8259020: null-check of g1 write_ref_field_pre_entry is not necessary

Reviewed-by: kbarrett, ayang, phh

Author: Xin Liu

src/hotspot/share/gc/g1/g1BarrierSetRuntime.cpp

@@ -45,11 +45,8 @@ void G1BarrierSetRuntime::write_ref_array_post_entry(HeapWord* dst, size_t lengt
 }
 
 // G1 pre write barrier slowpath
-JRT_LEAF(void, G1BarrierSetRuntime::write_ref_field_pre_entry(oopDesc* orig, JavaThread *thread))
-  if (orig == NULL) {
-    assert(false, "should be optimized out");
-    return;
-  }
+JRT_LEAF(void, G1BarrierSetRuntime::write_ref_field_pre_entry(oopDesc* orig, JavaThread* thread))
+  assert(orig != nullptr, "should be optimized out");
   assert(oopDesc::is_oop(orig, true /* ignore mark word */), "Error");
   // store the original value that was in the field reference
   SATBMarkQueue& queue = G1ThreadLocalData::satb_mark_queue(thread);