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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107767] [13 Regression] switch to table
 conversion happening even though using btq is better
Date: Fri, 02 Dec 2022 15:44:15 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107767

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #10)
> Looks like a general CFG optimization if we have N forwarders to a PHI wi=
th
> the same value then we can merge them to one (it's enough to have a single
> forwarder which we can use as the remaining one even).  Note that's kind-=
of
> a reverse
> mergephi for same values.
>=20
>  PHI <a, b, c, c>
>=20
> ->
>=20
>          forwarder
>             |
>  PHI <a, b, c>
>=20
> CFG cleanup will then eventually elide forwarders into the added forwarde=
r.

Are those actually forwarder blocks though?
Doesn't the GIMPLE_PREDICT statement at the start of each one of them preve=
nt
tree_forwarder_block_p from returning true?
As a hack I've removed them manually:
FOR_EACH_BB_FN (bb, cfun)
{
gimple_stmt_iterator gsi =3D gsi_after_labels (bb);
if (!gsi_end_p (gsi) && gimple_code (gsi_stmt (gsi)) =3D=3D GIMPLE_PREDICT)
gsi_remove (&gsi, true);
}
in pass_if_to_switch::execute before return TODO_cleanup_cfg;, but that did=
n't
help.=