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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 "CGCXXABI.h"
     16 #include "CGObjCRuntime.h"
     17 #include "CGOpenMPRuntime.h"
     18 #include "clang/Frontend/CodeGenOptions.h"
     19 #include "llvm/ADT/StringExtras.h"
     20 #include "llvm/IR/Intrinsics.h"
     21 #include "llvm/Support/Path.h"
     22 
     23 using namespace clang;
     24 using namespace CodeGen;
     25 
     26 static void EmitDeclInit(CodeGenFunction &CGF, const VarDecl &D,
     27                          ConstantAddress DeclPtr) {
     28   assert(D.hasGlobalStorage() && "VarDecl must have global storage!");
     29   assert(!D.getType()->isReferenceType() &&
     30          "Should not call EmitDeclInit on a reference!");
     31 
     32   QualType type = D.getType();
     33   LValue lv = CGF.MakeAddrLValue(DeclPtr, type);
     34 
     35   const Expr *Init = D.getInit();
     36   switch (CGF.getEvaluationKind(type)) {
     37   case TEK_Scalar: {
     38     CodeGenModule &CGM = CGF.CGM;
     39     if (lv.isObjCStrong())
     40       CGM.getObjCRuntime().EmitObjCGlobalAssign(CGF, CGF.EmitScalarExpr(Init),
     41                                                 DeclPtr, D.getTLSKind());
     42     else if (lv.isObjCWeak())
     43       CGM.getObjCRuntime().EmitObjCWeakAssign(CGF, CGF.EmitScalarExpr(Init),
     44                                               DeclPtr);
     45     else
     46       CGF.EmitScalarInit(Init, &D, lv, false);
     47     return;
     48   }
     49   case TEK_Complex:
     50     CGF.EmitComplexExprIntoLValue(Init, lv, /*isInit*/ true);
     51     return;
     52   case TEK_Aggregate:
     53     CGF.EmitAggExpr(Init, AggValueSlot::forLValue(lv,AggValueSlot::IsDestructed,
     54                                           AggValueSlot::DoesNotNeedGCBarriers,
     55                                                   AggValueSlot::IsNotAliased));
     56     return;
     57   }
     58   llvm_unreachable("bad evaluation kind");
     59 }
     60 
     61 /// Emit code to cause the destruction of the given variable with
     62 /// static storage duration.
     63 static void EmitDeclDestroy(CodeGenFunction &CGF, const VarDecl &D,
     64                             ConstantAddress addr) {
     65   CodeGenModule &CGM = CGF.CGM;
     66 
     67   // FIXME:  __attribute__((cleanup)) ?
     68 
     69   QualType type = D.getType();
     70   QualType::DestructionKind dtorKind = type.isDestructedType();
     71 
     72   switch (dtorKind) {
     73   case QualType::DK_none:
     74     return;
     75 
     76   case QualType::DK_cxx_destructor:
     77     break;
     78 
     79   case QualType::DK_objc_strong_lifetime:
     80   case QualType::DK_objc_weak_lifetime:
     81     // We don't care about releasing objects during process teardown.
     82     assert(!D.getTLSKind() && "should have rejected this");
     83     return;
     84   }
     85 
     86   llvm::Constant *function;
     87   llvm::Constant *argument;
     88 
     89   // Special-case non-array C++ destructors, where there's a function
     90   // with the right signature that we can just call.
     91   const CXXRecordDecl *record = nullptr;
     92   if (dtorKind == QualType::DK_cxx_destructor &&
     93       (record = type->getAsCXXRecordDecl())) {
     94     assert(!record->hasTrivialDestructor());
     95     CXXDestructorDecl *dtor = record->getDestructor();
     96 
     97     function = CGM.getAddrOfCXXStructor(dtor, StructorType::Complete);
     98     argument = llvm::ConstantExpr::getBitCast(
     99         addr.getPointer(), CGF.getTypes().ConvertType(type)->getPointerTo());
    100 
    101   // Otherwise, the standard logic requires a helper function.
