swift-mirror/lib/SILGen/SILGenBridging.cpp

//===--- SILGenBridging.cpp - SILGen for bridging to Clang ASTs -----------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "SILGenFunction.h"
#include "RValue.h"
#include "Scope.h"
#include "swift/AST/AST.h"
#include "swift/AST/ForeignErrorConvention.h"
#include "swift/AST/ParameterList.h"
#include "swift/Basic/Fallthrough.h"
#include "swift/SIL/SILArgument.h"
#include "swift/SIL/TypeLowering.h"

using namespace swift;
using namespace Lowering;

static ManagedValue emitBridgeStringToNSString(SILGenFunction &gen,
                                               SILLocation loc,
                                               ManagedValue str) {
  // func _convertStringToNSString(String) -> NSString
  SILValue stringToNSStringFn
    = gen.emitGlobalFunctionRef(loc, gen.SGM.getStringToNSStringFn());

  SILValue nsstr = gen.B.createApply(loc, stringToNSStringFn,
                           stringToNSStringFn->getType(),
                           gen.getLoweredType(gen.SGM.Types.getNSStringType()),
                           {}, str.forward(gen));
  return gen.emitManagedRValueWithCleanup(nsstr);
}

static ManagedValue emitBridgeNSStringToString(SILGenFunction &gen,
                                               SILLocation loc,
                                               ManagedValue nsstr) {
  SILValue bridgeFn =
      gen.emitGlobalFunctionRef(loc, gen.SGM.getNSStringToStringFn());

  Type inputType = nsstr.getType().getSwiftRValueType();
  if (!inputType->getOptionalObjectType()) {
    SILType loweredOptTy = gen.SGM.getLoweredType(OptionalType::get(inputType));
    auto *someDecl = gen.getASTContext().getOptionalSomeDecl();
    auto *enumInst = gen.B.createEnum(loc, nsstr.getValue(), someDecl,
                                      loweredOptTy);
    nsstr = ManagedValue(enumInst, nsstr.getCleanup());
  }

  SILType nativeTy = gen.getLoweredType(gen.SGM.Types.getStringType());
  SILValue str = gen.B.createApply(loc, bridgeFn, bridgeFn->getType(), nativeTy,
                                   {}, { nsstr.forward(gen) });

  return gen.emitManagedRValueWithCleanup(str);
}

static ManagedValue emitBridgeCollectionFromNative(SILGenFunction &gen,
                                                   SILLocation loc,
                                                   SILDeclRef bridgeFnRef,
                                                   ManagedValue collection,
                                                   SILType bridgedTy) {
  SILValue bridgeFn = gen.emitGlobalFunctionRef(loc, bridgeFnRef);

  // If the expected return is optional, we'll need to wrap it.
  OptionalTypeKind OTK = OTK_None;
  SILType origBridgedTy = bridgedTy;
  if (auto bridgedObjTy = bridgedTy.getAnyOptionalObjectType(gen.SGM.M, OTK)) {
    bridgedTy = bridgedObjTy;
  }

  // Figure out the type parameters.
  auto inputTy
    = collection.getType().getSwiftRValueType()->castTo<BoundGenericType>();
  auto subs = inputTy->getSubstitutions(gen.SGM.M.getSwiftModule(), nullptr);
  auto substFnType = bridgeFn->getType().substGenericArgs(gen.SGM.M, subs);
  SILValue bridged = gen.B.createApply(loc, bridgeFn,
                                       substFnType,
                                       bridgedTy,
                                       subs,
                                       { collection.forward(gen) });
  // Wrap the result if necessary.
  if (OTK != OTK_None) {
    bridged = gen.B.createEnum(loc, bridged,
                               gen.getASTContext().getOptionalSomeDecl(OTK),
                               origBridgedTy);
  }

  return gen.emitManagedRValueWithCleanup(bridged);
}

static ManagedValue emitBridgeCollectionToNative(SILGenFunction &gen,
                                                 SILLocation loc,
                                                 SILDeclRef bridgeFnRef,
                                                 ManagedValue collection,
                                                 SILType nativeTy) {
  SILValue bridgeFn = gen.emitGlobalFunctionRef(loc, bridgeFnRef);

  auto collectionTy = nativeTy.getSwiftRValueType()->castTo<BoundGenericType>();
  auto subs = collectionTy->getSubstitutions(gen.SGM.M.getSwiftModule(),
                                             nullptr);
  auto substFnType = bridgeFn->getType().substGenericArgs(gen.SGM.M, subs);

  Type inputType = collection.getType().getSwiftRValueType();
  if (!inputType->getOptionalObjectType()) {
    SILType loweredOptTy = gen.SGM.getLoweredType(OptionalType::get(inputType));
    auto *someDecl = gen.getASTContext().getOptionalSomeDecl();
    auto *enumInst = gen.B.createEnum(loc, collection.getValue(), someDecl,
                                      loweredOptTy);
    collection = ManagedValue(enumInst, collection.getCleanup());
  }

  SILValue result = gen.B.createApply(loc, bridgeFn,
                                      substFnType,
                                      nativeTy,
                                      subs,
                                      { collection.forward(gen) });

  return gen.emitManagedRValueWithCleanup(result);
}

static ManagedValue emitBridgeBoolToObjCBool(SILGenFunction &gen,
                                             SILLocation loc,
                                             ManagedValue swiftBool) {
  // func _convertBoolToObjCBool(Bool) -> ObjCBool
  SILValue boolToObjCBoolFn
    = gen.emitGlobalFunctionRef(loc, gen.SGM.getBoolToObjCBoolFn());

  SILType resultTy =gen.getLoweredLoadableType(gen.SGM.Types.getObjCBoolType());

