openjdk/zero: use double code for atomic64 on powerpc

[Andrew Haley]

On 06/30/2010 04:30 PM, Sebastian Andrzej Siewior wrote:
> this cute C code does the same thing on powerpc as the assembly code that
> was here before. If the compiler was built with the SPE extensions instead
> of traditional FPU and double operations are performed in HW then we are
> one step further: The compiler turns this into evldd & evstdd. Voila :)
> 
> This C code could also be activated on s390. The compiler turns this into
> a single mvc instruction which does the copy operation. I don't know if
> mvc's copy ability is atomic _or_ not and therefore I leave it as it.

I don't quite understand this.  Is it guaranteed that double stores on
ppc are atomic?

Andrew.