Abstract: A Branch Prediction Cache (BPC) selects from among multiple branch address entries for a single return-type instruction that returns to multiple callers. The BPC has a branch address associative memory, a return address associative memory, and word line logic used to validate and qualify entries. The branch address associative memory monitors program addresses for previously stored branch addresses. The return address stack (RtnStack) stores the return addresses for the most recent call-type instructions. The top of the stack is input to the return address associative memory. When a program address has multiple matches in the branch address associative memory, the return address associative memory enables only the entry that has an associated return address matching the top of the RtnStack. In an alternate embodiment, the return address associative memory is combined with a branch address cache and target address associative memory.

Abstract: The invention provides means and methods for extending an instruction-set architecture without impacting the software interface. This circumvents all software compatibility issues, and allows legacy software to benefit from new architectural extensions without recompilation and reassembly. The means employed are a translation engine for translating sequences of old architecture instructions into primary, new architecture instructions, and an extended instruction (EI) cache memory for storing the translations. A processor requesting a sequence of instructions will look first to the EI-cache for a translation, and if translations are unavailable, will look to a conventional cache memory for the sequence, and finally, if still unavailable, will look to a main memory.