6782820: Server VM fails with "unhandled implicit exception in compiled code"

Summary: Restore the code which sets a control edge for a klass load node.
Reviewed-by: never

src/share/vm/opto/compile.cpp

@@ -2192,6 +2192,7 @@ static void final_graph_reshaping_impl( Node *n, Final_Reshape_Counts &fpu ) {
 
   case Op_DecodeN:
     assert(!n->in(1)->is_EncodeP(), "should be optimized out");
+    assert(n->in(0) == NULL, "no control");
     break;
 
   case Op_EncodeP: {

src/share/vm/opto/macro.cpp

@@ -1724,6 +1724,13 @@ void PhaseMacroExpand::expand_lock_node(LockNode *lock) {
     if (klass_node == NULL) {
       Node* k_adr = basic_plus_adr(obj, oopDesc::klass_offset_in_bytes());
       klass_node = transform_later( LoadKlassNode::make(_igvn, mem, k_adr, _igvn.type(k_adr)->is_ptr()) );
+#ifdef _LP64
+      if (UseCompressedOops && klass_node->is_DecodeN()) {
+        assert(klass_node->in(1)->Opcode() == Op_LoadNKlass, "sanity");
+        klass_node->in(1)->init_req(0, ctrl);
+      } else
+#endif
+      klass_node->init_req(0, ctrl);
     }
     Node *proto_node = make_load(ctrl, mem, klass_node, Klass::prototype_header_offset_in_bytes() + sizeof(oopDesc), TypeX_X, TypeX_X->basic_type());