Those cell diagrams are very abstract illustrations of the underlying functionality and are in some parts even wrong [1]. The level you have to be looking at to

Those cell diagrams are very abstract illustrations of the underlying functionality and are in some parts even wrong [1]. The level you have to be looking at to find out more about short-circuits (transistors and their interconnections), is very much a secret. [1] "Wrong" in the sense that they are only proper abstractions for the officially supported functionality. For example, the DSP48E blocks of the Xilinx Virtex-5 can be chained for higher precision, but if you interpret the diagrams literally and try to build unsupported functions, it won't work as you expect.