1 //===-- StringPool.h - Interned string pool ---------------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file declares an interned string pool, which helps reduce the cost of 11 // strings by using the same storage for identical strings. 12 // 13 // To intern a string: 14 // 15 // StringPool Pool; 16 // PooledStringPtr Str = Pool.intern("wakka wakka"); 17 // 18 // To use the value of an interned string, use operator bool and operator*: 19 // 20 // if (Str) 21 // cerr << "the string is" << *Str << "\n"; 22 // 23 // Pooled strings are immutable, but you can change a PooledStringPtr to point 24 // to another instance. So that interned strings can eventually be freed, 25 // strings in the string pool are reference-counted (automatically). 26 // 27 //===----------------------------------------------------------------------===// 28 29 #ifndef LLVM_SUPPORT_STRINGPOOL_H 30 #define LLVM_SUPPORT_STRINGPOOL_H 31 32 #include "llvm/Support/Compiler.h" 33 #include "llvm/ADT/StringMap.h" 34 #include <cassert> 35 #include <new> 36 37 namespace llvm { 38 39 class PooledStringPtr; 40 41 /// StringPool - An interned string pool. Use the intern method to add a 42 /// string. Strings are removed automatically as PooledStringPtrs are 43 /// destroyed. 44 class StringPool { 45 /// PooledString - This is the value of an entry in the pool's interning 46 /// table. 47 struct PooledString { 48 StringPool *Pool; ///< So the string can remove itself. 49 unsigned Refcount; ///< Number of referencing PooledStringPtrs. 50 51 public: PooledStringPooledString52 PooledString() : Pool(nullptr), Refcount(0) { } 53 }; 54 55 friend class PooledStringPtr; 56 57 typedef StringMap<PooledString> table_t; 58 typedef StringMapEntry<PooledString> entry_t; 59 table_t InternTable; 60 61 public: 62 StringPool(); 63 ~StringPool(); 64 65 /// intern - Adds a string to the pool and returns a reference-counted 66 /// pointer to it. No additional memory is allocated if the string already 67 /// exists in the pool. 68 PooledStringPtr intern(StringRef Str); 69 70 /// empty - Checks whether the pool is empty. Returns true if so. 71 /// empty()72 inline bool empty() const { return InternTable.empty(); } 73 }; 74 75 /// PooledStringPtr - A pointer to an interned string. Use operator bool to 76 /// test whether the pointer is valid, and operator * to get the string if so. 77 /// This is a lightweight value class with storage requirements equivalent to 78 /// a single pointer, but it does have reference-counting overhead when 79 /// copied. 80 class PooledStringPtr { 81 typedef StringPool::entry_t entry_t; 82 entry_t *S; 83 84 public: PooledStringPtr()85 PooledStringPtr() : S(nullptr) {} 86 PooledStringPtr(entry_t * E)87 explicit PooledStringPtr(entry_t *E) : S(E) { 88 if (S) ++S->getValue().Refcount; 89 } 90 PooledStringPtr(const PooledStringPtr & That)91 PooledStringPtr(const PooledStringPtr &That) : S(That.S) { 92 if (S) ++S->getValue().Refcount; 93 } 94 95 PooledStringPtr &operator=(const PooledStringPtr &That) { 96 if (S != That.S) { 97 clear(); 98 S = That.S; 99 if (S) ++S->getValue().Refcount; 100 } 101 return *this; 102 } 103 clear()104 void clear() { 105 if (!S) 106 return; 107 if (--S->getValue().Refcount == 0) { 108 S->getValue().Pool->InternTable.remove(S); 109 S->Destroy(); 110 } 111 S = nullptr; 112 } 113 ~PooledStringPtr()114 ~PooledStringPtr() { clear(); } 115 begin()116 inline const char *begin() const { 117 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 118 return S->getKeyData(); 119 } 120 end()121 inline const char *end() const { 122 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 123 return S->getKeyData() + S->getKeyLength(); 124 } 125 size()126 inline unsigned size() const { 127 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 128 return S->getKeyLength(); 129 } 130 131 inline const char *operator*() const { return begin(); } 132 inline LLVM_EXPLICIT operator bool() const { return S != nullptr; } 133 134 inline bool operator==(const PooledStringPtr &That) const { return S == That.S; } 135 inline bool operator!=(const PooledStringPtr &That) const { return S != That.S; } 136 }; 137 138 } // End llvm namespace 139 140 #endif 141