    102   } else {
    103     function = CodeGenFunction(CGM)
    104         .generateDestroyHelper(addr, type, CGF.getDestroyer(dtorKind),
    105                                CGF.needsEHCleanup(dtorKind), &D);
    106     argument = llvm::Constant::getNullValue(CGF.Int8PtrTy);
    107   }
    108 
    109   CGM.getCXXABI().registerGlobalDtor(CGF, D, function, argument);
    110 }
    111 
    112 /// Emit code to cause the variable at the given address to be considered as
    113 /// constant from this point onwards.
    114 static void EmitDeclInvariant(CodeGenFunction &CGF, const VarDecl &D,
    115                               llvm::Constant *Addr) {
    116   // Don't emit the intrinsic if we're not optimizing.
    117   if (!CGF.CGM.getCodeGenOpts().OptimizationLevel)
    118     return;
    119 
    120   // Grab the llvm.invariant.start intrinsic.
    121   llvm::Intrinsic::ID InvStartID = llvm::Intrinsic::invariant_start;
    122   llvm::Constant *InvariantStart = CGF.CGM.getIntrinsic(InvStartID);
    123 
    124   // Emit a call with the size in bytes of the object.
    125   CharUnits WidthChars = CGF.getContext().getTypeSizeInChars(D.getType());
    126   uint64_t Width = WidthChars.getQuantity();
    127   llvm::Value *Args[2] = { llvm::ConstantInt::getSigned(CGF.Int64Ty, Width),
    128                            llvm::ConstantExpr::getBitCast(Addr, CGF.Int8PtrTy)};
    129   CGF.Builder.CreateCall(InvariantStart, Args);
    130 }
    131 
    132 void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
    133                                                llvm::Constant *DeclPtr,
    134                                                bool PerformInit) {
    135 
    136   const Expr *Init = D.getInit();
    137   QualType T = D.getType();
    138 
    139   // The address space of a static local variable (DeclPtr) may be different
    140   // from the address space of the "this" argument of the constructor. In that
    141   // case, we need an addrspacecast before calling the constructor.
    142   //
    143   // struct StructWithCtor {
    144   //   __device__ StructWithCtor() {...}
    145   // };
    146   // __device__ void foo() {
    147   //   __shared__ StructWithCtor s;
    148   //   ...
    149   // }
    150   //
    151   // For example, in the above CUDA code, the static local variable s has a
    152   // "shared" address space qualifier, but the constructor of StructWithCtor
    153   // expects "this" in the "generic" address space.
    154   unsigned ExpectedAddrSpace = getContext().getTargetAddressSpace(T);
    155   unsigned ActualAddrSpace = DeclPtr->getType()->getPointerAddressSpace();
    156   if (ActualAddrSpace != ExpectedAddrSpace) {
    157     llvm::Type *LTy = CGM.getTypes().ConvertTypeForMem(T);
    158     llvm::PointerType *PTy = llvm::PointerType::get(LTy, ExpectedAddrSpace);
    159     DeclPtr = llvm::ConstantExpr::getAddrSpaceCast(DeclPtr, PTy);
    160   }
    161 
    162   ConstantAddress DeclAddr(DeclPtr, getContext().getDeclAlign(&D));
    163 
    164   if (!T->isReferenceType()) {
    165     if (getLangOpts().OpenMP && D.hasAttr<OMPThreadPrivateDeclAttr>())
    166       (void)CGM.getOpenMPRuntime().emitThreadPrivateVarDefinition(
    167           &D, DeclAddr, D.getAttr<OMPThreadPrivateDeclAttr>()->getLocation(),
    168           PerformInit, this);
    169     if (PerformInit)
    170       EmitDeclInit(*this, D, DeclAddr);
    171     if (CGM.isTypeConstant(D.getType(), true))
    172       EmitDeclInvariant(*this, D, DeclPtr);
    173     else
    174       EmitDeclDestroy(*this, D, DeclAddr);
    175     return;
    176   }
    177 
    178   assert(PerformInit && "cannot have constant initializer which needs "
    179          "destruction for reference");
    180   RValue RV = EmitReferenceBindingToExpr(Init);
    181   EmitStoreOfScalar(RV.getScalarVal(), DeclAddr, false, T);
    182 }
    183 
    184 /// Create a stub function, suitable for being passed to atexit,
    185 /// which passes the given address to the given destructor function.
