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 |
6 | pub(super) struct SetLenOnDrop<'a> { |
7 | len: &'a mut usize, |
8 | local_len: usize, |
9 | } |
10 | |
11 | impl<'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 | |
28 | impl Drop for SetLenOnDrop<'_> { |
29 | #[inline ] |
30 | fn drop(&mut self) { |
31 | *self.len = self.local_len; |
32 | } |
33 | } |
34 | |