//===- MicrosoftDemangle.cpp ----------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines a demangler for MSVC-style mangled symbols.
//
// This file has no dependencies on the rest of LLVM so that it can be
// easily reused in other programs such as libcxxabi.
//
//===----------------------------------------------------------------------===//

#include "llvm/Demangle/Demangle.h"

#include "Compiler.h"
#include "StringView.h"
#include "Utility.h"

#include <cctype>

// This memory allocator is extremely fast, but it doesn't call dtors
// for allocated objects. That means you can't use STL containers
// (such as std::vector) with this allocator. But it pays off --
// the demangler is 3x faster with this allocator compared to one with
// STL containers.
namespace {
class ArenaAllocator {
  struct AllocatorNode {
    uint8_t *Buf = nullptr;
    size_t Used = 0;
    AllocatorNode *Next = nullptr;
  };

public:
  ArenaAllocator() : Head(new AllocatorNode) { Head->Buf = new uint8_t[Unit]; }

  ~ArenaAllocator() {
    while (Head) {
      assert(Head->Buf);
      delete[] Head->Buf;
      Head = Head->Next;
    }
  }

  void *alloc(size_t Size) {
    assert(Size < Unit);
    assert(Head && Head->Buf);

    uint8_t *P = Head->Buf + Head->Used;
    Head->Used += Size;
    if (Head->Used < Unit)
      return P;

    AllocatorNode *NewHead = new AllocatorNode;
    NewHead->Buf = new uint8_t[ArenaAllocator::Unit];
    NewHead->Next = Head;
    Head = NewHead;
    NewHead->Used = Size;
    return NewHead->Buf;
  }

private:
  static constexpr size_t Unit = 4096;

  AllocatorNode *Head = nullptr;
};
} // namespace

static bool startsWithDigit(StringView S) {
  return !S.empty() && std::isdigit(S.front());
}

// Writes a space if the last token does not end with a punctuation.
static void outputSpaceIfNecessary(OutputStream &OS) {
  if (OS.empty())
    return;

  char C = OS.back();
  if (isalnum(C) || C == '>')
    OS << " ";
}

void *operator new(size_t Size, ArenaAllocator &A) { return A.alloc(Size); }

// Storage classes
enum Qualifiers : uint8_t {
  Q_None = 0,
  Q_Const = 1 << 0,
  Q_Volatile = 1 << 1,
  Q_Far = 1 << 2,
  Q_Huge = 1 << 3,
  Q_Unaligned = 1 << 4,
  Q_Restrict = 1 << 5,
  Q_Pointer64 = 1 << 6
};

enum class StorageClass : uint8_t {
  None,
  PrivateStatic,
  ProtectedStatic,
  PublicStatic,
  Global,
  FunctionLocalStatic
};

enum class QualifierMangleMode { Drop, Mangle, Result };
enum class QualifierMangleLocation { Member, NonMember, Detect };

// Calling conventions
enum class CallingConv : uint8_t {
  None,
  Cdecl,
  Pascal,
  Thiscall,
  Stdcall,
  Fastcall,
  Clrcall,
  Eabi,
  Vectorcall,
  Regcall,
};

enum class ReferenceKind : uint8_t { None, LValueRef, RValueRef };

// Types
enum class PrimTy : uint8_t {
  Unknown,
  None,
  Function,
  Ptr,
  Ref,
  Array,

  Struct,
  Union,
  Class,
  Enum,

  Void,
  Bool,
  Char,
  Schar,
  Uchar,
  Short,
  Ushort,
  Int,
  Uint,
  Long,
  Ulong,
  Int64,
  Uint64,
  Wchar,
  Float,
  Double,
  Ldouble,
};

// Function classes
enum FuncClass : uint8_t {
  Public = 1 << 0,
  Protected = 1 << 1,
  Private = 1 << 2,
  Global = 1 << 3,
  Static = 1 << 4,
  Virtual = 1 << 5,
  Far = 1 << 6,
};

namespace {

struct Type;

// Represents a list of parameters (template params or function arguments.
// It's represented as a linked list.
struct ParamList {
  Type *Current = nullptr;

  ParamList *Next = nullptr;
};

// The type class. Mangled symbols are first parsed and converted to
// this type and then converted to string.
struct Type {
  virtual ~Type() {}

  virtual Type *clone(ArenaAllocator &Arena) const;

  // Write the "first half" of a given type.  This is a static functions to
  // give the code a chance to do processing that is common to a subset of
  // subclasses
  static void outputPre(OutputStream &OS, Type &Ty);

  // Write the "second half" of a given type.  This is a static functions to
  // give the code a chance to do processing that is common to a subset of
  // subclasses
  static void outputPost(OutputStream &OS, Type &Ty);

  virtual void outputPre(OutputStream &OS);
  virtual void outputPost(OutputStream &OS);

  // Primitive type such as Int.
  PrimTy Prim = PrimTy::Unknown;

  Qualifiers Quals = Q_None;
  StorageClass Storage = StorageClass::None; // storage class
};

// Represents an identifier which may be a template.
struct Name {
  // Name read from an MangledName string.
  StringView Str;

