text: //===--- IRGenDebugInfo.cpp - Debug Info Support --------------------------===//
  //
  // 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 IR debug info generation for Swift.
  //
  //===----------------------------------------------------------------------===//
  
  #define DEBUG_TYPE "debug-info"
  #include "IRGenDebugInfo.h"
  #include "GenOpaque.h"
  #include "GenType.h"
  #include "swift/AST/ASTMangler.h"
  #include "swift/AST/Expr.h"
  #include "swift/AST/IRGenOptions.h"
  #include "swift/AST/Module.h"
  #include "swift/AST/ModuleLoader.h"
  #include "swift/AST/Pattern.h"
  #include "swift/Basic/Dwarf.h"
  #include "swift/Basic/SourceManager.h"
  #include "swift/Basic/Version.h"
  #include "swift/ClangImporter/ClangImporter.h"
  #include "swift/Demangling/ManglingMacros.h"
  #include "swift/SIL/SILArgument.h"
  #include "swift/SIL/SILBasicBlock.h"
  #include "swift/SIL/SILDebugScope.h"
  #include "swift/SIL/SILModule.h"
  #include "clang/AST/ASTContext.h"
  #include "clang/AST/Decl.h"
  #include "clang/AST/ExternalASTSource.h"
  #include "clang/Basic/Module.h"
  #include "clang/Basic/SourceLocation.h"
  #include "clang/Basic/SourceManager.h"
  #include "clang/Basic/TargetInfo.h"
  #include "clang/Frontend/CompilerInstance.h"
  #include "clang/Serialization/ASTReader.h"
  #include "llvm/Config/config.h"
  #include "llvm/IR/DIBuilder.h"
  #include "llvm/IR/DebugInfo.h"
  #include "llvm/IR/Module.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/FileSystem.h"
  #include "llvm/Support/MemoryBuffer.h"
  #include "llvm/Support/Path.h"
  #include "llvm/Support/raw_ostream.h"
  #include "llvm/Transforms/Utils/Local.h"
  
  using namespace swift;
  using namespace irgen;
  
  namespace {
  typedef llvm::DenseMap<const llvm::MDString *, llvm::TrackingMDNodeRef>
      TrackingDIRefMap;
  
  class IRGenDebugInfoImpl : public IRGenDebugInfo {
    friend class IRGenDebugInfoImpl;
    const IRGenOptions &Opts;
    ClangImporter &CI;
    SourceManager &SM;
    llvm::DIBuilder DBuilder;
    IRGenModule &IGM;
  
    /// Used for caching SILDebugScopes without inline information.
    typedef std::pair<const void *, const void *> LocalScopeHash;
    struct LocalScope : public LocalScopeHash {
      LocalScope(const SILDebugScope *DS)
          : LocalScopeHash({DS->Loc.getOpaquePointerValue(),
                            // If there is no parent SIL function use the scope
                            // pointer as a unique id instead. This is safe
                            // because such a function could also never have been
                            // SIL-inlined.
                            DS->Parent.getOpaqueValue()
                                ? DS->Parent.getOpaqueValue()
                                : DS}) {}
    };
  
    /// Various caches.
    /// @{
    llvm::DenseMap<LocalScopeHash, llvm::TrackingMDNodeRef> ScopeCache;
    llvm::DenseMap<const SILDebugScope *, llvm::TrackingMDNodeRef> InlinedAtCache;
    llvm::DenseMap<const void *, SILLocation::DebugLoc> DebugLocCache;
    llvm::DenseMap<TypeBase *, llvm::TrackingMDNodeRef> DITypeCache;
    llvm::DenseMap<const void *, llvm::TrackingMDNodeRef> DIModuleCache;
    llvm::StringMap<llvm::TrackingMDNodeRef> DIFileCache;
    TrackingDIRefMap DIRefMap;
    /// @}
  
    /// A list of replaceable fwddecls that need to be RAUWed at the end.
    std::vector<std::pair<TypeBase *, llvm::TrackingMDRef>> ReplaceMap;
    /// The set of imported modules.
    llvm::DenseSet<ModuleDecl *> ImportedModules;
  
    llvm::BumpPtrAllocator DebugInfoNames;
    StringRef CWDName;                    /// The current working directory.
    SmallString<0> ConfigMacros;          /// User-provided -D macro definitions.
    llvm::DICompileUnit *TheCU = nullptr; /// The current compilation unit.
    llvm::DIFile *MainFile = nullptr;     /// The main file.
    llvm::DIModule *MainModule = nullptr; /// The current module.
    llvm::DIScope *EntryPointFn =
        nullptr;                     /// Scope of SWIFT_ENTRY_POINT_FUNCTION.
    TypeAliasDecl *MetadataTypeDecl; /// The type decl for swift.type.
    llvm::DIType *InternalType;      /// Catch-all type for opaque internal types.
  
    SILLocation::DebugLoc LastDebugLoc; /// The last location that was emitted.
    const SILDebugScope *LastScope;     /// The scope of that last location.
  
    /// Used by pushLoc.
    SmallVector<std::pair<SILLocation::DebugLoc, const SILDebugScope *>, 8>
        LocationStack;
  
  public:
    IRGenDebugInfoImpl(const IRGenOptions &Opts, ClangImporter &CI,
                       IRGenModule &IGM, llvm::Module &M, SourceFile *SF);
    void finalize();
  
    void setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
                       Optional<SILLocation> Loc = None);
    void clearLoc(IRBuilder &Builder);
    void pushLoc();
    void popLoc();
    void setArtificialTrapLocation(IRBuilder &Builder,
                                   const SILDebugScope *Scope);
    void setEntryPointLoc(IRBuilder &Builder);
    llvm::DIScope *getEntryPointFn();
    llvm::DIScope *getOrCreateScope(const SILDebugScope *DS);
    void emitImport(ImportDecl *D);
    llvm::DISubprogram *emitFunction(const SILDebugScope *DS, llvm::Function *Fn,
                                     SILFunctionTypeRepresentation Rep,
                                     SILType Ty, DeclContext *DeclCtx = nullptr,
                                     GenericEnvironment *GE = nullptr);
    llvm::DISubprogram *emitFunction(SILFunction &SILFn, llvm::Function *Fn);
    void emitArtificialFunction(IRBuilder &Builder, llvm::Function *Fn,
                                SILType SILTy);
    void emitVariableDeclaration(IRBuilder &Builder,
                                 ArrayRef<llvm::Value *> Storage,
                                 DebugTypeInfo Ty, const SILDebugScope *DS,
                                 ValueDecl *VarDecl, StringRef Name,
                                 unsigned ArgNo = 0,
                                 IndirectionKind = DirectValue,
                                 ArtificialKind = RealValue);
    void emitDbgIntrinsic(IRBuilder &Builder, llvm::Value *Storage,
                          llvm::DILocalVariable *Var, llvm::DIExpression *Expr,
                          unsigned Line, unsigned Col, llvm::DILocalScope *Scope,
                          const SILDebugScope *DS);
    void emitGlobalVariableDeclaration(llvm::GlobalVariable *Storage,
                                       StringRef Name, StringRef LinkageName,
                                       DebugTypeInfo DebugType,
                                       bool IsLocalToUnit,
                                       Optional<SILLocation> Loc);
    void emitTypeMetadata(IRGenFunction &IGF, llvm::Value *Metadata,
                          StringRef Name);
  
    /// Return the DIBuilder.
    llvm::DIBuilder &getBuilder() { return DBuilder; }
  
    /// Decode (and cache) a SourceLoc.
    SILLocation::DebugLoc decodeSourceLoc(SourceLoc SL);
  
  private:
    static StringRef getFilenameFromDC(const DeclContext *DC) {
      if (auto LF = dyn_cast<LoadedFile>(DC))
        return LF->getFilename();
      if (auto SF = dyn_cast<SourceFile>(DC))
        return SF->getFilename();
      else if (auto M = dyn_cast<ModuleDecl>(DC))
        return M->getModuleFilename();
      else
        return StringRef();
    }
  
    SILLocation::DebugLoc getDeserializedLoc(Pattern *) { return {}; }
    SILLocation::DebugLoc getDeserializedLoc(Expr *) { return {}; }
    SILLocation::DebugLoc getDeserializedLoc(Stmt *) { return {}; }
    SILLocation::DebugLoc getDeserializedLoc(Decl *D) {
      SILLocation::DebugLoc L;
      const DeclContext *DC = D->getDeclContext()->getModuleScopeContext();
      StringRef Filename = getFilenameFromDC(DC);
      if (!Filename.empty())
        L.Filename = Filename;
      return L;
    }
  
    /// Use the SM to figure out the actual line/column of a SourceLoc.
    template <typename WithLoc>
    SILLocation::DebugLoc getDebugLoc(IRGenDebugInfo &DI, WithLoc *S,
                                      bool End = false) {
      SILLocation::DebugLoc L;
      if (S == nullptr)
        return L;
  
      SourceLoc Loc = End ? S->getEndLoc() : S->getStartLoc();
      if (Loc.isInvalid())
        // This may be a deserialized or clang-imported decl. And modules
        // don't come with SourceLocs right now. Get at least the name of
        // the module.
        return getDeserializedLoc(S);
  
      return DI.decodeSourceLoc(Loc);
    }
  
    SILLocation::DebugLoc getStartLocation(Optional<SILLocation> OptLoc) {
      if (!OptLoc)
        return {};
      return decodeSourceLoc(OptLoc->getStartSourceLoc());
    }
  
    SILLocation::DebugLoc decodeDebugLoc(SILLocation Loc) {
      if (Loc.isDebugInfoLoc())
        return Loc.getDebugInfoLoc();
      return decodeSourceLoc(Loc.getDebugSourceLoc());
    }
  
    SILLocation::DebugLoc getDebugLocation(Optional<SILLocation> OptLoc) {
      if (!OptLoc || OptLoc->isInPrologue())
        return {};
      return decodeDebugLoc(*OptLoc);
    }
  
    /// Strdup a raw char array using the bump pointer.
    StringRef BumpAllocatedString(const char *Data, size_t Length) {
      char *Ptr = DebugInfoNames.Allocate<char>(Length + 1);
      memcpy(Ptr, Data, Length);
      *(Ptr + Length) = 0;
      return StringRef(Ptr, Length);
    }
  
    /// Strdup S using the bump pointer.
    StringRef BumpAllocatedString(std::string S) {
      return BumpAllocatedString(S.c_str(), S.length());
    }
  
    /// Strdup StringRef S using the bump pointer.
    StringRef BumpAllocatedString(StringRef S) {
      return BumpAllocatedString(S.data(), S.size());
    }
  
    /// Return the size reported by a type.
    static unsigned getSizeInBits(llvm::DIType *Ty) {
      // Follow derived types until we reach a type that
      // reports back a size.
      while (isa<llvm::DIDerivedType>(Ty) && !Ty->getSizeInBits()) {
        auto *DT = cast<llvm::DIDerivedType>(Ty);
        Ty = DT->getBaseType().resolve();
        if (!Ty)
          return 0;
      }
      return Ty->getSizeInBits();
    }
  
  #ifndef NDEBUG
  
    /// Return the size reported by the variable's type.
    static unsigned getSizeInBits(const llvm::DILocalVariable *Var) {
      llvm::DIType *Ty = Var->getType().resolve();
      return getSizeInBits(Ty);
    }
  
  #endif
  
    /// Determine whether this debug scope belongs to an explicit closure.
    static bool isExplicitClosure(const SILFunction *SILFn) {
      if (SILFn && SILFn->hasLocation())
        if (Expr *E = SILFn->getLocation().getAsASTNode<Expr>())
          if (isa<ClosureExpr>(E))
            return true;
      return false;
    }
  
    /// Determine whether this location is some kind of closure.
    static bool isAbstractClosure(const SILLocation &Loc) {
      if (Expr *E = Loc.getAsASTNode<Expr>())
        if (isa<AbstractClosureExpr>(E))
          return true;
      return false;
    }
  
