[llvm] [Offload][AMDGPU] Add env var to control device-to-device memory access (PR #215385)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> I can add code to detect single GPU device case, but that doesn't help single GPU device code running on a multi-GPU system. I don't think we can check the need-for-d2d at every memory access. Are you suggesting to try adding a handler for GPU memory access fault?

Could you explain a bit further what this is concretely trying to solve? D2D memory access, I would assume, is something managed by the runtime.

https://github.com/llvm/llvm-project/pull/215385