CGCXX.cpp revision 263508
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 // 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 // Give up if the calling conventions don't match. We could update the call, 96 // but it is probably not worth it. 97 const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(); 98 if (BaseD->getType()->getAs<FunctionType>()->getCallConv() != 99 D->getType()->getAs<FunctionType>()->getCallConv()) 100 return true; 101 102 return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base), 103 GlobalDecl(BaseD, Dtor_Base), 104 false); 105} 106 107/// Try to emit a definition as a global alias for another definition. 108/// If \p InEveryTU is true, we know that an equivalent alias can be produced 109/// in every translation unit. 110bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl, 111 GlobalDecl TargetDecl, 112 bool InEveryTU) { 113 if (!getCodeGenOpts().CXXCtorDtorAliases) 114 return true; 115 116 // The alias will use the linkage of the referrent. If we can't 117 // support aliases with that linkage, fail. 118 llvm::GlobalValue::LinkageTypes Linkage = getFunctionLinkage(AliasDecl); 119 120 // We can't use an alias if the linkage is not valid for one. 121 if (!llvm::GlobalAlias::isValidLinkage(Linkage)) 122 return true; 123 124 llvm::GlobalValue::LinkageTypes TargetLinkage = 125 getFunctionLinkage(TargetDecl); 126 127 // Check if we have it already. 128 StringRef MangledName = getMangledName(AliasDecl); 129 llvm::GlobalValue *Entry = GetGlobalValue(MangledName); 130 if (Entry && !Entry->isDeclaration()) 131 return false; 132 if (Replacements.count(MangledName)) 133 return false; 134 135 // Derive the type for the alias. 136 llvm::PointerType *AliasType 137 = getTypes().GetFunctionType(AliasDecl)->getPointerTo(); 138 139 // Find the referrent. Some aliases might require a bitcast, in 140 // which case the caller is responsible for ensuring the soundness 141 // of these semantics. 142 llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl)); 143 llvm::Constant *Aliasee = Ref; 144 if (Ref->getType() != AliasType) 145 Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType); 146 147 // Instead of creating as alias to a linkonce_odr, replace all of the uses 148 // of the aliassee. 149 if (llvm::GlobalValue::isDiscardableIfUnused(Linkage) && 150 (TargetLinkage != llvm::GlobalValue::AvailableExternallyLinkage || 151 !TargetDecl.getDecl()->hasAttr<AlwaysInlineAttr>())) { 152 // FIXME: An extern template instanciation will create functions with 153 // linkage "AvailableExternally". In libc++, some classes also define 154 // members with attribute "AlwaysInline" and expect no reference to 155 // be generated. It is desirable to reenable this optimisation after 156 // corresponding LLVM changes. 157 Replacements[MangledName] = Aliasee; 158 return false; 159 } 160 161 if (!InEveryTU) { 162 /// If we don't have a definition for the destructor yet, don't 163 /// emit. We can't emit aliases to declarations; that's just not 164 /// how aliases work. 165 if (Ref->isDeclaration()) 166 return true; 167 } 168 169 // Don't create an alias to a linker weak symbol. This avoids producing 170 // different COMDATs in different TUs. Another option would be to 171 // output the alias both for weak_odr and linkonce_odr, but that 172 // requires explicit comdat support in the IL. 173 if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) 174 return true; 175 176 // Create the alias with no name. 177 llvm::GlobalAlias *Alias = 178 new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule()); 179 180 // Switch any previous uses to the alias. 