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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107206] Bogus -Wuninitialized in
 std::optional
Date: Sun, 16 Oct 2022 17:27:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107206

--- Comment #6 from rguenther at suse dot de <rguenther at suse dot de> ---
> Am 14.10.2022 um 18:53 schrieb jamborm at gcc dot gnu.org <gcc-bugzilla@g=
cc.gnu.org>:
>=20
> =EF=BB=BFhttps://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107206
>=20
> --- Comment #5 from Martin Jambor <jamborm at gcc dot gnu.org> ---
> I believe this is fallout from the fix to PR 92706 where we started
> propagating accesses across assignments also from LHS to RHS and
> because everything is totally flow-insensitive, we have an access
> representing:
>=20
>   MEM[(union _StorageD.10576 *)&D.11678]._M_valueD.10616 =3D 1;
>=20
> which gets propagated across:
>=20
>  zD.11527.yD.11476.oD.11384 =3D D.11678;
>=20
> but this then triggers the LHS->RHS propagation across:
>=20
>  MEM[(struct YD.10174 *)&zD.11527].oD.11384 =3D MEM[(const struct YD.10174
> &)&D.11546].oD.11384;
>=20
> So another reason to re-invent SRA from scratch.

Yes

>  Apart from that, I
> don't have a good solution except for adding another flag to mark
> accesses that are result of LHS->RHS propagation and ignore them if
> their base did not get totally scalarized because in the PR they were
> added basically to prevent bad total scalarization.  But of course it
> is rather another band-aid than a real fix, but it seems to work for
> this case:
>=20
> diff --git a/gcc/tree-sra.cc b/gcc/tree-sra.cc
> index 1a3e12f18cc..6cbeddfc548 100644
> --- a/gcc/tree-sra.cc
> +++ b/gcc/tree-sra.cc
> @@ -260,6 +260,9 @@ struct access
>=20
>   /* Should TREE_NO_WARNING of a replacement be set?  */
>   unsigned grp_no_warning : 1;
> +
> +  /* Result of propagation accross link from LHS to RHS.  */
> +  unsigned grp_result_of_prop_from_lhs : 1;
> };
>=20
> typedef struct access *access_p;
> @@ -2532,6 +2535,9 @@ analyze_access_subtree (struct access *root, struct
> access *parent,
>   if (allow_replacements && expr_with_var_bounded_array_refs_p (root->exp=
r))
>     allow_replacements =3D false;
>=20
> +  if (!totally && root->grp_result_of_prop_from_lhs)
> +    allow_replacements =3D false;
> +
>   for (child =3D root->first_child; child; child =3D child->next_sibling)
>     {
>       hole |=3D covered_to < child->offset;
> @@ -2959,6 +2965,7 @@ propagate_subaccesses_from_lhs (struct access *lacc,
> struct access *racc)
>          struct access *new_acc
>            =3D create_artificial_child_access (racc, lchild, norm_offset,
>                                              true, false);
> +         new_acc->grp_result_of_prop_from_lhs =3D 1;
>          propagate_subaccesses_from_lhs (lchild, new_acc);
>        }
>       else

LGTM=