ignores 0 sized bitfields and 0 sized bases but *not* zero sized /// fields. The existing asserts suggest that LLVM assumes that *every* field /// has an underlying storage type. Therefore empty structures containing /// zero sized subobjects such as empty records or zero sized arrays still get /// a zero sized (empty struct) storage type. /// * Clang reads the complete type rather than the base type when generating /// code to access fields. Bitfields in tail position with tail padding may /// be clipped in the base class but not the complete class (we may discover /// that the tail padding is not used in the complete class.) However, /// because LLVM reads from the complete type it can generate incorrect code /// if we do not clip the tail padding off of the bitfield in the complete /// layout. This introduces a somewhat awkward extra unnecessary clip stage. /// The location of the clip is stored internally as a sentinal of type /// SCISSOR. If LLVM were updated to read base types (which it probably /// should because locations of things such as VBases are bogus in the llvm /// type anyway) then we could eliminate the SCISSOR. /// * Itanium allows nearly empty primary virtual bases. These bases don't get /// get their own storage because they're laid out as part of another base /// or at the beginning of the structure. Determining if a VBase actually /// gets storage awkwardly involves a walk of all bases. /// * VFPtrs and VBPtrs do *not* make a record NotZeroInitializable. struct CGRecordLowering { // MemberInfo is a helper structure that contains information about a record // member. In additional to the standard member types, there exists a // sentinal member type that ensures correct rounding. struct MemberInfo { CharUnits Offset; enum InfoKind { VFPtr, VBPtr, Field, Base, VBase, Scissor } Kind; llvm::Type *Data; union { const FieldDecl *FD; const CXXRecordDecl *RD; }; MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data, const FieldDecl *FD = nullptr) : Offset(Offset), Kind(Kind), Data(Data), FD(FD) {} MemberInfo(CharUnits Offset, InfoKind Kind, llvm::Type *Data, const CXXRecordDecl *RD) : Offset(Offset), Kind(Kind), Data(Data), RD(RD) {} // MemberInfos are sorted so we define a < operator. bool operator <(const MemberInfo& a) const { return Offset < a.Offset; } }; // The constructor. CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D, bool Packed); // Short helper routines. /// \brief Constructs a MemberInfo instance from an offset and llvm::Type *. MemberInfo StorageInfo(CharUnits Offset, llvm::Type *Data) { return MemberInfo(Offset, MemberInfo::Field, Data); } /// The Microsoft bitfield layout rule allocates discrete storage /// units of the field's formal type and only combines adjacent /// fields of the same formal type. We want to emit a layout with /// these discrete storage units instead of combining them into a /// continuous run. bool isDiscreteBitFieldABI() { return Context.getTargetInfo().getCXXABI().isMicrosoft() || D->isMsStruct(Context); } /// The Itanium base layout rule allows virtual bases to overlap /// other bases, which complicates layout in specific ways. /// /// Note specifically that the ms_struct attribute doesn't change this. bool isOverlappingVBaseABI() { return !Context.getTargetInfo().getCXXABI().isMicrosoft(); } /// \brief Wraps llvm::Type::getIntNTy with some implicit arguments. llvm::Type *getIntNType(uint64_t NumBits) { return llvm::Type::getIntNTy(Types.getLLVMContext(), (unsigned)llvm::RoundUpToAlignment(NumBits, 8)); } /// \brief Gets an llvm type of size NumBytes and alignment 1. llvm::Type *getByteArrayType(CharUnits NumBytes) { assert(!NumBytes.isZero() && "Empty byte arrays aren't allowed."); llvm::Type *Type = llvm::Type::getInt8Ty(Types.getLLVMContext()); return NumBytes == CharUnits::One() ? Type : (llvm::Type *)llvm::ArrayType::get(Type, NumBytes.getQuantity()); } /// \brief Gets the storage type for a field decl and handles storage /// for itanium bitfields that are smaller than their declared type. llvm::Type *getStorageType(const FieldDecl *FD) { llvm::Type *Type = Types.ConvertTypeForMem(FD->getType()); if (!FD->isBitField()) return Type; if (isDiscreteBitFieldABI()) return Type; return getIntNType(std::min(FD->getBitWidthValue(Context), (unsigned)Context.toBits(getSize(Type)))); } /// \brief Gets the llvm Basesubobject type from a CXXRecordDecl. llvm::Type *getStorageType(const CXXRecordDecl *RD) { return Types.getCGRecordLayout(RD).getBaseSubobjectLLVMType(); } CharUnits bitsToCharUnits(uint64_t BitOffset) { return Context.toCharUnitsFromBits(BitOffset); } CharUnits getSize(llvm::Type *Type) { return CharUnits::fromQuantity(DataLayout.getTypeAllocSize(Type)); } CharUnits getAlignment(llvm::Type *Type) { return CharUnits::fromQuantity(DataLayout.getABITypeAlignment(Type)); } bool isZeroInitializable(const FieldDecl *FD) { return Types.isZeroInitializable(FD->getType()); } bool isZeroInitializable(const RecordDecl *RD) { return Types.isZeroInitializable(RD); } void appendPaddingBytes(CharUnits Size) { if (!Size.isZero()) FieldTypes.push_back(getByteArrayType(Size)); } uint64_t getFieldBitOffset(const FieldDecl *FD) { return Layout.getFieldOffset(FD->getFieldIndex()); } // Layout routines. void setBitFieldInfo(const FieldDecl *FD, CharUnits StartOffset, llvm::Type *StorageType); /// \brief Lowers an ASTRecordLayout to a llvm type. void lower(bool NonVirtualBaseType); void lowerUnion(); void accumulateFields(); void accumulateBitFields(RecordDecl::field_iterator Field, RecordDecl::field_iterator FieldEnd); void accumulateBases(); void accumulateVPtrs(); void accumulateVBases(); /// \brief Recursively searches all of the bases to find out if a vbase is /// not the primary vbase of some base class. bool hasOwnStorage(const CXXRecordDecl *Decl, const CXXRecordDecl *Query); void calculateZeroInit(); /// \brief Lowers bitfield storage types to I8 arrays for bitfields with tail /// padding that is or can potentially be used. void clipTailPadding(); /// \brief Determines if we need a packed llvm struct. void determinePacked(bool NVBaseType); /// \brief Inserts padding everwhere it's needed. void insertPadding(); /// \brief Fills out the structures that are ultimately consumed. void fillOutputFields(); // Input memoization fields. CodeGenTypes &Types; const ASTContext &Context; const RecordDecl *D; const CXXRecordDecl *RD; const ASTRecordLayout &Layout; const llvm::DataLayout &DataLayout; // Helpful intermediate data-structures. std::vector<MemberInfo> Members; // Output fields, consumed by CodeGenTypes::ComputeRecordLayout. SmallVector<llvm::Type *, 16> FieldTypes; llvm::DenseMap<const FieldDecl *, unsigned> Fields; llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields; llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases; llvm::DenseMap<const CXXRecordDecl *, unsigned> VirtualBases; bool IsZeroInitializable : 1; bool IsZeroInitializableAsBase : 1; bool Packed : 1; private: CGRecordLowering(const CGRecordLowering &) = delete; void operator =(const CGRecordLowering &) = delete; }; } // namespace { CGRecordLowering::CGRecordLowering(CodeGenTypes &Types, const RecordDecl *D, bool Packed) : Types(Types), Context(Types.getContext()), D(D), RD(dyn_cast<CXXRecordDecl>(D)), Layout(Types.getContext().getASTRecordLayout(D)), DataLayout(Types.getDataLayout()), IsZeroInitializable(true), IsZeroInitializableAsBase(true), Packed(Packed) {} void CGRecordLowering::setBitFieldInfo( const FieldDecl *FD, CharUnits StartOffset, llvm::Type *StorageType) { CGBitFieldInfo &Info = BitFields[FD->getCanonicalDecl()]; Info.IsSigned = FD->getType()->isSignedIntegerOrEnumerationType(); Info.Offset = (unsigned)(getFieldBitOffset(FD) - Context.toBits(StartOffset)); Info.Size = FD->getBitWidthValue(Context); Info.StorageSize = (unsigned)DataLayout.getTypeAllocSizeInBits(StorageType); Info.StorageOffset = StartOffset; if (Info.Size > Info.StorageSize) Info.Size = Info.StorageSize; // Reverse the bit offsets for big endian machines. Because we represent // a bitfield as a single large integer load, we can imagine the bits // counting from the most-significant-bit instead of the // least-significant-bit. if (DataLayout.isBigEndian()) Info.Offset = Info.StorageSize - (Info.Offset + Info.Size); } void CGRecordLowering::lower(bool NVBaseType) { // The lowering process implemented in this function takes a variety of // carefully ordered phases. // 1) Store all members (fields and bases) in a list and sort them by offset. // 2) Add a 1-byte capstone member at the Size of the structure. // 3) Clip bitfield storages members if their tail padding is or might be // used by another field or base. The clipping process uses the capstone // by treating it as another object that occurs after the record. // 4) Determine if the llvm-struct requires packing. It's important that this // phase occur after clipping, because clipping changes the llvm type. // This phase reads the offset of the capstone when determining packedness // and updates the alignment of the capstone to be equal of the alignment // of the record after doing so. // 5) Insert padding everywhere it is needed. This phase requires 'Packed' to // have been computed and needs to know the alignment of the record in // order to understand if explicit tail padding is needed. // 6) Remove the capstone, we don't need it anymore. // 7) Determine if this record can be zero-initialized. This phase could have // been placed anywhere after phase 1. // 8) Format the complete list of members in a way that can be consumed by // CodeGenTypes::ComputeRecordLayout. CharUnits Size = NVBaseType ? Layout.getNonVirtualSize() : Layout.getSize(); if (D->isUnion()) return lowerUnion(); accumulateFields(); // RD implies C++. if (RD) { accumulateVPtrs(); accumulateBases(); if (Members.empty()) return appendPaddingBytes(Size); if (!NVBaseType) accumulateVBases(); } std::stable_sort(Members.begin(), Members.end()); Members.push_back(StorageInfo(Size, getIntNType(8))); clipTailPadding(); determinePacked(NVBaseType); insertPadding(); Members.pop_back(); calculateZeroInit(); fillOutputFields(); } void CGRecordLowering::lowerUnion() { CharUnits LayoutSize = Layout.getSize(); llvm::Type *StorageType = nullptr; bool SeenNamedMember = false; // Iterate through the fields setting bitFieldInfo and the Fields array. Also // locate the "most appropriate" storage type. The heuristic for finding the // storage type isn't necessary, the first (non-0-length-bitfield) field's // type would work fine and be simpler but would be different than what we've // been doing and cause lit tests to change. for (const auto *Field : D->fields()) { if (Field->isBitField()) { // Skip 0 sized bitfields. if (Field->getBitWidthValue(Context) == 0) continue; llvm::Type *FieldType = getStorageType(Field); if (LayoutSize < getSize(FieldType)) FieldType = getByteArrayType(LayoutSize); setBitFieldInfo(Field, CharUnits::Zero(), FieldType); } Fields[Field->getCanonicalDecl()] = 0; llvm::Type *FieldType = getStorageType(Field); // Compute zero-initializable status. // This union might not be zero initialized: it may contain a pointer to // data member which might have some exotic initialization sequence. // If this is the case, then we aught not to try and come up with a "better" // type, it might not be very easy to come up with a Constant which // correctly initializes it. if (!SeenNamedMember) { SeenNamedMember = Field->getIdentifier(); if (!SeenNamedMember) if (const auto *FieldRD = dyn_cast_or_null<RecordDecl>(Field->getType()->getAsTagDecl())) SeenNamedMember = FieldRD->findFirstNamedDataMember(); if (SeenNamedMember && !isZeroInitializable(Field)) { IsZeroInitializable = IsZeroInitializableAsBase = false; StorageType = FieldType; } } // Because our union isn't zero initializable, we won't be getting a better // storage type. if (!IsZeroInitializable) continue; // Conditionally update our storage type if we've got a new "better" one. if (!StorageType || getAlignment(FieldType) > getAlignment(StorageType) || (getAlignment(FieldType) == getAlignment(StorageType) && getSize(FieldType) > getSize(StorageType))) StorageType = FieldType; } // If we have no storage type just pad to the appropriate size and return. if (!StorageType) return appendPaddingBytes(LayoutSize); // If our storage size was bigger than our required size (can happen in the // case of packed bitfields on Itanium) then just use an I8 array. if (LayoutSize < getSize(StorageType)) StorageType = getByteArrayType(LayoutSize); FieldTypes.push_back(StorageType); appendPaddingBytes(LayoutSize - getSize(StorageType)); // Set packed if we need it. if (LayoutSize % getAlignment(StorageType)) Packed = true; } void CGRecordLowering::accumulateFields() { for (RecordDecl::field_iterator Field = D->field_begin(), FieldEnd = D->field_end(); Field != FieldEnd;) if (Field->isBitField()) { RecordDecl::field_iterator Start = Field; // Iterate to gather the list of bitfields. for (++Field; Field != FieldEnd && Field->isBitField(); ++Field); accumulateBitFields(Start, Field); } else { Members.push_back(MemberInfo( bitsToCharUnits(getFieldBitOffset(*Field)), MemberInfo::Field, getStorageType(*Field), *Field)); ++Field; } } void CGRecordLowering::accumulateBitFields(RecordDecl::field_iterator Field, RecordDecl::field_iterator FieldEnd) { // Run stores the first element of the current run of bitfields. FieldEnd is // used as a special value to note that we don't have a current run. A // bitfield run is a contiguous collection of bitfields that can be stored in // the same storage block. Zero-sized bitfields and bitfields that would // cross an alignment boundary break a run and start a new one. RecordDecl::field_iterator Run = FieldEnd; // Tail is the offset of the first bit off the end of the current run. It's // used to determine if the ASTRecordLayout is treating these two bitfields as // contiguous. StartBitOffset is offset of the beginning of the Run. uint64_t StartBitOffset, Tail = 0; if (isDiscreteBitFieldABI()) { for (; Field != FieldEnd; ++Field) { uint64_t BitOffset = getFieldBitOffset(*Field); // Zero-width bitfields end runs. if (Field->getBitWidthValue(Context) == 0) { Run = FieldEnd; continue; } llvm::Type *Type = Types.ConvertTypeForMem(Field->getType()); // If we don't have a run yet, or don't live within the previous run's // allocated storage then we allocate some storage and start a new run. if (Run == FieldEnd || BitOffset >= Tail) { Run = Field; StartBitOffset = BitOffset; Tail = StartBitOffset + DataLayout.getTypeAllocSizeInBits(Type); // Add the storage member to the record. This must be added to the // record before the bitfield members so that it gets laid out before // the bitfields it contains get laid out. Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type)); } // Bitfields get the offset of their storage but come afterward and remain // there after a stable sort. Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset), MemberInfo::Field, nullptr, *Field)); } return; } for (;;) { // Check to see if we need to start a new run. if (Run == FieldEnd) { // If we're out of fields, return. if (Field == FieldEnd) break; // Any non-zero-length bitfield can start a new run. if (Field->getBitWidthValue(Context) != 0) { Run = Field; StartBitOffset = getFieldBitOffset(*Field); Tail = StartBitOffset + Field->getBitWidthValue(Context); } ++Field; continue; } // Add bitfields to the run as long as they qualify. if (Field != FieldEnd && Field->getBitWidthValue(Context) != 0 && Tail == getFieldBitOffset(*Field)) { Tail += Field->getBitWidthValue(Context); ++Field; continue; } // We've hit a break-point in the run and need to emit a storage field. llvm::Type *Type = getIntNType(Tail - StartBitOffset); // Add the storage member to the record and set the bitfield info for all of // the bitfields in the run. Bitfields get the offset of their storage but // come afterward and remain there after a stable sort. Members.push_back(StorageInfo(bitsToCharUnits(StartBitOffset), Type)); for (; Run != Field; ++Run) Members.push_back(MemberInfo(bitsToCharUnits(StartBitOffset), MemberInfo::Field, nullptr, *Run)); Run = FieldEnd; } } void CGRecordLowering::accumulateBases() { // If we've got a primary virtual base, we need to add it with the bases. if (Layout.isPrimaryBaseVirtual()) { const CXXRecordDecl *BaseDecl = Layout.getPrimaryBase(); Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::Base, getStorageType(BaseDecl), BaseDecl)); } // Accumulate the non-virtual bases. for (const auto &Base : RD->bases()) { if (Base.isVirtual()) continue; // Bases can be zero-sized even if not technically empty if they // contain only a trailing array member. const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl(); if (!BaseDecl->isEmpty() && !Context.getASTRecordLayout(BaseDecl).getNonVirtualSize().isZero()) Members.push_back(MemberInfo(Layout.getBaseClassOffset(BaseDecl), MemberInfo::Base, getStorageType(BaseDecl), BaseDecl)); } } void CGRecordLowering::accumulateVPtrs() { if (Layout.hasOwnVFPtr()) Members.push_back(MemberInfo(CharUnits::Zero(), MemberInfo::VFPtr, llvm::FunctionType::get(getIntNType(32), /*isVarArg=*/true)-> getPointerTo()->getPointerTo())); if (Layout.hasOwnVBPtr()) Members.push_back(MemberInfo(Layout.getVBPtrOffset(), MemberInfo::VBPtr, llvm::Type::getInt32PtrTy(Types.getLLVMContext()))); } void CGRecordLowering::accumulateVBases() { CharUnits ScissorOffset = Layout.getNonVirtualSize(); // In the itanium ABI, it's possible to place a vbase at a dsize that is // smaller than the nvsize. Here we check to see if such a base is placed // before the nvsize and set the scissor offset to that, instead of the // nvsize. if (isOverlappingVBaseABI()) for (const auto &Base : RD->vbases()) { const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl(); if (BaseDecl->isEmpty()) continue; // If the vbase is a primary virtual base of some base, then it doesn't // get its own storage location but instead lives inside of that base. if (Context.isNearlyEmpty(BaseDecl) && !hasOwnStorage(RD, BaseDecl)) continue; ScissorOffset = std::min(ScissorOffset, Layout.getVBaseClassOffset(BaseDecl)); } Members.push_back(MemberInfo(ScissorOffset, MemberInfo::Scissor, nullptr, RD)); for (const auto &Base : RD->vbases()) { const CXXRecordDecl *BaseDecl = Base.getType()->getAsCXXRecordDecl(); if (BaseDecl->isEmpty()) continue; CharUnits Offset = Layout.getVBaseClassOffset(BaseDecl); // If the vbase is a primary virtual base of some base, then it doesn't // get its own storage location but instead lives inside of that base. if (isOverlappingVBaseABI() && Context.isNearlyEmpty(BaseDecl) && !hasOwnStorage(RD, BaseDecl)) { Members.push_back(MemberInfo(Offset, MemberInfo::VBase, nullptr, BaseDecl)); continue; } // If we've got a vtordisp, add it as a storage type. if (Layout.getVBaseOffsetsMap().find(BaseDecl)->second.hasVtorDisp()) Members.push_back(StorageInfo(Offset - CharUnits::fromQuantity(4), getIntNType(32))); Members.push_back(MemberInfo(Offset, MemberInfo::VBase, getStorageType(BaseDecl), BaseDecl)); } } bool CGRecordLowering::hasOwnStorage(const CXXRecordDecl *Decl, const CXXRecordDecl *Query) { const ASTRecordLayout &DeclLayout = Context.getASTRecordLayout(Decl); if (DeclLayout.isPrimaryBaseVirtual() && DeclLayout.getPrimaryBase() == Query) return false; for (const auto &Base : Decl->bases()) if (!hasOwnStorage(Base.getType()->getAsCXXRecordDecl(), Query)) return false; return true; } void CGRecordLowering::calculateZeroInit() { for (std::vector<MemberInfo>::const_iterator Member = Members.begin(), MemberEnd = Members.end(); IsZeroInitializableAsBase && Member != MemberEnd; ++Member) { if (Member->Kind == MemberInfo::Field) { if (!Member->FD || isZeroInitializable(Member->FD)) continue; IsZeroInitializable = IsZeroInitializableAsBase = false; } else if (Member->Kind == MemberInfo::Base || Member->Kind == MemberInfo::VBase) { if (isZeroInitializable(Member->RD)) continue; IsZeroInitializable = false; if (Member->Kind == MemberInfo::Base) IsZeroInitializableAsBase = false; } } } void CGRecordLowering::clipTailPadding() { std::vector<MemberInfo>::iterator Prior = Members.begin(); CharUnits Tail = getSize(Prior->Data); for (std::vector<MemberInfo>::iterator Member = Prior + 1, MemberEnd = Members.end(); Member != MemberEnd; ++Member) { // Only members with data and the scissor can cut into tail padding. if (!Member->Data && Member->Kind != MemberInfo::Scissor) continue; if (Member->Offset < Tail) { assert(Prior->Kind == MemberInfo::Field && !Prior->FD && "Only storage fields have tail padding!"); Prior->Data = getByteArrayType(bitsToCharUnits(llvm::RoundUpToAlignment( cast<llvm::IntegerType>(Prior->Data)->getIntegerBitWidth(), 8))); } if (Member->Data) Prior = Member; Tail = Prior->Offset + getSize(Prior->Data); } } void CGRecordLowering::determinePacked(bool NVBaseType) { if (Packed) return; CharUnits Alignment = CharUnits::One(); CharUnits NVAlignment = CharUnits::One(); CharUnits NVSize = !NVBaseType && RD ? Layout.getNonVirtualSize() : CharUnits::Zero(); for (std::vector<MemberInfo>::const_iterator Member = Members.begin(), MemberEnd = Members.end(); Member != MemberEnd; ++Member) { if (!Member->Data) continue; // If any member falls at an offset that it not a multiple of its alignment, // then the entire record must be packed. if (Member->Offset % getAlignment(Member->Data)) Packed = true; if (Member->Offset < NVSize) NVAlignment = std::max(NVAlignment, getAlignment(Member->Data)); Alignment = std::max(Alignment, getAlignment(Member->Data)); } // If the size of the record (the capstone's offset) is not a multiple of the // record's alignment, it must be packed. if (Members.back().Offset % Alignment) Packed = true; // If the non-virtual sub-object is not a multiple of the non-virtual // sub-object's alignment, it must be packed. We cannot have a packed // non-virtual sub-object and an unpacked complete object or vise versa. if (NVSize % NVAlignment) Packed = true; // Update the alignment of the sentinal. if (!Packed) Members.back().Data = getIntNType(Context.toBits(Alignment)); } void CGRecordLowering::insertPadding() { std::vector<std::pair<CharUnits, CharUnits> > Padding; CharUnits Size = CharUnits::Zero(); for (std::vector<MemberInfo>::const_iterator Member = Members.begin(), MemberEnd = Members.end(); Member != MemberEnd; ++Member) { if (!Member->Data) continue; CharUnits Offset = Member->Offset; assert(Offset >= Size); // Insert padding if we need to. if (Offset != Size.RoundUpToAlignment(Packed ? CharUnits::One() : getAlignment(Member->Data))) Padding.push_back(std::make_pair(Size, Offset - Size)); Size = Offset + getSize(Member->Data); } if (Padding.empty()) return; // Add the padding to the Members list and sort it. for (std::vector<std::pair<CharUnits, CharUnits> >::const_iterator Pad = Padding.begin(), PadEnd = Padding.end(); Pad != PadEnd; ++Pad) Members.push_back(StorageInfo(Pad->first, getByteArrayType(Pad->second))); std::stable_sort(Members.begin(), Members.end()); } void