Three Superblock Scheduling Models for Superscalar and Superpipelined Processors (PostScript version, PDF version)
Pohua P. Chang, Nancy J. Warter, Scott Mahlke, William Y. Chen, and Wen-mei W. Hwu
Technical Report CRHC-91-29, Center for Reliable and High-Performance Computing, University of Illinois, Urbana, IL, Dec. 1991

To efficiently schedule superscalar and superpipelined processors, it is necessary to move instructions across branches. This requires increasing the scheduling scope beyond the basic block. Superblock scheduling, a static scheduling method, is a variant of trace scheduling that removes the bookkeeping complexity associated with branches into a trace by removing these entrances using a method called tail duplication. Once the scheduling scope is enlarged, there are hazards to moving an instruction above a conditional branch because the instruction is normally only executed on one path of the conditional branch. To allow the compiler to schedule code more aggressively, hardware support can be provided to prevent such hazards. In this paper we analyze the architecture support and performance of three superblock scheduling models.

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