--- a/src/hotspot/share/gc/cms/cmsHeap.cpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/cms/cmsHeap.cpp	Mon May 07 14:42:05 2018 +0200
@@ -100,7 +100,7 @@
   _young_manager = new GCMemoryManager("ParNew", "end of minor GC");
   _old_manager = new GCMemoryManager("ConcurrentMarkSweep", "end of major GC");
 
-  ParNewGeneration* young = (ParNewGeneration*) young_gen();
+  ParNewGeneration* young = young_gen();
   _eden_pool = new ContiguousSpacePool(young->eden(),
                                        "Par Eden Space",
                                        young->max_eden_size(),
@@ -128,18 +128,11 @@
 
 }
 
-void CMSHeap::check_gen_kinds() {
-  assert(young_gen()->kind() == Generation::ParNew,
-         "Wrong youngest generation type");
-  assert(old_gen()->kind() == Generation::ConcurrentMarkSweep,
-         "Wrong generation kind");
-}
-
 CMSHeap* CMSHeap::heap() {
   CollectedHeap* heap = Universe::heap();
   assert(heap != NULL, "Uninitialized access to CMSHeap::heap()");
   assert(heap->kind() == CollectedHeap::CMS, "Invalid name");
-  return (CMSHeap*) heap;
+  return static_cast<CMSHeap*>(heap);
 }
 
 void CMSHeap::gc_threads_do(ThreadClosure* tc) const {

--- a/src/hotspot/share/gc/cms/cmsHeap.hpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/cms/cmsHeap.hpp	Mon May 07 14:42:05 2018 +0200
@@ -26,6 +26,7 @@
 #define SHARE_VM_GC_CMS_CMSHEAP_HPP
 
 #include "gc/cms/concurrentMarkSweepGeneration.hpp"
+#include "gc/cms/parNewGeneration.hpp"
 #include "gc/shared/collectedHeap.hpp"
 #include "gc/shared/gcCause.hpp"
 #include "gc/shared/genCollectedHeap.hpp"
@@ -42,10 +43,6 @@
 class WorkGang;
 
 class CMSHeap : public GenCollectedHeap {
-
-protected:
-  virtual void check_gen_kinds();
-
 public:
   CMSHeap(GenCollectorPolicy *policy);
 
@@ -97,6 +94,16 @@
 
   GCMemoryManager* old_manager() const { return _old_manager; }
 
+  ParNewGeneration* young_gen() const {
+    assert(_young_gen->kind() == Generation::ParNew, "Wrong generation type");
+    return static_cast<ParNewGeneration*>(_young_gen);
+  }
+
+  ConcurrentMarkSweepGeneration* old_gen() const {
+    assert(_old_gen->kind() == Generation::ConcurrentMarkSweep, "Wrong generation kind");
+    return static_cast<ConcurrentMarkSweepGeneration*>(_old_gen);
+  }
+
 private:
   WorkGang* _workers;
   MemoryPool* _eden_pool;

--- a/src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/cms/concurrentMarkSweepGeneration.cpp	Mon May 07 14:42:05 2018 +0200
@@ -602,8 +602,7 @@
 
   // Support for parallelizing young gen rescan
   CMSHeap* heap = CMSHeap::heap();
-  assert(heap->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
-  _young_gen = (ParNewGeneration*)heap->young_gen();
+  _young_gen = heap->young_gen();
   if (heap->supports_inline_contig_alloc()) {
     _top_addr = heap->top_addr();
     _end_addr = heap->end_addr();
@@ -770,7 +769,6 @@
       log.trace("  Capacity " SIZE_FORMAT, capacity() / 1000);
       log.trace("  Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
       CMSHeap* heap = CMSHeap::heap();
-      assert(heap->is_old_gen(this), "The CMS generation should always be the old generation");
       size_t young_size = heap->young_gen()->capacity();
       log.trace("  Young gen size " SIZE_FORMAT, young_size / 1000);
       log.trace("  unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);

--- a/src/hotspot/share/gc/cms/jvmFlagConstraintsCMS.cpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/cms/jvmFlagConstraintsCMS.cpp	Mon May 07 14:42:05 2018 +0200
@@ -126,7 +126,7 @@
 
 static JVMFlag::Error CMSReservedAreaConstraintFunc(const char* name, size_t value, bool verbose) {
   if (UseConcMarkSweepGC) {
-    ConcurrentMarkSweepGeneration* cms = (ConcurrentMarkSweepGeneration*)GenCollectedHeap::heap()->old_gen();
+    ConcurrentMarkSweepGeneration* cms = CMSHeap::heap()->old_gen();
     const size_t ergo_max = cms->cmsSpace()->max_flag_size_for_task_size();
     if (value > ergo_max) {
       CommandLineError::print(verbose,
@@ -189,7 +189,7 @@
 
