Impact on performance of fused multiply-add units in aggressive VLIW architectures

Loops are the main time consuming part of programs based on floating point computations. The performance of the loops is limited either by recurrences in the computation or by the resources offered by the architecture. Several general-purpose superscalar microprocessors have been implemented with multiply-add fused floating-point units, that reduces the latency of the combined operation and the number of resources used. This paper analyses the influence of these two factors in the instruction-level parallelism exploitable from loops executed on a broad set of future aggressive processor configurations. The estimation of implementation costs (area and cycle time) enables a fair comparison of these configurations in terms of final performance and implementation feasibility. The paper performs technological projection for the next years in order to foresee the possible implementable alternatives. From this study we conclude that multiply-add fused units may have a deep impact in raising the performance of future processor architectures with a reasonable increase in cost