A novel renaming scheme to exploit value temporal locality through physical register reuse and unification

Hardware renaming schemes provide multiple physical locations (register or memory) for each logical name. In current renaming schemes, a new physical location is allocated for each dispatched instruction regardless of its result value. However, these values exhibit a high level of temporal locality (result redundancy). This paper proposes: Physical Register Reuse. To reuse a physical location whenever it is detected that an incoming result value matches a previous one. This is performed during register renaming and requires some VALUE-IDENTITY DETECTION hardware. By mapping several logical registers holding the same value to the same physical register, Physical Register Reuse gives the opportunities: SHARING-exploit the high level of value-redundancy in the register file to either reduce the file size and complexity, or effectively enlarge the active instruction window. Our results suggest reduction factors of 2 to 4 in some cases. Performance is increased either by the enlarged instruction window or by the higher frequency enabled by a smaller register file requiring fewer ports. RESULT REUSE AND DEPENDENCY REDIRECTION-move the responsibility of generating results: (1) From the functional units to the register renamer, resulting in the possible elimination of processed instructions from the execution stream. (2) From one instruction to an earlier instruction stream, possibly allowing instructions to be scheduled earlier. This way, large performance speedups are achieved. 2. Unification. To combine the memory renamer with the register renamer in order to extend the above-stated sharing and result reuse and dependency redirection ideas to both registers and memory locations. This allows even greater hardware savings and performance improvements. This also simplifies the processing of store instructions.