 JVMFlag::Error CMSSamplingGrainConstraintFunc(uintx value, bool verbose) {
   if (UseConcMarkSweepGC) {
-    size_t max_capacity = GenCollectedHeap::heap()->young_gen()->max_capacity();
+    size_t max_capacity = CMSHeap::heap()->young_gen()->max_capacity();
     if (value > max_uintx - max_capacity) {
     CommandLineError::print(verbose,
                             "CMSSamplingGrain (" UINTX_FORMAT ") must be "
@@ -212,7 +212,7 @@
   // Skip for current default value.
   if (UseConcMarkSweepGC && FLAG_IS_CMDLINE(CMSBitMapYieldQuantum)) {
     // CMSBitMapYieldQuantum should be compared with mark bitmap size.
-    ConcurrentMarkSweepGeneration* cms = (ConcurrentMarkSweepGeneration*)GenCollectedHeap::heap()->old_gen();
+    ConcurrentMarkSweepGeneration* cms = CMSHeap::heap()->old_gen();
     size_t bitmap_size = cms->collector()->markBitMap()->sizeInWords();
 
     if (value > bitmap_size) {

--- a/src/hotspot/share/gc/serial/defNewGeneration.cpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/serial/defNewGeneration.cpp	Mon May 07 14:42:05 2018 +0200
@@ -24,6 +24,8 @@
 
 #include "precompiled.hpp"
 #include "gc/serial/defNewGeneration.inline.hpp"
+#include "gc/serial/serialHeap.hpp"
+#include "gc/serial/tenuredGeneration.hpp"
 #include "gc/shared/adaptiveSizePolicy.hpp"
 #include "gc/shared/ageTable.inline.hpp"
 #include "gc/shared/cardTableRS.hpp"
@@ -34,7 +36,6 @@
 #include "gc/shared/gcTimer.hpp"
 #include "gc/shared/gcTrace.hpp"
 #include "gc/shared/gcTraceTime.inline.hpp"
-#include "gc/shared/genCollectedHeap.hpp"
 #include "gc/shared/genOopClosures.inline.hpp"
 #include "gc/shared/generationSpec.hpp"
 #include "gc/shared/preservedMarks.inline.hpp"
@@ -93,20 +94,18 @@
 void DefNewGeneration::FastKeepAliveClosure::do_oop(narrowOop* p) { DefNewGeneration::FastKeepAliveClosure::do_oop_work(p); }
 
 DefNewGeneration::FastEvacuateFollowersClosure::
-FastEvacuateFollowersClosure(GenCollectedHeap* gch,
+FastEvacuateFollowersClosure(SerialHeap* heap,
                              FastScanClosure* cur,
                              FastScanClosure* older) :
-  _gch(gch), _scan_cur_or_nonheap(cur), _scan_older(older)
+  _heap(heap), _scan_cur_or_nonheap(cur), _scan_older(older)
 {
-  assert(_gch->young_gen()->kind() == Generation::DefNew, "Generation should be DefNew");
-  _young_gen = (DefNewGeneration*)_gch->young_gen();
 }
 
 void DefNewGeneration::FastEvacuateFollowersClosure::do_void() {
   do {
-    _gch->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen, _scan_cur_or_nonheap, _scan_older);
-  } while (!_gch->no_allocs_since_save_marks());
-  guarantee(_young_gen->promo_failure_scan_is_complete(), "Failed to finish scan");
+    _heap->oop_since_save_marks_iterate(GenCollectedHeap::YoungGen, _scan_cur_or_nonheap, _scan_older);
+  } while (!_heap->no_allocs_since_save_marks());
+  guarantee(_heap->young_gen()->promo_failure_scan_is_complete(), "Failed to finish scan");
 }
 
 ScanClosure::ScanClosure(DefNewGeneration* g, bool gc_barrier) :
@@ -563,29 +562,29 @@
                                bool   is_tlab) {
   assert(full || size > 0, "otherwise we don't want to collect");
 
-  GenCollectedHeap* gch = GenCollectedHeap::heap();
+  SerialHeap* heap = SerialHeap::heap();
 
