if a branching statement is reached which does not get replaced with prediction, the warp will get split into 2 warps (divergent warps) which both will executed. At the end of the execution of both warps they are will be combined again into one warp and the result of the "wanted" warp will be used.
That is very strange, because SM 3.0 cards behave this way in the shader pipeline, but SM 4.0 cards only execute one branch.