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