If your cpu is dense enough to gravitationally bend light by any significant amount then you might have other problems. But we bounce light off of electric fie

If your cpu is dense enough to gravitationally bend light by any significant amount then you might have other problems. But we bounce light off of electric fields all the time, so the a flat chip is not really required (even if you made an all-optical chip). As others have said, it's all about heat distribution.