Commit 65b571af authored by Asahi Lina's avatar Asahi Lina Committed by Miguel Ojeda
Browse files

rust: Import upstream `alloc::vec::set_len_on_drop` module 

This is a subset of the Rust standard library `alloc` crate,
version 1.62.0, licensed under "Apache-2.0 OR MIT", from:

    https://github.com/rust-lang/rust/tree/1.62.0/library/alloc/src

The file is copied as-is, with no modifications whatsoever
(not even adding the SPDX identifiers).

For copyright details, please see:

    https://github.com/rust-lang/rust/blob/1.62.0/COPYRIGHT



Signed-off-by: default avatarAsahi Lina <lina@asahilina.net>
Link: https://lore.kernel.org/r/20230224-rust-vec-v1-1-733b5b5a57c5@asahilina.net


[ Import version 1.62.0 instead, to match the one in mainline. ]
Signed-off-by: default avatarMiguel Ojeda <ojeda@kernel.org>
parent 3c01a424

rust/alloc/vec/set_len_on_drop.rs

0 → 100644
+28 −0
Original line number Diff line number Diff line 
// Set the length of the vec when the `SetLenOnDrop` value goes out of scope.

//

// The idea is: The length field in SetLenOnDrop is a local variable

// that the optimizer will see does not alias with any stores through the Vec's data

// pointer. This is a workaround for alias analysis issue #32155

pub(super) struct SetLenOnDrop<'a> {

    len: &'a mut usize,

    local_len: usize,

}



impl<'a> SetLenOnDrop<'a> {

    #[inline]

    pub(super) fn new(len: &'a mut usize) -> Self {

        SetLenOnDrop { local_len: *len, len }

    }



    #[inline]

    pub(super) fn increment_len(&mut self, increment: usize) {

        self.local_len += increment;

    }

}



impl Drop for SetLenOnDrop<'_> {

    #[inline]

    fn drop(&mut self) {

        *self.len = self.local_len;

    }

}