I thought about this. But STORE_FAST x is followed by LOAD_FAST x just by accident. If you change the expression (1+x**2 or f(x**2)) they no longer be neighbors. I am not sure this pattern is common enough. There are more common pairs.

Also, note that LOAD_FAST belong to the different line of code. It should be preserved for debugging purpose. Otherwise you could not set a breakpoint on the first line of the loop body.