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From: "ktkachov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/109855] [14 Regression] ICE: in curr_insn_transform, at
 lra-constraints.cc:4231 unable to generate reloads for
 {aarch64_mlav4hi_vec_concatz_le} at -O1
Date: Mon, 22 May 2023 13:15:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109855

--- Comment #5 from ktkachov at gcc dot gnu.org ---
(In reply to rsandifo@gcc.gnu.org from comment #4)
> I guess the problem is that the define_subst output template has:
>=20
>   (match_operand:<VDBL> 0)
>=20
> which creates a new operand 0 with an empty predicate and constraint,
> as opposed to a (match_dup 0), which would be substituted with the
> original operand 0.  Unfortunately
>=20
>   (match_dup:<VDBL> 0)
>=20
> doesn't work as a way of inserting the original destination with
> a different mode, since the :<VDBL> is ignored.  Perhaps we should
> =E2=80=9Cfix=E2=80=9D that.  Alternatively:
>=20
>   (match_operand:<VDBL> 0 "register_operand" "=3Dw")
>=20
> should work, but probably locks us into using patterns that have one
> alternative only.

I think this approach is the most promising and probably okay for the vast
majority of cases we want to handle with these substs.=