src/hotspot/share/gc/shared/collectedHeap.hpp

rev 53257 : Cherry-pick: 8213199: GC abstraction for Assembler::needs_explicit_null_check() plus Shenandoah parts

*** 580,589 ****
--- 580,594 ----
  
    virtual bool is_oop(oop object) const;
  
    virtual size_t obj_size(oop obj) const;
  
+   // Cells are memory slices allocated by the allocator. Objects are initialized
+   // in cells. The cell itself may have a header, found at a negative offset of
+   // oops. Usually, the size of the cell header is 0, but it may be larger.
+   virtual ptrdiff_t cell_header_size() const { return 0; }
+ 
    // Non product verification and debugging.
  #ifndef PRODUCT
    // Support for PromotionFailureALot.  Return true if it's time to cause a
    // promotion failure.  The no-argument version uses
    // this->_promotion_failure_alot_count as the counter.