RFR: Use R15-relative bad-mask in interpreter and C1 on x86_64

[Per Liden]

Looks good!

(I also took this for a spin in our testing, no issues found)

/Per

On 03/07/2018 09:49 AM, Rickard Bäckman wrote:
> The Interpreter and C1 have so far used a test reg, [rip+offset] to
> execute the ZGC barrier.
> On some machines it seems the distance between the CodeCache and global
> statics are larger than what is possible to represent with a 32-bit
> displacement, causing crashes.
> 
> This patch modifies the barrier used by C1 and the Interpreter to
> instead use what C2 has been using by default. mov reg, [r15+offset],
> which is the thread local copy of the mask.
> 
> Here is the webrev:
> http://cr.openjdk.java.net/~rbackman/zgc_r15_barrier/
> 
> Thanks
> /R
>