  // Overloaded operators are represented as special BackReferences in mangled
  // symbols. If this is an operator name, "op" has an operator name (e.g.
  // ">>"). Otherwise, empty.
  StringView Operator;

  // Template parameters. Null if not a template.
  ParamList TemplateParams;

  // Nested BackReferences (e.g. "A::B::C") are represented as a linked list.
  Name *Next = nullptr;
};

struct PointerType : public Type {
  Type *clone(ArenaAllocator &Arena) const override;
  void outputPre(OutputStream &OS);
  void outputPost(OutputStream &OS) override;

  bool isMemberPointer() const { return false; }

  // Represents a type X in "a pointer to X", "a reference to X",
  // "an array of X", or "a function returning X".
  Type *Pointee = nullptr;
};

struct FunctionType : public Type {
  Type *clone(ArenaAllocator &Arena) const override;
  void outputPre(OutputStream &OS);
  void outputPost(OutputStream &OS);

  Type *ReturnType = nullptr;
  // If this is a reference, the type of reference.
  ReferenceKind RefKind;

  CallingConv CallConvention;
  FuncClass FunctionClass;

  ParamList Params;
};

struct UdtType : public Type {
  Type *clone(ArenaAllocator &Arena) const override;
  void outputPre(OutputStream &OS) override;

  Name *UdtName = nullptr;
};

struct ArrayType : public Type {
  Type *clone(ArenaAllocator &Arena) const override;
  void outputPre(OutputStream &OS) override;
  void outputPost(OutputStream &OS) override;

  // Either NextDimension or ElementType will be valid.
  ArrayType *NextDimension = nullptr;
  uint32_t ArrayDimension = 0;

  Type *ElementType = nullptr;
};

} // namespace

static void outputCallingConvention(OutputStream &OS, CallingConv CC) {
  outputSpaceIfNecessary(OS);

  switch (CC) {
  case CallingConv::Cdecl:
    OS << "__cdecl";
    break;
  case CallingConv::Fastcall:
    OS << "__fastcall";
    break;
  case CallingConv::Pascal:
    OS << "__pascal";
    break;
  case CallingConv::Regcall:
    OS << "__regcall";
    break;
  case CallingConv::Stdcall:
    OS << "__stdcall";
    break;
  case CallingConv::Thiscall:
    OS << "__thiscall";
    break;
  case CallingConv::Eabi:
    OS << "__eabi";
    break;
  case CallingConv::Vectorcall:
    OS << "__vectorcall";
    break;
  case CallingConv::Clrcall:
    OS << "__clrcall";
    break;
  default:
    break;
  }
}

// Write a function or template parameter list.
static void outputParameterList(OutputStream &OS, const ParamList &Params) {
  const ParamList *Head = &Params;
  while (Head) {
    Type::outputPre(OS, *Head->Current);
    Type::outputPost(OS, *Head->Current);

    Head = Head->Next;

    if (Head)
      OS << ", ";
  }
}

static void outputTemplateParams(OutputStream &OS, const Name &TheName) {
  if (!TheName.TemplateParams.Current)
    return;

  OS << "<";
  outputParameterList(OS, TheName.TemplateParams);
  OS << ">";
}

static void outputName(OutputStream &OS, const Name *TheName) {
  if (!TheName)
    return;

  outputSpaceIfNecessary(OS);

  // Print out namespaces or outer class BackReferences.
  for (; TheName->Next; TheName = TheName->Next) {
    OS << TheName->Str;
    outputTemplateParams(OS, *TheName);
    OS << "::";
  }

  // Print out a regular name.
  if (TheName->Operator.empty()) {
    OS << TheName->Str;
    outputTemplateParams(OS, *TheName);
    return;
  }

  // Print out ctor or dtor.
  if (TheName->Operator == "ctor" || TheName->Operator == "dtor") {
    OS << TheName->Str;
    outputTemplateParams(OS, *TheName);
    OS << "::";
    if (TheName->Operator == "dtor")
      OS << "~";
    OS << TheName->Str;
    outputTemplateParams(OS, *TheName);
    return;
  }

  // Print out an overloaded operator.
  if (!TheName->Str.empty())
    OS << TheName->Str << "::";
  OS << "operator" << TheName->Operator;
}

namespace {

Type *Type::clone(ArenaAllocator &Arena) const {
  return new (Arena) Type(*this);
}

// Write the "first half" of a given type.
void Type::outputPre(OutputStream &OS, Type &Ty) {
  // Function types require custom handling of const and static so we
  // handle them separately.  All other types use the same decoration
  // for these modifiers, so handle them here in common code.
  if (Ty.Prim == PrimTy::Function) {
    Ty.outputPre(OS);
    return;
  }

  switch (Ty.Storage) {
  case StorageClass::PrivateStatic:
  case StorageClass::PublicStatic:
  case StorageClass::ProtectedStatic:
    OS << "static ";
  default:
    break;
  }
  Ty.outputPre(OS);

  if (Ty.Quals & Q_Const) {
    outputSpaceIfNecessary(OS);
    OS << "const";
  }

  if (Ty.Quals & Q_Volatile) {
    outputSpaceIfNecessary(OS);
    OS << "volatile";
  }
}

