1 //===--- CodeGenTypes.cpp - TBAA information for LLVM CodeGen -------------===// 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 // This is the code that manages TBAA information and defines the TBAA policy 11 // for the optimizer to use. Relevant standards text includes: 12 // 13 // C99 6.5p7 14 // C++ [basic.lval] (p10 in n3126, p15 in some earlier versions) 15 // 16 //===----------------------------------------------------------------------===// 17 18 #include "CodeGenTBAA.h" 19 #include "clang/AST/ASTContext.h" 20 #include "clang/AST/Attr.h" 21 #include "clang/AST/Mangle.h" 22 #include "clang/AST/RecordLayout.h" 23 #include "clang/Frontend/CodeGenOptions.h" 24 #include "llvm/IR/Constants.h" 25 #include "llvm/IR/LLVMContext.h" 26 #include "llvm/IR/Metadata.h" 27 #include "llvm/IR/Type.h" 28 using namespace clang; 29 using namespace CodeGen; 30 31 CodeGenTBAA::CodeGenTBAA(ASTContext &Ctx, llvm::LLVMContext& VMContext, 32 const CodeGenOptions &CGO, 33 const LangOptions &Features, MangleContext &MContext) 34 : Context(Ctx), CodeGenOpts(CGO), Features(Features), MContext(MContext), 35 MDHelper(VMContext), Root(0), Char(0) { 36 } 37 38 CodeGenTBAA::~CodeGenTBAA() { 39 } 40 41 llvm::MDNode *CodeGenTBAA::getRoot() { 42 // Define the root of the tree. This identifies the tree, so that 43 // if our LLVM IR is linked with LLVM IR from a different front-end 44 // (or a different version of this front-end), their TBAA trees will 45 // remain distinct, and the optimizer will treat them conservatively. 46 if (!Root) 47 Root = MDHelper.createTBAARoot("Simple C/C++ TBAA"); 48 49 return Root; 50 } 51 52 llvm::MDNode *CodeGenTBAA::getChar() { 53 // Define the root of the tree for user-accessible memory. C and C++ 54 // give special powers to char and certain similar types. However, 55 // these special powers only cover user-accessible memory, and doesn't 56 // include things like vtables. 57 if (!Char) 58 Char = MDHelper.createTBAANode("omnipotent char", getRoot()); 59 60 return Char; 61 } 62 63 static bool TypeHasMayAlias(QualType QTy) { 64 // Tagged types have declarations, and therefore may have attributes. 65 if (const TagType *TTy = dyn_cast<TagType>(QTy)) 66 return TTy->getDecl()->hasAttr<MayAliasAttr>(); 67 68 // Typedef types have declarations, and therefore may have attributes. 69 if (const TypedefType *TTy = dyn_cast<TypedefType>(QTy)) { 70 if (TTy->getDecl()->hasAttr<MayAliasAttr>()) 71 return true; 72 // Also, their underlying types may have relevant attributes. 73 return TypeHasMayAlias(TTy->desugar()); 74 } 75 76 return false; 77 } 78 79 llvm::MDNode * 80 CodeGenTBAA::getTBAAInfo(QualType QTy) { 81 // At -O0 TBAA is not emitted for regular types. 82 if (CodeGenOpts.OptimizationLevel == 0 || CodeGenOpts.RelaxedAliasing) 83 return NULL; 84 85 // If the type has the may_alias attribute (even on a typedef), it is 86 // effectively in the general char alias class. 87 if (TypeHasMayAlias(QTy)) 88 return getChar(); 89 90 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr(); 91 92 if (llvm::MDNode *N = MetadataCache[Ty]) 93 return N; 94 95 // Handle builtin types. 96 if (const BuiltinType *BTy = dyn_cast<BuiltinType>(Ty)) { 97 switch (BTy->getKind()) { 98 // Character types are special and can alias anything. 99 // In C++, this technically only includes "char" and "unsigned char", 100 // and not "signed char". In C, it includes all three. For now, 101 // the risk of exploiting this detail in C++ seems likely to outweigh 102 // the benefit. 103 case BuiltinType::Char_U: 104 case BuiltinType::Char_S: 105 case BuiltinType::UChar: 106 case BuiltinType::SChar: 107 return getChar(); 108 109 // Unsigned types can alias their corresponding signed types. 110 case BuiltinType::UShort: 111 return getTBAAInfo(Context.ShortTy); 112 case BuiltinType::UInt: 113 return getTBAAInfo(Context.IntTy); 114 case BuiltinType::ULong: 115 return getTBAAInfo(Context.LongTy); 116 case BuiltinType::ULongLong: 117 return getTBAAInfo(Context.LongLongTy); 118 case BuiltinType::UInt128: 119 return getTBAAInfo(Context.Int128Ty); 120 121 // Treat all other builtin types as distinct types. This includes 122 // treating wchar_t, char16_t, and char32_t as distinct from their 123 // "underlying types". 