A survey of resource allocation methods in optimizing microcode compilers

This paper surveys results reported on resource allocation in optimizing microcode compilers. Resource allocation is the phase of microcode generation that binds variables and operators of program text to machine registers and functional units. The first substantial results on resource allocation in optimizing microcode compilers were reported by DeWitt, and subsequent results were reported by Kim and Tan and by Ma and Lewis. We examine each of these methods, focusing on the assumptions they make, how realistic those assumptions are, the algorithms employed and their foundational basis, the perceived difficulty of implementing the algorithms, their effectiveness, and their computational complexity. We conclude by summarizing the results and pointing out important areas for future research, particularly in the context of flow graph microcode generation.