// Write the "second half" of a given type.
void Type::outputPost(OutputStream &OS, Type &Ty) { Ty.outputPost(OS); }

void Type::outputPre(OutputStream &OS) {
  switch (Prim) {
  case PrimTy::Void:
    OS << "void";
    break;
  case PrimTy::Bool:
    OS << "bool";
    break;
  case PrimTy::Char:
    OS << "char";
    break;
  case PrimTy::Schar:
    OS << "signed char";
    break;
  case PrimTy::Uchar:
    OS << "unsigned char";
    break;
  case PrimTy::Short:
    OS << "short";
    break;
  case PrimTy::Ushort:
    OS << "unsigned short";
    break;
  case PrimTy::Int:
    OS << "int";
    break;
  case PrimTy::Uint:
    OS << "unsigned int";
    break;
  case PrimTy::Long:
    OS << "long";
    break;
  case PrimTy::Ulong:
    OS << "unsigned long";
    break;
  case PrimTy::Int64:
    OS << "__int64";
    break;
  case PrimTy::Uint64:
    OS << "unsigned __int64";
    break;
  case PrimTy::Wchar:
    OS << "wchar_t";
    break;
  case PrimTy::Float:
    OS << "float";
    break;
  case PrimTy::Double:
    OS << "double";
    break;
  case PrimTy::Ldouble:
    OS << "long double";
    break;
  default:
    assert(false && "Invalid primitive type!");
  }
}
void Type::outputPost(OutputStream &OS) {}

Type *PointerType::clone(ArenaAllocator &Arena) const {
  return new (Arena) PointerType(*this);
}

void PointerType::outputPre(OutputStream &OS) {
  Type::outputPre(OS, *Pointee);

  outputSpaceIfNecessary(OS);

  if (Quals & Q_Unaligned)
    OS << "__unaligned ";

  // "[]" and "()" (for function parameters) take precedence over "*",
  // so "int *x(int)" means "x is a function returning int *". We need
  // parentheses to supercede the default precedence. (e.g. we want to
  // emit something like "int (*x)(int)".)
  if (Pointee->Prim == PrimTy::Function || Pointee->Prim == PrimTy::Array)
    OS << "(";

  if (Prim == PrimTy::Ptr)
    OS << "*";
  else
    OS << "&";

  // FIXME: We should output this, but it requires updating lots of tests.
  // if (Ty.Quals & Q_Pointer64)
  //  OS << " __ptr64";
  if (Quals & Q_Restrict)
    OS << " __restrict";
}

void PointerType::outputPost(OutputStream &OS) {
  if (Pointee->Prim == PrimTy::Function || Pointee->Prim == PrimTy::Array)
    OS << ")";

  Type::outputPost(OS, *Pointee);
}

Type *FunctionType::clone(ArenaAllocator &Arena) const {
  return new (Arena) FunctionType(*this);
}

void FunctionType::outputPre(OutputStream &OS) {
  if (!(FunctionClass & Global)) {
    if (FunctionClass & Static)
      OS << "static ";
  }

  if (ReturnType)
    Type::outputPre(OS, *ReturnType);

  outputCallingConvention(OS, CallConvention);
}

void FunctionType::outputPost(OutputStream &OS) {
  OS << "(";
  outputParameterList(OS, Params);
  OS << ")";
  if (Quals & Q_Const)
    OS << " const";
  if (Quals & Q_Volatile)
    OS << " volatile";
  return;
}

Type *UdtType::clone(ArenaAllocator &Arena) const {
  return new (Arena) UdtType(*this);
}

void UdtType::outputPre(OutputStream &OS) {
  switch (Prim) {
  case PrimTy::Class:
    OS << "class ";
    break;
  case PrimTy::Struct:
    OS << "struct ";
    break;
  case PrimTy::Union:
    OS << "union ";
    break;
  case PrimTy::Enum:
    OS << "enum ";
    break;
  default:
    assert(false && "Not a udt type!");
  }

  outputName(OS, UdtName);
}

Type *ArrayType::clone(ArenaAllocator &Arena) const {
  return new (Arena) ArrayType(*this);
}

void ArrayType::outputPre(OutputStream &OS) {
  Type::outputPre(OS, *ElementType);
}

void ArrayType::outputPost(OutputStream &OS) {
  if (ArrayDimension > 0)
    OS << "[" << ArrayDimension << "]";
  if (NextDimension)
    Type::outputPost(OS, *NextDimension);
  else if (ElementType)
    Type::outputPost(OS, *ElementType);
}

} // namespace

namespace {

// Demangler class takes the main role in demangling symbols.
// It has a set of functions to parse mangled symbols into Type instances.
// It also has a set of functions to cnovert Type instances to strings.
class Demangler {
public:
  Demangler(OutputStream &OS, StringView s) : OS(OS), MangledName(s) {}

  // You are supposed to call parse() first and then check if error is true.  If
  // it is false, call output() to write the formatted name to the given stream.
  void parse();
  void output();

  // True if an error occurred.
  bool Error = false;

private:
  Type *demangleVariableEncoding();
  Type *demangleFunctionEncoding();

  Qualifiers demanglePointerExtQualifiers();

  // Parser functions. This is a recursive-descent parser.
  Type *demangleType(QualifierMangleMode QMM);
  Type *demangleBasicType();
  UdtType *demangleClassType();
  PointerType *demanglePointerType();

