Code Generation for Single-Dimension Software Pipelining of Multi-Dimensional Loops

• Authors: Hongbo Rong;Alban Douillet;R. Govindarajan;Guang R. Gao
• Venue: Proceedings of the international symposium on Code generation and optimization: feedback-directed and runtime optimization
• Year: 2004

Traditionally, software pipelining is applied either to theinnermost loop of a given loop nest or from the innermostloop to the outer loops. In a companion paper, we proposeda scheduling method, called Single-dimension SoftwarePipelining (SSP), to software pipeline a multi-dimensionalloop nest at an arbitrary loop level.In this paper, we describe our solution to SSP code generation.In contrast to traditional software pipelining, SSPhandles two distinct repetitive patterns, and thus requiresnew code generation algorithms. Further, these two distinctrepetitive patterns complicate register assignment and requiretwo levels of register renaming. As rotating registerssupport renaming at only one level, our solution is based ona combination of dynamic register renaming (using rotatingregisters) and static register renaming (using code replication).Finally, code size increase, an even more important issuefor SSP than for traditional software-pipelining, is alsoaddressed. Optimizations are proposed to reduce code sizewithout significant performance degradation.We first present a code generation scheme and subsequentlyimplement it for the IA-64 architecture, making effectiveuse of rotating registers and predicated execution.We present some initial experimental results, which demonstratenot only the feasibility and correctness of our codegeneration scheme, but also its code quality.