RFR(sh/jdk8): Fix register allocation for thread register is 32bit LRB

[Zhengyu Gu]

>>> Ok?
>>
>>
>>   144   Register thread = rsi;
>>   145   if (thread == dst) {
>>   146     thread = rbx;
>>   147   }
>>   148   assert_different_registers(dst, src.base(), src.index(), thread);
>>
>> Line#145 never true, Line#145 - 147 should be removed.
> 
> What makes this obvious to you? It is not obvious to me...

Oops, nevermind. I read "thread == rdx" ...

Looks good to me.

-Zhengyu

> 
> Roman
>