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SubjectControl dependency between prior load in while condition and later store?
Date
A question for memory-barriers.txt aficionados.

Is there a control dependency between the prior load of 'a' and the
later store of 'c'?:

while (READ_ONCE(a));
WRITE_ONCE(c, 1);

I have my doubts because memory-barriers.txt doesn't talk much about
loops and because of what that document says here:

In addition, control dependencies apply only to the then-clause and
else-clause of the if-statement in question. In particular, it does
not necessarily apply to code following the if-statement:

q = READ_ONCE(a);
if (q) {
WRITE_ONCE(b, 1);
} else {
WRITE_ONCE(b, 2);
}
WRITE_ONCE(c, 1); /* BUG: No ordering against the read from 'a'. */

It's not obvious to me how the then-clause/else-clause idea maps onto
loops, but if we think of the example at the top like this...

while (1) {
if (!READ_ONCE(a)) {
WRITE_ONCE(c, 1);
break;
}
}

...then the dependent store is within the then-clause. Viewed this way,
it seems there would be a control dependency between a and c.

Is that right?

Thanks,
Daniel

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