C++ (Cpp) CodeGenFunction::EmitCXXGlobalVarDeclInit Examples

Example #1

File: MicrosoftCXXABI.cpp Project: keryell/clang-1

void MicrosoftCXXABI::EmitGuardedInit(CodeGenFunction &CGF, const VarDecl &D,
                                      llvm::GlobalVariable *DeclPtr,
                                      bool PerformInit) {
  // FIXME: this code was only tested for global initialization.
  // Not sure whether we want thread-safe static local variables as VS
  // doesn't make them thread-safe.

  // Emit the initializer and add a global destructor if appropriate.
  CGF.EmitCXXGlobalVarDeclInit(D, DeclPtr, PerformInit);
}

Example #2

File: ItaniumCXXABI.cpp Project: ACSOP/android_external_clang

/// The ARM code here follows the Itanium code closely enough that we
/// just special-case it at particular places.
void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
                                    const VarDecl &D,
                                    llvm::GlobalVariable *GV) {
  CGBuilderTy &Builder = CGF.Builder;

  // We only need to use thread-safe statics for local variables;
  // global initialization is always single-threaded.
  bool threadsafe =
    (getContext().getLangOptions().ThreadsafeStatics && D.isLocalVarDecl());

  llvm::IntegerType *GuardTy;

  // If we have a global variable with internal linkage and thread-safe statics
  // are disabled, we can just let the guard variable be of type i8.
  bool useInt8GuardVariable = !threadsafe && GV->hasInternalLinkage();
  if (useInt8GuardVariable) {
    GuardTy = CGF.Int8Ty;
  } else {
    // Guard variables are 64 bits in the generic ABI and 32 bits on ARM.
    GuardTy = (IsARM ? CGF.Int32Ty : CGF.Int64Ty);
  }
  llvm::PointerType *GuardPtrTy = GuardTy->getPointerTo();

  // Create the guard variable.
  llvm::SmallString<256> GuardVName;
  llvm::raw_svector_ostream Out(GuardVName);
  getMangleContext().mangleItaniumGuardVariable(&D, Out);
  Out.flush();

  // Just absorb linkage and visibility from the variable.
  llvm::GlobalVariable *GuardVariable =
    new llvm::GlobalVariable(CGM.getModule(), GuardTy,
                             false, GV->getLinkage(),
                             llvm::ConstantInt::get(GuardTy, 0),
                             GuardVName.str());
  GuardVariable->setVisibility(GV->getVisibility());

  // Test whether the variable has completed initialization.
  llvm::Value *IsInitialized;

  // ARM C++ ABI 3.2.3.1:
  //   To support the potential use of initialization guard variables
  //   as semaphores that are the target of ARM SWP and LDREX/STREX
  //   synchronizing instructions we define a static initialization
  //   guard variable to be a 4-byte aligned, 4- byte word with the
  //   following inline access protocol.
  //     #define INITIALIZED 1
  //     if ((obj_guard & INITIALIZED) != INITIALIZED) {
  //       if (__cxa_guard_acquire(&obj_guard))
  //         ...
  //     }
  if (IsARM && !useInt8GuardVariable) {
    llvm::Value *V = Builder.CreateLoad(GuardVariable);
    V = Builder.CreateAnd(V, Builder.getInt32(1));
    IsInitialized = Builder.CreateIsNull(V, "guard.uninitialized");

  // Itanium C++ ABI 3.3.2:
  //   The following is pseudo-code showing how these functions can be used:
  //     if (obj_guard.first_byte == 0) {
  //       if ( __cxa_guard_acquire (&obj_guard) ) {
  //         try {
  //           ... initialize the object ...;
  //         } catch (...) {
  //            __cxa_guard_abort (&obj_guard);
  //            throw;
  //         }
  //         ... queue object destructor with __cxa_atexit() ...;
  //         __cxa_guard_release (&obj_guard);
  //       }
  //     }
  } else {
    // Load the first byte of the guard variable.
    llvm::Type *PtrTy = Builder.getInt8PtrTy();
    llvm::LoadInst *LI = 
      Builder.CreateLoad(Builder.CreateBitCast(GuardVariable, PtrTy));
    LI->setAlignment(1);

    // Itanium ABI:
    //   An implementation supporting thread-safety on multiprocessor
    //   systems must also guarantee that references to the initialized
    //   object do not occur before the load of the initialization flag.
    //
    // In LLVM, we do this by marking the load Acquire.
    if (threadsafe)
      LI->setAtomic(llvm::Acquire);

    IsInitialized = Builder.CreateIsNull(LI, "guard.uninitialized");
  }

  llvm::BasicBlock *InitCheckBlock = CGF.createBasicBlock("init.check");
  llvm::BasicBlock *EndBlock = CGF.createBasicBlock("init.end");

  // Check if the first byte of the guard variable is zero.
  Builder.CreateCondBr(IsInitialized, InitCheckBlock, EndBlock);

  CGF.EmitBlock(InitCheckBlock);

  // Variables used when coping with thread-safe statics and exceptions.
  if (threadsafe) {    
    // Call __cxa_guard_acquire.
    llvm::Value *V
      = Builder.CreateCall(getGuardAcquireFn(CGM, GuardPtrTy), GuardVariable);
               
    llvm::BasicBlock *InitBlock = CGF.createBasicBlock("init");
  
    Builder.CreateCondBr(Builder.CreateIsNotNull(V, "tobool"),
                         InitBlock, EndBlock);
  
    // Call __cxa_guard_abort along the exceptional edge.
    CGF.EHStack.pushCleanup<CallGuardAbort>(EHCleanup, GuardVariable);
    
    CGF.EmitBlock(InitBlock);
  }

  // Emit the initializer and add a global destructor if appropriate.
  CGF.EmitCXXGlobalVarDeclInit(D, GV);

  if (threadsafe) {
    // Pop the guard-abort cleanup if we pushed one.
    CGF.PopCleanupBlock();

    // Call __cxa_guard_release.  This cannot throw.
    Builder.CreateCall(getGuardReleaseFn(CGM, GuardPtrTy), GuardVariable);
  } else {
    Builder.CreateStore(llvm::ConstantInt::get(GuardTy, 1), GuardVariable);
  }

  CGF.EmitBlock(EndBlock);
}