--- a/src/share/vm/opto/type.hpp	Tue Jun 24 16:00:14 2008 -0700
+++ b/src/share/vm/opto/type.hpp	Thu Jun 26 13:34:00 2008 -0700
@@ -654,7 +654,8 @@
   virtual int  hash() const;             // Type specific hashing
   virtual bool singleton(void) const;    // TRUE if type is a singleton
   enum {
-   UNKNOWN_INSTANCE = 0
+   InstanceTop = -1,   // undefined instance
+   InstanceBot = 0     // any possible instance
   };
 protected:
 
@@ -667,14 +668,15 @@
   bool          _klass_is_exact;
   bool          _is_ptr_to_narrowoop;
 
-  int           _instance_id;  // if not UNKNOWN_INSTANCE, indicates that this is a particular instance
-                               // of this type which is distinct.  This is the  the node index of the
-                               // node creating this instance
+  // If not InstanceTop or InstanceBot, indicates that this is
+  // a particular instance of this type which is distinct.
+  // This is the the node index of the allocation node creating this instance.
+  int           _instance_id;
 
   static const TypeOopPtr* make_from_klass_common(ciKlass* klass, bool klass_change, bool try_for_exact);
 
-  int dual_instance()      const { return -_instance_id; }
-  int meet_instance(int uid) const;
+  int dual_instance_id() const;
+  int meet_instance_id(int uid) const;
 
 public:
   // Creates a type given a klass. Correctly handles multi-dimensional arrays
@@ -707,9 +709,9 @@
   // compressed oop references.
   bool is_ptr_to_narrowoop_nv() const { return _is_ptr_to_narrowoop; }
 
-  bool is_instance()       const { return _instance_id != UNKNOWN_INSTANCE; }
-  uint instance_id()       const { return _instance_id; }
-  bool is_instance_field() const { return _instance_id != UNKNOWN_INSTANCE && _offset >= 0; }
+  bool is_known_instance()       const { return _instance_id > 0; }
+  int  instance_id()             const { return _instance_id; }
+  bool is_known_instance_field() const { return is_known_instance() && _offset >= 0; }
 
   virtual intptr_t get_con() const;
 
@@ -717,7 +719,7 @@
 
   virtual const Type *cast_to_exactness(bool klass_is_exact) const;
 
-  virtual const TypeOopPtr *cast_to_instance(int instance_id) const;
+  virtual const TypeOopPtr *cast_to_instance_id(int instance_id) const;
 
   // corresponding pointer to klass, for a given instance
   const TypeKlassPtr* as_klass_type() const;
@@ -778,7 +780,7 @@
   }
 
   // Make a pointer to an oop.
-  static const TypeInstPtr *make(PTR ptr, ciKlass* k, bool xk, ciObject* o, int offset, int instance_id = 0 );
+  static const TypeInstPtr *make(PTR ptr, ciKlass* k, bool xk, ciObject* o, int offset, int instance_id = InstanceBot );
 
   // If this is a java.lang.Class constant, return the type for it or NULL.
   // Pass to Type::get_const_type to turn it to a type, which will usually
@@ -789,7 +791,7 @@
 
   virtual const Type *cast_to_exactness(bool klass_is_exact) const;
 
-  virtual const TypeOopPtr *cast_to_instance(int instance_id) const;
+  virtual const TypeOopPtr *cast_to_instance_id(int instance_id) const;
 
   virtual const TypePtr *add_offset( int offset ) const;
 
@@ -823,9 +825,9 @@
   const Type*    elem() const { return _ary->_elem; }
   const TypeInt* size() const { return _ary->_size; }
 
-  static const TypeAryPtr *make( PTR ptr, const TypeAry *ary, ciKlass* k, bool xk, int offset, int instance_id = 0);
+  static const TypeAryPtr *make( PTR ptr, const TypeAry *ary, ciKlass* k, bool xk, int offset, int instance_id = InstanceBot);
   // Constant pointer to array
-  static const TypeAryPtr *make( PTR ptr, ciObject* o, const TypeAry *ary, ciKlass* k, bool xk, int offset, int instance_id = 0);
+  static const TypeAryPtr *make( PTR ptr, ciObject* o, const TypeAry *ary, ciKlass* k, bool xk, int offset, int instance_id = InstanceBot);
 
   // Convenience
   static const TypeAryPtr *make(ciObject* o);
@@ -835,7 +837,7 @@
 
   virtual const Type *cast_to_exactness(bool klass_is_exact) const;
 
-  virtual const TypeOopPtr *cast_to_instance(int instance_id) const;
+  virtual const TypeOopPtr *cast_to_instance_id(int instance_id) const;
 
   virtual const TypeAryPtr* cast_to_size(const TypeInt* size) const;