These options are defined specifically for the AMD GCN port.
Set architecture type or tuning for gpu. Supported values for gpu are
Specify how many bytes of stack space will be requested for each GPU thread (wave-front). Beware that there may be many threads and limited memory available. The size of the stack allocation may also have an impact on run-time performance. The default is 32KB when using OpenACC or OpenMP, and 1MB otherwise.