A processor configured to selectively free physical registers during instruction retirement

摘要

A processor employing a map unit including register renaming hardware is shown. The map unit may assign virtual register numbers to source registers by scanning instruction operations to detect intraline dependencies. Subsequently, physical register numbers are mapped to the source register numbers responsive to the virtual register numbers. The map unit may stores (e.g. in a map silo) a current lookahead state corresponding to each line of instruction operations which are processed by the map unit. Additionally, the map unit stores an indication of which instruction operations within the line update logical registers, which logical registers are updated, and the physical register numbers assigned to the instruction operations. Upon detection of an exception condition for an instruction operation with a line, the current lookahead state corresponding to the line is restored from the map silo. Additionally, physical register numbers corresponding to instruction operations within the line which are prior to the instruction operation experiencing the exception are restored into the current lookahead state. The map unit may use the same physical register to store both a condition code result and an integer result. The physical register number identifying the physical register is recorded for both the condition code register and the integer register. The map unit pops the previous renames from the architected renames block upon retiring one or more instruction operations. The popped physical register numbers are cammed against the updated architectural state. If a cam match is detected, the popped physical register is not freed.