As noted in:
This doesn't accomplish anything on its own. It's the first step towards preserving and using branch weights with selects.
If this looks ok, the next step would be to make sure we're propagating the info in all of the other places where we create selects (SimplifyCFG, InstCombine, etc). I don't think there's an easy fix to make this happen; we have to look at each transform individually to determine how to correctly propagate the weights.
Along with that step, we need to then use the weights when making subsequent transform decisions such as discussed in http://reviews.llvm.org/D16836.