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Subject: [Bug tree-optimization/98464] [11 Regression] ICE: tree check:
 expected class 'type', have 'exceptional' (error_mark) in
 tree_nop_conversion_p, at tree.c:12825 by r11-4637
Date: Wed, 30 Dec 2020 07:43:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98464

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|                            |rguenth at gcc dot gnu.org

--- Comment #3 from Kewen Lin <linkw at gcc dot gnu.org> ---
My commit exposed one issue in FRE. The reason why the ICE occurs is that o=
ne
SSA_NAME used in loop's nb_iterations is actually in free list.

(unsigned long) _54 - (unsigned long) v$ptr__25

    arg:0 <ssa_name 0x7ffff5549558 type <error_mark 0x7ffff54a1188>
        nothrow
        def_stmt
        version:54 in-free-list>>

I noticed that FRE already has some codes to handle loop's nb_iterations, b=
ut
there are some inconsistence which cause FRE unable to replace the one in
loop's nb_iterations but later replace all uses of _54.

When FRE is processing BB 19, it's able to replace _54 with _53 like:

  <bb 19> [local count: 789698041]:
  ...
  if (_26 !=3D v$D4172$_M_impl$D4082$_M_finish$ptr__54)
    goto <bb 28>; [89.00%]

=3D>

  <bb 19> [local count: 789698041]:
  ...
  if (_26 !=3D __new_finish$ptr__53)
    goto <bb 28>; [89.00%]

since it calls eliminate_stmt which works with def_bb instead of current bb:

    sprime =3D eliminate_avail (gimple_bb (SSA_NAME_DEF_STMT (use)), use)

while rpo_vn_valueize only works with vn_context_bb.

For this particular case, _54's def_bb is BB 13, _53's def_bb is BB 11, it'=
s ok
for dominated_by_p_w_unex check. While vn_context_bb is BB 19,
dominated_by_p_w_unex check returns false for it.=