RFR: 8223451: Make optimistic types disabled by default

[Attila Szegedi]

I agree this is the best course of action.

+1.

Attila.

> On 2019. Jul 9., at 16:48, Hannes Wallnöfer <hannes.wallnoefer at oracle.com> wrote:
> 
> Please review:
> 
> JBS: https://bugs.openjdk.java.net/browse/JDK-8223451
> Webrev: http://cr.openjdk.java.net/~hannesw/8223451/webrev.00/
> 
> A lot of Nashorn usage we see is with command line scripts from the Node.js and Web ecosystems. These usually run for a short time, but can be quite complex and large. Optimistic compilation is a bad match for this type of application, as a lot of time is spent optimizing and recompiling code that is only run once. Additionally, optimistic types is both the newest and one of the most complex parts of Nashorn, so a large proportion of Nashorn bugs turn out to be related to it.
> 
> Based on these considerations this change disables optimistic types by default. Users that want to use it can easily continue to do so using a command line or engine option. The change is straightforward and does not affect user observable behaviour apart from the amount of time spent in script execution and compilation.
> 
> Hannes