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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/106131] [10/11/12/13 Regression]
 -fstrict-aliasing breaks normal program that does not use any pointer or
 reference
Date: Thu, 30 Jun 2022 08:31:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106131

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is in processing

  x =3D MEM[(const struct Pair &)_11];
  _47 =3D MEM[(const int &)&x + 4];

where we when visiting the def for 'x' continue the lookup with an
effective MEM[(const struct Pair &)_11 + 4]; but that looks for a store
of TBAA 'Pair' where we then correctly determine that _7->b =3D _46;
doesn't possibly alias.

A conservative fix restoring behavior before the relevant change is to
force alias set zero (no TBAA) for the offsetted lookup.=