8301222: Generalize check_release_entry in OopStorage

Reviewed-by: tschatzl, kbarrett

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

@@ -152,6 +152,10 @@ MetaspaceSummary CollectedHeap::create_metaspace_summary() {
                           ms_chunk_free_list_summary, class_chunk_free_list_summary);
 }
 
+bool CollectedHeap::contains_null(const oop* p) const {
+  return *p == nullptr;
+}
+
 void CollectedHeap::print_heap_before_gc() {
   LogTarget(Debug, gc, heap) lt;
   if (lt.is_enabled()) {

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

@@ -446,6 +446,12 @@ class CollectedHeap : public CHeapObj<mtGC> {
 
   MetaspaceSummary create_metaspace_summary();
 
+  // GCs are free to represent the bit representation for null differently in memory,
+  // which is typically not observable when using the Access API. However, if for
+  // some reason a context doesn't allow using the Access API, then this function
+  // explicitly checks if the given memory location contains a null value.
+  virtual bool contains_null(const oop* p) const;
+
   // Print heap information on the given outputStream.
   virtual void print_on(outputStream* st) const = 0;
   // The default behavior is to call print_on() on tty.

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

@@ -766,7 +766,7 @@ bool OopStorage::reduce_deferred_updates() {
 
 static inline void check_release_entry(const oop* entry) {
   assert(entry != nullptr, "Releasing null");
-  assert(*entry == nullptr, "Releasing uncleared entry: " PTR_FORMAT, p2i(entry));
+  assert(Universe::heap()->contains_null(entry), "Releasing uncleared entry: " PTR_FORMAT, p2i(entry));
 }
 
 void OopStorage::release(const oop* ptr) {