Re: [C++ Patch/RFC] PR 43906

[Paolo Carlini <paolo dot carlini at oracle dot com>]

Hi,

On 08/05/2014 03:58 AM, Jason Merrill wrote:
> On 08/04/2014 07:01 PM, Paolo Carlini wrote:
> > In fact I wondered about that a few minutes after sending my message...
> > And this is what I figured out: normally we have hard errors from
> > composite_pointer_type (eg, try scalar types, class types), even for
> > null values. The only exception I have been able to find earlier today
> > is that of pointer to the same function type, eg:
> >
> > extern void z();
> > typedef void (*ptr)();
> > void i() { if ( z != (ptr)0 ); }
> >
> > but in this case the C front-end too doesn't warn.
> I don't see why we wouldn't want to warn in this case; it's still the 
> case thet the comparison will always be false.
In general, I agree of course. I was trying to understand if keeping the 
issue as minimally one of consistency with the C front-end simplified it.
> We can also see this situation for non-function pointers:
>
> void f()
> {
>   int i;
>   if (&i != (int*)0);
> }
Sure. Then, however, we must be careful about the actual pointer types, 
otherwise we change hard errors to warnings. And void* is an exception 
to the general rule. I tried using ptr_reasonably_similar to avoid the 
explicit call of comptypes + separate VOID_TYPE_P, but unfortunately it 
appears too loose about at least pointers to function types.

Thanks!
Paolo.

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