[aarch64-port-dev ] population count intrinsic performance

[Alexeev, Alexander]

> > Now, what I am not clear on, is whether if you just use iRegI here
> > rather than iRregIorL2I you are guaranteed that the top 32 bits are 0.
> 
> If you can't use movw then src should be an iRegI.
Agreed.

>__ mov($tmp$$FloatRegister, __ T1D, 0, $src$$Register);
I've fixed that.

What would be the next step?