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      1 //===--- CGDeclCXX.cpp - Emit LLVM Code for C++ 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 code generation of C++ declarations
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "CodeGenFunction.h"
     15 #include "CGObjCRuntime.h"
     16 #include "CGCXXABI.h"
     17 #include "clang/Frontend/CodeGenOptions.h"
     18 #include "llvm/Intrinsics.h"
     19 
     20 using namespace clang;
     21 using namespace CodeGen;
     22 
     23 static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
     24                          llvm::Constant *DeclPtr) {
     25   assert(D.hasGlobalStorage() && "VarDecl must have global storage!");
     26   assert(!D.getType()->isReferenceType() &&
     27          "Should not call EmitDeclInit on a reference!");
     28 
     29   ASTContext &Context = CGF.getContext();
     30 
     31   CharUnits alignment = Context.getDeclAlign(&D);
     32   QualType type = D.getType();
     33   LValue lv = CGF.MakeAddrLValue(DeclPtr, type, alignment);
     34 
     35   const Expr *Init = D.getInit();
     36   if (!CGF.hasAggregateLLVMType(type)) {
     37     CodeGenModule &CGM = CGF.CGM;
     38     if (lv.isObjCStrong())
     39       CGM.getObjCRuntime().EmitObjCGlobalAssign(CGF, CGF.EmitScalarExpr(Init),
     40                                                 DeclPtr, D.isThreadSpecified());
     41     else if (lv.isObjCWeak())
     42       CGM.getObjCRuntime().EmitObjCWeakAssign(CGF, CGF.EmitScalarExpr(Init),
     43                                               DeclPtr);
     44     else
     45       CGF.EmitScalarInit(Init, &D, lv, false);
     46   } else if (type->isAnyComplexType()) {
     47     CGF.EmitComplexExprIntoAddr(Init, DeclPtr, lv.isVolatile());
     48   } else {
     49     CGF.EmitAggExpr(Init, AggValueSlot::forLValue(lv,AggValueSlot::IsDestructed,
     50                                           AggValueSlot::DoesNotNeedGCBarriers,
     51                                                   AggValueSlot::IsNotAliased));
     52   }
     53 }
     54 
     55 /// Emit code to cause the destruction of the given variable with
     56 /// static storage duration.
     57 static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
     58                             llvm::Constant *addr) {
     59   CodeGenModule &CGM = CGF.CGM;
     60 
     61   // FIXME:  __attribute__((cleanup)) ?
     62 
     63   QualType type = D.getType();
     64   QualType::DestructionKind dtorKind = type.isDestructedType();
     65 
     66   switch (dtorKind) {
     67   case QualType::DK_none:
     68     return;
     69 
     70   case QualType::DK_cxx_destructor:
     71     break;
     72 
     73   case QualType::DK_objc_strong_lifetime:
     74   case QualType::DK_objc_weak_lifetime:
     75     // We don't care about releasing objects during process teardown.
     76     return;
     77   }
     78 
     79   llvm::Constant *function;
     80   llvm::Constant *argument;
     81 
     82   // Special-case non-array C++ destructors, where there's a function
     83   // with the right signature that we can just call.
     84   const CXXRecordDecl *record = 0;
     85   if (dtorKind == QualType::DK_cxx_destructor &&
     86       (record = type->getAsCXXRecordDecl())) {
     87     assert(!record->hasTrivialDestructor());
     88     CXXDestructorDecl *dtor = record->getDestructor();
     89 
     90     function = CGM.GetAddrOfCXXDestructor(dtor, Dtor_Complete);
     91     argument = addr;
     92 
     93   // Otherwise, the standard logic requires a helper function.
     94   } else {
     95     function = CodeGenFunction(CGM).generateDestroyHelper(addr, type,
     96                                                   CGF.getDestroyer(dtorKind),
     97                                                   CGF.needsEHCleanup(dtorKind));
     98     argument = llvm::Constant::getNullValue(CGF.Int8PtrTy);
     99   }
    100 
    101   CGF.EmitCXXGlobalDtorRegistration(function, argument);
    102 }
    103 
    104 /// Emit code to cause the variable at the given address to be considered as
    105 /// constant from this point onwards.
