Testing new OCCA language transpiler with libCEED

[ypanke]

Hello

I am testing libCEED with a new OKL transpiler (https://github.com/libocca/occa-transpiler) and found a couple of possible bugs that were tolerated by the original OCCA transpilation:

• backends/occa/kernels/simplex-basis/cpu-simplex-basis.cpp line 34

inline void SIMPLEX_FUNCTION(gradElement)(const CeedScalar *Bx @dim(P, Q, DIM), const CeedScalar *Ue, CeedScalar *Ve, )

Redundant comma at the end of list of the arguments

• Function names in OCCA kernels
  Original OCCA was performing the macro expansion differently than the standard states, please refer to the issue: OKL incorrect macro expansion  libocca/occa#750
  That makes the code like TENSOR_FUNCTION(interpElement) or SIMPLEX_FUNCTION(interpElement) behave differently than expected, generating something like: simplex_DIMd_interpElementTranspose_QQ_PP

[jeremylt]

Unfortunately, the OCCA backend is highly experimental. I do recommend you use device native backends, such as the HIP and CUDA backends.

I do not know how long these issues would take to fix, as we do not have any OCCA users on the core libCEED development team.

[jedbrown]

@ypanke If you want to try fixing these issues, we'll be happy to review PRs. To my knowledge, nobody is using the OCCA backend, and despite being more lines of code in the implementation than the CUDA or HIP backends, it's substantially slower.