text: //===--- Ownership.h - Parser ownership helpers -----------------*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  //  This file contains classes for managing ownership of Stmt and Expr nodes.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_CLANG_SEMA_OWNERSHIP_H
  #define LLVM_CLANG_SEMA_OWNERSHIP_H
  
  #include "clang/Basic/LLVM.h"
  #include "llvm/ADT/ArrayRef.h"
  #include "llvm/ADT/PointerIntPair.h"
  
  //===----------------------------------------------------------------------===//
  // OpaquePtr
  //===----------------------------------------------------------------------===//
  
  namespace clang {
    class CXXCtorInitializer;
    class CXXBaseSpecifier;
    class Decl;
    class Expr;
    class ParsedTemplateArgument;
    class QualType;
    class Stmt;
    class TemplateName;
    class TemplateParameterList;
  
    /// \brief Wrapper for void* pointer.
    /// \tparam PtrTy Either a pointer type like 'T*' or a type that behaves like
    ///               a pointer.
    ///
    /// This is a very simple POD type that wraps a pointer that the Parser
    /// doesn't know about but that Sema or another client does.  The PtrTy
    /// template argument is used to make sure that "Decl" pointers are not
    /// compatible with "Type" pointers for example.
    template <class PtrTy>
    class OpaquePtr {
      void *Ptr;
      explicit OpaquePtr(void *Ptr) : Ptr(Ptr) {}
  
      typedef llvm::PointerLikeTypeTraits<PtrTy> Traits;
  
    public:
      OpaquePtr() : Ptr(0) {}
  
      static OpaquePtr make(PtrTy P) { OpaquePtr OP; OP.set(P); return OP; }
  
      /// \brief Returns plain pointer to the entity pointed by this wrapper.
      /// \tparam PointeeT Type of pointed entity.
      ///
      /// It is identical to getPtrAs<PointeeT*>.
      template <typename PointeeT> PointeeT* getPtrTo() const {
        return get();
      }
  
      /// \brief Returns pointer converted to the specified type.
      /// \tparam PtrT Result pointer type.  There must be implicit conversion
      ///              from PtrTy to PtrT.
      ///
      /// In contrast to getPtrTo, this method allows the return type to be
      /// a smart pointer.
      template <typename PtrT> PtrT getPtrAs() const {
        return get();
      }
  
      PtrTy get() const {
        return Traits::getFromVoidPointer(Ptr);
      }
  
      void set(PtrTy P) {
        Ptr = Traits::getAsVoidPointer(P);
      }
  
      LLVM_EXPLICIT operator bool() const { return Ptr != 0; }
  
      void *getAsOpaquePtr() const { return Ptr; }
      static OpaquePtr getFromOpaquePtr(void *P) { return OpaquePtr(P); }
    };
  
    /// UnionOpaquePtr - A version of OpaquePtr suitable for membership
    /// in a union.
    template <class T> struct UnionOpaquePtr {
      void *Ptr;
  
      static UnionOpaquePtr make(OpaquePtr<T> P) {
        UnionOpaquePtr OP = { P.getAsOpaquePtr() };
        return OP;
      }
  
      OpaquePtr<T> get() const { return OpaquePtr<T>::getFromOpaquePtr(Ptr); }
      operator OpaquePtr<T>() const { return get(); }
  
      UnionOpaquePtr &operator=(OpaquePtr<T> P) {
        Ptr = P.getAsOpaquePtr();
        return *this;
      }
    };
  }
  
  namespace llvm {
    template <class T>
    class PointerLikeTypeTraits<clang::OpaquePtr<T> > {
    public:
      static inline void *getAsVoidPointer(clang::OpaquePtr<T> P) {
        // FIXME: Doesn't work? return P.getAs< void >();
        return P.getAsOpaquePtr();
      }
      static inline clang::OpaquePtr<T> getFromVoidPointer(void *P) {
        return clang::OpaquePtr<T>::getFromOpaquePtr(P);
      }
      enum { NumLowBitsAvailable = 0 };
    };
  
    template <class T>
    struct isPodLike<clang::OpaquePtr<T> > { static const bool value = true; };
  }
  
  namespace clang {
    // Basic
    class DiagnosticBuilder;
  
    // Determines whether the low bit of the result pointer for the
    // given UID is always zero. If so, ActionResult will use that bit
    // for it's "invalid" flag.
    template<class Ptr>
    struct IsResultPtrLowBitFree {
      static const bool value = false;
    };
  
    /// ActionResult - This structure is used while parsing/acting on
    /// expressions, stmts, etc.  It encapsulates both the object returned by
    /// the action, plus a sense of whether or not it is valid.
    /// When CompressInvalid is true, the "invalid" flag will be
    /// stored in the low bit of the Val pointer.
    template<class PtrTy,
             bool CompressInvalid = IsResultPtrLowBitFree<PtrTy>::value>
    class ActionResult {
      PtrTy Val;
      bool Invalid;
  
    public:
      ActionResult(bool Invalid = false)
        : Val(PtrTy()), Invalid(Invalid) {}
      ActionResult(PtrTy val) : Val(val), Invalid(false) {}
      ActionResult(const DiagnosticBuilder &) : Val(PtrTy()), Invalid(true) {}
  
      // These two overloads prevent void* -> bool conversions.
      ActionResult(const void *);
      ActionResult(volatile void *);
  
      bool isInvalid() const { return Invalid; }
      bool isUsable() const { return !Invalid && Val; }
  
