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From: "segher at gcc dot gnu.org" <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: Sat, 15 Oct 2022 14:53:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107172

--- Comment #33 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to H.J. Lu from comment #32)
> > There is no actual comparison with 0, that is just notation.
>=20
> True.  But simplify-rtx.cc simplifies
>=20
> (ltu (reg 17) (const_int 0))
>=20
> to false when reg 17 is set.

Is set?  What does that even mean?  Is set to what?

> Use the actual comparison isn't issue.  The issue is how
>=20
> (ltu (reg 17) (const_int 0))
>=20
> should be simplified when reg 17 is known to be set.

You need to look at the setter.  It cannot be simplified otherwise.=