//===--- Linking.cpp - Name mangling for IRGen entities -------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
//  This file implements name mangling for IRGen entities with linkage.
//
//===----------------------------------------------------------------------===//

#include "swift/IRGen/Linking.h"
#include "IRGenMangler.h"
#include "IRGenModule.h"
#include "swift/AST/ASTMangler.h"
#include "swift/ClangImporter/ClangModule.h"
#include "swift/SIL/SILGlobalVariable.h"
#include "swift/SIL/FormalLinkage.h"
#include "llvm/ADT/Triple.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/raw_ostream.h"

#include "MetadataRequest.h"

using namespace swift;
using namespace irgen;
using namespace Mangle;

bool swift::irgen::useDllStorage(const llvm::Triple &triple) {
  return triple.isOSBinFormatCOFF() && !triple.isOSCygMing();
}

UniversalLinkageInfo::UniversalLinkageInfo(IRGenModule &IGM)
    : UniversalLinkageInfo(IGM.Triple, IGM.IRGen.hasMultipleIGMs(),
                           IGM.getSILModule().isWholeModule()) {}

UniversalLinkageInfo::UniversalLinkageInfo(const llvm::Triple &triple,
                                           bool hasMultipleIGMs,
                                           bool isWholeModule)
    : IsELFObject(triple.isOSBinFormatELF()),
      UseDLLStorage(useDllStorage(triple)), HasMultipleIGMs(hasMultipleIGMs),
      IsWholeModule(isWholeModule) {}

/// Mangle this entity into the given buffer.
void LinkEntity::mangle(SmallVectorImpl<char> &buffer) const {
  llvm::raw_svector_ostream stream(buffer);
  mangle(stream);
}

/// Mangle this entity into the given stream.
void LinkEntity::mangle(raw_ostream &buffer) const {
  std::string Result = mangleAsString();
  buffer.write(Result.data(), Result.size());
}

/// Mangle this entity as a std::string.
std::string LinkEntity::mangleAsString() const {
  IRGenMangler mangler;
  switch (getKind()) {
  case Kind::DispatchThunk: {
    auto *func = cast<FuncDecl>(getDecl());
    return mangler.mangleDispatchThunk(func);
  }

  case Kind::DispatchThunkInitializer: {
    auto *ctor = cast<ConstructorDecl>(getDecl());
    return mangler.mangleConstructorDispatchThunk(ctor,
                                                  /*isAllocating=*/false);
  }

  case Kind::DispatchThunkAllocator: {
    auto *ctor = cast<ConstructorDecl>(getDecl());
    return mangler.mangleConstructorDispatchThunk(ctor,
                                                  /*isAllocating=*/true);
  }

  case Kind::MethodDescriptor: {
    auto *func = cast<FuncDecl>(getDecl());
    return mangler.mangleMethodDescriptor(func);
  }

  case Kind::MethodDescriptorInitializer: {
    auto *ctor = cast<ConstructorDecl>(getDecl());
    return mangler.mangleConstructorMethodDescriptor(ctor,
                                                     /*isAllocating=*/false);
  }

  case Kind::MethodDescriptorAllocator: {
    auto *ctor = cast<ConstructorDecl>(getDecl());
    return mangler.mangleConstructorMethodDescriptor(ctor,
                                                     /*isAllocating=*/true);
  }

  case Kind::MethodLookupFunction: {
    auto *classDecl = cast<ClassDecl>(getDecl());
    return mangler.mangleMethodLookupFunction(classDecl);
  }

  case Kind::ValueWitness:
    return mangler.mangleValueWitness(getType(), getValueWitness());

  case Kind::ValueWitnessTable:
    return mangler.mangleValueWitnessTable(getType());

  case Kind::TypeMetadataAccessFunction:
    return mangler.mangleTypeMetadataAccessFunction(getType());

  case Kind::TypeMetadataLazyCacheVariable:
    return mangler.mangleTypeMetadataLazyCacheVariable(getType());

  case Kind::TypeMetadataInstantiationCache:
    return mangler.mangleTypeMetadataInstantiationCache(
                                            cast<NominalTypeDecl>(getDecl()));

  case Kind::TypeMetadataInstantiationFunction:
    return mangler.mangleTypeMetadataInstantiationFunction(
                                            cast<NominalTypeDecl>(getDecl()));

  case Kind::TypeMetadataSingletonInitializationCache:
    return mangler.mangleTypeMetadataSingletonInitializationCache(
                                            cast<NominalTypeDecl>(getDecl()));

  case Kind::TypeMetadataCompletionFunction:
    return mangler.mangleTypeMetadataCompletionFunction(
                                            cast<NominalTypeDecl>(getDecl()));

  case Kind::TypeMetadata:
    switch (getMetadataAddress()) {
      case TypeMetadataAddress::FullMetadata:
        return mangler.mangleTypeFullMetadataFull(getType());
      case TypeMetadataAddress::AddressPoint:
        return mangler.mangleTypeMetadataFull(getType());
    }
    llvm_unreachable("invalid metadata address");

  case Kind::TypeMetadataPattern:
    return mangler.mangleTypeMetadataPattern(
                                        cast<NominalTypeDecl>(getDecl()));

  case Kind::ForeignTypeMetadataCandidate:
    return mangler.mangleTypeMetadataFull(getType());

