예제 #1
0
/// Emit a checked cast to a protocol or protocol composition.
void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
                                  llvm::Value *value,
                                  SILType srcType,
                                  SILType destType,
                                  CheckedCastMode mode,
                                  Optional<MetatypeRepresentation> metatypeKind,
                                  Explosion &ex) {
  SmallVector<ProtocolDecl*, 4> allProtos;
  destType.getSwiftRValueType().getAnyExistentialTypeProtocols(allProtos);

  // Look up witness tables for the protocols that need them and get
  // references to the ObjC Protocol* values for the objc protocols.
  SmallVector<llvm::Value*, 4> objcProtos;
  SmallVector<llvm::Value*, 4> witnessTableProtos;

  bool hasClassConstraint = false;
  bool hasClassConstraintByProtocol = false;

  for (auto proto : allProtos) {
    // If the protocol introduces a class constraint, track whether we need
    // to check for it independent of protocol witnesses.
    if (proto->requiresClass()) {
      hasClassConstraint = true;
      if (proto->getKnownProtocolKind()
          && *proto->getKnownProtocolKind() == KnownProtocolKind::AnyObject) {
        // AnyObject only requires that the type be a class.
        continue;
      }
      
      // If this protocol is class-constrained but not AnyObject, checking its
      // conformance will check the class constraint too.
      hasClassConstraintByProtocol = true;
    }

    if (Lowering::TypeConverter::protocolRequiresWitnessTable(proto)) {
      auto descriptor = emitProtocolDescriptorRef(IGF, proto);
      witnessTableProtos.push_back(descriptor);
    }

    if (!proto->isObjC())
      continue;

    objcProtos.push_back(emitReferenceToObjCProtocol(IGF, proto));
  }
  
  llvm::Type *resultType;
  if (metatypeKind) {
    switch (*metatypeKind) {
    case MetatypeRepresentation::Thin:
      llvm_unreachable("can't cast to thin metatype");
    case MetatypeRepresentation::Thick:
      resultType = IGF.IGM.TypeMetadataPtrTy;
      break;
    case MetatypeRepresentation::ObjC:
      resultType = IGF.IGM.ObjCClassPtrTy;
      break;
    }
  } else {
    auto schema = IGF.getTypeInfo(destType).getSchema();
    resultType = schema[0].getScalarType();
  }
  // We only need to check the class constraint for metatype casts where
  // no protocol conformance indirectly requires the constraint for us.
  bool checkClassConstraint =
    (bool)metatypeKind && hasClassConstraint && !hasClassConstraintByProtocol;

  llvm::Value *resultValue = value;

  // If we don't have anything we really need to check, then trivially succeed.
  if (objcProtos.empty() && witnessTableProtos.empty() &&
      !checkClassConstraint) {
    resultValue = IGF.Builder.CreateBitCast(value, resultType);
    ex.add(resultValue);
    return;
  }

  // Check the ObjC protocol conformances if there were any.
  llvm::Value *objcCast = nullptr;
  if (!objcProtos.empty()) {
    // Get the ObjC instance or class object to check for these conformances.
    llvm::Value *objcObject;
    if (metatypeKind) {
      switch (*metatypeKind) {
      case MetatypeRepresentation::Thin:
        llvm_unreachable("can't cast to thin metatype");
      case MetatypeRepresentation::Thick: {
        // The metadata might be for a non-class type, which wouldn't have
        // an ObjC class object.
        objcObject = nullptr;
        break;
      }
      case MetatypeRepresentation::ObjC:
        // Metatype is already an ObjC object.
        objcObject = value;
        break;
      }
    } else {
      // Class instance is already an ObjC object.
      objcObject = value;
    }
    if (objcObject)
      objcObject = IGF.Builder.CreateBitCast(objcObject,
                                             IGF.IGM.UnknownRefCountedPtrTy);
    
