1 //===--- CGRecordLayout.h - LLVM Record Layout Information ------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 10 #ifndef CLANG_CODEGEN_CGRECORDLAYOUT_H 11 #define CLANG_CODEGEN_CGRECORDLAYOUT_H 12 13 #include "clang/AST/CharUnits.h" 14 #include "clang/AST/Decl.h" 15 #include "clang/Basic/LLVM.h" 16 #include "llvm/ADT/DenseMap.h" 17 #include "llvm/DerivedTypes.h" 18 19 namespace llvm { 20 class StructType; 21 } 22 23 namespace clang { 24 namespace CodeGen { 25 26 /// \brief Helper object for describing how to generate the code for access to a 27 /// bit-field. 28 /// 29 /// This structure is intended to describe the "policy" of how the bit-field 30 /// should be accessed, which may be target, language, or ABI dependent. 31 class CGBitFieldInfo { 32 public: 33 /// Descriptor for a single component of a bit-field access. The entire 34 /// bit-field is constituted of a bitwise OR of all of the individual 35 /// components. 36 /// 37 /// Each component describes an accessed value, which is how the component 38 /// should be transferred to/from memory, and a target placement, which is how 39 /// that component fits into the constituted bit-field. The pseudo-IR for a 40 /// load is: 41 /// 42 /// %0 = gep %base, 0, FieldIndex 43 /// %1 = gep (i8*) %0, FieldByteOffset 44 /// %2 = (i(AccessWidth) *) %1 45 /// %3 = load %2, align AccessAlignment 46 /// %4 = shr %3, FieldBitStart 47 /// 48 /// and the composed bit-field is formed as the boolean OR of all accesses, 49 /// masked to TargetBitWidth bits and shifted to TargetBitOffset. 50 struct AccessInfo { 51 /// Offset of the field to load in the LLVM structure, if any. 52 unsigned FieldIndex; 53 54 /// Byte offset from the field address, if any. This should generally be 55 /// unused as the cleanest IR comes from having a well-constructed LLVM type 56 /// with proper GEP instructions, but sometimes its use is required, for 57 /// example if an access is intended to straddle an LLVM field boundary. 58 CharUnits FieldByteOffset; 59 60 /// Bit offset in the accessed value to use. The width is implied by \see 61 /// TargetBitWidth. 62 unsigned FieldBitStart; 63 64 /// Bit width of the memory access to perform. 65 unsigned AccessWidth; 66 67 /// The alignment of the memory access, assuming the parent is aligned. 68 CharUnits AccessAlignment; 69 70 /// Offset for the target value. 71 unsigned TargetBitOffset; 72 73 /// Number of bits in the access that are destined for the bit-field. 74 unsigned TargetBitWidth; 75 }; 76 77 private: 78 /// The components to use to access the bit-field. We may need up to three 79 /// separate components to support up to i64 bit-field access (4 + 2 + 1 byte 80 /// accesses). 81 // 82 // FIXME: De-hardcode this, just allocate following the struct. 83 AccessInfo Components[3]; 84 85 /// The total size of the bit-field, in bits. 86 unsigned Size; 87 88 /// The number of access components to use. 89 unsigned NumComponents; 90 91 /// Whether the bit-field is signed. 92 bool IsSigned : 1; 93 94 public: 95 CGBitFieldInfo(unsigned Size, unsigned NumComponents, AccessInfo *_Components, 96 bool IsSigned) : Size(Size), NumComponents(NumComponents), 97 IsSigned(IsSigned) { 98 assert(NumComponents <= 3 && "invalid number of components!"); 99 for (unsigned i = 0; i != NumComponents; ++i) 100 Components[i] = _Components[i]; 101 102 // Check some invariants. 103 unsigned AccessedSize = 0; 104 for (unsigned i = 0, e = getNumComponents(); i != e; ++i) { 105 const AccessInfo &AI = getComponent(i); 106 AccessedSize += AI.TargetBitWidth; 107 108 // We shouldn't try to load 0 bits. 109 assert(AI.TargetBitWidth > 0); 110 111 // We can't load more bits than we accessed. 112 assert(AI.FieldBitStart + AI.TargetBitWidth <= AI.AccessWidth); 113 114 // We shouldn't put any bits outside the result size. 115 assert(AI.TargetBitWidth + AI.TargetBitOffset <= Size); 116 } 117 118 // Check that the total number of target bits matches the total bit-field 119 // size. 120 assert(AccessedSize == Size && "Total size does not match accessed size!"); 121 } 122 123 public: 124 /// \brief Check whether this bit-field access is (i.e., should be sign 125 /// extended on loads). 126 bool isSigned() const { return IsSigned; } 127 128 /// \brief Get the size of the bit-field, in bits. 129 unsigned getSize() const { return Size; } 130 131 /// @name Component Access 132 /// @{ 133 134 unsigned getNumComponents() const { return NumComponents; } 135 136 const AccessInfo &getComponent(unsigned Index) const { 137 assert(Index < getNumComponents() && "Invalid access!"); 138 return Components[Index]; 139 } 140 141 /// @} 142 143 void print(raw_ostream &OS) const; 144 void dump() const; 145 146 /// \brief Given a bit-field decl, build an appropriate helper object for 147 /// accessing that field (which is expected to have the given offset and 148 /// size). 