  case Kind::SwiftMetaclassStub:
    return mangler.mangleClassMetaClass(cast<ClassDecl>(getDecl()));

  case Kind::ObjCMetadataUpdateFunction:
    return mangler.mangleObjCMetadataUpdateFunction(cast<ClassDecl>(getDecl()));

  case Kind::ClassMetadataBaseOffset:               // class metadata base offset
    return mangler.mangleClassMetadataBaseOffset(cast<ClassDecl>(getDecl()));

  case Kind::NominalTypeDescriptor:
    return mangler.mangleNominalTypeDescriptor(
                                        cast<NominalTypeDecl>(getDecl()));

  case Kind::PropertyDescriptor:
    return mangler.manglePropertyDescriptor(
                                        cast<AbstractStorageDecl>(getDecl()));

  case Kind::ModuleDescriptor:
    return mangler.mangleModuleDescriptor(cast<ModuleDecl>(getDecl()));
  
  case Kind::ExtensionDescriptor:
    return mangler.mangleExtensionDescriptor(getExtension());

  case Kind::AnonymousDescriptor:
    return mangler.mangleAnonymousDescriptor(getDeclContext());

  case Kind::ProtocolDescriptor:
    return mangler.mangleProtocolDescriptor(cast<ProtocolDecl>(getDecl()));

  case Kind::ProtocolRequirementsBaseDescriptor:
    return mangler.mangleProtocolRequirementsBaseDescriptor(
                                                 cast<ProtocolDecl>(getDecl()));

  case Kind::AssociatedTypeDescriptor:
    return mangler.mangleAssociatedTypeDescriptor(
                                          cast<AssociatedTypeDecl>(getDecl()));

  case Kind::AssociatedConformanceDescriptor: {
    auto assocConformance = getAssociatedConformance();
    return mangler.mangleAssociatedConformanceDescriptor(
             cast<ProtocolDecl>(getDecl()),
             assocConformance.first,
             assocConformance.second);
  }

  case Kind::DefaultAssociatedConformanceAccessor: {
    auto assocConformance = getAssociatedConformance();
    return mangler.mangleDefaultAssociatedConformanceAccessor(
             cast<ProtocolDecl>(getDecl()),
             assocConformance.first,
             assocConformance.second);
  }

  case Kind::ProtocolConformanceDescriptor:
    return mangler.mangleProtocolConformanceDescriptor(
                   cast<NormalProtocolConformance>(getProtocolConformance()));

  case Kind::EnumCase:
    return mangler.mangleEnumCase(getDecl());

  case Kind::FieldOffset:
    return mangler.mangleFieldOffset(getDecl());

  case Kind::DirectProtocolWitnessTable:
    return mangler.mangleDirectProtocolWitnessTable(getProtocolConformance());

  case Kind::GenericProtocolWitnessTableInstantiationFunction:
    return mangler.mangleGenericProtocolWitnessTableInstantiationFunction(
                                                    getProtocolConformance());

  case Kind::ProtocolWitnessTablePattern:
    return mangler.mangleProtocolWitnessTablePattern(getProtocolConformance());

  case Kind::ProtocolWitnessTableLazyAccessFunction:
    return mangler.mangleProtocolWitnessTableLazyAccessFunction(getType(),
                                                    getProtocolConformance());

  case Kind::ProtocolWitnessTableLazyCacheVariable:
    return mangler.mangleProtocolWitnessTableLazyCacheVariable(getType(),
                                                    getProtocolConformance());

  case Kind::AssociatedTypeWitnessTableAccessFunction: {
    auto assocConf = getAssociatedConformance();
    return mangler.mangleAssociatedTypeWitnessTableAccessFunction(
                getProtocolConformance(), assocConf.first, assocConf.second);
  }

  case Kind::CoroutineContinuationPrototype:
    return mangler.mangleCoroutineContinuationPrototype(
                                            cast<SILFunctionType>(getType()));

    // An Objective-C class reference reference. The symbol is private, so
    // the mangling is unimportant; it should just be readable in LLVM IR.
  case Kind::ObjCClassRef: {
    llvm::SmallString<64> tempBuffer;
    StringRef name = cast<ClassDecl>(getDecl())->getObjCRuntimeName(tempBuffer);
    std::string Result("\01l_OBJC_CLASS_REF_$_");
    Result.append(name.data(), name.size());
    return Result;
  }

    // An Objective-C class reference;  not a swift mangling.
  case Kind::ObjCClass: {
    llvm::SmallString<64> TempBuffer;
    StringRef Name = cast<ClassDecl>(getDecl())->getObjCRuntimeName(TempBuffer);
    std::string Result("OBJC_CLASS_$_");
    Result.append(Name.data(), Name.size());
    return Result;
  }