  ArrayType *demangleArrayType();

  ParamList demangleParameterList();

  int demangleNumber();
  void demangleNamePiece(Name &Node, bool IsHead);

  StringView demangleString(bool memorize);
  void memorizeString(StringView s);
  Name *demangleName();
  void demangleOperator(Name *);
  StringView demangleOperatorName();
  int demangleFunctionClass();
  CallingConv demangleCallingConvention();
  StorageClass demangleVariableStorageClass();
  ReferenceKind demangleReferenceKind();

  Qualifiers demangleFunctionQualifiers();
  Qualifiers demangleVariablQualifiers();
  Qualifiers demangleReturnTypQualifiers();

  Qualifiers demangleQualifiers(
      QualifierMangleLocation Location = QualifierMangleLocation::Detect);

  // The result is written to this stream.
  OutputStream OS;

  // Mangled symbol. demangle* functions shorten this string
  // as they parse it.
  StringView MangledName;

  // A parsed mangled symbol.
  Type *SymbolType = nullptr;

  // The main symbol name. (e.g. "ns::foo" in "int ns::foo()".)
  Name *SymbolName = nullptr;

  // Memory allocator.
  ArenaAllocator Arena;

  // The first 10 BackReferences in a mangled name can be back-referenced by
  // special name @[0-9]. This is a storage for the first 10 BackReferences.
  StringView BackReferences[10];
  size_t BackRefCount = 0;
};
} // namespace

// Parser entry point.
void Demangler::parse() {
  // MSVC-style mangled symbols must start with '?'.
  if (!MangledName.consumeFront("?")) {
    SymbolName = new (Arena) Name;
    SymbolName->Str = MangledName;
    SymbolType = new (Arena) Type;
    SymbolType->Prim = PrimTy::Unknown;
  }

  // What follows is a main symbol name. This may include
  // namespaces or class BackReferences.
  SymbolName = demangleName();

  // Read a variable.
  if (startsWithDigit(MangledName)) {
    SymbolType = demangleVariableEncoding();
    return;
  }

  // Read a function.
  SymbolType = demangleFunctionEncoding();
}

// <type-encoding> ::= <storage-class> <variable-type>
// <storage-class> ::= 0  # private static member
//                 ::= 1  # protected static member
//                 ::= 2  # public static member
//                 ::= 3  # global
//                 ::= 4  # static local

Type *Demangler::demangleVariableEncoding() {
  StorageClass SC = demangleVariableStorageClass();

  Type *Ty = demangleType(QualifierMangleMode::Drop);

  Ty->Storage = SC;

  // <variable-type> ::= <type> <cvr-qualifiers>
  //                 ::= <type> <pointee-cvr-qualifiers> # pointers, references
  switch (Ty->Prim) {
  case PrimTy::Ptr:
  case PrimTy::Ref: {
    Qualifiers ExtraChildQuals = Q_None;
    Ty->Quals = Qualifiers(Ty->Quals | demanglePointerExtQualifiers());

    PointerType *PTy = static_cast<PointerType *>(Ty);
    QualifierMangleLocation Location = PTy->isMemberPointer()
                                           ? QualifierMangleLocation::Member
                                           : QualifierMangleLocation::NonMember;

    ExtraChildQuals = demangleQualifiers(Location);

    if (PTy->isMemberPointer()) {
      Name *BackRefName = demangleName();
      (void)BackRefName;
    }

    PTy->Pointee->Quals = Qualifiers(PTy->Pointee->Quals | ExtraChildQuals);
    break;
  }
  default:
    Ty->Quals = demangleQualifiers();
    break;
  }

  return Ty;
}

// Sometimes numbers are encoded in mangled symbols. For example,
// "int (*x)[20]" is a valid C type (x is a pointer to an array of
// length 20), so we need some way to embed numbers as part of symbols.
// This function parses it.
//
// <number>               ::= [?] <non-negative integer>
//
// <non-negative integer> ::= <decimal digit> # when 1 <= Number <= 10
//                        ::= <hex digit>+ @  # when Numbrer == 0 or >= 10
//
// <hex-digit>            ::= [A-P]           # A = 0, B = 1, ...
int Demangler::demangleNumber() {
  bool neg = MangledName.consumeFront("?");

  if (startsWithDigit(MangledName)) {
    int32_t Ret = MangledName[0] - '0' + 1;
    MangledName = MangledName.dropFront(1);
    return neg ? -Ret : Ret;
  }

  int Ret = 0;
  for (size_t i = 0; i < MangledName.size(); ++i) {
    char C = MangledName[i];
    if (C == '@') {
      MangledName = MangledName.dropFront(i + 1);
      return neg ? -Ret : Ret;
    }
    if ('A' <= C && C <= 'P') {
      Ret = (Ret << 4) + (C - 'A');
      continue;
    }
    break;
  }

