A minor correction: as far as I know, none of the modern GPUs or CPUs by Intel, AMD, or Nvidia are barrel processors. The Xeon Phis were the only exception, but I don't know whether they kept that part of the design after KNC.

edit: This document [1] on pages 26-28 describes both execution on pascal and volta GPUs and how they differ. AMD/Intel GPUs are something similar.

[1] http://images.nvidia.com/content/volta-architecture/pdf/volt...