1*3dcb652aSAsahi Lina // SPDX-License-Identifier: Apache-2.0 OR MIT 2*3dcb652aSAsahi Lina 365b571afSAsahi Lina // Set the length of the vec when the `SetLenOnDrop` value goes out of scope. 465b571afSAsahi Lina // 565b571afSAsahi Lina // The idea is: The length field in SetLenOnDrop is a local variable 665b571afSAsahi Lina // that the optimizer will see does not alias with any stores through the Vec's data 765b571afSAsahi Lina // pointer. This is a workaround for alias analysis issue #32155 865b571afSAsahi Lina pub(super) struct SetLenOnDrop<'a> { 965b571afSAsahi Lina len: &'a mut usize, 1065b571afSAsahi Lina local_len: usize, 1165b571afSAsahi Lina } 1265b571afSAsahi Lina 1365b571afSAsahi Lina impl<'a> SetLenOnDrop<'a> { 1465b571afSAsahi Lina #[inline] new(len: &'a mut usize) -> Self1565b571afSAsahi Lina pub(super) fn new(len: &'a mut usize) -> Self { 1665b571afSAsahi Lina SetLenOnDrop { local_len: *len, len } 1765b571afSAsahi Lina } 1865b571afSAsahi Lina 1965b571afSAsahi Lina #[inline] increment_len(&mut self, increment: usize)2065b571afSAsahi Lina pub(super) fn increment_len(&mut self, increment: usize) { 2165b571afSAsahi Lina self.local_len += increment; 2265b571afSAsahi Lina } 2365b571afSAsahi Lina 2465b571afSAsahi Lina #[inline] current_len(&self) -> usize2565b571afSAsahi Lina pub(super) fn current_len(&self) -> usize { 2665b571afSAsahi Lina self.local_len 2765b571afSAsahi Lina } 2865b571afSAsahi Lina } 2965b571afSAsahi Lina 3065b571afSAsahi Lina impl Drop for SetLenOnDrop<'_> { 31 #[inline] drop(&mut self)32 fn drop(&mut self) { 33 *self.len = self.local_len; 34 } 35 } 36