RFR: JDK-8223244: Extend arraycopy stub GC interface to allow GC replacement of the whole loop

[Stuart Monteith]

This looks good to me. (as a non-committer).

On Thu, 2 May 2019 at 22:43, Roman Kennke <rkennke at redhat.com> wrote:
>
> Currently, when doing oop arraycopy from C2 and C1, we call into runtime
> for pre-barrier, then do the arraycopy as fast-blt-loop, then call into
> runtime again for post-barrier.
>
> In Shenandoah we would like to call into runtime once, and do the
> arraycopy in a single-loop, when GC is active, and only do the
> fast-blt-loop outside of GC.
>
> This requires some GC interface changes to allow skipping the fast-loop
> when it's not needed, and to also pass the element type for doing the
> arraycopy loop and checkcasts in runtime.
>
> For the most part, the change is to add the klass Register, and the
> L_exit label to jump to. In aarch64, it also involves to actually
> add+bind those labels, plus a very minor shuffling of code, in order to
> preserve original element count before diving into the prologue.
>
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8223240
> Webrev:
> http://cr.openjdk.java.net/~rkennke/JDK-8223244/webrev.00/
>
> Testing: hotspot_gc_shenandoah, hotspot/tier1 (x86_64 and aarch64) will
> jdk-submit before pushing. Also, tried with the prototype for
> JDK-8222859 both x86_64 and aarch64.
>
> Can I please get reviews?
>
> Thanks,
> Roman
>