If <code>list</code> pointed to a cyclic list,
then the original program would never access <code>*p</code> or <code>*q</code>,
but the rewritten program would.
(Moving `*p` ahead would be safe if the compiler can prove `*p` will not panic;
moving `*q` ahead would also require the compiler proving that no other
goroutine can access `*q`.)
</p>

<p>
Not introducing data races also means not assuming that called functions

// existing file, such as a binary executable.
// It must be called before any data is written.
func (w *Writer) SetOffset(n int64) {
	if w.cw.count != 0 {
		panic("zip: SetOffset called after data was written")
	}
	w.cw.count = n
}

// Flush flushes any buffered data to the underlying writer.
// Calling Flush is not normally necessary; calling Close is sufficient.

func firstError(input *Input) (err error) {
	panicOnError = true
	defer func() {
		panicOnError = false
		switch e := recover(); e := e.(type) {
		case nil:
		case error:
			err = e
		default:
			panic(e)
		}
	}()

	for {
		tok := input.Next()
		if tok == scanner.EOF {
			return
		}
	}