8266845: Shenandoah: Simplify SBS::load_reference_barrier implementation

Reviewed-by: shade

Author: zhengyu123

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

@@ -100,24 +100,27 @@ inline oop ShenandoahBarrierSet::load_reference_barrier(oop obj) {
 
 template <DecoratorSet decorators, class T>
 inline oop ShenandoahBarrierSet::load_reference_barrier(oop obj, T* load_addr) {
+  if (obj == NULL) {
+    return NULL;
+  }
 
   // Prevent resurrection of unreachable phantom (i.e. weak-native) references.
-  if (HasDecorator<decorators, ON_PHANTOM_OOP_REF>::value && obj != NULL &&
+  if (HasDecorator<decorators, ON_PHANTOM_OOP_REF>::value &&
       _heap->is_concurrent_weak_root_in_progress() &&
       !_heap->marking_context()->is_marked(obj)) {
     return NULL;
   }
 
   // Prevent resurrection of unreachable weak references.
   if ((HasDecorator<decorators, ON_WEAK_OOP_REF>::value || HasDecorator<decorators, ON_UNKNOWN_OOP_REF>::value) &&
-      obj != NULL && _heap->is_concurrent_weak_root_in_progress() &&
+      _heap->is_concurrent_weak_root_in_progress() &&
       !_heap->marking_context()->is_marked_strong(obj)) {
     return NULL;
   }
 
   // Prevent resurrection of unreachable objects that are visited during
   // concurrent class-unloading.
-  if (HasDecorator<decorators, AS_NO_KEEPALIVE>::value && obj != NULL &&
+  if (HasDecorator<decorators, AS_NO_KEEPALIVE>::value &&
       _heap->is_evacuation_in_progress() &&
       !_heap->marking_context()->is_marked(obj)) {
     return obj;