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From: "kungfujesus06 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/108498] ppc64 big endian generates uninitialized
 reads with -fstore-merging
Date: Mon, 23 Jan 2023 15:48:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D108498

--- Comment #6 from Adam Stylinski <kungfujesus06 at gmail dot com> ---
(In reply to Richard Biener from comment #5)
> maybe a stack sharing issue?  Can you try -fstack-reuse=3Dnone?

So that does fix it, at least when the struct is backed by the stack.  And =
also
valgrind is no longer finding uninitialized memory being used:

adam@g5box ~ $ gcc -O2 -fstack-reuse=3Dnone bug_rep2.c -o test.out
adam@g5box ~ $ ./test.out=20
sat? =3D 0

adam@g5box ~ $ valgrind ./test.out
=3D=3D26982=3D=3D Memcheck, a memory error detector
=3D=3D26982=3D=3D Copyright (C) 2002-2022, and GNU GPL'd, by Julian Seward =
et al.
=3D=3D26982=3D=3D Using Valgrind-3.20.0 and LibVEX; rerun with -h for copyr=
ight info
=3D=3D26982=3D=3D Command: ./test.out
=3D=3D26982=3D=3D=20
sat? =3D 0
=3D=3D26982=3D=3D=20
=3D=3D26982=3D=3D HEAP SUMMARY:
=3D=3D26982=3D=3D     in use at exit: 0 bytes in 0 blocks
=3D=3D26982=3D=3D   total heap usage: 1 allocs, 1 frees, 1,024 bytes alloca=
ted
=3D=3D26982=3D=3D=20
=3D=3D26982=3D=3D All heap blocks were freed -- no leaks are possible
=3D=3D26982=3D=3D=20
=3D=3D26982=3D=3D For lists of detected and suppressed errors, rerun with: =
-s
=3D=3D26982=3D=3D ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 fr=
om 0)

Not sure what it might do if backed by the heap, but the code is written in=
 a
way that it initializes the struct on the stack, anyway.=