Test ppo3

PPC ppo3 (PPCPPOThree)
"is RR to same location in ppo?, intervening write variation"
{
0:r6=x; 0:r7=y; 0:r8=z;
1:r7=y; 1:r8=z;
2:r6=x;
}
P0            |P1           |P2           ;
lwz r1,0(r7)  |li r1,1      |li r1,1      ;
xor r9,r1,r1  |stw r1,0(r8) |stw r1,0(r6) ;
lwzx r3,r9,r6 |sync         |             ;
lwz r4,0(r6)  |li r2,2      |             ;
xor r10,r4,r4 |stw r2,0(r7) |             ;
lwzx r2,r10,r8|             |             ;

Observed
    0:r1=2; 0:r2=0; 0:r3=0; 0:r4=1;