src/hotspot/share/oops/oop.hpp

*** 26,45 ****
--- 26,82 ----
  #define SHARE_OOPS_OOP_HPP
  
  #include "memory/iterator.hpp"
  #include "memory/memRegion.hpp"
  #include "oops/access.hpp"
+ #include "oops/arrayStorageProperties.hpp"
  #include "oops/metadata.hpp"
  #include "runtime/atomic.hpp"
  #include "utilities/macros.hpp"
  
  // oopDesc is the top baseclass for objects classes. The {name}Desc classes describe
  // the format of Java objects so the fields can be accessed from C++.
  // oopDesc is abstract.
  // (see oopHierarchy for complete oop class hierarchy)
  //
  // no virtual functions allowed
+ //
+ // oopDesc::_mark - the "oop mark word" encoding to be found separately in markOop.hpp
+ //
+ // oopDesc::_metadata - encodes both the object's klass pointer and potentially
+ //                      "storage properties" (currently confined to arrays in the form of
+ //                      ArrayStorageProperties). Storage properties are peculiar to the
+ //                      *instance*, and not necessarily the "type".
+ //
+ // The overall size of the _metadata field is dependent on "UseCompressedClassPointers",
+ // hence the terms "narrow" (32 bits) vs "wide" (64 bits).
+ //
+ // "Wide" encoding of _metadata:
+ // bit number          |63             0|
+ // bit length          |--3|-----61-----|
+ // --------------------------------------
+ // _klass              [xxx| Klass*     ]
+ // _wide_storage_props [ sp|            ]
+ // --------------------------------------
+ // with:
+ //    xxx = klass_mask(), Klass* = Klass pointer to be masked
+ //    sp = storage properties, bit number: wide_storage_props_shift
+ //
+ // "Narrow" encoding of _metadata:
+ // bit number            |31             0|
+ // bit length            |--3|-----29-----|
+ // ----------------------------------------
+ // _compressed_klass     [xxx| narrowKlass]
+ // _narrow_storage_props [ sp|            ]
+ // ----------------------------------------
+ // with:
+ //   xxx = compressed_klass_mask(), narrowKlass = compressed Klass pointer to be masked
+ //         narrowKlass may be further decoded (Klass::decode_klass()) to produce Klass*
+ //   sp = storage properties, bit number: narrow_storage_props_shift
+ //
+ // Storage properties encodings are current confined to arrayStorageProperties.hpp
+ 
  
  extern bool always_do_update_barrier;
  
  // Forward declarations.
  class OopClosure;
*** 57,66 ****
--- 94,105 ----
   private:
    volatile markOop _mark;
    union _metadata {
      Klass*      _klass;
      narrowKlass _compressed_klass;
+     uintptr_t   _wide_storage_props;
+     uint32_t   _narrow_storage_props;
    } _metadata;
  
   public:
    inline markOop  mark()          const;
    inline markOop  mark_raw()      const;
*** 77,86 ****
--- 116,136 ----
    // Used only to re-initialize the mark word (e.g., of promoted
    // objects during a GC) -- requires a valid klass pointer
    inline void init_mark();
    inline void init_mark_raw();
  
+   enum {
+     storage_props_nof_bits     = LogKlassAlignmentInBytes, // This alignment gives us some "free bits"
+     narrow_storage_props_shift = (sizeof(narrowKlass) << 3) - storage_props_nof_bits,
+     wide_storage_props_shift   = (sizeof(Klass*) << 3) - storage_props_nof_bits,
+   };
+ 
+   static inline narrowKlass compressed_klass_mask();
+   static inline narrowKlass compressed_klass_masked(narrowKlass raw);
+   static inline uintptr_t   klass_mask();
+   static inline Klass*      klass_masked(uintptr_t raw);
+ 
    inline Klass* klass() const;
    inline Klass* klass_or_null() const volatile;
    inline Klass* klass_or_null_acquire() const volatile;
    static inline Klass** klass_addr(HeapWord* mem);
    static inline narrowKlass* compressed_klass_addr(HeapWord* mem);
*** 88,97 ****
--- 138,154 ----
    inline narrowKlass* compressed_klass_addr();
  
    inline void set_klass(Klass* k);
    static inline void release_set_klass(HeapWord* mem, Klass* klass);
  
+   // Extra container metadata specific to arrays (encoded into high bits of _metadata)
+   static inline uintptr_t* wide_metadata_addr(HeapWord* mem);
+   inline ArrayStorageProperties array_storage_properties() const;
+   inline void set_metadata(ArrayStorageProperties storage_props, Klass* k);
+   static inline void release_set_metadata(HeapWord* mem, ArrayStorageProperties storage_props, Klass* klass);
+ 
+ 
    // For klass field compression
    inline int klass_gap() const;
    inline void set_klass_gap(int z);
    static inline void set_klass_gap(HeapWord* mem, int z);
    // For when the klass pointer is being used as a linked list "next" field.