These options are defined specifically for the AMD GCN port.
-march=gpu
-mtune=gpu
Set architecture type or tuning for gpu. Supported values for gpu are
Compile for GCN3 Fiji devices (gfx803).
Compile for GCN5 Vega 10 devices (gfx900).
-mstack-size=bytes
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.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/AMD-GCN-Options.html