CGCXX.cpp revision 583f6de423aa42c8a4894cc64e72036484e6343b
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" 28using namespace clang; 29using namespace CodeGen; 30 31/// Try to emit a base destructor as an alias to its primary 32/// base-class destructor. 33bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) { 34 if (!getCodeGenOpts().CXXCtorDtorAliases) 35 return true; 36 37 // If the destructor doesn't have a trivial body, we have to emit it 38 // separately. 39 if (!D->hasTrivialBody()) 40 return true; 41 42 const CXXRecordDecl *Class = D->getParent(); 43 44 // If we need to manipulate a VTT parameter, give up. 45 if (Class->getNumVBases()) { 46 // Extra Credit: passing extra parameters is perfectly safe 47 // in many calling conventions, so only bail out if the ctor's 48 // calling convention is nonstandard. 49 return true; 50 } 51 52 // If any field has a non-trivial destructor, we have to emit the 53 // destructor separately. 54 for (CXXRecordDecl::field_iterator I = Class->field_begin(), 55 E = Class->field_end(); I != E; ++I) 56 if (I->getType().isDestructedType()) 57 return true; 58 59 // Try to find a unique base class with a non-trivial destructor. 60 const CXXRecordDecl *UniqueBase = 0; 61 for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(), 62 E = Class->bases_end(); I != E; ++I) { 63 64 // We're in the base destructor, so skip virtual bases. 65 if (I->isVirtual()) continue; 66 67 // Skip base classes with trivial destructors. 68 const CXXRecordDecl *Base 69 = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl()); 70 if (Base->hasTrivialDestructor()) continue; 71 72 // If we've already found a base class with a non-trivial 73 // destructor, give up. 74 if (UniqueBase) return true; 75 UniqueBase = Base; 76 } 77 78 // If we didn't find any bases with a non-trivial destructor, then 79 // the base destructor is actually effectively trivial, which can 80 // happen if it was needlessly user-defined or if there are virtual 81 // bases with non-trivial destructors. 82 if (!UniqueBase) 83 return true; 84 85 /// If we don't have a definition for the destructor yet, don't 86 /// emit. We can't emit aliases to declarations; that's just not 87 /// how aliases work. 88 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); 89 if (!BaseD->isImplicit() && !BaseD->hasBody()) 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 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base), 98 GlobalDecl(BaseD, Dtor_Base), 99 false); 100} 101 102/// Try to emit a definition as a global alias for another definition. 103/// If \p InEveryTU is true, we know that an equivalent alias can be produced 104/// in every translation unit. 105bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl, 106 GlobalDecl TargetDecl, 107 bool InEveryTU) { 108 if (!getCodeGenOpts().CXXCtorDtorAliases) 109 return true; 110 111 // The alias will use the linkage of the referrent. If we can't 112 // support aliases with that linkage, fail. 113 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl); 114 115 llvm::GlobalValue::LinkageTypes TargetLinkage 116 = getFunctionLinkage(TargetDecl); 117 118 // Don't create an alias to a linker weak symbol unless we know we can do 119 // that in every TU. This avoids producing different COMDATs in different 120 // TUs. 121 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) { 122 if (!InEveryTU) 123 return true; 124 125 // In addition to making sure we produce it in every TU, we have to make 126 // sure llvm keeps it. 127 // FIXME: Instead of outputting an alias we could just replace every use of 128 // AliasDecl with TargetDecl. 129 assert(Linkage == TargetLinkage); 130 Linkage = llvm::GlobalValue::WeakODRLinkage; 131 } 132 133 // We can't use an alias if the linkage is not valid for one. 134 if (!llvm::GlobalAlias::isValidLinkage(Linkage)) 135 return true; 136 137 // Check if we have it already. 138 StringRef MangledName = getMangledName(AliasDecl); 139 llvm::GlobalValue *Entry = GetGlobalValue(MangledName); 140 if (Entry && !Entry->isDeclaration()) 141 return false; 142 143 // Derive the type for the alias. 144 llvm::PointerType *AliasType 145 = getTypes().GetFunctionType(AliasDecl)->getPointerTo(); 146 147 // Find the referrent. Some aliases might require a bitcast, in 148 // which case the caller is responsible for ensuring the soundness 149 // of these semantics. 150 llvm::GlobalValue *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 // Create the alias with no name. 156 llvm::GlobalAlias *Alias = 157 new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule()); 158 159 // Switch any previous uses to the alias. 160 if (Entry) { 161 assert(Entry->getType() == AliasType && 162 "declaration exists with different type"); 163 Alias->takeName(Entry); 164 Entry->replaceAllUsesWith(Alias); 165 Entry->eraseFromParent(); 166 } else { 167 Alias->setName(MangledName); 168 } 169 170 // Finally, set up the alias with its proper name and attributes. 171 SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias); 172 173 return false; 174} 175 176void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor, 177 CXXCtorType ctorType) { 178 // The complete constructor is equivalent to the base constructor 179 // for classes with no virtual bases. Try to emit it as an alias. 180 if (getTarget().getCXXABI().hasConstructorVariants() && 181 !ctor->getParent()->getNumVBases() && 182 (ctorType == Ctor_Complete || ctorType == Ctor_Base)) { 183 bool ProducedAlias = 184 !