Yup.

I've got a function the gist of which is

  if (!cond())
    return val;

  do {
    // logic
  } while (cond());

  return val;

This looks like it could be simplified as

  while (cond())
    // logic
  }
  return val;

But if you do you lose out on 20% of performance due to branch mispredictions, and this is a very hot function. It looks like a mistake, like the two are equivalent, but they are actually not. So it gets a comment that explains what's happening.