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Re: 100x perfomance regression between gcc 3.4.5 and gcc 4.X


On 3/13/06, Richard Guenther <richard.guenther@gmail.com> wrote:
 > Starting with gcc 4.1.0 we have inline heuristics in place that will _always_
> inline such simple "wrappers".  So, if this still happens, there is a bug in the
> heuristics and that should be reported.  Before 4.1.0 the heuristics were bogus
> and wrappers were not inlined all the time.
> So, can you verify you are happy with the heuristics in 4.1.0
No i'm not, and i've used a pristine 4.1.0 in
http://gcc.gnu.org/ml/gcc/2006-03/msg00410.html
I haven't tried that particular testcase on 4.2.x, but some weeks ago
i had to go thru all my code again to put always_inline in some
forgotten places because i was seeing even empty ctors not being
inlined (to the effect of having a call to a ret). So in this regard,
4.1.0 & 4.2.x still exhibit that kind of behaviour.

It seems to trigger when some particular threshold is met, either for
a function or unit, then nothing at all gets inlined but functions
tagged with always_inline; of course major performance regression
ensues.


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