So stxp %w0, %2, %3, %1 in your inline asm or look out for how this is printed in the equivalent sync pattern. I'd look in iterators.md for some of the attributes to confirm this.
Hey, thanks Ramana that's it :)
just one more thing, there is a special internal constraint "Ump" on memory address for load/store pair operations, so is the Q constraint I used sufficient ?
Thanks Yvan