CGRecordLowering::fillOutputFields() { for (std::vector<MemberInfo>::const_iterator Member = Members.begin(), MemberEnd = Members.end(); Member != MemberEnd; ++Member) { if (Member->Data) FieldTypes.push_back(Member->Data); if (Member->Kind == MemberInfo::Field) { if (Member->FD) Fields[Member->FD->getCanonicalDecl()] = FieldTypes.size() - 1; // A field without storage must be a bitfield. if (!Member->Data) setBitFieldInfo(Member->FD, Member->Offset, FieldTypes.back()); } else if (Member->Kind == MemberInfo::Base) NonVirtualBases[Member->RD] = FieldTypes.size() - 1; else if (Member->Kind == MemberInfo::VBase) VirtualBases[Member->RD] = FieldTypes.size() - 1; } } CGBitFieldInfo CGBitFieldInfo::MakeInfo(CodeGenTypes &Types, const FieldDecl *FD, uint64_t Offset, uint64_t Size, uint64_t StorageSize, CharUnits StorageOffset) { // This function is vestigial from CGRecordLayoutBuilder days but is still // used in GCObjCRuntime.cpp. That usage has a "fixme" attached to it that // when addressed will allow for the removal of this function. llvm::Type *Ty = Types.ConvertTypeForMem(FD->getType()); CharUnits TypeSizeInBytes = CharUnits::fromQuantity(Types.getDataLayout().getTypeAllocSize(Ty)); uint64_t TypeSizeInBits = Types.getContext().toBits(TypeSizeInBytes); bool IsSigned = FD->getType()->isSignedIntegerOrEnumerationType(); if (Size > TypeSizeInBits) { // We have a wide bit-field. The extra bits are only used for padding, so // if we have a bitfield of type T, with size N: // // T t : N; // // We can just assume that it's: // // T t : sizeof(T); // Size = TypeSizeInBits; } // Reverse the bit offsets for big endian machines. Because we represent // a bitfield as a single large integer load, we can imagine the bits // counting from the most-significant-bit instead of the // least-significant-bit. if (Types.getDataLayout().isBigEndian()) { Offset = StorageSize - (Offset + Size); } return CGBitFieldInfo(Offset, Size, IsSigned, StorageSize, StorageOffset); } CGRecordLayout *CodeGenTypes::ComputeRecordLayout(const RecordDecl *D, llvm::StructType *Ty) { CGRecordLowering Builder(*this, D, /*Packed=*/false); Builder.lower(/*NonVirtualBaseType=*/false); // If we're in C++, compute the base subobject type. llvm::StructType *BaseTy = nullptr; if (isa<CXXRecordDecl>(D) && !D->isUnion() && !D->hasAttr<FinalAttr>()) { BaseTy = Ty; if (Builder.Layout.getNonVirtualSize() != Builder.Layout.getSize()) { CGRecordLowering BaseBuilder(*this, D, /*Packed=*/Builder.Packed); BaseBuilder.lower(/*NonVirtualBaseType=*/true); BaseTy = llvm::StructType::create( getLLVMContext(), BaseBuilder.FieldTypes, "", BaseBuilder.Packed); addRecordTypeName(D, BaseTy, ".base"); // BaseTy and Ty must agree on their packedness for getLLVMFieldNo to work // on both of them with the same index. assert(Builder.Packed == BaseBuilder.Packed && "Non-virtual and complete types must agree on packedness"); } } // Fill in the struct *after* computing the base type. Filling in the body // signifies that the type is no longer opaque and record layout is complete, // but we may need to recursively layout D while laying D out as a base type. Ty->setBody(Builder.FieldTypes, Builder.Packed); CGRecordLayout *RL = new CGRecordLayout(Ty, BaseTy, Builder.IsZeroInitializable, Builder.IsZeroInitializableAsBase); RL->NonVirtualBases.swap(Builder.NonVirtualBases); RL->CompleteObjectVirtualBases.swap(Builder.VirtualBases); // Add all the field numbers. RL->FieldInfo.swap(Builder.Fields); // Add bitfield info. RL->BitFields.swap(Builder.BitFields); // Dump the layout, if requested. if (getContext().getLangOpts().DumpRecordLayouts) { llvm::outs() << "\n*** Dumping IRgen Record Layout\n"; llvm::outs() << "Record: "; D->dump(llvm::outs()); llvm::outs() << "\nLayout: "; RL->print(llvm::outs()); } #ifndef NDEBUG // Verify that the computed LLVM struct size matches the AST