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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   unsigned alignment = Context.getDeclAlign(&D).getQuantity();
     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 void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
    105                                                llvm::Constant *DeclPtr) {
    106 
    107   const Expr *Init = D.getInit();
    108   QualType T = D.getType();
    109 
    110   if (!T->isReferenceType()) {
    111     EmitDeclInit(*this, D, DeclPtr);
    112     EmitDeclDestroy(*this, D, DeclPtr);
    113     return;
    114   }
    115 
    116   unsigned Alignment = getContext().getDeclAlign(&D).getQuantity();
    117   RValue RV = EmitReferenceBindingToExpr(Init, &D);
    118   EmitStoreOfScalar(RV.getScalarVal(), DeclPtr, false, Alignment, T);
    119 }
    120 
    121 void
    122 CodeGenFunction::EmitCXXGlobalDtorRegistration(llvm::Constant *DtorFn,
    123                                                llvm::Constant *DeclPtr) {
    124   // Generate a global destructor entry if not using __cxa_atexit.
    125   if (!CGM.getCodeGenOpts().CXAAtExit) {
    126     CGM.AddCXXDtorEntry(DtorFn, DeclPtr);
    127     return;
    128   }
    129 
    130   // Get the destructor function type
    131   llvm::Type *DtorFnTy =
    132     llvm::FunctionType::get(llvm::Type::getVoidTy(getLLVMContext()),
    133                             Int8PtrTy, false);
    134   DtorFnTy = llvm::PointerType::getUnqual(DtorFnTy);
    135 
    136   llvm::Type *Params[] = { DtorFnTy, Int8PtrTy, Int8PtrTy };
    137 
    138   // Get the __cxa_atexit function type
    139   // extern "C" int __cxa_atexit ( void (*f)(void *), void *p, void *d );
    140   llvm::FunctionType *AtExitFnTy =
    141     llvm::FunctionType::get(ConvertType(getContext().IntTy), Params, false);
    142 
    143   llvm::Constant *AtExitFn = CGM.CreateRuntimeFunction(AtExitFnTy,
    144                                                        "__cxa_atexit");
    145   if (llvm::Function *Fn = dyn_cast<llvm::Function>(AtExitFn))
    146     Fn->setDoesNotThrow();
    147 
    148   llvm::Constant *Handle = CGM.CreateRuntimeVariable(Int8PtrTy,
    149                                                      "__dso_handle");
    150   llvm::Value *Args[3] = { llvm::ConstantExpr::getBitCast(DtorFn, DtorFnTy),
    151                            llvm::ConstantExpr::getBitCast(DeclPtr, Int8PtrTy),
    152                            llvm::ConstantExpr::getBitCast(Handle, Int8PtrTy) };
    153   Builder.CreateCall(AtExitFn, Args);
    154 }
    155 
    156 void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
    157                                          llvm::GlobalVariable *DeclPtr) {
    158   // If we've been asked to forbid guard variables, emit an error now.
    159   // This diagnostic is hard-coded for Darwin's use case;  we can find
    160   // better phrasing if someone else needs it.
    161   if (CGM.getCodeGenOpts().ForbidGuardVariables)
    162     CGM.Error(D.getLocation(),
    163               "this initialization requires a guard variable, which "
    164               "the kernel does not support");
    165 
    166   CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr);
    167 }
    168 
    169 static llvm::Function *
    170 CreateGlobalInitOrDestructFunction(CodeGenModule &CGM,
    171                                    llvm::FunctionType *FTy,
    172                                    StringRef Name) {
    173   llvm::Function *Fn =
    174     llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
    175                            Name, &CGM.getModule());
    176   if (!CGM.getContext().getLangOptions().AppleKext) {
    177     // Set the section if needed.