    // An Objective-C metaclass reference;  not a swift mangling.
  case Kind::ObjCMetaclass: {
    llvm::SmallString<64> TempBuffer;
    StringRef Name = cast<ClassDecl>(getDecl())->getObjCRuntimeName(TempBuffer);
    std::string Result("OBJC_METACLASS_$_");
    Result.append(Name.data(), Name.size());
    return Result;
  }

  case Kind::SILFunction: {
    std::string Result(getSILFunction()->getName());
    if (isDynamicallyReplaceable()) {
      Result.append("TI");
    }
    return Result;
  }
  case Kind::DynamicallyReplaceableFunctionImpl: {
    assert(isa<AbstractFunctionDecl>(getDecl()));
    std::string Result;
    if (auto *Constructor = dyn_cast<ConstructorDecl>(getDecl())) {
      Result = mangler.mangleConstructorEntity(Constructor, true,
                                               /*isCurried=*/false);
    } else  {
      Result = mangler.mangleEntity(getDecl(), /*isCurried=*/false);
    }
    Result.append("TI");
    return Result;
  }

  case Kind::DynamicallyReplaceableFunctionVariable: {
    std::string Result(getSILFunction()->getName());
    Result.append("TX");
    return Result;
  }

  case Kind::DynamicallyReplaceableFunctionKey: {
    std::string Result(getSILFunction()->getName());
    Result.append("Tx");
    return Result;
  }


  case Kind::DynamicallyReplaceableFunctionVariableAST: {
    assert(isa<AbstractFunctionDecl>(getDecl()));
    std::string Result;
    if (auto *Constructor = dyn_cast<ConstructorDecl>(getDecl())) {
      Result = mangler.mangleConstructorEntity(Constructor, true,
                                               /*isCurried=*/false);
    } else  {
      Result = mangler.mangleEntity(getDecl(), /*isCurried=*/false);
    }
    Result.append("TX");
    return Result;
  }

  case Kind::DynamicallyReplaceableFunctionKeyAST: {
    assert(isa<AbstractFunctionDecl>(getDecl()));
    std::string Result;
    if (auto *Constructor = dyn_cast<ConstructorDecl>(getDecl())) {
      Result = mangler.mangleConstructorEntity(Constructor, true,
                                               /*isCurried=*/false);
    } else  {
      Result = mangler.mangleEntity(getDecl(), /*isCurried=*/false);
    }
    Result.append("Tx");
    return Result;
  }

  case Kind::SILGlobalVariable:
    return getSILGlobalVariable()->getName();

  case Kind::ReflectionBuiltinDescriptor:
    return mangler.mangleReflectionBuiltinDescriptor(getType());
  case Kind::ReflectionFieldDescriptor:
    return mangler.mangleReflectionFieldDescriptor(getType());
  case Kind::ReflectionAssociatedTypeDescriptor:
    return mangler.mangleReflectionAssociatedTypeDescriptor(
                                                    getProtocolConformance());
  }
  llvm_unreachable("bad entity kind!");
}

SILLinkage LinkEntity::getLinkage(ForDefinition_t forDefinition) const {
  // For when `this` is a protocol conformance of some kind.
  auto getLinkageAsConformance = [&] {
    return getLinkageForProtocolConformance(
        getProtocolConformance()->getRootNormalConformance(), forDefinition);
  };

  switch (getKind()) {
  case Kind::DispatchThunk:
  case Kind::DispatchThunkInitializer:
  case Kind::DispatchThunkAllocator: {
    auto *decl = getDecl();

    // Protocol requirements don't have their own access control
    if (auto *proto = dyn_cast<ProtocolDecl>(decl->getDeclContext()))
      decl = proto;

    return getSILLinkage(getDeclLinkage(decl), forDefinition);
  }

  case Kind::MethodDescriptor:
  case Kind::MethodDescriptorInitializer:
  case Kind::MethodDescriptorAllocator: {
    auto *decl = getDecl();

    // Protocol requirements don't have their own access control
    if (auto *proto = dyn_cast<ProtocolDecl>(decl->getDeclContext()))
      decl = proto;

    // Method descriptors for internal class initializers can be referenced
    // from outside the module.
    if (auto *ctor = dyn_cast<ConstructorDecl>(decl)) {
      auto *classDecl = cast<ClassDecl>(ctor->getDeclContext());
      if (classDecl->getEffectiveAccess() == AccessLevel::Open)
        decl = classDecl;
    }

    return getSILLinkage(getDeclLinkage(decl), forDefinition);
  }

  // Most type metadata depend on the formal linkage of their type.
  case Kind::ValueWitnessTable: {
    auto type = getType();

    // Builtin types, (), () -> () and so on are in the runtime.
    if (!type.getAnyNominal())
      return getSILLinkage(FormalLinkage::PublicUnique, forDefinition);

    // Imported types.
    if (isAccessorLazilyGenerated(getTypeMetadataAccessStrategy(type)))
      return SILLinkage::Shared;

    // Everything else is only referenced inside its module.
    return SILLinkage::Private;
  }

  case Kind::ObjCMetadataUpdateFunction:
  case Kind::TypeMetadataInstantiationCache:
  case Kind::TypeMetadataInstantiationFunction:
  case Kind::TypeMetadataSingletonInitializationCache:
  case Kind::TypeMetadataCompletionFunction:
  case Kind::TypeMetadataPattern:
    return SILLinkage::Private;

  case Kind::TypeMetadataLazyCacheVariable: {
    auto type = getType();

    // Imported types, non-primitive structural types.
    if (isAccessorLazilyGenerated(getTypeMetadataAccessStrategy(type)))
      return SILLinkage::Shared;

