1. A method comprising: automatically generating, by a processor of a host computer, an executable comparison block diagram model including: a first portion that represents a first simulation as a plurality of interconnected graphical blocks, outputs of at least some of the interconnected graphical blocks of the first portion representing intermediate outputs in the first simulation, and a second portion that represents a second simulation as a plurality of interconnected graphical blocks, outputs of at least some of the interconnected graphical blocks of the second portion representing intermediate outputs in the second simulation, where the first and second simulations represent different implementations of a design, and the first and second simulations are configured for independent execution; storing the executable comparison block diagram in a memory; identifying for comparison, with a difference block in the comparison block diagram model, a first intermediate output from the first simulation and a second intermediate output from the second simulation, the difference block being separate from the first and second portions that represent the first and second simulations; providing a switching capability at the second portion of the executable comparison block diagram model, the switching capability controlling whether a next component of the second portion of the executable comparison block diagram model receives: the first intermediate output of the first simulation, or the second intermediate output, where the next component of the second portion of the executable comparison block diagram model is relative to the second intermediate output in an execution order; instructing the first simulation and the second simulation to execute simultaneously in a locked-step manner during execution of the comparison block diagram model; automatically comparing, by the processor, at least one value of the first intermediate output with at least one value of the second intermediate output during the execution of the comparison block diagram model including the first and second portions that represent the first and second simulations; and generating a report comparing the first simulation with the second simulation.