[Bug libstdc++/51798] [4.7 regression] libstdc++ atomicity performance regression due to __sync_fetch_and_add

["amacleod at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798

--- Comment #19 from Andrew Macleod <amacleod at redhat dot com> 2012-01-27 12:49:27 UTC ---
(In reply to comment #17)
> (In reply to comment #13)
> > Any code that explicitly calls __sync_* in
> > libstdc++-v3 has introduced a performance regression.
> 
> But if it happens in code that is executed only rarely (e.g. the EH code will
> be dominated by time spent in the unwinder, not any barriers), then it might
> not be even measurable.  So I think we should first change atomicity.h and only
> if you can come up with a testcase which shows a significant regression for the
> libsupc++ or parallel bits, we should change those too at this point.  We are
> in stage4.

Precisely my thoughts... Its not a regression if it isn't measurable, and we
want to change as little as we possibly can at this stage.  The patch is what I
was thinking.  

I presume it generates the same code power use to get?