Ownership.h

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//===- Ownership.h - Parser ownership helpers -------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  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/AST/Expr.h"
#include "clang/Basic/LLVM.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/Support/PointerLikeTypeTraits.h"
#include "llvm/Support/type_traits.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
 
//===----------------------------------------------------------------------===//
// OpaquePtr
//===----------------------------------------------------------------------===//
 
namespace clang {
 
class CXXBaseSpecifier;
class CXXCtorInitializer;
class Decl;
class Expr;
class ParsedTemplateArgument;
class QualType;
class Stmt;
class TemplateName;
class TemplateParameterList;
 
  /// 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 = nullptr;
 
    explicit OpaquePtr(void *Ptr) : Ptr(Ptr) {}
 
    using Traits = llvm::PointerLikeTypeTraits<PtrTy>;
 
  public:
    OpaquePtr(std::nullptr_t = nullptr) {}
 
    static OpaquePtr make(PtrTy P) { OpaquePtr OP; OP.set(P); return OP; }
 
    /// 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();
    }
 
    /// 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);
    }
 
    explicit operator bool() const { return Ptr != nullptr; }
 
    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 clang
 
namespace llvm {
 
  template <class T>
  struct PointerLikeTypeTraits<clang::OpaquePtr<T>> {
    static constexpr int NumLowBitsAvailable = 0;
 
    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);
    }
  };
 
} // namespace llvm
 
namespace clang {
 
class StreamingDiagnostic;
 
// 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;
};
 
/// The result of parsing/analyzing an expression, statement etc.
///
/// It may be:
/// - usable: a valid pointer to the result object
/// - unset (null but valid): for constructs that may legitimately be absent
///   (for example, the condition of a for loop)
/// - invalid: indicating an error
///   (no detail is provided, usually the error has already been diagnosed)
template <class PtrTy, bool Compress = IsResultPtrLowBitFree<PtrTy>::value>
class ActionResult {
  PtrTy Val = {};
  bool Invalid = false;
 
public:
  ActionResult(bool Invalid = false) : Val(PtrTy()), Invalid(Invalid) {}
  ActionResult(PtrTy Val) { *this = Val; }
  ActionResult(const DiagnosticBuilder &) : ActionResult(/*Invalid=*/true) {}
 
  // These two overloads prevent void* -> bool conversions.
  ActionResult(const void *) = delete;
  ActionResult(volatile void *) = delete;
 
  bool isInvalid() const { return Invalid; }
  bool isUnset() const { return !Invalid && !Val; }
  bool isUsable() const { return !isInvalid() && !isUnset(); }
 
  PtrTy get() const { return Val; }
  template <typename T> T *getAs() { return static_cast<T *>(get()); }
 
  ActionResult &operator=(PtrTy RHS) {
    Val = RHS;
    Invalid = false;
    return *this;
  }
};
 
// If we PtrTy has a free bit, we can represent "invalid" as nullptr|1.
template <typename PtrTy> class ActionResult<PtrTy, true> {
  static constexpr uintptr_t UnsetValue = 0x0;
  static constexpr uintptr_t InvalidValue = 0x1;
 
  uintptr_t Value = UnsetValue;
 
  using PtrTraits = llvm::PointerLikeTypeTraits<PtrTy>;
 
public:
  ActionResult(bool Invalid = false)
      : Value(Invalid ? InvalidValue : UnsetValue) {}
  ActionResult(PtrTy V) { *this = V; }
  ActionResult(const DiagnosticBuilder &) : ActionResult(/*Invalid=*/true) {}
 
  // These two overloads prevent void* -> bool conversions.
  ActionResult(const void *) = delete;
  ActionResult(volatile void *) = delete;
 
  bool isInvalid() const { return Value == InvalidValue; }
  bool isUnset() const { return Value == UnsetValue; }
  bool isUsable() const { return !isInvalid() && !isUnset(); }
 
  PtrTy get() const {
    void *VP = reinterpret_cast<void *>(Value & ~0x01);
    return PtrTraits::getFromVoidPointer(VP);
  }
  template <typename T> T *getAs() { return static_cast<T *>(get()); }
 
  ActionResult &operator=(PtrTy RHS) {
    void *VP = PtrTraits::getAsVoidPointer(RHS);
    Value = reinterpret_cast<uintptr_t>(VP);
    assert((Value & 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.Value = (uintptr_t)P;
    assert(Result.isInvalid() ||
           PtrTraits::getAsVoidPointer(Result.get()) == P);
    return Result;
  }
  void *getAsOpaquePointer() const { return (void *)Value; }
};
 
/// An opaque type for threading parsed type information through the parser.
using ParsedType = OpaquePtr<QualType>;
using UnionParsedType = UnionOpaquePtr<QualType>;
 
// 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;
};
 
using ExprResult = ActionResult<Expr *>;
using StmtResult = ActionResult<Stmt *>;
using TypeResult = ActionResult<ParsedType>;
using BaseResult = ActionResult<CXXBaseSpecifier *>;
using MemInitResult = ActionResult<CXXCtorInitializer *>;
 
using DeclResult = ActionResult<Decl *>;
using ParsedTemplateTy = OpaquePtr<TemplateName>;
using UnionParsedTemplateTy = UnionOpaquePtr<TemplateName>;
 
using MultiExprArg = MutableArrayRef<Expr *>;
using MultiStmtArg = MutableArrayRef<Stmt *>;
using ASTTemplateArgsPtr = MutableArrayRef<ParsedTemplateArgument>;
using MultiTypeArg = MutableArrayRef<ParsedType>;
using MultiTemplateParamsArg = MutableArrayRef<TemplateParameterList *>;
 
inline ExprResult ExprError() { return ExprResult(true); }
inline StmtResult StmtError() { return StmtResult(true); }
inline TypeResult TypeError() { return TypeResult(true); }
 
inline ExprResult ExprError(const StreamingDiagnostic &) { return ExprError(); }
inline StmtResult StmtError(const StreamingDiagnostic &) { 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();
}
 
} // namespace clang
 
#endif // LLVM_CLANG_SEMA_OWNERSHIP_H