    178     if (const char *Section =
    179           CGM.getContext().getTargetInfo().getStaticInitSectionSpecifier())
    180       Fn->setSection(Section);
    181   }
    182 
    183   if (!CGM.getLangOptions().Exceptions)
    184     Fn->setDoesNotThrow();
    185 
    186   return Fn;
    187 }
    188 
    189 void
    190 CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
    191                                             llvm::GlobalVariable *Addr) {
    192   llvm::FunctionType *FTy
    193     = llvm::FunctionType::get(llvm::Type::getVoidTy(VMContext),
    194                               false);
    195 
    196   // Create a variable initialization function.
    197   llvm::Function *Fn =
    198     CreateGlobalInitOrDestructFunction(*this, FTy, "__cxx_global_var_init");
    199 
    200   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr);
    201 
    202   if (D->hasAttr<InitPriorityAttr>()) {
    203     unsigned int order = D->getAttr<InitPriorityAttr>()->getPriority();
    204     OrderGlobalInits Key(order, PrioritizedCXXGlobalInits.size());
    205     PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
    206     DelayedCXXInitPosition.erase(D);
    207   }
    208   else {
    209     llvm::DenseMap<const Decl *, unsigned>::iterator I =
    210       DelayedCXXInitPosition.find(D);
    211     if (I == DelayedCXXInitPosition.end()) {
    212       CXXGlobalInits.push_back(Fn);
    213     } else {
    214       assert(CXXGlobalInits[I->second] == 0);
    215       CXXGlobalInits[I->second] = Fn;
    216       DelayedCXXInitPosition.erase(I);
    217     }
    218   }
    219 }
    220 
    221 void
    222 CodeGenModule::EmitCXXGlobalInitFunc() {
    223   while (!CXXGlobalInits.empty() && !CXXGlobalInits.back())
    224     CXXGlobalInits.pop_back();
    225 
    226   if (CXXGlobalInits.empty() && PrioritizedCXXGlobalInits.empty())
    227     return;
    228 
    229   llvm::FunctionType *FTy
    230     = llvm::FunctionType::get(llvm::Type::getVoidTy(VMContext),
    231                               false);
    232 
    233   // Create our global initialization function.
    234   llvm::Function *Fn =
    235     CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__I_a");
    236 
    237   if (!PrioritizedCXXGlobalInits.empty()) {
    238     SmallVector<llvm::Constant*, 8> LocalCXXGlobalInits;
    239     llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(),
    240                          PrioritizedCXXGlobalInits.end());
    241     for (unsigned i = 0; i < PrioritizedCXXGlobalInits.size(); i++) {
    242       llvm::Function *Fn = PrioritizedCXXGlobalInits[i].second;
    243       LocalCXXGlobalInits.push_back(Fn);
    244     }
    245     LocalCXXGlobalInits.append(CXXGlobalInits.begin(), CXXGlobalInits.end());
    246     CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
    247                                                     &LocalCXXGlobalInits[0],
    248                                                     LocalCXXGlobalInits.size());
    249   }
    250   else
    251     CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn,
    252                                                      &CXXGlobalInits[0],
    253                                                      CXXGlobalInits.size());
    254   AddGlobalCtor(Fn);
    255   CXXGlobalInits.clear();
    256   PrioritizedCXXGlobalInits.clear();
    257 }
    258 
    259 void CodeGenModule::EmitCXXGlobalDtorFunc() {
    260   if (CXXGlobalDtors.empty())
    261     return;
    262 
    263   llvm::FunctionType *FTy
    264     = llvm::FunctionType::get(llvm::Type::getVoidTy(VMContext),
    265                               false);
    266 
    267   // Create our global destructor function.
    268   llvm::Function *Fn =
    269     CreateGlobalInitOrDestructFunction(*this, FTy, "_GLOBAL__D_a");
    270 
    271   CodeGenFunction(*this).GenerateCXXGlobalDtorFunc(Fn, CXXGlobalDtors);
    272   AddGlobalDtor(Fn);
    273 }
    274 
    275 /// Emit the code necessary to initialize the given global variable.
