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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/95622] [11 Regression] force_output flag on a
 variable prevents optimization  / regresses
 c-c++-common/goacc/kernels-alias-ipa-pta{-2,-4,}.c
Date: Fri, 26 Mar 2021 08:21:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95622

--- Comment #9 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 25 Mar 2021, burnus at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95622
>=20
> --- Comment #8 from Tobias Burnus <burnus at gcc dot gnu.org> ---
> I am not sure whether this is a sensible solution, but it fixes
> the issue for c-c++-common/goacc/kernels-alias-ipa-pta-2.c ...
>=20
>=20
> diff --git a/gcc/tree-ssa-structalias.c b/gcc/tree-ssa-structalias.c
> index 529ec3a5b80..c93e9b46d8d 100644
> --- a/gcc/tree-ssa-structalias.c
> +++ b/gcc/tree-ssa-structalias.c
> @@ -8132,7 +8132,7 @@ refered_from_nonlocal_fn (struct cgraph_node *node,=
 void
> *data)
>    *nonlocal_p |=3D (node->used_from_other_partition
>                   || DECL_EXTERNAL (node->decl)
>                   || TREE_PUBLIC (node->decl)
> -                 || node->force_output
> +                 || (node->force_output && !node->offloadable)
>                   || lookup_attribute ("noipa", DECL_ATTRIBUTES (node->de=
cl)));
>    return false;
>  }
> @@ -8195,7 +8195,7 @@ ipa_pta_execute (void)
>        bool nonlocal_p =3D (node->used_from_other_partition
>                          || DECL_EXTERNAL (node->decl)
>                          || TREE_PUBLIC (node->decl)
> -                        || node->force_output
> +                        || (node->force_output && !node->offloadable)
>                          || lookup_attribute ("noipa",
>                                               DECL_ATTRIBUTES (node->decl=
)));
>        node->call_for_symbol_thunks_and_aliases (refered_from_nonlocal_fn,

It's for sure incorrect since node->force_output could be set for other
reasons.  But of course the reason for the node->force_output check
is that it is set by __attribute__((used)) which means a function/variable
can be invoked/accessed by means not visible to the compiler.

As said elsewhere the "fix" is to make the offload reference visible
to IPA early enough.=