LLVM May Get A TGSI Gallium3D Compiler Back-End
A proposal has been made to develop a new LLVM compiler back-end that would generate TGSI instructions, the intermediate representation used by Mesa's Gallium3D drivers.
Francisco Jerez, the open-source developer that has long been involved with Nouveau and did an X.Org EVoC project to work on Gallium3D OpenCL, is the developer proposing this LLVM TGSI back-end. During his "Endless Vacation of Code" project for the X.Org Foundation, the student made the Gallium3D OpenCL state tracker nearly work. Well, it does work for OpenCL on Nouveau to some extent.
This developer with experience is proposing to do this new back-end as a Google Summer of Code project for LLVM. Jerez was quick to acknowledge that it will likely take more than a couple summer months to make a fully working TGSI back-end, but he's committed to seeing it through even after GSoC has been completed.
With a back-end to LLVM generating TGSI, it could in effect be understood by any of the Gallium3D drivers as they all accept TGSI for their IR as is done for graphics. Jerez's focus would be though on testing against the Nouveau drivers and seeing what sort of OpenCL could be handled this way.
Francisco writes in his mailing list proposal, "TGSI is the intermediate representation that all open-source GPU drivers using the Gallium3D architecture understand. Until now it's mainly beenused for graphics (vertex and fragment shaders and such), but doing general-purpose computing with it is possible in principle (actually, necessary for GL4), and it's been the object of a number of extensions and improvements during the last couple of years to make it more suitable for that purpose. The objective of the project would be to set a basis for a compiler back-end targeting the TGSI language."
Francisco adds, "The first to be benefited from such a back-end would be the Nouveau nv50 and nve4 drivers, that would get OpenCL support easily without much additional work, other Gallium drivers will also benefit from it as they implement the missing language and API bits."
This isn't the first time a TGSI back-end for LLVM has been discussed, and it wouldn't be without some limitations, but hopefully it will be able to materialize this year as part of Google Summer of Code. If all else fails, hopefully the X.Org Foundation will sponsor the development through another EVoC.
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