SILDeclRef.cpp

//===--- SILDeclRef.cpp - Implements SILDeclRef ---------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "swift/SIL/SILDeclRef.h"
#include "swift/AST/ASTContext.h"
#include "swift/AST/ASTMangler.h"
#include "swift/AST/AnyFunctionRef.h"
#include "swift/AST/Initializer.h"
#include "swift/AST/ParameterList.h"
#include "swift/AST/PropertyWrappers.h"
#include "swift/AST/SourceFile.h"
#include "swift/Basic/Assertions.h"
#include "swift/ClangImporter/ClangImporter.h"
#include "swift/ClangImporter/ClangModule.h"
#include "swift/SIL/SILLinkage.h"
#include "swift/SIL/SILLocation.h"
#include "swift/SILOptimizer/Utils/SpecializationMangler.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attr.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclObjC.h"
#include "clang/AST/Mangle.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/raw_ostream.h"
using namespace swift;

/// Get the method dispatch mechanism for a method.
MethodDispatch
swift::getMethodDispatch(AbstractFunctionDecl *method) {
  // Some methods are forced to be statically dispatched.
  if (method->hasForcedStaticDispatch())
    return MethodDispatch::Static;

  if (method->getAttrs().hasAttribute<DistributedActorAttr>())
    return MethodDispatch::Static;

  // Import-as-member declarations are always statically referenced.
  if (method->isImportAsMember())
    return MethodDispatch::Static;

  auto dc = method->getDeclContext();

  if (dc->getSelfClassDecl()) {
    if (method->shouldUseObjCDispatch()) {
      return MethodDispatch::Class;
    }

    // Final methods can be statically referenced.
    if (method->isFinal())
      return MethodDispatch::Static;

    // Imported class methods are dynamically dispatched.
    if (method->isObjC() && method->hasClangNode())
      return MethodDispatch::Class;

    // Members defined directly inside a class are dynamically dispatched.
    if (isa<ClassDecl>(dc)) {
      // Native convenience initializers are not dynamically dispatched unless
      // required.
      if (auto ctor = dyn_cast<ConstructorDecl>(method)) {
        if (!ctor->isRequired() && !ctor->isDesignatedInit()
            && !requiresForeignEntryPoint(ctor))
          return MethodDispatch::Static;
      }
      return MethodDispatch::Class;
    }
  }

  // Otherwise, it can be referenced statically.
  return MethodDispatch::Static;
}

bool swift::requiresForeignToNativeThunk(ValueDecl *vd) {
  // Functions imported from C, Objective-C methods imported from Objective-C,
  // as well as methods in @objc protocols (even protocols defined in Swift)
  // require a foreign to native thunk.
  auto dc = vd->getDeclContext();
  if (auto proto = dyn_cast<ProtocolDecl>(dc))
    if (proto->isObjC())
      return true;

  if (auto fd = dyn_cast<FuncDecl>(vd))
    return fd->hasClangNode();

  return false;
}

bool swift::requiresForeignEntryPoint(ValueDecl *vd) {
  assert(!isa<AbstractStorageDecl>(vd));

  if (vd->shouldUseObjCDispatch()) {
    return true;
  }

  if (vd->isObjC() && isa<ProtocolDecl>(vd->getDeclContext()))
    return true;

  if (vd->isImportAsMember())
    return true;

  if (vd->hasClangNode())
    return true;

  if (auto *accessor = dyn_cast<AccessorDecl>(vd)) {
    // Property accessors should be generated alongside the property.
    if (accessor->isGetterOrSetter()) {
      auto *asd = accessor->getStorage();
      if (asd->isObjC() && asd->hasClangNode())
        return true;
    }
  }

  return false;
}

SILDeclRef::SILDeclRef(ValueDecl *vd, SILDeclRef::Kind kind, bool isForeign,
                       bool isDistributedThunk, bool isKnownToBeLocal,
                       bool isRuntimeAccessible,
                       SILDeclRef::BackDeploymentKind backDeploymentKind,
                       AutoDiffDerivativeFunctionIdentifier *derivativeId)
    : loc(vd), kind(kind), isForeign(isForeign), distributedThunk(isDistributedThunk),
      isKnownToBeLocal(isKnownToBeLocal),
      isRuntimeAccessible(isRuntimeAccessible),
      backDeploymentKind(backDeploymentKind), defaultArgIndex(0),
      isAsyncLetClosure(0), pointer(derivativeId) {}

SILDeclRef::SILDeclRef(SILDeclRef::Loc baseLoc, bool asForeign,
                       bool asDistributed, bool asDistributedKnownToBeLocal)
    : isRuntimeAccessible(false),
      backDeploymentKind(SILDeclRef::BackDeploymentKind::None),
      defaultArgIndex(0), isAsyncLetClosure(0),
      pointer((AutoDiffDerivativeFunctionIdentifier *)nullptr) {
  if (auto *vd = baseLoc.dyn_cast<ValueDecl*>()) {
    if (auto *fd = dyn_cast<FuncDecl>(vd)) {
      // Map FuncDecls directly to Func SILDeclRefs.
      loc = fd;
      kind = Kind::Func;
    }
    // Map ConstructorDecls to the Allocator SILDeclRef of the constructor.
    else if (auto *cd = dyn_cast<ConstructorDecl>(vd)) {
      loc = cd;
      kind = Kind::Allocator;
    }
    // Map EnumElementDecls to the EnumElement SILDeclRef of the element.
    else if (auto *ed = dyn_cast<EnumElementDecl>(vd)) {
      loc = ed;
      kind = Kind::EnumElement;
    }
    // VarDecl constants require an explicit kind.
    else if (isa<VarDecl>(vd)) {
      llvm_unreachable("must create SILDeclRef for VarDecl with explicit kind");
    }
    // Map DestructorDecls to the Deallocator of the destructor.
    else if (auto dtor = dyn_cast<DestructorDecl>(vd)) {
      loc = dtor;
      kind = Kind::Deallocator;
    }
    else {
      llvm_unreachable("invalid loc decl for SILDeclRef!");
    }
  } else if (auto *ACE = baseLoc.dyn_cast<AbstractClosureExpr *>()) {
    loc = ACE;
    kind = Kind::Func;
    if (ACE->getASTContext().LangOpts.hasFeature(
            Feature::RegionBasedIsolation)) {
      assert(ACE->getASTContext().LangOpts.hasFeature(
                 Feature::SendingArgsAndResults) &&
             "Sending args and results should always be enabled");
      if (auto *autoClosure = dyn_cast<AutoClosureExpr>(ACE)) {
        isAsyncLetClosure =
            autoClosure->getThunkKind() == AutoClosureExpr::Kind::AsyncLet;
      }
    }
  } else {
    llvm_unreachable("impossible SILDeclRef loc");
  }

  isForeign = asForeign;
  distributedThunk = asDistributed;
  isKnownToBeLocal = asDistributedKnownToBeLocal;
}

SILDeclRef::SILDeclRef(SILDeclRef::Loc baseLoc,
                       GenericSignature prespecializedSig)
    : SILDeclRef(baseLoc, false, false) {
  pointer = prespecializedSig.getPointer();
}

std::optional<AnyFunctionRef> SILDeclRef::getAnyFunctionRef() const {
  switch (getLocKind()) {
  case LocKind::Decl:
    if (auto *afd = getAbstractFunctionDecl())
      return AnyFunctionRef(afd);
    return std::nullopt;
  case LocKind::Closure:
    return AnyFunctionRef(getAbstractClosureExpr());
  case LocKind::File:
    return std::nullopt;
  }
  llvm_unreachable("Unhandled case in switch");
}

DeclContext *SILDeclRef::getInnermostDeclContext() const {
  if (!loc)
    return nullptr;
  switch (getLocKind()) {
  case LocKind::Decl:
    return getDecl()->getInnermostDeclContext();
  case LocKind::Closure:
    return getAbstractClosureExpr();
  case LocKind::File:
    return getFileUnit();
  }
  llvm_unreachable("Unhandled case in switch");
}

ASTContext &SILDeclRef::getASTContext() const {
  auto *DC = getInnermostDeclContext();
  assert(DC && "Must have a decl context");
  return DC->getASTContext();
}

std::optional<AvailabilityRange> SILDeclRef::getAvailabilityForLinkage() const {
  // Back deployment thunks and fallbacks don't have availability since they
  // are non-ABI.
  // FIXME: Generalize this check to all kinds of non-ABI functions.
  if (backDeploymentKind != SILDeclRef::BackDeploymentKind::None)
    return std::nullopt;

  return getDecl()->getAvailabilityForLinkage();
}

bool SILDeclRef::isThunk() const {
  return isForeignToNativeThunk() || isNativeToForeignThunk() ||
         isDistributedThunk() || isBackDeploymentThunk();
}

bool SILDeclRef::isClangImported() const {
  if (!hasDecl())
    return false;

