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From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111760] risc-v regression: COND_LEN_*
 incorrect fold/simplify in middle-end
Date: Tue, 10 Oct 2023 22:08:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111760

--- Comment #5 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
(In reply to Robin Dapp from comment #2)
> https://gcc.gnu.org/pipermail/gcc-patches/2023-September/629904.html
>=20
> prevents the wrong code but still leaves us with a redundant negation (and
> it is not the only missed optimization of that kind):
>=20
>   vect_neg_xi_14.4_23 =3D -vect_xi_13.3_22;
>   vect_res_2.5_24 =3D .COND_LEN_ADD ({ -1, ... }, vect_res_1.0_17,
> vect_neg_xi_14.4_23, vect_res_1.0_17, _29, 0);
>=20
> That's because my "hackaround" doesn't recognize a valueized sequence
> _30 =3D vect_res_1.0_17 - vect_xi_13.3_22;
>=20
> Of course I could (reverse valueize) recognize that again and convert it =
to
> a COND_LEN... but that doesn't seem elegant at all.  There must be a simp=
ler
> way that I'm missing entirely right now.  That said, converting the last
> statement of such a sequence should be sufficient?

Yeah. That's what I want to point it out. Your patch will disable the
optimization
I made in GIMPLE_FOLD for COND_LEN_xxx.

I am not sure how to fix it, I think we need Richi's help for that since he
knows
the GIMPLE FOLD stuff the best.=