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From: "jamborm at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/38474] slow compilation at -O0 due to expand's temp slot goo
Date: Tue, 26 Jun 2012 15:01:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38474

--- Comment #64 from Martin Jambor <jamborm at gcc dot gnu.org> 2012-06-26 15:01:28 UTC ---
(In reply to comment #62)
> (In reply to comment #61)
> > (In reply to comment #57)
> > 
> > Anyway, on the machine where are debugged this, compilation at -O3
> > took over 16 seconds which dropped to about 13.5 seconds when I also
> 
> What?  Must be a future machine.  On everything I have access to the reduced
> testcase (6309 lines) takes about 800 to 1000 seconds.  Do you build without
> any checking?

Minutes! Of course I meant minutes, the drop is thus from ~1000
seconds to ~810 seconds.  I forgot I was using bash time instead of
/usr/bin/time -f%U which I was regularly using only a few days ago.

> 
> In any case, the proposed patch does reduce the time to basically nothing for
> the alias tree walker, so: thanks :)

I've experimentally disabled the walker in
is_parm_modified_before_stmt and am now waiting for results but I
guess it won't have any measurable impact.