8264041: Incorrect comments for ParallelCompactData::summarize_dense_…

…prefix

Reviewed-by: tschatzl

src/hotspot/share/gc/parallel/psParallelCompact.hpp

@@ -428,8 +428,8 @@ class ParallelCompactData
   void add_obj(oop p, size_t len) { add_obj(cast_from_oop<HeapWord*>(p), len); }
 
   // Fill in the regions covering [beg, end) so that no data moves; i.e., the
-  // destination of region n is simply the start of region n.  The argument beg
-  // must be region-aligned; end need not be.
+  // destination of region n is simply the start of region n.  Both arguments
+  // beg and end must be region-aligned.
   void summarize_dense_prefix(HeapWord* beg, HeapWord* end);
 
   HeapWord* summarize_split_space(size_t src_region, SplitInfo& split_info,