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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/105740] missed optimization switch transformation for conditions with duplicate conditions
Date: Tue, 21 Jun 2022 09:12:54 +0000	[thread overview]
Message-ID: <bug-105740-4-OyDYBsyLzP@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-105740-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105740

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The problem with switch-conversion done multiple times is that when it is done
early, it can do worse job than when it is done late, e.g. we can have better
range information later which allows (unfortunately switch-conversion doesn't
use that yet, there is a PR about it) to ignore some never reachable values
etc.
So ideally we either need to be able to undo switch-conversion and redo it if
things have changed, or do it only late and for e.g. inlining costs perform it
only in analysis mode and record somewhere what kind of lowering would be done
and how much it would cost.
With multiple if-to-switch, don't we risk that we turn some ifs into switch,
then
switch-conversion lowers it back to ifs and then another if-to-switch matches
it again and again lowers it?

  parent reply	other threads:[~2022-06-21  9:12 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-26 11:26 [Bug tree-optimization/105740] New: " b.buschinski at googlemail dot com
2022-05-30  9:57 ` [Bug tree-optimization/105740] " marxin at gcc dot gnu.org
2022-06-21  2:45 ` luoxhu at gcc dot gnu.org
2022-06-21  7:30 ` marxin at gcc dot gnu.org
2022-06-21  9:02 ` rguenth at gcc dot gnu.org
2022-06-21  9:12 ` jakub at gcc dot gnu.org [this message]
2022-06-21  9:26 ` rguenther at suse dot de
2022-06-21  9:29 ` cvs-commit at gcc dot gnu.org
2022-06-22  6:19 ` luoxhu at gcc dot gnu.org
2022-06-27 13:58 ` marxin at gcc dot gnu.org
2022-07-01  2:06 ` luoxhu at gcc dot gnu.org
2022-07-08 10:46 ` marxin at gcc dot gnu.org
2023-06-26  6:43 ` b.buschinski at googlemail dot com

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