Preserving Program Dependencies in a Distributed Microarchitecture

We discuss how time tags can be used for the enforcement of program dependencies. Time tags can serve as the basic ordering enforcement mechanism when large numbers of instructions are executing concurrently. Proposed and future microarchitectures can have hundreds or several hundreds of instructions in flight simultaneously and using standard reservation tags, physical register addresses, and reorder buffers do not scale well for very large instruction windows. The design, use and management of time tags will be discussed. We also provide simulation data for an example microarchitecture that takes advantage of time tags for its dependency ordering.