  SILValue result = gen.B.createApply(loc, boolToObjCBoolFn,
                                      boolToObjCBoolFn->getType(),
                                      resultTy, {}, swiftBool.forward(gen));
  return gen.emitManagedRValueWithCleanup(result);
}

static ManagedValue emitBridgeBoolToDarwinBoolean(SILGenFunction &gen,
                                                  SILLocation loc,
                                                  ManagedValue swiftBool) {
  // func _convertBoolToDarwinBoolean(Bool) -> DarwinBoolean
  SILValue boolToDarwinBooleanFn
    = gen.emitGlobalFunctionRef(loc, gen.SGM.getBoolToDarwinBooleanFn());

  SILType resultTy =
      gen.getLoweredLoadableType(gen.SGM.Types.getDarwinBooleanType());

  SILValue result = gen.B.createApply(loc, boolToDarwinBooleanFn,
                                      boolToDarwinBooleanFn->getType(),
                                      resultTy, {}, swiftBool.forward(gen));
  return gen.emitManagedRValueWithCleanup(result);
}

static ManagedValue emitBridgeForeignBoolToBool(SILGenFunction &gen,
                                                SILLocation loc,
                                                ManagedValue foreignBool,
                                                SILDeclRef bridgingFnRef) {
  // func _convertObjCBoolToBool(ObjCBool) -> Bool
  SILValue bridgingFn = gen.emitGlobalFunctionRef(loc, bridgingFnRef);

  SILType resultTy = gen.getLoweredLoadableType(gen.SGM.Types.getBoolType());

  SILValue result = gen.B.createApply(loc, bridgingFn, bridgingFn->getType(),
                                      resultTy, {}, foreignBool.forward(gen));
  return gen.emitManagedRValueWithCleanup(result);
}

static void buildFuncToBlockInvokeBody(SILGenFunction &gen,
                                       SILLocation loc,
                                       CanSILFunctionType blockTy,
                                       CanSILBlockStorageType blockStorageTy,
                                       CanSILFunctionType funcTy) {
  Scope scope(gen.Cleanups, CleanupLocation::get(loc));
  SILBasicBlock *entry = &*gen.F.begin();

  // Get the captured native function value out of the block.
  auto storageAddrTy = SILType::getPrimitiveAddressType(blockStorageTy);
  auto storage = new (gen.SGM.M) SILArgument(entry, storageAddrTy);
  auto capture = gen.B.createProjectBlockStorage(loc, storage);
  auto &funcTL = gen.getTypeLowering(funcTy);
  auto fn = gen.emitLoad(loc, capture, funcTL, SGFContext(), IsNotTake);

  // Collect the block arguments, which may have nonstandard conventions.
  assert(blockTy->getParameters().size()
         == funcTy->getParameters().size()
         && "block and function types don't match");

  SmallVector<ManagedValue, 4> args;
  for (unsigned i : indices(funcTy->getParameters())) {
    auto &funcParam = funcTy->getParameters()[i];
    auto &param = blockTy->getParameters()[i];
    SILValue v = new (gen.SGM.M) SILArgument(entry, param.getSILType());

    ManagedValue mv;
    
    // If the parameter is a block, we need to copy it to ensure it lives on
    // the heap. The adapted closure value might outlive the block's original
    // scope.
    if (param.getSILType().isBlockPointerCompatible()) {
      // We still need to consume the original block if it was owned.
      switch (param.getConvention()) {
      case ParameterConvention::Direct_Owned:
        gen.emitManagedRValueWithCleanup(v);
        break;
        
      case ParameterConvention::Direct_Deallocating:
      case ParameterConvention::Direct_Guaranteed:
      case ParameterConvention::Direct_Unowned:
        break;
        
      case ParameterConvention::Indirect_In:
      case ParameterConvention::Indirect_In_Guaranteed:
      case ParameterConvention::Indirect_Inout:
      case ParameterConvention::Indirect_InoutAliasable:
        llvm_unreachable("indirect params to blocks not supported");
      }
      
      SILValue blockCopy = gen.B.createCopyBlock(loc, v);
      mv = gen.emitManagedRValueWithCleanup(blockCopy);
    } else {
      switch (param.getConvention()) {
      case ParameterConvention::Direct_Owned:
        // Consume owned parameters at +1.
        mv = gen.emitManagedRValueWithCleanup(v);
        break;

      case ParameterConvention::Direct_Guaranteed:
      case ParameterConvention::Direct_Unowned:
        // We need to independently retain the value.
        mv = gen.emitManagedRetain(loc, v);
        break;

      case ParameterConvention::Direct_Deallocating:
        // We do not need to retain the value since the value is already being
        // deallocated.
        mv = ManagedValue::forUnmanaged(v);
        break;

      case ParameterConvention::Indirect_In_Guaranteed:
      case ParameterConvention::Indirect_In:
      case ParameterConvention::Indirect_Inout:
      case ParameterConvention::Indirect_InoutAliasable:
        llvm_unreachable("indirect arguments to blocks not supported");
      }
    }
    
    args.push_back(gen.emitBridgedToNativeValue(loc, mv,
                                SILFunctionTypeRepresentation::CFunctionPointer,
                                funcParam.getType()));
  }

  // Call the native function.
  assert(!funcTy->hasIndirectResults()
         && "block thunking func with indirect result not supported");
  assert(funcTy->getNumDirectResults() <= 1
         && "block thunking func with multiple results not supported");
  ManagedValue result = gen.emitMonomorphicApply(loc, fn, args,
                         funcTy->getSILResult().getSwiftRValueType(),
                                                 ApplyOptions::None,
                                                 None, None)
    .getAsSingleValue(gen, loc);

