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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102902] [12 Regression] -O3 produces code
 that uses an uninitialized variable but originally was not used by r12-3876
Date: Mon, 25 Oct 2021 08:57:41 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102902

--- Comment #4 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
(In reply to Martin Li=C5=A1ka from comment #3)
> I guess fixed with:
>=20
> commit aa15952d646fd5dd569fce287b719a737ae66e4f (HEAD -> master,
> origin/trunk, origin/master, origin/HEAD)
> Author: Richard Biener <rguenther@suse.de>
> Date:   Mon Oct 25 09:33:15 2021 +0200
>=20
>     tree-optimization/102920 - fix PHI VN with undefined args
>=20=20=20=20=20
>     This fixes a latent issue exposed by now allowing VN_TOP in PHI
>     arguments.  We may only use optimistic equality when merging values on
>     different edges, not when merging values on the same edge - in partic=
ular
>     we may not choose the undef value on any edge when there's a not undef
>     value as well.
>=20=20=20=20=20
>     2021-10-25  Richard Biener  <rguenther@suse.de>
>=20=20=20=20=20
>             PR tree-optimization/102920
>             * tree-ssa-sccvn.h (expressions_equal_p): Add argument
>             controlling VN_TOP matching behavior.
>             * tree-ssa-sccvn.c (expressions_equal_p): Likewise.
>             (vn_phi_eq): Do not optimistically match VN_TOP.
>=20=20=20=20=20
>             * gcc.dg/torture/pr102920.c: New testcase.

Sorry, wrong PR.=