C++ LValue::setNonGC方法代码示例

//.........这里部分代码省略.........
      // Make sure that it's really an empty and not a failure of
      // semantic analysis.
      for (RecordDecl::field_iterator Field = record->field_begin(),
                                   FieldEnd = record->field_end();
           Field != FieldEnd; ++Field)
        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
#endif
      return;
    }

    // FIXME: volatility
    FieldDecl *Field = E->getInitializedFieldInUnion();

    LValue FieldLoc = CGF.EmitLValueForFieldInitialization(DestPtr, Field, 0);
    if (NumInitElements) {
      // Store the initializer into the field
      EmitInitializationToLValue(E->getInit(0), FieldLoc);
    } else {
      // Default-initialize to null.
      EmitNullInitializationToLValue(FieldLoc);
    }

    return;
  }

  // We'll need to enter cleanup scopes in case any of the member
  // initializers throw an exception.
  SmallVector<EHScopeStack::stable_iterator, 16> cleanups;
  llvm::Instruction *cleanupDominator = 0;

  // Here we iterate over the fields; this makes it simpler to both
  // default-initialize fields and skip over unnamed fields.
  unsigned curInitIndex = 0;
  for (RecordDecl::field_iterator field = record->field_begin(),
                               fieldEnd = record->field_end();
       field != fieldEnd; ++field) {
    // We're done once we hit the flexible array member.
    if (field->getType()->isIncompleteArrayType())
      break;

    // Always skip anonymous bitfields.
    if (field->isUnnamedBitfield())
      continue;

    // We're done if we reach the end of the explicit initializers, we
    // have a zeroed object, and the rest of the fields are
    // zero-initializable.
    if (curInitIndex == NumInitElements && Dest.isZeroed() &&
        CGF.getTypes().isZeroInitializable(E->getType()))
      break;
    
    // FIXME: volatility
    LValue LV = CGF.EmitLValueForFieldInitialization(DestPtr, *field, 0);
    // We never generate write-barries for initialized fields.
    LV.setNonGC(true);
    
    if (curInitIndex < NumInitElements) {
      // Store the initializer into the field.
      EmitInitializationToLValue(E->getInit(curInitIndex++), LV);
    } else {
      // We're out of initalizers; default-initialize to null
      EmitNullInitializationToLValue(LV);
    }

    // Push a destructor if necessary.
    // FIXME: if we have an array of structures, all explicitly
    // initialized, we can end up pushing a linear number of cleanups.
    bool pushedCleanup = false;
    if (QualType::DestructionKind dtorKind
          = field->getType().isDestructedType()) {
      assert(LV.isSimple());
      if (CGF.needsEHCleanup(dtorKind)) {
        if (!cleanupDominator)
          cleanupDominator = CGF.Builder.CreateUnreachable(); // placeholder

        CGF.pushDestroy(EHCleanup, LV.getAddress(), field->getType(),
                        CGF.getDestroyer(dtorKind), false);
        cleanups.push_back(CGF.EHStack.stable_begin());
        pushedCleanup = true;
      }
    }
    
    // If the GEP didn't get used because of a dead zero init or something
    // else, clean it up for -O0 builds and general tidiness.
    if (!pushedCleanup && LV.isSimple()) 
      if (llvm::GetElementPtrInst *GEP =
            dyn_cast<llvm::GetElementPtrInst>(LV.getAddress()))
        if (GEP->use_empty())
          GEP->eraseFromParent();
  }

  // Deactivate all the partial cleanups in reverse order, which
  // generally means popping them.
  for (unsigned i = cleanups.size(); i != 0; --i)
    CGF.DeactivateCleanupBlock(cleanups[i-1], cleanupDominator);

  // Destroy the placeholder if we made one.
  if (cleanupDominator)
    cleanupDominator->eraseFromParent();
}

//.........这里部分代码省略.........
        return;
      }
    }

    uint64_t NumArrayElements = AType->getNumElements();
    QualType ElementType = CGF.getContext().getCanonicalType(E->getType());
    ElementType = CGF.getContext().getAsArrayType(ElementType)->getElementType();

    // FIXME: were we intentionally ignoring address spaces and GC attributes?

    for (uint64_t i = 0; i != NumArrayElements; ++i) {
      llvm::Value *NextVal = Builder.CreateStructGEP(DestPtr, i, ".array");
      LValue LV = CGF.MakeAddrLValue(NextVal, ElementType);
      if (i < NumInitElements)
        EmitInitializationToLValue(E->getInit(i), LV, ElementType);

      else
        EmitNullInitializationToLValue(LV, ElementType);
    }
    return;
  }

  assert(E->getType()->isRecordType() && "Only support structs/unions here!");

  // Do struct initialization; this code just sets each individual member
  // to the approprate value.  This makes bitfield support automatic;
  // the disadvantage is that the generated code is more difficult for
  // the optimizer, especially with bitfields.
  unsigned NumInitElements = E->getNumInits();
  RecordDecl *SD = E->getType()->getAs<RecordType>()->getDecl();
  
  // If we're initializing the whole aggregate, just do it in place.
  // FIXME: This is a hack around an AST bug (PR6537).
  if (NumInitElements == 1 && E->getType() == E->getInit(0)->getType()) {
    EmitInitializationToLValue(E->getInit(0),
                               CGF.MakeAddrLValue(DestPtr, E->getType()),
                               E->getType());
    return;
  }
  
  
  if (E->getType()->isUnionType()) {
    // Only initialize one field of a union. The field itself is
    // specified by the initializer list.
    if (!E->getInitializedFieldInUnion()) {
      // Empty union; we have nothing to do.

#ifndef NDEBUG
      // Make sure that it's really an empty and not a failure of
      // semantic analysis.
      for (RecordDecl::field_iterator Field = SD->field_begin(),
                                   FieldEnd = SD->field_end();
           Field != FieldEnd; ++Field)
        assert(Field->isUnnamedBitfield() && "Only unnamed bitfields allowed");
#endif
      return;
    }

    // FIXME: volatility
    FieldDecl *Field = E->getInitializedFieldInUnion();
    LValue FieldLoc = CGF.EmitLValueForFieldInitialization(DestPtr, Field, 0);

    if (NumInitElements) {
      // Store the initializer into the field
      EmitInitializationToLValue(E->getInit(0), FieldLoc, Field->getType());
    } else {
      // Default-initialize to null
      EmitNullInitializationToLValue(FieldLoc, Field->getType());
    }

    return;
  }

  // Here we iterate over the fields; this makes it simpler to both
  // default-initialize fields and skip over unnamed fields.
  unsigned CurInitVal = 0;
  for (RecordDecl::field_iterator Field = SD->field_begin(),
                               FieldEnd = SD->field_end();
       Field != FieldEnd; ++Field) {
    // We're done once we hit the flexible array member
    if (Field->getType()->isIncompleteArrayType())
      break;

    if (Field->isUnnamedBitfield())
      continue;

    // FIXME: volatility
    LValue FieldLoc = CGF.EmitLValueForFieldInitialization(DestPtr, *Field, 0);
    // We never generate write-barries for initialized fields.
    FieldLoc.setNonGC(true);
    if (CurInitVal < NumInitElements) {
      // Store the initializer into the field.
      EmitInitializationToLValue(E->getInit(CurInitVal++), FieldLoc,
                                 Field->getType());
    } else {
      // We're out of initalizers; default-initialize to null
      EmitNullInitializationToLValue(FieldLoc, Field->getType());
    }
  }
}