  // Bridge the result back to ObjC.
  result = gen.emitNativeToBridgedValue(loc, result,
                        SILFunctionTypeRepresentation::CFunctionPointer,
                        blockTy->getSILResult().getSwiftRValueType());

  auto resultVal = result.forward(gen);
  scope.pop();

  gen.B.createReturn(loc, resultVal);
}

/// Bridge a native function to a block with a thunk.
ManagedValue SILGenFunction::emitFuncToBlock(SILLocation loc,
                                             ManagedValue fn,
                                             CanSILFunctionType blockTy) {
  // Build the invoke function signature. The block will capture the original
  // function value.
  auto fnTy = fn.getType().castTo<SILFunctionType>();
  auto storageTy = SILBlockStorageType::get(fnTy);

  // Build the invoke function type.
  SmallVector<SILParameterInfo, 4> params;
  params.push_back(SILParameterInfo(storageTy,
                                 ParameterConvention::Indirect_InoutAliasable));
  std::copy(blockTy->getParameters().begin(),
            blockTy->getParameters().end(),
            std::back_inserter(params));

  auto invokeTy =
    SILFunctionType::get(nullptr,
                     SILFunctionType::ExtInfo()
                       .withRepresentation(SILFunctionType::Representation::
                                           CFunctionPointer),
                     ParameterConvention::Direct_Unowned,
                     params,
                     blockTy->getAllResults(),
                     blockTy->getOptionalErrorResult(),
                     getASTContext());

  // Create the invoke function. Borrow the mangling scheme from reabstraction
  // thunks, which is what we are in spirit.
  auto thunk = SGM.getOrCreateReabstractionThunk(nullptr,
                                                 invokeTy,
                                                 fnTy,
                                                 blockTy,
                                                 F.isFragile());

  // Build it if necessary.
  if (thunk->empty()) {
    SILGenFunction thunkSGF(SGM, *thunk);
    auto loc = RegularLocation::getAutoGeneratedLocation();
    buildFuncToBlockInvokeBody(thunkSGF, loc, blockTy, storageTy, fnTy);
  }

  // Form the block on the stack.
  auto storageAddrTy = SILType::getPrimitiveAddressType(storageTy);
  auto storage = emitTemporaryAllocation(loc, storageAddrTy);
  auto capture = B.createProjectBlockStorage(loc, storage);
  // Store the function to the block without claiming it, so that it still
  // gets cleaned up in scope. Copying the block will create an independent
  // reference.
  B.createStore(loc, fn.getValue(), capture);
  auto invokeFn = B.createFunctionRef(loc, thunk);
  auto stackBlock = B.createInitBlockStorageHeader(loc, storage, invokeFn,
                                      SILType::getPrimitiveObjectType(blockTy));

  // Copy the block so we have an independent heap object we can hand off.
  auto heapBlock = B.createCopyBlock(loc, stackBlock);
  return emitManagedRValueWithCleanup(heapBlock);
}

static ManagedValue emitNativeToCBridgedNonoptionalValue(SILGenFunction &gen,
                                                         SILLocation loc,
                                                         ManagedValue v,
                                                         SILType bridgedTy) {
  CanType loweredBridgedTy = bridgedTy.getSwiftRValueType();
  CanType loweredNativeTy = v.getType().getSwiftRValueType();
  if (loweredNativeTy == loweredBridgedTy)
    return v;

  // If the input is a native type with a bridged mapping, convert it.
#define BRIDGE_TYPE(BridgedModule,BridgedType, NativeModule,NativeType,Opt) \
  if (loweredNativeTy == gen.SGM.Types.get##NativeType##Type()              \
      && loweredBridgedTy == gen.SGM.Types.get##BridgedType##Type()) {      \
    return emitBridge##NativeType##To##BridgedType(gen, loc, v);            \
  }
#include "swift/SIL/BridgedTypes.def"

  // Bridge thick to Objective-C metatypes.
  if (auto bridgedMetaTy = dyn_cast<AnyMetatypeType>(loweredBridgedTy)) {
    if (bridgedMetaTy->getRepresentation() == MetatypeRepresentation::ObjC) {
      SILValue native = gen.B.emitThickToObjCMetatype(loc, v.getValue(),
                           SILType::getPrimitiveObjectType(loweredBridgedTy));
      return ManagedValue(native, v.getCleanup());
    }
  }

  // Bridge native functions to blocks.
  auto bridgedFTy = dyn_cast<SILFunctionType>(loweredBridgedTy);
  if (bridgedFTy
      && bridgedFTy->getRepresentation() == SILFunctionType::Representation::Block){
    auto nativeFTy = cast<SILFunctionType>(loweredNativeTy);

    if (nativeFTy->getRepresentation() != SILFunctionType::Representation::Block)
      return gen.emitFuncToBlock(loc, v, bridgedFTy);
  }

  // Bridge Array to NSArray.
  if (auto arrayDecl = gen.getASTContext().getArrayDecl()) {
    if (v.getType().getSwiftRValueType().getAnyNominal() == arrayDecl) {
      SILDeclRef bridgeFn = gen.SGM.getArrayToNSArrayFn();
      return emitBridgeCollectionFromNative(gen, loc, bridgeFn, v, bridgedTy);
    }
  }

  // Bridge Dictionary to NSDictionary.
  if (auto dictDecl = gen.getASTContext().getDictionaryDecl()) {
    if (v.getType().getSwiftRValueType().getAnyNominal() == dictDecl) {
      SILDeclRef bridgeFn = gen.SGM.getDictionaryToNSDictionaryFn();
      return emitBridgeCollectionFromNative(gen, loc, bridgeFn, v, bridgedTy);
    }
  }

  // Bridge Set to NSSet.
  if (auto setDecl = gen.getASTContext().getSetDecl()) {
    if (v.getType().getSwiftRValueType().getAnyNominal() == setDecl) {
      SILDeclRef bridgeFn = gen.SGM.getSetToNSSetFn();
      return emitBridgeCollectionFromNative(gen, loc, bridgeFn, v, bridgedTy);
    }
  }

  return v;
}

static ManagedValue emitNativeToCBridgedValue(SILGenFunction &gen,
                                              SILLocation loc,
                                              ManagedValue v,
                                              SILType bridgedTy) {
  CanType loweredBridgedTy = bridgedTy.getSwiftRValueType();
  CanType loweredNativeTy = v.getType().getSwiftRValueType();
  if (loweredNativeTy == loweredBridgedTy)
    return v;

  if (loweredNativeTy.getAnyOptionalObjectType()) {
    return gen.emitOptionalToOptional(loc, v, bridgedTy,
                                      emitNativeToCBridgedValue);
  }
  
