HeDGE: Hybrid Dataflow Graph Execution in the Issue Logic

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Executive Summary

Exposing more instruction-level parallelism in out-of-order super-scalar processors requires increasing the number of dynamic in-flight instructions. However, large instruction windows increase power consumption and latency in the issue logic. The authors propose a design called Hybrid Dataflow Graph Execution (HeDGE) for conventional Instruction Set Architectures (ISAs). HeDGE explicitly maintains dependences between instructions in the issue window by modifying the issue, register renaming, and wakeup logic. The HeDGE wakeup logic notifies only consumer instructions when data values arrive. Explicit consumer encoding naturally leads to the use of Random Access Memory (RAM) instead of Content Addressable Memory (CAM) needed for broadcast.

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