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From: "lin1.hu at intel dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/114700] Front-end optimization generates wrong code with -fsanitize=undefined
Date: Fri, 12 Apr 2024 06:44:04 +0000 [thread overview]
Message-ID: <bug-114700-4-0EeewLsj4s@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114700-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114700
--- Comment #11 from lin1.hu at intel dot com ---
(In reply to Richard Biener from comment #9)
> That that GCC doesn't promise that -ftrapv preserves all overflows and
> traps, it merely guarantees that all overflows that actually happen trap.
> So GCC is fine to contract some expressions where the overall number of
> overflows can only
> decrease.
>
> That's not a bug with -ftrapv.
>
> It is considered a bug with -fsanitize=undefined though.
I think it doesn't mean that's not a bug with -ftrapv, it should preserve all
overflow traps. Because it doesn't work, we use -fsanitize=undefined instead of
it.
refer: Gcc's trapv is known not always to work correctly.
The current behavior is correct for -fsanitize=undefined, because the integer
signed overflow is well-defined, so GCC can eliminate some variables. I just
think GCC can optimize `z = c - y - c + a + y - b` to `z = a - b`. But it
doesn't mean is a bug for -fsanitize=undefined.
next prev parent reply other threads:[~2024-04-12 6:44 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-12 2:22 [Bug c/114700] New: Front-end optimization generates wrong code with -ftrapv lin1.hu at intel dot com
2024-04-12 2:34 ` [Bug middle-end/114700] " pinskia at gcc dot gnu.org
2024-04-12 2:47 ` lin1.hu at intel dot com
2024-04-12 2:47 ` lin1.hu at intel dot com
2024-04-12 3:21 ` pinskia at gcc dot gnu.org
2024-04-12 3:26 ` pinskia at gcc dot gnu.org
2024-04-12 3:35 ` pinskia at gcc dot gnu.org
2024-04-12 3:53 ` lin1.hu at intel dot com
2024-04-12 3:56 ` lin1.hu at intel dot com
2024-04-12 5:56 ` rguenth at gcc dot gnu.org
2024-04-12 6:33 ` [Bug middle-end/114700] Front-end optimization generates wrong code with -fsanitize=undefined xry111 at gcc dot gnu.org
2024-04-12 6:44 ` lin1.hu at intel dot com [this message]
2024-04-12 7:12 ` lin1.hu at intel dot com
2024-04-12 7:14 ` xry111 at gcc dot gnu.org
2024-04-12 8:51 ` lin1.hu at intel dot com
2024-04-12 10:15 ` [Bug middle-end/114700] middle-end " jakub at gcc dot gnu.org
2024-04-12 10:25 ` jakub at gcc dot gnu.org
2024-04-15 3:43 ` [Bug middle-end/114700] middle-end optimization generates causes -fsanitize=undefined not to happen in some cases lin1.hu at intel dot com
2024-04-15 6:49 ` jakub at gcc dot gnu.org
2024-04-15 7:44 ` lin1.hu at intel dot com
2024-04-17 1:50 ` lin1.hu at intel dot com
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