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 <cassert> 34 35 namespace llvm { 36 37 class PooledStringPtr; 38 39 /// StringPool - An interned string pool. Use the intern method to add a 40 /// string. Strings are removed automatically as PooledStringPtrs are 41 /// destroyed. 42 class StringPool { 43 /// PooledString - This is the value of an entry in the pool's interning 44 /// table. 45 struct PooledString { 46 StringPool *Pool; ///< So the string can remove itself. 47 unsigned Refcount; ///< Number of referencing PooledStringPtrs. 48 49 public: PooledStringPooledString50 PooledString() : Pool(nullptr), Refcount(0) { } 51 }; 52 53 friend class PooledStringPtr; 54 55 typedef StringMap<PooledString> table_t; 56 typedef StringMapEntry<PooledString> entry_t; 57 table_t InternTable; 58 59 public: 60 StringPool(); 61 ~StringPool(); 62 63 /// intern - Adds a string to the pool and returns a reference-counted 64 /// pointer to it. No additional memory is allocated if the string already 65 /// exists in the pool. 66 PooledStringPtr intern(StringRef Str); 67 68 /// empty - Checks whether the pool is empty. Returns true if so. 69 /// empty()70 inline bool empty() const { return InternTable.empty(); } 71 }; 72 73 /// PooledStringPtr - A pointer to an interned string. Use operator bool to 74 /// test whether the pointer is valid, and operator * to get the string if so. 75 /// This is a lightweight value class with storage requirements equivalent to 76 /// a single pointer, but it does have reference-counting overhead when 77 /// copied. 78 class PooledStringPtr { 79 typedef StringPool::entry_t entry_t; 80 entry_t *S; 81 82 public: PooledStringPtr()83 PooledStringPtr() : S(nullptr) {} 84 PooledStringPtr(entry_t * E)85 explicit PooledStringPtr(entry_t *E) : S(E) { 86 if (S) ++S->getValue().Refcount; 87 } 88 PooledStringPtr(const PooledStringPtr & That)89 PooledStringPtr(const PooledStringPtr &That) : S(That.S) { 90 if (S) ++S->getValue().Refcount; 91 } 92 93 PooledStringPtr &operator=(const PooledStringPtr &That) { 94 if (S != That.S) { 95 clear(); 96 S = That.S; 97 if (S) ++S->getValue().Refcount; 98 } 99 return *this; 100 } 101 clear()102 void clear() { 103 if (!S) 104 return; 105 if (--S->getValue().Refcount == 0) { 106 S->getValue().Pool->InternTable.remove(S); 107 S->Destroy(); 108 } 109 S = nullptr; 110 } 111 ~PooledStringPtr()112 ~PooledStringPtr() { clear(); } 113 begin()114 inline const char *begin() const { 115 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 116 return S->getKeyData(); 117 } 118 end()119 inline const char *end() const { 120 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 121 return S->getKeyData() + S->getKeyLength(); 122 } 123 size()124 inline unsigned size() const { 125 assert(*this && "Attempt to dereference empty PooledStringPtr!"); 126 return S->getKeyLength(); 127 } 128 129 inline const char *operator*() const { return begin(); } 130 inline explicit operator bool() const { return S != nullptr; } 131 132 inline bool operator==(const PooledStringPtr &That) const { return S == That.S; } 133 inline bool operator!=(const PooledStringPtr &That) const { return S != That.S; } 134 }; 135 136 } // End llvm namespace 137 138 #endif 139