A Framework for Resource-Constrained Rate-Optimal Software Pipelining
The rapid advances in high-performance computer architecture and compilation techniques provide both challenges and opportunities to exploit the rich solution space of software pipelined loop schedules. In this paper, we develop a framework to construct a software pipelined loop schedule which runs on the given architecture (with a fixed number of processor resources) at the maximum possible iteration rate (a la rate-optimal) while minimizing the number of buffers-a close approximation to minimizing the number of registers. The main contributions of this paper are: First, we demonstrate that such problem can be described by a simple mathematical formulation with precise optimization objectives under a periodic linear scheduling framework. The mathematical formulation provides a clear picture which permits one to visualize the overall solution space (for rate-optimal schedules) under different sets of constraints. Secondly, we show that a precise mathematical formulation and its solution does make a significant performance difference. We evaluated the performance of our method against three leading contemporary heuristic methods. Experimental results show that the method described in this paper performed significantly better than these methods. The techniques proposed in this paper are useful in two different ways: 1) As a compiler option which can be used in generating faster schedules for performance-critical loops (if the interested users are willing to trade the cost of longer compile time with faster runtime). 2) As a framework for compiler writers to evaluate and improve other heuristics-based approaches by providing quantitative information as to where and how much their heuristic methods could be further improved.

title: Co-scheduling hardware and software pipelines
abstract: In this paper we propose co-scheduling, a framework for simultaneous design of hardware pipelines structures and software-pipelined schedules. Two important components of the co-scheduling framework are: (1) An extension to the analysis of hardware pipeline design that meets the needs of periodic (or software pipelined) schedules. Reservation tables, forbidden latencies, collision vectors, and state diagrams from classical pipeline theory are revisited and extended to solve the new problems. (2) An efficient method, based on the above extension of pipeline analysis, to perform (a) software pipeline scheduling and (b) hardware pipeline reconfiguration which are mutually "compatible". The proposed method has been implemented and preliminary experimental results for 1008 kernel loops are reported. Co-scheduling successfully obtains a schedule for 95% of these loops. The median time to obtain these schedules is 0.25 seconds on a Sparc-20.

title: Exploiting short-lived variables in superscalar processors
abstract: In this paper we present experimental evidence showing that a significant number of program variables are short-lived in the sense that their live ranges span only a few instructions. In dynamically scheduled superscalar processors using mechanisms like the reorder buffer, the live ranges for these short-lived variables may occur entirely within the reorder buffer. Therefore, there should be no need to retire (commit) the values produced by these live ranges to the register file. On the basis of this observation, we have proposed a scheme that includes a compiler analysis and a simple architecture extension to avoid the useless commits of the values generated for these short-lived variables. Moreover we have proposed an extension to the existing register allocation mechanism that does not assign these short-lived variables to locations in the register file. Analyses and results are presented.