Adaptive Pipeline Structures for Speculation Control

Pipelining is a common method for improving the throughput of a system, especially when the majority of the processing is sequential. Unfortunately when the se-quentiality is broken, a pipelined system suffers additional delay and, most importantly for this work, energy waste which is roughly proportional to the pipeline depth. Stan-dard pipelines cannot be modified once they are built so their depth is fixed. This paper proposes a method that al-lows the dynamic adaptation of the structure of an asyn-chronous pipeline, so that pipeline stages can be merged and split at run-time, allowing greater flexibility. It is based on novel latch controllers that can be configured dynami-cally as ‘normal ’ or ‘collapsed’, i.e. keeping their latches permanently transparent. Using these controllers a model of AMULET3 was designed that is capable of changing its pipeline depth dynamically when branches are anticipated, in order to alleviate the energy loss when the branch finally arrives. 1