[aarch64-port-dev ] RFR: 8150394: aarch64: add support for 8.1 LSE CAS instructions

[Edward Nevill]

Hi,

Please review the following webrev

http://cr.openjdk.java.net/~enevill/8150394/webrev.0/

This adds support for the CAS instructions in armv8.1.

The use of the instructions is enabled/disabled by the use of -XX:+/-UseLSE. This is enabled automatically if detected in the hwcap. If UseLSE is enabled on a CPU which does not support these instructions a warning is issued but the instructions are enabled in any case. This is to allow use of the LSE extensions on 8.1 systems which are running older kernels.

Tested before and after with jcstress (default mode). In both cases there was 1 failure which is due to a missing Unsafe method and always occurs with jdk9.

Thanks for the review,
Ed.