static void optimize(final File f, final File d, final Remapper remapper)
            throws IOException {
        if (f.isDirectory()) {
            File[] files = f.listFiles();
            for (int i = 0; i < files.length; ++i) {
                optimize(files[i], d, remapper);
            }
        } else if (f.getName().endsWith(".class")) {
            ConstantPool cp = new ConstantPool();
            ClassReader cr = new ClassReader(new FileInputStream(f));
            ClassWriter cw = new ClassWriter(0);
            ClassConstantsCollector ccc = new ClassConstantsCollector(cw, cp);
            ClassOptimizer co = new ClassOptimizer(ccc, remapper);
            cr.accept(co, ClassReader.SKIP_DEBUG);

            Set<Constant> constants = new TreeSet<Constant>(
                    new ConstantComparator());
            constants.addAll(cp.values());

            cr = new ClassReader(cw.toByteArray());
            cw = new ClassWriter(0);
            Iterator<Constant> i = constants.iterator();
            while (i.hasNext()) {
                Constant c = i.next();
                c.write(cw);
            }
            cr.accept(cw, ClassReader.SKIP_DEBUG);

            if (MAPPING.get(cr.getClassName() + "/remove") != null) {
                return;
            }
            String n = remapper.mapType(cr.getClassName());
            File g = new File(d, n + ".class");
            if (!g.exists() || g.lastModified() < f.lastModified()) {
                if (!g.getParentFile().exists() && !g.getParentFile().mkdirs()) {
                    throw new IOException("Cannot create directory "
                            + g.getParentFile());
                }
                OutputStream os = new FileOutputStream(g);
                try {
                    os.write(cw.toByteArray());
                } finally {
                    os.close();
                }
            }
        }
    }