Consider code like this:
{code}
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        try (StandardJavaFileManager fm = compiler.getStandardFileManager(null, null, null)) {
            for (int i = 0; i < 10; i++) {
                compiler.getTask(null, fm, d -> {}, Arrays.asList("-classpath", jars, "-proc:none"), null, Arrays.asList(new JavaSource())).call();
            }
        }
{code}

Where "jars" is a path containing many jars, each of the compilations will be much slower on JDK 9 (301.05ms) that it used to be on JDK 8 (15.275).

This is using:
$ java -version
java version "1.8.0_40"
Java(TM) SE Runtime Environment (build 1.8.0_40-b25)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode)

and
$ java -version
java version "9-ea"
Java(TM) SE Runtime Environment (build 9-ea+105-2016-02-10-210515.javare.4433.nc)
Java HotSpot(TM) 64-Bit Server VM (build 9-ea+105-2016-02-10-210515.javare.4433.nc, mixed mode)

To reproduce:
1. wget http://download.netbeans.org/netbeans/8.1/final/zip/netbeans-8.1-201510222201-javase.zip, unpack it
2.download the attached testcase, unpack
3. edit test.sh to fill in paths to JDK 8 and JDK 9
4. run test.sh, passing the "netbeans" directory from step 1 as a parameter