1 // SPDX-License-Identifier: Apache-2.0 OR MIT
2 
3 // Set the length of the vec when the `SetLenOnDrop` value goes out of scope.
4 //
5 // The idea is: The length field in SetLenOnDrop is a local variable
6 // that the optimizer will see does not alias with any stores through the Vec's data
7 // pointer. This is a workaround for alias analysis issue #32155
8 pub(super) struct SetLenOnDrop<'a> {
9     len: &'a mut usize,
10     local_len: usize,
11 }
12 
13 impl<'a> SetLenOnDrop<'a> {
14     #[inline]
15     pub(super) fn new(len: &'a mut usize) -> Self {
16         SetLenOnDrop { local_len: *len, len }
17     }
18 
19     #[inline]
20     pub(super) fn increment_len(&mut self, increment: usize) {
21         self.local_len += increment;
22     }
23 }
24 
25 impl Drop for SetLenOnDrop<'_> {
26     #[inline]
27     fn drop(&mut self) {
28         *self.len = self.local_len;
29     }
30 }
31