Exactly. Memory access is a major factor in runtime, often more important than instruction counts. And in the vast, vast majority of cases it doesn't matter. I trust the compiler to make reasonable choices, something would have to be deployed at a very large scale before the programmer time of considering such things became cheaper than the hardware savings from doing it. And the vast majority of code simply doesn't execute often enough to matter one way or the other.

Save your brainpower for the right algorithms and for the inner loops the profiler identifies (I did not expect to learn that the slowest piece of code was referring to SQL fields by name!) Ignore the rest.