    106 static void EmitDeclInvariant(CodeGenFunction &CGF, const VarDecl &D,
    107                               llvm::Constant *Addr) {
    108   // Don't emit the intrinsic if we're not optimizing.
    109   if (!CGF.CGM.getCodeGenOpts().OptimizationLevel)
    110     return;
    111 
    112   // Grab the llvm.invariant.start intrinsic.
    113   llvm::Intrinsic::ID InvStartID = llvm::Intrinsic::invariant_start;
    114   llvm::Constant *InvariantStart = CGF.CGM.getIntrinsic(InvStartID);
    115 
    116   // Emit a call with the size in bytes of the object.
    117   CharUnits WidthChars = CGF.getContext().getTypeSizeInChars(D.getType());
    118   uint64_t Width = WidthChars.getQuantity();
    119   llvm::Value *Args[2] = { llvm::ConstantInt::getSigned(CGF.Int64Ty, Width),
    120                            llvm::ConstantExpr::getBitCast(Addr, CGF.Int8PtrTy)};
    121   CGF.Builder.CreateCall(InvariantStart, Args);
    122 }
    123 
    124 void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
    125                                                llvm::Constant *DeclPtr,
    126                                                bool PerformInit) {
    127 
    128   const Expr *Init = D.getInit();
    129   QualType T = D.getType();
    130 
    131   if (!T->isReferenceType()) {
    132     if (PerformInit)
    133       EmitDeclInit(*this, D, DeclPtr);
    134     if (CGM.isTypeConstant(D.getType(), true))
    135       EmitDeclInvariant(*this, D, DeclPtr);
    136     else
    137       EmitDeclDestroy(*this, D, DeclPtr);
    138     return;
    139   }
    140 
    141   assert(PerformInit && "cannot have constant initializer which needs "
    142          "destruction for reference");
    143   unsigned Alignment = getContext().getDeclAlign(&D).getQuantity();
    144   RValue RV = EmitReferenceBindingToExpr(Init, &D);
    145   EmitStoreOfScalar(RV.getScalarVal(), DeclPtr, false, Alignment, T);
    146 }
    147 
    148 /// Register a global destructor using __cxa_atexit.
    149 static void emitGlobalDtorWithCXAAtExit(CodeGenFunction &CGF,
    150                                         llvm::Constant *dtor,
    151                                         llvm::Constant *addr) {
    152   // We're assuming that the destructor function is something we can
    153   // reasonably call with the default CC.  Go ahead and cast it to the
    154   // right prototype.
    155   llvm::Type *dtorTy =
    156     llvm::FunctionType::get(CGF.VoidTy, CGF.Int8PtrTy, false)->getPointerTo();
    157 
    158   // extern "C" int __cxa_atexit(void (*f)(void *), void *p, void *d);
    159   llvm::Type *paramTys[] = { dtorTy, CGF.Int8PtrTy, CGF.Int8PtrTy };
    160   llvm::FunctionType *atexitTy =
    161     llvm::FunctionType::get(CGF.IntTy, paramTys, false);
    162 
    163   // Fetch the actual function.
    164   llvm::Constant *atexit =
    165     CGF.CGM.CreateRuntimeFunction(atexitTy, "__cxa_atexit");
    166   if (llvm::Function *fn = dyn_cast<llvm::Function>(atexit))
    167     fn->setDoesNotThrow();
    168 
    169   // Create a variable that binds the atexit to this shared object.
    170   llvm::Constant *handle =
    171     CGF.CGM.CreateRuntimeVariable(CGF.Int8Ty, "__dso_handle");
    172 
    173   llvm::Value *args[] = {
    174     llvm::ConstantExpr::getBitCast(dtor, dtorTy),
    175     llvm::ConstantExpr::getBitCast(addr, CGF.Int8PtrTy),
    176     handle
    177   };
    178   CGF.Builder.CreateCall(atexit, args);
    179 }
    180 
    181 static llvm::Function *
    182 CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
    183                                    llvm::FunctionType *ty,
    184                                    const Twine &name);
    185 
    186 /// Create a stub function, suitable for being passed to atexit,
    187 /// which passes the given address to the given destructor function.
