RFR: 8159052: aarch64: optimise unaligned copies in pd_disjoint_words and pd_conjoint_words

[Edward Nevill]

Hi,

Please review the following webrev

http://cr.openjdk.java.net/~enevill/8159052/webrev

JIRA Issue: https://bugs.openjdk.java.net/browse/JDK-8159052

Some partners HW has large unaligned access penalties.

This webrev optimises unaligned copies in pd_disjoint_words and
pd_conjoint_words.

There is no performance degradation on other partners HW.

The following JMH test was used to benchmark performance.

http://cr.openjdk.java.net/~enevill/8159052/JMHSample_97_GCStress.java

The following graphs show the performance of the above test on two
partners HW, partner A which has a penalty for unaligned accesses and
partner B which does not. The test was repeated for three different
garbage collectors, G1GC, ParallelGC and CMS. The units are time, so
lower is better.

http://cr.openjdk.java.net/~enevill/8159052/gcstress_res.pdf

I understand that this cannot be pushed to jdk 9 at the moment because
jdk 9 is FC, however I would like to push this to the aarch64 port jdk8u
repo so it has a save home to be migrated to jdk 9/jdk 9u/jdk 10 in the
future.

OK to push to jdk8u?
Ed.