Deprecating arithmetic on std::atomic<void*>

[Jonathan Wakely]

On 20/04/17 11:43 +0200, Florian Weimer wrote:
>On 04/20/2017 11:25 AM, Jonathan Wakely wrote:
>
>>>I mean, with -pedantic-errors we already error on void * arighmetics
>>>or function pointer arithmetics.  If std::atomic<void*> would use
>>>the void * arithmetics, it would also reject it.  Or does it use integer
>>>arithmetics instead?
>>
>>No, it does it on void*, but the __atomic built-ins still perform that
>>arithmetic even with -pedantic-errors.
>
>sizeof is not defined for the relevant types, either, and already 
>triggers a warning by default:
>
>t.cc:25:58: warning: invalid application of ‘sizeof’ to a void type 
>[-Wpointer-arith]
>   _M_type_size(ptrdiff_t __d) const { return __d * sizeof(_PTp); }

That could be easily avoided if we care about supporting arithmetic on
std::atomic<void*>.

>I think the actual problem here is the suppression of warnings from 
>system headers.

The atomic built-ins still don't warn even with -Wsystem-headers