From: Jonny Grant <jg@jguk.org>
To: Jonathan Wakely <jwakely.gcc@gmail.com>, Xi Ruoyao <xry111@xry111.site>
Cc: gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: std::string add nullptr attribute
Date: Mon, 20 Feb 2023 19:21:15 +0000 [thread overview]
Message-ID: <241687c0-8dca-3c85-84e9-cfab85536324@jguk.org> (raw)
In-Reply-To: <CAH6eHdQQKyy5vrTGhJV8R1OW7MckKxHHTdDYRd+Pn36mxYZsDw@mail.gmail.com>
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.
https://godbolt.org/z/haq18bvPP
Kind regards
Jonny
next prev parent reply other threads:[~2023-02-20 19:21 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 [this message]
2023-02-20 19:35 ` Jonathan Wakely
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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