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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/106922] [12 Regression] Bogus uninitialized
 warning on boost::optional<<std::vector<std::string>>>, missed FRE
Date: Mon, 17 Oct 2022 13:10:29 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106922

--- Comment #28 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-12 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:e8d5f3a1b5a5839cb1db57d6f6766469cc4f8747

commit r12-8835-ge8d5f3a1b5a5839cb1db57d6f6766469cc4f8747
Author: Richard Biener <rguenther@suse.de>
Date:   Wed Sep 21 13:52:56 2022 +0200

    tree-optimization/106922 - missed FRE/PRE

    The following enhances the store-with-same-value trick in
    vn_reference_lookup_3 by not only looking for

      a =3D val;
      *ptr =3D val;
      .. =3D a;

    but also

      *ptr =3D val;
      other =3D x;
      .. =3D a;

    where the earlier store is more than one hop away.  It does this
    by queueing the actual value to compare until after the walk but
    as disadvantage only allows a single such skipped store from a
    constant value.

    Unfortunately we cannot handle defs from non-constants this way
    since we're prone to pick up values from the past loop iteration
    this way and we have no good way to identify values that are
    invariant in the currently iterated cycle.  That's why we keep
    the single-hop lookup for those cases.  gcc.dg/tree-ssa/pr87126.c
    would be a testcase that's un-XFAILed when we'd handle those
    as well.

            PR tree-optimization/106922
            * tree-ssa-sccvn.cc (vn_walk_cb_data::same_val): New member.
            (vn_walk_cb_data::finish): Perform delayed verification of
            a skipped may-alias.
            (vn_reference_lookup_pieces): Likewise.
            (vn_reference_lookup): Likewise.
            (vn_reference_lookup_3): When skipping stores of the same
            value also handle constant stores that are more than a
            single VDEF away by delaying the verification.

            * gcc.dg/tree-ssa/ssa-fre-100.c: New testcase.
            * g++.dg/tree-ssa/pr106922.C: Adjust.

    (cherry picked from commit 9baee6181b4e427e0b5ba417e51424c15858dce7)=