Assignment to volatile objects

[David Brown]

On 30/01/12 23:22, Paul_Koning@Dell.com wrote:
> I would prefer this to generate a warning.  The C language standard
> change you refer to is a classic example of a misguided change, and
> any code whose behavior depends on this deserves a warning message,
> NOT an option to work one way or the other.
>

Until gcc gets a feature allowing it to whack the programmer on the back 
of the head with Knuth's "The Art of Computer Programming" for writing 
such stupid code that relies on the behaviour of volatile "a = b = 0;", 
then a warning seems like a good idea.

mvh.,

David


> paul
>
> -----Original Message----- From: gcc-owner@gcc.gnu.org
> [mailto:gcc-owner@gcc.gnu.org] On Behalf Of Zoltán Kócsi Sent:
> Monday, January 30, 2012 5:03 PM To: gcc@gcc.gnu.org Subject:
> Assignment to volatile objects
>
> Now that the new C standard is out, is there any chance that gcc's
> behaviour regarding to volatile lhs in an assignment changes?
>
> This is what it does today:
>
> volatile int a, b;
>
> a = b = 0;
>
> translates to
>
> b = 0; a = b;
>
> because the standard (up to and including C99) stated that the value
> of the assignment operator is the value of the lhs after the
> assignment.
>
> The C11 standard says the same but then it explicitely states that
> the compiler does not have to read back the value of the lhs, not
> even when the lhs is volatile.
>
> So it is actually legal now not to read back the lhs. Is there a
> chance for the compiler to get a switch which would tell it
> explicitely not to read the value back?
>
> Zoltan
>