REP MOVE string instruction execution by selecting loop microinstruction sequence or unrolled sequence based on flag state indicative of low count repeat

摘要

A microprocessor REP MOVS macroinstruction specifies the word length of the string in the IA-32 ECX register. The microprocessor includes a memory, configured to store a first and second sequence of microinstructions. The first sequence conditionally transfers control to a microinstruction within the first sequence based on the ECX register. The second sequence does not conditionally transfer control based on the ECX register. The microprocessor includes an instruction translator, coupled to the memory. In response to a macroinstruction that moves an immediate value into the ECX register, the instruction translator sets a flag and saves the immediate value. In response to a macroinstruction that modifies the ECX register in a different manner, the translator clears the flag. In response to a REP MOVS macroinstruction, the instruction translator transfers control to the first sequence if the flag is clear; and transfers control to the second sequence if the flag is set.