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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107274] Incorrect -Wuninitialized on indexed
 initialization
Date: Mon, 17 Oct 2022 08:00:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107274

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |24639
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
No, the issue is that you are accessing 8 bytes on the read and thus the
padding you access that way is not initialized.  Use *(unsigned int)b and t=
he
diagnostic goes away.

[internally GCC doesn't consider an indirect load of size 8 ever aliasing
a store to a 4 byte object - otherwise we wouldn't diagnose a partial
uninit value -- like

void
example(unsigned long val)
{
        char b[8];

        b[0] =3D val;
        b[1] =3D val >> 8;
        b[2] =3D val >> 16;
        b[3] =3D val >> 24;

        val =3D *(unsigned long *)b;
}

which isn't diagnosed]


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D24639
[Bug 24639] [meta-bug] bug to track all Wuninitialized issues=