    // Everything else is only referenced inside its module.
    return SILLinkage::Private;
  }

  case Kind::TypeMetadata:
    switch (getMetadataAddress()) {
    case TypeMetadataAddress::FullMetadata:
      // The full metadata object is private to the containing module.
      return SILLinkage::Private;
    case TypeMetadataAddress::AddressPoint: {
      auto *nominal = getType().getAnyNominal();
      return getSILLinkage(nominal
                           ? getDeclLinkage(nominal)
                           : FormalLinkage::PublicUnique,
                           forDefinition);
    }
    }
    llvm_unreachable("bad kind");

  // ...but we don't actually expose individual value witnesses (right now).
  case Kind::ValueWitness: {
    auto *nominal = getType().getAnyNominal();
    if (getDeclLinkage(nominal) == FormalLinkage::PublicNonUnique)
      return SILLinkage::Shared;
    return forDefinition ? SILLinkage::Private : SILLinkage::PrivateExternal;
  }

  // Foreign type metadata candidates are always shared; the runtime
  // does the uniquing.
  case Kind::ForeignTypeMetadataCandidate:
    return SILLinkage::Shared;

  case Kind::TypeMetadataAccessFunction:
    switch (getTypeMetadataAccessStrategy(getType())) {
    case MetadataAccessStrategy::PublicUniqueAccessor:
      return getSILLinkage(FormalLinkage::PublicUnique, forDefinition);
    case MetadataAccessStrategy::HiddenUniqueAccessor:
      return getSILLinkage(FormalLinkage::HiddenUnique, forDefinition);
    case MetadataAccessStrategy::PrivateAccessor:
      return getSILLinkage(FormalLinkage::Private, forDefinition);
    case MetadataAccessStrategy::ForeignAccessor:
    case MetadataAccessStrategy::NonUniqueAccessor:
      return SILLinkage::Shared;
    }
    llvm_unreachable("bad metadata access kind");

  case Kind::ObjCClassRef:
    return SILLinkage::Private;

  // Continuation prototypes need to be external or else LLVM will fret.
  case Kind::CoroutineContinuationPrototype:
    return SILLinkage::PublicExternal;


  case Kind::EnumCase: {
    auto *elementDecl = cast<EnumElementDecl>(getDecl());
    return getSILLinkage(getDeclLinkage(elementDecl), forDefinition);
  }

  case Kind::FieldOffset: {
    auto *varDecl = cast<VarDecl>(getDecl());

    auto linkage = getDeclLinkage(varDecl);

    // Resilient classes don't expose field offset symbols.
    if (cast<ClassDecl>(varDecl->getDeclContext())->isResilient()) {
      assert(linkage != FormalLinkage::PublicNonUnique &&
            "Cannot have a resilient class with non-unique linkage");

      if (linkage == FormalLinkage::PublicUnique)
        linkage = FormalLinkage::HiddenUnique;
    }

    return getSILLinkage(linkage, forDefinition);
  }

  case Kind::PropertyDescriptor: {
    // Return the linkage of the getter, which may be more permissive than the
    // property itself (for instance, with a private/internal property whose
    // accessor is @inlinable or @usableFromInline)
    auto getterDecl = cast<AbstractStorageDecl>(getDecl())->getGetter();
    return getSILLinkage(getDeclLinkage(getterDecl), forDefinition);
  }

  case Kind::AssociatedConformanceDescriptor:
  case Kind::ObjCClass:
  case Kind::ObjCMetaclass:
  case Kind::SwiftMetaclassStub:
  case Kind::NominalTypeDescriptor:
  case Kind::ClassMetadataBaseOffset:
  case Kind::ProtocolDescriptor:
  case Kind::ProtocolRequirementsBaseDescriptor:
  case Kind::MethodLookupFunction:
    return getSILLinkage(getDeclLinkage(getDecl()), forDefinition);

  case Kind::AssociatedTypeDescriptor:
    return getSILLinkage(getDeclLinkage(getAssociatedType()->getProtocol()),
                         forDefinition);

  case Kind::DirectProtocolWitnessTable:
  case Kind::ProtocolConformanceDescriptor:
    return getLinkageAsConformance();

  case Kind::ProtocolWitnessTablePattern:
    if (getLinkageAsConformance() == SILLinkage::Shared)
      return SILLinkage::Shared;
    return SILLinkage::Private;

  case Kind::ProtocolWitnessTableLazyAccessFunction:
  case Kind::ProtocolWitnessTableLazyCacheVariable: {
    auto *nominal = getType().getAnyNominal();
    assert(nominal);
    if (getDeclLinkage(nominal) == FormalLinkage::Private ||
        getLinkageAsConformance() == SILLinkage::Private) {
      return SILLinkage::Private;
    } else {
      return SILLinkage::Shared;
    }
  }

  case Kind::AssociatedTypeWitnessTableAccessFunction:
  case Kind::DefaultAssociatedConformanceAccessor:
  case Kind::GenericProtocolWitnessTableInstantiationFunction:
    return SILLinkage::Private;

  case Kind::DynamicallyReplaceableFunctionKey:
  case Kind::SILFunction:
    return getSILFunction()->getEffectiveSymbolLinkage();

  case Kind::DynamicallyReplaceableFunctionImpl:
  case Kind::DynamicallyReplaceableFunctionKeyAST:
    return getSILLinkage(getDeclLinkage(getDecl()), forDefinition);


