The problem is that the code is not semantically identical, there is no way for the compiler to know that nothing else has changed while the loop is executing.

The problem is that the code is not semantically identical, there is no way for the compiler to know that nothing else has changed while the loop is executing. It's like the frequent optimization case of int len = array.length for(i = 0; i < len; i++){ } vs. for(i = 0; i < array.length; i++){ } The code is semantically different and therefore has a different performance profile.