1 //===--- CGCXX.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 "CodeGenModule.h" 17 #include "CGCXXABI.h" 18 #include "CodeGenFunction.h" 19 #include "clang/AST/ASTContext.h" 20 #include "clang/AST/Decl.h" 21 #include "clang/AST/DeclCXX.h" 22 #include "clang/AST/DeclObjC.h" 23 #include "clang/AST/Mangle.h" 24 #include "clang/AST/RecordLayout.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 /// Try to emit a base destructor as an alias to its primary 32 /// base-class destructor. 33 bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) { 34 if (!getCodeGenOpts().CXXCtorDtorAliases) 35 return true; 36 37 // Producing an alias to a base class ctor/dtor can degrade debug quality 38 // as the debugger cannot tell them appart. 39 if (getCodeGenOpts().OptimizationLevel == 0) 40 return true; 41 42 // If the destructor doesn't have a trivial body, we have to emit it 43 // separately. 44 if (!D->hasTrivialBody()) 45 return true; 46 47 const CXXRecordDecl *Class = D->getParent(); 48 49 // If we need to manipulate a VTT parameter, give up. 50 if (Class->getNumVBases()) { 51 // Extra Credit: passing extra parameters is perfectly safe 52 // in many calling conventions, so only bail out if the ctor's 53 // calling convention is nonstandard. 54 return true; 55 } 56 57 // If any field has a non-trivial destructor, we have to emit the 58 // destructor separately. 59 for (CXXRecordDecl::field_iterator I = Class->field_begin(), 60 E = Class->field_end(); I != E; ++I) 61 if (I->getType().isDestructedType()) 62 return true; 63 64 // Try to find a unique base class with a non-trivial destructor. 65 const CXXRecordDecl *UniqueBase = 0; 66 for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(), 67 E = Class->bases_end(); I != E; ++I) { 68 69 // We're in the base destructor, so skip virtual bases. 70 if (I->isVirtual()) continue; 71 72 // Skip base classes with trivial destructors. 73 const CXXRecordDecl *Base 74 = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl()); 75 if (Base->hasTrivialDestructor()) continue; 76 77 // If we've already found a base class with a non-trivial 78 // destructor, give up. 79 if (UniqueBase) return true; 80 UniqueBase = Base; 81 } 82 83 // If we didn't find any bases with a non-trivial destructor, then 84 // the base destructor is actually effectively trivial, which can 85 // happen if it was needlessly user-defined or if there are virtual 86 // bases with non-trivial destructors. 87 if (!UniqueBase) 88 return true; 89 90 // If the base is at a non-zero offset, give up. 91 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class); 92 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero()) 93 return true; 94 95 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); 96 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base), 97 GlobalDecl(BaseD, Dtor_Base), 98 false); 99 } 100 101 /// Try to emit a definition as a global alias for another definition. 102 /// If \p InEveryTU is true, we know that an equivalent alias can be produced 103 /// in every translation unit. 104 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl, 105 GlobalDecl TargetDecl, 106 bool InEveryTU) { 107 if (!getCodeGenOpts().CXXCtorDtorAliases) 108 return true; 109 110 // The alias will use the linkage of the referrent. If we can't 111 // support aliases with that linkage, fail. 112 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl); 113 114 // We can't use an alias if the linkage is not valid for one. 115 if (!llvm::GlobalAlias::isValidLinkage(Linkage)) 116 return true; 117 118 llvm::GlobalValue::LinkageTypes TargetLinkage = 119 getFunctionLinkage(TargetDecl); 120 121 // Check if we have it already. 122 StringRef MangledName = getMangledName(AliasDecl); 123 llvm::GlobalValue *Entry = GetGlobalValue(MangledName); 124 if (Entry && !Entry->isDeclaration()) 125 return false; 126 if (Replacements.count(MangledName)) 127 return false; 128 129 // Derive the type for the alias. 130 llvm::PointerType *AliasType 131 = getTypes().GetFunctionType(AliasDecl)->getPointerTo(); 132 133 // Find the referrent. Some aliases might require a bitcast, in 134 // which case the caller is responsible for ensuring the soundness 135 // of these semantics. 