    /// Both the code that is used to set up a closure object and the
    /// (beginning of) the closure itself has the AbstractClosureExpr as
    /// location. We are only interested in the latter case and want to
    /// ignore the setup code.
    ///
    /// callWithClosure(
    ///  { // <-- a breakpoint here should only stop inside of the closure.
    ///    foo();
    ///  })
    ///
    /// The actual closure has a closure expression as scope.
    static bool shouldIgnoreAbstractClosure(Optional<SILLocation> Loc,
                                            const SILDebugScope *DS) {
      return Loc && isAbstractClosure(*Loc) && DS &&
             !isAbstractClosure(DS->Loc) && !Loc->is<ImplicitReturnLocation>();
    }
  
    llvm::MDNode *createInlinedAt(const SILDebugScope *DS) {
      auto *CS = DS->InlinedCallSite;
      if (!CS)
        return nullptr;
  
      auto CachedInlinedAt = InlinedAtCache.find(CS);
      if (CachedInlinedAt != InlinedAtCache.end())
        return cast<llvm::MDNode>(CachedInlinedAt->second);
  
      auto L = decodeDebugLoc(CS->Loc);
      auto Scope = getOrCreateScope(CS->Parent.dyn_cast<const SILDebugScope *>());
      auto InlinedAt =
          llvm::DebugLoc::get(L.Line, L.Column, Scope, createInlinedAt(CS));
      InlinedAtCache.insert(
          {CS, llvm::TrackingMDNodeRef(InlinedAt.getAsMDNode())});
      return InlinedAt;
    }
  
  #ifndef NDEBUG
    /// Perform a couple of sanity checks on scopes.
    static bool parentScopesAreSane(const SILDebugScope *DS) {
      auto *Parent = DS;
      while ((Parent = Parent->Parent.dyn_cast<const SILDebugScope *>())) {
        if (!DS->InlinedCallSite)
          assert(!Parent->InlinedCallSite &&
                 "non-inlined scope has an inlined parent");
      }
      return true;
    }
  #endif
  
    llvm::DIFile *getOrCreateFile(StringRef Filename) {
      if (Filename.empty())
        return MainFile;
  
      // Look in the cache first.
      auto CachedFile = DIFileCache.find(Filename);
      if (CachedFile != DIFileCache.end()) {
        // Verify that the information still exists.
        if (llvm::Metadata *V = CachedFile->second)
          return cast<llvm::DIFile>(V);
      }
  
      // Detect the main file.
      if (MainFile && Filename.endswith(MainFile->getFilename())) {
        SmallString<256> AbsThisFile, AbsMainFile;
        AbsThisFile = Filename;
        llvm::sys::fs::make_absolute(AbsThisFile);
        llvm::sys::path::append(AbsMainFile, MainFile->getDirectory(),
                                MainFile->getFilename());
        if (AbsThisFile == AbsMainFile) {
          DIFileCache[Filename] = llvm::TrackingMDNodeRef(MainFile);
          return MainFile;
        }
      }
  
      // Create a new one.
      StringRef File = llvm::sys::path::filename(Filename);
      llvm::SmallString<512> Path(Filename);
      llvm::sys::path::remove_filename(Path);
      llvm::DIFile *F = DBuilder.createFile(File, Path);
  
      // Cache it.
      DIFileCache[Filename] = llvm::TrackingMDNodeRef(F);
      return F;
    }
  
    StringRef getName(const FuncDecl &FD) {
      // Getters and Setters are anonymous functions, so we forge a name
      // using its parent declaration.
      if (FD.isAccessor())
        if (ValueDecl *VD = FD.getAccessorStorageDecl()) {
          const char *Kind;
          switch (FD.getAccessorKind()) {
          case AccessorKind::NotAccessor:
            llvm_unreachable("this is an accessor");
          case AccessorKind::IsGetter:
            Kind = ".get";
            break;
          case AccessorKind::IsSetter:
            Kind = ".set";
            break;
          case AccessorKind::IsWillSet:
            Kind = ".willset";
            break;
          case AccessorKind::IsDidSet:
            Kind = ".didset";
            break;
          case AccessorKind::IsMaterializeForSet:
            Kind = ".materialize";
            break;
          case AccessorKind::IsAddressor:
            Kind = ".addressor";
            break;
          case AccessorKind::IsMutableAddressor:
            Kind = ".mutableAddressor";
            break;
          }
  
          SmallVector<char, 64> Buf;
          StringRef Name = (VD->getBaseName().userFacingName() +
                            Twine(Kind)).toStringRef(Buf);
          return BumpAllocatedString(Name);
        }
  
      if (FD.hasName())
        return FD.getName().str();
  
      return StringRef();
    }
  
    StringRef getName(SILLocation L) {
      if (L.isNull())
        return StringRef();
  
      if (FuncDecl *FD = L.getAsASTNode<FuncDecl>())
        return getName(*FD);
  
      if (L.isASTNode<ConstructorDecl>())
        return "init";
  
      if (L.isASTNode<DestructorDecl>())
        return "deinit";
  
      return StringRef();
    }
  
    static CanSILFunctionType getFunctionType(SILType SILTy) {
      if (!SILTy)
        return CanSILFunctionType();
  
      auto FnTy = SILTy.getAs<SILFunctionType>();
      if (!FnTy) {
        DEBUG(llvm::dbgs() << "Unexpected function type: "; SILTy.dump();
              llvm::dbgs() << "\n");
        return CanSILFunctionType();
      }
  
      return FnTy;
    }
  
    llvm::DIScope *getOrCreateContext(DeclContext *DC) {
      if (!DC)
        return TheCU;
  
      if (isa<FuncDecl>(DC))
        if (auto *Decl = IGM.getSILModule().lookUpFunction(SILDeclRef(
                cast<AbstractFunctionDecl>(DC), SILDeclRef::Kind::Func)))
          return getOrCreateScope(Decl->getDebugScope());
  
      switch (DC->getContextKind()) {
      // The interesting cases are already handled above.
      case DeclContextKind::AbstractFunctionDecl:
      case DeclContextKind::AbstractClosureExpr:
  
      // We don't model these in DWARF.
      case DeclContextKind::SerializedLocal:
      case DeclContextKind::Initializer:
      case DeclContextKind::ExtensionDecl:
      case DeclContextKind::SubscriptDecl:
      case DeclContextKind::TopLevelCodeDecl:
        return getOrCreateContext(DC->getParent());
  
      case DeclContextKind::Module:
        return getOrCreateModule(
            {ModuleDecl::AccessPathTy(), cast<ModuleDecl>(DC)});
      case DeclContextKind::FileUnit:
        // A module may contain multiple files.
        return getOrCreateContext(DC->getParent());
      case DeclContextKind::GenericTypeDecl: {
        auto *NTD = cast<NominalTypeDecl>(DC);
        auto *Ty = NTD->getDeclaredType().getPointer();
        if (auto *DITy = getTypeOrNull(Ty))
          return DITy;
  
        // Create a Forward-declared type.
        auto Loc = getDebugLoc(*this, NTD);
        auto File = getOrCreateFile(Loc.Filename);
        auto Line = Loc.Line;
        auto FwdDecl = DBuilder.createReplaceableCompositeType(
            llvm::dwarf::DW_TAG_structure_type, NTD->getName().str(),
            getOrCreateContext(DC->getParent()), File, Line,
            llvm::dwarf::DW_LANG_Swift, 0, 0);
        ReplaceMap.emplace_back(
            std::piecewise_construct, std::make_tuple(Ty),
            std::make_tuple(static_cast<llvm::Metadata *>(FwdDecl)));
        return FwdDecl;
      }
      }
      return TheCU;
    }
  
    void createParameterType(llvm::SmallVectorImpl<llvm::Metadata *> &Parameters,
                             SILType type, DeclContext *DeclCtx,
                             GenericEnvironment *GE) {
      auto RealType = type.getSwiftRValueType();
      if (type.isAddress())
        RealType = CanInOutType::get(RealType);
      auto DbgTy = DebugTypeInfo::getFromTypeInfo(DeclCtx, GE, RealType,
                                                  IGM.getTypeInfo(type));
      Parameters.push_back(getOrCreateType(DbgTy));
    }
  
    // This is different from SILFunctionType::getAllResultsType() in some subtle
    // ways.
    static SILType getResultTypeForDebugInfo(CanSILFunctionType fnTy) {
      if (fnTy->getNumResults() == 1) {
        return fnTy->getResults()[0].getSILStorageType();
      } else if (!fnTy->getNumIndirectFormalResults()) {
        return fnTy->getDirectFormalResultsType();
      } else {
        SmallVector<TupleTypeElt, 4> eltTys;
        for (auto &result : fnTy->getResults()) {
          eltTys.push_back(result.getType());
        }
        return SILType::getPrimitiveAddressType(
            CanType(TupleType::get(eltTys, fnTy->getASTContext())));
      }
    }
  
    llvm::DITypeRefArray createParameterTypes(SILType SILTy, DeclContext *DeclCtx,
                                              GenericEnvironment *GE) {
      if (!SILTy)
        return nullptr;
      return createParameterTypes(SILTy.castTo<SILFunctionType>(), DeclCtx, GE);
    }
  
    llvm::DITypeRefArray createParameterTypes(CanSILFunctionType FnTy,
                                              DeclContext *DeclCtx,
                                              GenericEnvironment *GE) {
      SmallVector<llvm::Metadata *, 16> Parameters;
  
      GenericContextScope scope(IGM, FnTy->getGenericSignature());
  
      // The function return type is the first element in the list.
      createParameterType(Parameters, getResultTypeForDebugInfo(FnTy), DeclCtx,
                          GE);
  
      // Actually, the input type is either a single type or a tuple
      // type. We currently represent a function with one n-tuple argument
      // as an n-ary function.
      for (auto Param : FnTy->getParameters())
        createParameterType(Parameters, IGM.silConv.getSILType(Param), DeclCtx,
                            GE);
  
      return DBuilder.getOrCreateTypeArray(Parameters);
    }
  
    /// FIXME: replace this condition with something more sane.
    static bool isAllocatingConstructor(SILFunctionTypeRepresentation Rep,
                                        DeclContext *DeclCtx) {
      return Rep != SILFunctionTypeRepresentation::Method && DeclCtx &&
             isa<ConstructorDecl>(DeclCtx);
    }
  
    llvm::DIModule *getOrCreateModule(const void *Key, llvm::DIScope *Parent,
                                      StringRef Name, StringRef IncludePath,
                                      StringRef ConfigMacros = StringRef()) {
      // Look in the cache first.
      auto Val = DIModuleCache.find(Key);
      if (Val != DIModuleCache.end())
        return cast<llvm::DIModule>(Val->second);
  
      StringRef Sysroot = IGM.Context.SearchPathOpts.SDKPath;
      auto M =
          DBuilder.createModule(Parent, Name, ConfigMacros, IncludePath, Sysroot);
      DIModuleCache.insert({Key, llvm::TrackingMDNodeRef(M)});
      return M;
    }
  
    llvm::DIModule *
    getOrCreateModule(clang::ExternalASTSource::ASTSourceDescriptor Desc) {
      // Handle Clang modules.
      if (const clang::Module *ClangModule = Desc.getModuleOrNull()) {
        llvm::DIModule *Parent = nullptr;
        if (ClangModule->Parent)
          Parent = getOrCreateModule(*ClangModule->Parent);
  
        return getOrCreateModule(ClangModule, Parent,
                                 Desc.getModuleName(), Desc.getPath(),
                                 ConfigMacros);
      }
      // Handle PCH.
      return getOrCreateModule(Desc.getASTFile().bytes_begin(), nullptr,
                               Desc.getModuleName(), Desc.getPath(),
                               ConfigMacros);
    };
  
    llvm::DIModule *getOrCreateModule(ModuleDecl::ImportedModule IM) {
      ModuleDecl *M = IM.second;
      if (auto *ClangModule = M->findUnderlyingClangModule())
        return getOrCreateModule(*ClangModule);
  
      StringRef Path = getFilenameFromDC(M);
      StringRef Name = M->getName().str();
      return getOrCreateModule(M, TheCU, Name, Path);
    }
  
    TypeAliasDecl *getMetadataType() {
      if (!MetadataTypeDecl) {
        MetadataTypeDecl = new (IGM.Context) TypeAliasDecl(
            SourceLoc(), SourceLoc(), IGM.Context.getIdentifier("$swift.type"),
            SourceLoc(),
            /*genericparams*/ nullptr, IGM.Context.TheBuiltinModule);
        MetadataTypeDecl->setUnderlyingType(IGM.Context.TheRawPointerType);
      }
      return MetadataTypeDecl;
    }
  