  case Kind::DynamicallyReplaceableFunctionVariable:
    return getSILFunction()->getEffectiveSymbolLinkage();
  case Kind::DynamicallyReplaceableFunctionVariableAST:
    return getSILLinkage(getDeclLinkage(getDecl()), forDefinition);

  case Kind::SILGlobalVariable:
    return getSILGlobalVariable()->getLinkage();

  case Kind::ReflectionBuiltinDescriptor:
  case Kind::ReflectionFieldDescriptor: {
    // Reflection descriptors for imported types have shared linkage,
    // since we may emit them in other TUs in the same module.
    if (auto *nominal = getType().getAnyNominal())
      if (getDeclLinkage(nominal) == FormalLinkage::PublicNonUnique)
        return SILLinkage::Shared;
    return SILLinkage::Private;
  }
  case Kind::ReflectionAssociatedTypeDescriptor:
    if (getLinkageAsConformance() == SILLinkage::Shared)
      return SILLinkage::Shared;
    return SILLinkage::Private;

  case Kind::ModuleDescriptor:
  case Kind::ExtensionDescriptor:
  case Kind::AnonymousDescriptor:
    return SILLinkage::Shared;
  }
  llvm_unreachable("bad link entity kind");
}

static bool isAvailableExternally(IRGenModule &IGM, SILFunction *F) {
  // TODO
  return true;
}

static bool isAvailableExternally(IRGenModule &IGM, const DeclContext *dc) {
  dc = dc->getModuleScopeContext();
  if (isa<ClangModuleUnit>(dc) ||
      dc == IGM.getSILModule().getAssociatedContext())
    return false;
  return true;
}

static bool isAvailableExternally(IRGenModule &IGM, const Decl *decl) {
  return isAvailableExternally(IGM, decl->getDeclContext());
}

static bool isAvailableExternally(IRGenModule &IGM, Type type) {
  if (auto decl = type->getAnyNominal())
    return isAvailableExternally(IGM, decl->getDeclContext());
  return true;
}

bool LinkEntity::isAvailableExternally(IRGenModule &IGM) const {
  switch (getKind()) {
  case Kind::DispatchThunk:
  case Kind::DispatchThunkInitializer:
  case Kind::DispatchThunkAllocator: {
    auto *decl = getDecl();

    // Protocol requirements don't have their own access control
    if (auto *proto = dyn_cast<ProtocolDecl>(decl->getDeclContext()))
      decl = proto;

    return ::isAvailableExternally(IGM, getDecl());
  }

  case Kind::MethodDescriptor:
  case Kind::MethodDescriptorInitializer:
  case Kind::MethodDescriptorAllocator: {
    auto *decl = getDecl();

    // Protocol requirements don't have their own access control
    if (auto *proto = dyn_cast<ProtocolDecl>(decl->getDeclContext()))
      decl = proto;

    // Method descriptors for internal class initializers can be referenced
    // from outside the module.
    if (auto *ctor = dyn_cast<ConstructorDecl>(decl)) {
      auto *classDecl = cast<ClassDecl>(ctor->getDeclContext());
      if (classDecl->getEffectiveAccess() == AccessLevel::Open)
        decl = classDecl;
    }

    return ::isAvailableExternally(IGM, getDecl());
  }

  case Kind::ValueWitnessTable:
  case Kind::TypeMetadata:
    return ::isAvailableExternally(IGM, getType());

  case Kind::ForeignTypeMetadataCandidate:
    assert(!::isAvailableExternally(IGM, getType()));
    return false;

  case Kind::ObjCClass:
  case Kind::ObjCMetaclass:
    // FIXME: Removing this triggers a linker bug
    return true;

  case Kind::AssociatedConformanceDescriptor:
  case Kind::SwiftMetaclassStub:
  case Kind::ClassMetadataBaseOffset:
  case Kind::PropertyDescriptor:
  case Kind::NominalTypeDescriptor:
  case Kind::ProtocolDescriptor:
  case Kind::ProtocolRequirementsBaseDescriptor:
  case Kind::MethodLookupFunction:
    return ::isAvailableExternally(IGM, getDecl());

  case Kind::AssociatedTypeDescriptor:
    return ::isAvailableExternally(
                           IGM,
                           (const Decl *)getAssociatedType()->getProtocol());

  case Kind::EnumCase:
    return ::isAvailableExternally(IGM, getDecl());

  case Kind::DirectProtocolWitnessTable:
  case Kind::ProtocolConformanceDescriptor:
    return ::isAvailableExternally(IGM, getProtocolConformance()->getDeclContext());

  case Kind::ProtocolWitnessTablePattern:
  case Kind::ObjCClassRef:
  case Kind::ModuleDescriptor:
  case Kind::ExtensionDescriptor:
  case Kind::AnonymousDescriptor:
  case Kind::TypeMetadataInstantiationCache:
  case Kind::TypeMetadataInstantiationFunction:
  case Kind::TypeMetadataSingletonInitializationCache:
  case Kind::TypeMetadataCompletionFunction:
  case Kind::TypeMetadataPattern:
  case Kind::DefaultAssociatedConformanceAccessor:
    return false;
  case Kind::DynamicallyReplaceableFunctionKey:
  case Kind::DynamicallyReplaceableFunctionVariable:
    return true;