    186 llvm::Constant *CodeGenFunction::createAtExitStub(const VarDecl &VD,
    187                                                   llvm::Constant *dtor,
    188                                                   llvm::Constant *addr) {
    189   // Get the destructor function type, void(*)(void).
    190   llvm::FunctionType *ty = llvm::FunctionType::get(CGM.VoidTy, false);
    191   SmallString<256> FnName;
    192   {
    193     llvm::raw_svector_ostream Out(FnName);
    194     CGM.getCXXABI().getMangleContext().mangleDynamicAtExitDestructor(&VD, Out);
    195   }
    196 
    197   const CGFunctionInfo &FI = CGM.getTypes().arrangeNullaryFunction();
    198   llvm::Function *fn = CGM.CreateGlobalInitOrDestructFunction(ty, FnName.str(),
    199                                                               FI,
    200                                                               VD.getLocation());
    201 
    202   CodeGenFunction CGF(CGM);
    203 
    204   CGF.StartFunction(&VD, CGM.getContext().VoidTy, fn, FI, FunctionArgList());
    205 
    206   llvm::CallInst *call = CGF.Builder.CreateCall(dtor, addr);
    207 
    208  // Make sure the call and the callee agree on calling convention.
    209   if (llvm::Function *dtorFn =
    210         dyn_cast<llvm::Function>(dtor->stripPointerCasts()))
    211     call->setCallingConv(dtorFn->getCallingConv());
    212 
    213   CGF.FinishFunction();
    214 
    215   return fn;
    216 }
    217 
    218 /// Register a global destructor using the C atexit runtime function.
    219 void CodeGenFunction::registerGlobalDtorWithAtExit(const VarDecl &VD,
    220                                                    llvm::Constant *dtor,
    221                                                    llvm::Constant *addr) {
    222   // Create a function which calls the destructor.
    223   llvm::Constant *dtorStub = createAtExitStub(VD, dtor, addr);
    224 
    225   // extern "C" int atexit(void (*f)(void));
    226   llvm::FunctionType *atexitTy =
    227     llvm::FunctionType::get(IntTy, dtorStub->getType(), false);
    228 
    229   llvm::Constant *atexit =
    230     CGM.CreateRuntimeFunction(atexitTy, "atexit");
    231   if (llvm::Function *atexitFn = dyn_cast<llvm::Function>(atexit))
    232     atexitFn->setDoesNotThrow();
    233 
    234   EmitNounwindRuntimeCall(atexit, dtorStub);
    235 }
    236 
    237 void CodeGenFunction::EmitCXXGuardedInit(const VarDecl &D,
    238                                          llvm::GlobalVariable *DeclPtr,
    239                                          bool PerformInit) {
    240   // If we've been asked to forbid guard variables, emit an error now.
    241   // This diagnostic is hard-coded for Darwin's use case;  we can find
    242   // better phrasing if someone else needs it.
    243   if (CGM.getCodeGenOpts().ForbidGuardVariables)
    244     CGM.Error(D.getLocation(),
    245               "this initialization requires a guard variable, which "
    246               "the kernel does not support");
    247 
    248   CGM.getCXXABI().EmitGuardedInit(*this, D, DeclPtr, PerformInit);
    249 }
    250 
    251 llvm::Function *CodeGenModule::CreateGlobalInitOrDestructFunction(
    252     llvm::FunctionType *FTy, const Twine &Name, const CGFunctionInfo &FI,
    253     SourceLocation Loc, bool TLS) {
    254   llvm::Function *Fn =
    255     llvm::Function::Create(FTy, llvm::GlobalValue::InternalLinkage,
    256                            Name, &getModule());
    257   if (!getLangOpts().AppleKext && !TLS) {
    258     // Set the section if needed.
