8360664: Null pointer dereference in src/hotspot/share/prims/jvmtiTagMap.cpp in IterateOverHeapObjectClosure::do_object()

Found by Linux Verification Center (linuxtesting.org) with SVACE.
Signed-off-by: Artem Semenov <savoptik@altlinux.org>.

Reviewed-by: sspitsyn, amenkov, cjplummer

Author: savoptik

src/hotspot/share/prims/jvmtiTagMap.cpp

@@ -944,6 +944,7 @@ class IterateOverHeapObjectClosure: public ObjectClosure {
 
 // invoked for each object in the heap
 void IterateOverHeapObjectClosure::do_object(oop o) {
+  assert(o != nullptr, "Heap iteration should never produce null!");
   // check if iteration has been halted
   if (is_iteration_aborted()) return;
 
@@ -953,7 +954,7 @@ void IterateOverHeapObjectClosure::do_object(oop o) {
   }
 
   // skip if object is a dormant shared object whose mirror hasn't been loaded
-  if (o != nullptr && o->klass()->java_mirror() == nullptr) {
+  if (o->klass()->java_mirror() == nullptr) {
     log_debug(aot, heap)("skipped dormant archived object " INTPTR_FORMAT " (%s)", p2i(o),
                          o->klass()->external_name());
     return;
@@ -1032,14 +1033,15 @@ class IterateThroughHeapObjectClosure: public ObjectClosure {
 
 // invoked for each object in the heap
 void IterateThroughHeapObjectClosure::do_object(oop obj) {
+  assert(obj != nullptr, "Heap iteration should never produce null!");
   // check if iteration has been halted
   if (is_iteration_aborted()) return;
 
   // apply class filter
   if (is_filtered_by_klass_filter(obj, klass())) return;
 
   // skip if object is a dormant shared object whose mirror hasn't been loaded
-  if (obj != nullptr &&   obj->klass()->java_mirror() == nullptr) {
+  if (obj->klass()->java_mirror() == nullptr) {
     log_debug(aot, heap)("skipped dormant archived object " INTPTR_FORMAT " (%s)", p2i(obj),
                          obj->klass()->external_name());
     return;