RFR: 8153713 : aarch64: improve short array clearing using store pair

[Felix Yang]

Done.  New webrev: http://cr.openjdk.java.net/~fyang/8153713/webrev.01

Tested with JTreg hotspot, langtools and jdk.

Thanks,
Felix

On 7 April 2016 at 23:35, Andrew Haley <aph at redhat.com> wrote:

> On 04/07/2016 04:01 PM, Felix Yang wrote:
> >     Please review webrev:
> http://cr.openjdk.java.net/~fyang/8153713/webrev.00/
> >     JIRA Issue: https://bugs.openjdk.java.net/browse/JDK-8153713
> >
> >     Currently, C2 compiler generate independent stores to clear
> >     short arrays whose size is no bigger than parameter
> >     InitArrayShortSize (refer to ClearArrayNode::Ideal function).
> >     For the aarch64 port, we have store pair instruction which can
> >     zero two memory words at a time and this will be good for code
> >     size and maybe performance for some micro-archs.
> >
> >     For Spark Terasort, an extra of 550 stp (xzr, xzr) instructions
> >     are generated with the patch, which mean about 2KB reduction in
> >     codesize.
> >
> >     Tested with JTreg hotspot, langtools and jdk.  Is it OK?
>
> It looks reasonable.  It's rather a big slab of code for aarch64.ad,
> and I think that it should be in MacroAssembler.  Long Chen created
> MacroAssembler::zero_words, and you should create an overload of
> zero_words which takes a constant int as an argument.
>
> Andrew.
>
>
>
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