136 llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl)); 137 llvm::Constant *Aliasee = Ref; 138 if (Ref->getType() != AliasType) 139 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType); 140 141 // Instead of creating as alias to a linkonce_odr, replace all of the uses 142 // of the aliassee. 143 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) && 144 (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage || 145 !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) { 146 // FIXME: An extern template instanciation will create functions with 147 // linkage "AvailableExternally". In libc++, some classes also define 148 // members with attribute "AlwaysInline" and expect no reference to 149 // be generated. It is desirable to reenable this optimisation after 150 // corresponding LLVM changes. 151 Replacements[MangledName] = Aliasee; 152 return false; 153 } 154 155 if (!InEveryTU) { 156 /// If we don't have a definition for the destructor yet, don't 157 /// emit. We can't emit aliases to declarations; that's just not 158 /// how aliases work. 159 if (Ref->isDeclaration()) 160 return true; 161 } 162 163 // Don't create an alias to a linker weak symbol. This avoids producing 164 // different COMDATs in different TUs. Another option would be to 165 // output the alias both for weak_odr and linkonce_odr, but that 166 // requires explicit comdat support in the IL. 167 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) 168 return true; 169 170 // Create the alias with no name. 171 llvm::GlobalAlias *Alias = 172 new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule()); 173 174 // Switch any previous uses to the alias. 175 if (Entry) { 176 assert(Entry->getType() == AliasType && 177 "declaration exists with different type"); 178 Alias->takeName(Entry); 179 Entry->replaceAllUsesWith(Alias); 180 Entry->eraseFromParent(); 181 } else { 182 Alias->setName(MangledName); 183 } 184 185 // Finally, set up the alias with its proper name and attributes. 186 SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias); 187 188 return false; 189 } 190 191 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor, 192 CXXCtorType ctorType) { 193 // The complete constructor is equivalent to the base constructor 194 // for classes with no virtual bases. Try to emit it as an alias. 195 if (getTarget().getCXXABI().hasConstructorVariants() && 196 !ctor->getParent()->getNumVBases() && 197 (ctorType == Ctor_Complete || ctorType == Ctor_Base)) { 198 bool ProducedAlias = 199 !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete), 200 GlobalDecl(ctor, Ctor_Base), true); 201 if (ctorType == Ctor_Complete && ProducedAlias) 202 return; 203 } 204 205 const CGFunctionInfo &fnInfo = 206 getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 207 208 llvm::Function *fn = 209 cast<llvm::Function>(GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo)); 210 setFunctionLinkage(GlobalDecl(ctor, ctorType), fn); 211 212 CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo); 213 214 SetFunctionDefinitionAttributes(ctor, fn); 215 SetLLVMFunctionAttributesForDefinition(ctor, fn); 216 } 217 218 llvm::GlobalValue * 219 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor, 220 CXXCtorType ctorType, 221 const CGFunctionInfo *fnInfo) { 222 GlobalDecl GD(ctor, ctorType); 223 224 StringRef name = getMangledName(GD); 225 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 226 return existing; 227 228 if (!fnInfo) 229 fnInfo = &getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 230 231 llvm::FunctionType *fnType = getTypes().GetFunctionType(*fnInfo); 232 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 233 /*ForVTable=*/false)); 234 } 235 236 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor, 237 CXXDtorType dtorType) { 238 // The complete destructor is equivalent to the base destructor for 239 // classes with no virtual bases, so try to emit it as an alias. 240 if (!dtor->getParent()->getNumVBases() && 241 (dtorType == Dtor_Complete || dtorType == Dtor_Base)) { 242 bool ProducedAlias = 243 !