question: void restrictTo8Bits ( Register r ) { PhysicalRegisterSet phys = ( PhysicalRegisterSet ) this . phys ; Register ESP = phys . getESP ( ) ; Register EBP = phys . getEBP ( ) ; Register ESI = phys . getESI ( ) ; Register EDI = phys . getEDI ( ) ; addRestriction ( r , ESP ) ; addRestriction ( r , EBP ) ; addRestriction ( r , ESI ) ; addRestriction ( r , EDI ) ; }
target:  Ensures that a particular register is only assigned to AL, BL, CL, or DL, since these are the only 8-bit registers we normally address.