  // Check if we need to wrap the bridged result in an optional.
  OptionalTypeKind OTK;
  if (SILType bridgedObjectType =
        bridgedTy.getAnyOptionalObjectType(gen.SGM.M, OTK)) {
    auto bridgedPayload
      = emitNativeToCBridgedNonoptionalValue(gen, loc, v, bridgedObjectType);
    
    return gen.getOptionalSomeValue(loc, bridgedPayload,
                                    gen.getTypeLowering(bridgedTy));
  }
  
  return emitNativeToCBridgedNonoptionalValue(gen, loc, v, bridgedTy);
}

ManagedValue SILGenFunction::emitNativeToBridgedValue(SILLocation loc,
                                                      ManagedValue v,
                                                SILFunctionTypeRepresentation destRep,
                                                      CanType loweredBridgedTy){
  switch (getSILFunctionLanguage(destRep)) {
  case SILFunctionLanguage::Swift:
    // No additional bridging needed for native functions.
    return v;
  case SILFunctionLanguage::C:
    return emitNativeToCBridgedValue(*this, loc, v,
                           SILType::getPrimitiveObjectType(loweredBridgedTy));
  }
  llvm_unreachable("bad CC");
}

static void buildBlockToFuncThunkBody(SILGenFunction &gen,
                                      SILLocation loc,
                                      CanSILFunctionType blockTy,
                                      CanSILFunctionType funcTy) {
  // Collect the native arguments, which should all be +1.
  Scope scope(gen.Cleanups, CleanupLocation::get(loc));

  assert(blockTy->getParameters().size()
           == funcTy->getParameters().size()
         && "block and function types don't match");

  SmallVector<ManagedValue, 4> args;
  SILBasicBlock *entry = &*gen.F.begin();
  for (unsigned i : indices(funcTy->getParameters())) {
    auto &param = funcTy->getParameters()[i];
    auto &blockParam = blockTy->getParameters()[i];

    auto &tl = gen.getTypeLowering(param.getSILType());
    assert((tl.isTrivial()
              ? param.getConvention() == ParameterConvention::Direct_Unowned
              : param.getConvention() == ParameterConvention::Direct_Owned)
           && "nonstandard conventions for native functions not implemented");
    SILValue v = new (gen.SGM.M) SILArgument(entry, param.getSILType());
    auto mv = gen.emitManagedRValueWithCleanup(v, tl);
    args.push_back(gen.emitNativeToBridgedValue(loc, mv,
                              SILFunctionTypeRepresentation::Block,
                              blockParam.getType()));
  }

  // Add the block argument.
  SILValue blockV
    = new (gen.SGM.M) SILArgument(entry,
                                  SILType::getPrimitiveObjectType(blockTy));
  ManagedValue block = gen.emitManagedRValueWithCleanup(blockV);

  // Call the block.
  assert(!funcTy->hasIndirectResults()
         && "block thunking func with indirect result not supported");
  ManagedValue result = gen.emitMonomorphicApply(loc, block, args,
                         funcTy->getSILResult().getSwiftRValueType(),
                         ApplyOptions::None,
                         /*override CC*/ SILFunctionTypeRepresentation::Block,
                         /*foreign error*/ None)
    .getAsSingleValue(gen, loc);

  // Return the result at +1.
#ifndef NDEBUG
  for (auto result : funcTy->getDirectResults()) {
    assert((gen.getTypeLowering(result.getSILType()).isTrivial()
             ? result.getConvention() == ResultConvention::Unowned
             : result.getConvention() == ResultConvention::Owned)
           && "nonstandard conventions for return not implemented");
  }
#endif

  auto r = result.forward(gen);
  scope.pop();
  gen.B.createReturn(loc, r);
}

/// Bridge a native function to a block with a thunk.
ManagedValue
SILGenFunction::emitBlockToFunc(SILLocation loc,
                                ManagedValue block,
                                CanSILFunctionType funcTy) {
  CanSILFunctionType substFnTy;
  SmallVector<Substitution, 4> subs;

  // Declare the thunk.
  auto blockTy = block.getType().castTo<SILFunctionType>();
  auto thunkTy = buildThunkType(block, funcTy, substFnTy, subs);
  auto thunk = SGM.getOrCreateReabstractionThunk(F.getContextGenericParams(),
                                                 thunkTy,
                                                 blockTy,
                                                 funcTy,
                                                 F.isFragile());

  // Build it if necessary.
  if (thunk->empty()) {
    SILGenFunction thunkSGF(SGM, *thunk);
    thunk->setContextGenericParams(F.getContextGenericParams());
    auto loc = RegularLocation::getAutoGeneratedLocation();
    buildBlockToFuncThunkBody(thunkSGF, loc, blockTy, funcTy);
  }

  // Create it in the current function.
  auto thunkValue = B.createFunctionRef(loc, thunk);
  auto thunkedFn = B.createPartialApply(loc, thunkValue,
                                    SILType::getPrimitiveObjectType(substFnTy),
                                    subs, block.forward(*this),
                                    SILType::getPrimitiveObjectType(funcTy));
  return emitManagedRValueWithCleanup(thunkedFn);
}

static ManagedValue emitCBridgedToNativeValue(SILGenFunction &gen,
                                              SILLocation loc,
                                              ManagedValue v,
                                              SILType nativeTy) {
  CanType loweredNativeTy = nativeTy.getSwiftRValueType();
  CanType loweredBridgedTy = v.getType().getSwiftRValueType();
  if (loweredNativeTy == loweredBridgedTy)
    return v;

  if (loweredNativeTy.getAnyOptionalObjectType()) {
    return gen.emitOptionalToOptional(loc, v, nativeTy,
                                      emitCBridgedToNativeValue);
  }

