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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
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 08:45:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102902

--- Comment #3 from Martin Li=C5=A1ka <marxin at gcc dot gnu.org> ---
I guess fixed with:

commit aa15952d646fd5dd569fce287b719a737ae66e4f (HEAD -> master, origin/tru=
nk,
origin/master, origin/HEAD)
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Oct 25 09:33:15 2021 +0200

    tree-optimization/102920 - fix PHI VN with undefined args

    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 particul=
ar
    we may not choose the undef value on any edge when there's a not undef
    value as well.

    2021-10-25  Richard Biener  <rguenther@suse.de>

            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.

            * gcc.dg/torture/pr102920.c: New testcase.=