8350905: Shenandoah: Releasing a WeakHandle's referent may extend its lifetime

Reviewed-by: shade, ysr

Author: William Kemper

src/hotspot/share/gc/shenandoah/shenandoahBarrierSet.inline.hpp

@@ -152,10 +152,19 @@ inline void ShenandoahBarrierSet::enqueue(oop obj) {
 
 template <DecoratorSet decorators, typename T>
 inline void ShenandoahBarrierSet::satb_barrier(T *field) {
+  // Uninitialized and no-keepalive stores do not need barrier.
   if (HasDecorator<decorators, IS_DEST_UNINITIALIZED>::value ||
       HasDecorator<decorators, AS_NO_KEEPALIVE>::value) {
     return;
   }
+
+  // Stores to weak/phantom require no barrier. The original references would
+  // have been enqueued in the SATB buffer by the load barrier if they were needed.
+  if (HasDecorator<decorators, ON_WEAK_OOP_REF>::value ||
+      HasDecorator<decorators, ON_PHANTOM_OOP_REF>::value) {
+    return;
+  }
+
   if (ShenandoahSATBBarrier && _heap->is_concurrent_mark_in_progress()) {
     T heap_oop = RawAccess<>::oop_load(field);
     if (!CompressedOops::is_null(heap_oop)) {
@@ -260,6 +269,7 @@ inline void ShenandoahBarrierSet::AccessBarrier<decorators, BarrierSetT>::oop_st
 template <DecoratorSet decorators, typename BarrierSetT>
 template <typename T>
 inline void ShenandoahBarrierSet::AccessBarrier<decorators, BarrierSetT>::oop_store_not_in_heap(T* addr, oop value) {
+  assert((decorators & ON_UNKNOWN_OOP_REF) == 0, "Reference strength must be known");
   oop_store_common(addr, value);
 }