It would be nice if that were true, but it's not. The ability to assume incrementing a counter won't overflow makes range analysis possible in many cases where it otherwise wouldn't be. Because of this you can perform vectorization because the compiler can assume it knows how many times the loop will run.

The performance differences are not small.

You can also tell some compilers to treat signed integer overflow as wrapping-- but people don't usually do this because the optimizations you lose are valuable.