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

[Reid Kleckner]

On Wed, May 13, 2015 at 6:11 AM, David Chisnall <David.Chisnall at cl.cam.ac.uk
> wrote:

> 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).
>

Honestly, SPIR-V seems a little bit more like a quirky program
serialization format. It's not a source language or an ISA. It might be
better to treat it like the bitcode reader/writer and have both in one
place. Something like lib/Target/SPIRV/(Writer|Reader)?
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