8275298: Remove unnecessary weak_oops_do call in adjust weak roots phase

Reviewed-by: tschatzl, sjohanss

src/hotspot/share/gc/g1/g1ConcurrentMark.cpp

@@ -1645,9 +1645,6 @@ void G1ConcurrentMark::weak_refs_work() {
            "Mark stack should be empty (unless it has overflown)");
 
     assert(rp->num_queues() == active_workers, "why not");
-
-    rp->verify_no_references_recorded();
-    assert(!rp->discovery_enabled(), "Post condition");
   }
 
   if (has_overflown()) {

src/hotspot/share/gc/g1/g1FullGCAdjustTask.cpp

@@ -81,7 +81,6 @@ class G1AdjustRegionClosure : public HeapRegionClosure {
 G1FullGCAdjustTask::G1FullGCAdjustTask(G1FullCollector* collector) :
     G1FullGCTask("G1 Adjust", collector),
     _root_processor(G1CollectedHeap::heap(), collector->workers()),
-    _references_done(false),
     _weak_proc_task(collector->workers()),
     _hrclaimer(collector->workers()),
     _adjust(collector) {
@@ -97,14 +96,12 @@ void G1FullGCAdjustTask::work(uint worker_id) {
   G1FullGCMarker* marker = collector()->marker(worker_id);
   marker->preserved_stack()->adjust_during_full_gc();
 
-  // Adjust the weak roots.
-  if (!Atomic::cmpxchg(&_references_done, false, true)) {
-    G1CollectedHeap::heap()->ref_processor_stw()->weak_oops_do(&_adjust);
+  {
+    // Adjust the weak roots.
+    AlwaysTrueClosure always_alive;
+    _weak_proc_task.work(worker_id, &always_alive, &_adjust);
   }
 
-  AlwaysTrueClosure always_alive;
-  _weak_proc_task.work(worker_id, &always_alive, &_adjust);
-
   CLDToOopClosure adjust_cld(&_adjust, ClassLoaderData::_claim_strong);
   CodeBlobToOopClosure adjust_code(&_adjust, CodeBlobToOopClosure::FixRelocations);
   _root_processor.process_all_roots(&_adjust, &adjust_cld, &adjust_code);

src/hotspot/share/gc/g1/g1FullGCAdjustTask.hpp

@@ -36,7 +36,6 @@ class G1CollectedHeap;
 
 class G1FullGCAdjustTask : public G1FullGCTask {
   G1RootProcessor          _root_processor;
-  volatile bool            _references_done;
   WeakProcessor::Task      _weak_proc_task;
   HeapRegionClaimer        _hrclaimer;
   G1AdjustClosure          _adjust;

src/hotspot/share/gc/g1/g1YoungCollector.cpp

@@ -984,8 +984,6 @@ void G1YoungCollector::process_discovered_references(G1ParScanThreadStateSet* pe
 
   _g1h->make_pending_list_reachable();
 
-  rp->verify_no_references_recorded();
-
   phase_times()->record_ref_proc_time((Ticks::now() - start).seconds() * MILLIUNITS);
 }
 

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

@@ -1923,8 +1923,6 @@ bool PSParallelCompact::invoke_no_policy(bool maximum_heap_compaction) {
     old_gen->object_space()->check_mangled_unused_area_complete();
   }
 
-  NOT_PRODUCT(ref_processor()->verify_no_references_recorded());
-
   collection_exit.update();
 
   heap->print_heap_after_gc();
@@ -2161,8 +2159,6 @@ class PSAdjustTask final : public WorkerTask {
 
   enum PSAdjustSubTask {
     PSAdjustSubTask_code_cache,
-    PSAdjustSubTask_old_ref_process,
-    PSAdjustSubTask_young_ref_process,
 
     PSAdjustSubTask_num_elements
   };
@@ -2204,16 +2200,6 @@ public:
       CodeBlobToOopClosure adjust_code(&adjust, CodeBlobToOopClosure::FixRelocations);
       CodeCache::blobs_do(&adjust_code);
     }
-    if (_sub_tasks.try_claim_task(PSAdjustSubTask_old_ref_process)) {
-      PSParallelCompact::ref_processor()->weak_oops_do(&adjust);
-    }
-    if (_sub_tasks.try_claim_task(PSAdjustSubTask_young_ref_process)) {
-      // Roots were visited so references into the young gen in roots
-      // may have been scanned.  Process them also.
-      // Should the reference processor have a span that excludes
-      // young gen objects?
-      PSScavenge::reference_processor()->weak_oops_do(&adjust);
-    }
     _sub_tasks.all_tasks_claimed();
   }
 };

src/hotspot/share/gc/parallel/psScavenge.cpp

@@ -654,8 +654,6 @@ bool PSScavenge::invoke_no_policy() {
     DerivedPointerTable::update_pointers();
 #endif
 
-    NOT_PRODUCT(reference_processor()->verify_no_references_recorded());
-
     // Re-verify object start arrays
     if (VerifyObjectStartArray &&
         VerifyAfterGC) {

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

@@ -798,8 +798,6 @@ void GenCollectedHeap::full_process_roots(bool is_adjust_phase,
 
 void GenCollectedHeap::gen_process_weak_roots(OopClosure* root_closure) {
   WeakProcessor::oops_do(root_closure);
-  _young_gen->ref_processor()->weak_oops_do(root_closure);
-  _old_gen->ref_processor()->weak_oops_do(root_closure);
 }
 
 bool GenCollectedHeap::no_allocs_since_save_marks() {

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

@@ -216,6 +216,9 @@ ReferenceProcessorStats ReferenceProcessor::process_discovered_references(RefPro
 
   phase_times.set_total_time_ms((os::elapsedTime() - start_time) * 1000);
 
+  // Elements on discovered lists were pushed to the pending list.
+  verify_no_references_recorded();
+
   return stats;
 }
 

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

@@ -420,8 +420,6 @@ public:
   // iterate over oops
   void weak_oops_do(OopClosure* f);       // weak roots
 
-  void verify_list(DiscoveredList& ref_list);
-
   // Discover a Reference object, using appropriate discovery criteria
   virtual bool discover_reference(oop obj, ReferenceType rt);