    259     if (const char *Section = getTarget().getStaticInitSectionSpecifier())
    260       Fn->setSection(Section);
    261   }
    262 
    263   SetInternalFunctionAttributes(nullptr, Fn, FI);
    264 
    265   Fn->setCallingConv(getRuntimeCC());
    266 
    267   if (!getLangOpts().Exceptions)
    268     Fn->setDoesNotThrow();
    269 
    270   if (!isInSanitizerBlacklist(Fn, Loc)) {
    271     if (getLangOpts().Sanitize.hasOneOf(SanitizerKind::Address |
    272                                         SanitizerKind::KernelAddress))
    273       Fn->addFnAttr(llvm::Attribute::SanitizeAddress);
    274     if (getLangOpts().Sanitize.has(SanitizerKind::Thread))
    275       Fn->addFnAttr(llvm::Attribute::SanitizeThread);
    276     if (getLangOpts().Sanitize.has(SanitizerKind::Memory))
    277       Fn->addFnAttr(llvm::Attribute::SanitizeMemory);
    278     if (getLangOpts().Sanitize.has(SanitizerKind::SafeStack))
    279       Fn->addFnAttr(llvm::Attribute::SafeStack);
    280   }
    281 
    282   return Fn;
    283 }
    284 
    285 /// Create a global pointer to a function that will initialize a global
    286 /// variable.  The user has requested that this pointer be emitted in a specific
    287 /// section.
    288 void CodeGenModule::EmitPointerToInitFunc(const VarDecl *D,
    289                                           llvm::GlobalVariable *GV,
    290                                           llvm::Function *InitFunc,
    291                                           InitSegAttr *ISA) {
    292   llvm::GlobalVariable *PtrArray = new llvm::GlobalVariable(
    293       TheModule, InitFunc->getType(), /*isConstant=*/true,
    294       llvm::GlobalValue::PrivateLinkage, InitFunc, "__cxx_init_fn_ptr");
    295   PtrArray->setSection(ISA->getSection());
    296   addUsedGlobal(PtrArray);
    297 
    298   // If the GV is already in a comdat group, then we have to join it.
    299   if (llvm::Comdat *C = GV->getComdat())
    300     PtrArray->setComdat(C);
    301 }
    302 
    303 void
    304 CodeGenModule::EmitCXXGlobalVarDeclInitFunc(const VarDecl *D,
    305                                             llvm::GlobalVariable *Addr,
    306                                             bool PerformInit) {
    307   // Check if we've already initialized this decl.
    308   auto I = DelayedCXXInitPosition.find(D);
    309   if (I != DelayedCXXInitPosition.end() && I->second == ~0U)
    310     return;
    311 
    312   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
    313   SmallString<256> FnName;
    314   {
    315     llvm::raw_svector_ostream Out(FnName);
    316     getCXXABI().getMangleContext().mangleDynamicInitializer(D, Out);
    317   }
    318 
    319   // Create a variable initialization function.
    320   llvm::Function *Fn =
    321       CreateGlobalInitOrDestructFunction(FTy, FnName.str(),
    322                                          getTypes().arrangeNullaryFunction(),
    323                                          D->getLocation());
    324 
    325   auto *ISA = D->getAttr<InitSegAttr>();
    326   CodeGenFunction(*this).GenerateCXXGlobalVarDeclInitFunc(Fn, D, Addr,
    327                                                           PerformInit);
    328 
    329   llvm::GlobalVariable *COMDATKey =
    330       supportsCOMDAT() && D->isExternallyVisible() ? Addr : nullptr;
    331 
    332   if (D->getTLSKind()) {
    333     // FIXME: Should we support init_priority for thread_local?
    334     // FIXME: Ideally, initialization of instantiated thread_local static data
    335     // members of class templates should not trigger initialization of other
    336     // entities in the TU.
    337     // FIXME: We only need to register one __cxa_thread_atexit function for the
    338     // entire TU.
    339     CXXThreadLocalInits.push_back(Fn);
    340     CXXThreadLocalInitVars.push_back(D);
    341   } else if (PerformInit && ISA) {
    342     EmitPointerToInitFunc(D, Addr, Fn, ISA);
    343   } else if (auto *IPA = D->getAttr<InitPriorityAttr>()) {
    344     OrderGlobalInits Key(IPA->getPriority(), PrioritizedCXXGlobalInits.size());
    345     PrioritizedCXXGlobalInits.push_back(std::make_pair(Key, Fn));
    346   } else if (isTemplateInstantiation(D->getTemplateSpecializationKind())) {
    347     // C++ [basic.start.init]p2:
    348     //   Definitions of explicitly specialized class template static data
    349     //   members have ordered initialization. Other class template static data
    350     //   members (i.e., implicitly or explicitly instantiated specializations)
    351     //   have unordered initialization.