181 if (Entry) { 182 assert(Entry->getType() == AliasType && 183 "declaration exists with different type"); 184 Alias->takeName(Entry); 185 Entry->replaceAllUsesWith(Alias); 186 Entry->eraseFromParent(); 187 } else { 188 Alias->setName(MangledName); 189 } 190 191 // Finally, set up the alias with its proper name and attributes. 192 SetCommonAttributes(cast<NamedDecl>(AliasDecl.getDecl()), Alias); 193 194 return false; 195} 196 197void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *ctor, 198 CXXCtorType ctorType) { 199 // The complete constructor is equivalent to the base constructor 200 // for classes with no virtual bases. Try to emit it as an alias. 201 if (getTarget().getCXXABI().hasConstructorVariants() && 202 !ctor->getParent()->getNumVBases() && 203 (ctorType == Ctor_Complete || ctorType == Ctor_Base)) { 204 bool ProducedAlias = 205 !TryEmitDefinitionAsAlias(GlobalDecl(ctor, Ctor_Complete), 206 GlobalDecl(ctor, Ctor_Base), true); 207 if (ctorType == Ctor_Complete && ProducedAlias) 208 return; 209 } 210 211 const CGFunctionInfo &fnInfo = 212 getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 213 214 llvm::Function *fn = 215 cast<llvm::Function>(GetAddrOfCXXConstructor(ctor, ctorType, &fnInfo)); 216 setFunctionLinkage(GlobalDecl(ctor, ctorType), fn); 217 218 CodeGenFunction(*this).GenerateCode(GlobalDecl(ctor, ctorType), fn, fnInfo); 219 220 SetFunctionDefinitionAttributes(ctor, fn); 221 SetLLVMFunctionAttributesForDefinition(ctor, fn); 222} 223 224llvm::GlobalValue * 225CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *ctor, 226 CXXCtorType ctorType, 227 const CGFunctionInfo *fnInfo) { 228 GlobalDecl GD(ctor, ctorType); 229 230 StringRef name = getMangledName(GD); 231 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 232 return existing; 233 234 if (!fnInfo) 235 fnInfo = &getTypes().arrangeCXXConstructorDeclaration(ctor, ctorType); 236 237 llvm::FunctionType *fnType = getTypes().GetFunctionType(*fnInfo); 238 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 239 /*ForVTable=*/false)); 240} 241 242void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *dtor, 243 CXXDtorType dtorType) { 244 // The complete destructor is equivalent to the base destructor for 245 // classes with no virtual bases, so try to emit it as an alias. 246 if (!dtor->getParent()->getNumVBases() && 247 (dtorType == Dtor_Complete || dtorType == Dtor_Base)) { 248 bool ProducedAlias = 249 !TryEmitDefinitionAsAlias(GlobalDecl(dtor, Dtor_Complete), 250 GlobalDecl(dtor, Dtor_Base), true); 251 if (ProducedAlias) { 252 if (dtorType == Dtor_Complete) 253 return; 254 if (dtor->isVirtual()) 255 getVTables().EmitThunks(GlobalDecl(dtor, Dtor_Complete)); 256 } 257 } 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 (dtorType == Dtor_Base && !TryEmitBaseDestructorAsAlias(dtor)) 264 return; 265 266 const CGFunctionInfo &fnInfo = 267 getTypes().arrangeCXXDestructor(dtor, dtorType); 268 269 llvm::Function *fn = 270 cast<llvm::Function>(GetAddrOfCXXDestructor(dtor, dtorType, &fnInfo)); 271 setFunctionLinkage(GlobalDecl(dtor, dtorType), fn); 272 273 CodeGenFunction(*this).GenerateCode(GlobalDecl(dtor, dtorType), fn, fnInfo); 274 275 SetFunctionDefinitionAttributes(dtor, fn); 276 