You are underestimating the rate at which the number of possibilities to be searched explodes exponentially. Read the paper on Denali, an optimizer that conceptually tries all possible instruction sequences to compile a piece of a program optimally. Even though they used sophisticated pruning techniques and state of the art combinatorial solvers it didn't work for anything beyond a couple of instructions (less than 10), and AFAIK nothing practical ever came of it. Say you can currently successfully synthesize instruction sequences of length 6. The thing with exponential growth is that even if computers became a million times faster, then you might be able to achieve instruction sequences of length 9, not of length 6 million.