1//===- llvm/ADT/CachedHashString.h - Prehashed string/StringRef -*- 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 CachedHashString and CachedHashStringRef. These are owning
10// and not-owning string types that store their hash in addition to their string
11// data.
12//
13// Unlike std::string, CachedHashString can be used in DenseSet/DenseMap
14// (because, unlike std::string, CachedHashString lets us have empty and
15// tombstone values).
16//
17//===----------------------------------------------------------------------===//
18
19#ifndef LLVM_ADT_CACHEDHASHSTRING_H
20#define LLVM_ADT_CACHEDHASHSTRING_H
21
22#include "llvm/ADT/DenseMapInfo.h"
23#include "llvm/ADT/StringRef.h"
24
25namespace llvm {
26
27/// A container which contains a StringRef plus a precomputed hash.
28class CachedHashStringRef {
29 const char *P;
30 uint32_t Size;
31 uint32_t Hash;
32
33public:
34 // Explicit because hashing a string isn't free.
35 explicit CachedHashStringRef(StringRef S)
36 : CachedHashStringRef(S, DenseMapInfo<StringRef>::getHashValue(S)) {}
37
38 CachedHashStringRef(StringRef S, uint32_t Hash)
39 : P(S.data()), Size(S.size()), Hash(Hash) {
40 assert(S.size() <= std::numeric_limits<uint32_t>::max());
41 }
42
43 StringRef val() const { return StringRef(P, Size); }
44 const char *data() const { return P; }
45 uint32_t size() const { return Size; }
46 uint32_t hash() const { return Hash; }
47};
48
49template <> struct DenseMapInfo<CachedHashStringRef> {
50 static CachedHashStringRef getEmptyKey() {
51 return CachedHashStringRef(DenseMapInfo<StringRef>::getEmptyKey(), 0);
52 }
53 static CachedHashStringRef getTombstoneKey() {
54 return CachedHashStringRef(DenseMapInfo<StringRef>::getTombstoneKey(), 1);
55 }
56 static unsigned getHashValue(const CachedHashStringRef &S) {
57 assert(!isEqual(S, getEmptyKey()) && "Cannot hash the empty key!");
58 assert(!isEqual(S, getTombstoneKey()) && "Cannot hash the tombstone key!");
59 return S.hash();
60 }
61 static bool isEqual(const CachedHashStringRef &LHS,
62 const CachedHashStringRef &RHS) {
63 return LHS.hash() == RHS.hash() &&
64 DenseMapInfo<StringRef>::isEqual(LHS.val(), RHS.val());
65 }
66};
67
68/// A container which contains a string, which it owns, plus a precomputed hash.
69///
70/// We do not null-terminate the string.
71class CachedHashString {
72 friend struct DenseMapInfo<CachedHashString>;
73
74 char *P;
75 uint32_t Size;
76 uint32_t Hash;
77
78 static char *getEmptyKeyPtr() { return DenseMapInfo<char *>::getEmptyKey(); }
79 static char *getTombstoneKeyPtr() {
80 return DenseMapInfo<char *>::getTombstoneKey();
81 }
82
83 bool isEmptyOrTombstone() const {
84 return P == getEmptyKeyPtr() || P == getTombstoneKeyPtr();
85 }
86
87 struct ConstructEmptyOrTombstoneTy {};
88
89 CachedHashString(ConstructEmptyOrTombstoneTy, char *EmptyOrTombstonePtr)
90 : P(EmptyOrTombstonePtr), Size(0), Hash(0) {
91 assert(isEmptyOrTombstone());
92 }
93
94 // TODO: Use small-string optimization to avoid allocating.
95
96public:
97 explicit CachedHashString(const char *S) : CachedHashString(StringRef(S)) {}
98
99 // Explicit because copying and hashing a string isn't free.
100 explicit CachedHashString(StringRef S)
101 : CachedHashString(S, DenseMapInfo<StringRef>::getHashValue(S)) {}
102
103 CachedHashString(StringRef S, uint32_t Hash)
104 : P(new char[S.size()]), Size(S.size()), Hash(Hash) {
105 memcpy(P, S.data(), S.size());
106 }
107
108 // Ideally this class would not be copyable. But SetVector requires copyable
109 // keys, and we want this to be usable there.
110 CachedHashString(const CachedHashString &Other)
111 : Size(Other.Size), Hash(Other.Hash) {
112 if (Other.isEmptyOrTombstone()) {
113 P = Other.P;
114 } else {
115 P = new char[Size];
116 memcpy(P, Other.P, Size);
117 }
118 }
119
120 CachedHashString &operator=(CachedHashString Other) {
121 swap(*this, Other);
122 return *this;
123 }
124
125 CachedHashString(CachedHashString &&Other) noexcept
126 : P(Other.P), Size(Other.Size), Hash(Other.Hash) {
127 Other.P = getEmptyKeyPtr();
128 }
129
130 ~CachedHashString() {
131 if (!isEmptyOrTombstone())
132 delete[] P;
133 }
134
135 StringRef val() const { return StringRef(P, Size); }
136 uint32_t size() const { return Size; }
137 uint32_t hash() const { return Hash; }
138
139 operator StringRef() const { return val(); }
140 operator CachedHashStringRef() const {
141 return CachedHashStringRef(val(), Hash);
142 }
143
144 friend void swap(CachedHashString &LHS, CachedHashString &RHS) {
145 using std::swap;
146 swap(LHS.P, RHS.P);
147 swap(LHS.Size, RHS.Size);
148 swap(LHS.Hash, RHS.Hash);
149 }
150};
151
152template <> struct DenseMapInfo<CachedHashString> {
153 static CachedHashString getEmptyKey() {
154 return CachedHashString(CachedHashString::ConstructEmptyOrTombstoneTy(),
155 CachedHashString::getEmptyKeyPtr());
156 }
157 static CachedHashString getTombstoneKey() {
158 return CachedHashString(CachedHashString::ConstructEmptyOrTombstoneTy(),
159 CachedHashString::getTombstoneKeyPtr());
160 }
161 static unsigned getHashValue(const CachedHashString &S) {
162 assert(!isEqual(S, getEmptyKey()) && "Cannot hash the empty key!");
163 assert(!isEqual(S, getTombstoneKey()) && "Cannot hash the tombstone key!");
164 return S.hash();
165 }
166 static bool isEqual(const CachedHashString &LHS,
167 const CachedHashString &RHS) {
168 if (LHS.hash() != RHS.hash())
169 return false;
170 if (LHS.P == CachedHashString::getEmptyKeyPtr())
171 return RHS.P == CachedHashString::getEmptyKeyPtr();
172 if (LHS.P == CachedHashString::getTombstoneKeyPtr())
173 return RHS.P == CachedHashString::getTombstoneKeyPtr();
174
175 // This is safe because if RHS.P is the empty or tombstone key, it will have
176 // length 0, so we'll never dereference its pointer.
177 return LHS.val() == RHS.val();
178 }
179};
180
181} // namespace llvm
182
183#endif
184