Loop Parallelization using the 3D Iteration Space Visualizer

Abstract

A 3D iteration space visualizer (ISV) is presented to analyze the parallelism in loops and to find loop transformations which enhance the parallelism. Using automatic program instrumentation, the iteration space dependency graph (ISDG) is constructed, which shows the exact data dependencies of arbitrarily nested loops. Various graphical operations such as rotation, zooming, clipping, coloring and filtering, permit a detailed examination of the dependence relations. Furthermore, an animated dataflow execution shows the maximal parallelism and the parallel loops are indicated automatically by an embedded data dependence analysis. In addition, the user may discover and indicate additional parallelism for which a suitable unimodular loop transformation is calculated and verified. The ISV has been applied to parallelize algorithmic kernel programs, a computational fluid dynamics (CFD) simulation code, the detection of statement-level parallelism and loop variable privatization. The applications show that the visualizer is a versatile and easy to use tool for the high-performance application programmer.