RFR(sh/jdk11): Shenandoah: Isolate shared-code changes

[Roman Kennke]

On Wed, 2020-07-08 at 10:14 +0200, Roland Westrelin wrote:
> > Hmm, but it does exist in jdk11u and the intention here was to make
> > clear
> > that we don't possibly change existing behaviour by introducing
> > Shenandoah
> > to upstream jdk11u. E.g. compile to the exact same code when
> > building with
> > -shenandoahgc.
> 
> I understand but it feels silly that the easiest forward is to make a
> useless change. Anyway, I don't object to it.

Yeah. That is unfortunately the condition on which we have a chance to
take it upstream. And it doesn't look quite as silly when seen in the
context of the actual upstream diff:

https://cr.openjdk.java.net/~rkennke/shenandoah-jdk11u-upstream/webrev.05-shared/src/hotspot/share/opto/ifnode.cpp.udiff.html

I believe if we wanted to remove that line altogether in jdk11u, it
should be discussed separately from Shenandoah upstreaming.

Thanks,
Roman