[Bug tree-optimization/47738] ICE: verify_ssa failed: no immediate_use list with -O3 -fno-tree-vectorize

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47738

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at gcc dot gnu.org

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-02-16 12:32:43 UTC ---
We are removing the definition of D.2738_12 in remove_stmt but the PHI
use which was created by tree_transform_and_unroll_loop is not in the
list of stmts to be removed. It is created by
PHI copying of tree_transform_and_unroll_loop

      phi_rest = create_phi_node (new_init, rest);
      SSA_NAME_DEF_STMT (new_init) = phi_rest;

      add_phi_arg (phi_rest, init, precond_edge, UNKNOWN_LOCATION);
      add_phi_arg (phi_rest, next, new_exit, UNKNOWN_LOCATION);
      SET_USE (op, new_init);
    }

  remove_path (exit);

>From tree_transform_and_unroll_loop we call execute_pred_commoning_cbck

  /* Transform the loop.  */
  if (transform)
    (*transform) (loop, data);

which also does the stmt removal, then we verify SSA form in

  ok = gimple_duplicate_loop_to_header_edge
          (loop, loop_latch_edge (loop), factor - 1,
           wont_exit, new_exit, &to_remove, DLTHE_FLAG_UPDATE_FREQ);

which fails.

I wonder if the simplest fix is to kill that stmt removal code as it looks
like unconditionally removing the loads isn't going to work for the
peeled iterations.

Zdenek?