Identification of regular patterns within sparse data structures
Date
2020
Authors
Augustine, Travis, author
Pouchet, Louis-Noël, advisor
Rajopadhye, Sanjay, committee member
Bohm, Anton, committee member
Wilson, James, committee member
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Abstract
Sparse matrix-vector multiplication (SpMV) is an essential computation in linear algebra. There is a well-known trade-off between operating on a dense or a sparse structure when performing SpMV. In the dense version of SpMV, useless operations are performed but the computation is amenable SIMD vectorization. In the sparse version, only useful operations are executed. However, an indirection array must be used, thus hindering the compiler's ability to perform optimizations that exploit the vector units available on the majority of modern processors. Our process automatically builds sets of regular sub-computations from the irregular sparse data structure. We mine for regular regions in the irregular data structure, grouping together non-contiguous points from the reorderable set of coordinates representing the sparse structure. The coordinates become partitioned into groupings of coordinates of pre-defined shapes using polyhedra. This partition models the exact same points from the input set of coordinates in a way that is specialized to the input's sparsity pattern. Once we have obtained a partition of the points into sets of polyhedra, we then scan these polyhedra to synthesize code that does not store any coordinates of zero-valued elements and does not require any indirection array to access data, thus making it amenable to SIMD vectorization.
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Subject
SpMV