fn inner(&self) -> &ArcInner<T> {
        // This unsafety is ok because while this arc is alive we're guaranteed
        // that the inner pointer is valid. Furthermore, we know that the
        // `ArcInner` structure itself is `Sync` because the inner data is
        // `Sync` as well, so we're ok loaning out an immutable pointer to these
        // contents.
        unsafe { self.ptr.as_ref() }
    }
Allocates an `ArcInner<T>` with sufficient space for
a possibly-unsized inner value where the value has the layout provided,
returning an error if allocation fails.

The function `mem_t
benchmarks/haystacks/code/rust-library.rs