From 65b571afdfdcefa09508274488086b218e34906d Mon Sep 17 00:00:00 2001 From: Asahi Lina Date: Fri, 24 Feb 2023 18:11:47 +0900 Subject: 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: Asahi Lina 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: Miguel Ojeda --- rust/alloc/vec/set_len_on_drop.rs | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) create mode 100644 rust/alloc/vec/set_len_on_drop.rs (limited to 'rust') diff --git a/rust/alloc/vec/set_len_on_drop.rs b/rust/alloc/vec/set_len_on_drop.rs new file mode 100644 index 0000000000000..8b66bc8121296 --- /dev/null +++ b/rust/alloc/vec/set_len_on_drop.rs @@ -0,0 +1,28 @@ +// 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; + } +} -- cgit 1.2.3-korg