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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/114203] [13/14 Regression] Miscompilation: A
 possible miscompilation in GCC 13 and 14 with option -Os
Date: Mon, 04 Mar 2024 09:36:40 +0000
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X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: needs-bisection, wrong-code
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Message-ID: <bug-114203-4-GMDGnX14NO@http.gcc.gnu.org/bugzilla/>
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114203

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot =
gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
  (set_nb_iterations_in_loop =3D b_3(D) !=3D 0 ? (unsigned int) (32 - __bui=
ltin_clz
((unsigned int) b_3(D))) : 24))

The issue is for prec <=3D i_prec we do

     call =3D build_call_expr (fn, 1, src);
      if (define_at_zero)
        {
          tree is_zero =3D fold_build2 (NE_EXPR, boolean_type_node, src,
                                      build_zero_cst (TREE_TYPE (src)));
          call =3D fold_build3 (COND_EXPR, integer_type_node, is_zero, call,
                              build_int_cst (integer_type_node, prec));
        }

      if (leading && prec < i_prec)
        call =3D fold_build2 (MINUS_EXPR, integer_type_node, call,
                            build_int_cst (integer_type_node, i_prec - prec=
));

but that's the wrong way around, 'define_at_zero' should happen after the
adjustment for leading.=