[Bug middle-end/59448] Code generation doesn't respect C11 address-dependency

[algrant at acm dot org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59448

--- Comment #13 from algrant at acm dot org ---
I see what you mean - there is a race if threadB reads the data when the
flag is not set, i.e. in the case when the read value is never used.
Moving the read of data after the test (as in the fragment in comment 4)
would fix the race.