1 //===--- CGDecl.cpp - Emit LLVM Code for declarations ---------------------===// 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 contains code dealing with C++ code generation. 11 // 12 //===----------------------------------------------------------------------===// 13 14 // We might split this into multiple files if it gets too unwieldy 15 16 #include "CGCXXABI.h" 17 #include "CodeGenFunction.h" 18 #include "CodeGenModule.h" 19 #include "Mangle.h" 20 #include "clang/AST/ASTContext.h" 21 #include "clang/AST/RecordLayout.h" 22 #include "clang/AST/Decl.h" 23 #include "clang/AST/DeclCXX.h" 24 #include "clang/AST/DeclObjC.h" 25 #include "clang/AST/StmtCXX.h" 26 #include "clang/Frontend/CodeGenOptions.h" 27 #include "llvm/ADT/StringExtras.h" 28 using namespace clang; 29 using namespace CodeGen; 30 31 /// Determines whether the given function has a trivial body that does 32 /// not require any specific codegen. 33 static bool HasTrivialBody(const FunctionDecl *FD) { 34 Stmt *S = FD->getBody(); 35 if (!S) 36 return true; 37 if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty()) 38 return true; 39 return false; 40 } 41 42 /// Try to emit a base destructor as an alias to its primary 43 /// base-class destructor. 44 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) { 45 if (!getCodeGenOpts().CXXCtorDtorAliases) 46 return true; 47 48 // If the destructor doesn't have a trivial body, we have to emit it 49 // separately. 50 if (!HasTrivialBody(D)) 51 return true; 52 53 const CXXRecordDecl *Class = D->getParent(); 54 55 // If we need to manipulate a VTT parameter, give up. 56 if (Class->getNumVBases()) { 57 // Extra Credit: passing extra parameters is perfectly safe 58 // in many calling conventions, so only bail out if the ctor's 59 // calling convention is nonstandard. 60 return true; 61 } 62 63 // If any fields have a non-trivial destructor, we have to emit it 64 // separately. 65 for (CXXRecordDecl::field_iterator I = Class->field_begin(), 66 E = Class->field_end(); I != E; ++I) 67 if (const RecordType *RT = (*I)->getType()->getAs<RecordType>()) 68 if (!cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor()) 69 return true; 70 71 // Try to find a unique base class with a non-trivial destructor. 72 const CXXRecordDecl *UniqueBase = 0; 73 for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(), 74 E = Class->bases_end(); I != E; ++I) { 75 76 // We're in the base destructor, so skip virtual bases. 77 if (I->isVirtual()) continue; 78 79 // Skip base classes with trivial destructors. 80 const CXXRecordDecl *Base 81 = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl()); 82 if (Base->hasTrivialDestructor()) continue; 83 84 // If we've already found a base class with a non-trivial 85 // destructor, give up. 86 if (UniqueBase) return true; 87 UniqueBase = Base; 88 } 89 90 // If we didn't find any bases with a non-trivial destructor, then 91 // the base destructor is actually effectively trivial, which can 92 // happen if it was needlessly user-defined or if there are virtual 93 // bases with non-trivial destructors. 94 if (!UniqueBase) 95 return true; 96 97 /// If we don't have a definition for the destructor yet, don't 98 /// emit. We can't emit aliases to declarations; that's just not 99 /// how aliases work. 100 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); 101 if (!BaseD->isImplicit() && !BaseD->hasBody()) 102 return true; 103 104 // If the base is at a non-zero offset, give up. 105 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class); 106 if (ClassLayout.getBaseClassOffset(UniqueBase) != 0) 107 return true; 108 109 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base), 110 GlobalDecl(BaseD, Dtor_Base)); 111 } 112 113 /// Try to emit a definition as a global alias for another definition. 114 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl, 115 GlobalDecl TargetDecl) { 116 if (!getCodeGenOpts().CXXCtorDtorAliases) 117 return true; 118 119 // The alias will use the linkage of the referrent. If we can't 120 // support aliases with that linkage, fail. 121 llvm::GlobalValue::LinkageTypes Linkage 122 = getFunctionLinkage(cast<FunctionDecl>(AliasDecl.getDecl())); 123 124 switch (Linkage) { 125 // We can definitely emit aliases to definitions with external linkage. 