RFR: C2: Avoid potentially superfluous mov instruction in load barrier stub

[Stefan Karlsson]

Looks good.

StefanK

On 2018-03-14 09:25, Per Liden wrote:
> Tiny optimization to avoid a sometimes superfluous mov instruction in 
> C2's load barrier slow path stub.
> 
> http://cr.openjdk.java.net/~pliden/zgc/opt_move/webrev.0/
> 
> /Per