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 apart. 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 // For exported destructors, we need a full definition. 48 if (D->hasAttr<DLLExportAttr>()) 49 return true; 50 51 const CXXRecordDecl *Class = D->getParent(); 52 53 // If we need to manipulate a VTT parameter, give up. 54 if (Class->getNumVBases()) { 55 // Extra Credit: passing extra parameters is perfectly safe 56 // in many calling conventions, so only bail out if the ctor's 57 // calling convention is nonstandard. 58 return true; 59 } 60 61 // If any field has a non-trivial destructor, we have to emit the 62 // destructor separately. 63 for (const auto *I : Class->fields()) 64 if (I->getType().isDestructedType()) 65 return true; 66 67 // Try to find a unique base class with a non-trivial destructor. 68 const CXXRecordDecl *UniqueBase = nullptr; 69 for (const auto &I : Class->bases()) { 70 71 // We're in the base destructor, so skip virtual bases. 72 if (I.isVirtual()) continue; 73 74 // Skip base classes with trivial destructors. 75 const auto *Base = 76 cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl()); 77 if (Base->hasTrivialDestructor()) continue; 78 79 // If we've already found a base class with a non-trivial 80 // destructor, give up. 81 if (UniqueBase) return true; 82 UniqueBase = Base; 83 } 84 85 // If we didn't find any bases with a non-trivial destructor, then 86 // the base destructor is actually effectively trivial, which can 87 // happen if it was needlessly user-defined or if there are virtual 88 // bases with non-trivial destructors. 89 if (!UniqueBase) 90 return true; 91 92 // If the base is at a non-zero offset, give up. 93 const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class); 94 if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero()) 95 return true; 96 97 // Give up if the calling conventions don't match. We could update the call, 98 // but it is probably not worth it. 99 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); 100 if (BaseD->getType()->getAs<FunctionType>()->getCallConv() != 101 D->getType()->getAs<FunctionType>()->getCallConv()) 102 return true; 103 104 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base), 105 GlobalDecl(BaseD, Dtor_Base), 106 false); 107 } 108 109 /// Try to emit a definition as a global alias for another definition. 110 /// If \p InEveryTU is true, we know that an equivalent alias can be produced 111 /// in every translation unit. 112 bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl, 113 GlobalDecl TargetDecl, 114 bool InEveryTU) { 115 if (!getCodeGenOpts().CXXCtorDtorAliases) 116 return true; 117 118 // The alias will use the linkage of the referent. If we can't 119 // support aliases with that linkage, fail. 120 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl); 121 122 // We can't use an alias if the linkage is not valid for one. 123 if (!llvm::GlobalAlias::isValidLinkage(Linkage)) 124 return true; 125 126 llvm::GlobalValue::LinkageTypes TargetLinkage = 127 getFunctionLinkage(TargetDecl); 128 129 // Check if we have it already. 130 StringRef MangledName = getMangledName(AliasDecl); 131 llvm::GlobalValue *Entry = GetGlobalValue(MangledName); 132 if (Entry && !Entry->isDeclaration()) 133 return false; 134 if (Replacements.count(MangledName)) 135 return false; 136 137 // Derive the type for the alias. 138 llvm::PointerType *AliasType 139 = getTypes().GetFunctionType(AliasDecl)->getPointerTo(); 140 141 // Find the referent. Some aliases might require a bitcast, in 142 // which case the caller is responsible for ensuring the soundness 143 // of these semantics. 144 auto *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl)); 145 llvm::Constant *Aliasee = Ref; 146 if (Ref->getType() != AliasType) 147 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType); 148 149 // Instead of creating as alias to a linkonce_odr, replace all of the uses 150 // of the aliasee. 151 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) && 152 (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage || 153 !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) { 154 // FIXME: An extern template instantiation will create functions with 155 // linkage "AvailableExternally". In libc++, some classes also define 156 // members with attribute "AlwaysInline" and expect no reference to 157 // be generated. It is desirable to reenable this optimisation after 158 // corresponding LLVM changes. 159 Replacements[MangledName] = Aliasee; 160 return false; 161 } 162 163 if (!InEveryTU) { 164 /// If we don't have a definition for the destructor yet, don't 165 /// emit. We can't emit aliases to declarations; that's just not 166 /// how aliases work. 167 if (Ref->isDeclaration()) 168 return true; 169 } 170 171 // Don't create an alias to a linker weak symbol. This avoids producing 172 // different COMDATs in different TUs. Another option would be to 173 // output the alias both for weak_odr and linkonce_odr, but that 174 // requires explicit comdat support in the IL. 175 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) 176 return true; 177 178 // Create the alias with no name. 179 auto *Alias = llvm::GlobalAlias::create(AliasType->getElementType(), 0, 180 Linkage, "", Aliasee, &getModule()); 181 182 // Switch any previous uses to the alias. 183 if (Entry) { 184 assert(Entry->getType() == AliasType && 185 "declaration exists with different type"); 186 Alias->takeName(Entry); 187 Entry->replaceAllUsesWith(Alias); 188 Entry->eraseFromParent(); 189 } else { 190 Alias->setName(MangledName); 191 } 192 193 // Finally, set up the alias with its proper name and attributes. 194 SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias); 195 196 return false; 197 } 198 199 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor, 200 CXXCtorType ctorType) { 201 if (!getTarget().getCXXABI().hasConstructorVariants()) { 202 // If there are no constructor variants, always emit the complete destructor. 