[mhh__]

Realistically when you get into real world questions about performance the only way to be sure is to measure it.

In this case I imagine you're right. Although also worth pointing out that due to the way modern CPUs are basically frontends to generate uOps that it could actually perform the optimization by itself anyway. Time to break out PAPI (very cool tool for anyone unaware, you can get instruction level profiling in your program with basically 4 function calls and a header file).