149 static CGBitFieldInfo MakeInfo(class CodeGenTypes &Types, const FieldDecl *FD, 150 uint64_t FieldOffset, uint64_t FieldSize); 151 152 /// \brief Given a bit-field decl, build an appropriate helper object for 153 /// accessing that field (which is expected to have the given offset and 154 /// size). The field decl should be known to be contained within a type of at 155 /// least the given size and with the given alignment. 156 static CGBitFieldInfo MakeInfo(CodeGenTypes &Types, const FieldDecl *FD, 157 uint64_t FieldOffset, uint64_t FieldSize, 158 uint64_t ContainingTypeSizeInBits, 159 unsigned ContainingTypeAlign); 160 }; 161 162 /// CGRecordLayout - This class handles struct and union layout info while 163 /// lowering AST types to LLVM types. 164 /// 165 /// These layout objects are only created on demand as IR generation requires. 166 class CGRecordLayout { 167 friend class CodeGenTypes; 168 169 CGRecordLayout(const CGRecordLayout&); // DO NOT IMPLEMENT 170 void operator=(const CGRecordLayout&); // DO NOT IMPLEMENT 171 172 private: 173 /// The LLVM type corresponding to this record layout; used when 174 /// laying it out as a complete object. 175 llvm::StructType *CompleteObjectType; 176 177 /// The LLVM type for the non-virtual part of this record layout; 178 /// used when laying it out as a base subobject. 179 llvm::StructType *BaseSubobjectType; 180 181 /// Map from (non-bit-field) struct field to the corresponding llvm struct 182 /// type field no. This info is populated by record builder. 183 llvm::DenseMap<const FieldDecl *, unsigned> FieldInfo; 184 185 /// Map from (bit-field) struct field to the corresponding llvm struct type 186 /// field no. This info is populated by record builder. 187 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo> BitFields; 188 189 // FIXME: Maybe we could use a CXXBaseSpecifier as the key and use a single 190 // map for both virtual and non virtual bases. 191 llvm::DenseMap<const CXXRecordDecl *, unsigned> NonVirtualBases; 192 193 /// Map from virtual bases to their field index in the complete object. 194 llvm::DenseMap<const CXXRecordDecl *, unsigned> CompleteObjectVirtualBases; 195 196 /// False if any direct or indirect subobject of this class, when 197 /// considered as a complete object, requires a non-zero bitpattern 198 /// when zero-initialized. 199 bool IsZeroInitializable : 1; 200 201 /// False if any direct or indirect subobject of this class, when 202 /// considered as a base subobject, requires a non-zero bitpattern 203 /// when zero-initialized. 204 bool IsZeroInitializableAsBase : 1; 205 206 public: 207 CGRecordLayout(llvm::StructType *CompleteObjectType, 208 llvm::StructType *BaseSubobjectType, 209 bool IsZeroInitializable, 210 bool IsZeroInitializableAsBase) 211 : CompleteObjectType(CompleteObjectType), 212 BaseSubobjectType(BaseSubobjectType), 213 IsZeroInitializable(IsZeroInitializable), 214 IsZeroInitializableAsBase(IsZeroInitializableAsBase) {} 215 216 /// \brief Return the "complete object" LLVM type associated with 217 /// this record. 218 llvm::StructType *getLLVMType() const { 219 return CompleteObjectType; 220 } 221 222 /// \brief Return the "base subobject" LLVM type associated with 223 /// this record. 224 llvm::StructType *getBaseSubobjectLLVMType() const { 225 return BaseSubobjectType; 226 } 227 228 /// \brief Check whether this struct can be C++ zero-initialized 229 /// with a zeroinitializer. 230 bool isZeroInitializable() const { 231 return IsZeroInitializable; 232 } 233 234 /// \brief Check whether this struct can be C++ zero-initialized 235 /// with a zeroinitializer when considered as a base subobject. 236 bool isZeroInitializableAsBase() const { 237 return IsZeroInitializableAsBase; 238 } 239 240 /// \brief Return llvm::StructType element number that corresponds to the 241 /// field FD. 242 unsigned getLLVMFieldNo(const FieldDecl *FD) const { 243 assert(!FD->isBitField() && "Invalid call for bit-field decl!"); 244 assert(FieldInfo.count(FD) && "Invalid field for record!"); 245 return FieldInfo.lookup(FD); 246 } 247 248 unsigned getNonVirtualBaseLLVMFieldNo(const CXXRecordDecl *RD) const { 249 assert(NonVirtualBases.count(RD) && "Invalid non-virtual base!"); 250 return NonVirtualBases.lookup(RD); 251 } 252 253 /// \brief Return the LLVM field index corresponding to the given 254 /// virtual base. Only valid when operating on the complete object. 255 unsigned getVirtualBaseIndex(const CXXRecordDecl *base) const { 256 assert(CompleteObjectVirtualBases.count(base) && "Invalid virtual base!"); 257 return CompleteObjectVirtualBases.lookup(base); 258 } 259 260 /// \brief Return the BitFieldInfo that corresponds to the field FD. 261 const CGBitFieldInfo &getBitFieldInfo(const FieldDecl *FD) const { 262 assert(FD->isBitField() && "Invalid call for non bit-field decl!"); 263 llvm::DenseMap<const FieldDecl *, CGBitFieldInfo>::const_iterator 264 it = BitFields.find(FD); 265 assert(it != BitFields.end() && "Unable to find bitfield info"); 266 return it->second; 267 } 268 269 void print(raw_ostream &OS) const; 270 void dump() const; 271 }; 272 273 } // end namespace CodeGen 274 } // end namespace clang 275 276 #endif 277