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete), 244 GlobalDecl(dtor, Dtor_Base), true); 245 if (ProducedAlias) { 246 if (dtorType == Dtor_Complete) 247 return; 248 if (dtor->isVirtual()) 249 getVTables().EmitThunks(GlobalDecl(dtor, Dtor_Complete)); 250 } 251 } 252 253 // The base destructor is equivalent to the base destructor of its 254 // base class if there is exactly one non-virtual base class with a 255 // non-trivial destructor, there are no fields with a non-trivial 256 // destructor, and the body of the destructor is trivial. 257 if (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor)) 258 return; 259 260 const CGFunctionInfo &fnInfo = 261 getTypes().arrangeCXXDestructor(dtor, dtorType); 262 263 llvm::Function *fn = 264 cast<llvm::Function>(GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo)); 265 setFunctionLinkage(GlobalDecl(dtor, dtorType), fn); 266 267 CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo); 268 269 SetFunctionDefinitionAttributes(dtor, fn); 270 SetLLVMFunctionAttributesForDefinition(dtor, fn); 271 } 272 273 llvm::GlobalValue * 274 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor, 275 CXXDtorType dtorType, 276 const CGFunctionInfo *fnInfo, 277 llvm::FunctionType *fnType) { 278 GlobalDecl GD(dtor, dtorType); 279 280 StringRef name = getMangledName(GD); 281 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 282 return existing; 283 284 if (!fnType) { 285 if (!fnInfo) fnInfo = &getTypes().arrangeCXXDestructor(dtor, dtorType); 286 fnType = getTypes().GetFunctionType(*fnInfo); 287 } 288 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 289 /*ForVTable=*/false)); 290 } 291 292 static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF, 293 GlobalDecl GD, 294 llvm::Type *Ty, 295 const CXXRecordDecl *RD) { 296 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() && 297 "No kext in Microsoft ABI"); 298 GD = GD.getCanonicalDecl(); 299 CodeGenModule &CGM = CGF.CGM; 300 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); 301 Ty = Ty->getPointerTo()->getPointerTo(); 302 VTable = CGF.Builder.CreateBitCast(VTable, Ty); 303 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null"); 304 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD); 305 uint64_t AddressPoint = 306 CGM.getItaniumVTableContext().getVTableLayout(RD) 307 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero())); 308 VTableIndex += AddressPoint; 309 llvm::Value *VFuncPtr = 310 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt"); 311 return CGF.Builder.CreateLoad(VFuncPtr); 312 } 313 314 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making 315 /// indirect call to virtual functions. It makes the call through indexing 316 /// into the vtable. 317 llvm::Value * 318 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD, 319 NestedNameSpecifier *Qual, 320 llvm::Type *Ty) { 321 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) && 322 "BuildAppleKextVirtualCall - bad Qual kind"); 323 324 const Type *QTy = Qual->getAsType(); 325 QualType T = QualType(QTy, 0); 326 const RecordType *RT = T->getAs<RecordType>(); 327 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record"); 328 const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl()); 329 330 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) 331 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD); 332 333 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD); 334 } 335 336 /// BuildVirtualCall - This routine makes indirect vtable call for 337 /// call to virtual destructors. It returns 0 if it could not do it. 338 llvm::Value * 339 CodeGenFunction::BuildAppleKextVirtualDestructorCall( 340 const CXXDestructorDecl *DD, 341 CXXDtorType Type, 342 const CXXRecordDecl *RD) { 343 const CXXMethodDecl *MD = cast<CXXMethodDecl>(DD); 344 // FIXME. Dtor_Base dtor is always direct!! 345 // It need be somehow inline expanded into the caller. 346 // -O does that. But need to support -O0 as well. 347 if (MD->isVirtual() && Type != Dtor_Base) { 348 // Compute the function type we're calling. 349 const CGFunctionInfo &FInfo = 350 CGM.getTypes().arrangeCXXDestructor(DD, Dtor_Complete); 351 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo); 352 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD); 353 } 354 return 0; 355 } 356