  ValueDecl *d = getDecl();
  DeclContext *moduleContext = d->getDeclContext()->getModuleScopeContext();

  if (isa<ClangModuleUnit>(moduleContext)) {
    if (isClangGenerated())
      return true;

    if (isa<ConstructorDecl>(d) || isa<EnumElementDecl>(d))
      return !isForeign;

    if (auto *FD = dyn_cast<FuncDecl>(d))
      if (isa<AccessorDecl>(FD) ||
          isa<NominalTypeDecl>(d->getDeclContext()))
        return !isForeign;
  }
  return false;
}

bool SILDeclRef::isClangGenerated() const {
  if (!hasDecl())
    return false;

  return isClangGenerated(getDecl()->getClangNode());
}

// FIXME: this is a weird predicate.
bool SILDeclRef::isClangGenerated(ClangNode node) {
  if (auto nd = dyn_cast_or_null<clang::NamedDecl>(node.getAsDecl())) {
    // ie, 'static inline' functions for which we must ask Clang to emit a body
    // for explicitly
    if (!nd->isExternallyVisible())
      return true;
  }

  return false;
}

bool SILDeclRef::isImplicit() const {
  switch (getLocKind()) {
  case LocKind::Decl:
    return getDecl()->isImplicit();
  case LocKind::Closure:
    return getAbstractClosureExpr()->isImplicit();
  case LocKind::File:
    // Files are currently never considered implicit.
    return false;
  }
  llvm_unreachable("Unhandled case in switch");
}

bool SILDeclRef::hasUserWrittenCode() const {
  // Non-implicit decls generally have user-written code.
  if (!isImplicit()) {
    switch (kind) {
    case Kind::PropertyWrapperBackingInitializer: {
      // Only has user-written code if any of the property wrappers have
      // arguments to apply. Otherwise, it's just a forwarding initializer for
      // the wrappedValue.
      auto *var = cast<VarDecl>(getDecl());
      return llvm::any_of(var->getAttachedPropertyWrappers(), [&](auto *attr) {
        return attr->hasArgs();
      });
    }
    case Kind::PropertyWrapperInitFromProjectedValue:
      // Never has user-written code, is just a forwarding initializer.
      return false;
    default:
      if (auto decl = getDecl()) {
        // Declarations synthesized by ClangImporter by definition don't have
        // user written code, but despite that they aren't always marked
        // implicit.
        auto moduleContext = decl->getDeclContext()->getModuleScopeContext();
        if (isa<ClangModuleUnit>(moduleContext))
          return false;
      }
      // TODO: This checking is currently conservative, we ought to
      // exhaustively handle all the cases here, and use emitOrDelayFunction
      // in more cases to take advantage of it.
      return true;
    }
    llvm_unreachable("Unhandled case in switch!");
  }

  // Implicit decls generally don't have user-written code, but some splice
  // user code into their body.
  switch (kind) {
  case Kind::Func: {
    if (getAbstractClosureExpr()) {
      // Auto-closures have user-written code.
      if (auto *ACE = getAutoClosureExpr()) {
        // Currently all types of auto-closures can contain user code. Note this
        // logic does not affect delayed emission, as we eagerly emit all
        // closure definitions. This does however affect profiling.
        switch (ACE->getThunkKind()) {
        case AutoClosureExpr::Kind::None:
        case AutoClosureExpr::Kind::SingleCurryThunk:
        case AutoClosureExpr::Kind::DoubleCurryThunk:
        case AutoClosureExpr::Kind::AsyncLet:
          return true;
        }
        llvm_unreachable("Unhandled case in switch!");
      }
      // Otherwise, assume an implicit closure doesn't have user code.
      return false;
    }

    // Lazy getters splice in the user-written initializer expr.
    if (auto *accessor = dyn_cast<AccessorDecl>(getFuncDecl())) {
      auto *storage = accessor->getStorage();
      if (accessor->isGetter() && !storage->isImplicit() &&
          storage->getAttrs().hasAttribute<LazyAttr>()) {
        return true;
      }
    }
    return false;
  }
  case Kind::StoredPropertyInitializer: {
    // Property wrapper initializers for the implicit backing storage can splice
    // in the user-written initializer on the original property.
    auto *var = cast<VarDecl>(getDecl());
    if (auto *originalProperty = var->getOriginalWrappedProperty()) {
      if (originalProperty->isPropertyMemberwiseInitializedWithWrappedType())
        return true;
    }
    return false;
  }
  case Kind::Allocator:
  case Kind::Initializer:
  case Kind::EnumElement:
  case Kind::Destroyer:
  case Kind::Deallocator:
  case Kind::IsolatedDeallocator:
  case Kind::GlobalAccessor:
  case Kind::DefaultArgGenerator:
  case Kind::IVarInitializer:
  case Kind::IVarDestroyer:
  case Kind::PropertyWrapperBackingInitializer:
  case Kind::PropertyWrapperInitFromProjectedValue:
  case Kind::EntryPoint:
  case Kind::AsyncEntryPoint:
    // Implicit decls for these don't splice in user-written code.
    return false;
  }
  llvm_unreachable("Unhandled case in switch!");
}

bool SILDeclRef::shouldBeEmittedForDebugger() const {
  if (!isFunc())
    return false;

  if (getASTContext().SILOpts.OptMode != OptimizationMode::NoOptimization)
    return false;;

  if (!getASTContext().SILOpts.ShouldFunctionsBePreservedToDebugger)
    return false;

  if (getASTContext().LangOpts.hasFeature(Feature::Embedded))
    return false;

  ValueDecl *decl = getDecl();
  DeclAttributes &attrs = decl->getAttrs();
  if (attrs.hasSemanticsAttr("no.preserve.debugger"))
    return false;

  if (getLinkage(ForDefinition) == SILLinkage::Shared)
    return false;
  
  if (auto decl = getDecl()) 
    if (!decl->isImplicit())
      return true;

  // Synthesized getters are still callable in the debugger.
  if (auto *accessor = dyn_cast_or_null<AccessorDecl>(getFuncDecl())) {
    return accessor->isSynthesized() && accessor->isGetterOrSetter();
  };

  return false;
}

namespace {
enum class LinkageLimit {
  /// No limit.
  None,
  /// The linkage should behave as if the decl is private.
  Private,
  /// The declaration is emitted on-demand; it should end up with internal
  /// or shared linkage.
  OnDemand,
  /// The declaration should never be made public.
  NeverPublic,
  /// The declaration should always be emitted into the client,
  AlwaysEmitIntoClient,
};
} // end anonymous namespace

/// Compute the linkage limit for a given SILDeclRef. This augments the
/// mapping of access level to linkage to provide a maximum or minimum linkage.
static LinkageLimit getLinkageLimit(SILDeclRef constant) {
  using Limit = LinkageLimit;
  using Kind = SILDeclRef::Kind;

  auto *d = constant.getDecl();
  ASSERT(ABIRoleInfo(d).providesAPI() && "getLinkageLimit() for ABI decl?");