    352     //
    353     // As a consequence, we can put them into their own llvm.global_ctors entry.
    354     //
    355     // If the global is externally visible, put the initializer into a COMDAT
    356     // group with the global being initialized.  On most platforms, this is a
    357     // minor startup time optimization.  In the MS C++ ABI, there are no guard
    358     // variables, so this COMDAT key is required for correctness.
    359     AddGlobalCtor(Fn, 65535, COMDATKey);
    360   } else if (D->hasAttr<SelectAnyAttr>()) {
    361     // SelectAny globals will be comdat-folded. Put the initializer into a
    362     // COMDAT group associated with the global, so the initializers get folded
    363     // too.
    364     AddGlobalCtor(Fn, 65535, COMDATKey);
    365   } else {
    366     I = DelayedCXXInitPosition.find(D); // Re-do lookup in case of re-hash.
    367     if (I == DelayedCXXInitPosition.end()) {
    368       CXXGlobalInits.push_back(Fn);
    369     } else if (I->second != ~0U) {
    370       assert(I->second < CXXGlobalInits.size() &&
    371              CXXGlobalInits[I->second] == nullptr);
    372       CXXGlobalInits[I->second] = Fn;
    373     }
    374   }
    375 
    376   // Remember that we already emitted the initializer for this global.
    377   DelayedCXXInitPosition[D] = ~0U;
    378 }
    379 
    380 void CodeGenModule::EmitCXXThreadLocalInitFunc() {
    381   getCXXABI().EmitThreadLocalInitFuncs(
    382       *this, CXXThreadLocals, CXXThreadLocalInits, CXXThreadLocalInitVars);
    383 
    384   CXXThreadLocalInits.clear();
    385   CXXThreadLocalInitVars.clear();
    386   CXXThreadLocals.clear();
    387 }
    388 
    389 void
    390 CodeGenModule::EmitCXXGlobalInitFunc() {
    391   while (!CXXGlobalInits.empty() && !CXXGlobalInits.back())
    392     CXXGlobalInits.pop_back();
    393 
    394   if (CXXGlobalInits.empty() && PrioritizedCXXGlobalInits.empty())
    395     return;
    396 
    397   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
    398   const CGFunctionInfo &FI = getTypes().arrangeNullaryFunction();
    399 
    400   // Create our global initialization function.
    401   if (!PrioritizedCXXGlobalInits.empty()) {
    402     SmallVector<llvm::Function *, 8> LocalCXXGlobalInits;
    403     llvm::array_pod_sort(PrioritizedCXXGlobalInits.begin(),
    404                          PrioritizedCXXGlobalInits.end());
    405     // Iterate over "chunks" of ctors with same priority and emit each chunk
    406     // into separate function. Note - everything is sorted first by priority,
    407     // second - by lex order, so we emit ctor functions in proper order.
    408     for (SmallVectorImpl<GlobalInitData >::iterator
    409            I = PrioritizedCXXGlobalInits.begin(),
    410            E = PrioritizedCXXGlobalInits.end(); I != E; ) {
    411       SmallVectorImpl<GlobalInitData >::iterator
    412         PrioE = std::upper_bound(I + 1, E, *I, GlobalInitPriorityCmp());
    413 
    414       LocalCXXGlobalInits.clear();
    415       unsigned Priority = I->first.priority;
    416       // Compute the function suffix from priority. Prepend with zeroes to make
    417       // sure the function names are also ordered as priorities.
    418       std::string PrioritySuffix = llvm::utostr(Priority);
    419       // Priority is always <= 65535 (enforced by sema).
    420       PrioritySuffix = std::string(6-PrioritySuffix.size(), '0')+PrioritySuffix;
    421       llvm::Function *Fn = CreateGlobalInitOrDestructFunction(
    422           FTy, "_GLOBAL__I_" + PrioritySuffix, FI);
    423 
    424       for (; I < PrioE; ++I)
    425         LocalCXXGlobalInits.push_back(I->second);
    426 
    427       CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn, LocalCXXGlobalInits);
    428       AddGlobalCtor(Fn, Priority);
    429     }
    430     PrioritizedCXXGlobalInits.clear();
    431   }
    432 
    433   SmallString<128> FileName;
    434   SourceManager &SM = Context.getSourceManager();
    435   if (const FileEntry *MainFile = SM.getFileEntryForID(SM.getMainFileID())) {
    436     // Include the filename in the symbol name. Including "sub_" matches gcc and
    437     // makes sure these symbols appear lexicographically behind the symbols with
    438     // priority emitted above.