126 case llvm::GlobalValue::ExternalLinkage: 127 case llvm::GlobalValue::ExternalWeakLinkage: 128 break; 129 130 // Same with local linkage. 131 case llvm::GlobalValue::InternalLinkage: 132 case llvm::GlobalValue::PrivateLinkage: 133 case llvm::GlobalValue::LinkerPrivateLinkage: 134 break; 135 136 // We should try to support linkonce linkages. 137 case llvm::GlobalValue::LinkOnceAnyLinkage: 138 case llvm::GlobalValue::LinkOnceODRLinkage: 139 return true; 140 141 // Other linkages will probably never be supported. 142 default: 143 return true; 144 } 145 146 llvm::GlobalValue::LinkageTypes TargetLinkage 147 = getFunctionLinkage(cast<FunctionDecl>(TargetDecl.getDecl())); 148 149 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) 150 return true; 151 152 // Derive the type for the alias. 153 const llvm::PointerType *AliasType 154 = getTypes().GetFunctionType(AliasDecl)->getPointerTo(); 155 156 // Find the referrent. Some aliases might require a bitcast, in 157 // which case the caller is responsible for ensuring the soundness 158 // of these semantics. 159 llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl)); 160 llvm::Constant *Aliasee = Ref; 161 if (Ref->getType() != AliasType) 162 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType); 163 164 // Create the alias with no name. 165 llvm::GlobalAlias *Alias = 166 new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule()); 167 168 // Switch any previous uses to the alias. 169 llvm::StringRef MangledName = getMangledName(AliasDecl); 170 llvm::GlobalValue *Entry = GetGlobalValue(MangledName); 171 if (Entry) { 172 assert(Entry->isDeclaration() && "definition already exists for alias"); 173 assert(Entry->getType() == AliasType && 174 "declaration exists with different type"); 175 Alias->takeName(Entry); 176 Entry->replaceAllUsesWith(Alias); 177 Entry->eraseFromParent(); 178 } else { 179 Alias->setName(MangledName); 180 } 181 182 // Finally, set up the alias with its proper name and attributes. 183 SetCommonAttributes(AliasDecl.getDecl(), Alias); 184 185 return false; 186 } 187 188 void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) { 189 // The constructor used for constructing this as a complete class; 190 // constucts the virtual bases, then calls the base constructor. 191 EmitGlobal(GlobalDecl(D, Ctor_Complete)); 192 193 // The constructor used for constructing this as a base class; 194 // ignores virtual bases. 195 EmitGlobal(GlobalDecl(D, Ctor_Base)); 196 } 197 198 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *D, 199 CXXCtorType Type) { 200 // The complete constructor is equivalent to the base constructor 201 // for classes with no virtual bases. Try to emit it as an alias. 202 if (Type == Ctor_Complete && 203 !D->getParent()->getNumVBases() && 204 !TryEmitDefinitionAsAlias(GlobalDecl(D, Ctor_Complete), 205 GlobalDecl(D, Ctor_Base))) 206 return; 207 208 llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXConstructor(D, Type)); 209 setFunctionLinkage(D, Fn); 210 211 CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn); 212 213 SetFunctionDefinitionAttributes(D, Fn); 214 SetLLVMFunctionAttributesForDefinition(D, Fn); 215 } 216 217 llvm::GlobalValue * 218 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *D, 219 CXXCtorType Type) { 220 GlobalDecl GD(D, Type); 221 222 llvm::StringRef Name = getMangledName(GD); 223 if (llvm::GlobalValue *V = GetGlobalValue(Name)) 224 return V; 225 226 const FunctionProtoType *FPT = D->getType()->getAs<FunctionProtoType>(); 227 const llvm::FunctionType *FTy = 228 getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), 229 FPT->isVariadic()); 230 return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FTy, GD)); 231 } 232 233 void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) { 234 // The destructor in a virtual table is always a 'deleting' 235 // destructor, which calls the complete destructor and then uses the 236 // appropriate operator delete. 237 if (D->isVirtual()) 238 EmitGlobal(GlobalDecl(D, Dtor_Deleting)); 239 240 // The destructor used for destructing this as a most-derived class; 241 // call the base destructor and then destructs any virtual bases. 242 EmitGlobal(GlobalDecl(D, Dtor_Complete)); 243 244 // The destructor used for destructing this as a base class; ignores 245 // virtual bases. 