  Error = true;
  return 0;
}

// Read until the next '@'.
StringView Demangler::demangleString(bool Memorize) {
  for (size_t i = 0; i < MangledName.size(); ++i) {
    if (MangledName[i] != '@')
      continue;
    StringView ret = MangledName.substr(0, i);
    MangledName = MangledName.dropFront(i + 1);

    if (Memorize)
      memorizeString(ret);
    return ret;
  }

  Error = true;
  return "";
}

// First 10 strings can be referenced by special BackReferences ?0, ?1, ..., ?9.
// Memorize it.
void Demangler::memorizeString(StringView S) {
  if (BackRefCount >= sizeof(BackReferences) / sizeof(*BackReferences))
    return;
  for (size_t i = 0; i < BackRefCount; ++i)
    if (S == BackReferences[i])
      return;
  BackReferences[BackRefCount++] = S;
}

void Demangler::demangleNamePiece(Name &Node, bool IsHead) {
  if (startsWithDigit(MangledName)) {
    size_t I = MangledName[0] - '0';
    if (I >= BackRefCount) {
      Error = true;
      return;
    }
    MangledName = MangledName.dropFront();
    Node.Str = BackReferences[I];
  } else if (MangledName.consumeFront("?$")) {
    // Class template.
    Node.Str = demangleString(false);
    Node.TemplateParams = demangleParameterList();
    if (!MangledName.consumeFront('@')) {
      Error = true;
      return;
    }
  } else if (!IsHead && MangledName.consumeFront("?A")) {
    // Anonymous namespace starts with ?A.  So does overloaded operator[],
    // but the distinguishing factor is that namespace themselves are not
    // mangled, only the variables and functions inside of them are.  So
    // an anonymous namespace will never occur as the first item in the
    // name.
    Node.Str = "`anonymous namespace'";
    if (!MangledName.consumeFront('@')) {
      Error = true;
      return;
    }
  } else if (MangledName.consumeFront("?")) {
    // Overloaded operator.
    demangleOperator(&Node);
  } else {
    // Non-template functions or classes.
    Node.Str = demangleString(true);
  }
}

// Parses a name in the form of A@B@C@@ which represents C::B::A.
Name *Demangler::demangleName() {
  Name *Head = nullptr;

  while (!MangledName.consumeFront("@")) {
    Name *Elem = new (Arena) Name;

    assert(!Error);
    demangleNamePiece(*Elem, Head == nullptr);
    if (Error)
      return nullptr;

    Elem->Next = Head;
    Head = Elem;
  }

  return Head;
}

void Demangler::demangleOperator(Name *OpName) {
  OpName->Operator = demangleOperatorName();
  if (!Error && !MangledName.empty() && MangledName.front() != '@')
    demangleNamePiece(*OpName, false);
}

StringView Demangler::demangleOperatorName() {
  SwapAndRestore<StringView> RestoreOnError(MangledName, MangledName);
  RestoreOnError.shouldRestore(false);

  switch (MangledName.popFront()) {
  case '0':
    return "ctor";
  case '1':
    return "dtor";
  case '2':
    return " new";
  case '3':
    return " delete";
  case '4':
    return "=";
  case '5':
    return ">>";
  case '6':
    return "<<";
  case '7':
    return "!";
  case '8':
    return "==";
  case '9':
    return "!=";
  case 'A':
    return "[]";
  case 'C':
    return "->";
  case 'D':
    return "*";
  case 'E':
    return "++";
  case 'F':
    return "--";
  case 'G':
    return "-";
  case 'H':
    return "+";
  case 'I':
    return "&";
  case 'J':
    return "->*";
  case 'K':
    return "/";
  case 'L':
    return "%";
  case 'M':
    return "<";
  case 'N':
    return "<=";
  case 'O':
    return ">";
  case 'P':
    return ">=";
  case 'Q':
    return ",";
  case 'R':
    return "()";
  case 'S':
    return "~";
  case 'T':
    return "^";
  case 'U':
    return "|";
  case 'V':
    return "&&";
  case 'W':
    return "||";
  case 'X':
    return "*=";
  case 'Y':
    return "+=";
  case 'Z':
    return "-=";
  case '_': {
    if (MangledName.empty())
      break;

    switch (MangledName.popFront()) {
    case '0':
      return "/=";
    case '1':
      return "%=";
    case '2':
      return ">>=";
    case '3':
      return "<<=";
    case '4':
      return "&=";
    case '5':
      return "|=";
    case '6':
      return "^=";
    case 'U':
      return " new[]";
    case 'V':
      return " delete[]";
    case '_':
      if (MangledName.consumeFront("L"))
        return " co_await";
    }
  }
  }

  Error = true;
  RestoreOnError.shouldRestore(true);
  return "";
}

int Demangler::demangleFunctionClass() {
  SwapAndRestore<StringView> RestoreOnError(MangledName, MangledName);
  RestoreOnError.shouldRestore(false);

  switch (MangledName.popFront()) {
  case 'A':
    return Private;
  case 'B':
    return Private | Far;
  case 'C':
    return Private | Static;
  case 'D':
    return Private | Static;
  case 'E':
    return Private | Virtual;
  case 'F':
    return Private | Virtual;
  case 'I':
    return Protected;
  case 'J':
    return Protected | Far;
  case 'K':
    return Protected | Static;
  case 'L':
    return Protected | Static | Far;
  case 'M':
    return Protected | Virtual;
  case 'N':
    return Protected | Virtual | Far;
  case 'Q':
    return Public;
  case 'R':
    return Public | Far;
  case 'S':
    return Public | Static;
  case 'T':
    return Public | Static | Far;
  case 'U':
    return Public | Virtual;
  case 'V':
    return Public | Virtual | Far;
  case 'Y':
    return Global;
  case 'Z':
    return Global | Far;
  }

