Energy-Efficient Branch Predictor via Instruction Block Type Prediction in Decoupled Frontend

The branch predictor is widely used to enhance processor performance, but it also constitutes one of the major energy-consuming components in processors. We found that approximately 32% of instruction blocks in a decoupled frontend do not contain branch instructions, while 30.8% of instruction blocks contain only conditional branches. However, because the type of instructions within a block cannot be determined during prediction, branch prediction must be executed every cycle. In this work, we propose the next block type (NBT) and no branch sequence table (NST) for predicting instruction block types. These mechanisms occupy minimal space and are straightforward to implement. For a four-way out-of-order processor, the NBT and NST reduce the branch predictor’s energy consumption by 52.36% and processor’s energy consumption by 4.1% without sacrificing the processor’s instructions per cycle (IPC) and branch prediction accuracy.