    // Pick the cast function based on the cast mode and on whether we're
    // casting a Swift metatype or ObjC object.
    llvm::Value *castFn;
    switch (mode) {
    case CheckedCastMode::Unconditional:
      castFn = objcObject
        ? IGF.IGM.getDynamicCastObjCProtocolUnconditionalFn()
        : IGF.IGM.getDynamicCastTypeToObjCProtocolUnconditionalFn();
      break;
    case CheckedCastMode::Conditional:
      castFn = objcObject
        ? IGF.IGM.getDynamicCastObjCProtocolConditionalFn()
        : IGF.IGM.getDynamicCastTypeToObjCProtocolConditionalFn();
      break;
    }
    llvm::Value *objcCastObject = objcObject ? objcObject : value;
    
    Address protoRefsBuf = IGF.createAlloca(
                                        llvm::ArrayType::get(IGF.IGM.Int8PtrTy,
                                                             objcProtos.size()),
                                        IGF.IGM.getPointerAlignment(),
                                        "objc_protocols");
    protoRefsBuf = IGF.Builder.CreateBitCast(protoRefsBuf,
                                             IGF.IGM.Int8PtrPtrTy);

    for (unsigned index : indices(objcProtos)) {
      Address protoRefSlot = IGF.Builder.CreateConstArrayGEP(
                                                     protoRefsBuf, index,
                                                     IGF.IGM.getPointerSize());
      IGF.Builder.CreateStore(objcProtos[index], protoRefSlot);
      ++index;
    }

    
    objcCast = IGF.Builder.CreateCall(
        castFn,
        {objcCastObject, IGF.IGM.getSize(Size(objcProtos.size())),
         protoRefsBuf.getAddress()});
    resultValue = IGF.Builder.CreateBitCast(objcCast, resultType);
  }

  // If we don't need to look up any witness tables, we're done.
  if (witnessTableProtos.empty() && !checkClassConstraint) {
    ex.add(resultValue);
    return;
  }

  // If we're doing a conditional cast, and the ObjC protocol checks failed,
  // then the cast is done.
  Optional<ConditionalDominanceScope> condition;
  llvm::BasicBlock *origBB = nullptr, *successBB = nullptr, *contBB = nullptr;
  if (!objcProtos.empty()) {
    switch (mode) {
    case CheckedCastMode::Unconditional:
      break;
    case CheckedCastMode::Conditional: {
      origBB = IGF.Builder.GetInsertBlock();
      successBB = IGF.createBasicBlock("success");
      contBB = IGF.createBasicBlock("cont");
      auto isNull = IGF.Builder.CreateICmpEQ(objcCast,
                               llvm::ConstantPointerNull::get(
                                 cast<llvm::PointerType>(objcCast->getType())));
      IGF.Builder.CreateCondBr(isNull, contBB, successBB);
      IGF.Builder.emitBlock(successBB);
      condition.emplace(IGF);
    }
    }
  }

  // Get the Swift type metadata for the type.
  llvm::Value *metadataValue;
  if (metatypeKind) {
    switch (*metatypeKind) {
    case MetatypeRepresentation::Thin:
      llvm_unreachable("can't cast to thin metatype");
    case MetatypeRepresentation::Thick:
      // The value is already a native metatype.
      metadataValue = value;
      break;
    case MetatypeRepresentation::ObjC:
      // Get the type metadata from the ObjC class, which may be a wrapper.
      metadataValue = emitObjCMetadataRefForMetadata(IGF, value);
    }
  } else {
    // Get the type metadata for the instance.
    metadataValue = emitDynamicTypeOfHeapObject(IGF, value, srcType);
  }

