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From: "akim.demaille at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/98753] -Wfree-nonheap-object on unreachable code
 with -O0
Date: Wed, 20 Jan 2021 17:34:54 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98753

--- 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 =3D &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 sho=
uld
not impossible in that precise case).  But it just emphasizes again that the
*wording* is wrong.

> warning: =E2=80=98void free(void*)=E2=80=99 called on unallocated object =
=E2=80=98yyssa=E2=80=99

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

Cheers!=