  Error = true;
  RestoreOnError.shouldRestore(true);
  return 0;
}

Qualifiers Demangler::demangleFunctionQualifiers() {
  SwapAndRestore<StringView> RestoreOnError(MangledName, MangledName);
  RestoreOnError.shouldRestore(false);

  switch (MangledName.popFront()) {
  case 'A':
    return Q_None;
  case 'B':
    return Q_Const;
  case 'C':
    return Q_Volatile;
  case 'D':
    return Qualifiers(Q_Const | Q_Volatile);
  }

  Error = true;
  RestoreOnError.shouldRestore(true);
  return Q_None;
}

CallingConv Demangler::demangleCallingConvention() {
  switch (MangledName.popFront()) {
  case 'A':
  case 'B':
    return CallingConv::Cdecl;
  case 'C':
  case 'D':
    return CallingConv::Pascal;
  case 'E':
  case 'F':
    return CallingConv::Thiscall;
  case 'G':
  case 'H':
    return CallingConv::Stdcall;
  case 'I':
  case 'J':
    return CallingConv::Fastcall;
  case 'M':
  case 'N':
    return CallingConv::Clrcall;
  case 'O':
  case 'P':
    return CallingConv::Eabi;
  case 'Q':
    return CallingConv::Vectorcall;
  }

  return CallingConv::None;
};

StorageClass Demangler::demangleVariableStorageClass() {
  assert(std::isdigit(MangledName.front()));

  switch (MangledName.popFront()) {
  case '0':
    return StorageClass::PrivateStatic;
  case '1':
    return StorageClass::ProtectedStatic;
  case '2':
    return StorageClass::PublicStatic;
  case '3':
    return StorageClass::Global;
  case '4':
    return StorageClass::FunctionLocalStatic;
  }
  Error = true;
  return StorageClass::None;
}

Qualifiers Demangler::demangleVariablQualifiers() {
  SwapAndRestore<StringView> RestoreOnError(MangledName, MangledName);
  RestoreOnError.shouldRestore(false);

  switch (MangledName.popFront()) {
  case 'A':
    return Q_None;
  case 'B':
    return Q_Const;
  case 'C':
    return Q_Volatile;
  case 'D':
    return Qualifiers(Q_Const | Q_Volatile);
  case 'E':
    return Q_Far;
  case 'F':
    return Qualifiers(Q_Const | Q_Far);
  case 'G':
    return Qualifiers(Q_Volatile | Q_Far);
  case 'H':
    return Qualifiers(Q_Const | Q_Volatile | Q_Far);
  }

  Error = true;
  RestoreOnError.shouldRestore(true);
  return Q_None;
}

Qualifiers Demangler::demangleReturnTypQualifiers() {
  if (!MangledName.consumeFront("?"))
    return Q_None;

  SwapAndRestore<StringView> RestoreOnError(MangledName, MangledName);
  RestoreOnError.shouldRestore(false);

  switch (MangledName.popFront()) {
  case 'A':
    return Q_None;
  case 'B':
    return Q_Const;
  case 'C':
    return Q_Volatile;
  case 'D':
    return Qualifiers(Q_Const | Q_Volatile);
  }

  Error = true;
  RestoreOnError.shouldRestore(true);
  return Q_None;
}

Qualifiers Demangler::demangleQualifiers(QualifierMangleLocation Location) {
  if (Location == QualifierMangleLocation::Detect) {
    switch (MangledName.front()) {
    case 'Q':
    case 'R':
    case 'S':
    case 'T':
      Location = QualifierMangleLocation::Member;
      break;
    case 'A':
    case 'B':
    case 'C':
    case 'D':
      Location = QualifierMangleLocation::NonMember;
      break;
    default:
      Error = true;
      return Q_None;
    }
  }

  if (Location == QualifierMangleLocation::Member) {
    switch (MangledName.popFront()) {
    // Member qualifiers
    case 'Q':
      return Q_None;
    case 'R':
      return Q_Const;
    case 'S':
      return Q_Volatile;
    case 'T':
      return Qualifiers(Q_Const | Q_Volatile);
    }
  } else {
    switch (MangledName.popFront()) {
    // Non-Member qualifiers
    case 'A':
      return Q_None;
    case 'B':
      return Q_Const;
    case 'C':
      return Q_Volatile;
    case 'D':
      return Qualifiers(Q_Const | Q_Volatile);
    }
  }
  Error = true;
  return Q_None;
}

// <variable-type> ::= <type> <cvr-qualifiers>
//                 ::= <type> <pointee-cvr-qualifiers> # pointers, references
Type *Demangler::demangleType(QualifierMangleMode QMM) {
  Qualifiers Quals = Q_None;
  if (QMM == QualifierMangleMode::Mangle)
    Quals = Qualifiers(Quals | demangleQualifiers());
  else if (QMM == QualifierMangleMode::Result) {
    if (MangledName.consumeFront('?'))
      Quals = Qualifiers(Quals | demangleQualifiers());
  }

