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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/112657] [13/14 Regression] missed
 optimization: cmove not used with multiple returns
Date: Wed, 22 Nov 2023 09:28:40 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112657

--- Comment #4 from Uro=C5=A1 Bizjak <ubizjak at gmail dot com> ---
(In reply to Uro=C5=A1 Bizjak from comment #3)
> (In reply to Andrew Pinski from comment #2)
>=20
> > Someone will have to debug ifcvt.cc to see why it fails on x86_64 but w=
orks
> > on aarch64.  Note there are some new changes to ifcvt.cc in review which
> > might improve this, though I am not sure.
>=20
> x86_64 targetm.noce_conversion_profitable_p returns false for:

Actually, the cost function goes to default_noce_conversion_profitable_p,
where:

(gdb) p cost
$1 =3D 16
(gdb) p if_info->original_cost=20
$2 =3D 8
(gdb) p if_info->max_seq_cost=20
$3 =3D 0

For some reason, max_seq_cost remains zero, while on aarch64:

(gdb) p cost
$2 =3D 12
(gdb) p if_info->original_cost
$3 =3D 8
(gdb) p if_info->max_seq_cost
$4 =3D 12

So, x86_64 returns false from the default cost function:

  /* When compiling for size, we can make a reasonably accurately guess
     at the size growth.  When compiling for speed, use the maximum.  */
  return speed_p && cost <=3D if_info->max_seq_cost;=