Energy-efficient issue queue design

The out-of-order issue queue (IQ), used in modern superscalar processors is a considerable source of energy dissipation. We consider design alternatives that result in significant reductions in the power dissipation of the IQ (by as much as 75%) through the use of comparators that dissipate energy mainly on a tag match, 0-B encoding of operands to imply the presence of bytes with all zeros and, bitline segmentation. Our results are validated by the execution of SPEC 95 benchmarks on a true hardware level, cycle-by-cycle simulator for a superscalar processor and SPICE measurements for actual layouts of the IQ in a 0.18m CMOS process.