Physical rename register for efficiently storing floating point, integer, condition code, and multimedia values

Abstract

A register renaming apparatus includes one or more physical registers which may be assigned to store a floating point value, a multimedia value, an integer value and corresponding condition codes, or condition codes only. The classification of the instruction (e.g. floating point, multimedia, integer, flags-only) defines which lookahead register state is updated (e.g. floating point, integer, flags, etc.), but the physical register can be selected from the one or more physical registers for any of the instruction types. Determining if enough physical registers are free for assignment to the instructions being selected for dispatch includes considering the number of instructions selected for dispatch and the number of free physical registers, but excludes the data type of the instruction. When a code sequence includes predominately instructions of a particular data type, many of the physical registers may be assigned to that data type (efficiently using the physical register resource). By contrast, if different sets of physical registers are provided for different data types, only the physical registers used for the particular data type may be used for the aforementioned code sequence. Additional efficiencies may be realized in embodiments in which an integer register and condition codes are both updated by many instructions. One physical register may concurrently represent the architected state of both the flags register and the integer register. Accordingly, a given functional unit may forward a single physical register number for both results.