Prebypass: Software Register File Bypassing for Reduced Interconnection Architectures

Exposed Datapath Architectures (EDPAs) with aggressively pruned data-path connectivity, where not all function units in the design have connections to a centralized register file, are promising solutions for energy-efficient computation. A direct bypassing of data between function units without temporary copies to the register file is a prime optimization for programming such architectures. However, traditional compiler frameworks, such as LLVM, assume function-units connect to register-files and allocate all live variables in register-files. This leads to schedule inefficiencies in terms of instruction-level parallelism and register accesses in the EDPAs. To address these inefficiencies, we propose Prebypass; a new optimization pass for EDPA compiler backends. Experimental results on an EDPA class of architecture, Transport-Triggered Architecture, show that Prebypass improves the runtime, register reads, and register writes up to 16%, 26%, and 37% respectively, when the datapath is extremely pruned. Evaluation in a 28-nm FDSOI technology reveals that
Prebypass improves the core-level Energy by 17.5% over the current heuristic scheduler.