SYCL/DPC++: FFT Library

[ax3l]

Just a reminder for ourselves to add a SYCL/DPC++ FFT library for PSATD support.

https://github.com/ECP-WarpX/WarpX/blob/development/Source/FieldSolver/SpectralSolver/AnyFFT.H

Potential candidates:

• oneMKL: https://docs.oneapi.com/versions/latest/onemkl/fourier-transform-functions.html (part of oneAPI Math Kernel Library)
  • limitation: at the moment limited to 1D FFT on device
  • update: this seems to be only an issue of outdated documentation and there are indeed 3D FFTs

[ax3l]

cc @WeiqunZhang do you potentially have the free energy to implement SYCL FFTs in our wrapper?