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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/104322] New: Dead code in gcc/tree-vect-loop.cc
Date: Tue, 01 Feb 2022 10:03:56 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D104322

            Bug ID: 104322
           Summary: Dead code in gcc/tree-vect-loop.cc
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: rguenth at gcc dot gnu.org
  Target Milestone: ---

I noticed the following dead code:
gcc/tree-vect-loop.cc:6643


  if (STMT_VINFO_DEF_TYPE (stmt_info) =3D=3D vect_reduction_def)
    stmt_info =3D vect_stmt_to_vectorize (STMT_VINFO_REDUC_DEF (stmt_info));
  else
    {
      gcc_assert (STMT_VINFO_DEF_TYPE (stmt_info)
                  =3D=3D vect_double_reduction_def);
      use_operand_p use_p;
      gimple *use_stmt;
      bool res =3D single_imm_use (gimple_phi_result (stmt_info->stmt),
                                 &use_p, &use_stmt);
      gcc_assert (res);
      phi_info =3D loop_vinfo->lookup_stmt (use_stmt);
      stmt_info =3D vect_stmt_to_vectorize (STMT_VINFO_REDUC_DEF (phi_info)=
);
    }

  /* PHIs should not participate in patterns.  */
  gcc_assert (!STMT_VINFO_RELATED_STMT (phi_info));
  gphi *reduc_def_phi =3D as_a <gphi *> (phi_info->stmt);

  /* Verify following REDUC_IDX from the latch def leads us back to the PHI
     and compute the reduction chain length.  Discover the real
     reduction operation stmt on the way (stmt_info and slp_for_stmt_info).=
  */
  tree reduc_def
    =3D PHI_ARG_DEF_FROM_EDGE (reduc_def_phi,
                             loop_latch_edge
                               (gimple_bb (reduc_def_phi)->loop_father));
  unsigned reduc_chain_length =3D 0;
  bool only_slp_reduc_chain =3D true;
  stmt_info =3D NULL;

As seen the 2 assignments to stmt_info are dead.=