    188 static llvm::Constant *createAtExitStub(CodeGenModule &CGM,
    189                                         llvm::Constant *dtor,
    190                                         llvm::Constant *addr) {
    191   // Get the destructor function type, void(*)(void).
    192   llvm::FunctionType *ty = llvm::FunctionType::get(CGM.VoidTy, false);
    193   llvm::Function *fn =
    194     CreateGlobalInitOrDestructFunction(CGM, ty,
    195                                        Twine("__dtor_", addr->getName()));
    196 
    197   CodeGenFunction CGF(CGM);
    198 
    199   CGF.StartFunction(GlobalDecl(), CGM.getContext().VoidTy, fn,
    200                     CGM.getTypes().arrangeNullaryFunction(),
    201                     FunctionArgList(), SourceLocation());
    202 
    203   llvm::CallInst *call = CGF.Builder.CreateCall(dtor, addr);
    204 
    205  // Make sure the call and the callee agree on calling convention.
    206   if (llvm::Function *dtorFn =
    207         dyn_cast<llvm::Function>(dtor->stripPointerCasts()))
    208     call->setCallingConv(dtorFn->getCallingConv());
    209 
    210   CGF.FinishFunction();
    211 
    212   return fn;
    213 }
    214 
    215 /// Register a global destructor using atexit.
    216 static void emitGlobalDtorWithAtExit(CodeGenFunction &CGF,
    217                                      llvm::Constant *dtor,
    218                                      llvm::Constant *addr) {
    219   // Create a function which calls the destructor.
    220   llvm::Constant *dtorStub = createAtExitStub(CGF.CGM, dtor, addr);
    221 
    222   // extern "C" int atexit(void (*f)(void));
    223   llvm::FunctionType *atexitTy =
    224     llvm::FunctionType::get(CGF.IntTy, dtorStub->getType(), false);
    225 
    226   llvm::Constant *atexit =
    227     CGF.CGM.CreateRuntimeFunction(atexitTy, "atexit");
    228   if (llvm::Function *atexitFn = dyn_cast<llvm::Function>(atexit))
    229     atexitFn->setDoesNotThrow();
    230 
    231   CGF.Builder.CreateCall(atexit, dtorStub);
    232 }
    233 
    234 void CodeGenFunction::EmitCXXGlobalDtorRegistration(llvm::Constant *dtor,
    235                                                     llvm::Constant *addr) {
    236   // Use __cxa_atexit if available.
    237   if (CGM.getCodeGenOpts().CXAAtExit) {
    238     emitGlobalDtorWithCXAAtExit(*this, dtor, addr);
    239     return;
    240   }
    241 
    242   // In Apple kexts, we want to add a global destructor entry.
    243   // FIXME: shouldn't this be guarded by some variable?
    244   if (CGM.getContext().getLangOpts().AppleKext) {
    245     // Generate a global destructor entry.
    246     CGM.AddCXXDtorEntry(dtor, addr);
    247     return;
    248   }
    249 
    250   // Otherwise, we just use atexit.
    251   emitGlobalDtorWithAtExit(*this, dtor, addr);
    252 }
    253 
    254 void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
    255                                          llvm::GlobalVariable *DeclPtr,
    256                                          bool PerformInit) {
    257   // If we've been asked to forbid guard variables, emit an error now.
    258   // This diagnostic is hard-coded for Darwin's use case;  we can find
    259   // better phrasing if someone else needs it.
