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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110891] [14 Regression] Dead Code Elimination
 Regression since r14-2674-gd0de3bf9175
Date: Sat, 26 Aug 2023 00:06:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110891

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> One thing I noticed (I don't know if causes the missed optimization) is t=
hat
> we have before PRE:
> ```
>   <bb 4> [local count: 1073531371]:
>   if (a.0_1 !=3D 0)
>     goto <bb 6>; [50.00%]
>   else
>     goto <bb 5>; [50.00%]
>=20
>   <bb 5> [local count: 536765686]:
>   if (_28 =3D=3D &d)
>     goto <bb 9>; [30.00%]
>   else
>     goto <bb 7>; [70.00%]
>=20
>   <bb 6> [local count: 536765685]:
>   if (_28 =3D=3D &d)
>     goto <bb 9>; [30.00%]
>   else
>     goto <bb 7>; [70.00%]
> ```
> Which obvious should just be `if (_28 =3D=3D &d) goto bb9; else goto bb7;=
` and
> not check `a.0_1` at all.

I wonder if ifcombine could optimize that instead of requiring PRE. I think
that might even fix the issue too.=