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From: "rguenth 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 14:58:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38474

--- Comment #63 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-06-26 14:58:31 UTC ---
(In reply to comment #61)
> (In reply to comment #57)
> > 
> > I will, on Monday.
> 
> And by Monday I obviously meant yesterday ;-)
> 
> 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
> added -fno-devirtualize (-ftime-report showed that alias stmt walking
> dropped from 82% to 75%).  This is mainly due to calls to
> detect_type_change from compute_known_type_jump_func, there are 36454
> of them and all are of course completely pointless because we do not
> devirtualize in Fortran.
> 
> Looking into the code, it is apparent that I even attempted to avoid
> such situations but somehow was not paying enough attention.  The
> rather obvious patch below fixes that.  With it, the compile time at
> -O3 drops to 13.5 without any additional options (~50 calls to
> detect_type_change_ssa and detect_type change from other places remain
> but those are not a big problem here, they are not so easy to get rid
> of and I hope to eventually remove the type detection machinery from
> IPA altogether so I'll keep those for later).
> 
> I'll bootstrap and test the patch and post it to the mailing list
> soon.
> 
> Index: gcc/ipa-prop.c
> ===================================================================
> --- gcc/ipa-prop.c      (revision 188931)
> +++ gcc/ipa-prop.c      (working copy)
> @@ -912,8 +912,8 @@ compute_known_type_jump_func (tree op, s
>        || is_global_var (base))
>      return;
> 
> -  if (detect_type_change (op, base, call, jfunc, offset)
> -      || !TYPE_BINFO (TREE_TYPE (base)))
> +  if (!TYPE_BINFO (TREE_TYPE (base))
> +      || detect_type_change (op, base, call, jfunc, offset))
>      return;

That change qualifies for a backport to all branches it applies to ...