I maintain https://github.com/thewilsonator/llvm/tree/compute and https://github.com/thewilsonator/llvm-target-spirv which has (unused) tablegen definitions for SPIR-V, for LDC and DCompute.
I'm _hoping_ to get some consensus on backend integration into LLVM trunk at IWOCL in May.
More users of the backend are useful for convincing the LLVM folks of the usefulness of having a single backend in trunk.