Reduction operations in a synchronous parallel thread processing system with disabled execution threads

A system and method for successfully performing reduction operations in a multi-threaded SIMD (single-instruction multiple-data) system while one or more threads are disabled allows for the reduction operations to be performed without a performance penalty compared with performing the same operation with all of the threads enabled. The source data for each intermediate computation of the reduction operation is remapped by a configurable crossbar as needed to avoid using invalid data from the disabled threads. The remapping function is transparent to the user and enables correct execution of order invariant reduction operations and order dependent prefix-reduction operations.