Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 35 insertions, 0 deletions

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 0000000000..d3c7297b80
--- /dev/null
+++ b/rust/alloc/vec/set_len_on_drop.rs
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// 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;
+    }
+
+    #[inline]
+    pub(super) fn current_len(&self) -> usize {
+        self.local_len
+    }
+}
+
+impl Drop for SetLenOnDrop<'_> {
+    #[inline]
+    fn drop(&mut self) {
+        *self.len = self.local_len;
+    }
+}