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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
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107833

--- 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 t=
o 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.=