From: "Marc Nieper-Wißkirchen" <marc.nieper+gnu@gmail.com>
To: Bruno Haible <bruno@clisp.org>
Cc: "Marc Nieper-Wißkirchen" <marc.nieper+gnu@gmail.com>, bug-gnulib@gnu.org
Subject: Re: Unused parameter warnings
Date: Sat, 10 Oct 2020 16:31:52 +0200 [thread overview]
Message-ID: <CAEYrNrSTnYcY-PiaVwN=UAOPpEg8+UvtL9SA+jeBs0jTyRQGWA@mail.gmail.com> (raw)
In-Reply-To: <2217733.79xrSNMHMn@omega>
I can ask for a better description of "pure" in the GCC manual. In any
case, if a function doesn't return at all due to a function call
marked with _Noreturn, it does not affect the observable state locally
and GCC can avoid "emitting some calls in repeated invocations of the
function with the same argument values". As I wrote before, this is an
important observation as otherwise "assert" couldn't be used in "pure"
functions.
Anyway, the function gl_linked_iterator_from_to in Gnulib should
probably be fixed independently by adding the "pure" attribute so that
the code is compilable with -Werror -Wall -Wextra.
Am Sa., 10. Okt. 2020 um 15:50 Uhr schrieb Bruno Haible <bruno@clisp.org>:
>
> Marc Nieper-Wißkirchen wrote:
> > > And a function that may invoke abort () does "affect observable state".
> >
> > This description of the a pure function does not seem to be accurate.
> > When a function calls another function like abort that is marked with
> > _Noreturn in a pure context, for the compiler the function can still
> > be pure (but not const). It can eliminate a second call to the
> > function with the same parameters. I am pretty sure that the warning
> > of GCC in line 938 is correct.
>
> The documentation of ATTRIBUTE_PURE in Gnulib is taken from the GCC
> documentation [1][2], therefore if you think it needs to be fixed, it's
> through a GCC bug report.
>
> Bruno
>
> [1] https://lists.gnu.org/archive/html/bug-gnulib/2020-05/msg00105.html
> [2] https://gcc.gnu.org/onlinedocs/gcc-10.2.0/gcc/Common-Function-Attributes.html
>
next prev parent reply other threads:[~2020-10-10 14:32 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-04 20:23 Unused parameter warnings Marc Nieper-Wißkirchen
2020-10-04 22:08 ` Bruno Haible
2020-10-06 5:58 ` Marc Nieper-Wißkirchen
2020-10-06 21:05 ` Bruno Haible
2020-10-07 6:07 ` Marc Nieper-Wißkirchen
2020-10-10 13:50 ` Bruno Haible
2020-10-10 14:31 ` Marc Nieper-Wißkirchen [this message]
2020-10-10 14:39 ` Bruno Haible
2020-10-10 15:00 ` Marc Nieper-Wißkirchen
2020-10-10 18:50 ` Paul Eggert
2020-10-10 21:00 ` Bruno Haible
2020-10-11 23:10 ` Paul Eggert
2020-10-12 2:21 ` Jeffrey Walton
2020-10-14 1:24 ` 'const' function attribute Bruno Haible
2020-10-14 14:57 ` Paul Eggert
2020-10-18 14:27 ` Bruno Haible
2020-10-10 20:43 ` Unused parameter warnings Bruno Haible
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