Date: Mon, 05 Sep 2011 18:43:45 +0200 From: Matthias Andree <matthias.andree@gmx.de> To: freebsd-ports@freebsd.org Subject: Re: reasons for rewriting regular memory Message-ID: <4E64FC41.2080702@gmx.de> In-Reply-To: <4e6491d0.MNLKNzL63JK0kXDG%perryh@pluto.rain.com> References: <20110725155920.GA83490@freebsd.org> <4E631DBF.9000106@yandex.ru> <20110904101252.526de5ef@nonamehost.> <4E632A09.8060904@FreeBSD.org> <20110904114550.71c63078@nonamehost.> <4E63516B.7000805@FreeBSD.org> <20110904130659.7a94cce8@raksha.tavi.co.uk> <4E637DD8.50700@gmx.de> <4e6491d0.MNLKNzL63JK0kXDG%perryh@pluto.rain.com>
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Am 05.09.2011 11:09, schrieb perryh@pluto.rain.com:
> Matthias Andree <matthias.andree@gmx.de> wrote:
>>> I agree, but I can think of another valid exception. System with
>>> Hamming correction on the memory, gets a single bit (correctable)
>>> error. Need to rewrite the memory contents to reset all the parity
>>> bits!
>> That's a matter of the EDAC stuff, not the business of applications.
>
> True, but it may explain why clang does not flag "*x = *x;" when it
> does flag "x = x;". A compiler cannot know the context in which the
> compiled code will be used.
And a compiler is free to optimize either away unless the storage class
is "volatile", so the original point stands:
> BTW I agree that an understanding is needed of _why_ the code in
> question was included.
Which waits on the original author.
On the other issue:
> I have seen "x = x;" -- x being a formal
> parameter -- used to prevent an "unused argument" warning in a
> function which did not in fact need the argument in question, but
> had to declare it for uniformity with other functions pointed to
> by the same function pointer type.
The portable and concise solution is to cast unused arguments to void,
as in this example:
int f(int used, int unused) {
(void)unused; // avoids warnings
// ...
// now do something with used
// ...
return 42;
}
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