allocator_api2/stable/vec/
set_len_on_drop.rs

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(always)]
13    pub(super) fn new(len: &'a mut usize) -> Self {
14        SetLenOnDrop {
15            local_len: *len,
16            len,
17        }
18    }
19
20    #[inline(always)]
21    pub(super) fn increment_len(&mut self, increment: usize) {
22        self.local_len += increment;
23    }
24}
25
26impl Drop for SetLenOnDrop<'_> {
27    #[inline(always)]
28    fn drop(&mut self) {
29        *self.len = self.local_len;
30    }
31}