WCET-Aware Re-Scheduling Register Allocation for Real-Time Embedded Systems With Clustered VLIW Architecture

Worst-case execution time (WCET) is one of the most important metric in real-time embedded system design. For embedded systems with clustered very long instruction word (VLIW) architecture, register allocation, instruction scheduling, and cluster assignment are three key activities for code optimization, which have profound impact on WCET. At the same time, these three activities exhibit a phase ordering problem, i.e., independently performing register allocation, scheduling, and cluster assignment could have a negative effect on the other phases, thereby generating sub-optimal compiled code. In this paper, a compiler level optimization, namely WCET-aware re-scheduling register allocation, is proposed to achieve WCET minimization for real-time embedded systems with clustered VLIW architecture. The novelty of the proposed approach is that the effects of register allocation, instruction scheduling, and cluster assignment on the quality of generated code are taken into account for WCET minimization. These three compilation processes are integrated into a single phase to obtain a balanced result. The proposed technique is implemented in Trimaran 4.0. The experimental results show that the proposed technique can reduce WCET effectively, by 34% on average.