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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/108657] [13 Regression] csmith: possible wrong
 checksum with -O3 and -ftrivial-auto-var-init=zero
Date: Wed, 15 Feb 2023 18:56:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108657

--- Comment #19 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
With the deferred stuff (why don't we DCE it for variables which are otherw=
ise
not used?), all looks fine until fre5.
In fre4 we have
  k =3D{v} {CLOBBER(eol)};
  c =3D -1;
  c =3D 1;
  foo ();
  return 0;
at the end which is reasonable, the outer loop iterates c =3D 1, c =3D 0 an=
d c =3D -1
and then c =3D 1 is stored, dse4 optimizes it to:
  k =3D{v} {CLOBBER(eol)};
  c =3D 1;
  foo ();
  return 0;
in split-path, we have in bb2
  c =3D 1;
then in one of the conditionalized bbs
  c =3D 0;
and finally still
  <bb 8> [local count: 38651690]:
  k =3D{v} {CLOBBER(eol)};
  c =3D 1;
  foo ();
  return 0;
at the end, but fre5 keeps those c =3D 1; and c =3D 0; early stores and dro=
ps the
last one.=