  Type *Ty = nullptr;
  switch (MangledName.front()) {
  case 'T': // union
  case 'U': // struct
  case 'V': // class
  case 'W': // enum
    Ty = demangleClassType();
    break;
  case 'A': // foo &
  case 'P': // foo *
  case 'Q': // foo *const
  case 'R': // foo *volatile
  case 'S': // foo *const volatile
    Ty = demanglePointerType();
    break;
  case 'Y':
    Ty = demangleArrayType();
    break;
  default:
    Ty = demangleBasicType();
    break;
  }
  Ty->Quals = Qualifiers(Ty->Quals | Quals);
  return Ty;
}

static bool functionHasThisPtr(const FunctionType &Ty) {
  assert(Ty.Prim == PrimTy::Function);
  if (Ty.FunctionClass & Global)
    return false;
  if (Ty.FunctionClass & Static)
    return false;
  return true;
}

ReferenceKind Demangler::demangleReferenceKind() {
  if (MangledName.consumeFront('G'))
    return ReferenceKind::LValueRef;
  else if (MangledName.consumeFront('H'))
    return ReferenceKind::RValueRef;
  return ReferenceKind::None;
}

Type *Demangler::demangleFunctionEncoding() {
  FunctionType *FTy = new (Arena) FunctionType;

  FTy->Prim = PrimTy::Function;
  FTy->FunctionClass = (FuncClass)demangleFunctionClass();
  if (functionHasThisPtr(*FTy)) {
    FTy->Quals = demanglePointerExtQualifiers();
    FTy->RefKind = demangleReferenceKind();
    FTy->Quals = Qualifiers(FTy->Quals | demangleQualifiers());
  }

  // Fields that appear on both member and non-member functions.
  FTy->CallConvention = demangleCallingConvention();

  // <return-type> ::= <type>
  //               ::= @ # structors (they have no declared return type)
  bool IsStructor = MangledName.consumeFront('@');
  if (!IsStructor)
    FTy->ReturnType = demangleType(QualifierMangleMode::Result);

  FTy->Params = demangleParameterList();

  return FTy;
}

// Reads a primitive type.
Type *Demangler::demangleBasicType() {
  Type *Ty = new (Arena) Type;

  switch (MangledName.popFront()) {
  case 'X':
    Ty->Prim = PrimTy::Void;
    break;
  case 'D':
    Ty->Prim = PrimTy::Char;
    break;
  case 'C':
    Ty->Prim = PrimTy::Schar;
    break;
  case 'E':
    Ty->Prim = PrimTy::Uchar;
    break;
  case 'F':
    Ty->Prim = PrimTy::Short;
    break;
  case 'G':
    Ty->Prim = PrimTy::Ushort;
    break;
  case 'H':
    Ty->Prim = PrimTy::Int;
    break;
  case 'I':
    Ty->Prim = PrimTy::Uint;
    break;
  case 'J':
    Ty->Prim = PrimTy::Long;
    break;
  case 'K':
    Ty->Prim = PrimTy::Ulong;
    break;
  case 'M':
    Ty->Prim = PrimTy::Float;
    break;
  case 'N':
    Ty->Prim = PrimTy::Double;
    break;
  case 'O':
    Ty->Prim = PrimTy::Ldouble;
    break;
  case '_': {
    if (MangledName.empty()) {
      Error = true;
      return nullptr;
    }
    switch (MangledName.popFront()) {
    case 'N':
      Ty->Prim = PrimTy::Bool;
      break;
    case 'J':
      Ty->Prim = PrimTy::Int64;
      break;
    case 'K':
      Ty->Prim = PrimTy::Uint64;
      break;
    case 'W':
      Ty->Prim = PrimTy::Wchar;
      break;
    default:
      assert(false);
    }
    break;
  }
  }
  return Ty;
}

UdtType *Demangler::demangleClassType() {
  UdtType *UTy = new (Arena) UdtType;

  switch (MangledName.popFront()) {
  case 'T':
    UTy->Prim = PrimTy::Union;
    break;
  case 'U':
    UTy->Prim = PrimTy::Struct;
    break;
  case 'V':
    UTy->Prim = PrimTy::Class;
    break;
  case 'W':
    if (MangledName.popFront() != '4') {
      Error = true;
      return nullptr;
    }
    UTy->Prim = PrimTy::Enum;
    break;
  default:
    assert(false);
  }

  UTy->UdtName = demangleName();
  return UTy;
}

// <pointer-type> ::= E? <pointer-cvr-qualifiers> <ext-qualifiers> <type>
//                       # the E is required for 64-bit non-static pointers
PointerType *Demangler::demanglePointerType() {
  PointerType *Pointer = new (Arena) PointerType;

