As I understand it, clang is a C front-end for the Low Level Virtual Machine infrastructure. It's fantastic that the benchmarks show it actually performing better than gcc in many cases, although it's not quite a valid comparison, given that the two programs are not outputting the same pixel values.
This is true, but clang is new software under active development. The intention of the project is not to trade off speed for correctness but to eventually be correct and fast.
According to the follow-up posts, the differences in rendering may largely be due to bugs in the floating point code generation. Once these are fixed, it is entirely possible that clang could generate the correct images at the higher speed. We won't know until then, however.
