RFR: JDK-8162381: ldrd/strd from unaligned address results in low performance

[Sergey Nazarkin]

Hi!

Please review performance improvement patch.

Pref profile on SPECjvm2088 xml.transform without call graph shows next hot methods: 
5.72% java [kernel.kallsyms] [k] do_alignment 
1.32% java [kernel.kallsyms] [k] do_alignment_ldrdstrd 
This mean that kernel is makes memory accesses when address is not aligned and reduces performance dramatically 

Issue: https://bugs.openjdk.java.net/browse/JDK-8162381
Review: http://cr.openjdk.java.net/~snazarki/8162381/

Sergey Nazarkin