    /// Return the DIFile that is the ancestor of Scope.
    llvm::DIFile *getFile(llvm::DIScope *Scope) {
      while (!isa<llvm::DIFile>(Scope)) {
        switch (Scope->getTag()) {
        case llvm::dwarf::DW_TAG_lexical_block:
          Scope = cast<llvm::DILexicalBlock>(Scope)->getScope();
          break;
        case llvm::dwarf::DW_TAG_subprogram:
          Scope = cast<llvm::DISubprogram>(Scope)->getFile();
          break;
        default:
          return MainFile;
        }
        if (Scope)
          return MainFile;
      }
      return cast<llvm::DIFile>(Scope);
    }
  
    static Size getStorageSize(const llvm::DataLayout &DL,
                               ArrayRef<llvm::Value *> Storage) {
      unsigned size = 0;
      for (llvm::Value *Piece : Storage)
        size += DL.getTypeSizeInBits(Piece->getType());
      return Size(size);
    }
  
    StringRef getMangledName(DebugTypeInfo DbgTy) {
      if (MetadataTypeDecl && DbgTy.getDecl() == MetadataTypeDecl)
        return BumpAllocatedString(DbgTy.getDecl()->getName().str());
  
      Mangle::ASTMangler Mangler;
      std::string Name = Mangler.mangleTypeForDebugger(
          DbgTy.getType(), DbgTy.getDeclContext(), DbgTy.getGenericEnvironment());
      return BumpAllocatedString(Name);
    }
  
    llvm::DIDerivedType *createMemberType(DebugTypeInfo DbgTy, StringRef Name,
                                          unsigned &OffsetInBits,
                                          llvm::DIScope *Scope,
                                          llvm::DIFile *File,
                                          llvm::DINode::DIFlags Flags) {
      unsigned SizeOfByte = CI.getTargetInfo().getCharWidth();
      auto *Ty = getOrCreateType(DbgTy);
      auto *DITy = DBuilder.createMemberType(Scope, Name, File, 0,
                                             SizeOfByte * DbgTy.size.getValue(),
                                             0, OffsetInBits, Flags, Ty);
      OffsetInBits += getSizeInBits(Ty);
      OffsetInBits =
          llvm::alignTo(OffsetInBits, SizeOfByte * DbgTy.align.getValue());
      return DITy;
    }
  
    llvm::DINodeArray
    getTupleElements(TupleType *TupleTy, llvm::DIScope *Scope, llvm::DIFile *File,
                     llvm::DINode::DIFlags Flags, DeclContext *DeclContext,
                     GenericEnvironment *GE, unsigned &SizeInBits) {
      SmallVector<llvm::Metadata *, 16> Elements;
      unsigned OffsetInBits = 0;
      auto genericSig = IGM.getSILTypes().getCurGenericContext();
      for (auto ElemTy : TupleTy->getElementTypes()) {
        auto &elemTI = IGM.getTypeInfoForUnlowered(
            AbstractionPattern(genericSig, ElemTy->getCanonicalType()), ElemTy);
        auto DbgTy =
            DebugTypeInfo::getFromTypeInfo(DeclContext, GE, ElemTy, elemTI);
        Elements.push_back(createMemberType(DbgTy, StringRef(), OffsetInBits,
                                            Scope, File, Flags));
      }
      SizeInBits = OffsetInBits;
      return DBuilder.getOrCreateArray(Elements);
    }
  
    llvm::DINodeArray getStructMembers(NominalTypeDecl *D, Type BaseTy,
                                       llvm::DIScope *Scope, llvm::DIFile *File,
                                       llvm::DINode::DIFlags Flags,
                                       unsigned &SizeInBits) {
      SmallVector<llvm::Metadata *, 16> Elements;
      unsigned OffsetInBits = 0;
      for (VarDecl *VD : D->getStoredProperties()) {
        auto memberTy =
            BaseTy->getTypeOfMember(IGM.getSwiftModule(), VD, nullptr);
  
        auto DbgTy = DebugTypeInfo::getFromTypeInfo(
            VD->getDeclContext(),
            VD->getDeclContext()->getGenericEnvironmentOfContext(),
            VD->getInterfaceType(),
            IGM.getTypeInfoForUnlowered(
                IGM.getSILTypes().getAbstractionPattern(VD), memberTy));
        Elements.push_back(createMemberType(DbgTy, VD->getName().str(),
                                            OffsetInBits, Scope, File, Flags));
      }
      if (OffsetInBits > SizeInBits)
        SizeInBits = OffsetInBits;
      return DBuilder.getOrCreateArray(Elements);
    }
  
    llvm::DICompositeType *
    createStructType(DebugTypeInfo DbgTy, NominalTypeDecl *Decl, Type BaseTy,
                     llvm::DIScope *Scope, llvm::DIFile *File, unsigned Line,
                     unsigned SizeInBits, unsigned AlignInBits,
                     llvm::DINode::DIFlags Flags, llvm::DIType *DerivedFrom,
                     unsigned RuntimeLang, StringRef UniqueID) {
      StringRef Name = Decl->getName().str();
  
      // Forward declare this first because types may be recursive.
      auto FwdDecl = llvm::TempDIType(DBuilder.createReplaceableCompositeType(
          llvm::dwarf::DW_TAG_structure_type, Name, Scope, File, Line,
          llvm::dwarf::DW_LANG_Swift, SizeInBits, 0, Flags, UniqueID));
  
  #ifndef NDEBUG
      if (UniqueID.empty())
        assert(!Name.empty() &&
               "no mangled name and no human readable name given");
      else
        assert((UniqueID.startswith("_T") ||
                UniqueID.startswith(MANGLING_PREFIX_STR)) &&
               "UID is not a mangled name");
  #endif
  
      auto TH = llvm::TrackingMDNodeRef(FwdDecl.get());
      DITypeCache[DbgTy.getType()] = TH;
      auto Members =
          getStructMembers(Decl, BaseTy, Scope, File, Flags, SizeInBits);
      auto DITy = DBuilder.createStructType(
          Scope, Name, File, Line, SizeInBits, AlignInBits, Flags, DerivedFrom,
          Members, RuntimeLang, nullptr, UniqueID);
      DBuilder.replaceTemporary(std::move(FwdDecl), DITy);
      return DITy;
    }
  
    llvm::DINodeArray getEnumElements(DebugTypeInfo DbgTy, EnumDecl *ED,
                                      llvm::DIScope *Scope, llvm::DIFile *File,
                                      llvm::DINode::DIFlags Flags) {
      SmallVector<llvm::Metadata *, 16> Elements;
  
      for (auto *ElemDecl : ED->getAllElements()) {
        // FIXME <rdar://problem/14845818> Support enums.
        // Swift Enums can be both like DWARF enums and discriminated unions.
        DebugTypeInfo ElemDbgTy;
        if (ED->hasRawType())
          // An enum with a raw type (enum E : Int {}), similar to a
          // DWARF enum.
          //
          // The storage occupied by the enum may be smaller than the
          // one of the raw type as long as it is large enough to hold
          // all enum values. Use the raw type for the debug type, but
          // the storage size from the enum.
          ElemDbgTy =
              DebugTypeInfo(ED, DbgTy.getGenericEnvironment(), ED->getRawType(),
                            DbgTy.StorageType, DbgTy.size, DbgTy.align, true);
        else if (auto ArgTy = ElemDecl->getArgumentInterfaceType()) {
          // A discriminated union. This should really be described as a
          // DW_TAG_variant_type. For now only describing the data.
          ArgTy = ElemDecl->getParentEnum()->mapTypeIntoContext(ArgTy);
          auto &TI = IGM.getTypeInfoForUnlowered(ArgTy);
          ElemDbgTy = DebugTypeInfo::getFromTypeInfo(
              ElemDecl->getDeclContext(),
              ElemDecl->getDeclContext()->getGenericEnvironmentOfContext(), ArgTy,
              TI);
        } else {
          // Discriminated union case without argument. Fallback to Int
          // as the element type; there is no storage here.
          Type IntTy = IGM.Context.getIntDecl()->getDeclaredType();
          ElemDbgTy = DebugTypeInfo(
              ElemDecl->getDeclContext(),
              ElemDecl->getDeclContext()->getGenericEnvironmentOfContext(), IntTy,
              DbgTy.StorageType, Size(0), Alignment(1), true);
        }
        unsigned Offset = 0;
        auto MTy = createMemberType(ElemDbgTy, ElemDecl->getName().str(), Offset,
                                    Scope, File, Flags);
        Elements.push_back(MTy);
      }
      return DBuilder.getOrCreateArray(Elements);
    }
  
    llvm::DICompositeType *createEnumType(DebugTypeInfo DbgTy, EnumDecl *Decl,
                                          StringRef MangledName,
                                          llvm::DIScope *Scope,
                                          llvm::DIFile *File, unsigned Line,
                                          llvm::DINode::DIFlags Flags) {
      unsigned SizeOfByte = CI.getTargetInfo().getCharWidth();
      unsigned SizeInBits = DbgTy.size.getValue() * SizeOfByte;
      // Default, since Swift doesn't allow specifying a custom alignment.
      unsigned AlignInBits = 0;
  
      // FIXME: Is DW_TAG_union_type the right thing here?
      // Consider using a DW_TAG_variant_type instead.
      auto FwdDecl = llvm::TempDIType(DBuilder.createReplaceableCompositeType(
          llvm::dwarf::DW_TAG_union_type, MangledName, Scope, File, Line,
          llvm::dwarf::DW_LANG_Swift, SizeInBits, AlignInBits, Flags,
          MangledName));
  
      auto TH = llvm::TrackingMDNodeRef(FwdDecl.get());
      DITypeCache[DbgTy.getType()] = TH;
  
      auto DITy = DBuilder.createUnionType(
          Scope, Decl->getName().str(), File, Line, SizeInBits, AlignInBits,
          Flags, getEnumElements(DbgTy, Decl, Scope, File, Flags),
          llvm::dwarf::DW_LANG_Swift, MangledName);
  
      DBuilder.replaceTemporary(std::move(FwdDecl), DITy);
      return DITy;
    }
  
    llvm::DIType *getOrCreateDesugaredType(Type Ty, DebugTypeInfo DbgTy) {
      DebugTypeInfo BlandDbgTy(
          DbgTy.getDeclContext(), DbgTy.getGenericEnvironment(), Ty,
          DbgTy.StorageType, DbgTy.size, DbgTy.align, DbgTy.DefaultAlignment);
      return getOrCreateType(BlandDbgTy);
    }
  
    uint64_t getSizeOfBasicType(DebugTypeInfo DbgTy) {
      uint64_t SizeOfByte = CI.getTargetInfo().getCharWidth();
      uint64_t BitWidth = DbgTy.size.getValue() * SizeOfByte;
      llvm::Type *StorageType = DbgTy.StorageType
                                    ? DbgTy.StorageType
                                    : IGM.DataLayout.getSmallestLegalIntType(
                                          IGM.getLLVMContext(), BitWidth);
  
      if (StorageType)
        return IGM.DataLayout.getTypeSizeInBits(StorageType);
  