   _gc_timer->register_gc_start();
   DefNewTracer gc_tracer;
-  gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
+  gc_tracer.report_gc_start(heap->gc_cause(), _gc_timer->gc_start());
 
-  _old_gen = gch->old_gen();
+  _old_gen = heap->old_gen();
 
   // If the next generation is too full to accommodate promotion
   // from this generation, pass on collection; let the next generation
   // do it.
   if (!collection_attempt_is_safe()) {
     log_trace(gc)(":: Collection attempt not safe ::");
-    gch->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
+    heap->set_incremental_collection_failed(); // Slight lie: we did not even attempt one
     return;
   }
   assert(to()->is_empty(), "Else not collection_attempt_is_safe");
 
   init_assuming_no_promotion_failure();
 
-  GCTraceTime(Trace, gc, phases) tm("DefNew", NULL, gch->gc_cause());
+  GCTraceTime(Trace, gc, phases) tm("DefNew", NULL, heap->gc_cause());
 
-  gch->trace_heap_before_gc(&gc_tracer);
+  heap->trace_heap_before_gc(&gc_tracer);
 
   // These can be shared for all code paths
   IsAliveClosure is_alive(this);
@@ -596,23 +595,23 @@
   // The preserved marks should be empty at the start of the GC.
   _preserved_marks_set.init(1);
 
-  gch->rem_set()->prepare_for_younger_refs_iterate(false);
+  heap->rem_set()->prepare_for_younger_refs_iterate(false);
 
-  assert(gch->no_allocs_since_save_marks(),
+  assert(heap->no_allocs_since_save_marks(),
          "save marks have not been newly set.");
 
   FastScanClosure fsc_with_no_gc_barrier(this, false);
   FastScanClosure fsc_with_gc_barrier(this, true);
 
   CLDScanClosure cld_scan_closure(&fsc_with_no_gc_barrier,
-                                  gch->rem_set()->cld_rem_set()->accumulate_modified_oops());
+                                  heap->rem_set()->cld_rem_set()->accumulate_modified_oops());
 
   set_promo_failure_scan_stack_closure(&fsc_with_no_gc_barrier);
-  FastEvacuateFollowersClosure evacuate_followers(gch,
+  FastEvacuateFollowersClosure evacuate_followers(heap,
                                                   &fsc_with_no_gc_barrier,
                                                   &fsc_with_gc_barrier);
 
-  assert(gch->no_allocs_since_save_marks(),
+  assert(heap->no_allocs_since_save_marks(),
          "save marks have not been newly set.");
 
   {
@@ -621,10 +620,10 @@
     // See: CardTableRS::non_clean_card_iterate_possibly_parallel.
     StrongRootsScope srs(0);
 
-    gch->young_process_roots(&srs,
-                             &fsc_with_no_gc_barrier,
-                             &fsc_with_gc_barrier,
-                             &cld_scan_closure);
+    heap->young_process_roots(&srs,
+                              &fsc_with_no_gc_barrier,
+                              &fsc_with_gc_barrier,
+                              &cld_scan_closure);
   }
 
   // "evacuate followers".
@@ -641,12 +640,12 @@
   gc_tracer.report_tenuring_threshold(tenuring_threshold());
   pt.print_all_references();
 
-  assert(gch->no_allocs_since_save_marks(), "save marks have not been newly set.");
+  assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");
 
   WeakProcessor::weak_oops_do(&is_alive, &keep_alive);
 
   // Verify that the usage of keep_alive didn't copy any objects.
-  assert(gch->no_allocs_since_save_marks(), "save marks have not been newly set.");
+  assert(heap->no_allocs_since_save_marks(), "save marks have not been newly set.");
 
   if (!_promotion_failed) {
     // Swap the survivor spaces.
@@ -670,9 +669,9 @@
 
     // A successful scavenge should restart the GC time limit count which is
     // for full GC's.
-    AdaptiveSizePolicy* size_policy = gch->size_policy();
+    AdaptiveSizePolicy* size_policy = heap->size_policy();
     size_policy->reset_gc_overhead_limit_count();
-    assert(!gch->incremental_collection_failed(), "Should be clear");
+    assert(!heap->incremental_collection_failed(), "Should be clear");
   } else {
     assert(_promo_failure_scan_stack.is_empty(), "post condition");
     _promo_failure_scan_stack.clear(true); // Clear cached segments.
@@ -686,14 +685,14 @@
     // and from-space.
     swap_spaces();   // For uniformity wrt ParNewGeneration.
     from()->set_next_compaction_space(to());
-    gch->set_incremental_collection_failed();
+    heap->set_incremental_collection_failed();
 
