1//===- ComparisonCategories.h - Three Way Comparison Data -------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file defines the Comparison Category enum and data types, which
10// store the types and expressions needed to support operator<=>
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_CLANG_AST_COMPARISONCATEGORIES_H
15#define LLVM_CLANG_AST_COMPARISONCATEGORIES_H
16
17#include "clang/Basic/LLVM.h"
18#include "llvm/ADT/APSInt.h"
19#include "llvm/ADT/DenseMap.h"
20#include <array>
21#include <cassert>
22#include <optional>
23#include <vector>
24
25namespace llvm {
26 class StringRef;
27 class APSInt;
28}
29
30namespace clang {
31
32class ASTContext;
33class VarDecl;
34class CXXRecordDecl;
35class Sema;
36class QualType;
37class NamespaceDecl;
38
39/// An enumeration representing the different comparison categories
40/// types.
41///
42/// C++20 [cmp.categories.pre] The types partial_ordering, weak_ordering, and
43/// strong_ordering are collectively termed the comparison category types.
44enum class ComparisonCategoryType : unsigned char {
45 PartialOrdering,
46 WeakOrdering,
47 StrongOrdering,
48 First = PartialOrdering,
49 Last = StrongOrdering
50};
51
52/// Determine the common comparison type, as defined in C++2a
53/// [class.spaceship]p4.
54inline ComparisonCategoryType commonComparisonType(ComparisonCategoryType A,
55 ComparisonCategoryType B) {
56 return A < B ? A : B;
57}
58
59/// Get the comparison category that should be used when comparing values of
60/// type \c T.
61std::optional<ComparisonCategoryType>
62getComparisonCategoryForBuiltinCmp(QualType T);
63
64/// An enumeration representing the possible results of a three-way
65/// comparison. These values map onto instances of comparison category types
66/// defined in the standard library. e.g. 'std::strong_ordering::less'.
67enum class ComparisonCategoryResult : unsigned char {
68 Equal,
69 Equivalent,
70 Less,
71 Greater,
72 Unordered,
73 Last = Unordered
74};
75
76class ComparisonCategoryInfo {
77 friend class ComparisonCategories;
78 friend class Sema;
79
80public:
81 ComparisonCategoryInfo(const ASTContext &Ctx, const CXXRecordDecl *RD,
82 ComparisonCategoryType Kind)
83 : Ctx(Ctx), Record(RD), Kind(Kind) {}
84
85 struct ValueInfo {
86 ComparisonCategoryResult Kind;
87 VarDecl *VD;
88
89 ValueInfo(ComparisonCategoryResult Kind, VarDecl *VD)
90 : Kind(Kind), VD(VD) {}
91
92 /// True iff we've successfully evaluated the variable as a constant
93 /// expression and extracted its integer value.
94 bool hasValidIntValue() const;
95
96 /// Get the constant integer value used by this variable to represent
97 /// the comparison category result type.
98 llvm::APSInt getIntValue() const;
99 };
100private:
101 const ASTContext &Ctx;
102
103 /// A map containing the comparison category result decls from the
104 /// standard library. The key is a value of ComparisonCategoryResult.
105 mutable llvm::SmallVector<
106 ValueInfo, static_cast<unsigned>(ComparisonCategoryResult::Last) + 1>
107 Objects;
108
109 /// Lookup the ValueInfo struct for the specified ValueKind. If the
110 /// VarDecl for the value cannot be found, nullptr is returned.
111 ///
112 /// If the ValueInfo does not have a valid integer value the variable
113 /// is evaluated as a constant expression to determine that value.
114 ValueInfo *lookupValueInfo(ComparisonCategoryResult ValueKind) const;
115
116public:
117 /// The declaration for the comparison category type from the
118 /// standard library.
