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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102546] [12 Regregression] Missed Dead Code
 Elimination regression (trunk vs 11.2.0) at -O3
Date: Fri, 01 Oct 2021 06:30:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102546

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Aldy Hernandez from comment #2)
> By VRP1 we seem to be calculating the following:
>=20
> (f_8 << f_8) && (f_8 =3D=3D 0)
>=20
> This would fold to false, which would elide the foo():
>=20
>  <bb 7> [local count: 59055800]:
>   b =3D 0;
>   _3 =3D f_8 << f_8;
>   _4 =3D (char) _3;
>   _5 =3D (int) _4;
>   if (_4 > 0)
>     goto <bb 8>; [64.06%]
>   else
>     goto <bb 10>; [35.94%]
>=20
>   <bb 8> [local count: 34842922]:
>   if (f_8 =3D=3D 0)
>     goto <bb 9>; [71.10%]
>   else
>     goto <bb 10>; [28.90%]
>=20
>   <bb 9> [local count: 12809203]:
>   foo ();

I think it's similar to in the other PR, with old EVRP when visiting BB 8
we pushed [1, +INF] as the global range for _4, then supposedly ranger
manages to evaluate f_8 =3D=3D 0 with its backward infering somehow.

We no longer do this "path sensitive" adjustment of (global) ranges since
you removed the EVRP DOM walk algorithm.=