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
8pub(super) struct SetLenOnDrop<'a> {
9    len: &'a mut usize,
10    local_len: usize,
11}
12
13impl<'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    #[inline]
25    pub(super) fn current_len(&self) -> usize {
26        self.local_len
27    }
28}
29
30impl Drop for SetLenOnDrop<'_> {
31    #[inline]
32    fn drop(&mut self) {
33        *self.len = self.local_len;
34    }
35}
36