246 EmitGlobal(GlobalDecl(D, Dtor_Base)); 247 } 248 249 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *D, 250 CXXDtorType Type) { 251 // The complete destructor is equivalent to the base destructor for 252 // classes with no virtual bases, so try to emit it as an alias. 253 if (Type == Dtor_Complete && 254 !D->getParent()->getNumVBases() && 255 !TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Complete), 256 GlobalDecl(D, Dtor_Base))) 257 return; 258 259 // The base destructor is equivalent to the base destructor of its 260 // base class if there is exactly one non-virtual base class with a 261 // non-trivial destructor, there are no fields with a non-trivial 262 // destructor, and the body of the destructor is trivial. 263 if (Type == Dtor_Base && !TryEmitBaseDestructorAsAlias(D)) 264 return; 265 266 llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXDestructor(D, Type)); 267 setFunctionLinkage(D, Fn); 268 269 CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn); 270 271 SetFunctionDefinitionAttributes(D, Fn); 272 SetLLVMFunctionAttributesForDefinition(D, Fn); 273 } 274 275 llvm::GlobalValue * 276 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *D, 277 CXXDtorType Type) { 278 GlobalDecl GD(D, Type); 279 280 llvm::StringRef Name = getMangledName(GD); 281 if (llvm::GlobalValue *V = GetGlobalValue(Name)) 282 return V; 283 284 const llvm::FunctionType *FTy = 285 getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), false); 286 287 return cast<llvm::Function>(GetOrCreateLLVMFunction(Name, FTy, GD)); 288 } 289 290 llvm::Constant * 291 CodeGenModule::GetCXXMemberFunctionPointerValue(const CXXMethodDecl *MD) { 292 assert(MD->isInstance() && "Member function must not be static!"); 293 294 MD = MD->getCanonicalDecl(); 295 296 const llvm::Type *PtrDiffTy = Types.ConvertType(Context.getPointerDiffType()); 297 298 // Get the function pointer (or index if this is a virtual function). 299 if (MD->isVirtual()) { 300 uint64_t Index = VTables.getMethodVTableIndex(MD); 301 302 // FIXME: We shouldn't use / 8 here. 303 uint64_t PointerWidthInBytes = Context.Target.getPointerWidth(0) / 8; 304 305 // Itanium C++ ABI 2.3: 306 // For a non-virtual function, this field is a simple function pointer. 307 // For a virtual function, it is 1 plus the virtual table offset 308 // (in bytes) of the function, represented as a ptrdiff_t. 309 return llvm::ConstantInt::get(PtrDiffTy, (Index * PointerWidthInBytes) + 1); 310 } 311 312 const FunctionProtoType *FPT = MD->getType()->getAs<FunctionProtoType>(); 313 const llvm::Type *Ty; 314 // Check whether the function has a computable LLVM signature. 315 if (!CodeGenTypes::VerifyFuncTypeComplete(FPT)) { 316 // The function has a computable LLVM signature; use the correct type. 317 Ty = Types.GetFunctionType(Types.getFunctionInfo(MD), FPT->isVariadic()); 318 } else { 319 // Use an arbitrary non-function type to tell GetAddrOfFunction that the 320 // function type is incomplete. 321 Ty = PtrDiffTy; 322 } 323 324 llvm::Constant *FuncPtr = GetAddrOfFunction(MD, Ty); 325 return llvm::ConstantExpr::getPtrToInt(FuncPtr, PtrDiffTy); 326 } 327 328 static llvm::Value *BuildVirtualCall(CodeGenFunction &CGF, uint64_t VTableIndex, 329 llvm::Value *This, const llvm::Type *Ty) { 330 Ty = Ty->getPointerTo()->getPointerTo()->getPointerTo(); 331 332 llvm::Value *VTable = CGF.Builder.CreateBitCast(This, Ty); 333 VTable = CGF.Builder.CreateLoad(VTable); 334 335 llvm::Value *VFuncPtr = 336 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn"); 337 return CGF.Builder.CreateLoad(VFuncPtr); 338 } 339 340 llvm::Value * 341 CodeGenFunction::BuildVirtualCall(const CXXMethodDecl *MD, llvm::Value *This, 342 const llvm::Type *Ty) { 343 MD = MD->getCanonicalDecl(); 344 uint64_t VTableIndex = CGM.getVTables().getMethodVTableIndex(MD); 345 346 return ::BuildVirtualCall(*this, VTableIndex, This, Ty); 347 } 348 349 llvm::Value * 350 CodeGenFunction::BuildVirtualCall(const CXXDestructorDecl *DD, CXXDtorType Type, 351 llvm::Value *&This, const llvm::Type *Ty) { 352 DD = cast<CXXDestructorDecl>(DD->getCanonicalDecl()); 353 uint64_t VTableIndex = 354 CGM.getVTables().getMethodVTableIndex(GlobalDecl(DD, Type)); 355 356 return ::BuildVirtualCall(*this, VTableIndex, This, Ty); 357 } 358 359 CXXABI::~CXXABI() {} 360