Did you have a look into the "Working With the Inline Assembler" chapter of the Targeting_Embedded_PowerPC.pdf manual?
Anyway, not sure what the problem is you try to solve, the following code builds fine for me:
static int test(register int reg_b)
{
register int reg_a;
__asm(lbz reg_a,1(reg_b));
return reg_a;
}
Daniel