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The Liberty Research Group

The Compiler Foundations Project

The Partial Reverse If-Conversion Framework for Balancing Control Flow and Predication [abstract]
David I. August, Wen-mei W. Hwu, and Scott A. Mahlke
International Journal of Parallel Programming (IJPP), Volume 27, Number 5, October 1999. Invited.
Special issue composed of "outstanding papers" selected by the Program Committee of the 30th Annual ACM/IEEE International Symposium on Microarchitecture.

Predicated execution is a promising architectural feature for exploiting instruction-level parallelism in the presence of control flow. Compiling for predicated execution involves converting program control flow into conditional, or predicated, instructions. This process is known as if-conversion. In order to apply if-conversion effectively, one must address two major issues: what should be if-converted and when the if-conversion should be performed. A compiler's use of predication as a representation is most effective when large amounts of code are if-converted and when if-conversion is performed early in the compilation procedure. On the other hand, efficient execution of code generated for a processor with predicated execution requires a delicate balance between control flow and predication. The appropriate balance is tightly coupled with scheduling decisions and detailed processor characteristics. This paper presents a compilation framework based on partial reverse if-conversion that allows the compiler to maximize the benefits of predication as a compiler representation while delaying the final balancing of control flow and predication to schedule time.