  // Bridge Bool to ObjCBool or DarwinBoolean when requested.
  if (loweredNativeTy == gen.SGM.Types.getBoolType()) {
    if (loweredBridgedTy == gen.SGM.Types.getObjCBoolType()) {
      return emitBridgeForeignBoolToBool(gen, loc, v,
                                         gen.SGM.getObjCBoolToBoolFn());
    }
    if (loweredBridgedTy == gen.SGM.Types.getDarwinBooleanType()) {
      return emitBridgeForeignBoolToBool(gen, loc, v,
                                         gen.SGM.getDarwinBooleanToBoolFn());
    }
  }

  // Bridge Objective-C to thick metatypes.
  if (auto bridgedMetaTy = dyn_cast<AnyMetatypeType>(loweredBridgedTy)){
    if (bridgedMetaTy->getRepresentation() == MetatypeRepresentation::ObjC) {
      SILValue native = gen.B.emitObjCToThickMetatype(loc, v.getValue(),
                                        gen.getLoweredType(loweredNativeTy));
      return ManagedValue(native, v.getCleanup());
    }
  }

  // Bridge blocks back into native function types.
  auto bridgedFTy = dyn_cast<SILFunctionType>(loweredBridgedTy);
  if (bridgedFTy
      && bridgedFTy->getRepresentation() == SILFunctionType::Representation::Block){
    auto nativeFTy = cast<SILFunctionType>(loweredNativeTy);

    if (nativeFTy->getRepresentation() != SILFunctionType::Representation::Block)
      return gen.emitBlockToFunc(loc, v, nativeFTy);
  }

  // Bridge NSString to String.
  if (auto stringDecl = gen.getASTContext().getStringDecl()) {
    if (nativeTy.getSwiftRValueType()->getAnyNominal() == stringDecl) {
      return emitBridgeNSStringToString(gen, loc, v);
    }
  }

  // Bridge NSArray to Array.
  if (auto arrayDecl = gen.getASTContext().getArrayDecl()) {
    if (nativeTy.getSwiftRValueType()->getAnyNominal() == arrayDecl) {
      SILDeclRef bridgeFn = gen.SGM.getNSArrayToArrayFn();
      return emitBridgeCollectionToNative(gen, loc, bridgeFn, v, nativeTy);
    }
  }

  // Bridge NSDictionary to Dictionary.
  if (auto dictDecl = gen.getASTContext().getDictionaryDecl()) {
    if (nativeTy.getSwiftRValueType()->getAnyNominal() == dictDecl) {
      SILDeclRef bridgeFn = gen.SGM.getNSDictionaryToDictionaryFn();
      return emitBridgeCollectionToNative(gen, loc, bridgeFn, v, nativeTy);
    }
  }

  // Bridge NSSet to Set.
  if (auto setDecl = gen.getASTContext().getSetDecl()) {
    if (nativeTy.getSwiftRValueType()->getAnyNominal() == setDecl) {
      SILDeclRef bridgeFn = gen.SGM.getNSSetToSetFn();
      return emitBridgeCollectionToNative(gen, loc, bridgeFn, v, nativeTy);
    }
  }

  return v;
}

ManagedValue SILGenFunction::emitBridgedToNativeValue(SILLocation loc,
                                          ManagedValue v,
                                          SILFunctionTypeRepresentation srcRep,
                                          CanType nativeTy) {
  switch (getSILFunctionLanguage(srcRep)) {
  case SILFunctionLanguage::Swift:
    // No additional bridging needed for native functions.
    return v;

  case SILFunctionLanguage::C:
    return emitCBridgedToNativeValue(*this, loc, v, getLoweredType(nativeTy));
  }
  llvm_unreachable("bad CC");
}

/// Bridge an optional foreign error type to ErrorProtocol.
ManagedValue SILGenFunction::emitBridgedToNativeError(SILLocation loc,
                                                  ManagedValue bridgedError) {
#ifndef NDEBUG
  {
    OptionalTypeKind optKind;
    auto objType = bridgedError.getType().getSwiftRValueType()
                                         .getAnyOptionalObjectType(optKind);
    assert(optKind == OTK_Optional && "not Optional type");
    assert(objType == SGM.Types.getNSErrorType() &&
           "only handling NSError for now");
  }
#endif

  auto bridgeFn = emitGlobalFunctionRef(loc, SGM.getNSErrorToErrorProtocolFn());
  auto bridgeFnType = bridgeFn->getType().castTo<SILFunctionType>();
  assert(bridgeFnType->getNumAllResults() == 1);
  assert(bridgeFnType->getAllResults()[0].getConvention()
           == ResultConvention::Owned);
  auto nativeErrorProtocol = bridgeFnType->getAllResults()[0].getSILType();
  assert(bridgeFnType->getParameters()[0].getConvention()
           == ParameterConvention::Direct_Owned);

  SILValue nativeError = B.createApply(loc, bridgeFn, bridgeFn->getType(),
                                       nativeErrorProtocol, {},
                                       bridgedError.forward(*this));
  return emitManagedRValueWithCleanup(nativeError);
}