      // This type is too large to fit in a register.
      assert(BitWidth > IGM.DataLayout.getLargestLegalIntTypeSizeInBits());
      return BitWidth;
    }
  
    llvm::DIType *createPointerSizedStruct(llvm::DIScope *Scope, StringRef Name,
                                           llvm::DIFile *File, unsigned Line,
                                           llvm::DINode::DIFlags Flags,
                                           StringRef MangledName) {
      if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes) {
        auto FwdDecl = DBuilder.createForwardDecl(
            llvm::dwarf::DW_TAG_structure_type, Name, Scope, File, Line,
            llvm::dwarf::DW_LANG_Swift, 0, 0);
        return createPointerSizedStruct(Scope, Name, FwdDecl, File, Line, Flags,
                                        MangledName);
      } else {
        unsigned SizeInBits = CI.getTargetInfo().getPointerWidth(0);
        return createOpaqueStruct(Scope, Name, File, Line, SizeInBits, 0, Flags,
                                  MangledName);
      }
    }
  
    llvm::DIType *createPointerSizedStruct(llvm::DIScope *Scope, StringRef Name,
                                           llvm::DIType *PointeeTy,
                                           llvm::DIFile *File, unsigned Line,
                                           llvm::DINode::DIFlags Flags,
                                           StringRef MangledName) {
      unsigned PtrSize = CI.getTargetInfo().getPointerWidth(0);
      auto PtrTy = DBuilder.createPointerType(PointeeTy, PtrSize, 0);
      llvm::Metadata *Elements[] = {DBuilder.createMemberType(
          Scope, "ptr", File, 0, PtrSize, 0, 0, Flags, PtrTy)};
      return DBuilder.createStructType(
          Scope, Name, File, Line, PtrSize, 0, Flags,
          /* DerivedFrom */ nullptr, DBuilder.getOrCreateArray(Elements),
          llvm::dwarf::DW_LANG_Swift, nullptr, MangledName);
    }
  
    llvm::DIType *
    createDoublePointerSizedStruct(llvm::DIScope *Scope, StringRef Name,
                                   llvm::DIType *PointeeTy, llvm::DIFile *File,
                                   unsigned Line, llvm::DINode::DIFlags Flags,
                                   StringRef MangledName) {
      unsigned PtrSize = CI.getTargetInfo().getPointerWidth(0);
      llvm::Metadata *Elements[] = {
          DBuilder.createMemberType(
              Scope, "ptr", File, 0, PtrSize, 0, 0, Flags,
              DBuilder.createPointerType(PointeeTy, PtrSize, 0)),
          DBuilder.createMemberType(
              Scope, "_", File, 0, PtrSize, 0, 0, Flags,
              DBuilder.createPointerType(nullptr, PtrSize, 0))};
      return DBuilder.createStructType(
          Scope, Name, File, Line, 2 * PtrSize, 0, Flags,
          /* DerivedFrom */ nullptr, DBuilder.getOrCreateArray(Elements),
          llvm::dwarf::DW_LANG_Swift, nullptr, MangledName);
    }
  
    llvm::DIType *createFunctionPointer(DebugTypeInfo DbgTy, llvm::DIScope *Scope,
                                        unsigned SizeInBits, unsigned AlignInBits,
                                        llvm::DINode::DIFlags Flags,
                                        StringRef MangledName) {
      auto FwdDecl = llvm::TempDINode(DBuilder.createReplaceableCompositeType(
          llvm::dwarf::DW_TAG_subroutine_type, MangledName, Scope, MainFile, 0,
          llvm::dwarf::DW_LANG_Swift, SizeInBits, AlignInBits, Flags,
          MangledName));
  
      auto TH = llvm::TrackingMDNodeRef(FwdDecl.get());
      DITypeCache[DbgTy.getType()] = TH;
  
      CanSILFunctionType FunTy;
      TypeBase *BaseTy = DbgTy.getType();
      if (auto *SILFnTy = dyn_cast<SILFunctionType>(BaseTy))
        FunTy = CanSILFunctionType(SILFnTy);
      // FIXME: Handling of generic parameters in SIL type lowering is in flux.
      // DebugInfo doesn't appear to care about the generic context, so just
      // throw it away before lowering.
      else if (isa<GenericFunctionType>(BaseTy)) {
        auto *fTy = cast<AnyFunctionType>(BaseTy);
        auto *nongenericTy = FunctionType::get(fTy->getInput(), fTy->getResult(),
                                               fTy->getExtInfo());
  
        FunTy = IGM.getLoweredType(nongenericTy).castTo<SILFunctionType>();
      } else
        FunTy = IGM.getLoweredType(BaseTy).castTo<SILFunctionType>();
      auto Params = createParameterTypes(FunTy, DbgTy.getDeclContext(),
                                         DbgTy.getGenericEnvironment());
  
      auto FnTy = DBuilder.createSubroutineType(Params, Flags);
      llvm::DIType *DITy;
      if (FunTy->getRepresentation() == SILFunctionType::Representation::Thick) {
        if (SizeInBits == 2 * CI.getTargetInfo().getPointerWidth(0))
          // This is a FunctionPairTy: { i8*, %swift.refcounted* }.
          DITy = createDoublePointerSizedStruct(Scope, MangledName, FnTy,
                                                MainFile, 0, Flags, MangledName);
        else
          // This is a generic function as noted above.
          DITy = createOpaqueStruct(Scope, MangledName, MainFile, 0, SizeInBits,
                                    AlignInBits, Flags, MangledName);
      } else {
        assert(SizeInBits == CI.getTargetInfo().getPointerWidth(0));
        DITy = createPointerSizedStruct(Scope, MangledName, FnTy, MainFile, 0,
                                        Flags, MangledName);
      }
      DBuilder.replaceTemporary(std::move(FwdDecl), DITy);
      return DITy;
    }
  
    llvm::DIType *createTuple(DebugTypeInfo DbgTy, llvm::DIScope *Scope,
                              unsigned SizeInBits, unsigned AlignInBits,
                              llvm::DINode::DIFlags Flags,
                              StringRef MangledName) {
      TypeBase *BaseTy = DbgTy.getType();
      auto *TupleTy = BaseTy->castTo<TupleType>();
      auto FwdDecl = llvm::TempDINode(DBuilder.createReplaceableCompositeType(
          llvm::dwarf::DW_TAG_structure_type, MangledName, Scope, MainFile, 0,
          llvm::dwarf::DW_LANG_Swift, SizeInBits, AlignInBits, Flags,
          MangledName));
  
      DITypeCache[DbgTy.getType()] = llvm::TrackingMDNodeRef(FwdDecl.get());
  
      unsigned RealSize;
      auto Elements = getTupleElements(TupleTy, Scope, MainFile, Flags,
                                       DbgTy.getDeclContext(),
                                       DbgTy.getGenericEnvironment(), RealSize);
      // FIXME: Handle %swift.opaque members and make this into an assertion.
      if (!RealSize)
        RealSize = SizeInBits;
  
      auto DITy = DBuilder.createStructType(
          Scope, MangledName, MainFile, 0, RealSize, AlignInBits, Flags,
          nullptr, // DerivedFrom
          Elements, llvm::dwarf::DW_LANG_Swift, nullptr, MangledName);
  
      DBuilder.replaceTemporary(std::move(FwdDecl), DITy);
      return DITy;
    }
  
    llvm::DIType *createOpaqueStruct(llvm::DIScope *Scope, StringRef Name,
                                     llvm::DIFile *File, unsigned Line,
                                     unsigned SizeInBits, unsigned AlignInBits,
                                     llvm::DINode::DIFlags Flags,
                                     StringRef MangledName) {
      return DBuilder.createStructType(
          Scope, Name, File, Line, SizeInBits, AlignInBits, Flags,
          /* DerivedFrom */ nullptr,
          DBuilder.getOrCreateArray(ArrayRef<llvm::Metadata *>()),
          llvm::dwarf::DW_LANG_Swift, nullptr, MangledName);
    }
  
    llvm::DIType *createType(DebugTypeInfo DbgTy, StringRef MangledName,
                             llvm::DIScope *Scope, llvm::DIFile *File) {
      // FIXME: For SizeInBits, clang uses the actual size of the type on
      // the target machine instead of the storage size that is alloca'd
      // in the LLVM IR. For all types that are boxed in a struct, we are
      // emitting the storage size of the struct, but it may be necessary
      // to emit the (target!) size of the underlying basic type.
      uint64_t SizeOfByte = CI.getTargetInfo().getCharWidth();
      uint64_t SizeInBits = DbgTy.size.getValue() * SizeOfByte;
      unsigned AlignInBits =
          DbgTy.DefaultAlignment ? 0 : DbgTy.align.getValue() * SizeOfByte;
      unsigned Encoding = 0;
      llvm::DINode::DIFlags Flags = llvm::DINode::FlagZero;
  
      TypeBase *BaseTy = DbgTy.getType();
  
      if (!BaseTy) {
        DEBUG(llvm::dbgs() << "Type without TypeBase: "; DbgTy.getType()->dump();
              llvm::dbgs() << "\n");
        if (!InternalType) {
          StringRef Name = "<internal>";
          InternalType = DBuilder.createForwardDecl(
              llvm::dwarf::DW_TAG_structure_type, Name, Scope, File,
              /*Line*/ 0, llvm::dwarf::DW_LANG_Swift, SizeInBits, AlignInBits);
        }
        return InternalType;
      }
  
      // Here goes!
      switch (BaseTy->getKind()) {
      case TypeKind::BuiltinInteger: {
        Encoding = llvm::dwarf::DW_ATE_unsigned;
        SizeInBits = getSizeOfBasicType(DbgTy);
        break;
      }
  
      case TypeKind::BuiltinFloat: {
        auto *FloatTy = BaseTy->castTo<BuiltinFloatType>();
        // Assuming that the bitwidth and FloatTy->getFPKind() are identical.
        SizeInBits = FloatTy->getBitWidth();
        Encoding = llvm::dwarf::DW_ATE_float;
        break;
      }
  
      case TypeKind::BuiltinUnknownObject: {
        // The builtin opaque Objective-C pointer type. Useful for pushing
        // an Objective-C type through swift.
        unsigned PtrSize = CI.getTargetInfo().getPointerWidth(0);
        auto IdTy = DBuilder.createForwardDecl(llvm::dwarf::DW_TAG_structure_type,
                                               MangledName, Scope, File, 0,
                                               llvm::dwarf::DW_LANG_ObjC, 0, 0);
        return DBuilder.createPointerType(IdTy, PtrSize, 0,
                                          /* DWARFAddressSpace */ None,
                                          MangledName);
      }
  
      case TypeKind::BuiltinNativeObject: {
        unsigned PtrSize = CI.getTargetInfo().getPointerWidth(0);
        auto PTy =
            DBuilder.createPointerType(nullptr, PtrSize, 0,
                                       /* DWARFAddressSpace */ None, MangledName);
        return DBuilder.createObjectPointerType(PTy);
      }
  
      case TypeKind::BuiltinBridgeObject: {
        unsigned PtrSize = CI.getTargetInfo().getPointerWidth(0);
        auto PTy =
            DBuilder.createPointerType(nullptr, PtrSize, 0,
                                       /* DWARFAddressSpace */ None, MangledName);
        return DBuilder.createObjectPointerType(PTy);
      }
  
      case TypeKind::BuiltinRawPointer: {
        unsigned PtrSize = CI.getTargetInfo().getPointerWidth(0);
        return DBuilder.createPointerType(nullptr, PtrSize, 0,
                                          /* DWARFAddressSpace */ None,
                                          MangledName);
      }
  
      case TypeKind::DynamicSelf: {
        // Self. We don't have a way to represent instancetype in DWARF,
        // so we emit the static type instead. This is similar to what we
        // do with instancetype in Objective-C.
        auto *DynamicSelfTy = BaseTy->castTo<DynamicSelfType>();
        auto SelfTy =
            getOrCreateDesugaredType(DynamicSelfTy->getSelfType(), DbgTy);
        return DBuilder.createTypedef(SelfTy, MangledName, File, 0, File);
      }
  
      // Even builtin swift types usually come boxed in a struct.
      case TypeKind::Struct: {
        auto *StructTy = BaseTy->castTo<StructType>();
        auto *Decl = StructTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        if (auto *ClangDecl = Decl->getClangDecl()) {
          auto ClangSrcLoc = ClangDecl->getLocStart();
          clang::SourceManager &ClangSM =
              CI.getClangASTContext().getSourceManager();
          L.Line = ClangSM.getPresumedLineNumber(ClangSrcLoc);
          L.Filename = ClangSM.getBufferName(ClangSrcLoc);
        }
        auto *File = getOrCreateFile(L.Filename);
        if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes)
          return createStructType(DbgTy, Decl, StructTy, Scope, File, L.Line,
                                  SizeInBits, AlignInBits, Flags,
                                  nullptr, // DerivedFrom
                                  llvm::dwarf::DW_LANG_Swift, MangledName);
        else
          return createOpaqueStruct(Scope, Decl->getName().str(), File, L.Line,
                                    SizeInBits, AlignInBits, Flags, MangledName);
      }
  
      case TypeKind::Class: {
        // Classes are represented as DW_TAG_structure_type. This way the
        // DW_AT_APPLE_runtime_class(DW_LANG_Swift) attribute can be
        // used to differentiate them from C++ and ObjC classes.
        auto *ClassTy = BaseTy->castTo<ClassType>();
        auto *Decl = ClassTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        if (auto *ClangDecl = Decl->getClangDecl()) {
          auto ClangSrcLoc = ClangDecl->getLocStart();
          clang::SourceManager &ClangSM =
              CI.getClangASTContext().getSourceManager();
          L.Line = ClangSM.getPresumedLineNumber(ClangSrcLoc);
          L.Filename = ClangSM.getBufferName(ClangSrcLoc);
        }
        assert(SizeInBits == CI.getTargetInfo().getPointerWidth(0));
        return createPointerSizedStruct(Scope, Decl->getNameStr(),
                                        getOrCreateFile(L.Filename), L.Line,
                                        Flags, MangledName);
      }
  
      case TypeKind::Protocol: {
        auto *ProtocolTy = BaseTy->castTo<ProtocolType>();
        auto *Decl = ProtocolTy->getDecl();
        // FIXME: (LLVM branch) This should probably be a DW_TAG_interface_type.
        auto L = getDebugLoc(*this, Decl);
        auto File = getOrCreateFile(L.Filename);
        return createOpaqueStruct(Scope, Decl ? Decl->getNameStr() : MangledName,
                                  File, L.Line, SizeInBits, AlignInBits, Flags,
                                  MangledName);
      }
  
      case TypeKind::ProtocolComposition: {
        auto *Decl = DbgTy.getDecl();
        auto L = getDebugLoc(*this, Decl);
        auto File = getOrCreateFile(L.Filename);
  
