RFR: Here are some easy patches

[Martin Buchholz]

Michael,  Thanks.

This may be tricky.  isArray is a native method, and we don't want to pay
for native method overhead - we're depending on hotspot intrinsification.
I suspect isArray will lose with -Xint and perhaps also with C1.  In the
hotspot sources I see an ominous
virtual bool is_array_klass_slow().  Perhaps other engineers can give an
authoritative recommendation on which way to go.


On Wed, May 2, 2018 at 1:51 PM, Michael Rasmussen <
Michael.Rasmussen at roguewave.com> wrote:

> Hi Martin,
>
>
> Did you consider using Class::isArray in the loop? Something like
> the following:
>
> for (Object element : a) {
>   final int elementHash;
>   if (element == null) {
>     elementHash = 0;
>   }
>   else {
>     final Class<?> cl = element.getClass();
>     if (!cl.isArray())
>       elementHash = element.hashCode();
>     else if (element instanceof Object[])
>       elementHash = deepHashCode((Object[]) element);
>     else
>       elementHash = primitiveArrayHashCode(element,
> cl.getComponentType());
>   }
>
>   result = 31 * result + elementHash;
> }
>
> In my quick JMH test running on Java 10, it improved the performance
> with your test array (Object[100000] full of Integers) from 244 us/op to
> 160 us/op (vs current JDK: 399 us/op).
>
>
> /Michael
> ------------------------------
> *From:* core-libs-dev <core-libs-dev-bounces at openjdk.java.net> on behalf
> of Martin Buchholz <martinrb at google.com>
> *Sent:* 02 May 2018 21:17:19
> *To:* Paul Sandoz
> *Cc:* core-libs-dev
> *Subject:* Re: RFR: Here are some easy patches
>
> Hi Paul,
>
> On Mon, Apr 30, 2018 at 2:03 PM, Paul Sandoz <paul.sandoz at oracle.com>
> wrote:
>
> >
> >
> > On Apr 30, 2018, at 11:18 AM, Martin Buchholz <martinrb at google.com>
> wrote:
> >
> >
> >
> > On Mon, Apr 30, 2018 at 10:35 AM, Paul Sandoz <paul.sandoz at oracle.com>
> > wrote:
> >
> >> An obvious optimization:
> >>
> >> 8202398: Optimize Arrays.deepHashCode
> >> http://cr.openjdk.java.net/~martin/webrevs/jdk/deepHashCode-optimize/
> >> https://bugs.openjdk.java.net/browse/JDK-8202398
> >>
> >> I would prefer that the deeply nested ternary expressions be changed to
> a
> >> more expected if/else if/else
> >>
> >
> > My brain much prefers code transforming tabular data to "look tabular".
> >
> >
> >
> > I think you will like expression switch :-) in the interim i would stick
> > with the less eyebrow raising syntax.
> >
> >
> I'm going to claim committer's privilege and check in with my preferred
> tabular style.  You can rewrite using suburban sprawl style when us
> dinosaurs from the last milllenium have gone extinct.
>