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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/103271] ICE in assign_stack_temp_for_type with
 -ftrivial-auto-var-init=pattern and VLAs and -mno-strict-align on riscv64
Date: Fri, 26 Nov 2021 07:16:28 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103271

--- Comment #7 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 26 Nov 2021, wilson at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103271
>=20
> Jim Wilson <wilson at gcc dot gnu.org> changed:
>=20
>            What    |Removed                     |Added
> -------------------------------------------------------------------------=
---
>                  CC|                            |wilson at gcc dot gnu.org
>=20
> --- Comment #5 from Jim Wilson <wilson at gcc dot gnu.org> ---
> SiFive doesn't support -mno-strict-align so I've never tested it.  I doub=
t that
> it works correctly, i.e. I doubt that it optimizes as intended.  I've men=
tioned
> this to other RVI members, but there hasn't been anyone other than SiFive
> actively working on upstream gcc so I don't think anyone ever looked at i=
t.  It
> shouldn't give an ICE though.
>=20
> Looking at this, it appears to be another "if only we had a movti pattern"
> issue.
>=20
> In expand_DEFERRED_INIT in internal-fn.c, in the reg_lhs =3D=3D TRUE case=
, there is
> a test
>           && have_insn_for (SET, var_mode))
> which fails because var_mode is TImode and we don't have a movti pattern.=
  The
> code calls build_zero_cst which returns a constructor with an array type.=
  We
> then call expand_assignment which gets confused as it doesn't know the si=
ze of
> the array it is copying.

That seems to be the bug - in this path we shouldn't ever create an
entity with VLA size since we do know the actual size.  But it all
is a bit awkward.=