Large register files offered by current processors allow reductions in memory traffic, since most of the data needed by a procedure are held in the processor registers. Function calls are responsible for a significant part of the overall memory traffic through register saving and restoring (RSR). This paper proposes a new policy, called policy G, for RSR across function calls. Policy G only applies to single-window file registers.

The main basic policies for RSR are clearly presented in the paper. Classic policies are static since they do not take into account the actual use of registers during execution. To reduce the RSR traffic, most compilers support intraprocedural and interprocedural optimizations for the register allocation. The main contribution of this paper is to show how hardware may be used to reduce the RSR traffic. The extra hardware is used to monitor the register usage, and a register is only saved or restored when needed: the policy is dynamic. Moreover, the authors show that the combination of a dynamic policy and compiler optimization gives better results than either method can provide by itself.

The detailed presentation of policy G is followed by a practical implementation example. This case study, based on the RISC II processor, shows that the required support hardware is simple and that most of the operations related to RSR may be performed concurrently with normal processor tasks. The authors also address the implications for the processor cycle time. The last part of the paper is dedicated to the evaluation of the obtained RSR traffic. In this section, policy G is compared to numerous policies and shows good results.

This long paper is both clear and complete. Reading it is advisable for people involved in computer architecture and processor design.