10% slowdown when using iterators

[jbalintbiro]

    fn find(&self, key: &K) -> Option<&V> {
        let mut cur: *mut Node<K, V> = ptr::mut_null();

/*      unsafe {
            for (level, root) in self.roots.iter().enumerate().rev() {
                if cur == ptr::mut_null() {
                    let croot = *root;
                    if croot != ptr::mut_null() && (*croot).key <= *key {
                        cur = croot;
                    }
                }

                if cur != ptr::mut_null() {
                    loop {
                        let next = *(*cur).pointer(level);
                        if next != ptr::mut_null() && (*next).key <= *key {
                            cur = next;
                        } else {
                            break;
                        }
                    }
                }
            }
            if cur != ptr::mut_null() && (*cur).key == *key {
                Some(&(*cur).value)
            } else {
                None
            }
        }
*/
        unsafe {
            for level in range(0, self.roots.len()).rev() {
                if cur == ptr::mut_null() {
                    let croot = self.roots.as_slice()[level];
                    if croot != ptr::mut_null() && (*croot).key <= *key {
                        cur = croot;
                    }
                }

                if cur != ptr::mut_null() {
                    loop {
                        let next = *(*cur).pointer(level);
                        if next != ptr::mut_null() && (*next).key <= *key {
                            cur = next;
                        } else {
                            break;
                        }
                    }
                }
            }
            if cur != ptr::mut_null() && (*cur).key == *key {
                Some(&(*cur).value)
            } else {
                None
            }
        }
    }

the commented out code runs 10% slower, whole file: https://github.com/saati/skiplist-rs/blob/6ddf457bd0dd7ac02d21cd36bca966b700037034/skiplist.rs

with iterators:
test bench::bench_search_short ... bench: 102 ns/iter (+/- 8)

without iterators:
test bench::bench_search_short ... bench: 92 ns/iter (+/- 8)

[huonw]

This is possibly #11751.

[thestinger]

I believe this is fixed now. Please re-open if it's still not performing as well for you.