    439     FileName = llvm::sys::path::filename(MainFile->getName());
    440   } else {
    441     FileName = "<null>";
    442   }
    443 
    444   for (size_t i = 0; i < FileName.size(); ++i) {
    445     // Replace everything that's not [a-zA-Z0-9._] with a _. This set happens
    446     // to be the set of C preprocessing numbers.
    447     if (!isPreprocessingNumberBody(FileName[i]))
    448       FileName[i] = '_';
    449   }
    450 
    451   llvm::Function *Fn = CreateGlobalInitOrDestructFunction(
    452       FTy, llvm::Twine("_GLOBAL__sub_I_", FileName), FI);
    453 
    454   CodeGenFunction(*this).GenerateCXXGlobalInitFunc(Fn, CXXGlobalInits);
    455   AddGlobalCtor(Fn);
    456 
    457   CXXGlobalInits.clear();
    458 }
    459 
    460 void CodeGenModule::EmitCXXGlobalDtorFunc() {
    461   if (CXXGlobalDtors.empty())
    462     return;
    463 
    464   llvm::FunctionType *FTy = llvm::FunctionType::get(VoidTy, false);
    465 
    466   // Create our global destructor function.
    467   const CGFunctionInfo &FI = getTypes().arrangeNullaryFunction();
    468   llvm::Function *Fn =
    469       CreateGlobalInitOrDestructFunction(FTy, "_GLOBAL__D_a", FI);
    470 
    471   CodeGenFunction(*this).GenerateCXXGlobalDtorsFunc(Fn, CXXGlobalDtors);
    472   AddGlobalDtor(Fn);
    473 }
    474 
    475 /// Emit the code necessary to initialize the given global variable.
    476 void CodeGenFunction::GenerateCXXGlobalVarDeclInitFunc(llvm::Function *Fn,
    477                                                        const VarDecl *D,
    478                                                  llvm::GlobalVariable *Addr,
    479                                                        bool PerformInit) {
    480   // Check if we need to emit debug info for variable initializer.
    481   if (D->hasAttr<NoDebugAttr>())
    482     DebugInfo = nullptr; // disable debug info indefinitely for this function
    483 
    484   CurEHLocation = D->getLocStart();
    485 
    486   StartFunction(GlobalDecl(D), getContext().VoidTy, Fn,
    487                 getTypes().arrangeNullaryFunction(),
    488                 FunctionArgList(), D->getLocation(),
    489                 D->getInit()->getExprLoc());
    490 
    491   // Use guarded initialization if the global variable is weak. This
    492   // occurs for, e.g., instantiated static data members and
    493   // definitions explicitly marked weak.
    494   if (Addr->hasWeakLinkage() || Addr->hasLinkOnceLinkage()) {
    495     EmitCXXGuardedInit(*D, Addr, PerformInit);
    496   } else {
    497     EmitCXXGlobalVarDeclInit(*D, Addr, PerformInit);
    498   }
    499 
    500   FinishFunction();
    501 }
    502 
    503 void
    504 CodeGenFunction::GenerateCXXGlobalInitFunc(llvm::Function *Fn,
    505                                            ArrayRef<llvm::Function *> Decls,
    506                                            Address Guard) {
    507   {
    508     auto NL = ApplyDebugLocation::CreateEmpty(*this);
    509     StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    510                   getTypes().arrangeNullaryFunction(), FunctionArgList());
    511     // Emit an artificial location for this function.
    512     auto AL = ApplyDebugLocation::CreateArtificial(*this);
    513 
    514     llvm::BasicBlock *ExitBlock = nullptr;
    515     if (Guard.isValid()) {
    516       // If we have a guard variable, check whether we've already performed
    517       // these initializations. This happens for TLS initialization functions.