/// Bridge ErrorProtocol to a foreign error type.
ManagedValue SILGenFunction::emitNativeToBridgedError(SILLocation loc,
                                                  ManagedValue nativeError,
                                                      CanType bridgedErrorProtocol) {
  assert(bridgedErrorProtocol == SGM.Types.getNSErrorType() &&
         "only handling NSError for now");

  auto bridgeFn = emitGlobalFunctionRef(loc, SGM.getErrorProtocolToNSErrorFn());
  auto bridgeFnType = bridgeFn->getType().castTo<SILFunctionType>();
  assert(bridgeFnType->getNumAllResults() == 1);
  assert(bridgeFnType->getAllResults()[0].getConvention()
           == ResultConvention::Owned);
  auto bridgeErrorType = bridgeFnType->getAllResults()[0].getSILType();
  assert(bridgeFnType->getParameters()[0].getConvention()
           == ParameterConvention::Direct_Owned);

  SILValue bridgedError = B.createApply(loc, bridgeFn, bridgeFn->getType(),
                                        bridgeErrorType, {},
                                        nativeError.forward(*this));
  return emitManagedRValueWithCleanup(bridgedError);
}

//===----------------------------------------------------------------------===//
// ObjC method thunks
//===----------------------------------------------------------------------===//

static SILValue emitBridgeReturnValue(SILGenFunction &gen,
                                      SILLocation loc,
                                      SILValue result,
                                      SILFunctionTypeRepresentation fnTypeRepr,
                                      CanType bridgedTy) {
  Scope scope(gen.Cleanups, CleanupLocation::get(loc));

  ManagedValue native = gen.emitManagedRValueWithCleanup(result);
  ManagedValue bridged = gen.emitNativeToBridgedValue(loc, native, fnTypeRepr,
                                      bridgedTy);
  return bridged.forward(gen);
}

/// Take an argument at +0 and bring it to +1.
static SILValue emitObjCUnconsumedArgument(SILGenFunction &gen,
                                           SILLocation loc,
                                           SILValue arg) {
  auto &lowering = gen.getTypeLowering(arg->getType());
  // If address-only, make a +1 copy and operate on that.
  if (lowering.isAddressOnly()) {
    auto tmp = gen.emitTemporaryAllocation(loc, arg->getType().getObjectType());
    gen.B.createCopyAddr(loc, arg, tmp, IsNotTake, IsInitialization);
    return tmp;
  }

  lowering.emitRetainValue(gen.B, loc, arg);
  return arg;
}

/// Bridge argument types and adjust retain count conventions for an ObjC thunk.
static SILFunctionType *emitObjCThunkArguments(SILGenFunction &gen,
                                               SILLocation loc,
                                               SILDeclRef thunk,
                                               SmallVectorImpl<SILValue> &args,
                                               SILValue &foreignErrorSlot,
                              Optional<ForeignErrorConvention> &foreignError) {
  SILDeclRef native = thunk.asForeign(false);

  auto mod = gen.SGM.M.getSwiftModule();
  auto subs = gen.F.getForwardingSubstitutions();

  auto objcInfo = gen.SGM.Types.getConstantInfo(thunk);
  auto objcFnTy = objcInfo.SILFnType->substGenericArgs(gen.SGM.M, mod, subs);

  auto swiftInfo = gen.SGM.Types.getConstantInfo(native);
  auto swiftFnTy = swiftInfo.SILFnType->substGenericArgs(gen.SGM.M, mod, subs);

  // We must have the same context archetypes as the unthunked function.
  assert(objcInfo.ContextGenericParams == swiftInfo.ContextGenericParams);

  SmallVector<ManagedValue, 8> bridgedArgs;
  bridgedArgs.reserve(objcFnTy->getParameters().size());

  SILFunction *orig = gen.SGM.getFunction(native, NotForDefinition);

  // Find the foreign error convention if we have one.
  if (orig->getLoweredFunctionType()->hasErrorResult()) {
    auto func = cast<AbstractFunctionDecl>(thunk.getDecl());
    foreignError = func->getForeignErrorConvention();
    assert(foreignError && "couldn't find foreign error convention!");
  }

  // Emit the indirect result arguments, if any.
  // FIXME: we're just assuming that these match up exactly?
  for (auto indirectResult : objcFnTy->getIndirectResults()) {
    SILType argTy = gen.F.mapTypeIntoContext(indirectResult.getSILType());
    auto arg = new (gen.F.getModule()) SILArgument(gen.F.begin(), argTy);
    args.push_back(arg);
  }

  // Emit the other arguments, taking ownership of arguments if necessary.
  auto inputs = objcFnTy->getParameters();
  auto nativeInputs = swiftFnTy->getParameters();
  assert(inputs.size() ==
           nativeInputs.size() + unsigned(foreignError.hasValue()));
  for (unsigned i = 0, e = inputs.size(); i < e; ++i) {
    SILType argTy = gen.F.mapTypeIntoContext(inputs[i].getSILType());
    SILValue arg = new(gen.F.getModule()) SILArgument(gen.F.begin(), argTy);

    // If this parameter is the foreign error slot, pull it out.
    // It does not correspond to a native argument.
    if (foreignError && i == foreignError->getErrorParameterIndex()) {
      foreignErrorSlot = arg;
      continue;
    }

    // If this parameter is deallocating, emit an unmanaged rvalue and
    // continue. The object has the deallocating bit set so retain, release is
    // irrelevant.
    if (inputs[i].isDeallocating()) {
      bridgedArgs.push_back(ManagedValue::forUnmanaged(arg));
      continue;
    }

    // If the argument is a block, copy it.
    if (argTy.isBlockPointerCompatible()) {
      auto copy = gen.B.createCopyBlock(loc, arg);
      // If the argument is consumed, we're still responsible for releasing the
      // original.
      if (inputs[i].isConsumed())
        gen.emitManagedRValueWithCleanup(arg);
      arg = copy;
    }
    // Convert the argument to +1 if necessary.
    else if (!inputs[i].isConsumed()) {
      arg = emitObjCUnconsumedArgument(gen, loc, arg);
    }

    auto managedArg = gen.emitManagedRValueWithCleanup(arg);

    bridgedArgs.push_back(managedArg);
  }

  assert(bridgedArgs.size() + unsigned(foreignError.hasValue())
           == objcFnTy->getParameters().size() &&
         "objc inputs don't match number of arguments?!");
  assert(bridgedArgs.size() == swiftFnTy->getNumSILArguments() &&
         "swift inputs don't match number of arguments?!");
  assert((foreignErrorSlot || !foreignError) &&
         "didn't find foreign error slot");

