8329658: Serial: Refactor ContiguousSpace::_next_compaction_space

Reviewed-by: ayang, tschatzl

Author: lgxbslgx

src/hotspot/share/gc/serial/defNewGeneration.cpp

@@ -359,24 +359,12 @@ void DefNewGeneration::compute_space_boundaries(uintx minimum_eden_size,
   }
   from()->initialize(fromMR, clear_space, mangle_space);
   to()->initialize(toMR, clear_space, mangle_space);
-
-  // Set next compaction spaces.
-  eden()->set_next_compaction_space(from());
-  // The to-space is normally empty before a compaction so need
-  // not be considered.  The exception is during promotion
-  // failure handling when to-space can contain live objects.
-  from()->set_next_compaction_space(nullptr);
 }
 
 void DefNewGeneration::swap_spaces() {
   ContiguousSpace* s = from();
   _from_space        = to();
   _to_space          = s;
-  eden()->set_next_compaction_space(from());
-  // The to-space is normally empty before a compaction so need
-  // not be considered.  The exception is during promotion
-  // failure handling when to-space can contain live objects.
-  from()->set_next_compaction_space(nullptr);
 
   if (UsePerfData) {
     CSpaceCounters* c = _from_counters;
@@ -780,7 +768,6 @@ void DefNewGeneration::collect(bool   full,
     // as a result of a partial evacuation of eden
     // and from-space.
     swap_spaces();   // For uniformity wrt ParNewGeneration.
-    from()->set_next_compaction_space(to());
     heap->set_incremental_collection_failed();
 
     _gc_tracer->report_promotion_failed(_promotion_failed_info);
@@ -801,7 +788,6 @@ void DefNewGeneration::collect(bool   full,
 void DefNewGeneration::init_assuming_no_promotion_failure() {
   _promotion_failed = false;
   _promotion_failed_info.reset();
-  from()->set_next_compaction_space(nullptr);
 }
 
 void DefNewGeneration::remove_forwarding_pointers() {

src/hotspot/share/gc/serial/serialFullGC.cpp

@@ -267,7 +267,7 @@ class Compacter {
     _spaces[1].init(heap->young_gen()->eden());
     _spaces[2].init(heap->young_gen()->from());
 
-    bool is_promotion_failed = (heap->young_gen()->from()->next_compaction_space() != nullptr);
+    bool is_promotion_failed = !heap->young_gen()->to()->is_empty();
     if (is_promotion_failed) {
       _spaces[3].init(heap->young_gen()->to());
       _num_spaces = 4;

src/hotspot/share/gc/shared/space.cpp

@@ -43,7 +43,6 @@
 ContiguousSpace::ContiguousSpace():
   _bottom(nullptr),
   _end(nullptr),
-  _next_compaction_space(nullptr),
   _top(nullptr) {
   _mangler = new GenSpaceMangler(this);
 }
@@ -64,7 +63,6 @@ void ContiguousSpace::initialize(MemRegion mr,
   if (clear_space) {
     clear(mangle_space);
   }
-  _next_compaction_space = nullptr;
 }
 
 void ContiguousSpace::clear(bool mangle_space) {

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

@@ -64,9 +64,6 @@ class ContiguousSpace: public CHeapObj<mtGC> {
 private:
   HeapWord* _bottom;
   HeapWord* _end;
-
-  ContiguousSpace* _next_compaction_space;
-
   HeapWord* _top;
   // A helper for mangling the unused area of the space in debug builds.
   GenSpaceMangler* _mangler;
@@ -123,18 +120,6 @@ class ContiguousSpace: public CHeapObj<mtGC> {
   // had allocation performed in it, but is now to be considered empty.
   void clear(bool mangle_space);
 
-  // Returns the next space (in the current generation) to be compacted in
-  // the global compaction order.  Also is used to select the next
-  // space into which to compact.
-
-  ContiguousSpace* next_compaction_space() const {
-    return _next_compaction_space;
-  }
-
-  void set_next_compaction_space(ContiguousSpace* csp) {
-    _next_compaction_space = csp;
-  }
-
   // Accessors
   HeapWord* top() const            { return _top;    }
   void set_top(HeapWord* value)    { _top = value; }