        // FIXME: emit types
        // auto ProtocolCompositionTy = BaseTy->castTo<ProtocolCompositionType>();
        return createOpaqueStruct(Scope, Decl ? Decl->getNameStr() : MangledName,
                                  File, L.Line, SizeInBits, AlignInBits, Flags,
                                  MangledName);
      }
  
      case TypeKind::UnboundGeneric: {
        auto *UnboundTy = BaseTy->castTo<UnboundGenericType>();
        auto *Decl = UnboundTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        assert(SizeInBits == CI.getTargetInfo().getPointerWidth(0));
        return createPointerSizedStruct(Scope,
                                        Decl ? Decl->getNameStr() : MangledName,
                                        File, L.Line, Flags, MangledName);
      }
  
      case TypeKind::BoundGenericStruct: {
        auto *StructTy = BaseTy->castTo<BoundGenericStructType>();
        auto *Decl = StructTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        return createOpaqueStruct(Scope, Decl ? Decl->getNameStr() : MangledName,
                                  File, L.Line, SizeInBits, AlignInBits, Flags,
                                  MangledName);
      }
  
      case TypeKind::BoundGenericClass: {
        auto *ClassTy = BaseTy->castTo<BoundGenericClassType>();
        auto *Decl = ClassTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        // TODO: We may want to peek at Decl->isObjC() and set this
        // attribute accordingly.
        assert(SizeInBits == CI.getTargetInfo().getPointerWidth(0));
        return createPointerSizedStruct(Scope,
                                        Decl ? Decl->getNameStr() : MangledName,
                                        File, L.Line, Flags, MangledName);
      }
  
      case TypeKind::Tuple: {
        // Tuples are also represented as structs.
        if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes)
          return createTuple(DbgTy, Scope, SizeInBits, AlignInBits, Flags,
                             MangledName);
        else
          return createOpaqueStruct(Scope, MangledName, MainFile, 0, SizeInBits,
                                    AlignInBits, Flags, MangledName);
      }
  
      case TypeKind::InOut: {
        // This is an inout type. Naturally we would be emitting them as
        // DW_TAG_reference_type types, but LLDB can deal better with
        // pointer-sized struct that has the appropriate mangled name.
        auto ObjectTy = BaseTy->castTo<InOutType>()->getObjectType();
        auto Name = MangledName;
        if (auto *Decl = ObjectTy->getAnyNominal())
          Name = Decl->getName().str();
        if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes) {
          auto DT = getOrCreateDesugaredType(ObjectTy, DbgTy);
          return createPointerSizedStruct(Scope, Name, DT, File, 0, Flags,
                                          MangledName);
        } else
          return createOpaqueStruct(Scope, Name, File, 0, SizeInBits, AlignInBits,
                                    Flags, MangledName);
      }
  
      case TypeKind::Archetype: {
        auto *Archetype = BaseTy->castTo<ArchetypeType>();
        auto L = getDebugLoc(*this, Archetype->getAssocType());
        auto Superclass = Archetype->getSuperclass();
        auto DerivedFrom = Superclass.isNull()
                               ? nullptr
                               : getOrCreateDesugaredType(Superclass, DbgTy);
        auto FwdDecl = llvm::TempDIType(DBuilder.createReplaceableCompositeType(
            llvm::dwarf::DW_TAG_structure_type, MangledName, Scope, File, L.Line,
            llvm::dwarf::DW_LANG_Swift, SizeInBits, AlignInBits, Flags,
            MangledName));
  
        // Emit the protocols the archetypes conform to.
        SmallVector<llvm::Metadata *, 4> Protocols;
        for (auto *ProtocolDecl : Archetype->getConformsTo()) {
          auto PTy = IGM.getLoweredType(ProtocolDecl->getInterfaceType())
                         .getSwiftRValueType();
          auto PDbgTy = DebugTypeInfo::getFromTypeInfo(
              DbgTy.getDeclContext(), DbgTy.getGenericEnvironment(),
              ProtocolDecl->getInterfaceType(), IGM.getTypeInfoForLowered(PTy));
          auto PDITy = getOrCreateType(PDbgTy);
          Protocols.push_back(
              DBuilder.createInheritance(FwdDecl.get(), PDITy, 0, Flags));
        }
        auto DITy = DBuilder.createStructType(
            Scope, MangledName, File, L.Line, SizeInBits, AlignInBits, Flags,
            DerivedFrom, DBuilder.getOrCreateArray(Protocols),
            llvm::dwarf::DW_LANG_Swift, nullptr, MangledName);
  
        DBuilder.replaceTemporary(std::move(FwdDecl), DITy);
        return DITy;
      }
  
      case TypeKind::ExistentialMetatype:
      case TypeKind::Metatype: {
        // Metatypes are (mostly) singleton type descriptors, often without
        // storage.
        Flags |= llvm::DINode::FlagArtificial;
        auto L = getDebugLoc(*this, DbgTy.getDecl());
        auto File = getOrCreateFile(L.Filename);
        return DBuilder.createStructType(
            Scope, MangledName, File, L.Line, SizeInBits, AlignInBits, Flags,
            nullptr, nullptr, llvm::dwarf::DW_LANG_Swift, nullptr, MangledName);
      }
  
      case TypeKind::SILFunction:
      case TypeKind::Function:
      case TypeKind::GenericFunction: {
        if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes)
          return createFunctionPointer(DbgTy, Scope, SizeInBits, AlignInBits,
                                       Flags, MangledName);
        else
          return createOpaqueStruct(Scope, MangledName, MainFile, 0, SizeInBits,
                                    AlignInBits, Flags, MangledName);
      }
  
      case TypeKind::Enum: {
        auto *EnumTy = BaseTy->castTo<EnumType>();
        auto *Decl = EnumTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        auto *File = getOrCreateFile(L.Filename);
        if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes)
          return createEnumType(DbgTy, Decl, MangledName, Scope, File, L.Line,
                                Flags);
        else
          return createOpaqueStruct(Scope, Decl->getName().str(), File, L.Line,
                                    SizeInBits, AlignInBits, Flags, MangledName);
      }
  
      case TypeKind::BoundGenericEnum: {
        auto *EnumTy = BaseTy->castTo<BoundGenericEnumType>();
        auto *Decl = EnumTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        auto *File = getOrCreateFile(L.Filename);
        if (Opts.DebugInfoKind > IRGenDebugInfoKind::ASTTypes)
          return createEnumType(DbgTy, Decl, MangledName, Scope, File, L.Line,
                                Flags);
        else
          return createOpaqueStruct(Scope, Decl->getName().str(), File, L.Line,
                                    SizeInBits, AlignInBits, Flags, MangledName);
      }
  
      case TypeKind::BuiltinVector: {
        (void)MangledName; // FIXME emit the name somewhere.
        auto *BuiltinVectorTy = BaseTy->castTo<BuiltinVectorType>();
        DebugTypeInfo ElemDbgTy(DbgTy.getDeclContext(),
                                DbgTy.getGenericEnvironment(),
                                BuiltinVectorTy->getElementType(),
                                DbgTy.StorageType, DbgTy.size, DbgTy.align, true);
        auto Subscripts = nullptr;
        return DBuilder.createVectorType(BuiltinVectorTy->getNumElements(),
                                         AlignInBits, getOrCreateType(ElemDbgTy),
                                         Subscripts);
      }
  
      // Reference storage types.
      case TypeKind::UnownedStorage:
      case TypeKind::UnmanagedStorage:
      case TypeKind::WeakStorage: {
        auto *ReferenceTy = cast<ReferenceStorageType>(BaseTy);
        auto CanTy = ReferenceTy->getReferentType();
        auto L = getDebugLoc(*this, DbgTy.getDecl());
        auto File = getOrCreateFile(L.Filename);
        return DBuilder.createTypedef(getOrCreateDesugaredType(CanTy, DbgTy),
                                      MangledName, File, L.Line, File);
      }
  
      // Sugared types.
  
      case TypeKind::NameAlias: {
  
        auto *NameAliasTy = cast<NameAliasType>(BaseTy);
        auto *Decl = NameAliasTy->getDecl();
        auto L = getDebugLoc(*this, Decl);
        auto AliasedTy = NameAliasTy->getSinglyDesugaredType();
        auto File = getOrCreateFile(L.Filename);
        // For NameAlias types, the DeclContext for the aliasED type is
        // in the decl of the alias type.
        DebugTypeInfo AliasedDbgTy(
            DbgTy.getDeclContext(), DbgTy.getGenericEnvironment(), AliasedTy,
            DbgTy.StorageType, DbgTy.size, DbgTy.align, DbgTy.DefaultAlignment);
        return DBuilder.createTypedef(getOrCreateType(AliasedDbgTy), MangledName,
                                      File, L.Line, File);
      }
  
      case TypeKind::Paren: {
        auto Ty = cast<ParenType>(BaseTy)->getUnderlyingType();
        return getOrCreateDesugaredType(Ty, DbgTy);
      }
  
      // SyntaxSugarType derivations.
      case TypeKind::ArraySlice:
      case TypeKind::Optional:
      case TypeKind::ImplicitlyUnwrappedOptional: {
        auto *SyntaxSugarTy = cast<SyntaxSugarType>(BaseTy);
        auto *CanTy = SyntaxSugarTy->getSinglyDesugaredType();
        return getOrCreateDesugaredType(CanTy, DbgTy);
      }
  
      case TypeKind::Dictionary: {
        auto *DictionaryTy = cast<DictionaryType>(BaseTy);
        auto *CanTy = DictionaryTy->getDesugaredType();
        return getOrCreateDesugaredType(CanTy, DbgTy);
      }
  
      case TypeKind::GenericTypeParam: {
        auto *ParamTy = cast<GenericTypeParamType>(BaseTy);
        // FIXME: Provide a more meaningful debug type.
        return DBuilder.createUnspecifiedType(ParamTy->getName().str());
      }
      case TypeKind::DependentMember: {
        auto *MemberTy = cast<DependentMemberType>(BaseTy);
        // FIXME: Provide a more meaningful debug type.
        return DBuilder.createUnspecifiedType(MemberTy->getName().str());
      }
  
      // The following types exist primarily for internal use by the type
      // checker.
      case TypeKind::Error:
      case TypeKind::Unresolved:
      case TypeKind::LValue:
      case TypeKind::TypeVariable:
      case TypeKind::Module:
      case TypeKind::SILBlockStorage:
      case TypeKind::SILBox:
      case TypeKind::BuiltinUnsafeValueBuffer:
  
        DEBUG(llvm::errs() << "Unhandled type: "; DbgTy.getType()->dump();
              llvm::errs() << "\n");
        MangledName = "<unknown>";
      }
      return DBuilder.createBasicType(MangledName, SizeInBits, Encoding);
    }
  
    /// Determine if there exists a name mangling for the given type.
    static bool canMangle(TypeBase *Ty) {
      switch (Ty->getKind()) {
      case TypeKind::GenericFunction: // Not yet supported.
      case TypeKind::SILBlockStorage: // Not supported at all.
      case TypeKind::SILBox:
        return false;
      case TypeKind::InOut: {
        auto *ObjectTy = Ty->castTo<InOutType>()->getObjectType().getPointer();
        return canMangle(ObjectTy);
      }
      default:
        return true;
      }
    }
  
    llvm::DIType *getTypeOrNull(TypeBase *Ty) {
      auto CachedType = DITypeCache.find(Ty);
      if (CachedType != DITypeCache.end()) {
        // Verify that the information still exists.
        if (llvm::Metadata *Val = CachedType->second) {
          auto DITy = cast<llvm::DIType>(Val);
          return DITy;
        }
      }
      return nullptr;
    }
  
    llvm::DIType *getOrCreateType(DebugTypeInfo DbgTy) {
      // Is this an empty type?
      if (DbgTy.isNull())
        // We can't use the empty type as an index into DenseMap.
        return createType(DbgTy, "", TheCU, MainFile);
  
