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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c/114597] [GCC-14] Miscompilation of pointer assignment with
 inline assembly
Date: Fri, 05 Apr 2024 06:03:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114597

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #4 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to wierton from comment #3)
> Thanks a lot, I have checked it out.
>=20
> I'm still somewhat confused. Does the difference in compilation stem from
> GCC interpreting "=3Dm" and "=3Dr" differently, leading it to assume that=
 once
> "n.p" is declared as an output operand without matched input declaration
> (eg. "=3Dm" expects "m", "=3Dr" expects "r"), its value is expected to ch=
ange?
>=20
> ```
> asm("":"=3Dm"(n.p):"r"(n.p)); // n.p is expected to change
> asm("":"=3Dr"(n.p):"r"(n.p)); // n.p can retain its value
> asm("":"=3Dm"(n.p):"m"(n.p)); // n.p can retain its value
> ```

I believe the second form is still incorrect and it just works by luck.  To
ensure it work you have to do:

asm("mov %1,%0":"=3Dr"(n.p):"r"(n.p));

Or

asm("":"+r"(n.p));

Not so sure about the third form.=