124 default: 125 return MetadataCache[Ty] = 126 MDHelper.createTBAANode(BTy->getName(Features), getChar()); 127 } 128 } 129 130 // Handle pointers. 131 // TODO: Implement C++'s type "similarity" and consider dis-"similar" 132 // pointers distinct. 133 if (Ty->isPointerType()) 134 return MetadataCache[Ty] = MDHelper.createTBAANode("any pointer", 135 getChar()); 136 137 // Enum types are distinct types. In C++ they have "underlying types", 138 // however they aren't related for TBAA. 139 if (const EnumType *ETy = dyn_cast<EnumType>(Ty)) { 140 // In C mode, two anonymous enums are compatible iff their members 141 // are the same -- see C99 6.2.7p1. For now, be conservative. We could 142 // theoretically implement this by combining information about all the 143 // members into a single identifying MDNode. 144 if (!Features.CPlusPlus && 145 ETy->getDecl()->getTypedefNameForAnonDecl()) 146 return MetadataCache[Ty] = getChar(); 147 148 // In C++ mode, types have linkage, so we can rely on the ODR and 149 // on their mangled names, if they're external. 150 // TODO: Is there a way to get a program-wide unique name for a 151 // decl with local linkage or no linkage? 152 if (Features.CPlusPlus && 153 ETy->getDecl()->getLinkage() != ExternalLinkage) 154 return MetadataCache[Ty] = getChar(); 155 156 // TODO: This is using the RTTI name. Is there a better way to get 157 // a unique string for a type? 158 SmallString<256> OutName; 159 llvm::raw_svector_ostream Out(OutName); 160 MContext.mangleCXXRTTIName(QualType(ETy, 0), Out); 161 Out.flush(); 162 return MetadataCache[Ty] = MDHelper.createTBAANode(OutName, getChar()); 163 } 164 165 // For now, handle any other kind of type conservatively. 166 return MetadataCache[Ty] = getChar(); 167 } 168 169 llvm::MDNode *CodeGenTBAA::getTBAAInfoForVTablePtr() { 170 return MDHelper.createTBAANode("vtable pointer", getRoot()); 171 } 172 173 bool 174 CodeGenTBAA::CollectFields(uint64_t BaseOffset, 175 QualType QTy, 176 SmallVectorImpl<llvm::MDBuilder::TBAAStructField> & 177 Fields, 178 bool MayAlias) { 179 /* Things not handled yet include: C++ base classes, bitfields, */ 180 181 if (const RecordType *TTy = QTy->getAs<RecordType>()) { 182 const RecordDecl *RD = TTy->getDecl()->getDefinition(); 183 if (RD->hasFlexibleArrayMember()) 184 return false; 185 186 // TODO: Handle C++ base classes. 187 if (const CXXRecordDecl *Decl = dyn_cast<CXXRecordDecl>(RD)) 188 if (Decl->bases_begin() != Decl->bases_end()) 189 return false; 190 191 const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD); 192 193 unsigned idx = 0; 194 for (RecordDecl::field_iterator i = RD->field_begin(), 195 e = RD->field_end(); i != e; ++i, ++idx) { 196 uint64_t Offset = BaseOffset + 197 Layout.getFieldOffset(idx) / Context.getCharWidth(); 198 QualType FieldQTy = i->getType(); 199 if (!CollectFields(Offset, FieldQTy, Fields, 200 MayAlias || TypeHasMayAlias(FieldQTy))) 201 return false; 202 } 203 return true; 204 } 205 206 /* Otherwise, treat whatever it is as a field. */ 207 uint64_t Offset = BaseOffset; 208 uint64_t Size = Context.getTypeSizeInChars(QTy).getQuantity(); 209 llvm::MDNode *TBAAInfo = MayAlias ? getChar() : getTBAAInfo(QTy); 210 Fields.push_back(llvm::MDBuilder::TBAAStructField(Offset, Size, TBAAInfo)); 211 return true; 212 } 213 214 llvm::MDNode * 215 CodeGenTBAA::getTBAAStructInfo(QualType QTy) { 216 const Type *Ty = Context.getCanonicalType(QTy).getTypePtr(); 217 218 if (llvm::MDNode *N = StructMetadataCache[Ty]) 219 return N; 220 221 SmallVector<llvm::MDBuilder::TBAAStructField, 4> Fields; 222 if (CollectFields(0, QTy, Fields, TypeHasMayAlias(QTy))) 223 return MDHelper.createTBAAStructNode(Fields); 224 225 // For now, handle any other kind of type conservatively. 226 return StructMetadataCache[Ty] = NULL; 227 } 228
