Exploiting idle floating-point resources for integer execution

Abstract

In conventional superscalar microarchitectures with partitioned integer and floating-point resources, all floating-point resources are idle during execution of integer programs. Palacharla and Smith [26] addressed this drawback and proposed that the floating-point subsystem be augmented to support integer operations. The hardware changes required are expected to be fairly minimal.To exploit these idle floating resources, the compiler must identify integer code that can be profitably offloaded to the augmented floating-point subsystem. In this paper, we present two compiler algorithms to do this. The basic scheme offloads integer computation to the floating-point subsystem using existing program loads/stores for inter-partition communication. For the SPECINT95 benchmarks, we show that this scheme offloads from 5% to 29% of the total dynamic instructions to the floating-point subsystem. The advanced scheme inserts copy instructions and duplicates some instructions to further offload computation. We evaluate the effectiveness of the two schemes using timing simulation. We show that the advanced scheme can offload from 9% to 41% of the total dynamic instructions to the floating-point subsystem. In doing so, speedups from 3% to 23% are achieved over a conventional microarchitecture.