     // Inform the next generation that a promotion failure occurred.
     _old_gen->promotion_failure_occurred();
     gc_tracer.report_promotion_failed(_promotion_failed_info);
 
     // Reset the PromotionFailureALot counters.
-    NOT_PRODUCT(gch->reset_promotion_should_fail();)
+    NOT_PRODUCT(heap->reset_promotion_should_fail();)
   }
   // We should have processed and cleared all the preserved marks.
   _preserved_marks_set.reclaim();
@@ -707,7 +706,7 @@
   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
   update_time_of_last_gc(now);
 
-  gch->trace_heap_after_gc(&gc_tracer);
+  heap->trace_heap_after_gc(&gc_tracer);
 
   _gc_timer->register_gc_end();
 

--- a/src/hotspot/share/gc/serial/defNewGeneration.hpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/serial/defNewGeneration.hpp	Mon May 07 14:42:05 2018 +0200
@@ -39,6 +39,7 @@
 class STWGCTimer;
 class CSpaceCounters;
 class ScanWeakRefClosure;
+class SerialHeap;
 
 // DefNewGeneration is a young generation containing eden, from- and
 // to-space.
@@ -179,12 +180,11 @@
   };
 
   class FastEvacuateFollowersClosure: public VoidClosure {
-    GenCollectedHeap* _gch;
-    DefNewGeneration* _young_gen;
+    SerialHeap* _heap;
     FastScanClosure* _scan_cur_or_nonheap;
     FastScanClosure* _scan_older;
   public:
-    FastEvacuateFollowersClosure(GenCollectedHeap* gch,
+    FastEvacuateFollowersClosure(SerialHeap* heap,
                                  FastScanClosure* cur,
                                  FastScanClosure* older);
     void do_void();

--- a/src/hotspot/share/gc/serial/serialHeap.cpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/serial/serialHeap.cpp	Mon May 07 14:42:05 2018 +0200
@@ -25,9 +25,17 @@
 #include "precompiled.hpp"
 #include "gc/serial/defNewGeneration.hpp"
 #include "gc/serial/serialHeap.hpp"
+#include "gc/serial/tenuredGeneration.hpp"
 #include "gc/shared/genMemoryPools.hpp"
 #include "services/memoryManager.hpp"
 
+SerialHeap* SerialHeap::heap() {
+  CollectedHeap* heap = Universe::heap();
+  assert(heap != NULL, "Uninitialized access to SerialHeap::heap()");
+  assert(heap->kind() == CollectedHeap::Serial, "Invalid name");
+  return static_cast<SerialHeap*>(heap);
+}
+
 SerialHeap::SerialHeap(GenCollectorPolicy* policy) :
     GenCollectedHeap(policy,
                      Generation::DefNew,
@@ -42,7 +50,7 @@
 
 void SerialHeap::initialize_serviceability() {
 
-  DefNewGeneration* young = (DefNewGeneration*) young_gen();
+  DefNewGeneration* young = young_gen();
 
   // Add a memory pool for each space and young gen doesn't
   // support low memory detection as it is expected to get filled up.
@@ -54,7 +62,7 @@
                                                    "Survivor Space",
                                                    young->max_survivor_size(),
                                                    false /* support_usage_threshold */);
-  Generation* old = old_gen();
+  TenuredGeneration* old = old_gen();
   _old_pool = new GenerationPool(old, "Tenured Gen", true);
 
   _young_manager->add_pool(_eden_pool);
@@ -68,13 +76,6 @@
 
 }
 
-void SerialHeap::check_gen_kinds() {
-  assert(young_gen()->kind() == Generation::DefNew,
-         "Wrong youngest generation type");
-  assert(old_gen()->kind() == Generation::MarkSweepCompact,
-         "Wrong generation kind");
-}
-
 GrowableArray<GCMemoryManager*> SerialHeap::memory_managers() {
   GrowableArray<GCMemoryManager*> memory_managers(2);
   memory_managers.append(_young_manager);

--- a/src/hotspot/share/gc/serial/serialHeap.hpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/serial/serialHeap.hpp	Mon May 07 14:42:05 2018 +0200
@@ -25,12 +25,15 @@
 #ifndef SHARE_VM_GC_SERIAL_SERIALHEAP_HPP
 #define SHARE_VM_GC_SERIAL_SERIALHEAP_HPP
 