      // Look in the cache first.
      if (auto *DITy = getTypeOrNull(DbgTy.getType()))
        return DITy;
  
      // Second line of defense: Look up the mangled name. TypeBase*'s are
      // not necessarily unique, but name mangling is too expensive to do
      // every time.
      StringRef MangledName;
      llvm::MDString *UID = nullptr;
      if (canMangle(DbgTy.getType())) {
        MangledName = getMangledName(DbgTy);
        UID = llvm::MDString::get(IGM.getLLVMContext(), MangledName);
        if (llvm::Metadata *CachedTy = DIRefMap.lookup(UID)) {
          auto DITy = cast<llvm::DIType>(CachedTy);
          return DITy;
        }
      }
  
      // Retrieve the context of the type, as opposed to the DeclContext
      // of the variable.
      //
      // FIXME: Builtin and qualified types in LLVM have no parent
      // scope. TODO: This can be fixed by extending DIBuilder.
      llvm::DIScope *Scope = nullptr;
      DeclContext *Context = DbgTy.getType()->getNominalOrBoundGenericNominal();
      if (Context) {
        if (auto *D = Context->getAsNominalTypeOrNominalTypeExtensionContext())
          if (auto *ClangDecl = D->getClangDecl()) {
            clang::ASTReader &Reader = *CI.getClangInstance().getModuleManager();
            auto Idx = ClangDecl->getOwningModuleID();
            if (auto Info = Reader.getSourceDescriptor(Idx))
              Scope = getOrCreateModule(*Info);
          }
        Context = Context->getParent();
      }
      if (!Scope)
        Scope = getOrCreateContext(Context);
      llvm::DIType *DITy = createType(DbgTy, MangledName, Scope, getFile(Scope));
  
      // Incrementally build the DIRefMap.
      if (auto *CTy = dyn_cast<llvm::DICompositeType>(DITy)) {
  #ifndef NDEBUG
        // Sanity check.
        if (llvm::Metadata *V = DIRefMap.lookup(UID)) {
          auto *CachedTy = cast<llvm::DIType>(V);
          assert(CachedTy == DITy && "conflicting types for one UID");
        }
  #endif
        // If this type supports a UID, enter it to the cache.
        if (auto UID = CTy->getRawIdentifier()) {
          assert(UID->getString() == MangledName &&
                 "Unique identifier is different from mangled name ");
          DIRefMap[UID] = llvm::TrackingMDNodeRef(DITy);
        }
      }
  
      // Store it in the cache.
      DITypeCache.insert({DbgTy.getType(), llvm::TrackingMDNodeRef(DITy)});
  
      return DITy;
    }
  };
  
  IRGenDebugInfoImpl::IRGenDebugInfoImpl(const IRGenOptions &Opts,
                                         ClangImporter &CI, IRGenModule &IGM,
                                         llvm::Module &M, SourceFile *SF)
      : Opts(Opts), CI(CI), SM(IGM.Context.SourceMgr), DBuilder(M),
        IGM(IGM), MetadataTypeDecl(nullptr), InternalType(nullptr),
        LastDebugLoc({}), LastScope(nullptr) {
    assert(Opts.DebugInfoKind > IRGenDebugInfoKind::None &&
           "no debug info should be generated");
    StringRef SourceFileName =
        SF ? SF->getFilename() : StringRef(Opts.MainInputFilename);
    StringRef Dir;
    llvm::SmallString<256> AbsMainFile;
    if (SourceFileName.empty())
      AbsMainFile = "<unknown>";
    else {
      AbsMainFile = SourceFileName;
      llvm::sys::fs::make_absolute(AbsMainFile);
    }
  
    unsigned Lang = llvm::dwarf::DW_LANG_Swift;
    std::string Producer = version::getSwiftFullVersion(
        IGM.Context.LangOpts.EffectiveLanguageVersion);
    bool IsOptimized = Opts.Optimize;
    StringRef Flags = Opts.DWARFDebugFlags;
    unsigned Major, Minor;
    std::tie(Major, Minor) = version::getSwiftNumericVersion();
    unsigned MajorRuntimeVersion = Major;
  
    // No split DWARF on Darwin.
    StringRef SplitName = StringRef();
    // Note that File + Dir need not result in a valid path.
    // Clang is doing the same thing here.
    TheCU = DBuilder.createCompileUnit(
        Lang, DBuilder.createFile(AbsMainFile, Opts.DebugCompilationDir),
        Producer, IsOptimized, Flags, MajorRuntimeVersion, SplitName,
        Opts.DebugInfoKind > IRGenDebugInfoKind::LineTables
            ? llvm::DICompileUnit::FullDebug
            : llvm::DICompileUnit::LineTablesOnly);
    MainFile = getOrCreateFile(BumpAllocatedString(AbsMainFile));
  
    // Because the swift compiler relies on Clang to setup the Module,
    // the clang CU is always created first.  Several dwarf-reading
    // tools (older versions of ld64, and lldb) can get confused if the
    // first CU in an object is empty, so ensure that the Swift CU comes
    // first by rearranging the list of CUs in the LLVM module.
    llvm::NamedMDNode *CU_Nodes = M.getNamedMetadata("llvm.dbg.cu");
    SmallVector<llvm::DICompileUnit *, 2> CUs;
    for (auto *N : CU_Nodes->operands())
      CUs.push_back(cast<llvm::DICompileUnit>(N));
    CU_Nodes->dropAllReferences();
    for (auto CU = CUs.rbegin(), CE = CUs.rend(); CU != CE; ++CU)
      CU_Nodes->addOperand(*CU);
  
    // Create a module for the current compile unit.
    llvm::sys::path::remove_filename(AbsMainFile);
    MainModule = getOrCreateModule(IGM.getSwiftModule(), TheCU, Opts.ModuleName,
                                   AbsMainFile);
    DBuilder.createImportedModule(MainFile, MainModule, MainFile, 0);
  
    // Macro definitions that were defined by the user with "-Xcc -D" on the
    // command line. This does not include any macros defined by ClangImporter.
    llvm::raw_svector_ostream OS(ConfigMacros);
    unsigned I = 0;
    // Translate the macro definitions back into a commmand line.
    for (auto &Macro : Opts.ClangDefines) {
      if (++I > 1)
        OS << ' ';
      OS << '"';
      for (char c : Macro)
        switch (c) {
        case '\\': OS << "\\\\"; break;
        case '"':  OS << "\\\""; break;
        default: OS << c;
        }
      OS << '"';
    }
  }
  
  void IRGenDebugInfoImpl::finalize() {
    assert(LocationStack.empty() && "Mismatch of pushLoc() and popLoc().");
  
    // Get the list of imported modules (which may actually be different
    // from all ImportDecls).
    SmallVector<ModuleDecl::ImportedModule, 8> ModuleWideImports;
    IGM.getSwiftModule()->getImportedModules(ModuleWideImports,
                                             ModuleDecl::ImportFilter::All);
    for (auto M : ModuleWideImports)
      if (!ImportedModules.count(M.second))
        DBuilder.createImportedModule(MainFile, getOrCreateModule(M), MainFile,
                                      0);
  
    // Finalize all replaceable forward declarations.
    for (auto &Ty : ReplaceMap) {
      llvm::TempMDNode FwdDecl(cast<llvm::MDNode>(Ty.second));
      llvm::Metadata *Replacement;
      if (auto *FullType = getTypeOrNull(Ty.first))
        Replacement = FullType;
      else
        Replacement = Ty.second;
      DBuilder.replaceTemporary(std::move(FwdDecl),
                                cast<llvm::MDNode>(Replacement));
    }
    // Finalize the DIBuilder.
    DBuilder.finalize();
  }
  
  void IRGenDebugInfoImpl::setCurrentLoc(IRBuilder &Builder,
                                         const SILDebugScope *DS,
                                         Optional<SILLocation> Loc) {
    assert(DS && "empty scope");
    auto *Scope = getOrCreateScope(DS);
    if (!Scope)
      return;
  
    SILFunction *Fn = DS->getInlinedFunction();
    SILLocation::DebugLoc L;
  
    if (shouldIgnoreAbstractClosure(Loc, DS) || (Fn && Fn->isThunk())) {
      // Reuse the last source location if we are still in the same
      // scope to get a more contiguous line table.
      // Otherwise use a line 0 artificial location.
      if (DS == LastScope)
        L = LastDebugLoc;
      else
        L.Filename = LastDebugLoc.Filename;
    } else {
      // Decode the location.
      L = getDebugLocation(Loc);
    }
  
    auto *File = getOrCreateFile(L.Filename);
    if (File->getFilename() != Scope->getFilename()) {
      // We changed files in the middle of a scope. This happens, for
      // example, when constructors are inlined. Create a new scope to
      // reflect this.
      auto File = getOrCreateFile(L.Filename);
      Scope = DBuilder.createLexicalBlockFile(Scope, File);
    }
  
    // FIXME: Enable this assertion.
    // assert(lineNumberIsSane(Builder, L.Line) &&
    //       "-Onone, but line numbers are not monotonically increasing within
    //       bb");
    LastDebugLoc = L;
    LastScope = DS;
  
    auto *InlinedAt = createInlinedAt(DS);
    assert(((!InlinedAt) || (InlinedAt && Scope)) && "inlined w/o scope");
    assert(parentScopesAreSane(DS) && "parent scope sanity check failed");
    auto DL = llvm::DebugLoc::get(L.Line, L.Column, Scope, InlinedAt);
    Builder.SetCurrentDebugLocation(DL);
  }
  
  void IRGenDebugInfoImpl::clearLoc(IRBuilder &Builder) {
    LastDebugLoc = {};
    LastScope = nullptr;
    Builder.SetCurrentDebugLocation(llvm::DebugLoc());
  }
  
  /// Push the current debug location onto a stack and initialize the
  /// IRBuilder to an empty location.
  void IRGenDebugInfoImpl::pushLoc() {
    LocationStack.push_back(std::make_pair(LastDebugLoc, LastScope));
    LastDebugLoc = {};
    LastScope = nullptr;
  }
  
  /// Restore the current debug location from the stack.
  void IRGenDebugInfoImpl::popLoc() {
    std::tie(LastDebugLoc, LastScope) = LocationStack.pop_back_val();
  }
  
  /// Emit the final line 0 location for the unified trap block at the
  /// end of the function.
  void IRGenDebugInfoImpl::setArtificialTrapLocation(IRBuilder &Builder,
                                                     const SILDebugScope *Scope) {
    auto DL = llvm::DebugLoc::get(0, 0, getOrCreateScope(Scope));
    Builder.SetCurrentDebugLocation(DL);
  }
  
  void IRGenDebugInfoImpl::setEntryPointLoc(IRBuilder &Builder) {
    auto DL = llvm::DebugLoc::get(0, 0, getEntryPointFn(), nullptr);
    Builder.SetCurrentDebugLocation(DL);
  }
  
  llvm::DIScope *IRGenDebugInfoImpl::getEntryPointFn() {
    // Lazily create EntryPointFn.
    if (!EntryPointFn) {
      EntryPointFn = DBuilder.createReplaceableCompositeType(
          llvm::dwarf::DW_TAG_subroutine_type, SWIFT_ENTRY_POINT_FUNCTION,
          MainFile, MainFile, 0);
    }
    return EntryPointFn;
  }
  
  llvm::DIScope *IRGenDebugInfoImpl::getOrCreateScope(const SILDebugScope *DS) {
    if (DS == nullptr)
      return MainFile;
  
    // Try to find it in the cache first.
    auto CachedScope = ScopeCache.find(LocalScope(DS));
    if (CachedScope != ScopeCache.end())
      return cast<llvm::DIScope>(CachedScope->second);
  
    // If this is an (inlined) function scope, the function may
    // not have been created yet.
    if (auto *SILFn = DS->Parent.dyn_cast<SILFunction *>()) {
      auto *FnScope = SILFn->getDebugScope();
      // FIXME: This is a bug in the SIL deserialization.
      if (!FnScope)
        SILFn->setDebugScope(DS);
  
      auto CachedScope = ScopeCache.find(LocalScope(FnScope));
      if (CachedScope != ScopeCache.end())
        return cast<llvm::DIScope>(CachedScope->second);
  