  case Kind::SILFunction:
    return ::isAvailableExternally(IGM, getSILFunction());

  case Kind::FieldOffset: {
    return ::isAvailableExternally(IGM,
                                   cast<VarDecl>(getDecl())
                                     ->getDeclContext()
                                     ->getInnermostTypeContext());
  }
  
  case Kind::ObjCMetadataUpdateFunction:
  case Kind::ValueWitness:
  case Kind::TypeMetadataAccessFunction:
  case Kind::TypeMetadataLazyCacheVariable:
  case Kind::ProtocolWitnessTableLazyAccessFunction:
  case Kind::ProtocolWitnessTableLazyCacheVariable:
  case Kind::AssociatedTypeWitnessTableAccessFunction:
  case Kind::GenericProtocolWitnessTableInstantiationFunction:
  case Kind::SILGlobalVariable:
  case Kind::ReflectionBuiltinDescriptor:
  case Kind::ReflectionFieldDescriptor:
  case Kind::ReflectionAssociatedTypeDescriptor:
  case Kind::CoroutineContinuationPrototype:
  case Kind::DynamicallyReplaceableFunctionVariableAST:
  case Kind::DynamicallyReplaceableFunctionImpl:
  case Kind::DynamicallyReplaceableFunctionKeyAST:
    llvm_unreachable("Relative reference to unsupported link entity");
  }
  llvm_unreachable("bad link entity kind");
}

llvm::Type *LinkEntity::getDefaultDeclarationType(IRGenModule &IGM) const {
  switch (getKind()) {
  case Kind::ModuleDescriptor:
  case Kind::ExtensionDescriptor:
  case Kind::AnonymousDescriptor:
  case Kind::NominalTypeDescriptor:
  case Kind::PropertyDescriptor:
    return IGM.TypeContextDescriptorTy;
  case Kind::ProtocolDescriptor:
    return IGM.ProtocolDescriptorStructTy;
  case Kind::AssociatedTypeDescriptor:
  case Kind::AssociatedConformanceDescriptor:
  case Kind::ProtocolRequirementsBaseDescriptor:
    return IGM.ProtocolRequirementStructTy;
  case Kind::ProtocolConformanceDescriptor:
    return IGM.ProtocolConformanceDescriptorTy;
  case Kind::ObjCClassRef:
    return IGM.ObjCClassPtrTy;
  case Kind::ObjCClass:
  case Kind::ObjCMetaclass:
  case Kind::SwiftMetaclassStub:
    return IGM.ObjCClassStructTy;
  case Kind::TypeMetadataLazyCacheVariable:
    return IGM.TypeMetadataPtrTy;
  case Kind::TypeMetadataSingletonInitializationCache:
    // TODO: put a cache variable on IGM
    return llvm::StructType::get(IGM.getLLVMContext(),
                                 {IGM.TypeMetadataPtrTy, IGM.Int8PtrTy});
  case Kind::TypeMetadata:
    switch (getMetadataAddress()) {
    case TypeMetadataAddress::FullMetadata:
      if (getType().getClassOrBoundGenericClass())
        return IGM.FullHeapMetadataStructTy;
      else
        return IGM.FullTypeMetadataStructTy;
    case TypeMetadataAddress::AddressPoint:
      return IGM.TypeMetadataStructTy;
    }
    
  case Kind::TypeMetadataPattern:
    // TODO: Use a real type?
    return IGM.Int8Ty;
    
  case Kind::ClassMetadataBaseOffset:
    // TODO: put a cache variable on IGM
    return llvm::StructType::get(IGM.getLLVMContext(), {
      IGM.SizeTy,  // Immediate members offset
      IGM.Int32Ty, // Negative size in words
      IGM.Int32Ty  // Positive size in words
    });
    
  case Kind::TypeMetadataInstantiationCache:
    // TODO: put a cache variable on IGM
    return llvm::ArrayType::get(IGM.Int8PtrTy,
                                NumGenericMetadataPrivateDataWords);
  case Kind::ReflectionBuiltinDescriptor:
  case Kind::ReflectionFieldDescriptor:
  case Kind::ReflectionAssociatedTypeDescriptor:
    return IGM.FieldDescriptorTy;
  case Kind::ValueWitnessTable:
  case Kind::DirectProtocolWitnessTable:
  case Kind::ProtocolWitnessTablePattern:
    return IGM.WitnessTableTy;
  case Kind::FieldOffset:
    return IGM.SizeTy;
  case Kind::EnumCase:
    return IGM.Int32Ty;
  case Kind::ProtocolWitnessTableLazyCacheVariable:
    return IGM.WitnessTablePtrTy;
  case Kind::SILFunction:
    return IGM.FunctionPtrTy->getPointerTo();
  case Kind::MethodDescriptor:
  case Kind::MethodDescriptorInitializer:
  case Kind::MethodDescriptorAllocator:
    return IGM.MethodDescriptorStructTy;
  case Kind::DynamicallyReplaceableFunctionKey:
    return IGM.DynamicReplacementKeyTy;
  case Kind::DynamicallyReplaceableFunctionVariable:
    return IGM.DynamicReplacementLinkEntryTy;
  default:
    llvm_unreachable("declaration LLVM type not specified");
  }
}