    518       llvm::Value *GuardVal = Builder.CreateLoad(Guard);
    519       llvm::Value *Uninit = Builder.CreateIsNull(GuardVal,
    520                                                  "guard.uninitialized");
    521       llvm::BasicBlock *InitBlock = createBasicBlock("init");
    522       ExitBlock = createBasicBlock("exit");
    523       Builder.CreateCondBr(Uninit, InitBlock, ExitBlock);
    524       EmitBlock(InitBlock);
    525       // Mark as initialized before initializing anything else. If the
    526       // initializers use previously-initialized thread_local vars, that's
    527       // probably supposed to be OK, but the standard doesn't say.
    528       Builder.CreateStore(llvm::ConstantInt::get(GuardVal->getType(),1), Guard);
    529     }
    530 
    531     RunCleanupsScope Scope(*this);
    532 
    533     // When building in Objective-C++ ARC mode, create an autorelease pool
    534     // around the global initializers.
    535     if (getLangOpts().ObjCAutoRefCount && getLangOpts().CPlusPlus) {
    536       llvm::Value *token = EmitObjCAutoreleasePoolPush();
    537       EmitObjCAutoreleasePoolCleanup(token);
    538     }
    539 
    540     for (unsigned i = 0, e = Decls.size(); i != e; ++i)
    541       if (Decls[i])
    542         EmitRuntimeCall(Decls[i]);
    543 
    544     Scope.ForceCleanup();
    545 
    546     if (ExitBlock) {
    547       Builder.CreateBr(ExitBlock);
    548       EmitBlock(ExitBlock);
    549     }
    550   }
    551 
    552   FinishFunction();
    553 }
    554 
    555 void CodeGenFunction::GenerateCXXGlobalDtorsFunc(llvm::Function *Fn,
    556                   const std::vector<std::pair<llvm::WeakVH, llvm::Constant*> >
    557                                                 &DtorsAndObjects) {
    558   {
    559     auto NL = ApplyDebugLocation::CreateEmpty(*this);
    560     StartFunction(GlobalDecl(), getContext().VoidTy, Fn,
    561                   getTypes().arrangeNullaryFunction(), FunctionArgList());
    562     // Emit an artificial location for this function.
    563     auto AL = ApplyDebugLocation::CreateArtificial(*this);
    564 
    565     // Emit the dtors, in reverse order from construction.
    566     for (unsigned i = 0, e = DtorsAndObjects.size(); i != e; ++i) {
    567       llvm::Value *Callee = DtorsAndObjects[e - i - 1].first;
    568       llvm::CallInst *CI = Builder.CreateCall(Callee,
    569                                           DtorsAndObjects[e - i - 1].second);
    570       // Make sure the call and the callee agree on calling convention.
    571       if (llvm::Function *F = dyn_cast<llvm::Function>(Callee))
    572         CI->setCallingConv(F->getCallingConv());
    573     }
    574   }
    575 
    576   FinishFunction();
    577 }
    578 
    579 /// generateDestroyHelper - Generates a helper function which, when
    580 /// invoked, destroys the given object.  The address of the object
    581 /// should be in global memory.
    582 llvm::Function *CodeGenFunction::generateDestroyHelper(
    583     Address addr, QualType type, Destroyer *destroyer,
    584     bool useEHCleanupForArray, const VarDecl *VD) {
    585   FunctionArgList args;
    586   ImplicitParamDecl dst(getContext(), nullptr, SourceLocation(), nullptr,
    587                         getContext().VoidPtrTy);
    588   args.push_back(&dst);
    589 
    590   const CGFunctionInfo &FI = CGM.getTypes().arrangeFreeFunctionDeclaration(
    591       getContext().VoidTy, args, FunctionType::ExtInfo(), /*variadic=*/false);
    592   llvm::FunctionType *FTy = CGM.getTypes().GetFunctionType(FI);
    593   llvm::Function *fn = CGM.CreateGlobalInitOrDestructFunction(
    594       FTy, "__cxx_global_array_dtor", FI, VD->getLocation());
    595 
    596   CurEHLocation = VD->getLocStart();
    597 
    598   StartFunction(VD, getContext().VoidTy, fn, FI, args);
    599 
    600   emitDestroy(addr, type, destroyer, useEHCleanupForArray);
    601 
    602   FinishFunction();
    603 
    604   return fn;
    605 }
    606