  // Back deployment thunks and fallbacks are emitted into the client.
  if (constant.backDeploymentKind != SILDeclRef::BackDeploymentKind::None)
    return Limit::AlwaysEmitIntoClient;

  if (auto *fn = dyn_cast<AbstractFunctionDecl>(d)) {
    // Native-to-foreign thunks for top-level decls are created on-demand,
    // unless they are marked @_cdecl, in which case they expose a dedicated
    // entry-point with the visibility of the function.
    //
    // Native-to-foreign thunks for methods are always just private, since
    // they're anchored by Objective-C metadata.
    auto &attrs = fn->getAttrs();
    if (constant.isNativeToForeignThunk() && !attrs.hasAttribute<CDeclAttr>()) {
      auto isTopLevel = fn->getDeclContext()->isModuleScopeContext();
      return isTopLevel ? Limit::OnDemand : Limit::Private;
    }
  }

  if (auto fn = constant.getFuncDecl()) {
    // Forced-static-dispatch functions are created on-demand and have
    // at best shared linkage.
    if (fn->hasForcedStaticDispatch())
      return Limit::OnDemand;
  }
  
  if (isa<DestructorDecl>(d)) {
    // The destructor of a class implemented with @_objcImplementation is only
    // ever called by its ObjC thunk, so it should not be public.
    if (d->getDeclContext()->getSelfNominalTypeDecl()->hasClangNode())
      return Limit::OnDemand;
  }

  switch (constant.kind) {
  case Kind::Func:
  case Kind::Allocator:
  case Kind::Initializer:
  case Kind::Deallocator:
  case Kind::IsolatedDeallocator:
  case Kind::Destroyer: {
    // @_alwaysEmitIntoClient declarations are like the default arguments of
    // public functions; they are roots for dead code elimination and have
    // serialized bodies, but no public symbol in the generated binary.
    if (d->getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>())
      return Limit::AlwaysEmitIntoClient;
    if (auto accessor = dyn_cast<AccessorDecl>(d)) {
      auto *storage = accessor->getStorage();
      if (storage->getAttrs().hasAttribute<AlwaysEmitIntoClientAttr>())
        return Limit::AlwaysEmitIntoClient;
    }
    break;
  }
  case Kind::EnumElement:
    return Limit::OnDemand;

  case Kind::GlobalAccessor:
    // global unsafeMutableAddressor should be kept hidden if its decl
    // is resilient.
    return cast<VarDecl>(d)->isResilient() ? Limit::NeverPublic : Limit::None;

  case Kind::DefaultArgGenerator:
    // If the default argument is to be serialized, only use non-ABI public
    // linkage. If the argument is not to be serialized, don't use a limit.
    // This actually means that default arguments *can be ABI public* if
    // `isSerialized()` returns false and the effective access level is public,
    // which happens under `-enable-testing` with an internal decl.
    return constant.isSerialized() ? Limit::AlwaysEmitIntoClient : Limit::None;

  case Kind::PropertyWrapperBackingInitializer:
  case Kind::PropertyWrapperInitFromProjectedValue: {
    if (!d->getDeclContext()->isTypeContext()) {
      // If the backing initializer is to be serialized, only use non-ABI public
      // linkage. If the initializer is not to be serialized, don't use a limit.
      // This actually means that it *can be ABI public* if `isSerialized()`
      // returns false and the effective access level is public, which happens
      // under `-enable-testing` with an internal decl.
      return constant.isSerialized() ? Limit::AlwaysEmitIntoClient
                                     : Limit::None;
    }
    // Otherwise, regular property wrapper backing initializers (for properties)
    // are treated just like stored property initializers.
    LLVM_FALLTHROUGH;
  }
  case Kind::StoredPropertyInitializer: {
    // Stored property initializers get the linkage of their containing type.
    // There are three cases:
    //
    // 1) Type is formally @_fixed_layout/@frozen. Root initializers can be
    //    declared @inlinable. The property initializer must only reference
    //    public symbols, and is serialized, so we give it PublicNonABI linkage.
    //
    // 2) Type is not formally @_fixed_layout/@frozen and the module is not
    //    resilient. Root initializers can be declared @inlinable. This is the
    //    annoying case. We give the initializer public linkage if the type is
    //    public.
    //
    // 3) Type is resilient. The property initializer is never public because
    //    root initializers cannot be @inlinable.
    //
    // FIXME: Get rid of case 2 somehow.
    if (constant.isSerialized())
      return Limit::AlwaysEmitIntoClient;

    // FIXME: This should always be true.
    if (d->getModuleContext()->isStrictlyResilient())
      return Limit::NeverPublic;

    break;
  }
  case Kind::IVarInitializer:
  case Kind::IVarDestroyer:
    // ivar initializers and destroyers are completely contained within the
    // class from which they come, and never get seen externally.
    return Limit::NeverPublic;

  case Kind::EntryPoint:
  case Kind::AsyncEntryPoint:
    llvm_unreachable("Already handled");
  }
  return Limit::None;
}

SILLinkage SILDeclRef::getDefinitionLinkage() const {
  using Limit = LinkageLimit;

  auto privateLinkage = [&]() {
    // Private decls may still be serialized if they are e.g in an inlinable
    // function. In such a case, they receive shared linkage.
    return isNotSerialized() ? SILLinkage::Private : SILLinkage::Shared;
  };

  // Prespecializations are public.
  if (getSpecializedSignature())
    return SILLinkage::Public;

  // Closures can only be referenced from the same file.
  if (getAbstractClosureExpr())
    return privateLinkage();

  // The main entry-point is public.
  if (kind == Kind::EntryPoint)
    return SILLinkage::Public;
  if (kind == Kind::AsyncEntryPoint) {
    // async main entrypoint is referenced only from @main and
    // they are in the same SIL module. Hiding this entrypoint
    // from other object file makes it possible to link multiple
    // executable targets for SwiftPM testing with -entry-point-function-name
    return SILLinkage::Private;
  }

  // Calling convention thunks have shared linkage.
  if (isForeignToNativeThunk())
    return SILLinkage::Shared;

  // Declarations imported from Clang modules have shared linkage.
  if (isClangImported())
    return SILLinkage::Shared;

  const auto limit = getLinkageLimit(*this);
  if (limit == Limit::Private)
    return privateLinkage();

  auto *decl = getDecl();

  if (isPropertyWrapperBackingInitializer()) {
    auto *dc = decl->getDeclContext();

    // External property wrapper backing initializers have linkage based
    // on the access level of their function.
    if (isa<ParamDecl>(decl)) {
      if (isa<AbstractClosureExpr>(dc))
        return privateLinkage();

      decl = cast<ValueDecl>(dc->getAsDecl());
    }

    // Property wrappers in types have linkage based on the access level of
    // their nominal.
    if (dc->isTypeContext())
      decl = cast<NominalTypeDecl>(dc);
  }

  // Stored property initializers have linkage based on the access level of
  // their nominal.
  if (isStoredPropertyInitializer())
    decl = cast<NominalTypeDecl>(
               decl->getDeclContext()->getImplementedObjCContext());

  // Compute the effective access level, taking e.g testable into consideration.
  auto effectiveAccess = decl->getEffectiveAccess();

  // Private setter implementations for an internal storage declaration should
  // be at least internal as well, so that a dynamically-writable
  // keypath can be formed from other files in the same module.
  if (auto *accessor = dyn_cast<AccessorDecl>(decl)) {
    auto storageAccess = accessor->getStorage()->getEffectiveAccess();
    if (accessor->isSetter() && storageAccess >= AccessLevel::Internal)
      effectiveAccess = std::max(effectiveAccess, AccessLevel::Internal);
  }

  switch (effectiveAccess) {
  case AccessLevel::Private:
  case AccessLevel::FilePrivate:
    return privateLinkage();

  case AccessLevel::Internal:
    assert(!isSerialized() &&
           "Serialized decls should either be private (for decls in inlinable "
           "code), or they should be public");
    if (limit == Limit::OnDemand)
      return SILLinkage::Shared;
    return SILLinkage::Hidden;

  case AccessLevel::Package:
    switch (limit) {
    case Limit::None:
      return SILLinkage::Package;
    case Limit::AlwaysEmitIntoClient:
      // Drop the AEIC if the enclosing decl is not effectively public.
      // This matches what we do in the `internal` case.
      if (isSerialized())
        return SILLinkage::PackageNonABI;
      else return SILLinkage::Package;
    case Limit::OnDemand:
      return SILLinkage::Shared;
    case Limit::NeverPublic:
      return SILLinkage::Hidden;
    case Limit::Private:
      llvm_unreachable("Already handled");
    }
  case AccessLevel::Public:
  case AccessLevel::Open:
    switch (limit) {
    case Limit::None:
      return SILLinkage::Public;
    case Limit::AlwaysEmitIntoClient:
      return SILLinkage::PublicNonABI;
    case Limit::OnDemand:
      return SILLinkage::Shared;
    case Limit::NeverPublic:
      return SILLinkage::Hidden;
    case Limit::Private:
      llvm_unreachable("Already handled");
    }
  }
  llvm_unreachable("unhandled access");
}

SILLinkage SILDeclRef::getLinkage(ForDefinition_t forDefinition) const {
  // Add external to the linkage of the definition
  // (e.g. Public -> PublicExternal) if this is a declaration.
  auto linkage = getDefinitionLinkage();
  return forDefinition ? linkage : addExternalToLinkage(linkage);
}

SILDeclRef SILDeclRef::getDefaultArgGenerator(Loc loc,
                                              unsigned defaultArgIndex) {
  SILDeclRef result;
  result.loc = loc;
  result.kind = Kind::DefaultArgGenerator;
  result.defaultArgIndex = defaultArgIndex;
  return result;
}

