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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/107833] [12/13 Regression] wrong code at -Os and above on x86_64-linux-gnu since r12-5138-ge82c382971664d6f
Date: Thu, 01 Dec 2022 17:32:59 +0000	[thread overview]
Message-ID: <bug-107833-4-sIzWAZqcNe@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-107833-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107833

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Wasn't this discussed in the past in other PRs?  Whether uninitialized vars
mean anything or anything but same value each time a SSA_NAME initialized to it
is used?
Because as this testcase shows, not all uses of uninitialized SSA_NAMEs are
actually UB, at least their use in PHIs must be ok, and if IVOPTS or other
optimizations can construct some expressions computing a difference between
uninitialized loop iterator's PHI header between several iterations (e.g. to
compute final value), it better would be the second definition rather than the
first.

  parent reply	other threads:[~2022-12-01 17:32 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-23 12:48 [Bug tree-optimization/107833] New: wrong code at -Os and above on x86_64-linux-gnu zhendong.su at inf dot ethz.ch
2022-11-23 13:14 ` [Bug tree-optimization/107833] wrong code at -Os and above on x86_64-linux-gnu since r12-5138-ge82c382971664d6f marxin at gcc dot gnu.org
2022-11-23 14:12 ` aldyh at gcc dot gnu.org
2022-11-23 14:17 ` marxin at gcc dot gnu.org
2022-11-23 15:07 ` aldyh at gcc dot gnu.org
2022-11-23 19:22 ` marxin at gcc dot gnu.org
2022-11-23 20:56 ` [Bug tree-optimization/107833] [12/13 Regression] " rguenth at gcc dot gnu.org
2022-12-01 16:14 ` jakub at gcc dot gnu.org
2022-12-01 16:52 ` jakub at gcc dot gnu.org
2022-12-01 17:32 ` jakub at gcc dot gnu.org [this message]
2022-12-01 19:54 ` pinskia at gcc dot gnu.org
2022-12-02  8:19 ` rguenth at gcc dot gnu.org
2022-12-02 10:16 ` jakub at gcc dot gnu.org
2022-12-02 13:24 ` rguenther at suse dot de
2022-12-02 13:55 ` rguenth at gcc dot gnu.org
2022-12-05  9:32 ` cvs-commit at gcc dot gnu.org
2022-12-12 11:20 ` [Bug tree-optimization/107833] [12 " cvs-commit at gcc dot gnu.org
2022-12-12 11:22 ` rguenth at gcc dot gnu.org

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