Messages in this thread |  | | From | Daniel Jordan <> | Subject | Control dependency between prior load in while condition and later store? | Date | Wed, 4 Apr 2018 15:29:33 -0400 |
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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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