  // Look up witness tables for the protocols that need them.
  auto fn = emitExistentialScalarCastFn(IGF.IGM, witnessTableProtos.size(),
                                        mode, checkClassConstraint);

  llvm::SmallVector<llvm::Value *, 4> args;

  if (resultValue->getType() != IGF.IGM.Int8PtrTy)
    resultValue = IGF.Builder.CreateBitCast(resultValue, IGF.IGM.Int8PtrTy);
  args.push_back(resultValue);

  args.push_back(metadataValue);
  for (auto proto : witnessTableProtos)
    args.push_back(proto);

  auto valueAndWitnessTables = IGF.Builder.CreateCall(fn, args);

  resultValue = IGF.Builder.CreateExtractValue(valueAndWitnessTables, 0);
  if (resultValue->getType() != resultType)
    resultValue = IGF.Builder.CreateBitCast(resultValue, resultType);
  ex.add(resultValue);

  for (unsigned i = 0, e = witnessTableProtos.size(); i < e; ++i) {
    auto wt = IGF.Builder.CreateExtractValue(valueAndWitnessTables, i + 1);
    ex.add(wt);
  }

  // If we had conditional ObjC checks, join the failure paths.
  if (contBB) {
    condition.reset();
    IGF.Builder.CreateBr(contBB);
    IGF.Builder.emitBlock(contBB);
    
    // Return null on the failure path.
    Explosion successEx = std::move(ex);
    ex.reset();
    
    while (!successEx.empty()) {
      auto successVal = successEx.claimNext();
      auto failureVal = llvm::Constant::getNullValue(successVal->getType());
      auto phi = IGF.Builder.CreatePHI(successVal->getType(), 2);
      phi->addIncoming(successVal, successBB);
      phi->addIncoming(failureVal, origBB);
      ex.add(phi);
    }
  }
}
예제 #2
0
/// Emit a checked cast to a protocol or protocol composition.
void irgen::emitScalarExistentialDowncast(IRGenFunction &IGF,
                                  llvm::Value *value,
                                  SILType srcType,
                                  SILType destType,
                                  CheckedCastMode mode,
                                  Optional<MetatypeRepresentation> metatypeKind,
                                  Explosion &ex) {
  auto srcInstanceType = srcType.getSwiftRValueType();
  auto destInstanceType = destType.getSwiftRValueType();
  while (auto metatypeType = dyn_cast<ExistentialMetatypeType>(
           destInstanceType)) {
    destInstanceType = metatypeType.getInstanceType();
    srcInstanceType = cast<AnyMetatypeType>(srcInstanceType).getInstanceType();
  }

  auto layout = destInstanceType.getExistentialLayout();

  // Look up witness tables for the protocols that need them and get
  // references to the ObjC Protocol* values for the objc protocols.
  SmallVector<llvm::Value*, 4> objcProtos;
  SmallVector<llvm::Value*, 4> witnessTableProtos;

  bool hasClassConstraint = layout.requiresClass();
  bool hasClassConstraintByProtocol = false;

  bool hasSuperclassConstraint = bool(layout.superclass);

  for (auto protoTy : layout.getProtocols()) {
    auto *protoDecl = protoTy->getDecl();

    // If the protocol introduces a class constraint, track whether we need
    // to check for it independent of protocol witnesses.
    if (protoDecl->requiresClass()) {
      assert(hasClassConstraint);
      hasClassConstraintByProtocol = true;
    }

    if (Lowering::TypeConverter::protocolRequiresWitnessTable(protoDecl)) {
      auto descriptor = emitProtocolDescriptorRef(IGF, protoDecl);
      witnessTableProtos.push_back(descriptor);
    }

    if (protoDecl->isObjC())
      objcProtos.push_back(emitReferenceToObjCProtocol(IGF, protoDecl));
  }
  
  llvm::Type *resultType;
  if (metatypeKind) {
    switch (*metatypeKind) {
    case MetatypeRepresentation::Thin:
      llvm_unreachable("can't cast to thin metatype");
    case MetatypeRepresentation::Thick:
      resultType = IGF.IGM.TypeMetadataPtrTy;
      break;
    case MetatypeRepresentation::ObjC:
      resultType = IGF.IGM.ObjCClassPtrTy;
      break;
    }
  } else {
    auto schema = IGF.getTypeInfo(destType).getSchema();
    resultType = schema[0].getScalarType();
  }

