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From: "manu at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/109123] Bogus warning: pointer used after 'realloc' -Wuse-after-free with -O2
Date: Tue, 14 Mar 2023 10:22:02 +0000 [thread overview]
Message-ID: <bug-109123-4-fIQFPh4FM2@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109123-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109123
--- Comment #6 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #5)
> Is this code motion valid? Is there any point in the middle-end that checks
> the validity of the pointer beyond a free/realloc?
>
> If there is a point where such check happens, perhaps it would be a good
> place to apply no_warning attribute to the pointer.
Answering to myself: It seems the dispute is over the meaning of "use".
According to the middle-end and for the purposes of realloc/free, "use" means
dereference, while for the warning "use" is any read of the value.
By only warning for dereferences, the warning may miss some obvious cases like:
tmp = realloc(v->_begin, sizeof(double) * n);
v->_end = v->_begin + old_size;
v->_begin = tmp;
However, given that the assumption of the middle-end has worked for decades,
and it will be not possible to fix it, warning only for dereferences (or moving
warning for value-uses to a level not enabled by -Wall) would seem more
user-friendly.
next prev parent reply other threads:[~2023-03-14 10:22 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-14 9:41 [Bug c/109123] New: Bogus warning: pointer used after 'realloc' -Wuse-after-free manu at gcc dot gnu.org
2023-03-14 9:44 ` [Bug c/109123] Bogus warning: pointer used after 'realloc' -Wuse-after-free with -O2 manu at gcc dot gnu.org
2023-03-14 9:48 ` manu at gcc dot gnu.org
2023-03-14 9:55 ` rguenth at gcc dot gnu.org
2023-03-14 10:00 ` manu at gcc dot gnu.org
2023-03-14 10:03 ` manu at gcc dot gnu.org
2023-03-14 10:22 ` manu at gcc dot gnu.org [this message]
2023-03-14 12:17 ` rguenth at gcc dot gnu.org
2023-03-14 12:51 ` manu at gcc dot gnu.org
2023-03-15 8:16 ` rguenth at gcc dot gnu.org
2023-03-16 7:30 ` cvs-commit at gcc dot gnu.org
2023-03-16 7:31 ` [Bug c/109123] [12 Regression] " rguenth at gcc dot gnu.org
2023-05-08 12:26 ` [Bug tree-optimization/109123] " rguenth at gcc dot gnu.org
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