A global mode instruction minimization technique for embedded DSPs

Abstract

This paper addresses the problem of minimizing mode setting instructions for embedded DSPs. Many such processors use a state register to control the mode of ALU operations (e.g., sign extension, round, and shift). Often two or more modes can be changed by a single instruction. A method is given to determine the minimum number of instructions needed to properly set modes, assuming a schedule has been determined. Our approach models the problem as a minimum cover, and is not limited to a basic block. Block frequency information is exploited to encourage mode changes in less frequently executed blocks whenever possible. Special attention is given to the proper optimization of loops.