      // Force the debug info for the function to be emitted, even if it
      // is external or has been inlined.
      llvm::Function *Fn = nullptr;
      if (!SILFn->getName().empty() && !SILFn->isZombie())
        Fn = IGM.getAddrOfSILFunction(SILFn, NotForDefinition);
      auto *SP = emitFunction(*SILFn, Fn);
  
      // Cache it.
      ScopeCache[LocalScope(DS)] = llvm::TrackingMDNodeRef(SP);
      return SP;
    }
  
    auto *ParentScope = DS->Parent.get<const SILDebugScope *>();
    llvm::DIScope *Parent = getOrCreateScope(ParentScope);
    assert(isa<llvm::DILocalScope>(Parent) && "not a local scope");
  
    if (Opts.DebugInfoKind <= IRGenDebugInfoKind::LineTables)
      return Parent;
  
    assert(DS->Parent && "lexical block must have a parent subprogram");
    auto L = getStartLocation(DS->Loc);
    llvm::DIFile *File = getOrCreateFile(L.Filename);
    auto *DScope = DBuilder.createLexicalBlock(Parent, File, L.Line, L.Column);
  
    // Cache it.
    ScopeCache[LocalScope(DS)] = llvm::TrackingMDNodeRef(DScope);
    return DScope;
  }
  
  void IRGenDebugInfoImpl::emitImport(ImportDecl *D) {
    if (Opts.DebugInfoKind <= IRGenDebugInfoKind::LineTables)
      return;
  
    swift::ModuleDecl *M = IGM.Context.getModule(D->getModulePath());
    if (!M &&
        D->getModulePath()[0].first == IGM.Context.TheBuiltinModule->getName())
      M = IGM.Context.TheBuiltinModule;
    if (!M) {
      assert(M && "Could not find module for import decl.");
      return;
    }
    ModuleDecl::ImportedModule Imported = {D->getModulePath(), M};
    auto DIMod = getOrCreateModule(Imported);
    auto L = getDebugLoc(*this, D);
    auto *File = getOrCreateFile(L.Filename);
    DBuilder.createImportedModule(File, DIMod, File, L.Line);
    ImportedModules.insert(Imported.second);
  }
  
  llvm::DISubprogram *IRGenDebugInfoImpl::emitFunction(SILFunction &SILFn,
                                                       llvm::Function *Fn) {
    auto *DS = SILFn.getDebugScope();
    assert(DS && "SIL function has no debug scope");
    (void)DS;
    return emitFunction(SILFn.getDebugScope(), Fn, SILFn.getRepresentation(),
                        SILFn.getLoweredType(), SILFn.getDeclContext(),
                        SILFn.getGenericEnvironment());
  }
  
  llvm::DISubprogram *
  IRGenDebugInfoImpl::emitFunction(const SILDebugScope *DS, llvm::Function *Fn,
                                   SILFunctionTypeRepresentation Rep,
                                   SILType SILTy, DeclContext *DeclCtx,
                                   GenericEnvironment *GE) {
    auto Cached = ScopeCache.find(LocalScope(DS));
    if (Cached != ScopeCache.end()) {
      auto SP = cast<llvm::DISubprogram>(Cached->second);
      // If we created the DISubprogram for a forward declaration,
      // attach it to the function now.
      if (!Fn->getSubprogram() && !Fn->isDeclaration())
        Fn->setSubprogram(SP);
      return SP;
    }
  
    // Some IRGen-generated helper functions don't have a corresponding
    // SIL function, hence the dyn_cast.
    auto *SILFn = DS ? DS->Parent.dyn_cast<SILFunction *>() : nullptr;
    StringRef LinkageName;
    if (Fn)
      LinkageName = Fn->getName();
    else if (DS)
      LinkageName = SILFn->getName();
    else
      llvm_unreachable("function has no mangled name");
  
    StringRef Name;
    if (DS) {
      if (DS->Loc.isSILFile())
        Name = SILFn->getName();
      else
        Name = getName(DS->Loc);
    }
  
    SILLocation::DebugLoc L;
    unsigned ScopeLine = 0; /// The source line used for the function prologue.
    // Bare functions and thunks should not have any line numbers. This
    // is especially important for shared functions like reabstraction
    // thunk helpers, where DS->Loc is an arbitrary location of whichever use
    // was emitted first.
    if (DS && (!SILFn || (!SILFn->isBare() && !SILFn->isThunk()))) {
      L = decodeDebugLoc(DS->Loc);
      ScopeLine = L.Line;
      if (!DS->Loc.isDebugInfoLoc())
        L = decodeSourceLoc(DS->Loc.getSourceLoc());
    }
  
    auto Line = L.Line;
    auto File = getOrCreateFile(L.Filename);
    llvm::DIScope *Scope = MainModule;
    if (SILFn && SILFn->getDeclContext())
      Scope = getOrCreateContext(SILFn->getDeclContext()->getParent());
  
    // We know that main always comes from MainFile.
    if (LinkageName == SWIFT_ENTRY_POINT_FUNCTION) {
      if (L.Filename.empty())
        File = MainFile;
      Line = 1;
      Name = LinkageName;
    }
  
    CanSILFunctionType FnTy = getFunctionType(SILTy);
    auto Params = Opts.DebugInfoKind > IRGenDebugInfoKind::LineTables
                      ? createParameterTypes(SILTy, DeclCtx, GE)
                      : nullptr;
    llvm::DISubroutineType *DIFnTy = DBuilder.createSubroutineType(Params);
    llvm::DITemplateParameterArray TemplateParameters = nullptr;
    llvm::DISubprogram *Decl = nullptr;
  
    // Various flags.
    bool IsLocalToUnit = Fn ? Fn->hasInternalLinkage() : true;
    bool IsDefinition = true;
    bool IsOptimized = Opts.Optimize;
    llvm::DINode::DIFlags Flags = llvm::DINode::FlagZero;
  
    // Mark everything that is not visible from the source code (i.e.,
    // does not have a Swift name) as artificial, so the debugger can
    // ignore it. Explicit closures are exempt from this rule. We also
    // make an exception for toplevel code, which, although it does not
    // have a Swift name, does appear prominently in the source code.
    if ((Name.empty() && LinkageName != SWIFT_ENTRY_POINT_FUNCTION &&
         !isExplicitClosure(SILFn)) ||
        // ObjC thunks should also not show up in the linetable, because we
        // never want to set a breakpoint there.
        (Rep == SILFunctionTypeRepresentation::ObjCMethod) ||
        isAllocatingConstructor(Rep, DeclCtx)) {
      Flags |= llvm::DINode::FlagArtificial;
      ScopeLine = 0;
    }
  
    if (FnTy &&
        FnTy->getRepresentation() == SILFunctionType::Representation::Block)
      Flags |= llvm::DINode::FlagAppleBlock;
  
    // Get the throws information.
    llvm::DITypeArray Error = nullptr;
    if (FnTy)
      if (auto ErrorInfo = FnTy->getOptionalErrorResult()) {
        auto DTI = DebugTypeInfo::getFromTypeInfo(
            nullptr, nullptr, ErrorInfo->getType(),
            IGM.getTypeInfo(IGM.silConv.getSILType(*ErrorInfo)));
        Error = DBuilder.getOrCreateArray({getOrCreateType(DTI)}).get();
      }
  
    // Construct the DISubprogram.
    llvm::DISubprogram *SP = DBuilder.createFunction(
        Scope, Name, LinkageName, File, Line, DIFnTy, IsLocalToUnit, IsDefinition,
        ScopeLine, Flags, IsOptimized, TemplateParameters, Decl, Error);
  
    if (Fn && !Fn->isDeclaration())
      Fn->setSubprogram(SP);
  
    // RAUW the entry point function forward declaration with the real thing.
    if (LinkageName == SWIFT_ENTRY_POINT_FUNCTION) {
      if (EntryPointFn) {
        assert(EntryPointFn->isTemporary() &&
               "more than one entry point function");
        EntryPointFn->replaceAllUsesWith(SP);
        llvm::MDNode::deleteTemporary(EntryPointFn);
      }
      EntryPointFn = SP;
    }
  
    if (!DS)
      return nullptr;
  
    ScopeCache[LocalScope(DS)] = llvm::TrackingMDNodeRef(SP);
    return SP;
  }
  
  void IRGenDebugInfoImpl::emitArtificialFunction(IRBuilder &Builder,
                                                  llvm::Function *Fn,
                                                  SILType SILTy) {
    RegularLocation ALoc = RegularLocation::getAutoGeneratedLocation();
    const SILDebugScope *Scope = new (IGM.getSILModule()) SILDebugScope(ALoc);
    emitFunction(Scope, Fn, SILFunctionTypeRepresentation::Thin, SILTy);
    setCurrentLoc(Builder, Scope);
  }
  
  void IRGenDebugInfoImpl::emitVariableDeclaration(
      IRBuilder &Builder, ArrayRef<llvm::Value *> Storage, DebugTypeInfo DbgTy,
      const SILDebugScope *DS, ValueDecl *VarDecl, StringRef Name, unsigned ArgNo,
      IndirectionKind Indirection, ArtificialKind Artificial) {
    // Self is always an artificial argument.
    if (ArgNo > 0 && Name == IGM.Context.Id_self.str())
      Artificial = ArtificialValue;
  
    // FIXME: Make this an assertion.
    // assert(DS && "variable has no scope");
    if (!DS)
      return;
  
    if (Opts.DebugInfoKind <= IRGenDebugInfoKind::LineTables)
      return;
  
    // Currently, the DeclContext is needed to mangle archetypes. Bail out if
    // it's missing.
    if (DbgTy.Type->hasArchetype() && !DbgTy.DeclCtx)
      return;
  
    if (!DbgTy.size)
      DbgTy.size = getStorageSize(IGM.DataLayout, Storage);
  
    auto *Scope = dyn_cast<llvm::DILocalScope>(getOrCreateScope(DS));
    assert(Scope && "variable has no local scope");
    auto Loc = getDebugLoc(*this, VarDecl);
  
    // FIXME: this should be the scope of the type's declaration.
    // If this is an argument, attach it to the current function scope.
    if (ArgNo > 0) {
      while (isa<llvm::DILexicalBlock>(Scope))
        Scope = cast<llvm::DILexicalBlock>(Scope)->getScope();
    }
    assert(Scope && isa<llvm::DIScope>(Scope) && "variable has no scope");
    llvm::DIFile *Unit = getFile(Scope);
    llvm::DIType *DITy = getOrCreateType(DbgTy);
    assert(DITy && "could not determine debug type of variable");
  
    unsigned Line = Loc.Line;
    llvm::DINode::DIFlags Flags = llvm::DINode::FlagZero;
    if (Artificial || DITy->isArtificial() || DITy == InternalType)
      Flags |= llvm::DINode::FlagArtificial;
  
    // This could be Opts.Optimize if we would also unique DIVariables here.
    bool Optimized = false;
    // Create the descriptor for the variable.
    llvm::DILocalVariable *Var =
        (ArgNo > 0) ? DBuilder.createParameterVariable(
                          Scope, Name, ArgNo, Unit, Line, DITy, Optimized, Flags)
                    : DBuilder.createAutoVariable(Scope, Name, Unit, Line, DITy,
                                                  Optimized, Flags);
  
    // Running variables for the current/previous piece.
    bool IsPiece = Storage.size() > 1;
    uint64_t SizeOfByte = CI.getTargetInfo().getCharWidth();
    unsigned AlignInBits = SizeOfByte;
    unsigned OffsetInBits = 0;
    unsigned SizeInBits = 0;
  
    for (llvm::Value *Piece : Storage) {
      SmallVector<uint64_t, 3> Operands;
      if (Indirection)
        Operands.push_back(llvm::dwarf::DW_OP_deref);
  
      // There are variables without storage, such as "struct { func foo() {}
      // }". Emit them as constant 0.
      if (isa<llvm::UndefValue>(Piece))
        Piece = llvm::ConstantInt::get(IGM.Int64Ty, 0);
  
      if (IsPiece) {
        // Advance the offset and align it for the next piece.
        OffsetInBits += llvm::alignTo(SizeInBits, AlignInBits);
        SizeInBits = IGM.DataLayout.getTypeSizeInBits(Piece->getType());
        AlignInBits = IGM.DataLayout.getABITypeAlignment(Piece->getType());
        if (!AlignInBits)
          AlignInBits = SizeOfByte;
  
