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From: "roger at nextmovesoftware dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111519] [13/14 Regression] Wrong code at -O3
 on x86_64-linux-gnu since r13-455-g1fe04c497d
Date: Mon, 09 Oct 2023 22:05:50 +0000
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X-Bugzilla-Component: tree-optimization
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X-Bugzilla-Keywords: wrong-code
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111519

--- Comment #2 from Roger Sayle <roger at nextmovesoftware dot com> ---
Complicated.  Things have gone wrong before the strlen pass which is given:

  _73 =3D e;
  _72 =3D *_73;
...
  *_73 =3D prephitmp_23;
  d =3D _72;

Here the assignment to *_73 overwrites the value of f (at *e) which then
invalidates the use of _72 resulting in the wrong value for d.  But figuring
out which pass is at fault (perhaps complete loop unrolling?) is tricky.=