    260   if (CGM.getCodeGenOpts().ForbidGuardVariables)
    261     CGM.Error(D.getLocation(),
    262               "this initialization requires a guard variable, which "
    263               "the kernel does not support");
    264 
    265   CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr, PerformInit);
    266 }
    267 
    268 static llvm::Function *
    269 CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
    270                                    llvm::FunctionType *FTy,
    271                                    const Twine &Name) {
    272   llvm::Function *Fn =
    273     llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
    274                            Name, &CGM.getModule());
    275   if (!CGM.getContext().getLangOpts().AppleKext) {
    276     // Set the section if needed.
    277     if (const char *Section =
    278           CGM.getContext().getTargetInfo().getStaticInitSectionSpecifier())
    279       Fn->setSection(Section);
    280   }
    281 
    282   if (!CGM.getLangOpts().Exceptions)
    283     Fn->setDoesNotThrow();
    284 
    285   return Fn;
    286 }
    287 
    288 void
    289 CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
    290                                             llvm::GlobalVariable *Addr,
    291                                             bool PerformInit) {
    292   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
    293 
    294   // Create a variable initialization function.
    295   llvm::Function *Fn =
    296     CreateGlobalInitOrDestructFunction(*this, FTy, "__cxx_global_var_init");
    297 
    298   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
    299                                                           PerformInit);
    300 
    301   if (D->hasAttr<InitPriorityAttr>()) {
    302     unsigned int order = D->getAttr<InitPriorityAttr>()->getPriority();
    303     OrderGlobalInits Key(order, PrioritizedCXXGlobalInits.size());
    304     PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
    305     DelayedCXXInitPosition.erase(D);
    306   }
    307   else {
    308     llvm::DenseMap<const Decl *, unsigned>::iterator I =
    309       DelayedCXXInitPosition.find(D);
    310     if (I == DelayedCXXInitPosition.end()) {
    311       CXXGlobalInits.push_back(Fn);
    312     } else {
    313       assert(CXXGlobalInits[I->second] == 0);
    314       CXXGlobalInits[I->second] = Fn;
    315       DelayedCXXInitPosition.erase(I);
    316     }
    317   }
    318 }
    319 
    320 void
    321 CodeGenModule::EmitCXXGlobalInitFunc() {
    322   while (!CXXGlobalInits.empty() && !CXXGlobalInits.back())
    323     CXXGlobalInits.pop_back();
    324 
    325   if (CXXGlobalInits.empty() && PrioritizedCXXGlobalInits.empty())
    326     return;
    327 
    328   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
    329 
    330   // Create our global initialization function.
    331   llvm::Function *Fn =
    332     CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__I_a");
    333 
    334   if (!PrioritizedCXXGlobalInits.empty()) {
    335     SmallVector<llvm::Constant*, 8> LocalCXXGlobalInits;
    336     llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(),
    337                          PrioritizedCXXGlobalInits.end());
    338     for (unsigned i = 0; i < PrioritizedCXXGlobalInits.size(); i++) {
    339       llvm::Function *Fn = PrioritizedCXXGlobalInits[i].second;
    340       LocalCXXGlobalInits.push_back(Fn);
    341     }
    342     LocalCXXGlobalInits.append(CXXGlobalInits.begin(), CXXGlobalInits.end());
    343     CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
    344                                                     &LocalCXXGlobalInits[0],
    345                                                     LocalCXXGlobalInits.size());
    346   }
    347   else
    348     CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
    349                                                      &CXXGlobalInits[0],
    350                                                      CXXGlobalInits.size());
    351   AddGlobalCtor(Fn);
    352   CXXGlobalInits.clear();
    353   PrioritizedCXXGlobalInits.clear();
    354 }
    355 
    356 void CodeGenModule::EmitCXXGlobalDtorFunc() {
    357   if (CXXGlobalDtors.empty())
    358     return;
    359 
    360   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
    361 
    362   // Create our global destructor function.
    363   llvm::Function *Fn =
    364     CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__D_a");
    365 
    366   CodeGenFunction(*this).GenerateCXXGlobalDtorsFunc(Fn, CXXGlobalDtors);
    367   AddGlobalDtor(Fn);
    368 }
    369 
    370 /// Emit the code necessary to initialize the given global variable.
