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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/105346] [11/12 Regression] -Wno-free-nonheap-object
 false positive (on Bison-generated grammar code)
Date: Tue, 26 Apr 2022 10:09:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105346

--- Comment #9 from rguenther at suse dot de <rguenther at suse dot de> ---
On Tue, 26 Apr 2022, jakub at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D105346
>=20
> --- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> Started with r11-5732-gdce6c58db87ebf7f4477bd3126228e73e4eeee97
> The IL at -O0 -Wall looks during waccess pass like:
> void foo ()
> {
>   char * bufp;
>   char buf[20];
>=20
>   <bb 2> :
>   bufp_2 =3D &buf;
>   if (&buf !=3D bufp_2)
>     goto <bb 3>; [INV]
>   else
>     goto <bb 4>; [INV]
>=20
>   <bb 3> :
>   __builtin_free (bufp_2);
>=20
>   <bb 4> :
>   buf =3D{v} {CLOBBER(eol)};
>   return;
>=20
> }
>=20
> So, I think the waccess pass must be walking SSA_NAME_DEF_STMT to figure =
out it
> is a free of non-heap.  Either it shouldn't do that at -O0, or it should =
only
> walk them when they are in the same bb as the free call, or it needs to b=
e able
> to detect also conditionals like the above.

It's using the ptr-query framework which discovers the bufp_2 equivalence
but doesn't notice the conditional "invalidating" it.=