Ownership.h

//===- 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 {

  // Basic
  class StreamableDiagnosticBase;

  // 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 *) = delete;
    ActionResult(volatile void *) = delete;

    bool isInvalid() const { return Invalid; }
    bool isUsable() const { return !Invalid && Val; }
    bool isUnset() const { return !Invalid && !Val; }

    PtrTy get() const { return Val; }
    template <typename T> T *getAs() { 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;

    using PtrTraits = llvm::PointerLikeTypeTraits<PtrTy>;

  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 *) = delete;
    ActionResult(volatile void *) = delete;

    bool isInvalid() const { return PtrWithInvalid & 0x01; }
    bool isUsable() const { return PtrWithInvalid > 0x01; }
    bool isUnset() const { return PtrWithInvalid == 0; }

    PtrTy get() const {
      void *VP = reinterpret_cast<void *>(PtrWithInvalid & ~0x01);
      return PtrTraits::getFromVoidPointer(VP);
    }

    template <typename T> T *getAs() { 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.
  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 StreamableDiagnosticBase &) {
    return ExprError();
  }
  inline StmtResult StmtError(const StreamableDiagnosticBase &) {
    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