A forwarding-sensitive instruction scheduling approach to reduce register file constraints in VLIW architectures

This paper presents a forwarding-based approach to increase the code compaction and consequently the processing performance of VLIW media-processors that implement monolithic or partitioned register file (RF) organizations with reduced number of read/write ports. This approach exploits the forwarding mechanism implemented in common pipelined VLIW architectures to reduce the number of RF accesses, which is one of the main limiting factors of the code compaction process. This RF access reduction enables a higher instruction scheduling efficiency and eventually decreases the power consumption, without requiring extra hardware. A forwarding-sensitive code generation algorithm based on an enhanced list scheduling algorithm is described in detail. In addition, three case studies are presented, where the proposed scheduling algorithm leads to performance improvements of up to 8.4% when running common image and video codec tasks on a generic VLIW architecture. This is attractively close to the maximum performance improvement (11.4%) that can be achieved when investing in hardware by using a RF with twice the number of ports.