+#include "gc/serial/defNewGeneration.hpp"
+#include "gc/serial/tenuredGeneration.hpp"
 #include "gc/shared/genCollectedHeap.hpp"
 #include "utilities/growableArray.hpp"
 
 class GenCollectorPolicy;
 class GCMemoryManager;
 class MemoryPool;
+class TenuredGeneration;
 
 class SerialHeap : public GenCollectedHeap {
 private:
@@ -40,10 +43,9 @@
 
   virtual void initialize_serviceability();
 
-protected:
-  virtual void check_gen_kinds();
+public:
+  static SerialHeap* heap();
 
-public:
   SerialHeap(GenCollectorPolicy* policy);
 
   virtual Name kind() const {
@@ -61,6 +63,16 @@
   virtual bool is_in_closed_subset(const void* p) const {
     return is_in(p);
   }
+
+  DefNewGeneration* young_gen() const {
+    assert(_young_gen->kind() == Generation::DefNew, "Wrong generation type");
+    return static_cast<DefNewGeneration*>(_young_gen);
+  }
+
+  TenuredGeneration* old_gen() const {
+    assert(_old_gen->kind() == Generation::MarkSweepCompact, "Wrong generation type");
+    return static_cast<TenuredGeneration*>(_old_gen);
+  }
 };
 
 #endif // SHARE_VM_GC_CMS_CMSHEAP_HPP

--- a/src/hotspot/share/gc/shared/genCollectedHeap.cpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/shared/genCollectedHeap.cpp	Mon May 07 14:42:05 2018 +0200
@@ -176,7 +176,7 @@
 void GenCollectedHeap::post_initialize() {
   CollectedHeap::post_initialize();
   ref_processing_init();
-  check_gen_kinds();
+
   DefNewGeneration* def_new_gen = (DefNewGeneration*)_young_gen;
 
   initialize_size_policy(def_new_gen->eden()->capacity(),
@@ -249,7 +249,7 @@
 //   was a full collection because a partial collection (would
 //   have) failed and is likely to fail again
 bool GenCollectedHeap::should_try_older_generation_allocation(size_t word_size) const {
-  size_t young_capacity = young_gen()->capacity_before_gc();
+  size_t young_capacity = _young_gen->capacity_before_gc();
   return    (word_size > heap_word_size(young_capacity))
          || GCLocker::is_active_and_needs_gc()
          || incremental_collection_failed();
@@ -257,12 +257,12 @@
 
 HeapWord* GenCollectedHeap::expand_heap_and_allocate(size_t size, bool   is_tlab) {
   HeapWord* result = NULL;
-  if (old_gen()->should_allocate(size, is_tlab)) {
-    result = old_gen()->expand_and_allocate(size, is_tlab);
+  if (_old_gen->should_allocate(size, is_tlab)) {
+    result = _old_gen->expand_and_allocate(size, is_tlab);
   }
   if (result == NULL) {
-    if (young_gen()->should_allocate(size, is_tlab)) {
-      result = young_gen()->expand_and_allocate(size, is_tlab);
+    if (_young_gen->should_allocate(size, is_tlab)) {
+      result = _young_gen->expand_and_allocate(size, is_tlab);
     }
   }
   assert(result == NULL || is_in_reserved(result), "result not in heap");
@@ -287,7 +287,7 @@
     HandleMark hm; // Discard any handles allocated in each iteration.
 
     // First allocation attempt is lock-free.
-    Generation *young = young_gen();
+    Generation *young = _young_gen;
     assert(young->supports_inline_contig_alloc(),
       "Otherwise, must do alloc within heap lock");
     if (young->should_allocate(size, is_tlab)) {

--- a/src/hotspot/share/gc/shared/genCollectedHeap.hpp	Mon May 07 14:42:04 2018 +0200
+++ b/src/hotspot/share/gc/shared/genCollectedHeap.hpp	Mon May 07 14:42:05 2018 +0200
@@ -63,10 +63,11 @@
     OldGen
   };
 
-private:
+protected:
   Generation* _young_gen;
   Generation* _old_gen;
 
+private:
   GenerationSpec* _young_gen_spec;
   GenerationSpec* _old_gen_spec;
 
@@ -161,8 +162,6 @@
                    Generation::Name old,
                    const char* policy_counters_name);
 
-  virtual void check_gen_kinds() = 0;
-
 public:
 
   // Returns JNI_OK on success