  // Bridge the input types.
  Scope scope(gen.Cleanups, CleanupLocation::get(loc));
  assert(bridgedArgs.size() == nativeInputs.size());
  for (unsigned i = 0, size = bridgedArgs.size(); i < size; ++i) {
    SILType argTy = gen.F.mapTypeIntoContext(
                           swiftFnTy->getParameters()[i].getSILType());
    ManagedValue native =
      gen.emitBridgedToNativeValue(loc,
                                   bridgedArgs[i],
                                   SILFunctionTypeRepresentation::ObjCMethod,
                                   argTy.getSwiftType());
    SILValue argValue;

    if (nativeInputs[i].isConsumed())
      argValue = native.forward(gen);
    else
      argValue = native.getValue();
    
    args.push_back(argValue);
  }

  return objcFnTy;
}

void SILGenFunction::emitNativeToForeignThunk(SILDeclRef thunk) {
  assert(thunk.isForeign);
  SILDeclRef native = thunk.asForeign(false);

  auto loc = thunk.getAsRegularLocation();
  loc.markAutoGenerated();
  Scope scope(Cleanups, CleanupLocation::get(loc));

  // Bridge the arguments.
  SmallVector<SILValue, 4> args;
  Optional<ForeignErrorConvention> foreignError;
  SILValue foreignErrorSlot;
  auto objcFnTy = emitObjCThunkArguments(*this, loc, thunk, args,
                                         foreignErrorSlot, foreignError);
  auto nativeInfo = getConstantInfo(native);
  auto swiftResultTy =
    F.mapTypeIntoContext(nativeInfo.SILFnType->getSILResult());
  auto objcResultTy =
    F.mapTypeIntoContext(objcFnTy->getSILResult());

  // Call the native entry point.
  SILValue nativeFn = emitGlobalFunctionRef(loc, native, nativeInfo);
  auto subs = F.getForwardingSubstitutions();
  auto substTy = nativeInfo.SILFnType->substGenericArgs(
    SGM.M, SGM.M.getSwiftModule(), subs);
  SILType substSILTy = SILType::getPrimitiveObjectType(substTy);

  CanType bridgedResultType = objcResultTy.getSwiftRValueType();

  SILValue result;
  assert(foreignError.hasValue() == substTy->hasErrorResult());
  if (!substTy->hasErrorResult()) {
    // Create the apply.
    result = B.createApply(loc, nativeFn, substSILTy,
                           swiftResultTy, subs, args);

    // Leave the scope immediately.  This isn't really necessary; it
    // just limits lifetimes a little bit more.
    scope.pop();

    // Now bridge the return value.
    result = emitBridgeReturnValue(*this, loc, result,
                                   objcFnTy->getRepresentation(),
                                   bridgedResultType);
  } else {
    SILBasicBlock *contBB = createBasicBlock();
    SILBasicBlock *errorBB = createBasicBlock();
    SILBasicBlock *normalBB = createBasicBlock();
    B.createTryApply(loc, nativeFn, substSILTy, subs, args,
                     normalBB, errorBB);

    // Emit the non-error destination.
    {
      B.emitBlock(normalBB);
      SILValue nativeResult = normalBB->createBBArg(swiftResultTy);

      // In this branch, the eventual return value is mostly created
      // by bridging the native return value, but we may need to
      // adjust it slightly.
      SILValue bridgedResult =
        emitBridgeReturnValueForForeignError(loc, nativeResult, 
                                             objcFnTy->getRepresentation(),
                                             objcResultTy,
                                             foreignErrorSlot, *foreignError);
      B.createBranch(loc, contBB, bridgedResult);
    }

    // Emit the error destination.
    {
      B.emitBlock(errorBB);
      SILValue nativeError =
        errorBB->createBBArg(substTy->getErrorResult().getSILType());

      // In this branch, the eventual return value is mostly invented.
      // Store the native error in the appropriate location and return.
      SILValue bridgedResult =
        emitBridgeErrorForForeignError(loc, nativeError, objcResultTy,
                                       foreignErrorSlot, *foreignError);
      B.createBranch(loc, contBB, bridgedResult);
    }

    // Emit the join block.
    B.emitBlock(contBB);
    result = contBB->createBBArg(objcResultTy);

    // Leave the scope now.
    scope.pop();
  }

  B.createReturn(loc, result);
}

static SILValue
getThunkedForeignFunctionRef(SILGenFunction &gen,
                             SILLocation loc,
                             SILDeclRef foreign,
                             ArrayRef<ManagedValue> args,
                             ArrayRef<Substitution> subs,
                             const SILConstantInfo &foreignCI) {
  assert(!foreign.isCurried
         && "should not thunk calling convention when curried");

  // Produce a witness_method when thunking ObjC protocol methods.
  auto dc = foreign.getDecl()->getDeclContext();
  if (isa<ProtocolDecl>(dc) && cast<ProtocolDecl>(dc)->isObjC()) {
    assert(subs.size() == 1);
    auto thisType = subs[0].getReplacement()->getCanonicalType();
    assert(isa<ArchetypeType>(thisType) && "no archetype for witness?!");
    SILValue thisArg = args.back().getValue();

    SILValue OpenedExistential;
    if (!cast<ArchetypeType>(thisType)->getOpenedExistentialType().isNull())
      OpenedExistential = thisArg;
    auto conformance = ProtocolConformanceRef(cast<ProtocolDecl>(dc));
    return gen.B.createWitnessMethod(loc, thisType, conformance, foreign,
                                     foreignCI.getSILType(),
                                     OpenedExistential);

