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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/114800] redundant set-zero when initiate a
 struct
Date: Mon, 22 Apr 2024 23:33:03 +0000
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X-Bugzilla-Component: tree-optimization
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X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114800

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-04-22
     Ever confirmed|0                           |1
          Component|rtl-optimization            |tree-optimization

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  tr =3D {};
  tr.f1 =3D 1;
  tr.f3 =3D 3;
  foo (&tr);

We are able to do DSE for tr.f0 and tr.f2 but not the original tr =3D {}.


Note there is some slightly difference IR from the front-ends (C does not
produce the `=3D {};` part while C++ does)

C++ front-end (before gimplification):
  <<cleanup_point   struct thresh_restart tr =3D {.f1=3D1, .f2=3D2, .f3=3D3=
};>>;
  <<cleanup_point <<< Unknown tree: expr_stmt
    tr.f0 =3D b >>>>>;

C front-end:
    struct thresh_restart tr =3D {.f0=3Db, .f1=3D1, .f2=3D2, .f3=3D3};

Note this is the DECL_EXPR here.=