Method and system for efficiently mapping guest instruction in an emulation assist unit

The present invention provides a method and system for using hardware to assist software in emulating the guest instructions. The method and system comprises an emulation assist unit (EAU) which efficiently maps a guest instruction to a unique tag, an index, and an address of the corresponding semantic routine. The index determines where in a cache a plurality of tags are stored. A separate cache within the EAU stores each tag in association with the address the first time the corresponding guest instruction is emulated. Thus, the emulation assist unit also dynamically responds to the set of guest instructions being emulated. The first time a guest instruction is emulated, the EAU determines the address and stores the address in the cache in association with the tag. When the guest instruction is emulated again, the EAU uses the tag to access the stored addresses of the corresponding semantic routine.