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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug rtl-optimization/50904] [4.7 regression] pessimization when -fno-protect-parens is enabled by -Ofast
Date: Fri, 02 Dec 2011 09:49:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904

--- Comment #20 from rguenther at suse dot de <rguenther at suse dot de> 2011-12-02 09:49:39 UTC ---
On Thu, 1 Dec 2011, ebotcazou at gcc dot gnu.org wrote:

> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904
> 
> Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:
> 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Status|NEW                         |ASSIGNED
>                  CC|ebotcazou at gcc dot        |
>                    |gnu.org                     |
>           Component|tree-optimization           |rtl-optimization
>          AssignedTo|unassigned at gcc dot       |ebotcazou at gcc dot
>                    |gnu.org                     |gnu.org
> 
> --- Comment #19 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-12-01 19:53:15 UTC ---
> > lim3 was added as a "hack", now yes, cunroll needs ccp after it (but it's
> > there in the form of DOM and VRP).  It's a pass ordering issue that we
> > cannot ever solve.
> 
> OK, but that doesn't explain why LIM isn't able to hoist the loads...

If the expressions only become invariant after unrolling then the issue
is that without CCP LIM does not see they are invariant I suppose.
I'll have a closer look.