wip: getting started on gromacs

[vsoch]

We can likely move forward testing lammps, but I thought I'd give a quick shot at gromacs. There are many more libraries here (and the main executable is gmx) and the executable seemed to work ok, but I got an error for libgromacs:

We can debug this if/when needed.

[al42and]

Hi! Hope you don't mind me barging in.

If I understand correctly, this project aims to offer a nice way to JIT the code for the target hardware, right? If so, GROMACS is perhaps not the best subject if a performance benefit is expected. GROMACS uses explicit SIMD for all the hot code (not in md5.c, though; not sure what's wrong with it) configured by setting -DGMX_SIMD=... in CMake. It is only possible to choose one SIMD backend at a time, and I doubt LLVM is smart enough to convert, say, SSE4 intrinsics into optimal AVX512 intrinsics or vice-versa. The rest of the code might benefit from JIT, but I would not expect an impact on the overall MD performance remotely comparable with compiling with the optimal GMX_SIMD set. Analysis tools might get faster, though!