Alignment LinkEntity::getAlignment(IRGenModule &IGM) const {
  switch (getKind()) {
  case Kind::ModuleDescriptor:
  case Kind::ExtensionDescriptor:
  case Kind::AnonymousDescriptor:
  case Kind::NominalTypeDescriptor:
  case Kind::ProtocolDescriptor:
  case Kind::AssociatedTypeDescriptor:
  case Kind::AssociatedConformanceDescriptor:
  case Kind::ProtocolConformanceDescriptor:
  case Kind::ProtocolRequirementsBaseDescriptor:
  case Kind::ReflectionBuiltinDescriptor:
  case Kind::ReflectionFieldDescriptor:
  case Kind::ReflectionAssociatedTypeDescriptor:
  case Kind::PropertyDescriptor:
  case Kind::EnumCase:
  case Kind::MethodDescriptor:
  case Kind::MethodDescriptorInitializer:
  case Kind::MethodDescriptorAllocator:
    return Alignment(4);
  case Kind::ObjCClassRef:
  case Kind::ObjCClass:
  case Kind::TypeMetadataLazyCacheVariable:
  case Kind::TypeMetadataSingletonInitializationCache:
  case Kind::TypeMetadata:
  case Kind::TypeMetadataPattern:
  case Kind::ClassMetadataBaseOffset:
  case Kind::TypeMetadataInstantiationCache:
  case Kind::ValueWitnessTable:
  case Kind::FieldOffset:
  case Kind::ProtocolWitnessTableLazyCacheVariable:
  case Kind::DirectProtocolWitnessTable:
  case Kind::ProtocolWitnessTablePattern:
  case Kind::ObjCMetaclass:
  case Kind::SwiftMetaclassStub:
  case Kind::DynamicallyReplaceableFunctionVariable:
  case Kind::DynamicallyReplaceableFunctionKey:
    return IGM.getPointerAlignment();
  case Kind::SILFunction:
    return Alignment(1);
  default:
    llvm_unreachable("alignment not specified");
  }
}

bool LinkEntity::isWeakImported(ModuleDecl *module) const {
  switch (getKind()) {
  case Kind::SILGlobalVariable:
    if (getSILGlobalVariable()->getDecl())
      return getSILGlobalVariable()->getDecl()->isWeakImported(module);
    return false;
  case Kind::DynamicallyReplaceableFunctionKey:
  case Kind::DynamicallyReplaceableFunctionVariable:
  case Kind::SILFunction: {
    // For imported functions check the Clang declaration.
    if (auto clangOwner = getSILFunction()->getClangNodeOwner())
      return clangOwner->isWeakImported(module);

    // For native functions check a flag on the SILFunction
    // itself.
    if (getSILFunction()->isWeakLinked())
      return getSILFunction()->isAvailableExternally();
    return false;
  }

  case Kind::AssociatedConformanceDescriptor:
  case Kind::DefaultAssociatedConformanceAccessor: {
    // Associated conformance descriptors use the protocol as
    // their declaration, but are weak linked if the associated
    // type stored in extra storage area is weak linked.
    auto assocConformance = getAssociatedConformance();
    auto *depMemTy = assocConformance.first->castTo<DependentMemberType>();
    return depMemTy->getAssocType()->isWeakImported(module);
  }

  case Kind::TypeMetadata:
  case Kind::TypeMetadataAccessFunction: {
    if (auto *nominalDecl = getType()->getAnyNominal())
      return nominalDecl->isWeakImported(module);
    return false;
  }

  case Kind::DispatchThunk:
  case Kind::DispatchThunkInitializer:
  case Kind::DispatchThunkAllocator:
  case Kind::MethodDescriptor:
  case Kind::MethodDescriptorInitializer:
  case Kind::MethodDescriptorAllocator:
  case Kind::MethodLookupFunction:
  case Kind::EnumCase:
  case Kind::FieldOffset:
  case Kind::ObjCClass:
  case Kind::ObjCClassRef:
  case Kind::ObjCMetaclass:
  case Kind::SwiftMetaclassStub:
  case Kind::ObjCMetadataUpdateFunction:
  case Kind::ClassMetadataBaseOffset:
  case Kind::PropertyDescriptor:
  case Kind::NominalTypeDescriptor:
  case Kind::ModuleDescriptor:
  case Kind::ProtocolDescriptor:
  case Kind::ProtocolRequirementsBaseDescriptor:
  case Kind::AssociatedTypeDescriptor:
  case Kind::DynamicallyReplaceableFunctionKeyAST:
  case Kind::DynamicallyReplaceableFunctionVariableAST:
  case Kind::DynamicallyReplaceableFunctionImpl:
    return getDecl()->isWeakImported(module);

