Exploring Design Space of VLIW Architectures

Abstract

Architectures based on very long instruction word (VLIW) have found fertile ground in multimedia electronic appliances thanks to their ability to exploit high degrees of instruction level parallelism (ILP) with a reasonable tradeoff in complexity and silicon costs. Effective compiler support for predicated execution using the hyperblock, drastically increases the ILP even for control-dominated applications in which the branch instruction frequency is very high. The use of these techniques, however, is known to increase the instruction footprint, consequently putting pressure on the memory hierarchy. In this paper, we evaluate the performance/power trade-off in a system comprising a VLIW processor and a two-level hierarchical memory subsystem. Via simulation, we show that the efficiency of a compiler that is able to exploit predicate execution by hyperblock formation is greatly affected by the configuration of the memory subsystem as well as the configurable processor parameters. The enabling or disabling of hyperblock formation should therefore not be evaluated separately or independently, but seen as a further free parameter to be tuned in a strategy of design space exploration.