Survey on Combinatorial Register Allocation and Instruction Scheduling

Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to increase instruction-level parallelism) are essential tasks for generating efficient assembly code in a compiler. In the last three decades, combinatorial optimization has emerged as an alternative to traditional, heuristic algorithms for these two tasks. Combinatorial optimization approaches can deliver optimal solutions according to a model, can precisely capture trade-offs between conflicting decisions, and are more flexible at the expense of increased compilation time. This paper provides an exhaustive literature review and a classification of combinatorial optimization approaches to register allocation and instruction scheduling, with a focus on the techniques that are most applied in this context: integer programming, constraint programming, partitioned Boolean quadratic programming, and enumeration. Researchers in compilers and combinatorial optimization can benefit from identifying developments, trends, and challenges in the area; compiler practitioners may discern opportunities and grasp the potential benefit of applying combinatorial optimization

Welfare policy: The administrative frontier

The process of national welfare reform has been overtaken by local reform as states implement experimental programs under federal waivers. Most of these initiatives attempt to enforce work or otherwise control the lives of the dependent in return for support. Research, which traditionally stressed the social and economic aspects of welfare or poverty, must be reoriented to address the administrative issues raised by the emerging paternalism. A combination of field interviewing and analyses of reporting data can track implementation and connect program operations to outcomes. Such research assesses program performance less surely than experimental trials do but is more useful to operators and more relevant to current program goals. The frontiers of welfare research, like welfare policy, are institutional.