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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107172] [13 Regression] wrong code with "-O1 -ftree-vrp"
 on x86_64-linux-gnu since r13-1268-g8c99e307b20c502e
Date: Thu, 20 Oct 2022 19:03:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107172

--- Comment #44 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Segher Boessenkool from comment #42)
> (In reply to H.J. Lu from comment #41)
> > (In reply to Segher Boessenkool from comment #40)
> > > Let me repeat: A const_int cannot be assigned to a MODE_CC.  It has no
> > > meaning.
> > > This is invalid RTL.  If it ever works, or worked, that is an acciden=
t.
> >=20
> > Can we make it to work with a target hook? It will allow more backed
> > optimizations.
>=20
> No, you cannot.  A lot of generic code will not work with your special
> re-interpretation of basic RTL rules.  Just write correct code in your
> backend, it is not hard.

Does it look correct:

(set (reg:CCC FLAGS_REG)
     (unspec:CCC [(match_dup 1) (const_int 0)] UNSPEC_CC_NE))=