    371 void CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
    372                                                        const VarDecl *D,
    373                                                  llvm::GlobalVariable *Addr,
    374                                                        bool PerformInit) {
    375   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    376                 getTypes().arrangeNullaryFunction(),
    377                 FunctionArgList(), SourceLocation());
    378 
    379   // Use guarded initialization if the global variable is weak. This
    380   // occurs for, e.g., instantiated static data members and
    381   // definitions explicitly marked weak.
    382   if (Addr->getLinkage() == llvm::GlobalValue::WeakODRLinkage ||
    383       Addr->getLinkage() == llvm::GlobalValue::WeakAnyLinkage) {
    384     EmitCXXGuardedInit(*D, Addr, PerformInit);
    385   } else {
    386     EmitCXXGlobalVarDeclInit(*D, Addr, PerformInit);
    387   }
    388 
    389   FinishFunction();
    390 }
    391 
    392 void CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
    393                                                 llvm::Constant **Decls,
    394                                                 unsigned NumDecls) {
    395   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    396                 getTypes().arrangeNullaryFunction(),
    397                 FunctionArgList(), SourceLocation());
    398 
    399   RunCleanupsScope Scope(*this);
    400 
    401   // When building in Objective-C++ ARC mode, create an autorelease pool
    402   // around the global initializers.
    403   if (getLangOpts().ObjCAutoRefCount && getLangOpts().CPlusPlus) {
    404     llvm::Value *token = EmitObjCAutoreleasePoolPush();
    405     EmitObjCAutoreleasePoolCleanup(token);
    406   }
    407 
    408   for (unsigned i = 0; i != NumDecls; ++i)
    409     if (Decls[i])
    410       Builder.CreateCall(Decls[i]);
    411 
    412   Scope.ForceCleanup();
    413 
    414   FinishFunction();
    415 }
    416 
    417 void CodeGenFunction::GenerateCXXGlobalDtorsFunc(llvm::Function *Fn,
    418                   const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
    419                                                 &DtorsAndObjects) {
    420   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    421                 getTypes().arrangeNullaryFunction(),
    422                 FunctionArgList(), SourceLocation());
    423 
    424   // Emit the dtors, in reverse order from construction.
    425   for (unsigned i = 0, e = DtorsAndObjects.size(); i != e; ++i) {
    426     llvm::Value *Callee = DtorsAndObjects[e - i - 1].first;
    427     llvm::CallInst *CI = Builder.CreateCall(Callee,
    428                                             DtorsAndObjects[e - i - 1].second);
    429     // Make sure the call and the callee agree on calling convention.
    430     if (llvm::Function *F = dyn_cast<llvm::Function>(Callee))
    431       CI->setCallingConv(F->getCallingConv());
    432   }
    433 
    434   FinishFunction();
    435 }
    436 
    437 /// generateDestroyHelper - Generates a helper function which, when
    438 /// invoked, destroys the given object.
    439 llvm::Function *
    440 CodeGenFunction::generateDestroyHelper(llvm::Constant *addr,
    441                                        QualType type,
    442                                        Destroyer *destroyer,
    443                                        bool useEHCleanupForArray) {
    444   FunctionArgList args;
    445   ImplicitParamDecl dst(0, SourceLocation(), 0, getContext().VoidPtrTy);
    446   args.push_back(&dst);
    447 
    448   const CGFunctionInfo &FI =
    449     CGM.getTypes().arrangeFunctionDeclaration(getContext().VoidTy, args,
    450                                               FunctionType::ExtInfo(),
    451                                               /*variadic*/ false);
    452   llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI);
    453   llvm::Function *fn =
    454     CreateGlobalInitOrDestructFunction(CGM, FTy, "__cxx_global_array_dtor");
    455 
    456   StartFunction(GlobalDecl(), getContext().VoidTy, fn, FI, args,
    457                 SourceLocation());
    458 
    459   emitDestroy(addr, type, destroyer, useEHCleanupForArray);
    460 
    461   FinishFunction();
    462 
    463   return fn;
    464 }
    465