  Pointer->Quals = Q_None;
  switch (MangledName.popFront()) {
  case 'A':
    Pointer->Prim = PrimTy::Ref;
    break;
  case 'P':
    Pointer->Prim = PrimTy::Ptr;
    break;
  case 'Q':
    Pointer->Prim = PrimTy::Ptr;
    Pointer->Quals = Q_Const;
    break;
  case 'R':
    Pointer->Quals = Q_Volatile;
    Pointer->Prim = PrimTy::Ptr;
    break;
  case 'S':
    Pointer->Quals = Qualifiers(Q_Const | Q_Volatile);
    Pointer->Prim = PrimTy::Ptr;
    break;
  default:
    assert(false && "Ty is not a pointer type!");
  }

  if (MangledName.consumeFront("6")) {
    FunctionType *FTy = new (Arena) FunctionType;
    FTy->Prim = PrimTy::Function;
    FTy->CallConvention = demangleCallingConvention();

    FTy->ReturnType = demangleType(QualifierMangleMode::Drop);
    FTy->Params = demangleParameterList();

    if (!MangledName.consumeFront("@Z"))
      MangledName.consumeFront("Z");

    Pointer->Pointee = FTy;
    return Pointer;
  }

  Qualifiers ExtQuals = demanglePointerExtQualifiers();
  Pointer->Quals = Qualifiers(Pointer->Quals | ExtQuals);

  Pointer->Pointee = demangleType(QualifierMangleMode::Mangle);
  return Pointer;
}

Qualifiers Demangler::demanglePointerExtQualifiers() {
  Qualifiers Quals = Q_None;
  if (MangledName.consumeFront('E'))
    Quals = Qualifiers(Quals | Q_Pointer64);
  if (MangledName.consumeFront('I'))
    Quals = Qualifiers(Quals | Q_Restrict);
  if (MangledName.consumeFront('F'))
    Quals = Qualifiers(Quals | Q_Unaligned);

  return Quals;
}

ArrayType *Demangler::demangleArrayType() {
  assert(MangledName.front() == 'Y');
  MangledName.popFront();

  int Dimension = demangleNumber();
  if (Dimension <= 0) {
    Error = true;
    return nullptr;
  }

  ArrayType *ATy = new (Arena) ArrayType;
  ArrayType *Dim = ATy;
  for (int I = 0; I < Dimension; ++I) {
    Dim->Prim = PrimTy::Array;
    Dim->ArrayDimension = demangleNumber();
    Dim->NextDimension = new (Arena) ArrayType;
    Dim = Dim->NextDimension;
  }

  if (MangledName.consumeFront("$$C")) {
    if (MangledName.consumeFront("B"))
      ATy->Quals = Q_Const;
    else if (MangledName.consumeFront("C") || MangledName.consumeFront("D"))
      ATy->Quals = Qualifiers(Q_Const | Q_Volatile);
    else if (!MangledName.consumeFront("A"))
      Error = true;
  }

  ATy->ElementType = demangleType(QualifierMangleMode::Drop);
  Dim->ElementType = ATy->ElementType;
  return ATy;
}

// Reads a function or a template parameters.
ParamList Demangler::demangleParameterList() {
  // Within the same parameter list, you can backreference the first 10 types.
  Type *BackRef[10];
  int Idx = 0;

  ParamList *Head;
  ParamList **Current = &Head;
  while (!Error && !MangledName.startsWith('@') &&
         !MangledName.startsWith('Z')) {
    if (startsWithDigit(MangledName)) {
      int N = MangledName[0] - '0';
      if (N >= Idx) {
        Error = true;
        return {};
      }
      MangledName = MangledName.dropFront();

      *Current = new (Arena) ParamList;
      (*Current)->Current = BackRef[N]->clone(Arena);
      Current = &(*Current)->Next;
      continue;
    }

    size_t ArrayDimension = MangledName.size();

    *Current = new (Arena) ParamList;
    (*Current)->Current = demangleType(QualifierMangleMode::Drop);

    // Single-letter types are ignored for backreferences because
    // memorizing them doesn't save anything.
    if (Idx <= 9 && ArrayDimension - MangledName.size() > 1)
      BackRef[Idx++] = (*Current)->Current;
    Current = &(*Current)->Next;
  }

  return *Head;
}

void Demangler::output() {
  // Converts an AST to a string.
  //
  // Converting an AST representing a C++ type to a string is tricky due
  // to the bad grammar of the C++ declaration inherited from C. You have
  // to construct a string from inside to outside. For example, if a type
  // X is a pointer to a function returning int, the order you create a
  // string becomes something like this:
  //
  //   (1) X is a pointer: *X
  //   (2) (1) is a function returning int: int (*X)()
  //
  // So you cannot construct a result just by appending strings to a result.
  //
  // To deal with this, we split the function into two. outputPre() writes
  // the "first half" of type declaration, and outputPost() writes the
  // "second half". For example, outputPre() writes a return type for a
  // function and outputPost() writes an parameter list.
  Type::outputPre(OS, *SymbolType);
  outputName(OS, SymbolName);
  Type::outputPost(OS, *SymbolType);

  // Null terminate the buffer.
  OS << '\0';
}

char *llvm::microsoftDemangle(const char *MangledName, char *Buf, size_t *N,
                              int *Status) {
  OutputStream OS = OutputStream::create(Buf, N, 1024);

  Demangler D(OS, StringView(MangledName));
  D.parse();

  if (D.Error)
    *Status = llvm::demangle_invalid_mangled_name;
  else
    *Status = llvm::demangle_success;

  D.output();
  return OS.getBuffer();
}