The Radeon R600 LLVM back-end, which is used by the Radeon Gallium3D driver for Compute/OpenCL support and optionally for shader compilation, was merged for LLVM 3.3. While it was merged for LLVM 3.3 and has matured quite a bit, it remains an "experimental" back-end for the imminent LLVM release.
With LLVM 3.4, the R600 back-end is no longer deemed experimental. The R600 back-end in the LLVM 3.3 release requires the --enable-experimental-targets=R600 compiler switch, but per early LLVM 3.4 notes, "The R600 backend is not marked experimental anymore and is built by default."
Beyond this fundamental change, the R600 back-end in LLVM 3.4 has already picked up numerous Radeon improvements in the weeks since LLVM 3.3 was branched. For end-users, unfortunately the LLVM 3.4 release will likely not be here until around year's end.