1. A specialized processing block on a programmable integrated circuit device, said specialized processing block comprising: a multiplier having two multiplicand inputs and a product output; an adder having as one adder input said product output of said multiplier, and having a second adder input and an adder output; a direct-connect output of said adder output to a first other said specialized processing block; and a direct-connect input from a second other said specialized processing block, said direct-connect input connecting a direct-connect output of said adder output of said second other said specialized processing block to a first one of said multiplicand inputs.