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From: "akim.demaille at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/98753] -Wfree-nonheap-object on unreachable code with -O0
Date: Wed, 20 Jan 2021 17:34:54 +0000	[thread overview]
Message-ID: <bug-98753-4-a8BYPp2WPk@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-98753-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98753

--- Comment #8 from Akim Demaille <akim.demaille at gmail dot com> ---
Hi Richard,

(In reply to Richard Biener from comment #3)
> The issue is that we isolate a path that is impossible to take but on that
> path we have p = &foo; free (p); and thus a "proved" mistake.  But in
> reality it is guarded by an effective if (false) condition.  So it's not as
> simple as you think.

Point taken, thanks (though I'm not sure I understand why it would explore
branches below an 'if (false)', but I definitely don't know the details).

> (we also emit diagnostics on function bodies we do not
> know are actually never called)

I will not dispute that this is a hard job (I was just pointing that it should
not impossible in that precise case).  But it just emphasizes again that the
*wording* is wrong.

> warning: ‘void free(void*)’ called on unallocated object ‘yyssa’

This is plain false.  Free is provably *never* called with yyssa.  The wording
should stop being so affirmative, so that the users don't get the wrong
impression.

Cheers!

  parent reply	other threads:[~2021-01-20 17:34 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-19 20:18 [Bug c++/98753] New: -Wfree-nonheap-object on Bison generated code foss at grueninger dot de
2021-01-19 20:55 ` [Bug c++/98753] " msebor at gcc dot gnu.org
2021-01-20  5:22 ` akim.demaille at gmail dot com
2021-01-20  7:31 ` rguenth at gcc dot gnu.org
2021-01-20  7:40 ` foss at grueninger dot de
2021-01-20 16:48 ` msebor at gcc dot gnu.org
2021-01-20 17:00 ` foss at grueninger dot de
2021-01-20 17:34 ` [Bug middle-end/98753] -Wfree-nonheap-object on unreachable code with -O0 msebor at gcc dot gnu.org
2021-01-20 17:34 ` akim.demaille at gmail dot com [this message]
2021-01-20 17:40 ` akim.demaille at gmail dot com
2021-01-26 19:37 ` slyfox at gcc dot gnu.org
2021-01-29 11:29 ` boris at kolpackov dot net
2021-01-29 11:30 ` boris at kolpackov dot net
2021-01-29 11:30 ` boris at kolpackov dot net
2021-01-29 11:36 ` boris at kolpackov dot net
2021-01-29 16:48 ` msebor at gcc dot gnu.org
2024-01-02 16:08 ` stefan at bytereef dot org

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