8005895: Inefficient InstanceKlass field packing wasts memory.

Summary: Pack _misc_has_default_methods into the _misc_flags, move _idnum_allocated_count.
Reviewed-by: coleenp, shade

src/share/vm/oops/instanceKlass.hpp

@@ -225,12 +225,16 @@ class InstanceKlass: public Klass {
   u2              _java_fields_count;    // The number of declared Java fields
   int             _nonstatic_oop_map_size;// size in words of nonstatic oop map blocks
 
+  // _is_marked_dependent can be set concurrently, thus cannot be part of the
+  // _misc_flags.
   bool            _is_marked_dependent;  // used for marking during flushing and deoptimization
+
   enum {
     _misc_rewritten            = 1 << 0, // methods rewritten.
     _misc_has_nonstatic_fields = 1 << 1, // for sizing with UseCompressedOops
     _misc_should_verify_class  = 1 << 2, // allow caching of preverification
-    _misc_is_anonymous         = 1 << 3  // has embedded _inner_classes field
+    _misc_is_anonymous         = 1 << 3, // has embedded _inner_classes field
+    _misc_has_default_methods  = 1 << 4  // class/superclass/implemented interfaces has default methods
   };
   u2              _misc_flags;
   u2              _minor_version;        // minor version number of class file
@@ -253,10 +257,6 @@ class InstanceKlass: public Klass {
   jint            _cached_class_file_len;         // JVMTI: length of above
   JvmtiCachedClassFieldMap* _jvmti_cached_class_field_map;  // JVMTI: used during heap iteration
 
-  // true if class, superclass, or implemented interfaces have default methods
-  bool            _has_default_methods;
-
-  volatile u2     _idnum_allocated_count;         // JNI/JVMTI: increments with the addition of methods, old ids don't change
   // Method array.
   Array<Method*>* _methods;
   // Interface (Klass*s) this class declares locally to implement.
@@ -280,6 +280,8 @@ class InstanceKlass: public Klass {
   //     ...
   Array<u2>*      _fields;
 
+  volatile u2     _idnum_allocated_count;         // JNI/JVMTI: increments with the addition of methods, old ids don't change
+
   // Class states are defined as ClassState (see above).
   // Place the _init_state here to utilize the unused 2-byte after
   // _idnum_allocated_count.
@@ -616,8 +618,16 @@ class InstanceKlass: public Klass {
     return _jvmti_cached_class_field_map;
   }
 
-  bool has_default_methods() const { return _has_default_methods; }
-  void set_has_default_methods(bool b) { _has_default_methods = b; }
+  bool has_default_methods() const {
+    return (_misc_flags & _misc_has_default_methods) != 0;
+  }
+  void set_has_default_methods(bool b) {
+    if (b) {
+      _misc_flags |= _misc_has_default_methods;
+    } else {
+      _misc_flags &= ~_misc_has_default_methods;
+    }
+  }
 
   // for adding methods, ConstMethod::UNSET_IDNUM means no more ids available
   inline u2 next_method_idnum();