    276 void CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
    277                                                        const VarDecl *D,
    278                                                  llvm::GlobalVariable *Addr) {
    279   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    280                 getTypes().getNullaryFunctionInfo(),
    281                 FunctionArgList(), SourceLocation());
    282 
    283   // Use guarded initialization if the global variable is weak. This
    284   // occurs for, e.g., instantiated static data members and
    285   // definitions explicitly marked weak.
    286   if (Addr->getLinkage() == llvm::GlobalValue::WeakODRLinkage ||
    287       Addr->getLinkage() == llvm::GlobalValue::WeakAnyLinkage) {
    288     EmitCXXGuardedInit(*D, Addr);
    289   } else {
    290     EmitCXXGlobalVarDeclInit(*D, Addr);
    291   }
    292 
    293   FinishFunction();
    294 }
    295 
    296 void CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
    297                                                 llvm::Constant **Decls,
    298                                                 unsigned NumDecls) {
    299   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    300                 getTypes().getNullaryFunctionInfo(),
    301                 FunctionArgList(), SourceLocation());
    302 
    303   RunCleanupsScope Scope(*this);
    304 
    305   // When building in Objective-C++ ARC mode, create an autorelease pool
    306   // around the global initializers.
    307   if (getLangOptions().ObjCAutoRefCount && getLangOptions().CPlusPlus) {
    308     llvm::Value *token = EmitObjCAutoreleasePoolPush();
    309     EmitObjCAutoreleasePoolCleanup(token);
    310   }
    311 
    312   for (unsigned i = 0; i != NumDecls; ++i)
    313     if (Decls[i])
    314       Builder.CreateCall(Decls[i]);
    315 
    316   Scope.ForceCleanup();
    317 
    318   FinishFunction();
    319 }
    320 
    321 void CodeGenFunction::GenerateCXXGlobalDtorFunc(llvm::Function *Fn,
    322                   const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
    323                                                 &DtorsAndObjects) {
    324   StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    325                 getTypes().getNullaryFunctionInfo(),
    326                 FunctionArgList(), SourceLocation());
    327 
    328   // Emit the dtors, in reverse order from construction.
    329   for (unsigned i = 0, e = DtorsAndObjects.size(); i != e; ++i) {
    330     llvm::Value *Callee = DtorsAndObjects[e - i - 1].first;
    331     llvm::CallInst *CI = Builder.CreateCall(Callee,
    332                                             DtorsAndObjects[e - i - 1].second);
    333     // Make sure the call and the callee agree on calling convention.
    334     if (llvm::Function *F = dyn_cast<llvm::Function>(Callee))
    335       CI->setCallingConv(F->getCallingConv());
    336   }
    337 
    338   FinishFunction();
    339 }
    340 
    341 /// generateDestroyHelper - Generates a helper function which, when
    342 /// invoked, destroys the given object.
    343 llvm::Function *
    344 CodeGenFunction::generateDestroyHelper(llvm::Constant *addr,
    345                                        QualType type,
    346                                        Destroyer &destroyer,
    347                                        bool useEHCleanupForArray) {
    348   FunctionArgList args;
    349   ImplicitParamDecl dst(0, SourceLocation(), 0, getContext().VoidPtrTy);
    350   args.push_back(&dst);
    351 
    352   const CGFunctionInfo &FI =
    353     CGM.getTypes().getFunctionInfo(getContext().VoidTy, args,
    354                                    FunctionType::ExtInfo());
    355   llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI, false);
    356   llvm::Function *fn =
    357     CreateGlobalInitOrDestructFunction(CGM, FTy, "__cxx_global_array_dtor");
    358 
    359   StartFunction(GlobalDecl(), getContext().VoidTy, fn, FI, args,
    360                 SourceLocation());
    361 
    362   emitDestroy(addr, type, destroyer, useEHCleanupForArray);
    363 
    364   FinishFunction();
    365 
    366   return fn;
    367 }
    368 
    369