1// Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
2//
3// The idea is: The length field in SetLenOnDrop is a local variable
4// that the optimizer will see does not alias with any stores through the Vec's data
5// pointer. This is a workaround for alias analysis issue #32155
6pub(super) struct SetLenOnDrop<'a> {
7 len: &'a mut usize,
8 local_len: usize,
9}
10
11impl<'a> SetLenOnDrop<'a> {
12 #[inline]
13 pub(super) fn new(len: &'a mut usize) -> Self {
14 SetLenOnDrop { local_len: *len, len }
15 }
16
17 #[inline]
18 pub(super) fn increment_len(&mut self, increment: usize) {
19 self.local_len += increment;
20 }
21
22 #[inline]
23 pub(super) fn current_len(&self) -> usize {
24 self.local_len
25 }
26}
27
28impl Drop for SetLenOnDrop<'_> {
29 #[inline]
30 fn drop(&mut self) {
31 *self.len = self.local_len;
32 }
33}
34