Test LB+rs

PPC LB+rs (PPCAdirSix) "Register shadowing illustration"
(* was ppc-adir6 *)
{
 P0:r4=x; P1:r4=x; P0:r5=y; P1:r5=y;
 [x] = 0; [y] = 0;
}
   P0          |     P1           ;
lwz r1,0,r4    | lwz  r3,0,r5     ;
mr  r2, r1     | addi r3, r3, 1   ;
li  r1, 1      | stw  r3,0,r4     ;
stw r1,0,r5    |                  ;

Observed
    0:r1=1; 0:r2=2; 1:r3=2; x=2; y=1;
<<
genprog generated/ppc-adir6-prog.tex
essdump generated/ppc-adir6-ess.dot
show 0
>>
<<
show 0
readfrom generated/ppc-adir6-rf.dot
>>