203 ctorType = Ctor_Complete; 204 } else if (!ctor->getParent()->getNumVBases() && 205 (ctorType == Ctor_Complete || ctorType == Ctor_Base)) { 206 // The complete constructor is equivalent to the base constructor 207 // for classes with no virtual bases. Try to emit it as an alias. 208 bool ProducedAlias = 209 !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete), 210 GlobalDecl(ctor, Ctor_Base), true); 211 if (ctorType == Ctor_Complete && ProducedAlias) 212 return; 213 } 214 215 const CGFunctionInfo &fnInfo = 216 getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 217 218 auto *fn = cast<llvm::Function>( 219 GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo, true)); 220 setFunctionLinkage(GlobalDecl(ctor, ctorType), fn); 221 222 CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo); 223 224 setFunctionDefinitionAttributes(ctor, fn); 225 SetLLVMFunctionAttributesForDefinition(ctor, fn); 226 } 227 228 llvm::GlobalValue * 229 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor, 230 CXXCtorType ctorType, 231 const CGFunctionInfo *fnInfo, 232 bool DontDefer) { 233 GlobalDecl GD(ctor, ctorType); 234 235 StringRef name = getMangledName(GD); 236 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 237 return existing; 238 239 if (!fnInfo) 240 fnInfo = &getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 241 242 llvm::FunctionType *fnType = getTypes().GetFunctionType(*fnInfo); 243 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 244 /*ForVTable=*/false, 245 DontDefer)); 246 } 247 248 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor, 249 CXXDtorType dtorType) { 250 // The complete destructor is equivalent to the base destructor for 251 // classes with no virtual bases, so try to emit it as an alias. 252 if (!dtor->getParent()->getNumVBases() && 253 (dtorType == Dtor_Complete || dtorType == Dtor_Base)) { 254 bool ProducedAlias = 255 !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete), 256 GlobalDecl(dtor, Dtor_Base), true); 257 if (ProducedAlias) { 258 if (dtorType == Dtor_Complete) 259 return; 260 if (dtor->isVirtual()) 261 getVTables().EmitThunks(GlobalDecl(dtor, Dtor_Complete)); 262 } 263 } 264 265 // The base destructor is equivalent to the base destructor of its 266 // base class if there is exactly one non-virtual base class with a 267 // non-trivial destructor, there are no fields with a non-trivial 268 // destructor, and the body of the destructor is trivial. 269 if (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor)) 270 return; 271 272 const CGFunctionInfo &fnInfo = 273 getTypes().arrangeCXXDestructor(dtor, dtorType); 274 275 auto *fn = cast<llvm::Function>( 276 GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo, nullptr, true)); 277 setFunctionLinkage(GlobalDecl(dtor, dtorType), fn); 278 279 CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo); 280 281 setFunctionDefinitionAttributes(dtor, fn); 282 SetLLVMFunctionAttributesForDefinition(dtor, fn); 283 } 284 285 llvm::GlobalValue * 286 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor, 287 CXXDtorType dtorType, 288 const CGFunctionInfo *fnInfo, 289 llvm::FunctionType *fnType, 290 bool DontDefer) { 291 GlobalDecl GD(dtor, dtorType); 292 293 StringRef name = getMangledName(GD); 294 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 295 return existing; 296 297 if (!fnType) { 298 if (!fnInfo) fnInfo = &getTypes().arrangeCXXDestructor(dtor, dtorType); 299 fnType = getTypes().GetFunctionType(*fnInfo); 300 } 301 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 302 /*ForVTable=*/false, 303 DontDefer)); 304 } 305 306 static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF, 307 GlobalDecl GD, 308 llvm::Type *Ty, 309 const CXXRecordDecl *RD) { 310 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() && 311 "No kext in Microsoft ABI"); 312 GD = GD.getCanonicalDecl(); 313 CodeGenModule &CGM = CGF.CGM; 314 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); 315 Ty = Ty->getPointerTo()->getPointerTo(); 316 VTable = CGF.Builder.CreateBitCast(VTable, Ty); 317 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null"); 318 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD); 319 uint64_t AddressPoint = 320 CGM.getItaniumVTableContext().getVTableLayout(RD) 321 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero())); 322 VTableIndex += AddressPoint; 323 llvm::Value *VFuncPtr = 324 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt"); 325 return CGF.Builder.CreateLoad(VFuncPtr); 326 } 327 328 /// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making 329 /// indirect call to virtual functions. It makes the call through indexing 330 /// into the vtable. 331 llvm::Value * 332 CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD, 333 NestedNameSpecifier *Qual, 334 llvm::Type *Ty) { 335 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) && 336 "BuildAppleKextVirtualCall - bad Qual kind"); 337 338 const Type *QTy = Qual->getAsType(); 339 QualType T = QualType(QTy, 0); 340 const RecordType *RT = T->getAs<RecordType>(); 341 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record"); 342 const auto *RD = cast<CXXRecordDecl>(RT->getDecl()); 343 344 if (const auto *DD = dyn_cast<CXXDestructorDecl>(MD)) 345 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD); 346 347 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD); 348 } 349 350 /// BuildVirtualCall - This routine makes indirect vtable call for 351 /// call to virtual destructors. It returns 0 if it could not do it. 352 llvm::Value * 353 CodeGenFunction::BuildAppleKextVirtualDestructorCall( 354 const CXXDestructorDecl *DD, 355 CXXDtorType Type, 356 const CXXRecordDecl *RD) { 357 const auto *MD = cast<CXXMethodDecl>(DD); 358 // FIXME. Dtor_Base dtor is always direct!! 359 // It need be somehow inline expanded into the caller. 360 // -O does that. But need to support -O0 as well. 361 if (MD->isVirtual() && Type != Dtor_Base) { 362 // Compute the function type we're calling. 363 const CGFunctionInfo &FInfo = 364 CGM.getTypes().arrangeCXXDestructor(DD, Dtor_Complete); 365 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo); 366 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD); 367 } 368 return nullptr; 369 } 370
