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From: "qinzhao at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/102285] New flag -ftrivial-auto-var-init=zero causes
 crash in pr82421.c
Date: Mon, 04 Oct 2021 20:34:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102285

--- Comment #26 from qinzhao at gcc dot gnu.org ---
(In reply to qinzhao from comment #25)
> (In reply to Richard Biener from comment #22)
> > Hmm, my proposed patch seems to work.  I've adjusted it to not regress
> > previously correctly handled cases and will test it fully.
>=20
> I guess the reason for it worked for you because you tested it after the
> patch for 102587?
>=20
> --- a/gcc/internal-fn.c
> +++ b/gcc/internal-fn.c
> @@ -3035,7 +3035,8 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
>        /* Expand this memset call.  */
>        expand_builtin_memset (m_call, NULL_RTX, TYPE_MODE (var_type));
>      }
> -  else
> +  /* ???  Deal with poly-int sized registers.  */
> +  else if (tree_fits_uhwi_p (TYPE_SIZE_UNIT (var_type)))
>      {
>        /* If this variable is in a register, use expand_assignment might
>          generate better code.  */

because for the following IR:

 MEM[(int[0:D.1993] *)&fb.3] =3D .DEFERRED_INIT (16, 2, 1);

The "var_type" of the LHS is "int[0:D.1993]", which is not an integer const=
ant
(even though the type for fb.3 should be the new type for the new temporary
variable char[16]).=20

As a result, the new added check
> +  /* ???  Deal with poly-int sized registers.  */
> +  else if (tree_fits_uhwi_p (TYPE_SIZE_UNIT (var_type)))

excluded it from expanding through expand_assign.=