From: Jonathan Wakely <jwakely.gcc@gmail.com>
To: Jonny Grant <jg@jguk.org>
Cc: Xi Ruoyao <xry111@xry111.site>, gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: std::string add nullptr attribute
Date: Mon, 20 Feb 2023 19:35:41 +0000 [thread overview]
Message-ID: <CAH6eHdSF_8xzH4JHeOnTaEMaMhU6JYVPz0oqGX8pGZWhBT83UQ@mail.gmail.com> (raw)
In-Reply-To: <241687c0-8dca-3c85-84e9-cfab85536324@jguk.org>
[-- Attachment #1: Type: text/plain, Size: 1572 bytes --]
On Mon, 20 Feb 2023, 19:21 Jonny Grant, <jg@jguk.org> wrote:
>
>
> On 20/02/2023 13:44, Jonathan Wakely wrote:
> > On Mon, 20 Feb 2023 at 12:59, Xi Ruoyao <xry111@xry111.site> wrote:
> >>
> >> On Mon, 2023-02-20 at 11:30 +0000, Jonny Grant wrote:
> >>
> >>> Thank you for the suggestion, I gave that nonnull attribute a try, but
> >>> it doesn't appear to warn for this example.
> >>>
> >>> https://godbolt.org/z/boqTj6oWE
> >>
> >> Ouch... The optimizer inlined make_std_string so both -Wnonnull and -
> >> fanalyzer fails to catch the issue here.
> >>
> >> Adding noipa attribute for make_std_string will work, but will also
> >> cause the generated code stupidly slow. Maybe:
> >>
> >> #ifdef WANT_DIAGNOSTIC
> >> #define MAKE_STD_STRING_ATTR __attribute__ ((noipa, nonnull))
> >> #else
> >> #define MAKE_STD_STRING_ATTR
> >> #endif
> >>
> >> std::string make_std_string(const char * const str)
> MAKE_STD_STRING_ATTR;
> >>
> >> It still looks very stupid though.
> >>
> >>> Feels useful to get build warnings if compiler knows nullptr is going
> >>> to be dereferenced, as clang does.
> >>
> >> The problem is in this case nullptr is not dereferenced, at all. So if
> >> we want a warning here we'll have to invent some new __builtin or
> >> __attribute__ to give the compiler a hint. AFAIK there is no such
> >> facility now.
> >
> > I think __attribute__((access(read_only, 1))) should do it.
>
> I tried here, but no luck, is this example the way you mean? gcc trunk.
>
I don't mean it does do it, I mean it should do it.
https://godbolt.org/z/haq18bvPP
>
next prev parent reply other threads:[~2023-02-20 19:35 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-09 13:26 Jonny Grant
2023-02-09 14:56 ` Jonathan Wakely
2023-02-09 16:30 ` Xi Ruoyao
2023-02-09 17:52 ` Jonathan Wakely
2023-02-10 21:30 ` Jonny Grant
2023-02-10 22:03 ` Jonathan Wakely
2023-02-10 22:38 ` Jonny Grant
2023-02-11 0:32 ` Jonathan Wakely
2023-02-13 22:02 ` Jonny Grant
2023-02-19 20:43 ` Jonny Grant
2023-02-19 21:33 ` Jonny Grant
2023-02-20 10:26 ` Xi Ruoyao
2023-02-20 10:37 ` Jonathan Wakely
2023-02-20 10:54 ` Xi Ruoyao
2023-02-20 11:10 ` Gabriel Ravier
2023-02-20 11:18 ` Marc Glisse
2023-02-20 11:28 ` Segher Boessenkool
2023-02-20 12:00 ` Jonny Grant
2023-02-20 14:50 ` Gabriel Ravier
2023-02-20 11:44 ` Jonny Grant
2023-02-21 15:02 ` Jonny Grant
2023-02-20 11:38 ` Jonny Grant
2023-02-20 11:30 ` Jonny Grant
2023-02-20 12:59 ` Xi Ruoyao
2023-02-20 13:44 ` Jonathan Wakely
2023-02-20 19:21 ` Jonny Grant
2023-02-20 19:35 ` Jonathan Wakely [this message]
2023-02-20 19:39 ` Jonny Grant
2023-02-22 20:27 ` Jonny Grant
2023-02-21 15:04 ` Jonny Grant
2023-02-21 22:48 ` Jonny Grant
2023-03-04 15:00 ` Jonny Grant
2023-02-20 11:25 ` Jonny Grant
2023-03-12 22:10 ` Jonny Grant
2023-03-13 10:10 ` Jonathan Wakely
2023-03-13 19:55 ` Jonny Grant
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