      PtrTy get() const { return Val; }
      // FIXME: Replace with get.
      PtrTy release() const { return Val; }
      PtrTy take() const { return Val; }
      template <typename T> T *takeAs() { return static_cast<T*>(get()); }
  
      void set(PtrTy V) { Val = V; }
  
      const ActionResult &operator=(PtrTy RHS) {
        Val = RHS;
        Invalid = false;
        return *this;
      }
    };
  
    // This ActionResult partial specialization places the "invalid"
    // flag into the low bit of the pointer.
    template<typename PtrTy>
    class ActionResult<PtrTy, true> {
      // A pointer whose low bit is 1 if this result is invalid, 0
      // otherwise.
      uintptr_t PtrWithInvalid;
      typedef llvm::PointerLikeTypeTraits<PtrTy> PtrTraits;
    public:
      ActionResult(bool Invalid = false)
        : PtrWithInvalid(static_cast<uintptr_t>(Invalid)) { }
  
      ActionResult(PtrTy V) {
        void *VP = PtrTraits::getAsVoidPointer(V);
        PtrWithInvalid = reinterpret_cast<uintptr_t>(VP);
        assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer");
      }
      ActionResult(const DiagnosticBuilder &) : PtrWithInvalid(0x01) { }
  
      // These two overloads prevent void* -> bool conversions.
      ActionResult(const void *);
      ActionResult(volatile void *);
  
      bool isInvalid() const { return PtrWithInvalid & 0x01; }
      bool isUsable() const { return PtrWithInvalid > 0x01; }
  
      PtrTy get() const {
        void *VP = reinterpret_cast<void *>(PtrWithInvalid & ~0x01);
        return PtrTraits::getFromVoidPointer(VP);
      }
      // FIXME: Replace with get.
      PtrTy take() const { return get(); }
      PtrTy release() const { return get(); }
      template <typename T> T *takeAs() { return static_cast<T*>(get()); }
  
      void set(PtrTy V) {
        void *VP = PtrTraits::getAsVoidPointer(V);
        PtrWithInvalid = reinterpret_cast<uintptr_t>(VP);
        assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer");
      }
  
      const ActionResult &operator=(PtrTy RHS) {
        void *VP = PtrTraits::getAsVoidPointer(RHS);
        PtrWithInvalid = reinterpret_cast<uintptr_t>(VP);
        assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer");
        return *this;
      }
  
      // For types where we can fit a flag in with the pointer, provide
      // conversions to/from pointer type.
      static ActionResult getFromOpaquePointer(void *P) {
        ActionResult Result;
        Result.PtrWithInvalid = (uintptr_t)P;
        return Result;
      }
      void *getAsOpaquePointer() const { return (void*)PtrWithInvalid; }
    };
  
    /// An opaque type for threading parsed type information through the
    /// parser.
    typedef OpaquePtr<QualType> ParsedType;
    typedef UnionOpaquePtr<QualType> UnionParsedType;
  
    // We can re-use the low bit of expression, statement, base, and
    // member-initializer pointers for the "invalid" flag of
    // ActionResult.
    template<> struct IsResultPtrLowBitFree<Expr*> {
      static const bool value = true;
    };
    template<> struct IsResultPtrLowBitFree<Stmt*> {
      static const bool value = true;
    };
    template<> struct IsResultPtrLowBitFree<CXXBaseSpecifier*> {
      static const bool value = true;
    };
    template<> struct IsResultPtrLowBitFree<CXXCtorInitializer*> {
      static const bool value = true;
    };
  
    typedef ActionResult<Expr*> ExprResult;
    typedef ActionResult<Stmt*> StmtResult;
    typedef ActionResult<ParsedType> TypeResult;
    typedef ActionResult<CXXBaseSpecifier*> BaseResult;
    typedef ActionResult<CXXCtorInitializer*> MemInitResult;
  
    typedef ActionResult<Decl*> DeclResult;
    typedef OpaquePtr<TemplateName> ParsedTemplateTy;
  
    typedef llvm::MutableArrayRef<Expr*> MultiExprArg;
    typedef llvm::MutableArrayRef<Stmt*> MultiStmtArg;
    typedef llvm::MutableArrayRef<ParsedTemplateArgument> ASTTemplateArgsPtr;
    typedef llvm::MutableArrayRef<ParsedType> MultiTypeArg;
    typedef llvm::MutableArrayRef<TemplateParameterList*> MultiTemplateParamsArg;
  
    inline ExprResult ExprError() { return ExprResult(true); }
    inline StmtResult StmtError() { return StmtResult(true); }
  
    inline ExprResult ExprError(const DiagnosticBuilder&) { return ExprError(); }
    inline StmtResult StmtError(const DiagnosticBuilder&) { return StmtError(); }
  
    inline ExprResult ExprEmpty() { return ExprResult(false); }
    inline StmtResult StmtEmpty() { return StmtResult(false); }
  
    inline Expr *AssertSuccess(ExprResult R) {
      assert(!R.isInvalid() && "operation was asserted to never fail!");
      return R.get();
    }
  
    inline Stmt *AssertSuccess(StmtResult R) {
      assert(!R.isInvalid() && "operation was asserted to never fail!");
      return R.get();
    }
  }
  
  #endif
  