Test m3dwsw

PPC m3dwsw (PPCMThreeDepWritesSync)
"write-to_read causality, boehm adve PLDI'08 (Fig 5.)"
{
P0:r5=x; P0:r7=z ;
P1:r7=z; P1:r6=y;
P2:r5=x; P2:r6=y;
P0:r1=1; P0:r2=2; P1:r1=1;
} 
      P0    |       P1    |   P2         ;
stw r1,0,r5 | lwz r2,0,r7 | lwz r2,0,r6  ;
sync        | xor r9,r2,r2| xor r9,r2,r2 ;      
stw r2,0,r7 |stwx r1,r9,r6| lwzx r1,r9,r5;

exists (1:r2=2 /\ 2:r2=1 /\ 2:r1=0)