void appendStrings(JCTree tree) {
            tree = TreeInfo.skipParens(tree);
            if (tree.getTag() == JCTree.PLUS && tree.type.constValue() == null) {
                JCBinary op = (JCBinary) tree;
                if (op.operator.kind == MTH &&
                    ((OperatorSymbol) op.operator).opcode == string_add) {
                    appendStrings(op.lhs);
                    appendStrings(op.rhs);
                    return;
                }
            }
            genExpr(tree, tree.type).load();
            appendString(tree);
        }