SILDeclRef SILDeclRef::getMainDeclEntryPoint(ValueDecl *decl) {
  auto *file = cast<FileUnit>(decl->getDeclContext()->getModuleScopeContext());
  assert(file->getMainDecl() == decl);
  SILDeclRef result;
  result.loc = decl;
  result.kind = Kind::EntryPoint;
  return result;
}

SILDeclRef SILDeclRef::getAsyncMainDeclEntryPoint(ValueDecl *decl) {
  auto *file = cast<FileUnit>(decl->getDeclContext()->getModuleScopeContext());
  assert(file->getMainDecl() == decl);
  SILDeclRef result;
  result.loc = decl;
  result.kind = Kind::AsyncEntryPoint;
  return result;
}

SILDeclRef SILDeclRef::getAsyncMainFileEntryPoint(FileUnit *file) {
  assert(file->hasEntryPoint() && !file->getMainDecl());
  SILDeclRef result;
  result.loc = file;
  result.kind = Kind::AsyncEntryPoint;
  return result;
}

SILDeclRef SILDeclRef::getMainFileEntryPoint(FileUnit *file) {
  assert(file->hasEntryPoint() && !file->getMainDecl());
  SILDeclRef result;
  result.loc = file;
  result.kind = Kind::EntryPoint;
  return result;
}

bool SILDeclRef::hasClosureExpr() const {
  return loc.is<AbstractClosureExpr *>()
    && isa<ClosureExpr>(getAbstractClosureExpr());
}

bool SILDeclRef::hasAutoClosureExpr() const {
  return loc.is<AbstractClosureExpr *>()
    && isa<AutoClosureExpr>(getAbstractClosureExpr());
}

bool SILDeclRef::hasFuncDecl() const {
  return loc.is<ValueDecl *>() && isa<FuncDecl>(getDecl());
}

ClosureExpr *SILDeclRef::getClosureExpr() const {
  return dyn_cast_or_null<ClosureExpr>(getAbstractClosureExpr());
}
AutoClosureExpr *SILDeclRef::getAutoClosureExpr() const {
  return dyn_cast_or_null<AutoClosureExpr>(getAbstractClosureExpr());
}

FuncDecl *SILDeclRef::getFuncDecl() const {
  return dyn_cast_or_null<FuncDecl>(getDecl());
}

ModuleDecl *SILDeclRef::getModuleContext() const {
  if (hasDecl()) {
    return getDecl()->getModuleContext();
  } else if (hasFileUnit()) {
    return getFileUnit()->getParentModule();
  } else if (hasClosureExpr()) {
    return getClosureExpr()->getParentModule();
  } else if (hasAutoClosureExpr()) {
    return getAutoClosureExpr()->getParentModule();
  }
  llvm_unreachable("Unknown declaration reference");
}

bool SILDeclRef::isSetter() const {
  if (!hasDecl())
    return false;
  if (auto accessor = dyn_cast<AccessorDecl>(getDecl()))
    return accessor->isSetter();
  return false;
}

AbstractFunctionDecl *SILDeclRef::getAbstractFunctionDecl() const {
  return dyn_cast_or_null<AbstractFunctionDecl>(getDecl());
}

bool SILDeclRef::isInitAccessor() const {
  if (kind != Kind::Func || !hasDecl())
    return false;

  if (auto accessor = dyn_cast<AccessorDecl>(getDecl()))
    return accessor->getAccessorKind() == AccessorKind::Init;

  return false;
}

/// True if the function should be treated as transparent.
bool SILDeclRef::isTransparent() const {
  if (isEnumElement())
    return true;

  if (isStoredPropertyInitializer())
    return true;

  if (hasAutoClosureExpr()) {
    auto *ace = getAutoClosureExpr();
    switch (ace->getThunkKind()) {
    case AutoClosureExpr::Kind::None:
      return true;

    case AutoClosureExpr::Kind::AsyncLet:
    case AutoClosureExpr::Kind::DoubleCurryThunk:
    case AutoClosureExpr::Kind::SingleCurryThunk:
      break;
    }
  }

  // To support using metatypes as type hints in Embedded Swift. A default
  // argument generator might be returning a metatype, which we normally don't
  // support in Embedded Swift, but to still allow metatypes as type hints, we
  // make the generator always inline to the callee by marking it transparent.
  if (getASTContext().LangOpts.hasFeature(Feature::Embedded)) {
    if (isDefaultArgGenerator() && hasDecl()) {
      auto *decl = getDecl();
      auto *param = getParameterAt(decl, defaultArgIndex);
      Type paramType = param->getTypeOfDefaultExpr();
      if (paramType && paramType->is<MetatypeType>())
        return true;
    }
  }

  if (hasDecl()) {
    if (auto *AFD = dyn_cast<AbstractFunctionDecl>(getDecl()))
      return AFD->isTransparent();

    if (auto *ASD = dyn_cast<AbstractStorageDecl>(getDecl()))
      return ASD->isTransparent();
  }

  return false;
}

bool SILDeclRef::isSerialized() const {
  return getSerializedKind() == IsSerialized;
}

bool SILDeclRef::isNotSerialized() const {
  return getSerializedKind() == IsNotSerialized;
}

/// True if the function should have its body serialized.
SerializedKind_t SILDeclRef::getSerializedKind() const {
  if (auto closure = getAbstractClosureExpr()) {
    // Ask the AST if we're inside an @inlinable context.
    if (closure->getResilienceExpansion() == ResilienceExpansion::Minimal) {
      return IsSerialized;
    }

    return IsNotSerialized;
  }

  if (kind == Kind::EntryPoint || kind == Kind::AsyncEntryPoint)
    return IsNotSerialized;

  if (isIVarInitializerOrDestroyer())
    return IsNotSerialized;

  auto *d = getDecl();

  ASSERT(ABIRoleInfo(d).providesAPI()
            && "should not get serialization info from ABI-only decl");

  // Default and property wrapper argument generators are serialized if the
  // containing declaration is public.
  if (isDefaultArgGenerator() || (isPropertyWrapperBackingInitializer() &&
                                  isa<ParamDecl>(d))) {
    if (isPropertyWrapperBackingInitializer()) {
      if (auto *func = dyn_cast_or_null<ValueDecl>(d->getDeclContext()->getAsDecl())) {
        d = func;
      }
    }

    // Ask the AST if we're inside an @inlinable context.
    if (d->getDeclContext()->getResilienceExpansion()
          == ResilienceExpansion::Minimal) {
      return IsSerialized;
    }

    // Otherwise, check if the owning declaration is public.
    auto scope =
      d->getFormalAccessScope(/*useDC=*/nullptr,
                              /*treatUsableFromInlineAsPublic=*/true);

    if (scope.isPublic())
      return IsSerialized;
    return IsNotSerialized;
  }

  // Stored property initializers are inlinable if the type is explicitly
  // marked as @frozen.
  if (isStoredPropertyInitializer() || (isPropertyWrapperBackingInitializer() &&
                                        d->getDeclContext()->isTypeContext())) {
    auto *nominal = dyn_cast<NominalTypeDecl>(d->getDeclContext());

    // If this isn't in a nominal, it must be in an @objc @implementation
    // extension. We don't serialize those since clients outside the module
    // don't think of these as Swift classes.
    if (!nominal) {
      ASSERT(isa<ExtensionDecl>(d->getDeclContext()) &&
             cast<ExtensionDecl>(d->getDeclContext())->isObjCImplementation());
      return IsNotSerialized;
    }

    auto scope =
      nominal->getFormalAccessScope(/*useDC=*/nullptr,
                                    /*treatUsableFromInlineAsPublic=*/true);
    if (!scope.isPublic())
      return IsNotSerialized;
    if (nominal->isFormallyResilient())
      return IsNotSerialized;
    return IsSerialized;
  }

  // Note: if 'd' is a function, then 'dc' is the function itself, not
  // its parent context.
  auto *dc = d->getInnermostDeclContext();

  // Local functions are serializable if their parent function is
  // serializable.
  if (d->getDeclContext()->isLocalContext()) {
    if (dc->getResilienceExpansion() == ResilienceExpansion::Minimal)
      return IsSerialized;

    return IsNotSerialized;
  }

  // Anything else that is not public is not serializable.
  if (d->getEffectiveAccess() < AccessLevel::Public)
    return IsNotSerialized;

  // Enum element constructors are serializable if the enum is
  // @usableFromInline or public.
  if (isEnumElement())
    return IsSerialized;

