Back-up logic for dual execution unit processor

An apparatus and method provides additional logic in both execution units 9,11 of a dual execution unit processor in order to determine if the instruction is interruptable. Additionally, backout logic 17,19 is provided for saving the contents of unique registers 13,15. The backout logic 17,19 uses two decodes to determine if the instruction currently executing modifies the unique registers 13,15. It is possible for a single instruction to modify more than one unique register 13,15. The backout logic of the present invention resides in both of the execution units 9,11 and particularly in the unit which contains the unique register being modified by the executing instruction. If an instruction is being executed which modifies one of the unique registers 13,15, then the contents of that register are saved in a backout latch 17,19. A cancel signal is then provided if the interruptable instruction executes without causing an interrupt. However, if the interruptable instruction does cause an interrupt, then the contents of the backout latch are reloaded into the execution units.