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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/51798] [4.7 regression] libstdc++ atomicity performance regression due to __sync_fetch_and_add
Date: Wed, 25 Jan 2012 16:09:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798

--- Comment #9 from Andrew Macleod <amacleod at redhat dot com> 2012-01-25 15:36:23 UTC ---
(In reply to comment #8)
> > At least at this point I'd feel much safer if libstdc++ used just acq_rel
> > semantics for the all atomic_fetch_and_add places, instead of somewhere acq and
> > somewhere rel semantics.
> 
> Can we at least apply the ACQ_REL patch using the new atomic intrinsics?
> 

Well, I thought that was implicit since I wasn't suggesting we change the
__sync semantics, just the required libstdc++ bits.  

All that has to be done is replace the two __sync_fetch_and_add(...) with
__atomic_fetch_add(.., __ATOMIC_ACQ_REL)  in atomicity.h isn't it?