@group(0) @binding(0) var<storage, read_write> a : atomic<i32>;
@fragment
fn foo() -> @location(0) i32 {
discard;
var x = 0;
let result = atomicCompareExchangeWeak(&(a), 0, 1);
if (result.exchanged) {
x = result.old_value;
}
return x;