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// run-pass
// compile-flags: -O
// Make sure that `Ref` and `RefMut` do not make false promises about aliasing,
// because once they drop, their reference/pointer can alias other writes.
// Adapted from comex's proof of concept:
// https://github.com/rust-lang/rust/issues/63787#issuecomment-523588164
use std::cell::RefCell;
use std::ops::Deref;
pub fn break_if_r_is_noalias(rc: &RefCell<i32>, r: impl Deref<Target = i32>) -> i32 {
let ptr1 = &*r as *const i32;
let a = *r;
drop(r);
*rc.borrow_mut() = 2;
let r2 = rc.borrow();
let ptr2 = &*r2 as *const i32;
if ptr2 != ptr1 {
panic!();
}
// If LLVM knows the pointers are the same, and if `r` was `noalias`,
// then it may replace this with `a + a`, ignoring the earlier write.
a + *r2
}
fn main() {
let mut rc = RefCell::new(1);
let res = break_if_r_is_noalias(&rc, rc.borrow());
assert_eq!(res, 3);
*rc.get_mut() = 1;
let res = break_if_r_is_noalias(&rc, rc.borrow_mut());
assert_eq!(res, 3);
}
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