layout size. const ASTRecordLayout &Layout = getContext().getASTRecordLayout(D); uint64_t TypeSizeInBits = getContext().toBits(Layout.getSize()); assert(TypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(Ty) && "Type size mismatch!"); if (BaseTy) { CharUnits NonVirtualSize = Layout.getNonVirtualSize(); uint64_t AlignedNonVirtualTypeSizeInBits = getContext().toBits(NonVirtualSize); assert(AlignedNonVirtualTypeSizeInBits == getDataLayout().getTypeAllocSizeInBits(BaseTy) && "Type size mismatch!"); } // Verify that the LLVM and AST field offsets agree. llvm::StructType *ST = dyn_cast<llvm::StructType>(RL->getLLVMType()); const llvm::StructLayout *SL = getDataLayout().getStructLayout(ST); const ASTRecordLayout &AST_RL = getContext().getASTRecordLayout(D); RecordDecl::field_iterator it = D->field_begin(); for (unsigned i = 0, e = AST_RL.getFieldCount(); i != e; ++i, ++it) { const FieldDecl *FD = *it; // For non-bit-fields, just check that the LLVM struct offset matches the // AST offset. if (!FD->isBitField()) { unsigned FieldNo = RL->getLLVMFieldNo(FD); assert(AST_RL.getFieldOffset(i) == SL->getElementOffsetInBits(FieldNo) && "Invalid field offset!"); continue; } // Ignore unnamed bit-fields. if (!FD->getDeclName()) continue; // Don't inspect zero-length bitfields. if (FD->getBitWidthValue(getContext()) == 0) continue; const CGBitFieldInfo &Info = RL->getBitFieldInfo(FD); llvm::Type *ElementTy = ST->getTypeAtIndex(RL->getLLVMFieldNo(FD)); // Unions have overlapping elements dictating their layout, but for // non-unions we can verify that this section of the layout is the exact // expected size. if (D->isUnion()) { // For unions we verify that the start is zero and the size // is in-bounds. However, on BE systems, the offset may be non-zero, but // the size + offset should match the storage size in that case as it // "starts" at the back. if (getDataLayout().isBigEndian()) assert(static_cast<unsigned>(Info.Offset + Info.Size) == Info.StorageSize && "Big endian union bitfield does not end at the back"); else assert(Info.Offset == 0 && "Little endian union bitfield with a non-zero offset"); assert(Info.StorageSize <= SL->getSizeInBits() && "Union not large enough for bitfield storage"); } else { assert(Info.StorageSize == getDataLayout().getTypeAllocSizeInBits(ElementTy) && "Storage size does not match the element type size"); } assert(Info.Size > 0 && "Empty bitfield!"); assert(static_cast<unsigned>(Info.Offset) + Info.Size <= Info.StorageSize && "Bitfield outside of its allocated storage"); } #endif return RL; } void CGRecordLayout::print(raw_ostream &OS) const { OS << "<CGRecordLayout\n"; OS << " LLVMType:" << *CompleteObjectType << "\n"; if (BaseSubobjectType) OS << " NonVirtualBaseLLVMType:" << *BaseSubobjectType << "\n"; OS << " IsZeroInitializable:" << IsZeroInitializable << "\n"; OS << " BitFields:[\n"; // Print bit-field infos in declaration order. std::vector<std::pair<unsigned, const CGBitFieldInfo*> > BFIs; for (llvm::DenseMap<const FieldDecl*, CGBitFieldInfo>::const_iterator it = BitFields.begin(), ie = BitFields.end(); it != ie; ++it) { const RecordDecl *RD = it->first->getParent(); unsigned Index = 0; for (RecordDecl::field_iterator it2 = RD->field_begin(); *it2 != it->first; ++it2) ++Index; BFIs.push_back(std::make_pair(Index, &it->second)); } llvm::array_pod_sort(BFIs.begin(), BFIs.end()); for (unsigned i = 0, e = BFIs.size(); i != e; ++i) { OS.indent(4); BFIs[i].second->print(OS); OS << "\n"; } OS << "]>\n"; } void CGRecordLayout::dump() const { print(llvm::errs()); } void CGBitFieldInfo::print(raw_ostream &OS) const { OS << "<CGBitFieldInfo" << " Offset:" << Offset << " Size:" << Size << " IsSigned:" << IsSigned << " StorageSize:" << StorageSize << " StorageOffset:" << StorageOffset.getQuantity() << ">"; } void CGBitFieldInfo::dump() const { print(llvm::errs()); }