RFR: 8129426: aarch64: add support for PopCount in C2

[Edward Nevill]

Hi,

Aarch64 currently does not support the PopCountI and PopCountL nodes in aarch64.ad

The following webrev adds support for these using the SIMD instructions 'cnt' and 'addv'

http://cr.openjdk.java.net/~enevill/8129426/webrev.04

This patch was contributed by alexander.alexeev at caviumnetworks.com

The patch only modifies aarch64 specific files.

I have merged the patch in and tested it with JTreg / hotspot with the following results for both original and revised

Test results: passed: 858; failed: 4; error: 6

I have benchmarked the patch on four different partner platforms. The average improvement was 2.6X for PopCountI and 2.5X for PopCountL.

Please review,

Thanks,
Ed.