8041351: Crash in src/share/vm/opto/loopnode.cpp:3215 - assert(!had_error) failed: bad dominance

Summary: add missing is_mem() check when we collect load nodes in SuperWord::co_locate_pack().
Reviewed-by: iveresov

hotspot/src/share/vm/opto/superword.cpp

@@ -1266,8 +1266,9 @@ void SuperWord::co_locate_pack(Node_List* pk) {
     memops.clear();
     for (DUIterator i = upper_insert_pt->outs(); upper_insert_pt->has_out(i); i++) {
       Node* use = upper_insert_pt->out(i);
-      if (!use->is_Store())
+      if (use->is_Mem() && !use->is_Store()) {
         memops.push(use);
+      }
     }
 
     MemNode* lower_insert_pt = last;