Microsoft Corporation
Vectorizing conditional min-max sequence reduction loops

Abstract:

Algorithms, examples, and related technology for automatic vectorization of a particular class of loops is described. The loops, denoted "CMMSR loops", operate to find an extremum and also utilize an index denoting the position of the extremum in an array or other multi-element input. CMMSR loops are identified in a language translator by matching a specified template or having a specified set of parsing results, or both. Generated vectorization code includes, for example, code to compute candidates for the extremum, code to select the same instance of the extremum as a scalar execution when the input contains multiple instances, and wind-down code to compute an index expression based on the selected instance of the extremum. Vectorizations may execute on SIMD hardware or other vector processors.