//===- ComparisonCategories.h - Three Way Comparison Data -------*- 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 defines the Comparison Category enum and data types, which

//  store the types and expressions needed to support operator<=>

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_COMPARISONCATEGORIES_H

#define LLVM_CLANG_AST_COMPARISONCATEGORIES_H

#include "clang/Basic/LLVM.h"

#include "llvm/ADT/APSInt.h"

#include "llvm/ADT/DenseMap.h"

#include <array>

#include <cassert>

#include <vector>

namespace llvm {

  class StringRef;

  class APSInt;

}

namespace clang {

class ASTContext;

class VarDecl;

class CXXRecordDecl;

class Sema;

class QualType;

class NamespaceDecl;

/// An enumeration representing the different comparison categories

/// types.

///

/// C++2a [cmp.categories.pre] The types weak_equality, strong_equality,

/// partial_ordering, weak_ordering, and strong_ordering are collectively

/// termed the comparison category types.

enum class ComparisonCategoryType : unsigned char {

  PartialOrdering,

  WeakOrdering,

  StrongOrdering,

  First = PartialOrdering,

  Last = StrongOrdering

};

/// Determine the common comparison type, as defined in C++2a

/// [class.spaceship]p4.

inline ComparisonCategoryType commonComparisonType(ComparisonCategoryType A,

                                                   ComparisonCategoryType B) {

  return A < B ? 
A4
 : 
B698
;

}

/// Get the comparison category that should be used when comparing values of

/// type \c T.

Optional<ComparisonCategoryType> getComparisonCategoryForBuiltinCmp(QualType T);

/// An enumeration representing the possible results of a three-way

/// comparison. These values map onto instances of comparison category types

/// defined in the standard library. e.g. 'std::strong_ordering::less'.

enum class ComparisonCategoryResult : unsigned char {

  Equal,

  Equivalent,

  Less,

  Greater,

  Unordered,

  Last = Unordered

};

class ComparisonCategoryInfo {

  friend class ComparisonCategories;

  friend class Sema;

public:

  ComparisonCategoryInfo(const ASTContext &Ctx, CXXRecordDecl *RD,

                         ComparisonCategoryType Kind)

      : Ctx(Ctx), Record(RD), Kind(Kind) {}

  struct ValueInfo {

    ComparisonCategoryResult Kind;

    VarDecl *VD;

    ValueInfo(ComparisonCategoryResult Kind, VarDecl *VD)

        : Kind(Kind), VD(VD) {}

    /// True iff we've successfully evaluated the variable as a constant

    /// expression and extracted its integer value.

    bool hasValidIntValue() const;

    /// Get the constant integer value used by this variable to represent

    /// the comparison category result type.

    llvm::APSInt getIntValue() const;

  };

private:

  const ASTContext &Ctx;

  /// A map containing the comparison category result decls from the

  /// standard library. The key is a value of ComparisonCategoryResult.

  mutable llvm::SmallVector<

      ValueInfo, static_cast<unsigned>(ComparisonCategoryResult::Last) + 1>

      Objects;

  /// Lookup the ValueInfo struct for the specified ValueKind. If the

  /// VarDecl for the value cannot be found, nullptr is returned.

  ///

  /// If the ValueInfo does not have a valid integer value the variable

  /// is evaluated as a constant expression to determine that value.

  ValueInfo *lookupValueInfo(ComparisonCategoryResult ValueKind) const;

public:

  /// The declaration for the comparison category type from the

  /// standard library.

  const CXXRecordDecl *Record = nullptr;

  /// The Kind of the comparison category type

  ComparisonCategoryType Kind;

public:

  QualType getType() const;

  const ValueInfo *getValueInfo(ComparisonCategoryResult ValueKind) const {

    ValueInfo *Info = lookupValueInfo(ValueKind);

    assert(Info &&

           "comparison category does not contain the specified result kind");

    assert(Info->hasValidIntValue() &&

           "couldn't determine the integer constant for this value");

    return Info;

  }

  /// True iff the comparison is "strong". i.e. it checks equality and

  /// not equivalence.

  bool isStrong() const {

    using CCK = ComparisonCategoryType;

    return Kind == CCK::StrongOrdering;

  }

  /// True iff the comparison is not totally ordered.

  bool isPartial() const {

    using CCK = ComparisonCategoryType;

    return Kind == CCK::PartialOrdering;

  }

  /// Converts the specified result kind into the correct result kind

  /// for this category. Specifically it lowers strong equality results to

  /// weak equivalence if needed.

  ComparisonCategoryResult makeWeakResult(ComparisonCategoryResult Res) const {

    using CCR = ComparisonCategoryResult;

    if (!isStrong() && 
Res == CCR::Equal8
)

      return CCR::Equivalent;

    return Res;

  }

  const ValueInfo *getEqualOrEquiv() const {

    return getValueInfo(makeWeakResult(ComparisonCategoryResult::Equal));

  }

  const ValueInfo *getLess() const {

    return getValueInfo(ComparisonCategoryResult::Less);

  }

  const ValueInfo *getGreater() const {

    return getValueInfo(ComparisonCategoryResult::Greater);

  }

  const ValueInfo *getUnordered() const {

    assert(isPartial());

    return getValueInfo(ComparisonCategoryResult::Unordered);

  }

};

class ComparisonCategories {

public:

  static StringRef getCategoryString(ComparisonCategoryType Kind);

  static StringRef getResultString(ComparisonCategoryResult Kind);

  /// Return the list of results which are valid for the specified

  /// comparison category type.

  static std::vector<ComparisonCategoryResult>

  getPossibleResultsForType(ComparisonCategoryType Type);

  /// Return the comparison category information for the category

  /// specified by 'Kind'.

  const ComparisonCategoryInfo &getInfo(ComparisonCategoryType Kind) const {

    const ComparisonCategoryInfo *Result = lookupInfo(Kind);

    assert(Result != nullptr &&

           "information for specified comparison category has not been built");

    return *Result;

  }

  /// Return the comparison category information as specified by

  /// `getCategoryForType(Ty)`. If the information is not already cached,

  /// the declaration is looked up and a cache entry is created.

  /// NOTE: Lookup is expected to succeed. Use lookupInfo if failure is

  /// possible.

  const ComparisonCategoryInfo &getInfoForType(QualType Ty) const;

public:

  /// Return the cached comparison category information for the

  /// specified 'Kind'. If no cache entry is present the comparison category

  /// type is looked up. If lookup fails nullptr is returned. Otherwise, a

  /// new cache entry is created and returned

  const ComparisonCategoryInfo *lookupInfo(ComparisonCategoryType Kind) const;

  ComparisonCategoryInfo *lookupInfo(ComparisonCategoryType Kind) {

    const auto &This = *this;

    return const_cast<ComparisonCategoryInfo *>(This.lookupInfo(Kind));

  }

  const ComparisonCategoryInfo *lookupInfoForType(QualType Ty) const;

private:

  friend class ASTContext;

  explicit ComparisonCategories(const ASTContext &Ctx) : Ctx(Ctx) {}

  const ASTContext &Ctx;

  /// A map from the ComparisonCategoryType (represented as 'char') to the

  /// cached information for the specified category.

  mutable llvm::DenseMap<char, ComparisonCategoryInfo> Data;

  mutable NamespaceDecl *StdNS = nullptr;

};

} // namespace clang

#endif