We are running annotation processors that use javax.lang.model.util.Elements#getTypeElement a lot. It seems that the performance regressed almost 1000x when using --release 9 instead of --release 8 on the recent JDK9.

Test Code:

@SupportedAnnotationTypes(value = "mypackage.MyAnnotation")
public class MyAnnotationProcessor extends AbstractProcessor {

@Override
public SourceVersion getSupportedSourceVersion() {
return SourceVersion.latest();
}

    @Override
    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        String name = "mypackage.MyClass";
        Elements elementUtils = processingEnv.getElementUtils();
        long time = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            elementUtils.getTypeElement(name);
        }
        System.out.println((System.currentTimeMillis() - time) + "ms");
        return false;
    }

}

I've tested this also with a single iteration, where --release 8 took 0ms and --release 9 was 18ms.

Steps to reproduce on Linux Ubuntu:
unpack MyAnnotationProcessor.tar.gz
set JAVA_HOME to JDK 9.0.1
sh ./run.sh

The expected output is:
Running with --release 8
71ms
27ms
Running with --release 9
2325ms
1711ms