A New OpenCL Back-End For LLVM Is Published

Besides the open-source AMD Radeon support for OpenCL finally taking shape, there's more good open-source OpenCL news: a newly open-sourced LLVM OpenCL back-end.

Back in August I wrote about an OpenCL, GLSL back-end for LLVM that may soon open up. The work was the result of a German student writing the LLVM OpenCL back-end as part of his university thesis. OpenCL is generated from LLVM bit-code, similar to how the Emscripten project is generating JavaScript from LLVM bit-code. This work is what's finally being opened up.

As announced to the LLVM developers, Simon Moll, the student responsible for this work, has released his OpenCL back-end and control-flow restructuring framework. The restructuring framework re-does the instructions such that they can be expressed without goto statements and switch/loops, which is needed to emit source-code for strict control-flow structured languages like OpenCL and the GL Shading Language.

Simon's OpenCL LLVM back-end has been tested against both the recent AMD and NVIDIA drivers using the vendor demos/benchmarks, and it works with few caveats.

The OpenCL back-end has been updated so that it works against the current SVN development state of LLVM 3.0/3.1, but the GLSL back-end is currently living in the LLVM 2.9 days, but with word that it will be ported later to the latest LLVM interfaces.

The code for this interesting back-end has been published on BitBucket.org.

AMD has already commented on the work by this university student. In particular, Axtor (the restructuring framework) was compared to AMD's control-flow structizer in the AMDIL LLVM back-end AMD open-sourced a few months ago. AMD said it would be nice if the efforts could be merged, but the current licensing is incompatible. Simon Moll has already responded that he's looking at possibly putting out this code under a more permissive license.

Other related reading would be An Initial Version Of LunarGLASS-LLVM For Mesa and AMD Makes Progress With LLVM For Gallium3D.