        // Sanity checks.
        assert(SizeInBits && "zero-sized piece");
        assert(SizeInBits < getSizeInBits(Var) && "piece covers entire var");
        assert(OffsetInBits + SizeInBits <= getSizeInBits(Var) && "pars > totum");
  
        // Add the piece DWARF expression.
        Operands.push_back(llvm::dwarf::DW_OP_LLVM_fragment);
        Operands.push_back(OffsetInBits);
        Operands.push_back(SizeInBits);
      }
      emitDbgIntrinsic(Builder, Piece, Var, DBuilder.createExpression(Operands),
                       Line, Loc.Column, Scope, DS);
    }
  
    // Emit locationless intrinsic for variables that were optimized away.
    if (Storage.size() == 0)
      emitDbgIntrinsic(Builder, llvm::ConstantInt::get(IGM.Int64Ty, 0), Var,
                       DBuilder.createExpression(), Line, Loc.Column, Scope, DS);
  }
  
  void IRGenDebugInfoImpl::emitDbgIntrinsic(
      IRBuilder &Builder, llvm::Value *Storage, llvm::DILocalVariable *Var,
      llvm::DIExpression *Expr, unsigned Line, unsigned Col,
      llvm::DILocalScope *Scope, const SILDebugScope *DS) {
    // Set the location/scope of the intrinsic.
    auto *InlinedAt = createInlinedAt(DS);
    auto DL = llvm::DebugLoc::get(Line, Col, Scope, InlinedAt);
    auto *BB = Builder.GetInsertBlock();
  
    // An alloca may only be described by exactly one dbg.declare.
    if (isa<llvm::AllocaInst>(Storage) && llvm::FindAllocaDbgDeclare(Storage))
      return;
  
    // A dbg.declare is only meaningful if there is a single alloca for
    // the variable that is live throughout the function. With SIL
    // optimizations this is not guaranteed and a variable can end up in
    // two allocas (for example, one function inlined twice).
    if (auto *Alloca = dyn_cast<llvm::AllocaInst>(Storage)) {
      auto *ParentBB = Alloca->getParent();
      auto InsertBefore = std::next(Alloca->getIterator());
      if (InsertBefore != ParentBB->end())
        DBuilder.insertDeclare(Alloca, Var, Expr, DL, &*InsertBefore);
      else
        DBuilder.insertDeclare(Alloca, Var, Expr, DL, ParentBB);
      return;
    }
  
    // If the storage is an instruction, insert the dbg.value directly after it.
    if (auto *I = dyn_cast<llvm::Instruction>(Storage)) {
      auto InsPt = std::next(I->getIterator());
      auto E = I->getParent()->end();
      while (InsPt != E && isa<llvm::PHINode>(&*InsPt))
        ++InsPt;
      if (InsPt != E) {
        DBuilder.insertDbgValueIntrinsic(Storage, Var, Expr, DL, &*InsPt);
        return;
      }
    }
  
    // Otherwise just insert it at the current insertion point.
    DBuilder.insertDbgValueIntrinsic(Storage, Var, Expr, DL, BB);
  }
  
  void IRGenDebugInfoImpl::emitGlobalVariableDeclaration(
      llvm::GlobalVariable *Var, StringRef Name, StringRef LinkageName,
      DebugTypeInfo DbgTy, bool IsLocalToUnit, Optional<SILLocation> Loc) {
    if (Opts.DebugInfoKind <= IRGenDebugInfoKind::LineTables)
      return;
  
    llvm::DIType *Ty = getOrCreateType(DbgTy);
    if (Ty->isArtificial() || Ty == InternalType || !Loc)
      // FIXME: Really these should be marked as artificial, but LLVM
      // currently has no support for flags to be put on global
      // variables. In the mean time, elide these variables, they
      // would confuse both the user and LLDB.
      return;
  
    auto L = getStartLocation(Loc);
    auto File = getOrCreateFile(L.Filename);
  
    // Emit it as global variable of the current module.
    auto *Expr = Var ? nullptr : DBuilder.createConstantValueExpression(0);
    auto *GV = DBuilder.createGlobalVariableExpression(
        MainModule, Name, LinkageName, File, L.Line, Ty, IsLocalToUnit, Expr);
    if (Var)
      Var->addDebugInfo(GV);
  }
  
  void IRGenDebugInfoImpl::emitTypeMetadata(IRGenFunction &IGF,
                                            llvm::Value *Metadata,
                                            StringRef Name) {
    if (Opts.DebugInfoKind <= IRGenDebugInfoKind::LineTables)
      return;
  
    auto TName = BumpAllocatedString(("$swift.type." + Name).str());
    auto DbgTy = DebugTypeInfo::getMetadata(
        getMetadataType()->getDeclaredInterfaceType().getPointer(),
        Metadata->getType(), Size(CI.getTargetInfo().getPointerWidth(0)),
        Alignment(CI.getTargetInfo().getPointerAlign(0)));
    emitVariableDeclaration(IGF.Builder, Metadata, DbgTy, IGF.getDebugScope(),
                            nullptr, TName, 0,
                            // swift.type is already a pointer type,
                            // having a shadow copy doesn't add another
                            // layer of indirection.
                            DirectValue, ArtificialValue);
  }
  
  SILLocation::DebugLoc IRGenDebugInfoImpl::decodeSourceLoc(SourceLoc SL) {
    auto &Cached = DebugLocCache[SL.getOpaquePointerValue()];
    if (Cached.Filename.empty())
      Cached = SILLocation::decode(SL, SM);
    return Cached;
  }
  
  } // anonymous namespace
  
  IRGenDebugInfo *IRGenDebugInfo::createIRGenDebugInfo(const IRGenOptions &Opts,
                                                       ClangImporter &CI,
                                                       IRGenModule &IGM,
                                                       llvm::Module &M,
                                                       SourceFile *SF) {
    return new IRGenDebugInfoImpl(Opts, CI, IGM, M, SF);
  }
  
  
  IRGenDebugInfo::~IRGenDebugInfo() {}
  
  // Forwarding to the private implementation.
  void IRGenDebugInfo::finalize() {
    static_cast<IRGenDebugInfoImpl *>(this)->finalize();
  }
  
  void IRGenDebugInfo::setCurrentLoc(IRBuilder &Builder, const SILDebugScope *DS,
                                     Optional<SILLocation> Loc) {
    static_cast<IRGenDebugInfoImpl *>(this)->setCurrentLoc(Builder, DS, Loc);
  }
  
  void IRGenDebugInfo::clearLoc(IRBuilder &Builder) {
    static_cast<IRGenDebugInfoImpl *>(this)->clearLoc(Builder);
  }
  
  void IRGenDebugInfo::pushLoc() {
    static_cast<IRGenDebugInfoImpl *>(this)->pushLoc();
  }
  
  void IRGenDebugInfo::popLoc() {
    static_cast<IRGenDebugInfoImpl *>(this)->popLoc();
  }
  
  void IRGenDebugInfo::setArtificialTrapLocation(IRBuilder &Builder,
                                                 const SILDebugScope *Scope) {
    static_cast<IRGenDebugInfoImpl *>(this)->setArtificialTrapLocation(Builder,
                                                                       Scope);
  }
  
  void IRGenDebugInfo::setEntryPointLoc(IRBuilder &Builder) {
    static_cast<IRGenDebugInfoImpl *>(this)->setEntryPointLoc(Builder);
  }
  
  llvm::DIScope *IRGenDebugInfo::getEntryPointFn() {
    return static_cast<IRGenDebugInfoImpl *>(this)->getEntryPointFn();
  }
  
  llvm::DIScope *IRGenDebugInfo::getOrCreateScope(const SILDebugScope *DS) {
    return static_cast<IRGenDebugInfoImpl *>(this)->getOrCreateScope(DS);
  }
  
  void IRGenDebugInfo::emitImport(ImportDecl *D) {
    static_cast<IRGenDebugInfoImpl *>(this)->emitImport(D);
  }
  
  llvm::DISubprogram *
  IRGenDebugInfo::emitFunction(const SILDebugScope *DS, llvm::Function *Fn,
                               SILFunctionTypeRepresentation Rep, SILType Ty,
                               DeclContext *DeclCtx,
                               GenericEnvironment *GE) {
    return static_cast<IRGenDebugInfoImpl *>(this)->emitFunction(DS, Fn, Rep, Ty,
                                                          DeclCtx);
  }
  
  llvm::DISubprogram *IRGenDebugInfo::emitFunction(SILFunction &SILFn,
                                                   llvm::Function *Fn) {
    return static_cast<IRGenDebugInfoImpl *>(this)->emitFunction(SILFn, Fn);
  }
  
  void IRGenDebugInfo::emitArtificialFunction(IRBuilder &Builder,
                                              llvm::Function *Fn,
                                              SILType SILTy) {
    static_cast<IRGenDebugInfoImpl *>(this)->emitArtificialFunction(Builder,
                                                                    Fn, SILTy);
  }
  
  void IRGenDebugInfo::emitVariableDeclaration(
      IRBuilder &Builder, ArrayRef<llvm::Value *> Storage, DebugTypeInfo Ty,
      const SILDebugScope *DS, ValueDecl *VarDecl, StringRef Name,
      unsigned ArgNo, IndirectionKind Indirection,
        ArtificialKind Artificial) {
    static_cast<IRGenDebugInfoImpl *>(this)->emitVariableDeclaration(
        Builder, Storage, Ty, DS, VarDecl, Name, ArgNo, Indirection, Artificial);
  }
  
  void IRGenDebugInfo::emitDbgIntrinsic(IRBuilder &Builder, llvm::Value *Storage,
                                        llvm::DILocalVariable *Var,
                                        llvm::DIExpression *Expr, unsigned Line,
                                        unsigned Col, llvm::DILocalScope *Scope,
                                        const SILDebugScope *DS) {
    static_cast<IRGenDebugInfoImpl *>(this)->emitDbgIntrinsic(
        Builder, Storage, Var, Expr, Line, Col, Scope, DS);
  }
  
  void IRGenDebugInfo::emitGlobalVariableDeclaration(
      llvm::GlobalVariable *Storage, StringRef Name, StringRef LinkageName,
      DebugTypeInfo DebugType, bool IsLocalToUnit, Optional<SILLocation> Loc) {
    static_cast<IRGenDebugInfoImpl *>(this)->emitGlobalVariableDeclaration(
        Storage, Name, LinkageName, DebugType, IsLocalToUnit, Loc);
  }
  
  void IRGenDebugInfo::emitTypeMetadata(IRGenFunction &IGF, llvm::Value *Metadata,
                                        StringRef Name) {
    static_cast<IRGenDebugInfoImpl *>(this)->emitTypeMetadata(IGF, Metadata,
                                                              Name);
  }
  
  llvm::DIBuilder &IRGenDebugInfo::getBuilder() {
    return static_cast<IRGenDebugInfoImpl *>(this)->getBuilder();
  }
  
  SILLocation::DebugLoc IRGenDebugInfo::decodeSourceLoc(SourceLoc SL) {
    return static_cast<IRGenDebugInfoImpl *>(this)->decodeSourceLoc(SL);
  }
  
  AutoRestoreLocation::AutoRestoreLocation(IRGenDebugInfo *DI, IRBuilder &Builder)
      : DI(DI), Builder(Builder) {
    if (DI)
      SavedLocation = Builder.getCurrentDebugLocation();
  }
  
  /// Autorestore everything back to normal.
  AutoRestoreLocation::~AutoRestoreLocation() {
    if (DI)
      Builder.SetCurrentDebugLocation(SavedLocation);
  }
  
  ArtificialLocation::ArtificialLocation(const SILDebugScope *DS,
                                         IRGenDebugInfo *DI, IRBuilder &Builder)
      : AutoRestoreLocation(DI, Builder) {
    if (DI) {
      auto DL = llvm::DebugLoc::get(0, 0, DI->getOrCreateScope(DS));
      Builder.SetCurrentDebugLocation(DL);
    }
  }
  
  PrologueLocation::PrologueLocation(IRGenDebugInfo *DI, IRBuilder &Builder)
      : AutoRestoreLocation(DI, Builder) {
    if (DI)
      DI->clearLoc(Builder);
  }
  