  // The source of a scalar cast is statically known to be a class or a
  // metatype, so we only have to check the class constraint in two cases:
  //
  // 1) The destination type has an explicit superclass constraint that is
  //    more derived than what the source type is known to be.
  //
  // 2) We are casting between metatypes, in which case the source might
  //    be a non-class metatype.
  bool checkClassConstraint = false;
  if ((bool)metatypeKind &&
      hasClassConstraint &&
      !hasClassConstraintByProtocol &&
      !srcInstanceType->mayHaveSuperclass())
    checkClassConstraint = true;

  // If the source has an equal or more derived superclass constraint than
  // the destination, we can elide the superclass check.
  //
  // Note that destInstanceType is always an existential type, so calling
  // getSuperclass() returns the superclass constraint of the existential,
  // not the superclass of some concrete class.
  bool checkSuperclassConstraint =
    hasSuperclassConstraint &&
    !destInstanceType->getSuperclass()->isExactSuperclassOf(srcInstanceType);

  if (checkSuperclassConstraint)
    checkClassConstraint = true;

  llvm::Value *resultValue = value;

  // If we don't have anything we really need to check, then trivially succeed.
  if (objcProtos.empty() && witnessTableProtos.empty() &&
      !checkClassConstraint) {
    resultValue = IGF.Builder.CreateBitCast(value, resultType);
    ex.add(resultValue);
    return;
  }

  // Check the ObjC protocol conformances if there were any.
  llvm::Value *objcCast = nullptr;
  if (!objcProtos.empty()) {
    // Get the ObjC instance or class object to check for these conformances.
    llvm::Value *objcObject;
    if (metatypeKind) {
      switch (*metatypeKind) {
      case MetatypeRepresentation::Thin:
        llvm_unreachable("can't cast to thin metatype");
      case MetatypeRepresentation::Thick: {
        // The metadata might be for a non-class type, which wouldn't have
        // an ObjC class object.
        objcObject = nullptr;
        break;
      }
      case MetatypeRepresentation::ObjC:
        // Metatype is already an ObjC object.
        objcObject = value;
        break;
      }
    } else {
      // Class instance is already an ObjC object.
      objcObject = value;
    }
    if (objcObject)
      objcObject = IGF.Builder.CreateBitCast(objcObject,
                                             IGF.IGM.UnknownRefCountedPtrTy);
    
    // Pick the cast function based on the cast mode and on whether we're
    // casting a Swift metatype or ObjC object.
    llvm::Constant *castFn;
    switch (mode) {
    case CheckedCastMode::Unconditional:
      castFn = objcObject
        ? IGF.IGM.getDynamicCastObjCProtocolUnconditionalFn()
        : IGF.IGM.getDynamicCastTypeToObjCProtocolUnconditionalFn();
      break;
    case CheckedCastMode::Conditional:
      castFn = objcObject
        ? IGF.IGM.getDynamicCastObjCProtocolConditionalFn()
        : IGF.IGM.getDynamicCastTypeToObjCProtocolConditionalFn();
      break;
    }
    llvm::Value *objcCastObject = objcObject ? objcObject : value;
    
    Address protoRefsBuf = IGF.createAlloca(
                                        llvm::ArrayType::get(IGF.IGM.Int8PtrTy,
                                                             objcProtos.size()),
                                        IGF.IGM.getPointerAlignment(),
                                        "objc_protocols");
    protoRefsBuf = IGF.Builder.CreateBitCast(protoRefsBuf,
                                             IGF.IGM.Int8PtrPtrTy);

    for (unsigned index : indices(objcProtos)) {
      Address protoRefSlot = IGF.Builder.CreateConstArrayGEP(
                                                     protoRefsBuf, index,
                                                     IGF.IGM.getPointerSize());
      IGF.Builder.CreateStore(objcProtos[index], protoRefSlot);
      ++index;
    }

    
    auto cc = IGF.IGM.DefaultCC;
    if (auto fun = dyn_cast<llvm::Function>(castFn))
      cc = fun->getCallingConv();


    auto call = IGF.Builder.CreateCall(
        castFn,
        {objcCastObject, IGF.IGM.getSize(Size(objcProtos.size())),
         protoRefsBuf.getAddress()});
    call->setCallingConv(cc);
    objcCast = call;
    resultValue = IGF.Builder.CreateBitCast(objcCast, resultType);
  }