  // 'read' and 'modify' accessors synthesized on-demand are serialized if
  // visible outside the module.
  if (auto fn = dyn_cast<FuncDecl>(d))
    if (!isClangImported() &&
        fn->hasForcedStaticDispatch())
      return IsSerialized;

  if (isForeignToNativeThunk())
    return IsSerialized;

  // The allocating entry point for designated initializers are serialized
  // if the class is @usableFromInline or public. Actors are excluded because
  // whether the init is designated is not clearly reflected in the source code.
  if (kind == SILDeclRef::Kind::Allocator) {
    auto *ctor = cast<ConstructorDecl>(d);
    if (auto classDecl = ctor->getDeclContext()->getSelfClassDecl()) {
      if (!classDecl->isAnyActor() && ctor->isDesignatedInit())
        if (!ctor->hasClangNode())
          return IsSerialized;
    }
  }

  if (isForeign) {
    // @objc thunks for methods are not serializable since they're only
    // referenced from the method table.
    if (d->getDeclContext()->isTypeContext())
      return IsNotSerialized;

    // @objc thunks for top-level functions are serializable since they're
    // referenced from @convention(c) conversions inside inlinable
    // functions.
    return IsSerialized;
  }

  // Declarations imported from Clang modules are serialized if
  // referenced from an inlinable context.
  if (isClangImported())
    return IsSerialized;

  // Handle back deployed functions. The original back deployed function
  // should not be serialized, but the thunk and fallback should be since they
  // need to be emitted into the client.
  if (isBackDeployed()) {
    switch (backDeploymentKind) {
      case BackDeploymentKind::None:
        return IsNotSerialized;
      case BackDeploymentKind::Fallback:
      case BackDeploymentKind::Thunk:
        return IsSerialized;
    }
  }

  // Otherwise, ask the AST if we're inside an @inlinable context.
  if (dc->getResilienceExpansion() == ResilienceExpansion::Minimal)
    return IsSerialized;

  return IsNotSerialized;
}

/// True if the function has an @inline(never) attribute.
bool SILDeclRef::isNoinline() const {
  if (!hasDecl())
    return false;

  auto *decl = getDecl();
  ASSERT(ABIRoleInfo(decl).providesAPI()
            && "should not get inline attr from ABI-only decl");

  if (auto *attr = decl->getAttrs().getAttribute<InlineAttr>())
    if (attr->getKind() == InlineKind::Never)
      return true;

  if (auto *accessorDecl = dyn_cast<AccessorDecl>(decl)) {
    auto *storage = accessorDecl->getStorage();
    if (auto *attr = storage->getAttrs().getAttribute<InlineAttr>())
      if (attr->getKind() == InlineKind::Never)
        return true;
  }

  return false;
}

/// True if the function has the @inline(__always) attribute.
bool SILDeclRef::isAlwaysInline() const {
  swift::Decl *decl = nullptr;
  if (hasDecl()) {
    decl = getDecl();
  } else if (auto *ce = getAbstractClosureExpr()) {
    // Closures within @inline(__always) functions should be always inlined, too.
    // Note that this is different from @inline(never), because closures inside
    // @inline(never) _can_ be inlined within the inline-never function.
    decl = ce->getParent()->getInnermostDeclarationDeclContext();
    if (!decl)
      return false;
  } else {
    return false;
  }

  ASSERT(ABIRoleInfo(decl).providesAPI()
            && "should not get inline attr from ABI-only decl");

  if (auto attr = decl->getAttrs().getAttribute<InlineAttr>())
    if (attr->getKind() == InlineKind::Always)
      return true;

  if (auto *accessorDecl = dyn_cast<AccessorDecl>(decl)) {
    auto *storage = accessorDecl->getStorage();
    if (auto *attr = storage->getAttrs().getAttribute<InlineAttr>())
      if (attr->getKind() == InlineKind::Always)
        return true;
  }

  return false;
}

bool SILDeclRef::isBackDeployed() const {
  if (!hasDecl())
    return false;

  auto *decl = getDecl();

  ASSERT(ABIRoleInfo(decl).providesAPI()
            && "should not get backDeployed from ABI-only decl");

  if (auto afd = dyn_cast<AbstractFunctionDecl>(decl))
    return afd->isBackDeployed(getASTContext());

  return false;
}

bool SILDeclRef::isForeignToNativeThunk() const {
  // If this isn't a native entry-point, it's not a foreign-to-native thunk.
  if (isForeign)
    return false;

  // Non-decl entry points are never natively foreign, so they would never
  // have a foreign-to-native thunk.
  if (!hasDecl())
    return false;
  // A default argument generator for a C++ function is a Swift function, so no
  // thunk needed.
  if (isDefaultArgGenerator())
    return false;
  if (requiresForeignToNativeThunk(getDecl()))
    return true;
  // ObjC initializing constructors and factories are foreign.
  // We emit a special native allocating constructor though.
  if (isa<ConstructorDecl>(getDecl())
      && (kind == Kind::Initializer
          || cast<ConstructorDecl>(getDecl())->isFactoryInit())
      && getDecl()->hasClangNode())
    return true;
  return false;
}

bool SILDeclRef::isNativeToForeignThunk() const {
  // If this isn't a foreign entry-point, it's not a native-to-foreign thunk.
  if (!isForeign)
    return false;

  switch (getLocKind()) {
  case LocKind::Decl:
    // A decl with a clang node doesn't have a native entry-point to forward
    // onto.
    if (getDecl()->hasClangNode())
      return false;
    // No thunk is required if the decl directly references an external decl.
    if (getDecl()->getAttrs().hasAttribute<ExternAttr>())
      return false;

    // Only certain kinds of SILDeclRef can expose native-to-foreign thunks.
    return kind == Kind::Func || kind == Kind::Initializer ||
           kind == Kind::Deallocator;
  case LocKind::Closure:
    // We can have native-to-foreign thunks over closures.
    return true;
  case LocKind::File:
    return false;
  }
  llvm_unreachable("Unhandled case in switch");
}

bool SILDeclRef::isDistributedThunk() const {
  if (!distributedThunk)
    return false;
  return kind == Kind::Func;
}
bool SILDeclRef::isDistributed() const {
  if (!hasFuncDecl())
    return false;

  if (auto decl = getFuncDecl()) {
    return decl->isDistributed();
  }

  return false;
}

bool SILDeclRef::isBackDeploymentFallback() const {
  if (backDeploymentKind != BackDeploymentKind::Fallback)
    return false;
  return kind == Kind::Func || kind == Kind::Initializer ||
         kind == Kind::Allocator;
}

bool SILDeclRef::isBackDeploymentThunk() const {
  if (backDeploymentKind != BackDeploymentKind::Thunk)
    return false;
  return kind == Kind::Func || kind == Kind::Initializer ||
         kind == Kind::Allocator;
}

/// Use the Clang importer to mangle a Clang declaration.
static void mangleClangDeclViaImporter(raw_ostream &buffer,
                                       const clang::NamedDecl *clangDecl,
                                       ASTContext &ctx) {
  auto *importer = static_cast<ClangImporter *>(ctx.getClangModuleLoader());
  importer->getMangledName(buffer, clangDecl);
}

static std::string mangleClangDecl(Decl *decl, bool isForeign) {
  auto clangDecl = decl->getClangDecl();

  if (auto namedClangDecl = dyn_cast<clang::DeclaratorDecl>(clangDecl)) {
    if (auto asmLabel = namedClangDecl->getAttr<clang::AsmLabelAttr>()) {
      std::string s(1, '\01');
      s += asmLabel->getLabel();
      return s;
    } else if (namedClangDecl->hasAttr<clang::OverloadableAttr>() ||
               decl->getASTContext().LangOpts.EnableCXXInterop) {
      std::string storage;
      llvm::raw_string_ostream SS(storage);
      mangleClangDeclViaImporter(SS, namedClangDecl, decl->getASTContext());
      return SS.str();
    }
    return namedClangDecl->getName().str();
  } else if (auto objcDecl = dyn_cast<clang::ObjCMethodDecl>(clangDecl)) {
    if (objcDecl->isDirectMethod() && isForeign) {
      std::string storage;
      llvm::raw_string_ostream SS(storage);
      clang::ASTContext &ctx = clangDecl->getASTContext();
      std::unique_ptr<clang::MangleContext> mangler(ctx.createMangleContext());
      mangler->mangleObjCMethodName(objcDecl, SS, /*includePrefixByte=*/true,
                                    /*includeCategoryNamespace=*/false);
      return SS.str();
    }
  }

