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] new(len: &'a mut usize) -> Self13 pub(super) fn new(len: &'a mut usize) -> Self { 14 SetLenOnDrop { local_len: *len, len } 15 } 16 17 #[inline] increment_len(&mut self, increment: usize)18 pub(super) fn increment_len(&mut self, increment: usize) { 19 self.local_len += increment; 20 } 21 22 #[inline] current_len(&self) -> usize23 pub(super) fn current_len(&self) -> usize { 24 self.local_len 25 } 26 } 27 28 impl Drop for SetLenOnDrop<'_> { 29 #[inline] drop(&mut self)30 fn drop(&mut self) { 31 *self.len = self.local_len; 32 } 33 } 34