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete), 185 GlobalDecl(ctor, Ctor_Base), true); 186 if (ctorType == Ctor_Complete && ProducedAlias) 187 return; 188 } 189 190 const CGFunctionInfo &fnInfo = 191 getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 192 193 llvm::Function *fn = 194 cast<llvm::Function>(GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo)); 195 setFunctionLinkage(GlobalDecl(ctor, ctorType), fn); 196 197 CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo); 198 199 SetFunctionDefinitionAttributes(ctor, fn); 200 SetLLVMFunctionAttributesForDefinition(ctor, fn); 201} 202 203llvm::GlobalValue * 204CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor, 205 CXXCtorType ctorType, 206 const CGFunctionInfo *fnInfo) { 207 GlobalDecl GD(ctor, ctorType); 208 209 StringRef name = getMangledName(GD); 210 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 211 return existing; 212 213 if (!fnInfo) 214 fnInfo = &getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 215 216 llvm::FunctionType *fnType = getTypes().GetFunctionType(*fnInfo); 217 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 218 /*ForVTable=*/false)); 219} 220 221void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor, 222 CXXDtorType dtorType) { 223 // The complete destructor is equivalent to the base destructor for 224 // classes with no virtual bases, so try to emit it as an alias. 225 if (!dtor->getParent()->getNumVBases() && 226 (dtorType == Dtor_Complete || dtorType == Dtor_Base)) { 227 bool ProducedAlias = 228 !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete), 229 GlobalDecl(dtor, Dtor_Base), true); 230 if (ProducedAlias) { 231 if (dtorType == Dtor_Complete) 232 return; 233 if (dtor->isVirtual()) 234 getVTables().EmitThunks(GlobalDecl(dtor, Dtor_Complete)); 235 } 236 } 237 238 // The base destructor is equivalent to the base destructor of its 239 // base class if there is exactly one non-virtual base class with a 240 // non-trivial destructor, there are no fields with a non-trivial 241 // destructor, and the body of the destructor is trivial. 242 if (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor)) 243 return; 244 245 const CGFunctionInfo &fnInfo = 246 getTypes().arrangeCXXDestructor(dtor, dtorType); 247 248 llvm::Function *fn = 249 cast<llvm::Function>(GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo)); 250 setFunctionLinkage(GlobalDecl(dtor, dtorType), fn); 251 252 CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo); 253 254 SetFunctionDefinitionAttributes(dtor, fn); 255 SetLLVMFunctionAttributesForDefinition(dtor, fn); 256} 257 258llvm::GlobalValue * 259CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor, 260 CXXDtorType dtorType, 261 const CGFunctionInfo *fnInfo, 262 llvm::FunctionType *fnType) { 263 // If the class has no virtual bases, then the complete and base destructors 264 // are equivalent, for all C++ ABIs supported by clang. We can save on code 265 // size by calling the base dtor directly, especially if we'd have to emit a 266 // thunk otherwise. 267 // FIXME: We should do this for Itanium, after verifying that nothing breaks. 268 if (dtorType == Dtor_Complete && dtor->getParent()->getNumVBases() == 0 && 269 getCXXABI().useThunkForDtorVariant(dtor, Dtor_Complete)) 270 dtorType = Dtor_Base; 271 272 GlobalDecl GD(dtor, dtorType); 273 274 StringRef name = getMangledName(GD); 275 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 276 return existing; 277 278 if (!fnType) { 279 if (!fnInfo) fnInfo = &getTypes().arrangeCXXDestructor(dtor, dtorType); 280 fnType = getTypes().GetFunctionType(*fnInfo); 281 } 282 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 283 /*ForVTable=*/false)); 284} 285 286static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF, 287 GlobalDecl GD, 288 llvm::Type *Ty, 289 const CXXRecordDecl *RD) { 290 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() && 291 "No kext in Microsoft ABI"); 292 GD = GD.getCanonicalDecl(); 293 CodeGenModule &CGM = CGF.CGM; 294 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); 295 Ty = Ty->getPointerTo()->getPointerTo(); 296 VTable = CGF.Builder.CreateBitCast(VTable, Ty); 297 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null"); 298 uint64_t VTableIndex = CGM.getVTableContext().getMethodVTableIndex(GD); 299 uint64_t AddressPoint = 300 CGM.getVTableContext().getVTableLayout(RD) 301 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero())); 302 VTableIndex += AddressPoint; 303 llvm::Value *VFuncPtr = 304 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt"); 305 return CGF.Builder.CreateLoad(VFuncPtr); 306} 307 308/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making 309/// indirect call to virtual functions. It makes the call through indexing 310/// into the vtable. 311llvm::Value * 312CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD, 313 NestedNameSpecifier *Qual, 314 llvm::Type *Ty) { 315 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) && 316 "BuildAppleKextVirtualCall - bad Qual kind"); 317 318 const Type *QTy = Qual->getAsType(); 319 QualType T = QualType(QTy, 0); 320 const RecordType *RT = T->getAs<RecordType>(); 321 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record"); 322 const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl()); 323 324 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) 325 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD); 326 327 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD); 328} 329 330/// BuildVirtualCall - This routine makes indirect vtable call for 331/// call to virtual destructors. It returns 0 if it could not do it. 332llvm::Value * 333CodeGenFunction::BuildAppleKextVirtualDestructorCall( 334 const CXXDestructorDecl *DD, 335 CXXDtorType Type, 336 const CXXRecordDecl *RD) { 337 const CXXMethodDecl *MD = cast<CXXMethodDecl>(DD); 338 // FIXME. Dtor_Base dtor is always direct!! 339 // It need be somehow inline expanded into the caller. 340 // -O does that. But need to support -O0 as well. 341 if (MD->isVirtual() && Type != Dtor_Base) { 342 // Compute the function type we're calling. 343 const CGFunctionInfo &FInfo = 344 CGM.getTypes().arrangeCXXDestructor(DD, Dtor_Complete); 345 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo); 346 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD); 347 } 348 return 0; 349} 350