140 lines
4.1 KiB
C++
140 lines
4.1 KiB
C++
//===-- StringPool.h - Interned string pool ---------------------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file declares an interned string pool, which helps reduce the cost of
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// strings by using the same storage for identical strings.
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//
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// To intern a string:
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//
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// StringPool Pool;
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// PooledStringPtr Str = Pool.intern("wakka wakka");
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//
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// To use the value of an interned string, use operator bool and operator*:
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//
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// if (Str)
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// cerr << "the string is" << *Str << "\n";
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//
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// Pooled strings are immutable, but you can change a PooledStringPtr to point
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// to another instance. So that interned strings can eventually be freed,
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// strings in the string pool are reference-counted (automatically).
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_STRINGPOOL_H
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#define LLVM_SUPPORT_STRINGPOOL_H
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#include "llvm/ADT/StringMap.h"
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#include <new>
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#include <cassert>
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namespace llvm {
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class PooledStringPtr;
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/// StringPool - An interned string pool. Use the intern method to add a
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/// string. Strings are removed automatically as PooledStringPtrs are
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/// destroyed.
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class StringPool {
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/// PooledString - This is the value of an entry in the pool's interning
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/// table.
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struct PooledString {
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StringPool *Pool; ///< So the string can remove itself.
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unsigned Refcount; ///< Number of referencing PooledStringPtrs.
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public:
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PooledString() : Pool(0), Refcount(0) { }
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};
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friend class PooledStringPtr;
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typedef StringMap<PooledString> table_t;
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typedef StringMapEntry<PooledString> entry_t;
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table_t InternTable;
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public:
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StringPool();
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~StringPool();
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/// intern - Adds a string to the pool and returns a reference-counted
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/// pointer to it. No additional memory is allocated if the string already
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/// exists in the pool.
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PooledStringPtr intern(const StringRef &Str);
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/// empty - Checks whether the pool is empty. Returns true if so.
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///
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inline bool empty() const { return InternTable.empty(); }
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};
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/// PooledStringPtr - A pointer to an interned string. Use operator bool to
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/// test whether the pointer is valid, and operator * to get the string if so.
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/// This is a lightweight value class with storage requirements equivalent to
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/// a single pointer, but it does have reference-counting overhead when
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/// copied.
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class PooledStringPtr {
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typedef StringPool::entry_t entry_t;
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entry_t *S;
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public:
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PooledStringPtr() : S(0) {}
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explicit PooledStringPtr(entry_t *E) : S(E) {
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if (S) ++S->getValue().Refcount;
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}
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PooledStringPtr(const PooledStringPtr &That) : S(That.S) {
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if (S) ++S->getValue().Refcount;
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}
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PooledStringPtr &operator=(const PooledStringPtr &That) {
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if (S != That.S) {
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clear();
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S = That.S;
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if (S) ++S->getValue().Refcount;
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}
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return *this;
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}
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void clear() {
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if (!S)
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return;
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if (--S->getValue().Refcount == 0) {
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S->getValue().Pool->InternTable.remove(S);
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S->Destroy();
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}
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S = 0;
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}
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~PooledStringPtr() { clear(); }
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inline const char *begin() const {
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assert(*this && "Attempt to dereference empty PooledStringPtr!");
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return S->getKeyData();
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}
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inline const char *end() const {
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assert(*this && "Attempt to dereference empty PooledStringPtr!");
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return S->getKeyData() + S->getKeyLength();
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}
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inline unsigned size() const {
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assert(*this && "Attempt to dereference empty PooledStringPtr!");
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return S->getKeyLength();
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}
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inline const char *operator*() const { return begin(); }
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inline operator bool() const { return S != 0; }
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inline bool operator==(const PooledStringPtr &That) { return S == That.S; }
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inline bool operator!=(const PooledStringPtr &That) { return S != That.S; }
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};
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} // End llvm namespace
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#endif
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