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