119 const CXXRecordDecl *Record = nullptr;
120
121 /// The Kind of the comparison category type
122 ComparisonCategoryType Kind;
123
124public:
125 QualType getType() const;
126
127 const ValueInfo *getValueInfo(ComparisonCategoryResult ValueKind) const {
128 ValueInfo *Info = lookupValueInfo(ValueKind);
129 assert(Info &&
130 "comparison category does not contain the specified result kind");
131 assert(Info->hasValidIntValue() &&
132 "couldn't determine the integer constant for this value");
133 return Info;
134 }
135
136 /// True iff the comparison is "strong". i.e. it checks equality and
137 /// not equivalence.
138 bool isStrong() const {
139 using CCK = ComparisonCategoryType;
140 return Kind == CCK::StrongOrdering;
141 }
142
143 /// True iff the comparison is not totally ordered.
144 bool isPartial() const {
145 using CCK = ComparisonCategoryType;
146 return Kind == CCK::PartialOrdering;
147 }
148
149 /// Converts the specified result kind into the correct result kind
150 /// for this category. Specifically it lowers strong equality results to
151 /// weak equivalence if needed.
152 ComparisonCategoryResult makeWeakResult(ComparisonCategoryResult Res) const {
153 using CCR = ComparisonCategoryResult;
154 if (!isStrong() && Res == CCR::Equal)
155 return CCR::Equivalent;
156 return Res;
157 }
158
159 const ValueInfo *getEqualOrEquiv() const {
160 return getValueInfo(ValueKind: makeWeakResult(Res: ComparisonCategoryResult::Equal));
161 }
162 const ValueInfo *getLess() const {
163 return getValueInfo(ValueKind: ComparisonCategoryResult::Less);
164 }
165 const ValueInfo *getGreater() const {
166 return getValueInfo(ValueKind: ComparisonCategoryResult::Greater);
167 }
168 const ValueInfo *getUnordered() const {
169 assert(isPartial());
170 return getValueInfo(ValueKind: ComparisonCategoryResult::Unordered);
171 }
172};
173
174class ComparisonCategories {
175public:
176 static StringRef getCategoryString(ComparisonCategoryType Kind);
177 static StringRef getResultString(ComparisonCategoryResult Kind);
178
179 /// Return the list of results which are valid for the specified
180 /// comparison category type.
181 static std::vector<ComparisonCategoryResult>
182 getPossibleResultsForType(ComparisonCategoryType Type);
183
184 /// Return the comparison category information for the category
185 /// specified by 'Kind'.
186 const ComparisonCategoryInfo &getInfo(ComparisonCategoryType Kind) const {
187 const ComparisonCategoryInfo *Result = lookupInfo(Kind);
188 assert(Result != nullptr &&
189 "information for specified comparison category has not been built");
190 return *Result;
191 }
192
193 /// Return the comparison category information as specified by
194 /// `getCategoryForType(Ty)`. If the information is not already cached,
195 /// the declaration is looked up and a cache entry is created.
196 /// NOTE: Lookup is expected to succeed. Use lookupInfo if failure is
197 /// possible.
198 const ComparisonCategoryInfo &getInfoForType(QualType Ty) const;
199
200public:
201 /// Return the cached comparison category information for the
202 /// specified 'Kind'. If no cache entry is present the comparison category
203 /// type is looked up. If lookup fails nullptr is returned. Otherwise, a
204 /// new cache entry is created and returned
205 const ComparisonCategoryInfo *lookupInfo(ComparisonCategoryType Kind) const;
206
207 ComparisonCategoryInfo *lookupInfo(ComparisonCategoryType Kind) {
208 const auto &This = *this;
209 return const_cast<ComparisonCategoryInfo *>(This.lookupInfo(Kind));
210 }
211
212 const ComparisonCategoryInfo *lookupInfoForType(QualType Ty) const;
213
214private:
215 friend class ASTContext;
216
217 explicit ComparisonCategories(const ASTContext &Ctx) : Ctx(Ctx) {}
218
219 const ASTContext &Ctx;
220
221 /// A map from the ComparisonCategoryType (represented as 'char') to the
222 /// cached information for the specified category.
223 mutable llvm::DenseMap<char, ComparisonCategoryInfo> Data;
224 mutable NamespaceDecl *StdNS = nullptr;
225};
226
227} // namespace clang
228
229#endif
230