RFR(S)[13]: AArch64: float point register corruption in ZBarrierSetAssembler::load_at

[Stuart Monteith]

Hi Erik,
   I see that we get a tmp1 register, however I've found that is not
something we can reliably use - whether it is set to noreg or matches
the src/dst registers. I've found rscratch2 to be reliably untouched.
The use of scratch registers is something that needs to get fixed up
on AArch64.

Thanks,
   Stuart

On Thu, 20 Jun 2019 at 17:21, Erik Osterlund <erik.osterlund at oracle.com> wrote:
>
> Hi Stuart,
>
> You get a tmp1 register passed in to load_at, which has the intention of being a register you can reliably use in the barriers. Might want to use that instead of hoping for the best that rscratch2 isn’t used by anyone else (such as e.g. check-cast arraycopy stubs).
>
> Thanks,
> /Erik
>
> > On 20 Jun 2019, at 18:01, Stuart Monteith <stuart.monteith at linaro.org> wrote:
> >
> > Hello,
> >   There are incorrect values on VarHandle JCStress tests when ZGC is
> > enabled. A line was omitted that should have saved the first first
> > four registers. This change also removes a dependency on rscratch1 and
> > reuses rscratch2.
> >
> > Bug: https://bugs.openjdk.java.net/browse/JDK-8226515
> > Webrev: http://cr.openjdk.java.net/~smonteith/8226515/webrev.0/
> >
> > Tested with JCStress, jtreg tier1 and SpecJBB2015.
> >
> > This should be applied to jdk/jdk13 and jdk/jdk
> >
> > Thanks.
>