Adding a StringPool data structure, which GC will use.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44705 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 135 insertions, 0 deletions

diff --git a/include/llvm/Support/StringPool.h b/include/llvm/Support/StringPool.h
new file mode 100644
index 0000000000..07b2a8ddde
--- /dev/null
+++ b/include/llvm/Support/StringPool.h
@@ -0,0 +1,135 @@
+//===-- StringPool.h - Interned string pool -------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Gordon Henriksen and is distributed under the
+// University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares an interned string pool, which helps reduce the cost of
+// strings by using the same storage for identical strings.
+// 
+// To intern a string:
+// 
+//   StringPool Pool;
+//   PooledStringPtr Str = Pool.intern("wakka wakka");
+// 
+// To use the value of an interned string, use operator bool and operator*:
+// 
+//   if (Str)
+//     cerr << "the string is" << *Str << "\n";
+// 
+// Pooled strings are immutable, but you can change a PooledStringPtr to point
+// to another instance. So that interned strings can eventually be freed,
+// strings in the string pool are reference-counted (automatically).
+// 
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_STRINGPOOL_H
+#define LLVM_SUPPORT_STRINGPOOL_H
+
+#include <llvm/ADT/StringMap.h>
+#include <new>
+#include <cassert>
+
+namespace llvm {
+
+  class PooledStringPtr;
+
+  /// StringPool - An interned string pool. Use the intern method to add a
+  /// string. Strings are removed automatically as PooledStringPtrs are
+  /// destroyed.
+  class StringPool {
+    struct PooledString {
+      StringPool *Pool;  ///< So the string can remove itself.
+      unsigned Refcount; ///< Number of referencing PooledStringPtrs.
+      
+    public:
+      PooledString() : Pool(0), Refcount(0) { }
+    };
+    
+    friend class PooledStringPtr;
+    
+    typedef StringMap<PooledString> table_t;
+    typedef StringMapEntry<PooledString> entry_t;
+    table_t InternTable;
+    
+  public:
+    StringPool();
+    ~StringPool();
+    
+    PooledStringPtr intern(const char *Begin, const char *End);
+    inline PooledStringPtr intern(const char *Str);
+  };
+  
+  /// PooledStringPtr - A pointer to an interned string. Use operator bool to
+  /// test whether the pointer is valid, and operator * to get the string if so.
+  /// This is a lightweight value class with storage requirements equivalent to
+  /// a single pointer, but it does have reference-counting overhead when
+  /// copied.
+  class PooledStringPtr {
+    typedef StringPool::entry_t entry_t;
+    entry_t *S;
+    
+  public:
+    PooledStringPtr() : S(0) {}
+    
+    explicit PooledStringPtr(entry_t *E) : S(E) {
+      if (S) ++S->getValue().Refcount;
+    }
+    
+    PooledStringPtr(const PooledStringPtr &That) : S(That.S) {
+      if (S) ++S->getValue().Refcount;
+    }
+    
+    PooledStringPtr &operator=(const PooledStringPtr &That) {
+      if (S != That.S) {
+        clear();
+        S = That.S;
+        if (S) ++S->getValue().Refcount;
+      }
+      return *this;
+    }
+    
+    void clear() {
+      if (!S)
+        return;
+      if (--S->getValue().Refcount == 0) {
+        S->getValue().Pool->InternTable.remove(S);
+        delete S;
+      }
+      S = 0;
+    }
+    
+    ~PooledStringPtr() { clear(); }
+    
+    inline const char *begin() const {
+      assert(*this && "Attempt to dereference empty PooledStringPtr!");
+      return S->getKeyData();
+    }
+    
+    inline const char *end() const {
+      assert(*this && "Attempt to dereference empty PooledStringPtr!");
+      return S->getKeyData() + S->getKeyLength();
+    }
+    
+    inline unsigned size() const {
+      assert(*this && "Attempt to dereference empty PooledStringPtr!");
+      return S->getKeyLength();
+    }
+    
+    inline const char *operator*() const { return begin(); }
+    inline operator bool() const { return S != 0; }
+    
+    inline bool operator==(const PooledStringPtr &That) { return S == That.S; }
+    inline bool operator!=(const PooledStringPtr &That) { return S != That.S; }
+  };
+  
+  PooledStringPtr StringPool::intern(const char *Str) {
+    return intern(Str, Str + strlen(Str));
+  }
+
+} // End llvm namespace
+
+#endif