SetLLVMFunctionAttributesForDefinition(dtor, fn); 277} 278 279llvm::GlobalValue * 280CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *dtor, 281 CXXDtorType dtorType, 282 const CGFunctionInfo *fnInfo, 283 llvm::FunctionType *fnType) { 284 GlobalDecl GD(dtor, dtorType); 285 286 StringRef name = getMangledName(GD); 287 if (llvm::GlobalValue *existing = GetGlobalValue(name)) 288 return existing; 289 290 if (!fnType) { 291 if (!fnInfo) fnInfo = &getTypes().arrangeCXXDestructor(dtor, dtorType); 292 fnType = getTypes().GetFunctionType(*fnInfo); 293 } 294 return cast<llvm::Function>(GetOrCreateLLVMFunction(name, fnType, GD, 295 /*ForVTable=*/false)); 296} 297 298static llvm::Value *BuildAppleKextVirtualCall(CodeGenFunction &CGF, 299 GlobalDecl GD, 300 llvm::Type *Ty, 301 const CXXRecordDecl *RD) { 302 assert(!CGF.CGM.getTarget().getCXXABI().isMicrosoft() && 303 "No kext in Microsoft ABI"); 304 GD = GD.getCanonicalDecl(); 305 CodeGenModule &CGM = CGF.CGM; 306 llvm::Value *VTable = CGM.getCXXABI().getAddrOfVTable(RD, CharUnits()); 307 Ty = Ty->getPointerTo()->getPointerTo(); 308 VTable = CGF.Builder.CreateBitCast(VTable, Ty); 309 assert(VTable && "BuildVirtualCall = kext vtbl pointer is null"); 310 uint64_t VTableIndex = CGM.getItaniumVTableContext().getMethodVTableIndex(GD); 311 uint64_t AddressPoint = 312 CGM.getItaniumVTableContext().getVTableLayout(RD) 313 .getAddressPoint(BaseSubobject(RD, CharUnits::Zero())); 314 VTableIndex += AddressPoint; 315 llvm::Value *VFuncPtr = 316 CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfnkxt"); 317 return CGF.Builder.CreateLoad(VFuncPtr); 318} 319 320/// BuildAppleKextVirtualCall - This routine is to support gcc's kext ABI making 321/// indirect call to virtual functions. It makes the call through indexing 322/// into the vtable. 323llvm::Value * 324CodeGenFunction::BuildAppleKextVirtualCall(const CXXMethodDecl *MD, 325 NestedNameSpecifier *Qual, 326 llvm::Type *Ty) { 327 assert((Qual->getKind() == NestedNameSpecifier::TypeSpec) && 328 "BuildAppleKextVirtualCall - bad Qual kind"); 329 330 const Type *QTy = Qual->getAsType(); 331 QualType T = QualType(QTy, 0); 332 const RecordType *RT = T->getAs<RecordType>(); 333 assert(RT && "BuildAppleKextVirtualCall - Qual type must be record"); 334 const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl()); 335 336 if (const CXXDestructorDecl *DD = dyn_cast<CXXDestructorDecl>(MD)) 337 return BuildAppleKextVirtualDestructorCall(DD, Dtor_Complete, RD); 338 339 return ::BuildAppleKextVirtualCall(*this, MD, Ty, RD); 340} 341 342/// BuildVirtualCall - This routine makes indirect vtable call for 343/// call to virtual destructors. It returns 0 if it could not do it. 344llvm::Value * 345CodeGenFunction::BuildAppleKextVirtualDestructorCall( 346 const CXXDestructorDecl *DD, 347 CXXDtorType Type, 348 const CXXRecordDecl *RD) { 349 const CXXMethodDecl *MD = cast<CXXMethodDecl>(DD); 350 // FIXME. Dtor_Base dtor is always direct!! 351 // It need be somehow inline expanded into the caller. 352 // -O does that. But need to support -O0 as well. 353 if (MD->isVirtual() && Type != Dtor_Base) { 354 // Compute the function type we're calling. 355 const CGFunctionInfo &FInfo = 356 CGM.getTypes().arrangeCXXDestructor(DD, Dtor_Complete); 357 llvm::Type *Ty = CGM.getTypes().GetFunctionType(FInfo); 358 return ::BuildAppleKextVirtualCall(*this, GlobalDecl(DD, Type), Ty, RD); 359 } 360 return 0; 361} 362