  // TODO: Revisit some of the below, for weak conformances.
  case Kind::TypeMetadataPattern:
  case Kind::TypeMetadataInstantiationCache:
  case Kind::TypeMetadataInstantiationFunction:
  case Kind::TypeMetadataSingletonInitializationCache:
  case Kind::TypeMetadataCompletionFunction:
  case Kind::ExtensionDescriptor:
  case Kind::AnonymousDescriptor:
  case Kind::DirectProtocolWitnessTable:
  case Kind::ProtocolWitnessTablePattern:
  case Kind::GenericProtocolWitnessTableInstantiationFunction:
  case Kind::AssociatedTypeWitnessTableAccessFunction:
  case Kind::ReflectionAssociatedTypeDescriptor:
  case Kind::ProtocolConformanceDescriptor:
  case Kind::ProtocolWitnessTableLazyAccessFunction:
  case Kind::ProtocolWitnessTableLazyCacheVariable:
  case Kind::ValueWitness:
  case Kind::ValueWitnessTable:
  case Kind::TypeMetadataLazyCacheVariable:
  case Kind::ForeignTypeMetadataCandidate:
  case Kind::ReflectionBuiltinDescriptor:
  case Kind::ReflectionFieldDescriptor:
  case Kind::CoroutineContinuationPrototype:
    return false;
  }

  llvm_unreachable("Bad link entity kind");
}

const SourceFile *LinkEntity::getSourceFileForEmission() const {
  const SourceFile *sf;
  
  // Shared-linkage entities don't get emitted with any particular file.
  if (hasSharedVisibility(getLinkage(NotForDefinition)))
    return nullptr;
  
  auto getSourceFileForDeclContext =
  [](const DeclContext *dc) -> const SourceFile * {
    if (!dc)
      return nullptr;
    return dc->getParentSourceFile();
  };
  
  switch (getKind()) {
  case Kind::DispatchThunk:
  case Kind::DispatchThunkInitializer:
  case Kind::DispatchThunkAllocator:
  case Kind::MethodDescriptor:
  case Kind::MethodDescriptorInitializer:
  case Kind::MethodDescriptorAllocator:
  case Kind::MethodLookupFunction:
  case Kind::EnumCase:
  case Kind::FieldOffset:
  case Kind::ObjCClass:
  case Kind::ObjCMetaclass:
  case Kind::SwiftMetaclassStub:
  case Kind::ObjCMetadataUpdateFunction:
  case Kind::ClassMetadataBaseOffset:
  case Kind::PropertyDescriptor:
  case Kind::NominalTypeDescriptor:
  case Kind::TypeMetadataPattern:
  case Kind::TypeMetadataInstantiationCache:
  case Kind::TypeMetadataInstantiationFunction:
  case Kind::TypeMetadataSingletonInitializationCache:
  case Kind::TypeMetadataCompletionFunction:
  case Kind::ProtocolDescriptor:
  case Kind::ProtocolRequirementsBaseDescriptor:
  case Kind::AssociatedTypeDescriptor:
  case Kind::AssociatedConformanceDescriptor:
  case Kind::DefaultAssociatedConformanceAccessor:
  case Kind::DynamicallyReplaceableFunctionVariableAST:
  case Kind::DynamicallyReplaceableFunctionKeyAST:
  case Kind::DynamicallyReplaceableFunctionImpl:
    sf = getSourceFileForDeclContext(getDecl()->getDeclContext());
    if (!sf)
      return nullptr;
    break;
  
  case Kind::SILFunction:
  case Kind::DynamicallyReplaceableFunctionVariable:
  case Kind::DynamicallyReplaceableFunctionKey:
    sf = getSourceFileForDeclContext(getSILFunction()->getDeclContext());
    if (!sf)
      return nullptr;
    break;
  
  case Kind::SILGlobalVariable:
    if (auto decl = getSILGlobalVariable()->getDecl()) {
      sf = getSourceFileForDeclContext(decl->getDeclContext());
      if (!sf)
        return nullptr;
    } else {
      return nullptr;
    }
    break;
    
  case Kind::DirectProtocolWitnessTable:
  case Kind::ProtocolWitnessTablePattern:
  case Kind::GenericProtocolWitnessTableInstantiationFunction:
  case Kind::AssociatedTypeWitnessTableAccessFunction:
  case Kind::ReflectionAssociatedTypeDescriptor:
  case Kind::ProtocolConformanceDescriptor:
  case Kind::ProtocolWitnessTableLazyCacheVariable:
  case Kind::ProtocolWitnessTableLazyAccessFunction:
    sf = getSourceFileForDeclContext(
      getProtocolConformance()->getRootNormalConformance()->getDeclContext());
    if (!sf)
      return nullptr;
    break;
    
  case Kind::TypeMetadata: {
    auto ty = getType();
    // Only fully concrete nominal type metadata gets emitted eagerly.
    auto nom = ty->getAnyNominal();
    if (!nom || nom->isGenericContext())
      return nullptr;
    
    sf = getSourceFileForDeclContext(nom);
    if (!sf)
      return nullptr;
    break;
  }

  // Always shared linkage
  case Kind::ModuleDescriptor:
  case Kind::ExtensionDescriptor:
  case Kind::AnonymousDescriptor:
  case Kind::ObjCClassRef:
  case Kind::TypeMetadataAccessFunction:
  case Kind::TypeMetadataLazyCacheVariable:
  case Kind::ForeignTypeMetadataCandidate:
    return nullptr;

  // TODO
  case Kind::CoroutineContinuationPrototype:
  case Kind::ReflectionFieldDescriptor:
  case Kind::ReflectionBuiltinDescriptor:
  case Kind::ValueWitness:
  case Kind::ValueWitnessTable:
    return nullptr;
  }
  
  return sf;
}