  return "";
}

std::string SILDeclRef::mangle(ManglingKind MKind) const {
  ASSERT(!hasDecl() || ABIRoleInfo(getDecl()).providesAPI()
            && "SILDeclRef mangling ABI decl directly?");

  using namespace Mangle;
  ASTMangler mangler(getASTContext());

  if (auto *derivativeFunctionIdentifier = getDerivativeFunctionIdentifier()) {
    std::string originalMangled = asAutoDiffOriginalFunction().mangle(MKind);
    auto *silParameterIndices = autodiff::getLoweredParameterIndices(
        derivativeFunctionIdentifier->getParameterIndices(),
        getDecl()->getInterfaceType()->castTo<AnyFunctionType>());
    // FIXME: is this correct in the presence of curried types?
    auto *resultIndices = autodiff::getFunctionSemanticResultIndices(
      asAutoDiffOriginalFunction().getAbstractFunctionDecl(),
      derivativeFunctionIdentifier->getParameterIndices());
    AutoDiffConfig silConfig(
        silParameterIndices, resultIndices,
        derivativeFunctionIdentifier->getDerivativeGenericSignature());
    return mangler.mangleAutoDiffDerivativeFunction(
        asAutoDiffOriginalFunction().getAbstractFunctionDecl(),
        derivativeFunctionIdentifier->getKind(),
        silConfig);
  }

  // As a special case, Clang functions and globals don't get mangled at all
  // - except \c objc_direct decls.
  if (hasDecl() && !isDefaultArgGenerator()) {
    if (getDecl()->getClangDecl()) {
      if (!isForeignToNativeThunk() && !isNativeToForeignThunk()) {
        auto clangMangling = mangleClangDecl(getDecl(), isForeign);
        if (!clangMangling.empty())
          return clangMangling;
      }
    }
  }

  // Mangle prespecializations.
  if (getSpecializedSignature()) {
    SILDeclRef nonSpecializedDeclRef = *this;
    nonSpecializedDeclRef.pointer =
        (AutoDiffDerivativeFunctionIdentifier *)nullptr;
    auto mangledNonSpecializedString = nonSpecializedDeclRef.mangle();
    auto *funcDecl = cast<AbstractFunctionDecl>(getDecl());
    auto genericSig = funcDecl->getGenericSignature();
    return GenericSpecializationMangler::manglePrespecialization(
        getASTContext(), mangledNonSpecializedString, genericSig, getSpecializedSignature());
  }

  ASTMangler::SymbolKind SKind = ASTMangler::SymbolKind::Default;
  switch (MKind) {
    case SILDeclRef::ManglingKind::Default:
      if (isForeign) {
        SKind = ASTMangler::SymbolKind::SwiftAsObjCThunk;
      } else if (isForeignToNativeThunk()) {
        SKind = ASTMangler::SymbolKind::ObjCAsSwiftThunk;
      } else if (isDistributedThunk()) {
        SKind = ASTMangler::SymbolKind::DistributedThunk;
      } else if (isBackDeploymentThunk()) {
        SKind = ASTMangler::SymbolKind::BackDeploymentThunk;
      } else if (isBackDeploymentFallback()) {
        SKind = ASTMangler::SymbolKind::BackDeploymentFallback;
      }
      break;
    case SILDeclRef::ManglingKind::DynamicThunk:
      SKind = ASTMangler::SymbolKind::DynamicThunk;
      break;
  }

  switch (kind) {
  case SILDeclRef::Kind::Func:
    if (auto *ACE = getAbstractClosureExpr())
      return mangler.mangleClosureEntity(ACE, SKind);

    // As a special case, functions can have manually mangled names.
    // Use the SILGen name only for the original non-thunked, non-curried entry
    // point.
    if (auto NameA = getDecl()->getAttrs().getAttribute<SILGenNameAttr>())
      if (!NameA->Name.empty() && !isThunk()) {
        return NameA->Name.str();
      }

    if (auto *ExternA = ExternAttr::find(getDecl()->getAttrs(), ExternKind::C)) {
      assert(isa<FuncDecl>(getDecl()) && "non-FuncDecl with @_extern should be rejected by typechecker");
      return ExternA->getCName(cast<FuncDecl>(getDecl())).str();
    }

    // Use a given cdecl name for native-to-foreign thunks.
    if (auto CDeclA = getDecl()->getAttrs().getAttribute<CDeclAttr>())
      if (isNativeToForeignThunk()) {
        // If this is an @implementation @_cdecl, mangle it like the clang
        // function it implements.
        if (auto objcInterface = getDecl()->getImplementedObjCDecl()) {
          auto clangMangling = mangleClangDecl(objcInterface, isForeign);
          if (!clangMangling.empty())
            return clangMangling;
        }
        return CDeclA->Name.str();
      }

    if (SKind == ASTMangler::SymbolKind::DistributedThunk) {
      return mangler.mangleDistributedThunk(cast<FuncDecl>(getDecl()));
    }

    // Otherwise, fall through into the 'other decl' case.
    LLVM_FALLTHROUGH;

  case SILDeclRef::Kind::EnumElement:
    return mangler.mangleEntity(getDecl(), SKind);

  case SILDeclRef::Kind::Deallocator:
    return mangler.mangleDestructorEntity(cast<DestructorDecl>(getDecl()),
                                          DestructorKind::Deallocating, SKind);

  case SILDeclRef::Kind::Destroyer:
    return mangler.mangleDestructorEntity(cast<DestructorDecl>(getDecl()),
                                          DestructorKind::NonDeallocating,
                                          SKind);

  case SILDeclRef::Kind::IsolatedDeallocator:
    return mangler.mangleDestructorEntity(cast<DestructorDecl>(getDecl()),
                                          DestructorKind::IsolatedDeallocating,
                                          SKind);

  case SILDeclRef::Kind::Allocator:
    // As a special case, initializers can have manually mangled names.
    // Use the SILGen name only for the original non-thunked, non-curried entry
    // point.
    if (auto NameA = getDecl()->getAttrs().getAttribute<SILGenNameAttr>()) {
      if (!NameA->Name.empty() && !isThunk()) {
        return NameA->Name.str();
      }
    }

    return mangler.mangleConstructorEntity(cast<ConstructorDecl>(getDecl()),
                                           /*allocating*/ true,
                                           SKind);

  case SILDeclRef::Kind::Initializer:
    return mangler.mangleConstructorEntity(cast<ConstructorDecl>(getDecl()),
                                           /*allocating*/ false,
                                           SKind);

  case SILDeclRef::Kind::IVarInitializer:
  case SILDeclRef::Kind::IVarDestroyer:
    return mangler.mangleIVarInitDestroyEntity(cast<ClassDecl>(getDecl()),
                                  kind == SILDeclRef::Kind::IVarDestroyer,
                                  SKind);

  case SILDeclRef::Kind::GlobalAccessor:
    return mangler.mangleAccessorEntity(AccessorKind::MutableAddress,
                                        cast<AbstractStorageDecl>(getDecl()),
                                        /*isStatic*/ false,
                                        SKind);

  case SILDeclRef::Kind::DefaultArgGenerator:
    return mangler.mangleDefaultArgumentEntity(
                                        cast<DeclContext>(getDecl()),
                                        defaultArgIndex,
                                        SKind);

  case SILDeclRef::Kind::StoredPropertyInitializer:
    return mangler.mangleInitializerEntity(cast<VarDecl>(getDecl()), SKind);

  case SILDeclRef::Kind::PropertyWrapperBackingInitializer:
    return mangler.mangleBackingInitializerEntity(cast<VarDecl>(getDecl()),
                                                  SKind);

  case SILDeclRef::Kind::PropertyWrapperInitFromProjectedValue:
    return mangler.mangleInitFromProjectedValueEntity(cast<VarDecl>(getDecl()),
                                                      SKind);

  case SILDeclRef::Kind::AsyncEntryPoint: {
    return "async_Main";
  }
  case SILDeclRef::Kind::EntryPoint: {
    return getASTContext().getEntryPointFunctionName();
  }
  }

