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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/110683] wrong code with '-O2 -fpack-struct'
Date: Sun, 16 Jul 2023 16:20:47 +0000	[thread overview]
Message-ID: <bug-110683-4-oQvfNChH2b@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-110683-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110683

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to CTC from comment #3)
> The reduced program is
> 
> # cat mss.i
> struct a {
>   char b;
>   int c;
> };
> union {
>   struct a b;
>   short c;
> } d = {8, 1};
> void main() { printf("%d\n", d.c); }

This reduced case shows that -fpacked-struct will change the layout of struct a
and nothing more. Without the option there is some padding bytes which are
zero. Also also this reduced testcase depends on the endian of the target.

Maybe the original testcase has similar issues with the unions.

  parent reply	other threads:[~2023-07-16 16:20 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-16 15:07 [Bug c/110683] New: wrong code with '-O2' and specific optimizations 19373742 at buaa dot edu.cn
2023-07-16 15:07 ` [Bug c/110683] " 19373742 at buaa dot edu.cn
2023-07-16 15:11 ` 19373742 at buaa dot edu.cn
2023-07-16 15:44 ` [Bug c/110683] wrong code with '-O2 -fpack-struct' 19373742 at buaa dot edu.cn
2023-07-16 16:20 ` pinskia at gcc dot gnu.org [this message]
2023-07-16 17:02 ` pinskia at gcc dot gnu.org
2023-07-17  7:27 ` rguenth at gcc dot gnu.org

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