On Wed, 2015-03-04 at 16:20 +0000, BogDan wrote: > On Wednesday, March 4, 2015 5:22 PM, David Malcolm <dmalc...@redhat.com> > wrote: > On Wed, 2015-03-04 at 14:36 +0000, BogDan wrote: > > Hello folks, > > > > > > Probably is a little bit too early, but I'd like to ask if there is > > any chance to use gcc to produce SPIR-V [1]. > > It will be just great if we'll be able to write our shaders in e.g. > > C/C++/(any language supported by gcc) and use GCC to compile them as > > SPIR-V! > > It will be fantastic to use only one compiler collection for CPU and > > for GPU compute&graphics! > > > > Cheers, > > > > BogDan. > > [1] https://www.khronos.org/registry/spir-v/ > > I work on gcc, but in a former life I was a game developer [1], so this > piqued my interest :) > > > > WOW you've work on AVP! [for only about a month or so iirc, mostly just salvaging some of my UI code from a never-published space trading/combat game, fwiw :)]
> A few questions: > > (A) Does SPIR-V have an assembler? The URL you posted talks about it > being a binary format, but the example in there shows a "disassembled" > textual form. The reason I ask is that the internals of gcc's backend > expect to be writing out "assembler", which then goes through an > assembler program to produce a binary. In theory I guess one could have > the "assembler" format generated by the backend be binary, but it's > likely to be *much* easier to hack on if there's an intermediate textual > form. > SPIR-V it's an Intermediate Language binary format. First versions were > based on LLVM. SPIR-V has nothing to do with the old SPIR implementations, > but for some reason khronos decide to keep the name :) > This http://www.g-truc.net/post-0714.html great article explans better > what SPIR-V is. (nods); thanks. > (B) Are you thinking about this for primarly ahead-of-time > compilation, or are you interested in just-in-time compilation to > SPIR-V? I ask since I maintain the new "libgccjit" feature in GCC 5. > One of the current assumptions in libgccjit is that host==target, but I > hope to relax that for gcc 6 so that libgccjit could e.g. generate code > for a GPU. Another gcc 6 possibility could be multi-target support for > libgccjit, so that you can populate a gcc_jit_context with code, then > have it generate machine code for both the CPU and for the GPU (mostly > just thinking aloud here). > Even though most of the people will use it for ahead-of-time compilation, > but IMHO it can be both! Another use-case that occurred to me when I was looking at the link you posted above: using gcc for optimizing SPIR-V and compiling it e.g. to CPU code. As of gcc 5, libgccjit can be hooked up to a pre-existing language frontend, with the gcc backend emitting machine code for the CPU, assuming that the frontend is license-compatible with libgccjit's GPLv3-or-later. See this example, which uses libgccjit to build a compiler for brainf**k: https://gcc.gnu.org/onlinedocs/jit/intro/tutorial05.html So if there's a SPIR-V loader library that's license-compatible, you could write code to inject SPIR-V into libgccjit, and call gcc_jit_context_compile_to_file on it to optimize it and turn it into machine code. That use-case is probably doable today using gcc 5 (and could be written in C, C++, Python, or D, with the bindings we already have). Potentially such a library could also generate other kinds of code, including e.g. optimized SPIR-V... but that requires both (i) a gcc backend for the desired target code and (ii) libgccjit to support cross-compilation (which as I mentioned would probably be a gcc 6 thing). > (C) (probably most important) Is a SPIR-V backend something you'd be > up for working on? Any other volunteers out there? > (Maybe a GSoC thing?) > Personally, I never touched gcc source code before, and I don't have > any idea about (any) compilers internals (thought I have experience > working for free software projects [0]). Anyway I think it will be a > great experience to (at least try to :) ) help in my spare time. > A GSOC project is a great idea as well! I'm probably not the best person to help, as I've not written a gcc backend (the jit counts as a frontend, albeit a very unusual one). FWIW there seems to be a good tutorial on writing backends here: http://www.cse.iitb.ac.in/grc/intdocs/gcc-writing-md.html > Thanks, > BogDan > > > P.S. Sorry for the inline reply, I had to use yahoo mail and ... > > [0] > http://blog.qt.io/blog/2012/11/08/necessitas-android-port-contributed-to-the-qt-project Neat. Dave
