ROCm provides a good OpenCL 2.x implementation targeting AMD GCN. The compiler/optimizer is clang-based. It is open-source. One great thing is that ROCm OpenCL

ROCm provides a good OpenCL 2.x implementation targeting AMD GCN. The compiler/optimizer is clang-based. It is open-source. One great thing is that ROCm OpenCL supports GCN assembly in the OpenCL source, which is handy in some corner-cases that are not properly handled by the optimizer.