Allow explicit data transfers to GPUs

[ZuseZ4]

View all comments

So far we had our offload intrinsics handle data movement automatically to/from the gpu.
That's convenient (and reasonably fast once our LLVM opts land). However, Rust generally also allows being explicit. That might give perf benefits (where our LLVM opts fail), and it could also be nice for modelling, when passing data around but still preventing CPU users from accesing it.

• Tracking:
  Tracking Issue for GPU-offload #131513

[ZuseZ4]

Vendoring llvm/llvm-project#198033 for now.