  llvm_unreachable("bad entity kind!");
}

// Returns true if the given JVP/VJP SILDeclRef requires a new vtable entry.
// FIXME(https://github.com/apple/swift/issues/54833): Also consider derived declaration `@derivative` attributes.
static bool derivativeFunctionRequiresNewVTableEntry(SILDeclRef declRef) {
  assert(declRef.getDerivativeFunctionIdentifier() &&
         "Expected a derivative function SILDeclRef");
  auto overridden = declRef.getOverridden();
  if (!overridden)
    return false;
  // Get the derived `@differentiable` attribute.
  auto *derivedDiffAttr = *llvm::find_if(
      declRef.getDecl()->getAttrs().getAttributes<DifferentiableAttr>(),
      [&](const DifferentiableAttr *derivedDiffAttr) {
        return derivedDiffAttr->getParameterIndices() ==
               declRef.getDerivativeFunctionIdentifier()->getParameterIndices();
      });
  assert(derivedDiffAttr && "Expected `@differentiable` attribute");
  // Otherwise, if the base `@differentiable` attribute specifies a derivative
  // function, then the derivative is inherited and no new vtable entry is
  // needed. Return false.
  auto baseDiffAttrs =
      overridden.getDecl()->getAttrs().getAttributes<DifferentiableAttr>();
  for (auto *baseDiffAttr : baseDiffAttrs) {
    if (baseDiffAttr->getParameterIndices() ==
        declRef.getDerivativeFunctionIdentifier()->getParameterIndices())
      return false;
  }
  // Otherwise, if there is no base `@differentiable` attribute exists, then a
  // new vtable entry is needed. Return true.
  return true;
}

bool SILDeclRef::requiresNewVTableEntry() const {
  if (getDerivativeFunctionIdentifier())
    if (derivativeFunctionRequiresNewVTableEntry(*this))
      return true;
  if (!hasDecl())
    return false;
  if (isBackDeploymentThunk())
    return false;
  auto fnDecl = dyn_cast<AbstractFunctionDecl>(getDecl());
  if (!fnDecl)
    return false;
  if (fnDecl->needsNewVTableEntry())
    return true;
  return false;
}

bool SILDeclRef::requiresNewWitnessTableEntry() const {
  return cast<AbstractFunctionDecl>(getDecl())->requiresNewWitnessTableEntry();
}

SILDeclRef SILDeclRef::getOverridden() const {
  if (!hasDecl())
    return SILDeclRef();
  auto overridden = getDecl()->getOverriddenDecl();
  if (!overridden)
    return SILDeclRef();
  return withDecl(overridden);
}

SILDeclRef SILDeclRef::getNextOverriddenVTableEntry() const {
  if (auto overridden = getOverridden()) {
    // Back deployed methods should not be overridden.
    assert(backDeploymentKind == SILDeclRef::BackDeploymentKind::None);

    // If we overrode a foreign decl or dynamic method, if this is an
    // accessor for a property that overrides an ObjC decl, or if it is an
    // @NSManaged property, then it won't be in the vtable.
    if (overridden.getDecl()->hasClangNode())
      return SILDeclRef();

    // Distributed thunks are not in the vtable.
    if (isDistributedThunk())
      return SILDeclRef();

    // An @objc convenience initializer can be "overridden" in the sense that
    // its selector is reclaimed by a subclass's convenience init with the
    // same name. The AST models this as an override for the purposes of
    // ObjC selector validation, but it isn't for Swift method dispatch
    // purposes.
    if (overridden.kind == SILDeclRef::Kind::Allocator) {
      auto overriddenCtor = cast<ConstructorDecl>(overridden.getDecl());
      if (!overriddenCtor->isDesignatedInit()
          && !overriddenCtor->isRequired())
        return SILDeclRef();
    }

    // Initializing entry points for initializers won't be in the vtable.
    // For Swift designated initializers, they're only used in super.init
    // chains, which can always be statically resolved. Other native Swift
    // initializers only have allocating entry points. ObjC initializers always
    // have the initializing entry point (corresponding to the -init method)
    // but those are never in the vtable.
    if (overridden.kind == SILDeclRef::Kind::Initializer) {
      return SILDeclRef();
    }

    // Overrides of @objc dynamic declarations are not in the vtable.
    if (overridden.getDecl()->shouldUseObjCDispatch()) {
      return SILDeclRef();
    }

    if (auto *accessor = dyn_cast<AccessorDecl>(overridden.getDecl())) {
      auto *asd = accessor->getStorage();
      if (asd->hasClangNode())
        return SILDeclRef();
      if (asd->shouldUseObjCDispatch()) {
        return SILDeclRef();
      }
    }

    // If we overrode a decl from an extension, it won't be in a vtable
    // either. This can occur for extensions to ObjC classes.
    if (isa<ExtensionDecl>(overridden.getDecl()->getDeclContext()))
      return SILDeclRef();

    // JVPs/VJPs are overridden only if the base declaration has a
    // `@differentiable` attribute with the same parameter indices.
    if (getDerivativeFunctionIdentifier()) {
      auto overriddenAttrs =
          overridden.getDecl()->getAttrs().getAttributes<DifferentiableAttr>();
      for (const auto *attr : overriddenAttrs) {
        if (attr->getParameterIndices() !=
            getDerivativeFunctionIdentifier()->getParameterIndices())
          continue;
        auto *overriddenDerivativeId =
            overridden.getDerivativeFunctionIdentifier();
        overridden.pointer =
            AutoDiffDerivativeFunctionIdentifier::get(
                overriddenDerivativeId->getKind(),
                overriddenDerivativeId->getParameterIndices(),
                attr->getDerivativeGenericSignature(),
                getDecl()->getASTContext());
        return overridden;
      }
      return SILDeclRef();
    }
    return overridden;
  }
  return SILDeclRef();
}

SILDeclRef SILDeclRef::getOverriddenWitnessTableEntry() const {
  auto bestOverridden =
    getOverriddenWitnessTableEntry(cast<AbstractFunctionDecl>(getDecl()));
  return withDecl(bestOverridden);
}

AbstractFunctionDecl *SILDeclRef::getOverriddenWitnessTableEntry(
                                                 AbstractFunctionDecl *func) {
  if (!isa<ProtocolDecl>(func->getDeclContext()))
    return func;

  AbstractFunctionDecl *bestOverridden = nullptr;

  SmallVector<AbstractFunctionDecl *, 4> stack;
  SmallPtrSet<AbstractFunctionDecl *, 4> visited;
  stack.push_back(func);
  visited.insert(func);

  while (!stack.empty()) {
    auto current = stack.back();
    stack.pop_back();

    auto overriddenDecls = current->getOverriddenDecls();
    if (overriddenDecls.empty()) {
      // This entry introduced a witness table entry. Determine whether it is
      // better than the best entry we've seen thus far.
      if (!bestOverridden ||
          ProtocolDecl::compare(
                        cast<ProtocolDecl>(current->getDeclContext()),
                        cast<ProtocolDecl>(bestOverridden->getDeclContext()))
            < 0) {
        bestOverridden = cast<AbstractFunctionDecl>(current);
      }

      continue;
    }

    // Add overridden declarations to the stack.
    for (auto overridden : overriddenDecls) {
      auto overriddenFunc = cast<AbstractFunctionDecl>(overridden);
      if (visited.insert(overriddenFunc).second)
        stack.push_back(overriddenFunc);
    }
  }

  return bestOverridden;
}

SILDeclRef SILDeclRef::getOverriddenVTableEntry() const {
  SILDeclRef cur = *this, next = *this;
  do {
    cur = next;
    if (cur.requiresNewVTableEntry())
      return cur;
    next = cur.getNextOverriddenVTableEntry();
  } while (next);

  return cur;
}

SILLocation SILDeclRef::getAsRegularLocation() const {
  switch (getLocKind()) {
  case LocKind::Decl:
    return RegularLocation(getDecl());
  case LocKind::Closure:
    return RegularLocation(getAbstractClosureExpr());
  case LocKind::File:
    return RegularLocation::getModuleLocation();
  }
  llvm_unreachable("Unhandled case in switch");
}

SubclassScope SILDeclRef::getSubclassScope() const {
  if (!hasDecl())
    return SubclassScope::NotApplicable;

  auto *decl = getDecl();

  if (!isa<AbstractFunctionDecl>(decl))
    return SubclassScope::NotApplicable;

  DeclContext *context = decl->getDeclContext();

  // Only methods in non-final classes go in the vtable.
  auto *classType = dyn_cast<ClassDecl>(context);
  if (!classType || classType->isFinal())
    return SubclassScope::NotApplicable;

  // If a method appears in the vtable of a class, we must give it's symbol
  // special consideration when computing visibility because the SIL-level
  // linkage does not map to the symbol's visibility in a straightforward
  // way.
  //
  // In particular, the rules are:
  // - If the class metadata is not resilient, then all method symbols must
  //   be visible from any translation unit where a subclass might be defined,
  //   because the subclass metadata will re-emit all vtable entries.
  //
  // - For resilient classes, we do the opposite: generally, a method's symbol
  //   can be hidden from other translation units, because we want to enforce
  //   that resilient access patterns are used for method calls and overrides.
  //
  //   Constructors and final methods are the exception here, because they can
  //   be called directly.

