A processor buffers asynchronous threads. Instructions requiring operations provided by a plurality of execution units are divided into phases, each phase having at least one computation operation and at least one memory access operation. Instructions within each phase are qualified and prioritized. The instructions may be qualified based on the status of the execution unit needed to execute one or more of the current instructions. The instructions may also be qualified based on an age of each instruction, status of the execution units, a divergence potential, locality, thread diversity, and resource requirements. Qualified instructions may be prioritized based on execution units needed to execute instructions and the execution units in use. One or more of the prioritized instructions is issued per cycle to the plurality of execution units.