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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/100934] [9/10/11/12 Regression] wrong code at
 -O3 during unrolling since r9-6299
Date: Mon, 14 Jun 2021 12:59:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100934

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #8)
> --- a/gcc/tree-ssa-threadupdate.c
> +++ b/gcc/tree-ssa-threadupdate.c
> @@ -2379,12 +2379,15 @@ jump_thread_path_registry::duplicate_thread_path
> (edge entry,
>       missuses of the functions.  I.e. if you ask to copy something weird,
>       it will work, but the state of structures probably will not be
>       correct.  */
> +  bool loop_header_duplicated =3D false;
>    for (i =3D 0; i < n_region; i++)
>      {
>        /* We do not handle subloops, i.e. all the blocks must belong to t=
he
>          same loop.  */
>        if (region[i]->loop_father !=3D loop)
>         return false;
> +      if (region[i]->loop_father =3D=3D loop)
> +       loop_header_duplicated =3D true;

The if right above this returns false if loop_father is not loop, so
wouldn't be loop_header_duplicated =3D=3D true whenever n_region !=3D 0 (or=
 always)?=