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/ADT/StringMap.h" 33 #include <new> 34 #include <cassert> 35 36 namespace llvm { 37 38 class PooledStringPtr; 39 40 /// StringPool - An interned string pool. Use the intern method to add a 41 /// string. Strings are removed automatically as PooledStringPtrs are 42 /// destroyed. 43 class StringPool { 44 /// PooledString - This is the value of an entry in the pool's interning 45 /// table. 46 struct PooledString { 47 StringPool *Pool; ///< So the string can remove itself. 48 unsigned Refcount; ///< Number of referencing PooledStringPtrs. 49 50 public: PooledStringPooledString51 PooledString() : Pool(0), Refcount(0) { } 52 }; 53 54 friend class PooledStringPtr; 55 56 typedef StringMap<PooledString> table_t; 57 typedef StringMapEntry<PooledString> entry_t; 58 table_t InternTable; 59 60 public: 61 StringPool(); 62 ~StringPool(); 63 64 /// intern - Adds a string to the pool and returns a reference-counted 65 /// pointer to it. No additional memory is allocated if the string already 66 /// exists in the pool. 67 PooledStringPtr intern(StringRef Str); 68 69 /// empty - Checks whether the pool is empty. Returns true if so. 70 /// empty()71 inline bool empty() const { return InternTable.empty(); } 72 }; 73 74 /// PooledStringPtr - A pointer to an interned string. Use operator bool to 75 /// test whether the pointer is valid, and operator * to get the string if so. 76 /// This is a lightweight value class with storage requirements equivalent to 77 /// a single pointer, but it does have reference-counting overhead when 78 /// copied. 79 class PooledStringPtr { 80 typedef StringPool::entry_t entry_t; 81 entry_t *S; 82 83 public: PooledStringPtr()84 PooledStringPtr() : S(0) {} 85 PooledStringPtr(entry_t * E)86 explicit PooledStringPtr(entry_t *E) : S(E) { 87 if (S) ++S->getValue().Refcount; 88 } 89 PooledStringPtr(const PooledStringPtr & That)90 PooledStringPtr(const PooledStringPtr &That) : S(That.S) { 91 if (S) ++S->getValue().Refcount; 92 } 93 94 PooledStringPtr &operator=(const PooledStringPtr &That) { 95 if (S != That.S) { 96 clear(); 97 S = That.S; 98 if (S) ++S->getValue().Refcount; 99 } 100 return *this; 101 } 102 clear()103 void clear() { 104 if (!S) 105 return; 106 if (--S->getValue().Refcount == 0) { 107 S->getValue().Pool->InternTable.remove(S); 108 S->Destroy(); 109 } 110 S = 0; 111 } 112 ~PooledStringPtr()113 ~PooledStringPtr() { clear(); } 114 begin()115 inline const char *begin() const { 116 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 117 return S->getKeyData(); 118 } 119 end()120 inline const char *end() const { 121 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 122 return S->getKeyData() + S->getKeyLength(); 123 } 124 size()125 inline unsigned size() const { 126 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 127 return S->getKeyLength(); 128 } 129 130 inline const char *operator*() const { return begin(); } 131 inline operator bool() const { return S != 0; } 132 133 inline bool operator==(const PooledStringPtr &That) { return S == That.S; } 134 inline bool operator!=(const PooledStringPtr &That) { return S != That.S; } 135 }; 136 137 } // End llvm namespace 138 139 #endif 140