Except that's not how you shift on a compact. You almost always move the rear 1-2 gears in the opposite direction. So going from a 34-17 you shift the front and back to a 50-23, taking you from 55 gr-in to 60 gr-in. The new Shimano Di2 XTR even does this automatically.

The whole way a compact works is that you adjust the front ring to suit broad terrain, and the rear to handle small changes. Going uphill, 34 ring, get to the top, 50 ring. With a triple, you'd do the same thing, except you have a 39t ring that you need to skip over.