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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/102546] [12 Regregression] Missed Dead Code Elimination regression (trunk vs 11.2.0) at -O3
Date: Fri, 01 Oct 2021 06:30:37 +0000	[thread overview]
Message-ID: <bug-102546-4-NtHq4YbHFg@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-102546-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102546

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Aldy Hernandez from comment #2)
> By VRP1 we seem to be calculating the following:
> 
> (f_8 << f_8) && (f_8 == 0)
> 
> This would fold to false, which would elide the foo():
> 
>  <bb 7> [local count: 59055800]:
>   b = 0;
>   _3 = f_8 << f_8;
>   _4 = (char) _3;
>   _5 = (int) _4;
>   if (_4 > 0)
>     goto <bb 8>; [64.06%]
>   else
>     goto <bb 10>; [35.94%]
> 
>   <bb 8> [local count: 34842922]:
>   if (f_8 == 0)
>     goto <bb 9>; [71.10%]
>   else
>     goto <bb 10>; [28.90%]
> 
>   <bb 9> [local count: 12809203]:
>   foo ();

I think it's similar to in the other PR, with old EVRP when visiting BB 8
we pushed [1, +INF] as the global range for _4, then supposedly ranger
manages to evaluate f_8 == 0 with its backward infering somehow.

We no longer do this "path sensitive" adjustment of (global) ranges since
you removed the EVRP DOM walk algorithm.

  parent reply	other threads:[~2021-10-01  6:30 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-30 13:22 [Bug tree-optimization/102546] New: " theodort at inf dot ethz.ch
2021-09-30 13:22 ` [Bug tree-optimization/102546] " theodort at inf dot ethz.ch
2021-09-30 17:21 ` aldyh at gcc dot gnu.org
2021-09-30 17:44 ` aldyh at gcc dot gnu.org
2021-09-30 22:50 ` [Bug tree-optimization/102546] [12 Regregression] " pinskia at gcc dot gnu.org
2021-10-01  6:30 ` rguenth at gcc dot gnu.org [this message]
2021-10-01  9:18 ` aldyh at gcc dot gnu.org
2021-10-01  9:19 ` aldyh at gcc dot gnu.org
2021-10-01  9:36 ` zhendong.su at inf dot ethz.ch
2021-10-01 13:02 ` amacleod at redhat dot com
2021-10-01 22:04 ` cvs-commit at gcc dot gnu.org
2021-10-01 22:05 ` aldyh at gcc dot gnu.org
2021-10-01 22:20 ` jakub at gcc dot gnu.org
2021-10-01 22:24 ` aldyh at redhat dot com
2021-10-01 22:38 ` jakub at gcc dot gnu.org

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