Compilers are pretty good at restructuring code. As a programmer you need know some common situations when the compiler would like to reorder your code, but can

Compilers are pretty good at restructuring code. As a programmer you need know some common situations when the compiler would like to reorder your code, but can't. E.g. when you do summation using a for loop, and the compiler is trying to preserve the rounding-correctness your float operations. Or because you created a dependency graph with a for loop where each iteration requires the previous iteration's result.