  // FIXME: This is too narrow. Any class with resilient metadata should
  // probably have this, at least for method overrides that don't add new
  // vtable entries.
  bool isStrictResilientClass = classType->isStrictlyResilient();

  if (auto *CD = dyn_cast<ConstructorDecl>(decl)) {
    if (isStrictResilientClass)
      return SubclassScope::NotApplicable;
    // Initializing entry points do not appear in the vtable.
    if (kind == SILDeclRef::Kind::Initializer)
      return SubclassScope::NotApplicable;
    // Non-required convenience inits do not appear in the vtable.
    if (!CD->isRequired() && !CD->isDesignatedInit())
      return SubclassScope::NotApplicable;
  } else if (isa<DestructorDecl>(decl)) {
    // Destructors do not appear in the vtable.
    return SubclassScope::NotApplicable;
  } else {
    assert(isa<FuncDecl>(decl));
  }

  // Various forms of thunks don't go in the vtable.
  if (isThunk() || isForeign)
    return SubclassScope::NotApplicable;

  // Default arg generators don't go in the vtable.
  if (isDefaultArgGenerator())
    return SubclassScope::NotApplicable;

  if (decl->isFinal()) {
    // Final methods only go in the vtable if they override something.
    if (!decl->getOverriddenDecl())
      return SubclassScope::NotApplicable;

    // In the resilient case, we're going to be making symbols _less_
    // visible, so make sure we stop now; final methods can always be
    // called directly.
    if (isStrictResilientClass)
      return SubclassScope::Internal;
  }

  assert(decl->getEffectiveAccess() <= classType->getEffectiveAccess() &&
         "class must be as visible as its members");

  if (isStrictResilientClass) {
    // The symbol should _only_ be reached via the vtable, so we're
    // going to make it hidden.
    return SubclassScope::Resilient;
  }

  switch (classType->getEffectiveAccess()) {
  case AccessLevel::Private:
  case AccessLevel::FilePrivate:
    // If the class is private, it can only be subclassed from the same
    // SILModule, so we don't need to do anything.
    return SubclassScope::NotApplicable;
  case AccessLevel::Internal:
  case AccessLevel::Package:
  case AccessLevel::Public:
    // If the class is internal or public, it can only be subclassed from
    // the same AST Module, but possibly a different SILModule.
    return SubclassScope::Internal;
  case AccessLevel::Open:
    // If the class is open, it can be subclassed from a different
    // AST Module. All method symbols are public.
    return SubclassScope::External;
  }

  llvm_unreachable("Unhandled access level in switch.");
}

Expr *SILDeclRef::getInitializationExpr() const {
  switch (kind) {
  case Kind::StoredPropertyInitializer: {
    auto *var = cast<VarDecl>(getDecl());
    auto *pbd = var->getParentPatternBinding();
    unsigned idx = pbd->getPatternEntryIndexForVarDecl(var);
    auto *init = pbd->getInit(idx);
    assert(!pbd->isInitializerSubsumed(idx));

    // If this is the backing storage for a property with an attached wrapper
    // that was initialized with `=`, use that expression as the initializer.
    if (auto originalProperty = var->getOriginalWrappedProperty()) {
      if (originalProperty->isPropertyMemberwiseInitializedWithWrappedType()) {
        auto wrapperInfo =
            originalProperty->getPropertyWrapperInitializerInfo();
        auto *placeholder = wrapperInfo.getWrappedValuePlaceholder();
        init = placeholder->getOriginalWrappedValue();
        assert(init);
      }
    }
    return init;
  }
  case Kind::PropertyWrapperBackingInitializer: {
    auto *var = cast<VarDecl>(getDecl());
    auto wrapperInfo = var->getPropertyWrapperInitializerInfo();
    assert(wrapperInfo.hasInitFromWrappedValue());
    return wrapperInfo.getInitFromWrappedValue();
  }
  case Kind::PropertyWrapperInitFromProjectedValue: {
    auto *var = cast<VarDecl>(getDecl());
    auto wrapperInfo = var->getPropertyWrapperInitializerInfo();
    assert(wrapperInfo.hasInitFromProjectedValue());
    return wrapperInfo.getInitFromProjectedValue();
  }
  default:
    return nullptr;
  }
}

unsigned SILDeclRef::getParameterListCount() const {
  // Only decls can introduce currying.
  if (!hasDecl())
    return 1;

  // Always uncurried even if the underlying function is curried.
  if (kind == Kind::DefaultArgGenerator || kind == Kind::EntryPoint ||
      kind == Kind::AsyncEntryPoint)
    return 1;

  auto *vd = getDecl();

  if (isa<AbstractFunctionDecl>(vd) || isa<EnumElementDecl>(vd)) {
    // For functions and enum elements, the number of parameter lists is the
    // same as in their interface type.
    return vd->getNumCurryLevels();
  } else if (isa<ClassDecl>(vd)) {
    return 2;
  } else if (isa<VarDecl>(vd)) {
    return 1;
  } else {
    llvm_unreachable("Unhandled ValueDecl for SILDeclRef");
  }
}

static bool isDesignatedConstructorForClass(ValueDecl *decl) {
  if (auto *ctor = dyn_cast_or_null<ConstructorDecl>(decl))
    if (ctor->getDeclContext()->getSelfClassDecl())
      return ctor->isDesignatedInit();
  return false;
}

bool SILDeclRef::canBeDynamicReplacement() const {
  // The foreign entry of a @dynamicReplacement(for:) of @objc method in a
  // generic class can't be a dynamic replacement.
  if (isForeign && hasDecl() && getDecl()->isNativeMethodReplacement())
    return false;
  if (isDistributedThunk())
    return false;
  if (backDeploymentKind != SILDeclRef::BackDeploymentKind::None)
    return false;
  if (kind == SILDeclRef::Kind::Destroyer ||
      kind == SILDeclRef::Kind::DefaultArgGenerator)
    return false;
  if (kind == SILDeclRef::Kind::Initializer)
    return isDesignatedConstructorForClass(getDecl());
  if (kind == SILDeclRef::Kind::Allocator)
    return !isDesignatedConstructorForClass(getDecl());
  return true;
}

bool SILDeclRef::isDynamicallyReplaceable() const {
  // The non-foreign entry of a @dynamicReplacement(for:) of @objc method in a
  // generic class can't be a dynamically replaced.
  if (!isForeign && hasDecl() && getDecl()->isNativeMethodReplacement())
    return false;

  if (isDistributedThunk())
    return false;

  if (backDeploymentKind != SILDeclRef::BackDeploymentKind::None)
    return false;

  if (kind == SILDeclRef::Kind::DefaultArgGenerator)
    return false;
  if (isStoredPropertyInitializer() || isPropertyWrapperBackingInitializer())
    return false;

  // Class allocators are not dynamic replaceable.
  if (kind == SILDeclRef::Kind::Allocator &&
      isDesignatedConstructorForClass(getDecl()))
    return false;

  if (kind == SILDeclRef::Kind::Destroyer ||
      (kind == SILDeclRef::Kind::Initializer &&
       !isDesignatedConstructorForClass(getDecl())) ||
      kind == SILDeclRef::Kind::GlobalAccessor) {
    return false;
  }

  if (!hasDecl())
    return false;

  auto decl = getDecl();

  if (isForeign)
    return false;

  // We can't generate categories for generic classes. So the standard mechanism
  // for replacing @objc dynamic methods in generic classes does not work.
  // Instead we mark the non @objc entry dynamically replaceable and replace
  // that.
  // For now, we only support this behavior if -enable-implicit-dynamic is
  // enabled.
  return decl->shouldUseNativeMethodReplacement();
}

bool SILDeclRef::hasAsync() const {
  if (isDistributedThunk())
    return true;

  if (hasDecl()) {
    if (auto afd = dyn_cast<AbstractFunctionDecl>(getDecl())) {
      return afd->hasAsync();
    }
    return false;
  }
  return getAbstractClosureExpr()->isBodyAsync();
}

bool SILDeclRef::isCalleeAllocatedCoroutine() const {
  if (!hasDecl())
    return false;

  auto *accessor = dyn_cast<AccessorDecl>(getDecl());
  if (!accessor)
    return false;

  return requiresFeatureCoroutineAccessors(accessor->getAccessorKind());
}