public void visitExec(JCExpressionStatement tree) {
        // Optimize x++ to ++x and x-- to --x.
        JCExpression e = tree.expr;
        switch (e.getTag()) {
            case JCTree.POSTINC:
                ((JCUnary) e).setTag(JCTree.PREINC);
                break;
            case JCTree.POSTDEC:
                ((JCUnary) e).setTag(JCTree.PREDEC);
                break;
        }
        genExpr(tree.expr, tree.expr.type).drop();
    }