  // If we don't need to look up any witness tables, we're done.
  if (witnessTableProtos.empty() && !checkClassConstraint) {
    ex.add(resultValue);
    return;
  }

  // If we're doing a conditional cast, and the ObjC protocol checks failed,
  // then the cast is done.
  Optional<ConditionalDominanceScope> condition;
  llvm::BasicBlock *origBB = nullptr, *successBB = nullptr, *contBB = nullptr;
  if (!objcProtos.empty()) {
    switch (mode) {
    case CheckedCastMode::Unconditional:
      break;
    case CheckedCastMode::Conditional: {
      origBB = IGF.Builder.GetInsertBlock();
      successBB = IGF.createBasicBlock("success");
      contBB = IGF.createBasicBlock("cont");
      auto isNull = IGF.Builder.CreateICmpEQ(objcCast,
                               llvm::ConstantPointerNull::get(
                                 cast<llvm::PointerType>(objcCast->getType())));
      IGF.Builder.CreateCondBr(isNull, contBB, successBB);
      IGF.Builder.emitBlock(successBB);
      condition.emplace(IGF);
    }
    }
  }

  // Get the Swift type metadata for the type.
  llvm::Value *metadataValue;
  if (metatypeKind) {
    switch (*metatypeKind) {
    case MetatypeRepresentation::Thin:
      llvm_unreachable("can't cast to thin metatype");
    case MetatypeRepresentation::Thick:
      // The value is already a native metatype.
      metadataValue = value;
      break;
    case MetatypeRepresentation::ObjC:
      // Get the type metadata from the ObjC class, which may be a wrapper.
      metadataValue = emitObjCMetadataRefForMetadata(IGF, value);
    }
  } else {
    // Get the type metadata for the instance.
    metadataValue = emitDynamicTypeOfHeapObject(IGF, value, srcType);
  }

  // Look up witness tables for the protocols that need them.
  auto fn = emitExistentialScalarCastFn(IGF.IGM,
                                        witnessTableProtos.size(),
                                        mode,
                                        checkClassConstraint,
                                        checkSuperclassConstraint);

  llvm::SmallVector<llvm::Value *, 4> args;

  if (resultValue->getType() != IGF.IGM.Int8PtrTy)
    resultValue = IGF.Builder.CreateBitCast(resultValue, IGF.IGM.Int8PtrTy);
  args.push_back(resultValue);

  args.push_back(metadataValue);

  if (checkSuperclassConstraint)
    args.push_back(IGF.emitTypeMetadataRef(CanType(layout.superclass)));

  for (auto proto : witnessTableProtos)
    args.push_back(proto);

  auto valueAndWitnessTables = IGF.Builder.CreateCall(fn, args);

  resultValue = IGF.Builder.CreateExtractValue(valueAndWitnessTables, 0);
  if (resultValue->getType() != resultType)
    resultValue = IGF.Builder.CreateBitCast(resultValue, resultType);
  ex.add(resultValue);

  for (unsigned i = 0, e = witnessTableProtos.size(); i < e; ++i) {
    auto wt = IGF.Builder.CreateExtractValue(valueAndWitnessTables, i + 1);
    ex.add(wt);
  }

  // If we had conditional ObjC checks, join the failure paths.
  if (contBB) {
    condition.reset();
    IGF.Builder.CreateBr(contBB);
    IGF.Builder.emitBlock(contBB);
    
    // Return null on the failure path.
    Explosion successEx = std::move(ex);
    ex.reset();
    
    while (!successEx.empty()) {
      auto successVal = successEx.claimNext();
      auto failureVal = llvm::Constant::getNullValue(successVal->getType());
      auto phi = IGF.Builder.CreatePHI(successVal->getType(), 2);
      phi->addIncoming(successVal, successBB);
      phi->addIncoming(failureVal, origBB);
      ex.add(phi);
    }
  }
}