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Add 2+2W litmus test #4641

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Add 2+2W litmus test #4641

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24 changes: 24 additions & 0 deletions tests/pass/0weak_memory/weak.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -226,6 +226,29 @@ fn old_release_store() {
});
}

/// 2+2W variant https://johnwickerson.github.io/papers/memalloy.pdf §4.1
/// 3 SC + 1 Rel is the strongest ordering to still observe x==y==1
fn two_w_two_w() {
check_all_outcomes([1, 1], || {
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@RalfJung RalfJung Oct 22, 2025 •
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This only checks y, and it checks that that is always 1...?

The slice here is the set of all outcomes, so [1, 1] is equivalent to [1].

let x = static_atomic(0);
let y = static_atomic(0);

let t1 = spawn(move || {
x.store(1, SeqCst);
y.store(2, SeqCst);
x.load(Relaxed)
});
let t2 = spawn(move || {
y.store(1, Release);
x.store(2, SeqCst);
y.load(Relaxed)
Comment on lines +239 to +244
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Your code doesn't match the cppmem code. It should be:

Suggested change
x.load(Relaxed)
});
let t2 = spawn(move || {
y.store(1, Release);
x.store(2, SeqCst);
y.load(Relaxed)
y.load(Relaxed)
});
let t2 = spawn(move || {
y.store(1, Release);
x.store(2, SeqCst);
x.load(Relaxed)

});

t1.join().unwrap();
t2.join().unwrap()
});
}

fn main() {
relaxed();
seq_cst();
Expand All @@ -235,4 +258,5 @@ fn main() {
release_sequence();
weaker_release_sequences();
old_release_store();
two_w_two_w();
}