[LLVMdev] [RFC] Upstreaming LLVM/SPIR-V converter

[David Chisnall]

On 13 May 2015, at 13:56, Liu, Yaxun (Sam) <Yaxun.Liu at amd.com> wrote:
> 
> Khronos Group SPIR WG is working on a bi-way converter between LLVM bitcode and SPIR-V (https://www.khronos.org/registry/spir-v/specs/1.0/SPIRV.pdf ) binary and is willing to upstream it to the LLVM project.
> 
> The bi-way converter uses a common in-memory representation of SPIR-V. It works by breaking down a module to instructions and construct the translated module in memory then output it. Currently it supports SPIR-V common instructions and OpenCL specific instructions. Supporting of other languages is under consideration.
> 
> We plan to refactor the LLVM to SPIR-V converter as a backend at llvm/lib/Target/SPIRV to allow Clang targeting SPIR-V. Since this will result in an unconventional backend which does not use SelectionDAG/MC, we would like to know whether it is acceptable. We are open to the SelectionDAG/MC approach if the community recommends it.

I believe that the ‘how to write a backend’ documentation recommends against using SelectionDAG for generating code for other virtual instruction sets.  I don’t think that there’s any benefit to forcing a back end to use the generic infrastructure, unless it makes sense for that back end to do so.

> For the SPIR-V to LLVM converter, we are seeking suggestions on its proper location in the LLVM project.

To me, this is no different from any other front end, so should probably live in a separate repository (though ideally an LLVM-hosted one that is integrated with buildbots and kept up to date).

David