  // Produce a class_method when thunking imported ObjC methods.
  } else if (foreignCI.SILFnType->getRepresentation()
        == SILFunctionTypeRepresentation::ObjCMethod) {
    assert(subs.empty());
    SILValue thisArg = args.back().getValue();

    return gen.B.createClassMethod(loc, thisArg, foreign,
                         SILType::getPrimitiveObjectType(foreignCI.SILFnType),
                                   /*volatile*/ true);
  }
  // Otherwise, emit a function_ref.
  return gen.emitGlobalFunctionRef(loc, foreign);
}

/// Generate code to emit a thunk with native conventions that calls a
/// function with foreign conventions.
void SILGenFunction::emitForeignToNativeThunk(SILDeclRef thunk) {
  assert(!thunk.isForeign && "foreign-to-native thunks only");

  // Wrap the function in its original form.

  auto fd = cast<AbstractFunctionDecl>(thunk.getDecl());
  auto nativeCI = getConstantInfo(thunk);
  auto nativeFormalResultTy = nativeCI.LoweredInterfaceType.getResult();
  auto nativeFnTy = F.getLoweredFunctionType();
  assert(nativeFnTy == nativeCI.SILFnType);

  // Find the foreign error convention.
  Optional<ForeignErrorConvention> foreignError;
  if (nativeFnTy->hasErrorResult()) {
    foreignError = fd->getForeignErrorConvention();
    assert(foreignError && "couldn't find foreign error convention!");
  }

  // Forward the arguments.
  auto forwardedParameters = fd->getParameterLists();

  // For allocating constructors, 'self' is a metatype, not the 'self' value
  // formally present in the constructor body.
  Type allocatorSelfType;
  if (thunk.kind == SILDeclRef::Kind::Allocator) {
    allocatorSelfType = forwardedParameters[0]->getType(getASTContext());
    forwardedParameters = forwardedParameters.slice(1);
  }

  SmallVector<SILValue, 8> params;
  for (auto *paramList : reversed(forwardedParameters))
    bindParametersForForwarding(paramList, params);

  if (allocatorSelfType) {
    auto selfMetatype = CanMetatypeType::get(allocatorSelfType->getCanonicalType(),
                                             MetatypeRepresentation::Thick);
    auto selfArg = new (F.getModule()) SILArgument(
                                 F.begin(),
                                 SILType::getPrimitiveObjectType(selfMetatype),
                                 fd->getImplicitSelfDecl());
    params.push_back(selfArg);
  }

  // Set up the throw destination if necessary.
  CleanupLocation cleanupLoc(fd);
  if (foreignError) {
    prepareRethrowEpilog(cleanupLoc);
  }

  SILValue result;
  {
    Scope scope(Cleanups, fd);

    SILDeclRef foreignDeclRef = thunk.asForeign(true);
    SILConstantInfo foreignCI = getConstantInfo(foreignDeclRef);
    auto foreignFnTy = foreignCI.SILFnType;

    // Bridge all the arguments.
    SmallVector<ManagedValue, 8> args;
    unsigned foreignArgIndex = 0;

    // A helper function to add a function error argument in the
    // appropriate position.
    auto maybeAddForeignErrorArg = [&] {
      if (foreignError &&
          foreignArgIndex == foreignError->getErrorParameterIndex()) {
        args.push_back(ManagedValue());
        foreignArgIndex++;
      }
    };

    for (unsigned nativeParamIndex : indices(params)) {
      // Bring the parameter to +1.
      auto paramValue = params[nativeParamIndex];
      auto thunkParam = nativeFnTy->getParameters()[nativeParamIndex];
      // TODO: Could avoid a retain if the bridged parameter is also +0 and
      // doesn't require a bridging conversion.
      ManagedValue param;
      switch (thunkParam.getConvention()) {
      case ParameterConvention::Direct_Owned:
        param = emitManagedRValueWithCleanup(paramValue);
        break;
      case ParameterConvention::Direct_Guaranteed:
      case ParameterConvention::Direct_Unowned:
        param = emitManagedRetain(fd, paramValue);
        break;
      case ParameterConvention::Direct_Deallocating:
        param = ManagedValue::forUnmanaged(paramValue);
        break;
      case ParameterConvention::Indirect_Inout:
      case ParameterConvention::Indirect_InoutAliasable:
        param = ManagedValue::forUnmanaged(paramValue);
        break;
      case ParameterConvention::Indirect_In:
      case ParameterConvention::Indirect_In_Guaranteed:
        llvm_unreachable("indirect args in foreign thunked method not implemented");
      }

      maybeAddForeignErrorArg();

      SILType foreignArgTy =
        foreignFnTy->getParameters()[foreignArgIndex++].getSILType();
      args.push_back(emitNativeToBridgedValue(fd, param,
                                SILFunctionTypeRepresentation::CFunctionPointer,
                                foreignArgTy.getSwiftRValueType()));
    }

    maybeAddForeignErrorArg();

    // Call the original.
    auto subs = getForwardingSubstitutions();
    auto fn = getThunkedForeignFunctionRef(*this, fd, foreignDeclRef, args, subs,
                                           foreignCI);

    auto fnType = fn->getType().castTo<SILFunctionType>();
    fnType = fnType->substGenericArgs(SGM.M, SGM.SwiftModule, subs);

    result = emitApply(fd, ManagedValue::forUnmanaged(fn),
                       subs, args, fnType,
                       AbstractionPattern(nativeFormalResultTy),
                       nativeFormalResultTy,
                       ApplyOptions::None, None, foreignError,
                       SGFContext())
      .forwardAsSingleValue(*this, fd);
  }
  B.createReturn(ImplicitReturnLocation::getImplicitReturnLoc(fd), result);

  // Emit the throw destination.
  emitRethrowEpilog(fd);
}